Description:FIELD OF THE INVENTION
[0001] The present invention relates to electrode active material for use in metal-ion batteries. Particularly, the invention relates to a surface modified biomass derived substrate as the electrode active material.

BACKGROUND OF THE INVENTION
[0002] Typically, in a secondary battery for electrochemical energy conversion and storage, two electrodes and an electrolyte are commonly employed with electrochemical reactions proceeding at both electrodes with more or less significant changes in the composition of the electrolyte. Typical examples of metal-ion batteries reported in various studies include sodium-, lithium-, potassium, magnesium, zinc, calcium, and fluorine-ion batteries. In general, for any battery, electrode material is a critical factor affecting battery performance and cost relative to other materials. While several studies have been dedicated to electrode fabrication techniques, notable progress has been made on electrode active material front as well. Few state-of-the-art documents in this respect are discussed hereinbelow:
[0003] EP4010938A1 discloses a negative electrode material for a lithium-ion battery. The material comprises particles having a core containing silicon. The particles have one or more coating layers made of porous semi-conducting metal oxides selected from transition metal oxide and lanthanide metal oxide.
[0004] US9466855B2 discloses an additive for a sodium ion secondary battery. The additive includes a compound of at least one of a saturated cyclic carbonate having a fluoro group and a chain carbonate having a fluoro group. The document further discloses a sodium ion battery having an aqueous electrolytic solution that includes the aforesaid additive for sodium ion secondary batteries, and one of a non-aqueous solvent containing a saturated cyclic carbonate and a non-aqueous solvent containing a saturated cyclic carbonate and a chain carbonate; a positive electrode; and a negative electrode that includes a coating formed on the surface of the negative electrode, the coating containing a composite material containing carbon, oxygen, fluorine and sodium, and that includes a negative-electrode active material containing carbon.
[0005] US20170125815A1 describes a method for forming an energy storing device. The document discloses an electrode formed by blending of dry active powdery electrode forming materials with an aqueous binder dispersion, and the subsequent adhering of the wet binder/dry active powdery electrode-forming materials blend to an electroconductive substrate, resulting in an electrode.
[0006] Despite the advances in material development, one of the major challenges that still appear in most of the commercially available batteries is slow charging capability or low power potential. The inclusion of fast charging capabilities enables devices to offer rapid charging options, potentially benefiting electric vehicles by extending their range. It is also desired that improvement in the aforementioned properties should not downgrade other performance characteristics of the battery, such as voltage, energy density, power density and cycle stability. Of course, the selected materials need to be cost effective, should not require substantial modifications to the electrode fabrication techniques and can be developed via a commercially scalable method.
[0007] Accordingly, there is a dire need to provide an electrode active material effective in mitigating one or more of the challenges in the state of the art.

OBJECT OF THE INVENTION
[0008] An object of the present invention to provide an electrode active material effective in mitigating one or more of the challenges in the state of the art.
[0009] Still another object of the present invention is to provide a solution for the major challenges of the commercially available batteries having slow charging capability or low power potential.
[0010] Yet another embodiment of the present invention is to provide an electrode active material with fast charging capabilities further enabling the devices to offer rapid charging options, along with potentially benefiting the electric vehicles by extending their range

SUMMARY OF INVENTION
[0011] Surprisingly, it has been found that the above object is met by providing an electrode active material described hereinbelow.
[0012] Accordingly, in one aspect, the present invention relates to an electrode active material comprising of a core made of a biomass derived substrate, the core having one or more coating layer disposed around the core, said coating layer comprising an active material which is a transition metal oxide.
[0013] In an embodiment, the biomass is selected from the group consisting of petroleum pitch, tar, lignin, rice husk, coconut shell, glucose, sucrose, pet coke, dextrose, carbohydrate materials, cuttlebone, tea leaves, lotus stem, spinifex grass, recycled cork, and aromatic residues.
[0014] In another embodiment, the biomass derived substrate is selected from the group consisting of hard carbon, soft carbon, amorphous carbon, graphitized carbon, non-graphitized carbon, pitch, synthetic graphite, and natural graphite.
[0015] In yet another embodiment, the transition metal of the transition metal precursor is selected from the group consisting of lithium, sodium, potassium, aluminum, zinc, titanium, iron, magnesium, ruthenium, niobium, tantalum, zirconium, vanadium, chromium, tungsten, cobalt, nickel, copper, molybdenum, zirconium and manganese.
[0016] In still another embodiment, the transition metal precursor is a titanium precursor. In another aspect, the present invention describes a method for preparing the above electrode active material comprising the steps of:
(a) dispersing the biomass derived substrate in a solvent;
(b) adding a solution comprising the active material, and a non-ionic surfactant and/or linker to the biomass derived substrate of step (a) to obtain a pre-coated substrate; and
(c) heating the pre-coated substrate at a temperature ranging between 30°C to 1050°C to obtain the electrode active material.

[0017] In another embodiment, the solvent is selected from the group consisting of water, methanol, ethanol, acetone, isopropyl alcohol, dimethyl ether, dimethyl carbonate, benzene, toluene, xylene, and tetrahydrofuran.
[0018] In yet another embodiment, the non-ionic surfactant and/or linker is selected from the group consisting of pheoxypolyethoxyethanol, sodium dodecyl sulfate, cetyltrimethylammonium halides, sorbitan monooleate, lithium salt of polyacrylic acid, and sodium salt of polyacrylic acid.
[0019] In still another embodiment, the pre-coated substrate in step (c) is heated at a temperature ranging between 30°C to 200°C.
[0020] In yet another embodiment, the method further comprises the step of annealing the pre-coated substrate of step (c) in an inert atmosphere at temperatures ranging between 30°C to 1050°C to obtain the electrode active material.
[0021] In a further aspect, the present invention relates to an electrode for a metal-ion battery comprising the above electrode active material.
[0022] In a still further aspect, the present invention describes a method for preparing the above electrode by subjecting the electrode active material to at least one of the following methods: slurry casting, spray pyrolysis deposition, dry coating, wet coating, electrodeposition, and electrophoretic deposition.

BRIEF DESCRIPTION OF FIGURES
[0023] Figures 1(a)-(b) show the Scanning Electron Microscope (SEM) image of bare hard carbon, and surface modified hard carbon in accordance with an embodiment of the present invention.
[0024] Figure 2 shows X-Ray Photoelectron Spectroscopy (XPS) image of surface modified hard carbon in accordance with an embodiment of the present invention.
[0025] Figures 3(a)-(b) show charge discharge profile of surface modified hard carbon, and rate performance comparison of bare hard carbon vs surface modified hard carbon in accordance with an embodiment of the present invention.
[0026] Figure 4 shows long cycling performance (1500 cycles) of hard carbon-Surface modified electrode at 2C rate.

DETAILED DESCRIPTION OF THE INVENTION
[0027] Before the present invention is described, it is to be understood that the terminology used herein is not intended to be limiting since the scope of the presently claimed invention will be limited only by the appended claims.
[0028] The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of", "consists" and "consists of".
[0029] Furthermore, the terms "first", "second", "third" or "(a)", "(b)", "(c)", "(d)", etc. and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. In case the terms "first", "second", "third" or "(A)", "(B)", and "(C)" or "(a)", "(b)", "(c)", "(d)", "I", "ii", etc. relate to steps of a method or use or assay, there is no time or time interval coherence between the steps, that is, the steps may be carried out simultaneously or there may be intervals of seconds, minutes, hours, days, weeks, months, or even years between such steps, unless otherwise indicated in the application as set forth hereinabove or below.
[0030] In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.
[0031] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the presently claimed invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Further, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of this invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the appended claims, any of the claimed embodiments can be used in any combination.
[0032] Furthermore, the ranges defined throughout the specification include the end values as well, i.e., a range of 1 to 10 implies that both 1 and 10 are included in the range. For the avoidance of doubt, the applicant shall be entitled to any equivalents according to applicable law.
[0033] As used herein, the terms “charge” and “charging” may refer to a process of providing electrochemical energy to a cell.
[0034] As used herein, the terms “discharge” and “discharging” refer to a process for removing electrochemical energy from a cell, for example, when using the cell to perform desired work.
[0035] As used herein, the term “positive electrode” may refer to an electrode (often called a cathode) where electrochemical reduction / sodiation occur during a discharging process.
[0036] As used herein, the term “negative electrode” may refer to an electrode (often called an anode) where electrochemical oxidation / desodiation occurs during a discharging process.
[0037] An aspect of the present invention is directed towards an electrode active material.
[0038] In an embodiment, the electrode active material comprises of a core made of a biomass derived substrate, the core having one or more coating layer disposed around the core.

[0039] In the present context, “biomass derived substrate” refers to a substrate of any size and shape which has been obtained from a biomass source. The present invention is not limited by the size and shape of the substrate. Suitable biomass for the present invention can be selected from the group consisting of petroleum pitch, tar, lignin, lignocellulose, rice husk, coconut shell, glucose, sucrose, pet coke, dextrose, carbohydrate materials, cuttlebone, tea leaves, lotus stem, spinifex grass, recycled cork, and aromatic residues. In another embodiment, the biomass is selected from the carbonized coconut shell.
[0040] Accordingly, in an embodiment, the electrode active material comprises of the core made of coconut shell derived hard carbon, the core having one or more coating layer disposed around the core, said coating layer comprising the active material which is transition metal oxide.
[0041] Suitable techniques to convert the biomass to substrate are known to the person skilled in the art. Such techniques include, but are not limited to, pyrolysis which is carried out at high temperatures (usually > 1000°C) in inert atmosphere. The pyrolyzed biomass material can be further treated with a suitable acid and dried at temperatures upto 150°C. The present invention is not limited by the techniques for obtaining the biomass substrate. In fact, commercially available substrates may also be employed.
[0042] In yet another embodiment, the biomass derived substrate is selected from the group consisting of hard carbon, synthetic graphite, and natural graphite. In still another embodiment, the biomass derived substrate is hard carbon.
[0043] In another embodiment, the biomass derived substrate has a surface area ranging between 0.1 m2/g to 200 m2/g determined according to BET technique
[0044] In still another embodiment, the surface area ranges between 0.1 m2/g to 150 m2/g, or 5 m2/g to 150 m2/g, or 5 m2/g to 120 m2/g, or 10 m2/g to 120 m2/g. In yet another embodiment, the surface area ranges between 10 m2/g to 80 m2/g, or 15 m2/g to 80 m2/g, or 20 m2/g to 50 m2/g, or 25 m2/g to 50 m2/g.
[0045] Accordingly, in an embodiment, the electrode active material comprises of the core made of biomass derived substrate having surface area ranging between 0.1 m2/g to 200 m2/g, the substrate having one or more coating layer disposed around the substrate, said coating layer comprising the active material which is transition metal precursor.
[0046] In another embodiment, the electrode active material comprises of the core made of hard carbon having surface area ranging between 0.1 m2/g to 200 m2/g, the hard carbon having one or more coating layer disposed around the hard carbon, said coating layer comprising the active material which is transition metal precursor.
[0047] In an embodiment, the core is coated with at least one coating layer around it. In an exemplary embodiment, the core is coated with one, or two, or three, or four, and so on layers onto it. The coating layer comprises the active material which is transition metal precursor. In case of more than one coating layer, each of the said layers can be same or different.
[0048] Transition metal in the transition metal precursor is selected from the group consisting of lithium, sodium, potassium, aluminium, zinc, titanium, iron, magnesium, ruthenium, niobium, tantalum, zirconium, vanadium, chromium, tungsten, cobalt, nickel, copper, molybdenum, zirconium, and manganese. In an embodiment, the transition metal is selected from the group consisting of lithium, sodium, potassium, aluminium, zinc, titanium, iron, magnesium, ruthenium, niobium, tantalum, zirconium, vanadium, chromium, tungsten, cobalt, nickel, copper, and molybdenum. In another embodiment, the transition metal is selected from the group consisting of aluminium, zinc, titanium, iron, magnesium, ruthenium, niobium, tantalum, zirconium, vanadium, and chromium. In yet another embodiment, the transition metal is titanium.
[0049] Suitable precursors include oxides, alkoxides, nitrates, chlorides, acetates, ketonate, carboxylates, sulphates and a combination thereof
[0050] In an embodiment, the transition metal precursor is a titanium precursor, for example titanium oxide, titanium alkoxide, titanium tetrachloride and a combination thereof. The precursor may be in the form of solution, powder and/or particles with varied size range. The present invention is not limited by the form of transition metal precursor.
[0051] Accordingly, in an embodiment, the electrode active material comprises of the core made of biomass derived substrate, the substrate having one or more coating layer disposed around the substrate, said coating layer comprising the active material which is titanium precursor.
[0052] In a further embodiment, the electrode active material consists of the core made of biomass derived substrate, the substrate having one or more coating layer disposed around the substrate, said coating layer comprising the active material which is transition metal precursor.
[0053] Another aspect of the present invention is directed towards a method for preparing the electrode active material described hereinabove. Accordingly, the embodiments described hereinabove in respect of the electrode active material are applicable here as well.
[0054] In an embodiment, the method comprises the step of:
(a) dispersing the biomass derived substrate in a solvent,
(b) adding a solution comprising the active material, and a non-ionic surfactant and/or linker to the biomass derived substrate of step (a) to obtain a pre-coated substrate, and
(c) heating the pre-coated substrate at a temperature ranging between 30°C to 1050°C to obtain the electrode active material.
[0055] In one embodiment, the solvent is selected from the group consisting of water, methanol, ethanol, acetone, isopropyl alcohol, dimethyl ether, dimethyl carbonate, benzene, toluene, xylene, and tetrahydrofuran. In another embodiment, the solvent is selected from the group consisting of water, methanol, ethanol, acetone, isopropyl alcohol, benzene, toluene, xylene, and tetrahydrofuran. In yet another embodiment, the solvent is selected from the group consisting of water, methanol, ethanol, acetone, isopropyl alcohol, xylene, and tetrahydrofuran. In still another embodiment, the solvent is selected from the group consisting of water, methanol, ethanol, xylene, and tetrahydrofuran.
[0056] In an embodiment, the non-ionic surfactant and/or linker is selected from the group consisting of pheoxypolyethoxyethanol, sodium dodecyl sulfate, cetyltrimethylammonium halides, sorbitan monooleate, lithium salt of polyacrylic acid, and sodium salt of polyacrylic acid.

[0057] Stoichiometric amounts of the active material, and the non-ionic surfactant and/or linker are mixed to obtain the solution which is subsequently added to the biomass derived substrate to obtain the pre-coated substrate. Suitable mixing means in the present context are known to the person skilled in the art. For instance, a stirrer may be employed for mixing the solution. Other additives generally known in the art may also be added here.
[0058] In an embodiment, the amount of the non-ionic surfactant and/or linker in the solution ranges between 0.005 wt.% to 25 wt.% based on the total weight of the solution. In another embodiment, the amount the amount of the non-ionic surfactant and/or linker may range between 0.05 wt.% to 25 wt.%, or 0.05 wt.% to 22 wt.%, or 0.5 wt.% to 22 wt.%. In yet another embodiment, the amount ranges between 0.5 wt.% to 20 wt.%, or 0.5 wt.% to 18 wt.%, or 0.5 wt.% to 15 wt.%. In still another embodiment, the amount ranges between 1.0 wt.% to 15 wt.%, or 1.0 wt.% to 12 wt.%.
[0059] Accordingly, in an embodiment, the method comprises the steps of:
(a) dispersing hard carbon in the solvent,
(b) adding the solution comprising the active material, and the non-ionic surfactant and/or linker to hard carbon of step (a) to obtain the pre-coated substrate, wherein the amount of the non-ionic surfactant and/or linker ranges between 0.005 wt.% to 25 wt.% based on the total weight of the solution, and
(c) heating the pre-coated substrate at temperature ranging between 30°C to 1050°C to obtain the electrode active material.
[0060] The pre-coated substrate obtained herein is then subjected to heating at a temperature ranging between 30°C to 900°C. In an embodiment, the temperature ranges between 30°C to 800°C, or 30°C to 500°C, or 30°C to 200°C. In yet another embodiment, the temperature ranges between 30°C to 100°C, or 40°C to 80°C.
[0061] Accordingly, in an embodiment, the method comprises the steps of:
(a) dispersing hard carbon in the solvent,
(b) adding the solution comprising titanium precursor, and the non-ionic surfactant and/or linker to hard carbon of step (a) to obtain the pre-coated substrate, wherein the amount of the non-ionic surfactant and/or linker ranges between 0.005 wt.% to 25 wt.% based on the total weight of the solution, and
(c) heating the pre-coated substrate at temperature ranging between 30°C to 200°C to obtain the electrode active material
[0062] The method further comprises the step of annealing the pre-coated substrate of step (c) in an inert atmosphere at temperatures ranging between 30°C to 1050°C to obtain the electrode active material. The inert atmosphere includes argon, nitrogen, or vacuum conditions.
[0063] Accordingly, in an embodiment, the method comprises the step of:
(a) dispersing the biomass derived substrate in a solvent,
(b) adding a solution comprising the active material, and a non-ionic surfactant and/or linker to the biomass derived substrate of step (a) to obtain a pre-coated substrate,
(c) heating the pre-coated substrate at a temperature ranging between 30°C to 200°C, and
(d) annealing the pre-coated substrate of step (c) in an inert atmosphere at temperatures ranging between 30°C to 1050°C to obtain the electrode active material.
[0064] Another aspect of the present invention relates to an electrode for a metal-ion battery comprising the electrode active material, as described hereinabove. Accordingly, the embodiments described hereinabove in respect of the electrode active material are applicable here as well.
[0065] The electrode may also include, in addition to the electrode active material, one or more of binders, plasticizers, solvents, electrically conductive materials, and the likes. Suitable binders can be selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, polyacrylic acid, alginic acid, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluorinated rubber.
[0066] Suitable solvents can be selected from the group consisting of N-methylpyrrolidone (NMP), acetone, ethanol, and water.
[0067] As the electrically conductive material, any material that is generally used in a metal-ion battery may be used, and examples thereof include carbon-based materials such as carbon black, acetylene black, Ketjen black, reduced graphene oxide, and carbon nanotube; metal-based materials such as metal powder or metal fibers such as copper, nickel, aluminum, and silver; electrically conductive polymers such as polyphenylene derivatives; or mixtures thereof. The content of the electrically conductive material that is used may be suitably controlled.
[0068] Still another aspect of the present invention relates to a method for preparing the electrode.
[0069] Suitable methods for preparing the electrode are selected from the group consisting of slurry casting, spray pyrolysis deposition, dry coating, wet coating, electrodeposition, and electrophoretic deposition. For this, the electrode active material is subjected to any of the aforementioned techniques to obtain the electrode. Accordingly, the embodiments described hereinabove in respect of the electrode active material are applicable here as well.
[0070] In one embodiment, the method comprises the step of at least obtaining a slurry comprising the electrode active material, and one or more of binders, plasticizers, solvents, and the likes. The aforementioned ingredients are added in suitable amounts. For instance, the amount of the electrode active material in the slurry ranges between 50 wt.% to 90 wt.% based on the total weight of the slurry. The amount of the binder in the slurry ranges between 1 wt.% to 20 wt.% based on the total weight of the slurry.
[0071] Additionally, the slurry also includes one or more selected from the group consisting of electrically conductive carbon, precious metals, and metals. Suitable amounts of these materials include 1 wt.% to 20 wt.% based on the total weight of the slurry.
[0072] Subsequently, the slurry is coated on the electrically conductive material and finally dried to obtain the electrode. In the present disclosure, the slurry is applied to a surface of the electrically conductive material and a suitable thickness of the coating is achieved. The person skilled in the art is aware of suitable coating thickness and hence, the present invention is not limited by the same.
[0073] Still another aspect of the present invention relates to a metal-ion battery comprising the electrode, as described above, and an electrolyte. Accordingly, the embodiments described hereinabove in respect of the electrode are applicable here as well.
[0074] The electrode of the present invention may be employed in any metal-ion battery along with the typical components thereof, such as but not limited to, current collector, electrolyte and separator.
[0075] In the present disclosure, the current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. The current collector may be, for example, aluminum, nickel, titanium, fired carbon, copper or stainless steel, which may be optionally surface-treated with carbon, nickel, titanium, silver, or the like. Alternatively, the current collector may be an aluminum-cadmium alloy. In addition, fine irregularities may be formed on the surface of the current collector to enhance the binding force of the positive electrode active material to the surface, and the current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous material, foam, and a non-woven fabric.
[0076] In the present disclosure, the electrolyte may include a liquid electrolyte, a gel polymer, a solid electrolyte, or a combination thereof. The liquid electrolyte may include a sodium salt, an organic solvent, or a combination thereof; and the gel electrolyte may include an organic solid electrolyte containing a polymer compound, an inorganic solid electrolyte, or a combination thereof. The solid electrolyte may include an organic solid electrolyte containing a polymer compound, an inorganic solid electrolyte, or a combination thereof.
[0077] In the present disclosure, when the electrolyte is a liquid electrolyte, it includes an electrolyte salt and a solvent. The electrolyte salt that is used in the present invention includes one or more selected from the group consisting of sodium-containing hydroxides (e.g., sodium hydroxide (NaOH), etc.), borates (e.g., sodium metaborate (NaBO2), borax (Na2B4O7), boric acid (H3BO3), etc.), phosphates (e.g., sodium phosphate tribasic (Na3PO4), sodium pyrophosphate (Na2HPO4), etc.), chloric acid (e.g., NaClO4, etc.), NaAlCl4, NaAsF6, NaBF4, NaPF6, NaSbF6, NaCF3SO3, and NaN(SO2CF3)2, sodium fluoride, sodium sulfate, sodium nitrate, and sodium lignosulfonate.
[0078] In addition, in the present disclosure, a solvent may be used without particular limitation, as long as it may serve as a medium through which ions involved in the electrochemical reaction of the battery may move. Specifically, the solvent may be an aqueous solvent such as water or an alcohol, or a non-aqueous solvent such as an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, or a carbonate solvent. It is possible to use one or a mixture of two or more selected from among these solvents.
[0079] Suitable solvents can be selected from the group consisting of trimethyl phosphate (TMP), triethyl phosphate (TEP), methyl ethyl carbonate, methylpropionate carbonate, ethyl propionate, ethyl acetate, ethyl methyl carbonate, methyl formate, propylene carbonate, ethylene carbonate, vinylene carbonate, fluoroethylene carbonate, methyl acetate, triethylene glycoldimethyl ether, dimethyl sulfone, dimethyl ether, ethylene sulfite, diethyl carbonate, dimethyl carbonate, propylene oxide, propylene sulfite, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propyl acetate, methyl butanone, methyl isobutylketone, toluene cyclohexanone, ethylene glycol dimethylether and Tetraethylene glycol dimethyl ether.
[0080] In the present disclosure, the separator separates the negative electrode and the positive electrode from each other, and provides a channel for metal ions to move, and any known separator may be used for this purpose. Said otherwise, it is possible to use a separator having excellent electrolyte solution moisturizing ability while having low resistance to electrolyte ion movement. For example, the separator may be selected from among glass microfibers, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or combinations thereof, and may be in the form of nonwoven fabric or woven fabric. Preferably, a polyolefin-based polymer separator such as polyethylene or polypropylene is mainly used for metal-ion secondary battery, and a coated separator containing a ceramic component or a polymer material may also be used to ensure heat resistance or mechanical strength. Optionally, the separator may have a single-layer or multi-layer structure.
[0081] The electrode in accordance with the present invention is assembled along with other components to obtain the metal-ion battery.
[0082] Advantageously, the present invention provides for improved capacity and rate capability or fast charging capability. Furthermore, the surface modification does not result in downgrading of the performance characteristics of the battery, but instead provides an improved and/or acceptable property such as energy density, power density, cycle stability, voltage, etc. Moreover, the choice and selection of materials for making the electrode active material of the present invention renders the overall fabrication cost effective and facile.
[0083] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
Examples
[0084] The presently claimed invention is illustrated by the non-restrictive examples which are as follows:
[0085] To initiate the process, coconut shell was procured from Kerala, India. Biomass derived hard carbon was uniformly dispersed in methanol via sonication technique. Stoichiometric amount of titanium isopropoxide or titanium butoxide was added to the above solution which was mixed prior with the non-ionic surfactant and/or linker.
The non-ionic surfactant and/or linker is selected from the group consisting of pheoxypolyethoxyethanol, sodium dodecyl sulfate, cetyltrimethylammonium halides, sorbitan monooleate, lithium salt of polyacrylic acid, and sodium salt of polyacrylic acid. The solution was then heated to 60°C to remove the methanol and annealed in nitrogen atmosphere to obtain the electrode active material, i.e., surface modified hard carbon (HC-SM). Pristine hard carbon (HC-Bare) without any surface treatment was used for comparison purpose.
Example 1:
[0086] In a particular synthesis, 20 microliter of linker is transferred to a solution of 200 mg of carbon dispersed in 20 ml absolute methanol. This is followed by addition of 150 ul metal precursor resulting in surface adsorption and layer formation on carbon surface. Finally, the same is dried to evaporate the methanol content and later annealed at inert condition at 500°C for 1 hr.
Example 2:
[0087] In another synthesis, a precisely measured volume of 75 microliters of linker solution is carefully introduced into a solution containing 1 grams of dispersed carbon, dissolved in 100 milliliters of absolute ethanol. Following this step, 250 microliters of a metal precursor is meticulously added to the above solution. Subsequent to this reaction, the resultant mixture undergoes a thorough drying process to eliminate residual ethanol content, followed by annealing under inert conditions at a precisely controlled temperature of 400°C for a duration of 3 hours.
Example 3:
[0088] The samples (HC-Bare and HC-SM) were characterized using XRD, SEM, and XPS. From Figure 1, no change in morphology and crystal structure has been observed after surface modification. However, a significant difference in the surface chemistry was observed from the XPS data of Figure 2. Signal of Ti 2p and O1s is visible in the high-resolution spectrum which confirms the formation of TiOx coated hard carbon.
[0089] The surface modified hard carbon was further used to make positive electrodes prepared via the conventional slurry casting technique for a sodium ion battery. It was observed form Figures 3(a)-(b) that surface modification evokes significant changes in cell performances particularly at rates beyond C/2. On increasing the rate from 1C and above, the capacity of HC-SM retained above 175 mAh/g, while the pristine sample was able to retain only 80 mAh/g at 2C rate. From Figure 4, it can be observed that the HC-SM sample delivered excellent cycling stability of 1500 cycles when cycled at 2C for both charge and discharge.
[0090] From the foregoing, it can be concluded that the electrode slurry in accordance with the present invention results in enhanced electrochemical properties in the electrode.
, Claims:1. An electrode active material comprising a core made of a biomass derived substrate, the core having one or more coating layer disposed around the core, said coating layer comprising an active material which is a transition metal precursor.
2. The electrode active material as claimed in claim 1, wherein the biomass is selected from the group consisting of petroleum pitch, tar, lignin, rice husk, coconut shell, glucose, sucrose, pet coke, dextrose, carbohydrate materials, cuttlebone, tea leaves, lotus stem, spinifex grass, recycled cork, and aromatic residues.
3. The electrode active material as claimed in claim 1, wherein the biomass derived substrate is selected from the group consisting of hard carbon, soft carbon, amorphous carbon, graphitized carbon, non-graphitized carbon, pitch, synthetic graphite, and natural graphite.
4. The electrode active material as claimed in claim 1, wherein the transition metal of the transition metal precursor is selected from the group consisting of lithium, sodium, potassium, aluminum, zinc, titanium, iron, magnesium, ruthenium, niobium, tantalum, zirconium, vanadium, chromium, tungsten, cobalt, nickel, copper, molybdenum, zirconium and manganese.
5. The electrode active material as claimed in claim 1, wherein the transition metal precursor is a titanium precursor.
6. A method for preparing the electrode active material as claimed in claim 1, said method comprising the steps of:
(a) dispersing the biomass derived substrate in a solvent,
(b) adding a solution comprising the active material, and a non-ionic surfactant and/or linker to the biomass derived substrate of step (a) to obtain a pre-coated substrate, and
(c) heating the pre-coated substrate at a temperature ranging between 30°C to 1050°C to obtain the electrode active material.
7. The method as claimed in claim 6, wherein the solvent is selected from the group consisting of water, methanol, ethanol, acetone, isopropyl alcohol, dimethyl ether, dimethyl carbonate, benzene, toluene, xylene, and tetrahydrofuran.
8. The method as claimed in claim 6 or 7, wherein the non-ionic surfactant and/or linker is selected from the group consisting of pheoxypolyethoxyethanol, sodium dodecyl sulfate, cetyltrimethylammonium halides, sorbitan monooleate, lithium salt of polyacrylic acid, and sodium salt of polyacrylic acid.
9. The method as claimed in claims 6 to 8, wherein in step (c) the pre-coated substrate is heated at a temperature ranging between 30°C to 200°C.
10. The method as claimed in claims 6 to 9 further comprising the step of annealing the pre-coated substrate of step (c) in an inert atmosphere at temperatures ranging between 30°C to 1050°C to obtain the electrode active material.
11. The method as claimed in claim 6-10 by subjecting the electrode active material to at least one of the following methods: slurry casting, spray pyrolysis deposition, dry coating, wet coating, electrodeposition, and electrophoretic deposition.
12. An electrode for a metal-ion battery comprising the electrode active material as claimed in one or more of claims 1 to 5 or obtained from the method as claimed in one or more of claims 6 to 10.