Method for preparing a pre-lithiated anode for a lithium-ion secondary battery, lithium-ion secondary battery comprising the pre-lithiated anode; and use of a solid electrolyte in preparation of the prelithiathed anode

Abstract

The present invention relates to a method for preparing a pre-lithiated anode for a lithium-ion secondary battery. The present invention relates further to a lithium-ion secondary battery comprising the pre-lithiated anode. The present invention relates further to the use of a solid electrolyte in preparation of a pre-lithiated anode for a lithium-ion secondary battery.

Description

METHOD FOR PREPARING A PRE-LITHIATED ANODE FOR A LITHIUM-ION SECONDARY BATTERY, LITHIUM-ION SECONDARY BATTERY COMPRISING THE PRE-LITHIATED ANODE; AND USE OF A SOLID ELECTROLYTE IN PREPARATION OF THE PRELITHIATHED ANODE

[0001] The present invention relates to a method for preparing a pre-lithiated anode for a lithium-ion secondary battery. The present invention relates further to a lithium-ion secondary battery comprising the pre-lithiated anode. The present invention relates further to the use of a solid electrolyte in preparation of a pre-lithiated anode for a lithium-ion secondary battery.

[0002] As the application range of lithium-ion secondary batteries extends to not only portable electronic devices, but also electric vehicles (EV) and electric storage systems (ESS), demand for lithium-ion secondary batteries with high capacity, high energy density, and long lifetime is increasing.

[0003] In the first charging process, a lithium-ion secondary battery loses part of its capacity due to decomposition of the electrolyte on the surface of the anode, whereby the amount of lithium, which determines the capacity of the battery, is reduced. To increase the capacity of a b lithium secondary battery, lithium can be added to the lithium secondary battery, which is known as pre-lithiation. A variety of pre-lithiation methods is known in the art.

[0004] Chemical pre-lithiation with suitable chemical compounds. This method has, however the disadvantage that electrolyte / solvent is / are required, which can lead to contamination of the anode.

[0005] Addition of metallic lithium powder. This method has, however the disadvantage that a pyrophoric material must be used which is disadvantageous in view of safety aspects.

[0006] Evaporation of metallic lithium from a lithium source and the subsequent deposition on the surface of an anode. However, metallic lithium on the electrode surface is disadvantageous due to increased reactivity and possible side reactions.

[0007] Electrolysis of a lithium salt-containing solution followed by insertion of lithium ions in the anode of a lithium-ion secondary battery. This method has, however the disadvantage that electrolyte / solvent is / are required, which can lead to contamination of the anode.

[0008] Electrochemical pre-lithiation with a counter electrode made of metallic lithium. This method has, however the disadvantage that electrolyte / solvent is / are required, which can lead to contamination of the anode. Furthermore, if electrochemical pre-lithiation with a counter electrode made of metallic lithium is performed using a liquid electrolyte, the solvent of the liquid electrolyte has to be removed after pre-lithiation (drying of the anode) and a further process step is needed coming along with the respective additional energy consumption.

[0009] Therefore, there is a need to provide a pre-lithiated anodes and methods for preparing the same overcoming drawbacks of the prior art. Especially, a simplified method for electrochemically preparing pre-lithiated anodes without the need of drying of the anode after pre-lithiation.

[0010] The above problem is solved in accordance with the independent claims. Further embodiments result from the sub claims and / or the following detailed description.

[0011] Especially, in order to achieve the above objects, the present disclosure provides, in a first embodiment, a method for preparing a pre-lithiated anode for a lithium-ion secondary battery, the method comprising the steps:

[0012] - providing an anode comprising an anode active material;

[0013] - providing a counter-electrode comprising metallic lithium;

[0014] - providing a solid electrolyte between and in direct contact with both the anode active material and the counter-electrode;

[0015] - transferring lithium ions from the counter-electrode to the anode active material;

[0016] wherein

[0017] the solid electrolyte comprises

[0018] - a separator;

[0019] - an at least partially fluorinated polymer; and

[0020] - a lithium salt.

[0021] According to a second embodiment of the present disclosure, in the first embodiment, the separator is a polyolefin-based porous membrane.

[0022] According to a third embodiment of the present disclosure, in the first embodiment or the second embodiment, the separator is a porous polypropylene membrane.

[0023] According to a fourth embodiment of the present disclosure, in any of the first to the third embodiments, the at least partially fluorinated polymer is a perfluorinated polymer.

[0024] According to a fifth embodiment of the present disclosure, in any of the first to the fourth embodiments, the at least partially fluorinated polymer is a poly(vinylidene fluoride-co-hexafluoropropylene).

[0025] According to a sixth embodiment of the present disclosure, in any of the first to the fifth embodiments, the lithium salt is a lithium bis(perfluorinated C1to C6alkyl sulfonyl)imide.

[0026] According to a seventh embodiment of the present disclosure, in any of the first to the sixth embodiments, the lithium salt is lithium bis(pentafluoroethanesulfonyl)imide.

[0027] According to an eighth embodiment of the present disclosure, in any of the first to the seventh embodiments, the anode active material comprises silicon.

[0028] According to a ninth embodiment of the present disclosure, in any of the first to the eighth embodiments, the transferring of lithium ions from the counter-electrode to the anode active material comprises

[0029] - providing an external short circuit between the anode and the counter-electrode; or

[0030] - applying a current to the anode and the counter electrode.

[0031] According to a tenth embodiment, the present disclosure provides a lithium-ion secondary battery comprising

[0032] - a pre-lithiated anode;

[0033] - a solid electrolyte; and

[0034] - a cathode;

[0035] wherein

[0036] the solid electrolyte is arranged between and in direct contact with both the pre-lithiated anode and the cathode,

[0037] wherein the solid electrolyte comprises

[0038] - a separator;

[0039] - an at least partially fluorinated polymer; and

[0040] - a lithium salt.

[0041] According to an eleventh embodiment of the present disclosure, the present disclosure provides a use of a solid electrolyte in preparation of a pre-lithiated anode for a lithium-ion secondary battery,

[0042] wherein

[0043] the solid electrolyte comprises

[0044] - a separator;

[0045] - an at least partially fluorinated polymer; and

[0046] - a lithium salt.

[0047] The present invention provides solid electrolyte for a lithium-ion secondary battery which allows transfer of lithium ions from a lithium source to an anode and lithium deposition and / or lithium intercalation and / or lithium insertion and / or forming an intermetallic compound on the anode. In this way, the capacity of the battery can be increased. Surprisingly, by using the solid electrolyte according to the present invention, efficient pre-lithiation of the anode of a lithium-ion secondary battery is achieved without the need of solvents in the electrolyte. Furthermore, the solid electrolyte according to the present disclosure was surprisingly found to be easily removable after pre-lithiation, that is after transferring lithium ions from the counter-electrode to the anode active material, from a variety of materials including metallic lithium, Si-based anodes, NMC-based cathodes et. At the same time, the solid electrolyte according to the present disclosure provides good chemical stability in contact with metallic Li and a high Li-ion conductivity.

[0048] Fig. 1 shows digital images of cathodes (NCM622), Si-anodes and different solid electrolytes after contacting under a pressure of 10 bar.

[0049] Fig. 2a shows voltage profiles of Si-anodes of the electrochemical pre-lithiation process with counter electrodes of metallic lithium.

[0050] Figs. 2 b to d show digital images of Li-metal electrodes, Si-anodes and different solid electrolytes after pre-lithiation.

[0051] The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and should be construed in a sense and concept consistent with the technical idea of the present disclosure, based on the principle that the inventor can properly define the concept of a term to describe this invention in the best way possible.

[0052] Unless otherwise restricted, a detailed description defining or specifying the elements may be applied to all inventions and is not limited to descriptions of particular inventions. That is, the present disclosure also refers to combinations of the embodiments even if they are disclosed separately.

[0053] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms "a," "an," and "the" comprise plural referents unless the context clearly dictates otherwise. It is to be understood that the terms such as "comprise" or "have" as used in the present specification, are intended to designate the presence of stated features, numbers, steps, operations, components, parts or combinations thereof, but not to preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. The term "comprises" explicitly, even if not necessarily limited accordingly, includes the meaning "essentially comprising" and "consists of".

[0054] The term "essentially comprises" as used herein has the meaning of "comprising at least 70 %", preferably of "comprising at least 80 %", most preferred of "comprising at least 90 %". If reference is made to the amount of a constituent in a mixture of material, % is wt %, relative to the total weight of the respective mixture. For example, a material essentially comprising silicon comprises the silicon in an amount of at least 70 wt% with respect to the total weight of the material.

[0055] Additionally, the terms "about" and "substantially" as used herein are used in the sense of at, or nearly at, when given the manufacturing and material tolerances inherent in the stated circumstances and are used to prevent the unscrupulous infringer from unfairly taking advantage of the present disclosure where exact or absolute figures are stated as an aid to understanding the present disclosure.

[0056] As used herein, "A and / or B" means "A and B, or A or B".

[0057] The anode as referred to herein may also be referred to as negative electrode.

[0058] Hereinafter, the present disclosure will be described in more detail.

[0059] The present invention provides a method for preparing a pre-lithiated anode. The pre-lithiated anode is suitable for use as the anode (negative electrode) of a lithium-ion secondary battery. A lithium-ion secondary battery is a type of rechargeable battery that uses that uses the reversible intercalation (or insertion, or deposition, or alloying) of Li+ ions into electronically conducting solids to store energy.

[0060]

[0061] Anode materials

[0062] In the method for preparing a pre-lithiated anode according to the present invention, an anode comprising an anode active material is provided. The anode active material may be a porous anode active material (= anode active materials having pores). The anode may essentially comprise or consist of the anode active material. Alternatively, only a part of the anode may essentially comprise or consist of the anode active material, for example one or more layers of the anode.

[0063] In one embodiment the anode (= negative electrode) comprises essentially comprises or consists of a current collector and an anode active material layer, wherein the anode active material layer is provided on at least one surface of the current collector. In such a case, the current collector is a negative electrode current collector. The anode active material layer comprises, essentially comprises or consists of the anode active material.

[0064] The anode may be manufactured by coating the anode active material on a negative electrode current collector and drying.

[0065] The negative electrode current collector may be manufactured with the thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not limited to a particular type and may comprise any material having conductive properties without causing any chemical change to the corresponding battery, for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless-steel surface treated with carbon, nickel, titanium or silver, and aluminum-cadmium alloy. The negative electrode current collector may have microtexture on the surface to improve the adhesion strength of the anode active material, and may come in various types, for example, films, sheets, foils, nets, porous bodies, foams and non-woven fabrics.

[0066] For example, the porous anode active material may comprise silicon, silicon-containing alloys; carbons such as non-graphitizing carbon and graphite-based carbon; metal composite oxides such as LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), SnxMe1-xMe'yOz(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Groups 1, 2 and 3 elements of the periodic table, halogen; 0<x≤1; 1≤y≤3; 1≤z≤8); tin-containing alloys; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; and conductive polymers such as polyacetylene; preferably comprises, essentially comprises or consists of silicon.

[0067] The porous anode active material may include a binder. The binder included in the porous anode active material is usually added in an amount of 0.1 weight% to 30 weight% based on the total weight of the mixture comprising the porous anode active material. In an exemplary embodiment of the present application, the negative electrode binder may comprise at least one selected from the group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, an ethylene-propylene-diene monomer (EPDM), a sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, polyacrylic acid and a material in which the hydrogen thereof is substituted with Li, Na, Ca, or the like, and may also comprise various polymers thereof.

[0068] The porous anode active material may have a porosity of at least about 10%, at least 20%, or at least 25%. The porous anode active material may have a porosity of 90% or less, 80 % or less, 70% or less, 60% or less, 50% or less 40% or less 35% or less, or 30 % or less. Preferably, porous anode active material has a porosity from 20% to 35%, more preferably from 25% to 30%, such as about 30%. Such a porosity of the porous anode active material is advantageous in view of the amount of Li which can be deposited in the porous anode active material and in view of the achieved capacity of a lithium secondary battery using such a porous anode active material. The term "porosity" used in the present specification refers to a fraction of voids in a structure over the total volume and is indicated in %, and may be used interchangeably with void fraction, degree of porosity or the like. In the present disclosure, the porosity may be measured by mercury permeation method (Hg porosimeter) according to ASTM D-2873 in the version at the priority date of the present application.

[0069]

[0070] Counter electrode

[0071] In the method for preparing a pre-lithiated anode according to the present invention, a counter-electrode is provided. The counter-electrode comprises, essentially comprises or consists of metallic lithium. The counter-electrode may essentially comprise or consists of metallic lithium, a lithium containing alloy, such as a lithium-aluminum alloy, a lithium-indium-alloy, a lithium-gold-alloy etc., a lithium-containing intermetallic phase or a lithium-containing cathode active material, such as lithium-nickel-manganese-cobalt-oxide (NMC) or lithium-iron-phosphate (LFP). The counter-electrode may consist of metallic lithium and may preferably be in the form of a lithium disc, ingot, foil, rod, powder etc.

[0072]

[0073] Solid electrolyte

[0074] In the method for preparing a pre-lithiated anode according to the present invention, a solid electrolyte is provided. The solid electrolyte is arranged between and in direct contact with both the anode active material and the counter-electrode. The solid electrolyte may be arranged between the anode active material and the counter-electrode by firstly placing the solid electrolyte between and in direct contact with both the anode active material and the counter-electrode and then applying a pressure to the layer structure comprising the anode active material, the counter electrode and the solid electrolyte.

[0075] The pressure may be from 0.001 to 100 bar, 1.5 to 100 bar, from 2 to 20 bar, or from 5 to 15 bar, such as about 10 bar. By applying a respective pressure, an adhesion appropriate for the pre-lithiation process between the solid electrolyte and the anode active material and / or the counter electrode can be achieved. At the same time, applying such a pressure to the solid electrolyte and the anode active material and the counter electrode still ensures that the solid electrolyte can easily be separated from anode active material and the counter electrode after pre-lithiation.

[0076] Separator

[0077] The solid electrolyte comprises a separator. The separator may be made of a porous non-conductive or insulating material and enables transport of lithium ions between the positive electrode and the negative electrode. The separator may be used without special limitation, may be one conventionally used as a separator in a conventional lithium-sulfur battery. The separator may be an independent member such as a film.

[0078] The separator may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate commonly used for a lithium-sulfur battery, and porous polymer films may be used alone or by laminating them, and for example, a nonwoven fabric or a polyolefin-based porous membrane made of glass fibers, polyethylene terephthalate fibers, etc. having a high melting point may be used, but is not limited thereto.

[0079] The material of the porous substrate is not particularly limited in the present disclosure, and any material can be used as long as it is a porous substrate commonly used in an electrochemical device. For example, the porous substrate may comprise at least one material selected from the group consisting of polyolefin such as polyethylene and polypropylene, polyester such as polyethyleneterephthalate and polybutyleneterephthalate, polyamide, polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, poly(p-phenylene benzobisoxazole), and polyarylate.

[0080] It is preferred that the separator is a porous polypropylene membrane. Even more preferred, the separator is a porous polypropylene membrane.

[0081] The thickness of the separator is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. Although the thickness range of the separator is not particularly limited to the above-mentioned range, when the thickness is excessively thinner than the lower limit described above, mechanical properties are deteriorated and thus the separator may be easily damaged during pre-lithiation.

[0082] The separator may have pores and the average diameter and porosity of the pores present in the separator are also not particularly limited but may be 0.001 μm to 50 μm and 10% by volume to 95% by volume, respectively.

[0083] Partially fluorinated polymer

[0084] The solid electrolyte comprises further a partially fluorinated polymer. The partially fluorinated polymer may be comprised in the solid electrolyte in the form of a mixture with the lithium salt which will be described in more detail below.

[0085] The partially fluorinated polymer, especially the mixture of the partially fluorinated polymer and the lithium salt may be arranged on at least a part of the surface of the separator. Additionally, parts of the mixture of the partially fluorinated polymer and the lithium salt may be arranged inside the separator, that is, inside pores formed in the separator.

[0086] For preparing the solid electrolyte, the partially fluorinated polymer, especially the mixture of the partially fluorinated polymer and the lithium salt, may be coated on at least one surface of the separator by any conventional coating method, especially by coating a slurry comprising the partially fluorinated polymer, especially the mixture of the partially fluorinated polymer and the lithium salt, on at least one surface of the separator using doctor blade. The slurry comprising the partially fluorinated polymer, especially the mixture of the partially fluorinated polymer and the lithium salt, may further comprise a solvent to dissolve / disperse the partially fluorinated polymer and the lithium salt, such as N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO) or dimethylformamide (DMF).

[0087] The partially fluorinated polymer may be a perfluorinated polymer. The partially fluorinated polymer may be derived from monomers selected from the group consisting of vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, 1,1,3,3,3-pentafluoropropene, 1,2,3,3,3-pentafluoropropene, perfluoropropylvinylether, perfluoromethylvinylether, and mixtures thereof. The partially fluorinated polymer may be selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene and copolymers of two or more thereof. The partially fluorinated polymer may be selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene and copolymers of two or more thereof. Preferably, the at least partially fluorinated polymer is a poly(vinylidene fluoride-co-hexafluoropropylene).

[0088] Lithium salt

[0089] The solid electrolyte comprises further a lithium salt. The lithium salt may be comprised in the solid electrolyte in the form of a mixture with the partially fluorinated polymer.

[0090] The lithium salt can be any lithium salt commonly used in electrolytes of a lithium secondary battery. For example, the lithium salt may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl10, LiPF6, lithium bis(perfluorinated C1to C6alkyl sulfonyl)imide, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, lithium bis(perfluorinated C1to C6alkyl sulfonyl)imide, such as (CF3SO2)2NLi, or (C2F5SO2)2NLi, LiN(SO2F)2, lithium chloroborane, lithium lower aliphatic carboxylate, tetra-phenyl lithium borate, lithium imide, etc.

[0091] The lithium salt may be a lithium bis(perfluorinated C1to C6alkyl sulfonyl)imide. The lithium salt may be a lithium bis(perfluorinated C1to C5alkyl sulfonyl)imide. The lithium salt may be a lithium bis(perfluorinated C1to C4alkyl sulfonyl)imide. The lithium salt may be a lithium bis(perfluorinated C1to C3alkyl sulfonyl)imide. The lithium salt may be lithium bis(tetrafluoromethylsulfonyl)imide and / or lithium bis(pentafluoroethanesulfonyl)imide. The lithium salt may be lithium bis(pentafluoroethanesulfonyl)imide. In this way best adhesion of the separator and / or best pre-lithiation performance can be achieved.

[0092] The partially fluorinated polymer and the lithium salt may be comprised in the solid electrolyte in a weight ratio selected from the group consisting of from 50:1 to 1:20, from 30:1 to 1:10, from 20:1 to 1:1, from 15:1 to 2:1, and from 12:1 to 8:1, such as about 10:1.

[0093] The separator and the lithium salt may be comprised in the solid electrolyte in a weight ratio selected from the group consisting of from 25:1 to 1:10, from 12.5:1 to 1:5, from 6:1 to 1:2, from 3:1 to 1:1.5, from 2:1 to 1:1, and from 1.5:1 to 1:1, such as about 1.25:1.

[0094] The separator and the partially fluorinated polymer may be comprised in the solid electrolyte in a weight ratio selected from the group consisting of from 50:1 to 1:10, from 30:1 to 1:5, from 20:1 to 1:1, from 10:1 to 2:1, from 5:1 to 2.5:1, and from 4:1 to 3:1, such as about 3.33:1.

[0095] Further constituents of the solid electrolyte

[0096] The solid electrolyte may comprise, besides the lithium salt, one or more further salts, preferably organic salts, such as Pyr14TFSI.

[0097] The solid electrolyte may comprise further polymeric materials. For example, in case that the separator is a polyolefin-based porous membrane, the polyolefin-based porous membrane may be coated with a further polymeric material, such as polyethylene oxide.

[0098]

[0099] Transferring of lithium ions

[0100] The method for preparing a pre-lithiated anode according to the present invention comprises a step of transferring lithium ions from the counter-electrode to the anode active material.

[0101] The step of transferring lithium ions from the counter-electrode to the anode active material may comprise

[0102] - providing an external short circuit between the anode and the counter-electrode; or

[0103] - applying a current to the anode and the counter electrode.

[0104] Preferably, the step of transferring lithium ions from the counter-electrode to the anode active material may comprise applying a current to the anode and the counter electrode, especially with a current density selected from the group consisting of from 0.01 to 1 mA*cm-2, from 0.02 to 0.9 mA*cm-2, from 0.03 to 0.8 mA*cm-2, from 0.04 to 0.7 mA*cm-2, from 0.05 to 0.6 mA*cm-2, from 0.06 to 0.5 mA*cm-2, from 0.07 to 0.4 mA*cm-2, from 0.08 to 0.15 mA*cm-2, and from 0.09 to 0.11 mA*cm-2, such as about 0.1 mA*cm-2.

[0105] The step of transferring lithium ions from the counter-electrode to the anode active material may be performed at a temperature selected from the group consisting of from room temperature (about 23°C) to 100°C, 40°C to 80°C, and 50°C to 70°C, such as about 60°C.

[0106] The step of transferring lithium ions from the counter-electrode to the anode active material may be performed until a capacity of the anode is 6 mAh*cm-2, 5 mAh*cm-24 mAh*cm-2, 3 mAh*cm-2, or 2mAh*cm-2, preferably 1.8 mAh*cm-2.

[0107] The step of transferring lithium ions from the counter-electrode to the anode active material may be performed until a degree of prelithiation of the anode is 50%, 40%, 30%, or 20%, preferably about 15%.

[0108] The method may comprise a further step of removing the counter-electrode from the solid electrolyte. No special separation method is required in this regard, because the solid electrolyte has low adhesive properties (that is, it does not stick to the electrodes). The separation can be facilitated by heating to elevated temperatures, e.g. 60 °C or less.

[0109] The method may comprise a further step of removing the solid electrolyte from the pre-lithiated anode.

[0110]

[0111] Lithium-ion secondary battery

[0112] According to a further aspect, the present invention provides a lithium-ion secondary battery comprising a pre-lithiated anode, a solid electrolyte, and a cathode, wherein the solid electrolyte is arranged between and in direct contact with both the pre-lithiated anode and the cathode, wherein the solid electrolyte comprises a separator; an at least partially fluorinated polymer; and a lithium salt. The pre-lithiated anode may be the pre-lithiated anode obtainable by the method according to the present invention as specified in detail herein, especially described above.

[0113] According to a further aspect, the present invention provides a lithium-ion secondary battery comprising a pre-lithiated anode, electrolyte (including but not limited to liquid organic electrolytes, ionic liquids, solid polymer electrolytes, ceramic electrolytes, sulfide-based electrolytes etc.) and a cathode, wherein the solid electrolyte is arranged between and in direct contact with both the pre-lithiated anode and the cathode.

[0114] The lithium secondary battery according to the present disclosure can be manufactured by lamination, stacking, and folding processes of the separator and the electrodes, in addition to the usual winding process.

[0115] The shape of the lithium secondary battery is not particularly limited and may be various shapes such as a cylindrical shape, a laminate shape, and a coin shape.

[0116] Also, the present disclosure provides a battery module comprising the lithium-sulfur battery described above as a unit battery.

[0117] The battery module may be used as a power source for medium to large-sized devices requiring high temperature stability, long cycle characteristics, high capacity characteristics, and the like.

[0118] Examples of such medium to large-sized devices may comprise, but are not limited to, a power tool powered and moved by an electric motor; an electric car including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; an electric two-wheeled vehicle including an electric bike (E-bike) and an electric scooter (E-scooter); an electric golf cart; a power storage system, etc.

[0119] Cathode

[0120] The cathode (positive electrode) may be manufactured by coating a positive electrode material comprising a mixture of a positive electrode active material comprising positive electrode active material particles, a conductive material and a binder on a positive electrode current collector, and the positive electrode material may further comprise a filler if necessary.

[0121] In general, the positive electrode current collector is manufactured with the thickness of 3 ㎛ to 500 ㎛, and is not limited to a particular type and may include any material having high conductivity without causing any chemical change to the corresponding battery, for example, one selected from stainless steel, aluminum, nickel, titanium, and aluminum or stainless steel surface treated with carbon, nickel, titanium or silver, and specifically aluminum. The current collector may have macrotexture on the surface to improve the adhesion strength of the positive electrode active material, and may come in various types, for example, films, sheets, foils, nets, porous bodies, foams and non-woven fabrics.

[0122] In addition to the positive electrode active material particles, the positive electrode active material may comprise, for example, layered compounds or compounds with one or more transition metal such as lithium nickel oxide (LiNiO2); lithium manganese oxide such as formula Li1+xMn2-xO4(x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; Ni site lithium nickel oxide represented by formula LiNi1-xMxO2(M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); lithium manganese composite oxide represented by formula LiMn2-xMxO2(M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO8(M = Fe, Co, Ni, Cu or Zn); LiMn2O4with partial substitution of alkali earth metal ion for Li; disulfide compounds; Fe2(MoO4)3, but is not limited thereto.

[0123] The conductive material is usually added in an amount of 0.1 weight% to 30 weight% based on the total weight of the mixture comprising the positive electrode active material. The conductive material is not limited to any particular type when it has conductive properties while not causing a chemical change to the corresponding battery, and may include, for example, conductive materials, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metal fibers; fluorocarbon, metal powder such as aluminum powder and nickel powder; conductive whiskers such as oxide zinc and potassium titanate; conductive metal oxide such as titanium oxide; and polyphenylene derivatives.

[0124] The binder included in the positive electrode assists in binding the active material and the conductive material and binding to the current collector, and is usually added in an amount of 0.1 weight% to 30 weight% based on the total weight of the mixture comprising the positive electrode active material. Examples of the binder may comprise polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regeneratedcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, fluorine rubber and various types of copolymers.

[0125] In one embodiment, the binder present in the positive electrode has similar characteristics to the crystalline first binder present in the coating layer. In one embodiment, the same binder(s) are used in the positive electrode as in the first crystalline binder for the coating layer. For example, the crystalline first binder present in the coating layer may be a PVDF copolymer, and the binder present in the positive electrode may be a PVDF homopolymer. Because both the PVDF copolymer and the PVDF homopolymer have a similar backbone polymer structure, the polymers share a similar characteristic.

[0126] Anode

[0127] The pre-lithiated anode comprises, essentially comprises or consists of a porous anode active material and metallic lithium.

[0128] In one embodiment the pre-lithiated anode comprises essentially comprises or consists of a current collector, a porous anode active material layer (=anode active materials having pores), wherein the porous anode active material layer is provided on at least one surface of the current collector and metallic lithium. In such a case, the current collector is a negative electrode current collector. The porous anode active material layer comprises, essentially comprises or consists of the porous anode active material.

[0129] The anode may be manufactured by coating the porous anode active material on a negative electrode current collector and drying.

[0130] The negative electrode current collector may be manufactured with the thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not limited to a particular type and may comprise any material having conductive properties without causing any chemical change to the corresponding battery, for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless-steel surface treated with carbon, nickel, titanium or silver, and aluminum-cadmium alloy. The negative electrode current collector may have microtexture on the surface to improve the adhesion strength of the anode active material, and may come in various types, for example, films, sheets, foils, nets, porous bodies, foams and non-woven fabrics.

[0131] For example, the porous anode active material may comprise silicon, silicon-containing alloys; carbons such as non-graphitizing carbon and graphite-based carbon; metal composite oxides such as LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), SnxMe1-xMe'yOz(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Groups 1, 2 and 3 elements of the periodic table, halogen; 0<x≤1; 1≤y≤3; 1≤z≤8); tin-containing alloys; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; and conductive polymers such as polyacetylene; preferably comprises, essentially comprises or consists of silicon.

[0132] The porous anode active material may include a binder. The binder included in the porous anode active material is usually added in an amount of 0.1 weight% to 30 weight% based on the total weight of the mixture comprising the porous anode active material. In an exemplary embodiment of the present application, the negative electrode binder may comprise at least one selected from the group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, an ethylene-propylene-diene monomer (EPDM), a sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, polyacrylic acid and a material in which the hydrogen thereof is substituted with Li, Na, Ca, or the like, and may also comprise various polymers thereof.

[0133] The porous anode active material may have a porosity of at least about 10%, at least 20%, or at least 25%. The porous anode active material may have a porosity of 90% or less, 80 % or less, 70% or less, 60% or less, 50% or less 40% or less 35% or less, or 30 % or less. Preferably, porous anode active material has a porosity from 20% to 35%, more preferably from 25% to 30%, such as about 30%Such a porosity of the porous anode active material is advantageous in view of the amount of Li which can be deposited in the porous anode active material and in view of the achieved capacity of a lithium secondary battery using such a porous anode active material. The term "porosity" used in the present specification refers to a fraction of voids in a structure over the total volume and is indicated in %, and may be used interchangeably with void fraction, degree of porosity or the like. In the present disclosure, the porosity may be measured by mercury permeation method (Hg porosimeter) according to ASTM D-2873 in the version at the priority date of the present application.

[0134]

[0135] Use of a solid electrolyte in preparation of a pre-lithiated anode

[0136] According to a further aspect, the present invention provides the use of a solid electrolyte in preparation of a pre-lithiated anode for a lithium-ion secondary battery. The solid electrolyte comprises a separator, an at least partially fluorinated polymer and a lithium salt.

[0137] Separator

[0138] The solid electrolyte comprises a separator. The separator may be made of a porous non-conductive or insulating material and enables transport of lithium ions between the positive electrode and the negative electrode. The separator may be used without special limitation, may be one conventionally used as a separator in a conventional lithium-sulfur battery. The separator may be an independent member such as a film.

[0139] The separator may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate commonly used for a lithium-sulfur battery, and porous polymer films may be used alone or by laminating them, and for example, a nonwoven fabric or a polyolefin-based porous membrane made of glass fibers, polyethylene terephthalate fibers, etc. having a high melting point may be used, but is not limited thereto.

[0140] The material of the porous substrate is not particularly limited in the present disclosure, and any material can be used as long as it is a porous substrate commonly used in an electrochemical device. For example, the porous substrate may comprise at least one material selected from the group consisting of polyolefin such as polyethylene and polypropylene, polyester such as polyethyleneterephthalate and polybutyleneterephthalate, polyamide, polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, poly(p-phenylene benzobisoxazole), and polyarylate.

[0141] It is preferred that the separator is a porous polypropylene membrane. Even more preferred, the separator is a porous polypropylene membrane.

[0142] The thickness of the separator is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. Although the thickness range of the separator is not particularly limited to the above-mentioned range, when the thickness is excessively thinner than the lower limit described above, mechanical properties are deteriorated and thus the separator may be easily damaged during pre-lithiation.

[0143] The separator may have pores and the average diameter and porosity of the pores present in the separator are also not particularly limited but may be 0.001 μm to 50 μm and 10% by volume to 95% by volume, respectively.

[0144] Partially fluorinated polymer

[0145] The solid electrolyte comprises further a partially fluorinated polymer. The partially fluorinated polymer may be comprised in the solid electrolyte in the form of a mixture with the lithium salt which will be described in more detail below.

[0146] The partially fluorinated polymer, especially the mixture of the partially fluorinated polymer and the lithium salt may be arranged on at least a part of the surface of the separator. Additionally, parts of the mixture of the partially fluorinated polymer and the lithium salt may be arranged inside the separator, that is, inside pores formed in the separator.

[0147] For preparing the solid electrolyte, the partially fluorinated polymer, especially the mixture of the partially fluorinated polymer and the lithium salt, may be coated on at least one surface of the separator by any conventional coating method, especially by coating a slurry comprising the partially fluorinated polymer, especially the mixture of the partially fluorinated polymer and the lithium salt, on at least one surface of the separator using doctor blade. The slurry comprising the partially fluorinated polymer, especially the mixture of the partially fluorinated polymer and the lithium salt, may further comprise a solvent to dissolve / disperse the partially fluorinated polymer and the lithium salt, such as N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO) or dimethylformamide (DMF).

[0148] The partially fluorinated polymer may be a perfluorinated polymer. The partially fluorinated polymer may be derived from monomers selected from the group consisting of vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, 1,1,3,3,3-pentafluoropropene, 1,2,3,3,3-pentafluoropropene, perfluoropropylvinylether, perfluoromethylvinylether, and mixtures thereof. The partially fluorinated polymer may be selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene and copolymers of two or more thereof. The partially fluorinated polymer may be selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene and copolymers of two or more thereof. Preferably, the at least partially fluorinated polymer is a poly(vinylidene fluoride-co-hexafluoropropylene).

[0149] Lithium salt

[0150] The solid electrolyte comprises further a lithium salt. The lithium salt may be comprised in the solid electrolyte in the form of a mixture with the partially fluorinated polymer.

[0151] The lithium salt can be any lithium salt commonly used in electrolytes of a lithium secondary battery. For example, the lithium salt may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl10, LiPF6, lithium bis(perfluorinated C1to C6alkyl sulfonyl)imide, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, lithium bis(perfluorinated C1to C6alkyl sulfonyl)imide, such as (CF3SO2)2NLi, or (C2F5SO2)2NLi, LiN(SO2F)2, lithium chloroborane, lithium lower aliphatic carboxylate, tetra-phenyl lithium borate, lithium imide, etc.

[0152] The lithium salt may be a lithium bis(perfluorinated C1to C6alkyl sulfonyl)imide. The lithium salt may be a lithium bis(perfluorinated C1to C5alkyl sulfonyl)imide. The lithium salt may be a lithium bis(perfluorinated C1to C4alkyl sulfonyl)imide. The lithium salt may be a lithium bis(perfluorinated C1to C3alkyl sulfonyl)imide. The lithium salt may be lithium bis(tetrafluoromethylsulfonyl)imide and / or lithium bis(pentafluoroethanesulfonyl)imide. The lithium salt may be lithium bis(pentafluoroethanesulfonyl)imide. In this way best adhesion of the separator and / or best pre-lithiation performance can be achieved.

[0153] The partially fluorinated polymer and the lithium salt may be comprised in the solid electrolyte in a weight ratio selected from the group consisting of from 50:1 to 1:20, from 30:1 to 1:10, from 20:1 to 1:1, from 15:1 to 2:1, from 12:1 to 8:1, such as about 10:1.

[0154] The separator and the lithium salt may be comprised in the solid electrolyte in a weight ratio selected from the group consisting of from 25:1 to 1:10, from 12.5:1 to 1:5, from 6:1 to 1:2, from 3:1 to 1:1.5, from 2:1 to 1:1, and from 1.5:1 to 1:1, such as about 1.25:1.

[0155] The separator and the partially fluorinated polymer may be comprised in the solid electrolyte in a weight ratio selected from the group consisting of from 50:1 to 1:10, from 30:1 to 1:5, from 20:1 to 1:1, from 10:1 to 2:1, from 5:1 to 2.5:1, and from 4:1 to 3:1, such as about 3.33:1.

[0156] Pre-lithiation

[0157] The use of the solid electrolyte for preparing a pre-lithiated anode according to the present invention may comprise a step of providing the solid electrolyte on the surface of an anode.

[0158] In the use of the of the solid electrolyte for preparing a pre-lithiated anode according to the present invention, an anode comprising an anode active material may be provided. The anode active material may be a porous anode active material (= anode active materials having pores). The anode may essentially comprise or consist of the anode active material. Alternatively, only a part of the anode may essentially comprise or consist of the anode active material, for example one or more layers of the anode.

[0159] In one embodiment the anode (= negative electrode) comprises essentially comprises or consists of a current collector and an anode active material layer, wherein the anode active material layer is provided on at least one surface of the current collector. In such a case, the current collector is a negative electrode current collector. The anode active material layer comprises, essentially comprises or consists of the anode active material.

[0160] The anode may be manufactured by coating the anode active material on a negative electrode current collector and drying.

[0161] The negative electrode current collector may be manufactured with the thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not limited to a particular type and may comprise any material having conductive properties without causing any chemical change to the corresponding battery, for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless-steel surface treated with carbon, nickel, titanium or silver, and aluminum-cadmium alloy. The negative electrode current collector may have microtexture on the surface to improve the adhesion strength of the anode active material, and may come in various types, for example, films, sheets, foils, nets, porous bodies, foams and non-woven fabrics.

[0162] For example, the porous anode active material may comprise silicon, silicon-containing alloys; carbons such as non-graphitizing carbon and graphite-based carbon; metal composite oxides such as LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), SnxMe1-xMe'yOz(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Groups 1, 2 and 3 elements of the periodic table, halogen; 0<x≤1; 1≤y≤3; 1≤z≤8); tin-containing alloys; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; and conductive polymers such as polyacetylene; preferably comprises, essentially comprises or consists of silicon.

[0163] The porous anode active material may include a binder. The binder included in the porous anode active material is usually added in an amount of 0.1 weight% to 30 weight% based on the total weight of the mixture comprising the porous anode active material. In an exemplary embodiment of the present application, the negative electrode binder may comprise at least one selected from the group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, an ethylene-propylene-diene monomer (EPDM), a sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, polyacrylic acid and a material in which the hydrogen thereof is substituted with Li, Na, Ca, or the like, and may also comprise various polymers thereof.

[0164] The porous anode active material may have a porosity of at least about 10%, at least 20%, or at least 25%. The porous anode active material may have a porosity of 90% or less, 80 % or less, 70% or less, 60% or less, 50% or less 40% or less 35% or less, or 30 % or less. Preferably, porous anode active material has a porosity from 20% to 35%, more preferably from 25% to 30%, such as about 30%. Such a porosity of the porous anode active material is advantageous in view of the amount of Li which can be deposited in the porous anode active material and in view of the achieved capacity of a lithium secondary battery using such a porous anode active material. The term "porosity" used in the present specification refers to a fraction of voids in a structure over the total volume and is indicated in %, and may be used interchangeably with void fraction, degree of porosity or the like. In the present disclosure, the porosity may be measured by mercury permeation method (Hg porosimeter) according to ASTM D-2873 in the version at the priority date of the present application.

[0165] The use of the solid electrolyte for preparing a pre-lithiated anode according to the present invention may comprise a step of providing a counter-electrode on a surface of the solid electrolyte.

[0166] In the method for preparing a pre-lithiated anode according to the present invention, a counter-electrode is provided. The counter-electrode comprises, essentially comprises or consists of metallic lithium. The counter-electrode may essentially comprise or consists of metallic lithium, a lithium containing alloy, such as a lithium-aluminum alloy, a lithium-indium-alloy, a lithium-gold-alloy etc., a lithium-containing intermetallic phase or a lithium-containing cathode active material, such as lithium-nickel-manganese-cobalt-oxide (NMC) or lithium-iron-phosphate (LFP). The counter-electrode may consist of metallic lithium and may be in the form of a lithium disc, ingot, foil, rod etc.

[0167] The use of the solid electrolyte for preparing a pre-lithiated anode according to the present invention may comprise a step of transferring lithium ions from the counter-electrode to the anode active material.

[0168] The step of transferring lithium ions from the counter-electrode to the anode active material may comprise

[0169] - providing an external short circuit between the anode and the counter-electrode; or

[0170] - applying a current to the anode and the counter electrode.

[0171] Preferably, the step of transferring lithium ions from the counter-electrode to the anode active material may comprise applying a current to the anode and the counter electrode, especially with a current density selected from the group consisting of from 0.01 to 1 mA*cm-2, from 0.02 to 0.9 mA*cm-2, from 0.03 to 0.8 mA*cm-2, from 0.04 to 0.7 mA*cm-2, from 0.05 to 0.6 mA*cm-2, from 0.06 to 0.5 mA*cm-2, from 0.07 to 0.4 mA*cm-2, from 0.08 to 0.15 mA*cm-2, and from 0.09 to 0.11 mA*cm-2, such as about 0.1 mA*cm-2.

[0172] The step of transferring lithium ions from the counter-electrode to the anode active material may be performed at a temperature selected from the group consisting of from room temperature (about 23°C) to 100°C, 40°C to 80°C, and 50°C to 70°C, such as about 60°C.

[0173] The step of transferring lithium ions from the counter-electrode to the anode active material may be performed until a capacity of the anode is 6 mAh*cm-2, 5 mAh*cm-24 mAh*cm-2, 3 mAh*cm-2, or 2mAh*cm-2, preferably 1.8 mAh*cm-2.

[0174] The step of transferring lithium ions from the counter-electrode to the anode active material may be performed until a degree of prelithiation of the anode is 50%, 40%, 30%, or 20%, preferably about 15%.

[0175] The method may comprise a further step of removing the counter-electrode from the solid electrolyte. No special separation method is required in this regard, because the solid electrolyte has low adhesive properties (that is, it does not stick to the electrodes). The separation can be facilitated by heating to elevated temperatures, e.g. 60 °C or less.

[0176] The method may comprise a further step of removing the solid electrolyte from the pre-lithiated anode.

[0177]

[0178] EXAMPLES

[0179] Preparation of the solid electrolyte

[0180] Three different solid electrolytes

[0181] Comparative Example 1: Cg-PEO-LiTFSI,

[0182] Comparative Example 2: Cg-PEO-LiBETI, and

[0183] Inventive Example: Cg-PvdF-LiTFSI

[0184] have been prepared in accordance with Herbers et al. Adv. Energy Sustainability Res. 2023, 4, 2300153; and Zhang, Mengyi et al. J. Electochem. Soc. 2019, 166 (10), A2142.

[0185] Cg = Cellgard 2500

[0186] PEO = polyethylene oxide (Dow Chemical, molecular weight 4,000,000)

[0187] LiTFSI = Lithium bis(trifluoromethylsulfonyl)imide

[0188] LiBETI = Lithium bis(pentafluoroethanesulfonyl)imide

[0189] PvdF = Poly(vinylidene fluoride-co-hexafluoropropylene)

[0190]

[0191] Adhesion test

[0192] For use in a pre-lithiation process, the solid electrolyte must have sufficient adhesion to the anode and the counter electrode to ensure a connection during the process. However, after the pre-lithiation process the counter-electrode must be removed from the solid electrolyte and the solid electrolyte may be removed from the pre-lithiated anode.

[0193] Therefore, to investigate the suitability of different solid electrolytes for use in a pre-lithiation process, adhesion of the respective solid electrolytes to a Si-anode and a NCM-cathode have been tested. As a Si-anode, a Si electrode sheet (a Si electrode with the capacity of 11.9 mAh / cm2; LG ES) was used. As the NMC-cathode, an NMC622 electrodes (Electrode composition is 94:3:3 by weight (active material LiNi0.6Mn0.2Co0.2O2: conductive agent Super C65 : binder poly(vinylidene difluoride)) was used.

[0194] The respective solid electrolyte was placed between the anode and the cathode and a pressure of 10 bar was applied to the stack. Thereafter, the solid electrolyte was separated from the anode and the cathode. The different layers were separated one by one with tweezers at room temperature.

[0195] Fig. 1 shows digital images of the NCM-cathodes, the Si-anodes and the respective solid electrolyte obtained after separation.

[0196] It can be seen from Fig. 1a that parts of the anode and the cathode were attached to the Cg-PEO-LiTFSI solid electrolyte after separation showing that in this case the adhesion between the solid electrolyte and the electrodes was too strong to allow a clean separation.

[0197] Slightly better results were obtained for the Cg-PEO-LiBETI solid electrolyte (Fig. 1b), wherein, however, still significant amount of electrode materials remained on the surface of the solid electrolyte.

[0198] For the inventive example (Fig. 1c), in which Cg-PvdF-LiTFSI was used as the solid electrolyte, it can be seen that no electrode material remained on the surface of the solid electrolyte after separation. That is, when Cg-PvdF-LiTFSI is used as the solid electrolyte, this solid electrolyte can easily be removed from common anode and cathode materials.

[0199]

[0200] Pre-lithiation

[0201] Electrochemical prelithiation and subsequent adhesion of electrode active material to the solid electrolyte was performed in a coin cell using a Si-anode (a Si electrode with the capacity of 11.9 mAh / cm2; LG ES) and a metallic lithium counter-electrode.

[0202] Pre-lithiation was performed at 60°C and 0.1 mA*cm-2until the capacity of the Si-anode reached 1.8 mAh*cm-2(degree of pre-lithiation of 15%) (Fig. 2a).

[0203] As it can be seen from Figs. 2b an 2c, electrode active material remains on the surface of the comparative solid electrolytes Cg-PEO-LiTFSI and Cg-PEO-LiBETI. In contrast to that (Fig. 2d), for the inventive example in which Cg-PvdF-LiTFSI was used as the solid electrolyte, it can be seen that no significant amount of electrode active material remained on the surface of the solid electrolyte after separation.

[0204] These results show that solid electrolytes comprising besides a separator and a lithium salt an at least partially fluorinated polymer, such as Cg-PvdF-LiTFSI can successfully be used in the electrochemical pre-lithiation of anodes for lithium-ion secondary batteries.

[0205] The features disclosed in the foregoing description and in the dependent claims may, both separately and in any combination thereof, be material for realizing the aspects of the disclosure made in the independent claims, in diverse forms thereof.

Claims

1.A method for preparing a pre-lithiated anode for a lithium-ion secondary battery, the method comprising the steps:- providing an anode comprising an anode active material;- providing a counter-electrode comprising metallic lithium;- providing a solid electrolyte between and in direct contact with both the anode active material and the counter-electrode;- transferring lithium ions from the counter-electrode to the anode active material;wherein the solid electrolyte comprises- a separator;- an at least partially fluorinated polymer; and- a lithium salt.2.The method according to claim 1, wherein the separator is a polyolefin-based porous membrane.3.The method according to claim 1 or 2, wherein the separator is a porous polypropylene membrane.4.The method according to any one of the preceding claims, wherein the at least partially fluorinated polymer is a perfluorinated polymer.5.The method according to any one of the preceding claims, wherein the at least partially fluorinated polymer is a poly(vinylidene fluoride-co-hexafluoropropylene).6.The method according to any one of the preceding claims, wherein the lithium salt is a lithium bis(perfluorinated C1 to C6 alkyl sulfonyl)imide.7.The method according to any one of the preceding claims, wherein the lithium salt is lithium bis(pentafluoroethanesulfonyl)imide.8.The method according to any one of the preceding claims, wherein the anode active material comprises silicon.9.The method according to any one of the preceding claims, wherein the transferring of lithium ions from the counter-electrode to the anode active material comprises- providing an external short circuit between the anode and the counter-electrode; or- applying a current to the anode and the counter electrode.10.A lithium-ion secondary battery comprising- a pre-lithiated anode;- a solid electrolyte; and- a cathode;wherein the solid electrolyte is arranged between and in direct contact with both the pre-lithiated anode and the cathode,wherein the solid electrolyte comprises- a separator;- an at least partially fluorinated polymer; and- a lithium salt.11.Use of a solid electrolyte in preparation of a pre-lithiated anode for a lithium-ion secondary battery,wherein the solid electrolyte comprises- a separator;- an at least partially fluorinated polymer; and- a lithium salt.

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