DESC:BACKGROUND
FIELD OF THE DISCLOSURE
[0001] Various embodiments of the disclosure relate generally to lithium-ion (Li-ion) based energy storage devices. More specifically, various embodiments of the disclosure relate to a cathode of a lithium-ion battery and methods of making the same.
DESCRIPTION OF THE RELATED ART
[0002] Lithium-ion energy storage devices, for example, lithium-ion batteries (LIBs), are the most widely used power storage and generation devices currently due to their comprehensive superiority in power density, energy density, service life, and cost. The high energy density and low cost enable the LIBs to be used not only in portable devices such as phones and laptops but also find applications in electric vehicles.
[0003] The performance of a LIB mostly depends on the performance of its electrodes. For example, the higher the electrode density of an electrode, higher the energy density of the LIB. Therefore, the development of high-density electrodes may improve the overall performance of the LIB.
[0004] An electrode of the LIB is typically formed by applying an active material on a current collector. The active material may be applied through a dry process, i.e., in the absence of any solvent by way of a dry jet and mortar, or dry powder coating method. However, the application of the active material through the dry process is quite complex and requires sophisticated machinery and techniques. Alternatively, a wet slurry technique may be employed for making the electrodes. In the wet slurry technique, the active material is mixed with a conductive additive and a binder and dispersed in an organic solvent, or in an aqueous medium to form a wet slurry. The wet slurry is then applied to the current collector to form the electrode. However, due to the presence of the binder and solvent, it is a challenge to achieve high electrode density of the electrode and hence improved energy density of the LIB.
[0005] Limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of described systems with some aspects of the present disclosure, as set forth in the remainder of the present application and with reference to the drawings.
SUMMARY
[0006] According to the embodiments of the present disclosure, a cathode of a lithium-ion battery is provided. The cathode comprises a cathode material comprising a first active material and a second active material. A ratio of a particle size of the first active material to a particle size of the second active material is in a range of 10:1 to 4:1. The first active material and the second active material comprise lithium metal phosphate having the formula LiMPO4, where M is a metal selected from iron, manganese, cobalt, nickel, and any combinations thereof.
[0007] In one embodiment of the present disclosure, a method of making a cathode of a lithium-ion battery is provided. The method comprises providing a binder in a solvent to form a first mixture. The method further comprises providing a conductive additive in the first mixture to form a second mixture. The method further comprises providing a first active material and a second active material in the second active mixture to form an electroconductive slurry. The ratio of a particle size of the first active material to a particle size of the second active material is in the range of 10:1 to 4:1. The first active material and the second active material comprise lithium metal phosphate having the formula LiMPO4, where M is a metal selected from iron, manganese, cobalt, nickel and any combinations thereof. The method further comprises coating the electroconductive slurry on a current collector to form a coated current collector. The method further comprises drying and calendaring the coated current collector to form the cathode.
[0008] These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a schematic diagram of a lithium-ion battery comprising a cathode, in accordance with an embodiment of the disclosure; and
[0010] FIG. 2 represents a flowchart that illustrates a method of making a cathode of a lithium-ion battery, in accordance with an embodiment of the disclosure.
[0011] Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of embodiments is intended for illustration purposes only and is, therefore, not intended to necessarily limit the scope of the present disclosure.
DETAILED DESCRIPTION OF EMBODIMENTS
[0012] The following description illustrates some embodiments of the disclosed disclosure in detail. Those of skill in the art will recognize that there are numerous variations and modifications of this disclosure that are encompassed by its scope. Accordingly, the description of a certain embodiment should not be deemed to limit the scope of the present disclosure.
[0013] The term “comprising” as used herein is synonymous with “including” or “containing” and is inclusive or open-ended and does not exclude additional, unrecited elements, or method steps.
[0014] All numbers expressing quantities of ingredients, property measurements, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained.
[0015] As used herein, the term “lithium-ion based energy storage device” or “lithium-ion battery” (LIB) may refer to a rechargeable battery that uses reversible reduction of lithium ions to store energy. A typical LIB may include an anode, a cathode, a separator, an electrolyte, and two current collectors. During a charge cycle, Li ions migrate from the cathode toward the anode through the electrolyte while the electrons migrate from the cathode toward the anode via an external circuit. During a discharge cycle, Li ions migrate from the anode toward the cathode through the electrolyte while the electrons leave the anode and move through the external circuit to the cathode. Examples of LIBs may include anode-free LIBs, lithium-ion polymer batteries, batteries with liquid electrolytes, and solid-state batteries.
[0016] As used herein, the term “cathode” refers to an electrode of an electrochemical cell (e.g., a LIB) at which reduction occurs and that supplies electrons during the charging of the LIB. As used herein, the term “anode” refers to an electrode of the electrochemical cell at which oxidation occurs and that accepts electrons during the charging of the LIB. As used herein, the term “electrolyte” refers to a material that allows ions, for example, Li ions, to migrate therethrough, but does not allow electrons to conduct therethrough. As used herein, “current collectors” refer to bridging components that collect electrical current generated at the electrodes and connect with external circuits.
[0017] FIG. 1 is a schematic diagram of a lithium-ion battery (LIB) 100, in accordance with an embodiment of the disclosure. The LIB 100 includes a cathode 102, an anode 104, an electrolyte 106, and a separator 108. The cathode 102 is formed by disposing a cathode material 110 on a cathode current collector 112. The anode 104 is formed by disposing an anode material 114 on an anode current collector 116. The separator 108 is disposed between the cathode 102 and the anode 104 to keep them separate. The electrolyte 106 may be a solid electrolyte or a liquid electrolyte that allows Li ions to migrate therethrough. Non-limiting examples of the electrolyte 106 may include lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium bis(oxalato)borate (LiBOB), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), and lithium hexafluorophosphate (LiPF6).
[0018] The cathode current collector 112 and the anode current collector 116, independently, may be made of stainless steel, aluminum, nickel, titanium, copper, calcined carbon, carbon on the surface of aluminum or stainless steel, silver, or the like. In one embodiment, the cathode current collector 112 is made of aluminum and the anode current collector 116 is made of a carbon-based material. In another embodiment, both the cathode current collector 112 and the anode current collector 116 are made of aluminum. The cathode current collector 112 and the anode current collector 116, independently, may have a thickness in the range of 3 microns (µm) to 500 µm. The cathode current collector 112 and the anode current collector 116, independently, may be in the form of a film, a sheet, a foil, a mesh, a porous body, a foam, or a non-woven body.
[0019] The anode material 114 includes an anode active material. Non-limiting examples of the anode active material include graphite, silicon carbide (SiC) nanocomposites, lithium titanium oxides such as lithium titanium oxide (LiTiO2), lithium titanate (Li4Ti5O12), tin (Sn) particulates, or silicon (Si) particulates.
[0020] The cathode material 110 includes a cathode active material, a conductive additive, and a binder. According to an embodiment of the disclosure, the cathode active material includes a first active material and a second active material. In one embodiment, the first active material and the second active material, independently, include a lithium metal phosphate of formula LiMPO4, where M is a metal selected from iron, manganese, cobalt, nickel, and any combinations thereof. In an embodiment, lithium metal phosphate has an olivine structure. An example of an olivine-structured lithium metal phosphate is lithium iron phosphate (LiFePO4). In an embodiment, at least the first active material or the second active material is olivine-structured lithium metal phosphate. In a certain embodiment, the first active material and the second active material, independently, are olivine-structured lithium iron phosphate. In some other embodiments, the first active material and the second active material may include different lithium metal phosphates.
[0021] According to an embodiment of the disclosure, the first active material and the second active material are different in their particle sizes. As used herein, and hereinafter, the term, “particle size” refers to “particle size (D50)” and can be defined as an average diameter of the particles corresponding to 50% of the cumulative volume of material in a particle size distribution curve obtained by a measuring technique. In one embodiment, the particle size is measured using the laser diffraction technique. In another embodiment, other known particle size measurement techniques may be utilized for measuring the particle size. In general, the laser diffraction technique may be used to measure a particle size of several millimeters (mm) from a submicron region and can obtain high reproducibility and high-resolution results.
[0022] In an embodiment, the first active material contains large particles and the second active material contains smaller particles as compared to the particles of the first active material. A particle size of the first active material may be in a range of 2 µm to 10 µm. In a certain embodiment, the particle size of the first active material is in a range of 5 µm to 9 µm. Further, the second active material may have a particle size in a range of 0.1 µm to 1.5 µm. In a certain embodiment, the particle size of the second active material is in a range of 0.3 µm to 1 µm. In an embodiment, a ratio of the particle size of the first active material to the particle size of the second active material is in a range of 10:1 to 4:1. In a certain embodiment, the ratio of the particle size of the first active material to the particle size of the second active material is in a range of 9:1 to 5:1.
[0023] In addition, the first active material and the second active material may have different tap densities. As used herein, the term “tap density” is defined as the mass per volume of a material made of particles, and refers to a density in which the voids between particles are filled by constant tapping or vibrations. The tap density can be measured based on the ASTM D4781 test method from the American Society for Testing and Materials (ASTM) and can be calculated using the formula TD=W/V, where TD is the tap density, W is the weight of the sample material in grams, and V is the volume of the sample material after tapping. Several factors are favored to improve the tap density including the compactness or fitting of particles, morphology and size of the particles, and porosity of the material. The first active material may have a tap density in the range of 1.0 to 1.4 gcm-3. The second active material may have a tap density in the range of 0.9 to 1.2 gcm-3.
As known to skilled in the art, a high loading of an active material in a cathode is desirable to achieve high electrochemical performance of the cathode and thereby high electrochemical performance (e.g., specific capacity) of a LIB including the cathode. However, increase in the loading of the active material affects one or more attributes such as electrode density and mechanical stability of the cathode. As used herein, the term “loading” refers to an amount of a cathode active material provided in a cathode material per unit area. As used herein, the term “electrode density” is defined as the volumetric mass density of an electrode material (e.g., a cathode material including a cathode active material, a binder, and a conductive additive) in an electrode. The term “specific capacity” corresponds to an amount of electric charge (milliampere hours (mAh)) a material can deliver per gram of material. It is used to describe the performance of an electrode and is expressed as mAh per gram (mAh/g).
[0024] Typically, when a cathode material contains an active material of small particle size alone, a packing fraction of the active material is high, and hence a resulting cathode attains a high electrode density at a low loading of the active material, which adversely affects the electrochemical performance of the cathode. In another example, when a cathode material contains an active material of large particle size, the packing fraction of the active material is low. As a result, the electrode density of a resulting cathode does not increase with an increase in the loading of the active material. Additionally, the resulting cathode has low mechanical stability, and it tends to crumble and gets damaged while winding it for the fabrication of a LIB. As used herein, and hereinafter, the term “packing fraction” refers to a percentage or a ratio of the volume occupied by particles of a material to a total volume of the material. A high packing fraction of the material allows a higher density or compactness of the material.
[0025] In the embodiments disclosed herein, the presence of the first active material and the second active material having different particle sizes in the cathode material 110 provides improved loading of the cathode active material as well as electrode density of the cathode 102 while maintaining good mechanical stability. As a result, the cathode 102 exhibits good electrochemical performance and mechanical stability. In particular, the addition of the second active material (having particles of small particle size) to the first active material (having particles of large particle size) improves the packing fraction of the cathode active material. As a result, the electrode density of the cathode 102 increases with the increase in the loading of the cathode active material. In an embodiment, the electrode density of the cathode 102 is greater than 2.35 gcm-3, for example between 2.35 gcm-3 and 2.8 gcm-3. In a certain embodiment, the electrode density of the cathode 102 is in a range of from 2.4 gcm-3 to 2.7 gcm-3. Further, the cathode 102 may have good mechanical stability and can be wound without getting crumbled and/or damaged while fabricating the LIB 100.
[0026] The improvement in the packing fraction of the cathode active material may depend on the particle sizes, tap densities and amounts of the first active material and the second active material in the cathode material 110. A suitable ratio of an amount of the first active material to an amount of the second active material in the cathode material 110 may be in the range of 1:1 to 4:1 to achieve a desired packing fraction of the cathode active material. In one embodiment, the ratio of the amount of the first active material to the amount of the second active material in the cathode material 110 is 1:1 to 3:1.
[0027] In addition, the improved packing fraction of the cathode active material in the cathode material 110 and the cathode 102 helps in achieving fast charging rate and reducing irreversible capacity losses during the operation of the LIB 100. The improved packing fraction of the cathode active material provides shorter diffusion pathways in the cathode 102 as compared to a cathode that includes the first active material alone and hence improves Li-ion diffusion. The improved Li-ion diffusion in the cathode 102 helps in achieving a fast-charging rate for the LIB 100. Moreover, the improved packing fraction of the cathode active material suppresses active sites that help in reducing the reactive nature of the cathode material 110 and thereby the irreversible capacity losses. By reducing the irreversible capacity losses, the capacity of the Li-ion battery improves. In an embodiment, the improvement of the Li-ion diffusion and/or the reduction of the irreversible capacity losses may be controlled by optimizing the ratio of the amounts of the first active material and the second active material.
[0028] As described previously, the cathode 102 includes the conductive additive. The conductive additive may be a carbon-based additive. Examples of the carbon-based additive include, but are not limited to, carbon black, activated carbon, graphite, graphene, carbon nanotubes, carbon fibers, and vapor-grown carbon fibers (VGCF). The conductive additive comprises a carbon-based additive that has one of a particle-like morphology, a flake-like morphology, or a combination thereof. The conductive additive functions to improve the transportation of the electrons in the cathode 102, thereby enhancing the specific capacity and rate capability of the LIB 100. The term “rate capability” corresponds to an amount of specific charge in mAhg-1 transferred while maintaining a battery voltage limit. The conductive additive may be present in the cathode 102 in an amount of 0.1 weight percent (wt%) to 1.0 wt%, and preferably, in an amount of 0.3 wt% to 0.7 wt%. In one embodiment, the conductive additive is carbon black.
[0029] The cathode 102 includes the binder. Non-limiting examples of the binder include, but are not limited to, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, or any copolymers thereof. In one embodiment, the binder is PVDF. The binder supports binding between the cathode active material and the conductive additive, and also binds the cathode material 110 to the cathode current collector 112. Additionally, the binder may act as a thickening agent to form a slurry of desired viscosity. The binder may be present in the cathode material 110 in an amount of 30 wt% or less, preferably less than 20 wt%.
[0030] The cathode material 110 may be made by physically mixing the ingredients of the cathode material using a wet process. In certain embodiments, the cathode material 110 is prepared by forming a slurry. In an embodiment, the first active material and the second active material may be first mixed in dry form to prepare the cathode active material and then the prepared cathode active material is added during the slurry preparation. In another embodiment, the first active material and the second active material are added, separately during the slurry preparation. The formation of the cathode material 110 by the addition of the first active material and the second active material is described in detail with respect to FIG. 2.
[0031] FIG. 2 represents a flowchart 200 that illustrates a method of making a cathode (e.g., the cathode 102 of the LIB 100 of FIG. 1), in accordance with an embodiment of the disclosure. Referring to FIG. 2, a flowchart 200 that illustrates operations 202 through 210 of making the cathode is shown.
[0032] At 202, a binder is provided in a solvent to form the first mixture. Non-limiting examples of the solvent include N-methyl-2-pyrrolidone (NMP), propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, and any combinations thereof. In some embodiments, the solvent is NMP. The solvent functions as a dispersion medium for the cathode active material, the binder, and the conductive additive in the formation of a slurry.
[0033] In one embodiment, providing the binder in the solvent comprises adding the binder to the solvent with constant stirring to form the first mixture. The addition of the binder may be carried out at an ambient temperature, or at an elevated temperature that promotes mixing and at the same time avoids degradation of the binder. The term “ambient temperature” as used herein, refers to a temperature in a range of 20? to 45?. As used herein, the term “elevated temperature” refers to a temperature greater than ambient temperature and up to 120?.
[0034] Any suitable mixers or stirrers may be utilized such as an ultrasonicator, magnetic stirrers, or commercial mixers such as planetary mixers to provide the first mixture. Depending on the mixer and the mixing conditions, such as the time of mixing and the temperature, the mixing speed (in terms of rotations per minute (rpm)) may be determined. The term “constant stirring” refers to stirring, mixing, and/or agitation to promote uniform mixing. The term “constant stirring” as used herein, also includes the scenario where mixing is performed at one mixing rate (rpm) and is changed to a different mixing rate during the process. In one embodiment, the binder is added to the solvent with constant stirring at a stirring rate of 800 rpm to 1400 rpm over a period of 30 to 70 minutes to form the first mixture.
[0035] At 204, a conductive additive is provided in the first mixture to form a second mixture. Suitable examples of the conductive additive are described previously. In one embodiment, providing the conductive additive to form the second mixture comprises adding the conductive additive with constant stirring to the first mixture. In one embodiment, the conductive additive is added in batches. In one example of batch addition, an amount of the conductive additive is added to the first mixture followed by the addition of another amount of the conductive additive. In one embodiment, the conductive additive includes a first carbon-based conductive additive having a flake-like morphology and a second conductive carbon-based additive having a particle-like morphology. The first and second conductive additives having different morphology help in better loading of the cathode active material on the cathode 102, and thus enhances the electrode density of the cathode 102. In one example, the first carbon-based additive having a flake-like morphology is added followed by the addition of the second carbon-additive having a particle-like morphology. In another example, the carbon-based additive having the first carbon-based additive and the second carbon-based additive is added simultaneously with constant stirring. In one embodiment, the conductive additive is added to the first mixture with constant stirring at a stirring rate of 800 rpm to 1400 rpm over a period of 30 to 70 minutes to form the second mixture.
[0036] At 206, a first active material and a second active material (collectively called as “cathode active material” herein) are provided in the second mixture to form an electroconductive slurry. The first active material and the second active material are described previously. In an embodiment, the cathode active material including the first active material and the second active material may be added to the second mixture in a single addition with constant stirring over a period (e.g., 30-50 minutes), at ambient temperature. In another embodiment, the first active material and the second active material are added over a period of time with constant stirring. The period of time may range from 20 minutes to 1 hour. The stirring rate may range from 1000 rpm to 1200 rpm.
[0037] In yet another embodiment, the cathode active material comprising the first active material and the second active material is added in batches. In the batch addition, a batch (for example, a portion) of the cathode active material comprising the first active material and the second active material is added with constant stirring followed by the addition of a subsequent batch. The number of batches may vary from 2 to 5. In one embodiment, each batch comprises an equal amount of the cathode active material comprising the first active material and the second active material. In yet another embodiment, an amount of a first batch is different from a subsequent batch of the cathode active material. In an embodiment, the cathode active material is added to the second mixture with constant stirring at a stirring rate of 1000 rpm to 1200 rpm over a period of 30 minutes to 2 hours.
[0038] In one embodiment, the first active material and the second active material are added to the second mixture subsequently to form the electroconductive slurry. In a preferred embodiment, the second active material is added to the second mixture with constant stirring followed by the addition of the first active material with constant stirring. In such an example, the first active material and the second active material are added, separately, to the second mixture with constant stirring at a stirring rate of 1000 rpm to 1200 rpm over a period of 30 minutes to 2 hours.
[0039] As discussed, by optimizing the particle sizes and amounts of the first active material and the second active material in the cathode active material, the electrode density of the resulting cathode (e.g., the cathode 102 of FIG. 1) is increased. The sequential addition of the second active material and the first active material ensures that a slurry of desired viscosity is formed with minimal solvent, which further increases the electrode density.
[0040] In an embodiment, the electroconductive slurry has a solids content in the range of 60% to 80%. As used herein, the term “solids content” refers to a weight percent (wt%) of solids (for example, binders, active material, and conductive additive) to the total weight of the electroconductive slurry. A high solids content helps in achieving the desired viscosity of the electroconductive slurry.
[0041] At 208, the electroconductive slurry is coated on a cathode current collector (e.g., the cathode current collector 112 of FIG.1) to form a coated current collector. In one embodiment, the cathode current collector 112 is an aluminum foil having a thickness in the range of 10 to 20 µm. In certain embodiments, the cathode current collector 112 may be surface treated prior to coating with the electroconductive slurry. The surface treatment may include subjecting the surface of the cathode current collector 112 to at least one selected from the group consisting of a plasma treatment, laser treatment, wet chemical treatment, ion beam treatment, electron beam treatment, and thermal etching treatment.
[0042] The coating of the electroconductive slurry on the cathode current collector 112 may be accomplished by means of spray coating, spin coating, dip coating, or similar methods. In one embodiment, the electroconductive slurry is spray-coated on a surface of the cathode current collector 112 at ambient temperature. The coating may have a thickness in a range of 10 µm to 600 µm. A second surface or opposite surface of the current collector is coated subsequently.
[0043] At 210, the coated current collector is dried and calendared to form a cathode (for example the cathode 102 of FIG. 1). The drying may be performed at ambient temperature or at elevated temperature. It is preferred to have minimal or no solvent on the resulting cathode. Calendaring is performed to enhance the bonding, density, and porosity of the cathode material 110.
[0044] The cathode as prepared may be stamped and slit to the required dimension to fit the LIB cell design (for example, the LIB 100 of FIG. 1).
[0045] In one embodiment, the ratio of wt% of the cathode active material to the conductive additive to the binder in the electroconductive slurry, of step 206, or in the cathode material 110 or the cathode 102 formed therefrom is in the range of 85-98:2-8:2.5-8.
[0046] Three cathode samples (cathode sample 1, cathode sample 2, and cathode sample 3) were formed, separately, by coating an aluminum foil of thickness 15 µm with three different electroconductive slurries - sample slurry 1, sample slurry 2, and sample slurry 3, respectively. Each cathode sample was formed by using the method described with respect to FIG. 2. Sample slurry 1, sample slurry 2, and sample slurry 3 were prepared using the same conductive additive, binder, and solvent but with different cathode active materials. Sample slurry 1 was prepared using the first active material alone and sample slurry 2 was prepared using the second active material alone. Sample slurry 3 was prepared using the cathode active material including the first active material and the second active material. A ratio of the particle size (D50) of the first active material to the particle size (D50) of the second active material was in a range of 10:1 to 9:1 in the sample slurry 3. A ratio of the amount of the first active material to the amount of the second active material was 7:3 in the sample slurry 3. After the formation of cathode samples, cathode sample 1 included the first active material alone, cathode sample 2 included the second active material alone, and cathode sample 3 included the first active material and the second active material.
[0047] The electrode densities and the loadings of the cathode active materials of the respective cathode samples were measured. Table 1 shows the loadings of the cathode active materials and electrode densities of cathode sample 1, cathode sample 2, and cathode sample 3.
Table 1
Cathode Sample Loading (mg/cm2) Electrode Density (g/cm3)
Cathode sample 1 21.5 2.1
Cathode sample 2 18.5 2.3
Cathode sample 3 >22.5 >2.35

As shown, the loading and electrode density of cathode sample 3 prepared using sample slurry 3 (that includes the first active material and the second active material) were higher than the loadings and electrode densities of cathode sample 1 prepared using sample slurry 1 (that includes the first active material alone) and cathode sample 2 prepared using sample slurry 2 (that includes the second active material alone). The enhancement of the loading and electrode density of cathode sample 3 when compared to cathode sample 1 and cathode sample 2 is due to enhanced packing fraction and compaction of the cathode active material in cathode sample 3. Furthermore, although cathode sample 3 had higher loading than cathode sample 1 and cathode sample 2, cathode sample 3 had shown satisfactory mechanical stability. Unexpectedly, the improved packing fraction of the cathode sample 3 resulted in the superior mechanical stability of cathode sample 3. Furthermore, the higher loading of the cathode active material and electrode density of cathode sample 3 as compared to that of cathode sample 1 and cathode sample 2 are indicative of improved specific capacity of a Li-ion battery fabricated using cathode sample 3.
[0048] It is to be understood that the above description is intended to be illustrative, and not restrictive. Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific embodiments, it will be recognized that the disclosure is not limited to the embodiments described, but can be practiced with modification and alteration within the scope of the appended claims.
,CLAIMS:CLAIMS
We claim,
1. A cathode (102) of a lithium-ion battery (100) comprising:
a cathode material (110) comprising a first active material and a second active material, wherein a ratio of a particle size of the first active material to a particle size of the second active material is in a range of from 10:1 to 4:1, and wherein the first active material and the second active material comprise lithium metal phosphate having a formula LiMPO4, wherein M is a metal selected from iron, manganese, cobalt, nickel, and any combinations thereof.

2. The cathode (102) as claimed in claim 1, wherein a ratio of an amount of the first active material to an amount of the second active material in the cathode material (110) is in a range of 1:1 to 4:1.

3. The cathode (102) as claimed in claim 1, wherein a particle size of the first active material is in a range of from 2 microns to 10 microns.

4. The cathode (102) as claimed in claim 1, wherein a particle size of the second active material is in a range of from 0.1 micron to 1.5 microns.

5. The cathode (102) as claimed in claim 1, wherein the cathode material (110) comprises a conductive additive.

6. The cathode (102) as claimed in claim 5, wherein the conductive additive has a particle-like morphology, a flake-like morphology, or a combination thereof.

7. The cathode (102) as claimed in claim 5, wherein the conductive additive comprises carbon black, activated carbon, graphite, graphene, carbon nanotubes, carbon fibers, or vapor-grown carbon fibers (VGCF).

8. The cathode (102) as claimed in claim 1, wherein the cathode (102) has an electrode density between 2.35 gcm-3 and 2.8 gcm-3.

9. The cathode (102) as claimed in claim 1, wherein the ratio of the particle size of the first active material to the particle size of the second active material is in a range of from 9:1 to 5:1.

10. A method of making a cathode (102) of a lithium-ion battery (100) comprising:
providing a binder in a solvent to form a first mixture;
providing a conductive additive in the first mixture to form a second mixture;
providing a first active material and a second active material in the second mixture to form an electroconductive slurry, wherein a ratio of a particle size of the first active material to a particle size of the second active material is in a range of from 10:1 to 4:1, and wherein the first active material and the second active material comprise lithium metal phosphate having a formula LiMPO4, wherein M is a metal selected from iron, manganese, cobalt, nickel, and any combinations thereof;
coating the electroconductive slurry on a current collector (112) to form a coated current collector; and
drying and calendaring the coated current collector to form the cathode (102).

11. The method as claimed in claim 10, wherein the binder comprises polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, or polymethylmethacrylate.

12. The method as claimed in claim 10, wherein the solvent comprises N-methyl-2-pyrrolidone (NMP), propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, or ethyl propionate.

13. The method as claimed in claim 10, wherein the conductive additive comprises carbon black, activated carbon, graphite, graphene, carbon nanotubes, carbon fibers, or vapor-grown carbon fibers (VGCF).

14. The method as claimed in claim 10, wherein a ratio of an amount of the first active material to an amount of the second active material in the electroconductive slurry is in a range of from 1:1 to 4:1.

15. The method as claimed in claim 10, wherein the electroconductive slurry has a solids content in a range of 60% to 80%.