technical field
[One]
Cross-Citation with Related Applications
[2]
This application claims priority based on Korean Patent Application No. 10-2020-0063393 dated May 27, 2020, and all contents disclosed in the Korean patent application are incorporated as a part of this specification.
[3]
technical field
[4]
The present invention relates to a method for diagnosing the cause of deterioration of a lithium secondary battery. Specifically, it relates to a non-destructive diagnostic method for diagnosing the cause of deterioration of a lithium secondary battery using X-ray diffraction (XRD) data measured in a state in which the battery is not disassembled.
[5]
background
[6]
As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used. In particular, as the popularization of electric vehicles is rapidly progressing in recent years, the development of high-energy batteries that can be used as power sources for mid- to large-sized devices is becoming more important.
[7]
As the cathode active material of the lithium secondary battery, a lithium transition metal composite oxide is used, and among them, a lithium cobalt composite metal oxide such as LiCoO 2 having a high operating voltage and excellent capacity characteristics is mainly used. However, LiCoO 2 has very poor thermal properties due to the destabilization of the crystal structure due to delithiation. In addition, since the LiCoO 2 is expensive, there is a limit to its mass use as a power source in fields such as electric vehicles.
[8]
As a material for replacing the LiCoO 2 , a lithium manganese composite metal oxide (LiMnO 2 or LiMn 2O 4, etc.), a lithium iron phosphate compound (LiFePO 4 etc.), or a lithium nickel composite metal oxide (LiNiO 2 etc.) have been developed. Among them, research and development on lithium-nickel composite metal oxide, which has a high reversible capacity of about 200 mAh/g, and is easy to implement in a large-capacity battery, is being studied more actively. However, the LiNiO 2 has inferior thermal stability compared to LiCoO 2 , and when an internal short circuit occurs due to external pressure in a charged state, the positive active material itself is decomposed, resulting in rupture and ignition of the battery. Accordingly, as a method for improving low thermal stability while maintaining excellent reversible capacity of the LiNiO 2 , a lithium transition metal oxide in which a part of Ni is substituted with Co, Mn or Al has been developed.
[9]
However, in the case of lithium transition metal oxide in which a part of Ni is substituted with Co, Mn or Al, when the content of nickel is increased to 60 mol% or more to achieve high energy by increasing capacity characteristics, it exists in the positive electrode active material at high potential As lithium is released, a new phase is formed, and there is a problem in that the structural stability of the positive electrode active material is deteriorated by this phase change. As a result, there was a problem that deterioration of the battery occurred.
[10]
Conventionally, in order to diagnose specific causes of battery degradation, such as loss of available lithium, loss of positive electrode capacity, and loss of negative electrode capacity, the battery must be disassembled and the separated positive and negative electrodes are reassembled into half-cells. It had to be analyzed/verified. In this case, it takes a long time and high cost to diagnose the deterioration of the battery, and there is a problem that the disassembled battery cannot be used again.
[11]
Accordingly, there is a need for a method for diagnosing the cause of deterioration of a secondary battery that can classify and quantify the cause of deterioration of the battery without disassembling the secondary battery.
[12]
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[13]
In order to solve the above problems, the technical problem to be solved by the present invention is to provide a non-destructive diagnostic method capable of diagnosing the cause of deterioration of a lithium secondary battery without disassembling the battery.
[14]
means of solving the problem
[15]
The present invention is (A) a positive electrode comprising a layered positive electrode active material; and a negative electrode; preparing a lithium secondary battery comprising; (B) From the X-ray diffraction data obtained by measuring the lithium secondary battery while charging the first, the c-axis of the layered positive active material with respect to the number of moles of lithium ions desorbed during charging from the layered positive active material ) obtaining a first graph representing d-spacing values; (C) the c-axis d-spacing value of the layered positive electrode active material with respect to the number of moles of lithium ions desorbed from the layered positive electrode active material during charging from the X-ray diffraction data obtained by measuring the lithium secondary battery during the second charging obtaining a second graph representing and (D) classifying the cause of deterioration of the secondary battery by comparing the first graph with the second graph.
[16]
Effects of the Invention
[17]
According to the present invention, it is possible to classify and quantify the cause of deterioration of a secondary battery from X-ray diffraction data measured in a state in which the battery is not disassembled.
[18]
According to the diagnostic method of the present invention, without disassembling the battery, it is possible to determine whether the deterioration of the secondary battery is due to loss of available lithium, loss of positive electrode capacity, loss of available lithium and loss of positive electrode capacity, and the loss of available lithium and the Anode capacity loss can be quantified.
[19]
That is, the cause of deterioration of the lithium secondary battery can be diagnosed by a non-destructive and simple method.
[20]
Brief description of the drawing
[21]
1 is a view showing the charge potential profile of a full cell, a positive electrode and a negative electrode obtained by disassembling the full cell, and a positive electrode half cell and a negative electrode half cell in order to diagnose the cause of deterioration of a lithium secondary battery by a conventional method.
[22]
2 is a view showing the c-axis d-spacing value of the layered positive active material with respect to the number of moles of lithium ions desorbed during the first or second charging in the layered positive active material of the secondary battery of Example 1;
[23]
Best mode for carrying out the invention
[24]
Hereinafter, the present invention will be described in more detail to help the understanding of the present invention.
[25]
The terms or words used in the present specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention.
[26]
The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise.
[27]
In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the existence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, elements, or combinations thereof.
[28]
[29]

[30]
A method for diagnosing the cause of deterioration of a lithium secondary battery according to the present invention includes (A) a positive electrode comprising a layered positive electrode active material; and a negative electrode; preparing a lithium secondary battery comprising; (B) the c-axis d-spacing value of the layered positive electrode active material with respect to the number of moles of lithium ions desorbed during charging from the layered positive electrode active material from the X-ray diffraction data obtained by measuring the lithium secondary battery during the first charging obtaining a first graph representing (C) the c-axis d-spacing value of the layered positive electrode active material with respect to the number of moles of lithium ions desorbed from the layered positive electrode active material during charging from the X-ray diffraction data obtained by measuring the lithium secondary battery during the second charging obtaining a second graph representing and (D) classifying the cause of deterioration of the secondary battery by comparing the first graph with the second graph.
[31]
[32]
Conventionally, the cause of battery deterioration could not be confirmed only with the charge potential profile of a full-cell, so the cause of battery deterioration could be confirmed only by reassembling the positive and negative electrodes obtained by disassembling the full-cell and reassembling them into half cells and then analyzing/verifying them. . 1 is a view showing the charge potential profile of a full cell, a positive electrode and a negative electrode obtained by disassembling the full cell, and a positive electrode half cell and a negative electrode half cell in order to diagnose the cause of deterioration of a lithium secondary battery by a conventional method. The full cells in Figs. 1 (a) and 1 (b) are different full cells.
[33]
1 (a) and 1 (b), referring to the full-cell charging potential profile of the battery, the charging capacity of the solid line (charging capacity of the degenerated battery) decreased compared to the charging capacity of the dotted line (charging capacity of the initial battery) It can be seen that degeneration has progressed. However, the cause of deterioration of the battery cannot be confirmed only by the full-cell charge potential profile. Accordingly, the positive electrode and the negative electrode obtained by disassembling the full cell were assembled into a half cell to obtain a charge potential profile of each of the positive half cell and the negative half cell.
[34]
From the fact that there is no difference in the charging potential profile of the dotted line and the solid line in the positive electrode half-cell charging profile of FIG. Accordingly, in order to confirm the cause of battery deterioration, the full-cell charging potential profile of the solid line and the negative half-cell charging profile of the solid line in FIG. reflected in the current profile), and it was confirmed that the cause of battery deterioration was due to the loss of available lithium. In addition, it was confirmed that an unused region at the lower end of the anode (low potential) was generated due to deterioration due to a decrease in reversible lithium ions due to a side reaction that consumes lithium ions.
[35]
In the positive half-cell charging profile of FIG. 1 ( b ), the positive half-cell profile of the solid line did not overlap with the positive half-cell profile of the dotted line, so it could be confirmed that the cause of the deterioration of the battery was the loss of positive electrode capacity.
[36]
As described above, in the prior art, in order to diagnose the specific cause of battery deterioration, it was necessary to disassemble the battery and assemble the separated positive and negative electrodes again with a half battery for analysis/verification.There is a problem that not only requires high cost, but also the disassembled battery cannot be used again.
[37]
[38]
The present invention relates to a method for determining the cause of deterioration of a lithium secondary battery by obtaining a c-axis d-spacing value of a layered positive electrode active material from XRD data without disassembling a full cell. The method for diagnosing the cause of deterioration of a lithium secondary battery according to the present invention is a non-destructive diagnostic method. Accordingly, after confirming the cause of deterioration of the lithium secondary battery, if the lithium secondary battery is not completely degraded, the secondary battery can be reused.
[39]
[40]
Hereinafter, the present invention will be described in more detail step by step.
[41]
[42]
(A) step
[43]
First, the present invention is (A) a positive electrode comprising a layered positive electrode active material; and preparing a lithium secondary battery comprising a; and a negative electrode.
[44]
Specifically, the step (A) is a positive electrode comprising a layered positive electrode active material; a negative electrode present opposite to the positive electrode; a separator interposed between the anode and the cathode; And it may be to prepare a lithium secondary battery containing the electrolyte.
[45]
[46]
The positive electrode according to the present invention may be manufactured by coating a composition for forming a positive electrode including a layered positive electrode active material, a binder, a conductive material and a solvent on a positive electrode current collector to form a positive electrode active material layer. In addition, the composition for forming the positive electrode may optionally further include a dispersing agent, if necessary.
[47]
According to the present invention, in order to achieve high energy density of the secondary battery, the layered positive electrode active material may be a lithium transition metal oxide containing 60 mol% or more of nickel with respect to the total number of moles of transition metals excluding lithium. Specifically, according to the present invention, the layered positive electrode active material may be represented by the following formula (1).
[48]
[Formula 1]
[49]
Li 1+aNi xCo yM zO 2
[50]
In Formula 1, 0≤a≤0.3, 0.6≤x≤1.0, 0≤y≤0.2, 0≤z≤0.2, x+y+z=1, M may be at least one selected from Mn and Al .
[51]
In Chemical Formula 1, M may be an element substituted at a transition metal site in the oxide represented by Chemical Formula 1.
[52]
1+a represents the molar ratio of lithium in the oxide represented by Formula 1, and may be 0≤a≤0.3, preferably 0≤a≤0.2.
[53]
The x represents the molar ratio of Ni in the oxide represented by Formula 1, and may be 0.6≤x≤1.0, preferably 0.8≤x≤1.0.
[54]
The y represents the molar ratio of Co in the oxide represented by Formula 1, and may be 0≤y≤0.2, preferably 0≤y≤0.15.
[55]
The z represents the molar ratio of M in the oxide represented by Formula 1, and may be 0≤z≤0.2, preferably 0≤z≤0.15.
[56]
When the layered positive electrode active material contains nickel in an amount of 60 mol% or more, specifically, 80 mol% or more, based on the total number of moles of transition metal oxides excluding lithium, that is, the layered positive electrode active material contains nickel in a high content In this case, in particular, the phase of the positive electrode active material may change as lithium ions present in the positive electrode active material escape at a high potential. That is, the structural stability of the positive electrode active material may be deteriorated, which may cause deterioration of the positive electrode and, consequently, deterioration (performance degradation) of the lithium secondary battery. The method for diagnosing the cause of deterioration of a lithium secondary battery according to the present invention is characterized in that it can diagnose the cause of deterioration of the lithium secondary battery without disassembling the full cell.
[57]
In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.
[58]
The binder serves to improve adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used.
[59]
The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it does not cause chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one or a mixture of two or more thereof may be used.
[60]
The dispersant may be used without any particular limitation as long as it is used as a dispersant for the positive electrode, for example, an aqueous dispersant or an organic dispersant may be selectively used as needed. Preferably, the dispersant is a cellulose-based compound, polyalkylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl ether, polyvinyl sulfonic acid, polyvinyl chloride (PVC), polyvinylidene fluoride. Ride, chitosans, starch, amylose, polyacrylamide, poly-N-isopropylacrylamide, poly-N,N-dimethylacrylamide, polyethyleneimine, polyoxyethylene, poly(2-methoxy oxyethylene), poly(acrylamide-co-diallyldimethylammonium chloride), acrylonitrile/butadiene/styrene (ABS) polymer, acrylonitrile/styrene/acrylic ester (ASA) polymer, acrylonitrile/styrene/acrylic Mixture of ester (ASA) polymer and propylene carbonate, styrene/acrylonitrile (SAN) copolymer, methyl methacrylate/acrylonitrile/butadiene/styrene (MABS) polymer, styrene butadiene rubber, nitrile butadiene rubber, fluororubber, etc. and any one or a mixture of two or more thereof may be used. Hydrogenated nitrile butadiene rubber (H-NBR) can be used. When the positive active material layer further includes a dispersing agent, the dispersibility of components of the positive active material layer, particularly the conductive material, may be increased, but the present invention is not limited thereto.
[61]
The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water, and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity during application for the production of the positive electrode thereafter. do.
[62]
[63]
The negative electrode according to the present invention can be prepared by coating a composition for forming an anode including an anode active material, a binder, a conductive material and a solvent on an anode current collector to form an anode active material layer. In addition, the composition for forming the negative electrode may optionally further include a dispersing agent, if necessary.
[64]
As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Preferably, the negative electrode may include a silicon-based negative active material exhibiting high capacity characteristics. In addition, the negative active material may further include a carbon-based negative active material as well as a silicon-based negative active material. For example, when the negative active material includes a silicon-based negative active material and a carbon-based negative active material, the irreversible capacity may be reduced compared to the case in which only the silicon-based negative active material is included while having high capacity characteristics.
[65]
In the negative electrode, the negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface. Carbon, nickel, titanium, silver or the like surface-treated may be used. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.
[66]
The conductive material, binder, solvent or dispersant included in the composition for forming the negative electrode can be applied without any particular limitation as long as it can be conventionally used in the composition for forming an electrode, for example, the conductive material described in the composition for forming the positive electrode, Binders, solvents or dispersants may be applied.
[67]
[68]
On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and as long as it is used as a separator in a lithium secondary battery, it can be used without any particular limitation, especially for the movement of ions in the electrolyte Low resistance and excellent electrolyte moisture content it is preferable to do Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.
[69]
[70]
In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, which can be used in the manufacture of lithium secondary batteries, and are limited to these. it is not going to be
[71]
Specifically, the electrolyte may include an organic solvent and a lithium salt.
[72]
The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain a double bond aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolane (sulfolane) may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable.
[73]
The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is, LiPF 6, LiClO 4, LiAsF 6, LiBF 4, LiSbF 6, LiAlO 4, LiAlCl 4, LiCF 3SO 3, LiC 4F 9SO 3, LiN(C 2F 5SO 3) 2, LiN(C 2F 5SO 2) 2, LiN(CF 3SO 2) 2. LiCl, LiI, or LiB(C 2O 4) 2 and the like may be used.
[74]
In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included.
[75]
[76]
(B) step and (C) step
[77]
The present invention relates to (B) the c-axis d of the layered positive electrode active material with respect to the number of moles of lithium ions desorbed during charging from the layered positive electrode active material from the X-ray diffraction data obtained by measuring the lithium secondary battery during the first charging - obtaining a first graph representing the spacing values.
[78]
And, the present invention (C) from the X-ray diffraction data obtained by measuring the lithium secondary battery while charging the second, c- of the layered positive electrode active material with respect to the number of moles of lithium ions desorbed during charging from the layered positive electrode active material obtaining a second graph representing the axial d-spacing values.
[79]
[80]
In the present invention, the first charging refers to the initial charging. That is, the first charging refers to the first charging performed immediately after manufacturing the lithium secondary battery.
[81]
[82]
Since the present invention relates to a method for diagnosing deterioration of a full-cell lithium secondary battery, according to the present invention, the second charging is performed after discharging the lithium secondary battery that has performed the first charging, and then charging and discharging the lithium secondary battery. It may be charging after repeatedly performing one or more times. In addition, the second charging may be charging after discharging the lithium secondary battery that has performed the first charging, and then storing the lithium secondary battery at a temperature of -20 °C to 70 °C for a long period of time.
[83]
According to the method for diagnosing the cause of deterioration of a lithium secondary battery of the present invention, the cause of deterioration of the lithium secondary battery by repeatedly charging and discharging the lithium secondary battery in the driving voltage range of the battery, or by storing the lithium secondary battery for a long time after the first charge and discharge of the lithium secondary battery The cause of battery degradation can be identified in a simple and non-destructive way. Accordingly, even after diagnosing the cause of deterioration of the lithium secondary battery, if the secondary battery is not completely degraded, the secondary battery may be reused.
[84]
According to the present invention, the first charging and the second charging may be performed in a voltage range of 2.5V to 4.2V. Charging and discharging repeatedly performed one or more times may also be performed in a voltage range of 2.5V to 4.2V.
[85]
[86]
According to the present invention, the X-ray diffraction data may be obtained using a transmission X-ray diffraction analyzer. For example, the X-ray diffraction data is measured at a voltage of 50 kV and a current of 25 mA using an Ag-Kα (0.56 Å) target using a transmission X-ray diffraction analyzer of Bruker or Malvern Panalytical. may be obtained.
[87]
The present invention detects the diffracted X-rays transmitted through the lithium secondary battery by irradiating X-rays to the portion where the layered positive electrode active material is present while charging the lithium secondary battery for the first (initial charging) or the second charging, and the detected diffracted X-rays It can be used to determine the degree of deterioration of the secondary battery. The present invention utilizes the property that the distance between crystal planes of a layered positive electrode active material changes as lithium ions are desorbed when charging a lithium secondary battery.
[88]
Specifically, a d-spacing value, which is the distance between the c-axis crystal planes of the layered positive electrode active material, can be obtained from each X-ray diffraction data obtained during the first charging or the second charging of the lithium secondary battery, and the d-spacing value is It can be represented as a graph for the number of moles of lithium ions desorbed during the first charge or during the second charge, the first graph and the second graph showing the d-spacing value for the number of moles of lithium ions desorbed during the first charge 2 The degree of degradation of the secondary battery can be determined by comparing the second graph showing the d-spacing value with respect to the number of moles of lithium ions desorbed during charging. Specific details related to determining the degree of deterioration of the secondary battery through comparison of graphs will be described in more detail in step (D).
[89]
According to the present invention, the d-spacing value may be specifically a d-spacing value of the (003) plane of the layered positive electrode active material. For example, the d-spacing value may mean a long axis length of a hexagonal unit cell (space group = R3m). The unit cell means a structure in which the arrangement of the transition metal layer/oxygen layer/lithium layer of the positive electrode active material is minimally repeated.
[90]
[91]
(D) step
[92]
The present invention includes (D) classifying the cause of deterioration of the secondary battery by comparing the first graph and the second graph.
[93]
According to the present invention, the cause of deterioration of the secondary battery may be at least one of loss of available lithium and loss of positive electrode capacity. That is, in step (D), the cause of deterioration is checked by comparing the first graph and the second graph to determine whether the deterioration of the secondary battery is due to the loss of available lithium, the loss of positive electrode capacity, or the loss of available lithium and the loss of positive electrode capacity. It may include classifying
[94]
According to the present invention, in step (D), when the maximum value of the number of moles of lithium ions desorbed in the second graph is smaller than the maximum value of the number of moles of lithium ions desorbed in the first graph, the cause of deterioration of the secondary battery This is classified as the loss of available lithium, and the c-axis d-spacing value of the layered positive active material in the second graph is the maximum c-axis d-spacing value of the layered positive active material in the first graph. When the second graph is moved in parallel in the x-axis direction to maximize the number of moles of ions, the maximum value of the number of moles of lithium ions desorbed in the second graph is higher than the maximum value of the number of moles of lithium ions desorbed in the first graph. When the value obtained by adding the parallel shift value (the degree of parallel shift in the x-axis direction) is large, it may include classifying that the cause of deterioration of the secondary battery is a cathode capacity loss.
[95]
On the other hand, in relation to the occurrence of a positive electrode lower potential (low potential) unused region due to deterioration due to a decrease in reversible lithium ions due to a side reaction that consumes lithium ions, in the first graph, the c-axis of the layered positive electrode active material is d- In the second graph, the number of moles of desorbed lithium ions when the spacing value is maximum is higher than that of the layered positive electrode active material.When the number of moles of desorbed lithium ions when the c-axis d-spacing value is the maximum is small, it can be considered that the potential unused region at the lower end of the anode is generated.
[96]
According to the present invention, in the step (D), a value obtained by subtracting the maximum value of the number of moles of lithium ions desorbed in the second graph from the maximum value of the number of moles of lithium ions desorbed in the first graph is quantified as the amount of loss of available lithium may include doing The loss of available lithium is a value obtained by subtracting the maximum value of the number of moles of lithium ions desorbed in the second graph from the maximum value of the number of moles of lithium ions desorbed in the first graph. The maximum value of the number of moles of lithium ions desorbed in the first graph or the second graph is the maximum value of available lithium during the first charging or the second charging. That is, the amount of loss of available lithium obtained through the comparison of the first graph and the second graph is a value obtained by subtracting the maximum value of available lithium during the second charge from the maximum value of available lithium during the first charge. You can check whether
[97]
In addition, in step (D), the second graph moves in parallel (the c-axis-d-spacing value of the layered positive active material in the second graph is the c-axis d-spacing value of the layered positive active material in the first graph It may include quantifying the balance shift between the positive electrode and the negative electrode from the degree of parallel movement of the second graph in the x-axis direction to become the maximum in the number of moles of desorbed lithium ions at the maximum. In the present specification, the balance shift means deterioration due to a decrease in reversible lithium ions due to a side reaction that consumes lithium ions. The balance shift refers to the degree of parallel movement of the second graph, in the number of moles of lithium ions desorbed when the d-spacing value is the maximum in the first graph, and when the d-spacing value is the maximum in the second graph It is a value obtained by subtracting the number of moles of desorbed lithium ions. From the balance shift, it can be seen that the positive electrode is experiencing overcharge (and delithiation) as the operating range is changed.
[98]
And, the step (D) may include quantifying the amount of cathode capacity loss. The positive electrode capacity loss amount is a value obtained by adding the value of the desorbed lithium ion to the maximum value of the number of moles of lithium ions in the second graph and the value (the degree of parallel movement in the x-axis direction) as described above. It can be quantified by subtracting the maximum value of the number of moles of lithium ions.
[99]
That is, according to the present invention, it may be possible to quantify the cause of deterioration of the secondary battery.
[100]
The method for diagnosing the cause of deterioration of a lithium secondary battery according to the present invention may be to determine that the lithium secondary battery is degraded due to the loss of available lithium when the loss rate of available lithium according to Equation 1 is 14% or more.
[101]
[Equation 1]
[102]
Loss of available lithium = (loss of available lithium)/(the maximum value of the number of moles of lithium ions desorbed in the first graph) × 100.
[103]
End of Life (EOL), which is defined as the lifespan of a lithium secondary battery, generally means when the battery capacity reaches 80% of the initial capacity of the battery. That is, when the capacity of the lithium secondary battery is reduced by 20% compared to the initial capacity, it can be considered that the lithium secondary battery is degraded.
[104]
The degradation of secondary batteries includes loss of available lithium due to side reactions, positive electrode degradation due to positive electrode reaction area loss, negative electrode degradation due to negative electrode reaction area loss, etc. The inventor of the present invention does not disassemble the full-cell, By obtaining the c-axis d-spacing value of the layered positive electrode active material from the XRD data, it was confirmed that the degradation of the secondary battery, that is, the capacity decrease due to the loss of available lithium during the 20% capacity decrease was about 14%.
[105]
[106]
As a result, according to the method for diagnosing the cause of deterioration of a lithium secondary battery of the present invention, even if the battery is not disassembled after charging and discharging of the secondary battery, a decrease in the amount of available lithium and a decrease in the positive electrode capacity can be confirmed. The cause of deterioration of the lithium secondary battery can be identified. Therefore, even after diagnosing the cause of deterioration of the lithium secondary battery, the secondary battery can be reused.
[107]
Modes for carrying out the invention
[108]
Hereinafter, examples are given in order to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.
[109]
[110]
Example
[111]
Example 1
[112]
LiNi 0.8Co 0.1Mn 0.1O 2 as a positive electrode active material, a carbon black conductive material, a dispersant and a polyvinylidene fluoride binder were mixed in a weight ratio of 97.5:1:0.15:1.35, and this was mixed in an N-methylpyrrolidone solvent. A composition for forming a positive electrode was prepared. The composition for forming the positive electrode was applied to an aluminum foil having a thickness, dried, and roll pressed to prepare a positive electrode.
[113]
Meanwhile, a mixture of graphite and SiO in a weight ratio of 90:10 was used as an anode active material, and carbon black, a carbon nanotube conductive material and a binder were mixed in a weight ratio of 96:0.5:0.1:3.4, and this was added to the solvent. Thus, a composition for forming an anode was prepared. The composition for forming the negative electrode was applied on a copper current collector having a thickness of 6 μm, dried, and then roll pressed to prepare a negative electrode.
[114]
The positive and negative electrodes prepared above were laminated together with a safety reinforced separator (SRS) to prepare an electrode assembly, and then placed in a battery case and ethylene carbonate (EC): propylene carbonate (PC): ethyl methyl carbonate ( EMC) was injected in a solvent mixed with an electrolyte salt in a volume ratio of 25:5:70 to prepare a lithium secondary battery.
[115]
After the lithium secondary battery prepared as described above was mounted on a transmission X-ray diffraction analyzer (Bruker), the lithium secondary battery was initially charged with a constant current of 0.05C to 4.2V at 0.025C cut off and X-rays were irradiated, X-ray diffraction data of the (003) plane corresponding to the interlayer spacing of the positive electrode active material were obtained. (Measured at a voltage of 50 kV and a current of 25 mA using an Ag-Kα (0.56 Å) target)
[116]
From the X-ray diffraction data of the (003) plane, the d-spacing value of the (003) plane of the positive electrode active material is obtained, and from this, c of the layered positive active material with respect to the number of moles of lithium ions desorbed during initial charging from the layered positive active material A first graph of the -axis d-spacing values ​​was obtained, which is shown in FIG. 2(a).
[117]
Then, the lithium secondary battery, which had been initially charged, was stored at 60° C. for 6 weeks. After the lithium secondary battery was stored at 60°C for 6 weeks, the lithium secondary battery was mounted on a transmission X-ray diffraction analyzer (Bruker), and the lithium secondary battery was cut off at 0.025C up to 4.2V at 0.05C constant current. 2 X-rays were irradiated while charging to obtain X-ray diffraction data of the (003) plane corresponding to the interlayer spacing of the positive electrode active material. (Measured at a voltage of 50 kV and a current of 25 mA using an Ag-Kα (0.56 Å) target)
[118]
From the X-ray diffraction data of the (003) plane, the d-spacing value of the (003) plane of the positive electrode active material is obtained, and from this, A second graph of the c-axis d-spacing values ​​was obtained, which is shown in Fig. 2(a).
[119]
[120]
The cause of deterioration of the lithium secondary battery of Example 1 was confirmed through comparison of the first graph and the second graph of FIG. 2 (a).
[121]
Specifically, the difference (0.124 mol) between the maximum value (0.856 mol) of the number of moles of lithium ions desorbed in the first graph of FIG. 2 (a) and the maximum value (0.732 mol) of the number of moles of lithium ions desorbed in the second graph From this, it could be confirmed that the loss of available lithium was the cause of the deterioration of the lithium secondary battery, and it could be confirmed that the loss of available lithium was 0.124 mol. In addition, it was confirmed that the soluble lithium loss rate was 14.5%.
[122]
On the other hand, the c-axis-d-spacing value of the layered positive electrode active material in the second graph of FIG. 2 (a), the c-axis d-spacing value of the layered positive active material in the first graph of FIG. 2 (b) shows a graph in which the second graph is moved in parallel in the x-axis direction by about 0.15 to maximize the number of moles of desorbed lithium ions when . It was confirmed that the operating range of the positive electrode of the secondary battery of Example 1 was changed from the degree of parallel movement, that is, the balance shift was greater than 0, and overcharge (and delithiation) was experienced.
[123]
And, the maximum value (0.882 mol = 0.732) of the number of moles of lithium ions desorbed in the second graph of FIG. 2 (b) than the maximum value (0.856 mol) of the number of moles of lithium ions desorbed in the first graph of FIG. From the large mol+0.15 mol (balance shift value)), it was confirmed that not only the loss of available lithium but also the loss of the cathode capacity were the cause of degradation.
[124]
[125]
Accordingly, it can be seen that the cause of deterioration of a lithium secondary battery can be classified and quantified in a non-destructive and simple manner through the method for diagnosing the cause of deterioration of a lithium secondary battery of the present invention.
Claims
[Claim 1]
(A) a positive electrode comprising a layered positive electrode active material; and a negative electrode; preparing a lithium secondary battery comprising; (B) the c-axis d-spacing value of the layered positive electrode active material with respect to the number of moles of lithium ions desorbed during charging from the layered positive electrode active material from the X-ray diffraction data obtained by measuring the lithium secondary battery during the first charging obtaining a first graph representing (C) the c-axis d-spacing value of the layered positive electrode active material with respect to the number of moles of lithium ions desorbed from the layered positive electrode active material during charging from the X-ray diffraction data obtained by measuring the lithium secondary battery during the second charging obtaining a second graph representing and (D) the first graph and the second graph.A method for diagnosing the cause of deterioration of a lithium secondary battery, comprising the step of classifying the cause of deterioration of the secondary battery by comparison.
[Claim 2]
The method of claim 1 , wherein the cause of deterioration of the secondary battery is at least one of loss of available lithium and loss of positive electrode capacity.
[Claim 3]
The cause of deterioration of the secondary battery according to claim 1, wherein in step (D), the maximum value of the number of moles of lithium ions desorbed in the second graph is smaller than the maximum value of the number of moles of lithium ions desorbed in the first graph This is classified as the loss of available lithium, and the lithium desorbed when the c-axis-d-spacing value of the layered positive active material in the second graph is the maximum c-axis d-spacing value of the layered positive active material in the first graph When the second graph is moved in parallel in the x-axis direction to maximize the number of moles of ions, the maximum value of the number of moles of lithium ions desorbed in the second graph is higher than the maximum value of the number of moles of lithium ions desorbed in the first graph. A method for diagnosing the cause of deterioration of a lithium secondary battery, comprising classifying that the cause of deterioration of the secondary battery is a loss of positive electrode capacity when the sum of the parallel shifted values ​​is large.
[Claim 4]
The method according to claim 3, wherein in step (D), a value obtained by subtracting the maximum value of the number of moles of lithium ions desorbed in the second graph from the maximum value of the number of moles of lithium ions desorbed in the first graph is quantified as the amount of loss of available lithium A method for diagnosing the cause of deterioration of a lithium secondary battery, comprising:
[Claim 5]
The method according to claim 3, wherein in step (D), the maximum value of the number of moles of lithium ions desorbed in the first graph is obtained by adding a value obtained by parallel shifting to the maximum value of the number of moles of lithium ions desorbed in the second graph. A method for diagnosing the cause of deterioration of a lithium secondary battery, comprising quantifying the amount of loss of positive electrode capacity from the subtracted value.
[Claim 6]
The method for diagnosing the cause of deterioration of a lithium secondary battery according to claim 4, wherein it is determined that the lithium secondary battery is deteriorated due to the loss of available lithium when the loss rate of available lithium according to Equation 1 is 14% or more: [Equation 1] Available lithium Loss rate = (loss of available lithium)/(maximum value of the number of moles of lithium ions desorbed in the first graph) × 100.
[Claim 7]
The method for diagnosing the cause of deterioration of a lithium secondary battery according to claim 1, wherein the layered positive active material is a lithium transition metal oxide containing 60 mol% or more of nickel with respect to the total number of moles of transition metals excluding lithium.
[Claim 8]
The method according to claim 1, wherein the layered positive active material is a method for diagnosing the cause of deterioration of a lithium secondary battery that is represented by the following Chemical Formula 1: [Formula 1] Li 1+aNi xCo yM zO 2 In Chemical Formula 1, 0≤a≤0.3 , 0.6≤x≤1.0, 0≤y≤0.2, 0≤z≤0.2, x+y+z=1, and M is at least one selected from Mn and Al.
[Claim 9]
The method according to claim 1, wherein the second charging comprises: after discharging the lithium secondary battery that has been charged with the first charging, charging and discharging the lithium secondary battery repeatedly one or more times; Alternatively, after discharging the lithium secondary battery that has undergone the first charging, charging the lithium secondary battery after long-term storage at a temperature of -20 °C to 70 °C;
[Claim 10]
The method according to claim 1, wherein the first charging and the second charging are performed in a voltage range of 2.5V to 4.2V.
[Claim 11]
The method according to claim 1, wherein the X-ray diffraction data is obtained by using a transmission X-ray diffraction analyzer.
[Claim 12]
The method according to claim 1, wherein the d-spacing value is a d-spacing value of the (003) plane of the layered positive electrode active material.