Positive electrode sheet, method for manufacturing the same, and lithium ion battery

Abstract

The present application relates to the field of lithium ion batteries, and particularly relates to a positive electrode sheet, a preparation method thereof and a lithium ion battery. The positive electrode sheet comprises a current collector, an active material layer and a composite layer, the active material layer is arranged between the current collector and the composite layer; wherein the active material layer comprises active material with a TiOF2 coating layer; the composite layer contains LiPSCl; the active material with the TiOF2 coating layer comprises manganese-based positive electrode active material with a TiOF2 coating layer and / or iron-based positive electrode active material with a TiOF2 coating layer. The positive electrode sheet uses material formed by coating manganese-based and / or iron-based positive electrode active material particles with TiOF2 as the active main body of the electrode sheet, and a composite layer containing LiPSCl is arranged on the active material layer, which can greatly reduce the migration and deposition of high positive valence metal ions of the positive electrode to the surface of the negative electrode, and effectively improve the cycle performance and storage performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a positive electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] In lithium-ion batteries, the cathode material is typically composed of highly valence ions. During battery cycling and high-rate operation, these highly valence metal ions dissolve and deposit on the anode surface, significantly impacting the battery's cycle performance and storage performance. To address the issue of dissolution and deposition of highly valence metal ions and optimize battery performance, the industry has explored various approaches.

[0003] CN109346768A discloses a non-aqueous electrolyte for ion batteries, comprising an electrolyte lithium salt, a non-aqueous organic solvent, and a film-forming additive. The film-forming additive includes boric acid compounds, which can form a dense protective film on the surface of the positive electrode material, reducing the oxidation reaction of the electrolyte on the surface of the battery material. At the same time, it can complex divalent manganese ions in the electrolyte, preventing the divalent manganese ions from being reduced and deposited on the surface of the negative electrode.

[0004] CN103972490A discloses a coating method for lithium manganese oxide cathode material for lithium batteries. This method uses graphene to coat the lithium manganese oxide cathode material, which can effectively reduce the dissolution of manganese ions and improve the conductivity of lithium manganese oxide, thereby enhancing the specific capacity and rate performance of the lithium manganese oxide cathode material.

[0005] Adding additives to the electrolyte may reduce its conductivity, increase the risk of gas generation in the battery, increase internal resistance, and degrade battery performance. Coating with high-cost cathode materials such as graphene can optimize the conductivity of the cathode material and alleviate deposition problems to some extent, but it increases production costs and hinders marketization.

[0006] Therefore, there is still a need to provide an optimized solution to address the problem of high positive valence metal ion dissolution and deposition in the cathode, thereby improving battery cycle performance and storage performance. Summary of the Invention

[0007] The purpose of this invention is to overcome the problem in the prior art that high positive valence metal ions in the positive electrode of lithium-ion batteries dissolve and deposit on the surface of the negative electrode, thereby affecting the cycle performance and storage performance of the battery, and to provide a positive electrode sheet, its preparation method and lithium-ion battery.

[0008] To achieve the above objectives, a first aspect of the present invention provides a positive electrode sheet, comprising: a current collector, an active material layer, and a composite layer, wherein the active material layer is disposed between the current collector and the composite layer; wherein...

[0009] The active material layer comprises an active material with a TiOF2 coating layer; the composite layer contains LiPSCl;

[0010] The active material with a TiOF2 coating includes a manganese-based positive electrode active material with a TiOF2 coating and / or an iron-based positive electrode active material with a TiOF2 coating.

[0011] A second aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising:

[0012] (1) A slurry containing an active material is coated on the surface of the current collector, and after drying, an active material layer is formed on the surface of the current collector;

[0013] The active material includes a manganese-based positive electrode active material with a TiOF2 coating and / or an iron-based positive electrode active material with a TiOF2 coating.

[0014] (2-1) A slurry containing LiPSCl is coated on the surface of the active material layer. After drying, a composite layer is formed on the surface of the active material layer to obtain a positive electrode sheet.

[0015] or

[0016] (2-2) A slurry containing LiPSCl is coated to form a film, and after drying, a film layer is formed; then the film layer is hot-pressed onto the surface of the active material layer to form a composite layer, thus obtaining a positive electrode sheet.

[0017] The third aspect of the present invention provides a positive electrode sheet prepared by the method described in the second aspect above.

[0018] A fourth aspect of the present invention provides a lithium-ion battery comprising the positive electrode sheet described in the first or third aspect above.

[0019] Compared with the prior art, the positive electrode sheet provided by the present invention uses a positive electrode active material with a TiOF2 coating layer. During battery cycling, the TiOF2 coating layer can combine with the high positive valence metal ions dissolved from the positive electrode active material to form metal fluorides, preventing the migration of high positive valence metal ions. Furthermore, the positive electrode sheet has a composite structure, with a LiPSCl (lithium phosphine sulfide chloride) composite layer disposed on the outer surface of the active material layer. The LiPSCl forms a dense isolation layer at the microscopic level, which can further prevent the migration of large-sized high positive valence metal ions. Through the synergistic effect of the TiOF2 coating layer and the LiPSCl composite layer, the migration and deposition of positive high valence metal ions on the negative electrode surface can be effectively suppressed, thereby significantly improving the performance of lithium-ion batteries. It can achieve a capacity retention rate of more than 85% after 300 cycles at 0.5C / 1C at 25℃ and a storage capacity recovery rate of more than 83% after 28 days at 45℃. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0021] Figure 1 This is a SEM image of lithium manganese oxide, the raw material used in Preparation Example 1 of the present invention.

[0022] Figure 2 SEM image of lithium manganese oxide@TiOF2 prepared in Preparation Example 1 of the present invention. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] A first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising: a current collector, an active material layer, and a composite layer, wherein the active material layer is disposed between the current collector and the composite layer; wherein,

[0025] The active material layer comprises an active material with a TiOF2 coating layer; the composite layer contains LiPSCl;

[0026] The active material with a TiOF2 coating includes a manganese-based positive electrode active material with a TiOF2 coating and / or an iron-based positive electrode active material with a TiOF2 coating.

[0027] According to the present invention, the current collector in the positive electrode can be any conventional lithium-ion battery current collector in the art, and the present invention does not impose any particular limitation on the material selection or specifications of the current collector.

[0028] According to the present invention, the active material layer is located on the surface of the current collector, wherein the active material has a core and a TiOF2 coating layer covering the surface of the core. The core is made of a manganese-based positive electrode active material and / or an iron-based positive electrode active material. In the present invention, the definition of the manganese-based positive electrode active material and the iron-based positive electrode active material is relatively broad. Preferably, the manganese-based positive electrode active material can be selected from at least one of lithium-rich manganese-based positive electrode materials, lithium manganese oxide, lithium manganese nickel oxide, and lithium iron manganese phosphate; the iron-based positive electrode active material can be selected from at least one of lithium iron phosphate, lithium iron silicate, and lithium iron borate.

[0029] Typically, the aforementioned manganese-based and / or iron-based cathode active materials alone will generate highly positively charged metal ions (e.g., Mn) during the cycling process of lithium-ion batteries. 2+ Fe 2+ The high-valent metal ions dissolve out, migrating through the electrolyte to the negative electrode surface where they are reduced and deposited, leading to a decrease in battery capacity and a decline in cycle performance. The positive electrode provided by this invention uses an active material with a TiOF2 coating. The presence of the TiOF2 coating reduces direct contact between the core positive electrode active material and the electrolyte, slowing down the dissolution of high-valent metal ions. Furthermore, the TiOF2 material can combine with the dissolved high-valent metal ions, converting them into metal fluorides (such as MnF2 and FeF2), further reducing the migration of high-valent metal ions to the negative electrode. In addition, TiOF2 is a wide-bandgap ionic material with a cubic structure, which also helps improve battery kinetic performance.

[0030] According to the present invention, based on the total weight of the active material with TiOF2 coating, the content of TiOF2 in the active material with TiOF2 coating is 0.1-10 wt%, preferably 4-6 wt%.

[0031] In this invention, the TiOF2 content in the active material with the TiOF2 coating can be determined by elemental EDS testing using a scanning electron microscope (i.e., SEM-EDS).

[0032] According to the present invention, the active material layer in the positive electrode further contains a conductive agent and a first binder.

[0033] According to the present invention, based on the total weight of the active material layer, the content of TiOF2 in the active material layer is 3-5 wt%, preferably 3.5-4 wt%; the content of the conductive agent is 2-20 wt%; and the content of the first binder is 2-15 wt%. When the components of the active material layer meet the above-mentioned content ranges, they can better inhibit the migration and deposition of high-valent metal ions and result in better battery cycle life.

[0034] According to the present invention, the composite layer has a selective isolation function, wherein the contained LiPSCl forms a dense isolation layer at the microscopic level, which can prevent the passage of high-valence, large-sized metal ions. Due to the high ionic conductivity of LiPSCl, it allows relatively small-sized Li... + Rapidly passes through the composite layer, while ensuring Li + While migrating, it prevents large, highly positively charged metal ions from migrating to the negative electrode.

[0035] According to the present invention, the composite layer in the positive electrode further contains a second binder.

[0036] According to the present invention, based on the total weight of the composite layer, the content of LiPSCl in the composite layer is 5-50 wt%, preferably 20-40 wt%; and the content of the second binder is 45-90 wt%. When the components of the composite layer meet the above-mentioned content ranges, they can better prevent the migration and deposition of high-valent metal ions.

[0037] In this invention, the conductive agent and binder are not particularly limited and can be any conventional conductive agent and binder for lithium-ion battery electrodes in the art. For example, the conductive agent can be selected from at least one of acetylene black, carbon nanotubes, graphene, conductive carbon black, and conductive graphite; the first binder and the second binder can each be independently selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylate, polyurethane, polyethylene glycol, polyethylene oxide, epoxy resin, styrene-butadiene rubber, polymethyl cellulose, sodium polymethyl cellulose, hydroxypropyl methyl cellulose, and polyacryl alcohol.

[0038] According to the present invention, preferably, the weight ratio of TiOF2 to LiPSCl in the positive electrode is 1:(0.1-2).

[0039] According to the present invention, preferably, the thickness of the active material layer is 60-100 μm.

[0040] According to the present invention, preferably, the thickness of the composite layer is 5-30 μm.

[0041] The positive electrode sheet provided by this invention uses a material formed by coating manganese-based and / or iron-based positive electrode active material particles with TiOF2 as the active body of the electrode sheet, and a composite layer containing LiPSCl is formed on the surface of the active material layer. The above factors work synergistically to significantly reduce the migration and deposition of high positive valence metal ions in the positive electrode active material to the negative electrode surface, thereby greatly improving the cycle performance and storage performance of the battery. When the active material layer and the composite layer in the positive electrode sheet each have the above-defined composition and component content, the lithium-ion battery can achieve a capacity retention rate of more than 85% after 300 cycles at 0.5C / 1C at 25°C, and a storage capacity recovery rate of more than 83% after 28 days at 45°C. Furthermore, based on the above-mentioned limiting conditions, the weight ratio of TiOF2 to LiPSCl in the positive electrode sheet satisfies 1:(0.1-2), which can achieve a further preferred effect of the present invention, enabling manganese-based and iron-based lithium-ion batteries to retain a capacity of more than 93% after 300 cycles at 0.5C / 1C at 25°C, and to recover a storage capacity of more than 90% after 28 days at 45°C.

[0042] A second aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising:

[0043] (1) A slurry containing an active material is coated on the surface of the current collector, and after drying, an active material layer is formed on the surface of the current collector;

[0044] The active material includes a manganese-based positive electrode active material with a TiOF2 coating and / or an iron-based positive electrode active material with a TiOF2 coating.

[0045] (2-1) A slurry containing LiPSCl is coated on the surface of the active material layer. After drying, a composite layer is formed on the surface of the active material layer to obtain a positive electrode sheet.

[0046] or

[0047] (2-2) A slurry containing LiPSCl is coated to form a film, and after drying, a film layer is formed; then the film layer is hot-pressed onto the surface of the active material layer to form a composite layer, thus obtaining a positive electrode sheet.

[0048] According to the present invention, in step (1), the current collector can be any conventional lithium-ion battery current collector in the art, and the present invention does not impose any special limitations on its material selection or specifications.

[0049] According to the present invention, in step (1), the active material has a core and a TiOF2 coating layer covering the surface of the core. The core is made of a manganese-based positive electrode active material and / or an iron-based positive electrode active material. Preferably, the manganese-based positive electrode active material may be selected from at least one of lithium-rich manganese-based positive electrode materials, lithium manganese oxide, lithium manganese nickel oxide, and lithium iron manganese phosphate; the iron-based positive electrode active material may be selected from at least one of lithium iron phosphate, lithium iron silicate, and lithium iron borate.

[0050] In this invention, an active material with a TiOF2 coating is used as the active body of the positive electrode. This coating acts as a barrier, reducing direct contact between the core positive electrode active material and the electrolyte in the lithium-ion battery, thus slowing the dissolution of high-valent metal ions during battery operation. Furthermore, the coating also acts as a conversion layer, transforming the dissolved high-valent metal ions into metal fluorides (e.g., MnF2, FeF2), reducing the migration of high-valent metal ions to the negative electrode. In addition, TiOF2 can also improve the battery's kinetic performance.

[0051] According to the present invention, based on the total weight of the active material, the content of TiOF2 in the active material is 0.1-10 wt%, preferably 4-6 wt%.

[0052] According to the present invention, the preparation process of the active material in step (1) includes:

[0053] (i) A mixture is prepared by mixing a titanium source, a manganese-based positive electrode active material and / or an iron-based positive electrode active material and a solvent to obtain a mixture;

[0054] (ii) The mixture is mixed with ammonia water, and then solid-liquid separation and drying are performed to obtain the precursor;

[0055] (iii) The precursor is mixed with a fluorine source and the resulting mixture is calcined to obtain an active material.

[0056] According to the present invention, in step (i) above, it is preferable to first mix the titanium source and the solvent, and then add the manganese-based positive electrode active material and / or the iron-based positive electrode active material for a second mixing to obtain the mixture; wherein, preferably, the first mixing time is 0.5-1h; the second mixing time is 1-2h; and the solvent can be an alcohol solution.

[0057] According to the present invention, in step (ii) above, it is preferable to slowly add ammonia water to the mixture for a third mixing, then centrifuge the resulting mixture, and wash and dry the separated solid phase to obtain the precursor; wherein, preferably, the amount of ammonia water used is such that the pH value of the mixture obtained by the third mixing is 7.5-8.5; the third mixing time is 2-3 hours; and the drying temperature is 100-120°C.

[0058] According to the present invention, in step (iii) above, it is preferable to ball-mill and mix the precursor with a fluorine source, and then calcine it under an oxygen-containing atmosphere, and the resulting calcined product is the active material; wherein the calcination conditions include: a temperature of 200-400°C and a time of 3-5 h.

[0059] According to the present invention, in the preparation process of the active material, the titanium source is selected from at least one of tetrabutyl titanate and / or titanium tetrachloride, preferably tetrabutyl titanate; the fluorine source is selected from at least one of ammonium fluoride, ammonium hydrogen fluoride and tetramethylammonium fluoride, preferably ammonium fluoride.

[0060] According to the present invention, during the preparation of the active material, the amounts of the titanium source, manganese-based positive electrode active material and / or iron-based positive electrode active material, and fluorine source fed are such that the TiOF2 content in the obtained active material is 0.1-10 wt%.

[0061] According to the present invention, the slurry containing the active material further contains a conductive agent and a first binder.

[0062] According to the present invention, in step (1), the composition and amount of the slurry containing active material are such that, based on the total weight of the active material layer, the content of TiOF2 in the active material layer is 3-5 wt%, the content of the conductive agent is 2-20 wt%, the content of the first binder is 2-15 wt%, and the thickness of the active material layer is 60-100 μm.

[0063] According to the present invention, in step (1), the solvent used to prepare the slurry containing the active material, the preparation of the slurry, and the coating can all adopt conventional material selection, operation and parameters in the art, and the present invention does not make any special limitation in this regard.

[0064] According to the present invention, in steps (2-1) and (2-2), for the slurry containing LiPSCl, the concentration of LiPSCl is preferably 5-50 wt%.

[0065] According to the present invention, the slurry containing LiPSCl further contains a second binder.

[0066] According to the present invention, the slurry containing LiPSCl can be prepared by mixing its components. Preferably, the LiPSCl powder can be mixed with a second binder first, and then added to an organic solvent for further mixing to obtain a homogeneous slurry. The organic solvent can be selected from at least one of toluene, xylene, trimethylbenzene, chlorobenzene, acetone, acetonitrile, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, diethylformamide, tetrahydrofuran, and dimethyl sulfoxide.

[0067] According to the present invention, in steps (2-1) and (2-2), the coating can be performed using conventional operations and parameters in the art, followed by drying to remove the organic solvent from the wet film. Preferably, the drying conditions include a temperature of 90-120°C and a time of 1-3 hours.

[0068] According to the present invention, in step (2-2), the hot pressing conditions include: pressure of 0.1-5 MPa, temperature of 25-65°C, and time of 0.1-0.5 h.

[0069] According to the present invention, in order to enable better adhesion between the active material layer and the composite layer, it is preferable to form the composite layer on the surface of the active material layer in the manner of step (2-1).

[0070] According to the present invention, in steps (2-1) and (2-2), the composition and amount of the slurry containing LiPSCl are such that, based on the total weight of the composite layer, the content of LiPSCl in the composite layer is 5-50 wt%, the content of the second binder is 45-90 wt%, and the thickness of the composite layer is 5-30 μm.

[0071] In this invention, the conductive agent and binder are not particularly limited and can be any conventional conductive agent and binder for lithium-ion battery electrodes in the art. For example, the conductive agent can be selected from at least one of acetylene black, carbon nanotubes, graphene, conductive carbon black, and conductive graphite; the first binder and the second binder can each be independently selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylate, polyurethane, polyethylene glycol, polyethylene oxide, epoxy resin, styrene-butadiene rubber, polymethyl cellulose, sodium polymethyl cellulose, hydroxypropyl methyl cellulose, and polyacryl alcohol.

[0072] In this invention, a composite layer with selective isolation function is laminated onto the active material layer of the positive electrode, wherein the contained LiPSCl has high ionic conductivity, allowing for the formation of relatively small Li... + LiPSCl forms a dense isolation layer at the microscopic level, which can prevent high-valence, large-sized metal ions from passing through the composite layer and thus prevent them from migrating and depositing onto the negative electrode of the battery.

[0073] According to a preferred embodiment of the present invention, based on the above-mentioned limitations on the composition and dosage of the slurry containing the active material and the slurry containing LiPSCl, the dosage of the slurry containing the active material and the slurry containing LiPSCl is further such that the weight ratio of TiOF2 in the active material layer to LiPSCl in the composite layer is 1:(0.1-2), which can better exert the synergistic effect between the TiOF2-coated active material and the composite layer, further suppress the migration and deposition of high positive valence metal ions, and significantly improve the cycle performance and storage performance of the battery.

[0074] The third aspect of the present invention provides a positive electrode sheet prepared by the method described in the second aspect above.

[0075] According to the present invention, the structure, composition and performance of the positive electrode sheet prepared by the method described in the second aspect are the same as those of the positive electrode sheet described in the first aspect of the present invention, and will not be repeated here.

[0076] A fourth aspect of the present invention provides a lithium-ion battery comprising the positive electrode sheet described in the first or third aspect above.

[0077] The lithium-ion battery provided by this invention significantly reduces the dissolution and deposition of high positive-valence metal ions from the positive electrode, and the capacity of the positive electrode material does not decay rapidly, resulting in significantly improved cycle performance and storage performance.

[0078] The present invention will be described in detail below through examples. Unless otherwise specified, all reagents used in the following preparation examples, embodiments, and comparative examples are commercially available industrial products.

[0079] Preparation Example 1

[0080] This preparation example illustrates the preparation of manganese-based positive electrode active materials with a TiOF2 coating.

[0081] (i) Add 0.12 g of tetrabutyl titanate to 50 mL of ethanol aqueous solution and stir for 1 h; then add 3 g of lithium manganate and continue stirring for 2 h to obtain a mixture;

[0082] (ii) 0.8 mL of ammonia water was slowly added to the above mixture and stirred for 2 h to make the pH of the resulting mixture 7.5-8.5; then the resulting mixture was centrifuged and the separated solid phase was washed with deionized water and ethanol in sequence, and the washed solid phase was placed in a 120℃ drying oven for vacuum drying for 3 h to obtain the precursor.

[0083] (iii) The above precursor and ammonium fluoride were ball-milled and mixed at a weight ratio of 1:1.5, and the mixture was placed in a kiln and calcined at 350°C for 5 hours to obtain lithium manganese oxide@TiOF2 (denoted as Al).

[0084] Scanning electron microscopy (SEM) tests were performed on A1 and the raw material lithium manganese oxide, and the results are as follows: Figure 1 and Figure 2 As shown, Figure 1 Before coating, the raw material lithium manganese oxide can be observed to have relatively clear angular particles; Figure 2 For lithium manganese oxide@TiOF2 (i.e., Al), it can be observed that the edges of its particles are relatively... Figure 1 The edges of the lithium manganese oxide particles are smoother, which is due to the change in particle appearance caused by the coating layer formed on the surface of the lithium manganese oxide. EDS analysis showed that the chemical composition of the coating layer is TiOF2, and the content of TiOF2 coating layer in Al is 4.3 wt%.

[0085] Preparation Example 2

[0086] This preparation example illustrates the preparation of manganese-based positive electrode active materials with a TiOF2 coating.

[0087] (i) Add 0.15 g of tetrabutyl titanate to 50 mL of ethanol aqueous solution and stir for 1 h; then add 3 g of lithium manganate and continue stirring for 2 h to obtain a mixture.

[0088] (ii) Slowly add 1 mL of ammonia water to the above mixture and stir for 2 h to make the pH of the resulting mixture 7.5-8.5; then centrifuge the resulting mixture, wash the separated solid phase with deionized water and ethanol in sequence, and place the washed solid phase in a 120℃ drying oven for 3 h to obtain the precursor.

[0089] (iii) The above precursor and ammonium fluoride were ball-milled and mixed at a weight ratio of 1:2, and the mixture was placed in a kiln and calcined at 350°C for 5 hours to obtain lithium manganese oxide@TiOF2 (denoted as A2).

[0090] EDS analysis showed that the TiOF2 coating content in A2 was 7 wt%.

[0091] Preparation Example 3

[0092] This preparation example illustrates the preparation of iron-based cathode active materials with a TiOF2 coating.

[0093] (i) Add 0.08 g of tetrabutyl titanate to 50 mL of ethanol aqueous solution and stir for 1 h; then add 3 g of lithium manganese iron phosphate and continue stirring for 2 h to obtain a mixture.

[0094] (ii) 0.5 mL of ammonia water was slowly added to the above mixture and stirred for 2 h to make the pH of the resulting mixture 7.5-8.5; then the resulting mixture was centrifuged and the separated solid phase was washed with deionized water and ethanol in sequence, and the washed solid phase was placed in a 120℃ drying oven for vacuum drying for 3 h to obtain the precursor.

[0095] (iii) The above precursor and ammonium fluoride were ball-milled and mixed at a weight ratio of 1:0.5, and the mixture was placed in a kiln and calcined at 350°C for 5 hours to obtain lithium manganese iron phosphate@TiOF2 (denoted as A3).

[0096] EDS analysis showed that the TiOF2 coating content in A3 was 3 wt%.

[0097] Example 1

[0098] This embodiment is used to illustrate the preparation of the positive electrode sheet.

[0099] (1) The above active material A1, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 92:5:3:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector (of which the content of TiOF2 is 4 wt%, the content of conductive carbon black is 5 wt%, and the content of PVDF is 3 wt%).

[0100] (2) Mix LiPSCl powder and PVDF at a weight ratio of 0.5:1, then add to toluene and stir for 5 hours to obtain a slurry containing LiPSCl (wherein, the concentration of LiPSCl is 20wt%). Coat the slurry onto the active material layer in step (1), and dry at 120°C for 3 hours to form a composite layer with a thickness of 10μm on the surface of the active material layer (wherein, the content of LiPSCl is 33wt% and the content of PVDF is 67wt%), to obtain a positive electrode (denoted as P1).

[0101] In P1, the weight ratio of TiOF2 to LiPSCl is 1:0.5.

[0102] Example 2

[0103] This embodiment is used to illustrate the preparation of the positive electrode sheet.

[0104] (1) The above active material A1, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 92:5:3:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector (of which the content of TiOF2 is 4 wt%, the content of conductive carbon black is 5 wt%, and the content of PVDF is 3 wt%).

[0105] (2) Mix LiPSCl powder and PVDF at a weight ratio of 0.5:0.8, then add to toluene and stir for 5 hours to obtain a slurry containing LiPSCl (wherein, the concentration of LiPSCl is 22wt%). Coat the slurry onto the active material layer in step (1), and dry at 120°C for 3 hours to form a composite layer with a thickness of 10μm on the surface of the active material layer (wherein, the content of LiPSCl is 38wt% and the content of PVDF is 62wt%), to obtain a positive electrode (denoted as P2).

[0106] In P2, the weight ratio of TiOF2 to LiPSCl is 1:0.8.

[0107] Example 3

[0108] This embodiment is used to illustrate the preparation of the positive electrode sheet.

[0109] (1) The above active material A1, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 80:15:5:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector (wherein, the content of TiOF2 is 3.4 wt%, the content of conductive carbon black is 15 wt%, and the content of PVDF is 5 wt%).

[0110] (2) Mix LiPSCl powder and PVDF at a weight ratio of 0.5:2.5, then add to toluene and stir for 5 hours to obtain a slurry containing LiPSCl (wherein, the concentration of LiPSCl is 12.5 wt%). Coat the slurry onto the active material layer in step (1), and dry at 120°C for 3 hours to form a composite layer with a thickness of 10 μm on the surface of the active material layer (wherein, the content of LiPSCl is 17 wt% and the content of PVDF is 83 wt%), to obtain the positive electrode (denoted as P3).

[0111] In P3, the weight ratio of TiOF2 to LiPSCl is 1:0.2.

[0112] Example 4

[0113] This embodiment is used to illustrate the preparation of the positive electrode sheet.

[0114] (1) The above active material A1, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 70:18:12:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector (of which the content of TiOF2 is 3 wt%, the content of conductive carbon black is 18 wt%, and the content of PVDF is 12 wt%).

[0115] (2) Mix LiPSCl powder and PVDF at a weight ratio of 0.5:0.6, then add to toluene and stir for 5 hours to obtain a slurry containing LiPSCl (wherein, the concentration of LiPSCl is 24wt%). Coat the slurry onto the active material layer in step (1), and dry at 120°C for 3 hours to form a composite layer with a thickness of 10μm on the surface of the active material layer (wherein, the content of LiPSCl is 45wt% and the content of PVDF is 55wt%), to obtain the positive electrode (denoted as P4).

[0116] In P4, the weight ratio of TiOF2 to LiPSCl is 1:1.2.

[0117] Example 5

[0118] This embodiment is used to illustrate the preparation of the positive electrode sheet.

[0119] (1) The above active material A2, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 70:18:12:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector (of which the content of TiOF2 is 5 wt%, the content of conductive carbon black is 18 wt%, and the content of PVDF is 12 wt%).

[0120] (2) Mix LiPSCl powder and PVDF at a weight ratio of 0.5:0.6, then add to toluene and stir for 5 hours to obtain a slurry containing LiPSCl (wherein, the concentration of LiPSCl is 24wt%). Coat the slurry onto the active material layer in step (1), and dry at 120°C for 3 hours to form a composite layer with a thickness of 10μm on the surface of the active material layer (wherein, the content of LiPSCl is 45wt% and the content of PVDF is 55wt%), to obtain a positive electrode (denoted as P5).

[0121] In P5, the weight ratio of TiOF2 to LiPSCl is 1:0.3.

[0122] Example 6

[0123] This embodiment is used to illustrate the preparation of the positive electrode sheet.

[0124] (1) The above active material A1, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 70:18:12:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector (of which the content of TiOF2 is 3 wt%, the content of conductive carbon black is 18 wt%, and the content of PVDF is 12 wt%).

[0125] (2) Mix LiPSCl powder and PVDF at a weight ratio of 0.5:0.6, then add toluene and stir for 5 hours to obtain a slurry containing LiPSCl (wherein, the concentration of LiPSCl is 24wt%). Coat the slurry onto the active material layer in step (1), and dry at 120°C for 3 hours to form a composite layer with a thickness of 20μm on the surface of the active material layer (wherein, the content of LiPSCl is 45wt% and the content of PVDF is 55wt%), to obtain the positive electrode (denoted as P6).

[0126] In P6, the weight ratio of TiOF2 to LiPSCl is 1:1.8.

[0127] Example 7

[0128] This embodiment is used to illustrate the preparation of the positive electrode sheet.

[0129] (1) The above active material A1, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 70:18:12:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector (of which the content of TiOF2 is 3 wt%, the content of conductive carbon black is 18 wt%, and the content of PVDF is 12 wt%).

[0130] (2) Mix LiPSCl powder and PVDF at a weight ratio of 0.2:1.8, then add to toluene and stir for 5 hours to obtain a slurry containing LiPSCl (wherein, the concentration of LiPSCl is 24wt%). Coat the slurry onto the active material layer in step (1), and dry at 120°C for 3 hours to form a composite layer with a thickness of 10μm on the surface of the active material layer (wherein, the content of LiPSCl is 10wt% and the content of PVDF is 90wt%), to obtain a positive electrode (denoted as P7).

[0131] In P7, the weight ratio of TiOF2 to LiPSCl is 1:0.1.

[0132] Example 8

[0133] This embodiment is used to illustrate the preparation of the positive electrode sheet.

[0134] (1) The above active material A3, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 75:13:12:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector (of which the content of TiOF2 is 3.2 wt%, the content of conductive carbon black is 13 wt%, and the content of PVDF is 12 wt%).

[0135] (2) LiPSCl powder and PVDF were mixed at a weight ratio of 0.5:0.6, and then added to toluene and stirred for 5 hours to obtain a slurry containing LiPSCl (wherein, the concentration of LiPSCl was 24wt%). The slurry was coated on a stainless steel substrate and dried at 120°C for 3 hours to form a film. Then, the film was hot-pressed (hot-pressing temperature was 60°C, hot-pressing time was 0.5 hours, and pressure was 1MPa) to form a composite layer with a thickness of 10μm on the surface of the active material layer (wherein, the content of LiPSCl was 45wt% and the content of PVDF was 55wt%) to obtain a positive electrode (denoted as P8).

[0136] In P8, the weight ratio of TiOF2 to LiPSCl is 1:1.6.

[0137] Example 9

[0138] This embodiment is used to illustrate the preparation of the positive electrode sheet.

[0139] (1) The above active material A1, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 70:18:12:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector (of which the content of TiOF2 is 3 wt%, the content of conductive carbon black is 18 wt%, and the content of PVDF is 12 wt%).

[0140] (2) Mix LiPSCl powder and PVDF binder at a weight ratio of 1:18, then add to toluene and stir for 5 hours to obtain a slurry containing LiPSCl (wherein, the LiPSCl concentration is 24wt%). Coat the slurry onto the active material layer in step (1), and dry at 120°C for 3 hours to form a composite layer with a thickness of 10μm on the surface of the active material layer (wherein, the LiPSCl content is 5.2wt% and the PVDF content is 94.8wt%), to obtain the positive electrode (denoted as P9).

[0141] In P9, the weight ratio of TiOF2 to LiPSCl is 1:0.05.

[0142] Comparative Example 1

[0143] Lithium manganese oxide, conductive carbon black, PVDF, and N-methylpyrrolidone were mixed and stirred for 4 hours at a weight ratio of 92:5:3:22 to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil current collector with a thickness of 15 μm and dried at 90 °C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector, thus obtaining a positive electrode sheet (denoted as DP1).

[0144] Comparative Example 2

[0145] (1) Lithium manganese oxide, conductive carbon black, PVDF and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 92:5:3:22 to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector.

[0146] (2) Mix LiPSCl powder and PVDF at a weight ratio of 0.5:1, then add to toluene and stir for 5 hours to obtain a slurry containing LiPSCl (wherein, the concentration of LiPSCl is 20wt%). Coat the slurry onto the active material layer in step (1), and dry at 120°C for 3 hours to form a composite layer with a thickness of 10μm on the surface of the active material layer (wherein, the content of LiPSCl is 33wt% and the content of PVDF is 67wt%), to obtain the positive electrode (denoted as DP2).

[0147] Comparative Example 3

[0148] The above-mentioned active material A1, conductive carbon black, PVDF, and N-methylpyrrolidone were mixed and stirred for 4 hours in a weight ratio of 92:5:3:22 to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm and dried at 90°C for 2 hours to form an active material layer with a thickness of 85 μm on the current collector, thus obtaining a positive electrode sheet (denoted as DP3).

[0149] Test case

[0150] The above positive electrode sheets P1-P9 and DP1-DP3 are assembled with the negative electrode sheet (prepared by mixing graphite, conductive carbon black, PVDF and N-methylpyrrolidone in a weight ratio of 95:3:2:100 to form a negative electrode slurry, which is then uniformly coated on copper foil and prepared by baking and rolling) and the electrolyte (prepared by mixing lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a weight ratio of 10:30:30:30) to form a lithium-ion battery (referred to as B1-B9 and DB1-DB3 respectively).

[0151] After the lithium-ion batteries were placed at 45°C, formed in a high-temperature fixture, and resealed, they were subjected to routine capacity testing, followed by cycle performance and storage performance testing.

[0152] 1. Cyclic performance test:

[0153] At 25°C, the lithium-ion battery after capacity testing was left to stand for 120 minutes, then charged at a constant current rate of 0.5C to 4.3V. After charging, it was left to stand for 60 minutes, then discharged at a constant current rate of 1C to 3.0V. After repeating the above steps 300 times, the capacity retention rate of the 300th cycle was calculated (capacity retention rate of the 300th cycle (%) = discharge capacity of the 300th cycle / discharge capacity of the first cycle × 100%). The results are shown in Table 1.

[0154] 2. Storage performance test:

[0155] The lithium-ion batteries, after capacity testing, were charged to 4.3V at 0.33C and allowed to stand for 60 minutes. They were then discharged to 3.0V at 0.33C (discharge capacity C0 was recorded). The batteries were then charged again to 4.3V at 0.33C and allowed to stand for 60 minutes. The test was then completed. The batteries were subsequently placed in a 45℃ environmental chamber for 28 days. After 28 days, they were discharged to 3.0V at 0.33C (discharge capacity C1 was recorded) and allowed to stand for 60 minutes. They were then charged to 4.3V at 0.33C and allowed to stand for 60 minutes. Finally, they were discharged to 3.0V at 0.33C and allowed to stand for 60 minutes, ending the test. The discharge capacity C2 was recorded. The storage capacity recovery rate after 28 days at 45℃ was calculated (storage capacity recovery rate (%) = C2 / C0 × 100%), and the results are shown in Table 1.

[0156] Table 1

[0157]

[0158] As shown in Table 1, the positive electrode sheet provided by this invention has a specific active material layer formed by coating manganese-based and / or iron-based positive electrode materials with TiOF2, and a composite layer containing LiPSCl is disposed on the surface of the active material layer. Through the synergistic effect of the active material layer and the composite layer, the migration and deposition of high positive valence metal ions from the positive electrode to the negative electrode surface during battery cycling can be significantly reduced, resulting in a significant improvement in the cycle life and storage performance of the battery. Specifically, batteries B1-B9 can achieve a capacity retention rate of more than 85% after 300 cycles at 0.5C / 1C at 25℃, with a maximum of about 96%, and a storage capacity recovery rate of more than 83% after 28 days at 45℃, with a maximum of about 94%. In particular, DB1 uses a common positive electrode sheet, DB2 uses a positive electrode sheet whose active material does not have a TiOF2 coating layer, and DB3 uses a positive electrode sheet that does not contain a composite layer, resulting in their cycle life and storage performance being worse than those of B1-B9.

[0159] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positive electrode sheet for a lithium-ion battery, characterized in that, The positive electrode includes: a current collector, an active material layer, and a composite layer, wherein the active material layer is disposed between the current collector and the composite layer; wherein... The active material layer comprises an active material with a TiOF2 coating layer; the composite layer contains LiPSCl; The active material with TiOF2 coating includes manganese-based positive electrode active material with TiOF2 coating and / or iron-based positive electrode active material with TiOF2 coating; The thickness of the composite layer is 5-30 μm; The positive electrode sheet can reduce the direct contact between the positive electrode active material in the core and the electrolyte, thus slowing down the dissolution of high positive valence metal ions.

2. The positive electrode according to claim 1, wherein, The manganese-based cathode active material is selected from at least one of lithium-rich manganese-based cathode materials, lithium manganese oxide, lithium manganese nickel oxide, and lithium iron manganese phosphate. And / or, the iron-based positive electrode active material is selected from at least one of lithium iron phosphate, lithium iron silicate, and lithium iron borate.

3. The positive electrode according to claim 1 or 2, wherein, The active material with the TiOF2 coating has a TiOF2 content of 0.1-10 wt%.

4. The positive electrode according to claim 1 or 2, wherein, The active material with the TiOF2 coating has a TiOF2 content of 4-6 wt%.

5. The positive electrode according to claim 1 or 2, wherein, The active material layer also contains a conductive agent and a first binder.

6. The positive electrode according to claim 5, wherein, Based on the total weight of the active material layer, the content of TiOF2 in the active material layer is 3-5 wt%; the content of the conductive agent is 2-20 wt%; and the content of the first binder is 2-15 wt%.

7. The positive electrode according to claim 6, wherein, Based on the total weight of the active material layer, the content of TiOF2 in the active material layer is 3.5-4 wt%.

8. The positive electrode according to claim 1 or 2, wherein, The composite layer also contains a second adhesive.

9. The positive electrode according to claim 8, wherein, Based on the total weight of the composite layer, the content of LiPSCl in the composite layer is 5-50 wt%; the content of the second binder is 45-90 wt%.

10. The positive electrode according to claim 9, wherein, Based on the total weight of the composite layer, the content of LiPSCl in the composite layer is 20-40 wt%.

11. The positive electrode according to claim 1 or 2, wherein, The weight ratio of TiOF2 to LiPSCl is 1:(0.1-2).

12. The positive electrode according to claim 1 or 2, wherein, The thickness of the active material layer is 60-100 μm.

13. A method for preparing a lithium-ion battery positive electrode sheet according to claim 1, characterized in that, include: (1) A slurry containing an active material is coated on the surface of the current collector, and after drying, an active material layer is formed on the surface of the current collector; The active material includes a manganese-based positive electrode active material with a TiOF2 coating and / or an iron-based positive electrode active material with a TiOF2 coating. (2-1) A slurry containing LiPSCl is coated on the surface of the active material layer. After drying, a composite layer is formed on the surface of the active material layer to obtain a positive electrode sheet. or (2-2) A slurry containing LiPSCl is coated to form a film, and after drying, a film layer is formed; then the film layer is hot-pressed onto the surface of the active material layer to form a composite layer, thus obtaining a positive electrode sheet.

14. The method according to claim 13, wherein, The manganese-based cathode active material is selected from at least one of lithium-rich manganese-based cathode materials, lithium manganese oxide, lithium manganese nickel oxide, and lithium iron manganese phosphate. And / or, the iron-based positive electrode active material is selected from at least one of lithium iron phosphate, lithium iron silicate, and lithium iron borate.

15. The method according to claim 13, wherein, Based on the total weight of the active material, the TiOF2 content in the active material is 0.1-10 wt%.

16. The method according to claim 15, wherein, Based on the total weight of the active material, the content of TiOF2 in the active material is 4-6 wt%.

17. The method according to claim 15 or 16, wherein, The preparation process of the active material includes: (i) A mixture is prepared by mixing a titanium source, a manganese-based positive electrode active material and / or an iron-based positive electrode active material and a solvent to obtain a mixed solution; (ii) The mixture is mixed with ammonia water, and then subjected to solid-liquid separation and drying to obtain the precursor; (iii) The precursor is mixed with a fluorine source and the resulting mixture is calcined to obtain an active material.

18. The method according to claim 17, wherein, The amounts of titanium source, manganese-based positive electrode active material and / or iron-based positive electrode active material, and fluorine source fed are such that the TiOF2 content in the obtained active material is 0.1-10 wt%. And / or, the titanium source is selected from tetrabutyl titanate and / or titanium tetrachloride; And / or, the fluorine source is selected from at least one of ammonium fluoride, ammonium hydrogen fluoride, and tetramethylammonium fluoride; And / or, the calcination conditions include: a temperature of 200-400℃ and a time of 3-5h.

19. The method according to claim 13 or 14, wherein, The slurry containing active materials also contains a conductive agent and a first binder.

20. The method according to claim 19, wherein, The composition and amount of the slurry containing active materials are such that, based on the total weight of the active material layer, the content of TiOF2 in the active material layer is 3-5 wt%, the content of the conductive agent is 2-20 wt%, the content of the first binder is 2-15 wt%, and the thickness of the active material layer is 60-100 μm.

21. The method according to claim 13 or 14, wherein, The slurry containing LiPSCl also contains a second binder.

22. The method according to claim 21, wherein, The composition and amount of the LiPSCl-containing slurry are such that, based on the total weight of the composite layer, the LiPSCl content in the composite layer is 5-50 wt%, the second binder content is 45-90 wt%, and the thickness of the composite layer is 5-30 μm.

23. The method according to claim 13 or 14, wherein, The amount of the slurry containing the active material and the slurry containing LiPSCl are such that the weight ratio of TiOF2 in the active material layer to LiPSCl in the composite layer is 1:(0.1-2).

24. A lithium-ion battery cathode sheet prepared by the method of any one of claims 13-23.

25. A lithium-ion battery comprising the positive electrode sheet according to any one of claims 1-12 and 24.

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