Positive electrode lithium supplement agent, lithium ion battery and preparation method and application of lithium ion battery

Abstract

The invention discloses a positive electrode lithium supplement agent, a lithium ion battery and a preparation method and application of the lithium ion battery. The positive electrode lithium supplement agent comprises a core material and a flexible coating material, the chemical formula of the core material is LiaMbOc, M is selected from any one of Mg, Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn and C, a is greater than or equal to 2 and less than or equal to 8, b is greater than or equal to 0 and less than or equal to 6, and c is greater than or equal to 1 and less than or equal to 8; the flexible coating material is an organic polymer, the chemical formula of the flexible coating material is (CdYe) n, Y is selected from one or more of H, O, N, P and S, d is more than 0 and less than 10, e is more than 0 and less than 50, and n is more than or equal to 1000 and less than or equal to 100000; the outer surface of the core material is coated with the flexible coating material. When the positive electrode lithium supplement agent is applied to the lithium ion battery, the adverse effect caused by negative electrode expansion can be relieved, the cycle performance can be improved, and the long-acting lithium supplement effect can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode lithium supplement, a lithium ion battery, and a preparation method and application thereof. Background Art

[0002] With the rapid development and application of lithium-ion batteries in the field of new energy vehicles / electrochemical energy storage, conventional chemical systems are increasingly unable to meet the ever-increasing demands for energy density / cycle life. The emergence of pre-lithiation (lithium replenishment) technology has provided an effective solution and injected new vitality into the development of lithium-ion battery technology.

[0003] In the related art, since the formation of the negative electrode SEI film consumes a large amount of active lithium during the initial formation of lithium-ion batteries, this means that the lithium ions released from the positive electrode material are irreversibly consumed, especially when some high-capacity silicon-based negative electrode materials are added, which will greatly reduce the coulombic efficiency and battery capacity of the battery in the first week. The above problems can be effectively solved by supplementing active lithium. There are many ways to supplement active lithium that have been reported, mainly two categories: negative electrode lithium supplementation and positive electrode lithium supplementation. Among them, positive electrode lithium supplementation is to add lithium-containing compounds with high irreversible capacity to the positive electrode of the lithium-ion battery. According to the type of compound, it can be divided into binary lithium-containing compounds represented by Li2O, Li2O2, and Li2S, ternary lithium-containing compounds represented by Li6CoO4 and Li5FeO4, and organic lithium-containing compounds represented by Li2DHBN and Li2C2O4. However, in actual application, since more negative electrode active substances are required to release lithium ions due to positive polarization, the energy density is reduced, and there is a defect that it is difficult to achieve the effect of long-term lithium supplementation. In addition, the large volume expansion during the cycle, especially when using SiC, may accelerate capacity decay, which cannot be improved by simply replenishing lithium to increase active lithium.

[0004] Based on this, there is an urgent need to find a positive electrode lithium replenisher that can not only alleviate the expansion of the negative electrode and improve the cycle life, but also help improve the long-term lithium replenishment effect. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a positive electrode lithium replenisher, which is applied to lithium-ion batteries, which can not only alleviate the adverse effects of negative electrode expansion, but also help improve cycle performance, thereby achieving a long-term lithium replenishment effect.

[0006] The invention also provides a positive electrode sheet.

[0007] The invention also provides a lithium ion battery.

[0008] The invention also provides an electric device.

[0009] The first aspect of the present invention provides a positive electrode lithium supplement agent, comprising: Core material, the chemical formula of the core material is Li a M b O c , wherein M is selected from at least one of Mg, Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn, and C, and 2≤a≤8, 0≤b≤6, and 1≤c≤8; A flexible covering material, the flexible covering material covers at least a portion of the outer surface of the core material, the flexible covering material is an organic polymer, and the chemical formula is (C d Y e )n, wherein Y is selected from one or more of H, O, N, P, S, and 0<d<10, 0<e<50, n is the degree of polymerization, 1000≤n≤100000.

[0010] The positive electrode lithium supplement according to the embodiment of the present invention has at least the following beneficial effects: The positive electrode lithium supplement of the present invention is prepared by coating a lithium-containing compound with a flexible material. The present invention utilizes the characteristics of the flexible material itself having low conductivity and being easily broken after receiving a certain stress such as the stress caused by the volume expansion of the negative electrode, and coats it on the outer surface of the core material. After the lithium battery is circulated for a certain period of time, the negative electrode will inevitably expand in volume, and the stress generated by it will easily cause the flexible coating layer to break, thereby exposing the core material of the lithium supplement agent, so that it can play a capacity supplement role, while alleviating the adverse effects caused by the expansion of the negative electrode, thereby achieving a long-term lithium supplement effect.

[0011] In some embodiments of the present invention, the chemical formula of the core material is Li a M b O c , wherein M is selected from any one of Mg, Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn, and C, and 2≤a≤5, 0≤b≤4, and 4≤c≤7.

[0012] In some embodiments of the present invention, the core material is selected from any one of Li5FeO4, Li2NiO2, Li5FeO5, Li5FeO6, Li5FeO7, and Li5FeO8.

[0013] In some embodiments of the present invention, the flexible covering material is selected from at least one of polyethylene oxide, polypropylene, polyethylene, polystyrene (PS), polyester, synthetic rubber, polyurethane, and polyoxymethylene.

[0014] Preferably, the flexible covering material is selected from at least one of polyethylene oxide and polypropylene.

[0015] In some embodiments of the present invention, the tensile strength of the flexible coating material is 5-200 MPa.

[0016] In some embodiments of the present invention, the tensile strength of the flexible coating material is 5-150 MPa.

[0017] In some embodiments of the present invention, in the positive electrode lithium supplement, the mass fraction of the flexible coating material is 0.5% to 8%.

[0018] A second aspect of the present invention provides a positive electrode sheet, comprising the positive electrode lithium supplement agent as described in any one of the first aspects and a positive electrode active material.

[0019] In some embodiments of the present invention, the positive electrode active material is selected from at least one of LiFePO4, LiFePO5, LiFePO6 and LiFePO7.

[0020] In some preferred embodiments of the present invention, the positive electrode active material is selected from LiFePO4.

[0021] In some embodiments of the present invention, the mass ratio of the positive electrode lithium supplement to the positive electrode active material is 0.1-10:90-99.9.

[0022] A third aspect of the present invention provides a lithium-ion battery, comprising a negative electrode sheet and the positive electrode sheet according to the second aspect, wherein the negative electrode sheet comprises a negative electrode active material.

[0023] The lithium ion battery according to the embodiment of the present invention has at least the following beneficial effects: the lithium ion battery of the present invention has excellent cycle performance and service life.

[0024] In some embodiments of the present invention, the negative electrode active material includes at least one of graphite and silicon material.

[0025] In some embodiments of the present invention, the negative electrode active material is graphite, and the ratio of the tensile strength of the flexible coating material in the positive electrode lithium supplement to the particle size D50 of the graphite is: 1≤T / R1≤4; Wherein, T is the tensile strength of the flexible coating material in the positive electrode lithium supplement, in MPa; R1 is the particle size D50 of the graphite, in μm.

[0026] In some embodiments of the present invention, the mass fraction of the flexible coating material in the positive electrode lithium supplement is 1% to 8%.

[0027] In some embodiments of the present invention, the tensile strength of the flexible coating material in the positive electrode lithium supplement is 10-40 MPa.

[0028] In some embodiments of the present invention, the particle size D50 of the graphite is 10-15 μm.

[0029] In some embodiments of the present invention, the silicon material is elemental silicon.

[0030] In some embodiments of the present invention, the particle size D50 of the silicon material is 3-20 μm.

[0031] In some embodiments of the present invention, the negative electrode active material is graphite and silicon material, wherein the mass fraction of the silicon material in the negative electrode active material is 15% to 80%.

[0032] In some embodiments of the present invention, the ratio of the tensile strength of the flexible coating material in the positive electrode lithium supplement to the particle size D50 of the silicon material is: 3≤T / R2≤9; Wherein, T is the tensile strength of the flexible coating material in the positive electrode lithium supplement, in MPa; R2 is the particle size D50 of the silicon material, in μm.

[0033] In some embodiments of the present invention, the mass fraction of the flexible coating material in the positive electrode lithium supplement is 0.5% to 2%.

[0034] In some embodiments of the present invention, when the mass fraction of the silicon material in the negative electrode active material is 15% to 30%, the T / R2 is 4.0 to 5.5.

[0035] In some embodiments of the present invention, when the mass fraction of the silicon material in the negative electrode active material is greater than 30% and less than or equal to 70%, the T / R2 is 5.5-6.5.

[0036] In some embodiments of the present invention, when the mass fraction of the silicon material in the negative electrode active material is greater than 70% and less than or equal to 80%, the T / R2 is 6.5-8.5.

[0037] A fourth aspect of the present invention provides an electrical device comprising the lithium-ion battery as described in the first aspect.

[0038] Other features and advantages of the present invention will be set forth in the description which follows. DETAILED DESCRIPTION

[0039] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0040] The words "preferably", "more preferably", etc. in the present invention refer to embodiments of the present invention that may provide certain beneficial effects in certain circumstances. However, other embodiments may also be preferred under the same circumstances or other circumstances. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of the present invention.

[0041] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0042] In the description of the present invention, the reference term "and / or" includes all and any combinations of one or more of the associated listed items.

[0043] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0044] In the description of the present invention, the tensile strength is obtained by testing with a tensile testing machine, wherein the sample is stretched at an initial tensile speed of 1 mm / min until the sample fails (yields or breaks), and the thickness of the sample is 1-10 mm.

[0045] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0046] 1. Positive electrode lithium supplement: The present invention provides a positive electrode lithium supplement agent, which comprises: Core material, the chemical formula of the core material is Li a M b O c , wherein a is 2 to 8, b is 0 to 6, c is 1 to 8, and the element M is at least one selected from Mg, Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn, and C; and, The flexible covering material covers at least a portion of the outer surface of the core material, and is specifically an organic polymer with a certain tensile strength (T), and its general structural formula is: (C d Y e ) n ; Wherein Y is selected from one or more of H, O, N, P, S, etc., 0<d<10, 0<e<50, n is the degree of polymerization, 1000≤n≤100000; The mass fraction of the flexible coating material in the positive electrode lithium supplement is 0.5%~8%.

[0047] In some embodiments of the present invention, the chemical formula of the core material is Li a M b O c , wherein M is selected from any one of Mg, Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn, and C, and 2≤a≤5, 0≤b≤4, and 4≤c≤7; the M atom is preferably Fe and / or Ni.

[0048] Preferably, the core material is selected from any one of Li5FeO4, Li2NiO2, Li5FeO5, Li5FeO6, Li5FeO7, and Li5FeO8.

[0049] In some embodiments of the present invention, the degree of polymerization n of the organic polymer is 2000-6000.

[0050] In some preferred embodiments of the present invention, the flexible coating material is selected from any one of polyethylene oxide (PEO), polypropylene (PP), polyethylene (PE), polystyrene (PS), polyester (such as PET), synthetic rubber (such as styrene-butadiene rubber, SBR), polyurethane (PU), and polyoxymethylene (POM).

[0051] More preferably, the flexible covering material is selected from at least one of polyethylene oxide or polypropylene.

[0052] In some embodiments of the present invention, polyethylene oxide can be prepared by the following preparation method: Add appropriate amount of water and catalyst (sodium hydroxide) into the reactor, stir the mixture to ensure that the catalyst is completely dissolved; then gradually add ethylene oxide into the reactor, control the temperature of the reactor at 50~100℃ and the pressure at 0.1~1 MPa. Under the action of the catalyst, ethylene oxide undergoes ring-opening polymerization to form polyethylene oxide, and then terminate the reaction by lowering the temperature or adding a terminator (such as phosphoric acid, acetic acid, etc.).

[0053] The polymer solution obtained by the above reaction is poured into a precipitation tank, and a precipitant (such as acetone, ethanol, etc.) is added to precipitate PEO. Then, a filtering device is used to remove water and other impurities in the precipitation tank, and the precipitate is washed with pure water or an organic solvent to remove residual catalyst and unreacted ethylene oxide. Finally, the washed precipitate is placed in a drying device and dried to a constant weight to obtain polyethylene oxide powder.

[0054] In some embodiments of the present invention, polypropylene can be prepared by the following preparation method: Add catalyst precursors (such as triethylaluminum, titanium tetrachloride, etc.) and solvents into the reactor, stir the mixture to ensure that the catalyst precursors are evenly dispersed, then add propylene into the reactor, control the temperature of the reactor at 60~80℃, and the pressure at 1~3MPa; under the action of the catalyst, propylene monomers polymerize to form polypropylene, and finally terminate the reaction by lowering the temperature or adding terminators (such as alcohols, acids).

[0055] The polymer solution obtained from the above reaction is poured into a precipitation tank, and a precipitant (such as methanol, ethanol, etc.) is added to precipitate PP. The solvent and impurities in the precipitation tank are removed by filtering equipment, and the precipitate is then washed with a pure solvent to remove residual catalyst and unreacted propylene. Finally, the washed precipitate is placed in a drying device and dried to constant weight to obtain polypropylene powder.

[0056] 2. Preparation method of positive electrode lithium supplement: The present invention provides a method for preparing a positive electrode lithium supplement agent, comprising the following steps: The core material (such as Li5FeO4) particle raw materials are mixed with the flexible coating material to form a mixed material; then the mixture is dried in a protective atmosphere (such as nitrogen) so that the flexible coating material is dispersed on the surface of the core material particles to obtain a positive electrode lithium supplement.

[0057] 3. Positive electrode: The present invention provides a positive electrode sheet, comprising the positive electrode lithium replenisher and a positive electrode active material.

[0058] In some embodiments of the present invention, the positive electrode active material is selected from at least one of LiFePO4, LiFePO5, LiFePO6 and LiFePO7; preferably, the mass ratio of the positive electrode lithium supplement to the positive electrode active material is 0.1~10:90~99.9.

[0059] 4. Lithium-ion battery: The present invention provides a lithium ion battery, comprising a negative electrode sheet and the positive electrode sheet mentioned above, wherein the negative electrode sheet comprises a negative electrode active material.

[0060] In some embodiments of the present invention, the negative electrode active material includes at least one of graphite and silicon material.

[0061] In some embodiments of the present invention, the negative electrode active material is graphite, and the ratio of the tensile strength of the flexible coating material in the positive electrode lithium supplement to the particle size D50 of the graphite is: 1≤T / R1≤4; Where T is the tensile strength of the flexible coating material in the positive electrode lithium supplement, in MPa; R1 is the D50 of graphite, in μm.

[0062] In some embodiments of the present invention, the mass fraction of the flexible coating material in the positive electrode lithium supplement is 1% to 8%.

[0063] In some embodiments of the present invention, the tensile strength of the flexible coating material in the positive electrode lithium supplement is 10-40 MPa.

[0064] In some embodiments of the present invention, the particle size D50 of graphite is 10-15 μm.

[0065] In some embodiments of the present invention, the negative electrode active material includes graphite and silicon material, wherein the mass fraction of the silicon material in the negative electrode active material is 15% to 80%.

[0066] In some embodiments of the present invention, the ratio of the tensile strength of the flexible coating material in the positive electrode lithium supplement to the particle size D50 of the graphite is: 3≤T / R2≤9; Wherein T is the tensile strength of the flexible coating material in the positive electrode lithium supplement, in MPa; R2 is the particle size D50 of the silicon material, in μm.

[0067] In some embodiments of the present invention, the mass fraction of the flexible coating material in the positive electrode lithium supplement is 0.5% to 2%.

[0068] In some embodiments of the present invention, the particle size D50 of the silicon material is 3-20 μm.

[0069] In some embodiments of the present invention, when the mass fraction of the silicon material in the negative electrode active material is 15% to 30%, T / R2 is 4.0 to 5.5.

[0070] In some embodiments of the present invention, when the mass fraction of the silicon material in the negative electrode active material is greater than 30% and less than or equal to 70%, T / R2 is 5.5-6.5.

[0071] In some embodiments of the present invention, when the mass fraction of the silicon material in the negative electrode active material is greater than 70% and less than or equal to 80%, T / R2 is 6.5-8.5.

[0072] In some embodiments of the present invention, the lithium-ion battery further comprises an electrolyte and a separator.

[0073] The present invention will be described in further detail below in conjunction with specific implementation modes, but the implementation modes of the present invention are not limited thereto.

[0074] Embodiment 1: This embodiment provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein: a) The raw materials for preparing the positive electrode sheet include LiFePO4 (positive electrode active material), positive electrode lithium supplement, conductive carbon black and polyvinylidene fluoride, with a mass ratio of 99:1:8:12; the positive electrode lithium supplement is composed of the core material Li5FeO4 and the flexible coating material polyethylene oxide (model PEO-4000, manufacturer Sigma Aldrich). The mass fraction of the flexible coating material in the positive electrode lithium supplement is 1%, and the tensile strength is 10 MPa.

[0075] b) The raw materials for preparing the negative electrode sheet include graphite (negative electrode active material), conductive carbon black, styrene-butadiene rubber and carboxymethyl cellulose in a mass ratio of 96:1.5:1.5:1, wherein the particle size D50 of the graphite is 15 μm.

[0076] This embodiment also provides a method for preparing a lithium ion battery, which specifically includes the following steps: (1) Preparation of positive electrode sheet: The positive electrode active material, positive electrode lithium supplement, conductive carbon black and polyvinylidene fluoride are mixed, dispersed in N-methyl-2-pyrrolidone and ball-milled. The ball-milling time is 60 minutes and the rotation speed is set to 30 Hz to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of the aluminum foil, dried, calendered and vacuum dried, and the electrode ears are welded to obtain the positive electrode.

[0077] (2) Preparation of negative electrode sheet: The negative electrode active material, conductive carbon black, styrene-butadiene rubber and carboxymethyl cellulose are mixed and dispersed in deionized water to obtain a negative electrode slurry, and the negative electrode slurry is coated on both sides of the copper foil, and after drying, rolling and vacuum drying, the electrode ears are welded to obtain a negative electrode sheet. (3) Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a mass ratio of 20:10:70, and after mixing, 15% of lithium hexafluorophosphate based on the total mass of the electrolyte is added, and then 1% of fluoroethylene carbonate, 8% of fluoroethylene carbonate, 0.5% of 1,3-propylene glycol sulfonate, 1% of methyl carbonate and 0.5% of lithium difluorophosphate based on the total mass of the electrolyte are added; and 0.5% of triethyl phosphate additive based on the total mass of the electrolyte is added to prepare an electrolyte.

[0078] (4) Diaphragm: conventional PE diaphragm.

[0079] (5) Lithium-ion battery assembly: The prepared positive electrode sheet, separator and negative electrode sheet are placed on an automatic winding machine and wound to obtain a bare battery cell; the bare battery cell is placed in an aluminum-plastic film, sealed and packaged, and the electrolyte is injected into the dried battery cell, which is then sealed, left to stand, pre-charged, aged and divided to obtain a lithium-ion battery.

[0080] Embodiment 2: This embodiment provides a lithium ion battery, which differs from the embodiment 1 only in that the particle size of the negative electrode active material graphite is different, and the particle size D50 of the graphite used in this embodiment is 10 μm. The rest is the same as the embodiment 1 and will not be described again.

[0081] Embodiment 3: This embodiment provides a lithium ion battery, which differs from the embodiment 1 only in that the particle size of the negative electrode active material graphite is different, and the particle size D50 of the graphite used in this embodiment is 5 μm. The rest is the same as the embodiment 1 and will not be repeated.

[0082] Embodiment 4: This embodiment provides a lithium-ion battery, which differs from the embodiment 1 only in that the flexible coating material of the positive electrode lithium supplement is different, and the flexible coating material used in the embodiment 4 is polyethylene oxide (model PEO-8000, manufacturer Sigma Aldrich) with a tensile strength of 40 MPa. The rest is the same as the embodiment 1 and will not be repeated.

[0083] Embodiment 5: This embodiment provides a lithium ion battery, which differs from the embodiment 4 only in that the particle size of the negative electrode active material graphite is different, and the particle size D50 of the graphite used in this embodiment is 10 μm. The rest is the same as the embodiment 4 and will not be described again.

[0084] Embodiment 6: This embodiment provides a lithium ion battery, which differs from the embodiment 4 only in that the particle size of the negative electrode active material graphite is different, and the particle size D50 of the graphite used in this embodiment is 8 μm. The rest is the same as the embodiment 4 and will not be described again.

[0085] Embodiment 7: This embodiment provides a lithium ion battery, which is different from the embodiment 5 only in that the mass fraction of the flexible coating material in the positive electrode lithium supplement is 3%. The rest is the same as the embodiment 5 and will not be described again.

[0086] Embodiment 8: This embodiment provides a lithium ion battery, which is different from the embodiment 5 only in that the mass fraction of the flexible coating material in the positive electrode lithium supplement is 5%. The rest is the same as the embodiment 5 and will not be described again.

[0087] Embodiment 9: This embodiment provides a lithium ion battery, which is different from the embodiment 5 only in that the mass fraction of the flexible coating material in the positive electrode lithium supplement is 8%. The rest is the same as the embodiment 5 and will not be described again.

[0088] Embodiment 10: This embodiment provides a lithium-ion battery, which differs from the embodiment 2 only in that the flexible coating material of the positive electrode lithium supplement is different, and the flexible coating material used in the embodiment 10 is polypropylene (model PP-R, manufacturer Sigma Aldrich) with a tensile strength of 10 MPa. The rest is the same as the embodiment 2 and will not be repeated.

[0089] Embodiment 11: This embodiment provides a lithium ion battery, which is different from the embodiment 2 only in that the core material of the positive electrode lithium supplement is different, and the core material of the embodiment 11 is Li2NiO2. The rest is the same as the embodiment 2 and will not be repeated.

[0090] Embodiment 12: This embodiment provides a lithium ion battery, which differs from the embodiment 2 only in that the mass ratio of the positive electrode active material to the positive electrode lithium supplement is 99.9:0.1. The rest is the same as the embodiment 2 and will not be described again.

[0091] Embodiment 13: This embodiment provides a lithium ion battery, which differs from the embodiment 2 only in that the mass ratio of the positive electrode active material to the positive electrode lithium supplement is 92: 8. The rest is the same as the embodiment 2 and will not be described again.

[0092] Embodiment 14: This embodiment provides a lithium ion battery, which is different from the embodiment 2 only in that the mass ratio of the positive electrode active material to the positive electrode lithium supplement is 90: 10. The rest is the same as the embodiment 2 and will not be described again.

[0093] Embodiment 15: This embodiment provides a lithium-ion battery, which differs from the embodiment 1 only in that: the flexible coating material of the positive electrode lithium supplement is different, and the flexible coating material used in the embodiment 15 is polyethylene oxide (model PEO-10000, manufacturer Sigma Aldrich) with a tensile strength of 60 MPa. The negative electrode active material is different. In terms of mass percentage, the negative electrode active material of the embodiment 15 is composed of 15% Si elemental substance and 85% graphite, wherein the particle size D50 of Si is 15 μm, and the particle size D50 of graphite is 10 μm. The rest is the same as the embodiment 1 and will not be repeated.

[0094] Embodiment 16: This embodiment provides a lithium-ion battery, which differs from the embodiment 15 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 16 is 8 μm. The flexible coating material of the positive electrode lithium supplement is different, and the flexible coating material used in the embodiment 16 is polyethylene oxide (model PEO-8000, manufacturer Sigma Aldrich) with a tensile strength of 40 MPa. The rest is the same as the embodiment 15 and will not be repeated.

[0095] Embodiment 17 This embodiment provides a lithium ion battery, which is different from the embodiment 15 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 17 is 11 μm. The rest is the same as the embodiment 15 and will not be described again.

[0096] Embodiment 18: This embodiment provides a lithium-ion battery, which differs from the embodiment 17 only in that the flexible coating material of the positive electrode lithium supplement is different, and the flexible coating material used in the embodiment 18 is polyethylene oxide (model PEO-8000, manufacturer Sigma Aldrich) with a tensile strength of 40 MPa. The rest is the same as the embodiment 17 and will not be repeated.

[0097] Embodiment 19: This embodiment provides a lithium ion battery, which is different from the embodiment 15 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 19 is 10 μm. The rest is the same as the embodiment 15 and will not be described again.

[0098] Embodiment 20: This embodiment provides a lithium ion battery, which is different from the embodiment 15 only in that the mass fraction of the flexible coating material in the positive electrode lithium supplement is 0.5%. The rest is the same as the embodiment 15 and will not be described again.

[0099] Embodiment 21: This embodiment provides a lithium ion battery, which is different from the embodiment 15 only in that the mass fraction of the flexible coating material in the positive electrode lithium supplement is 2%. The rest is the same as the embodiment 15 and will not be described again.

[0100] Embodiment 22: This embodiment provides a lithium-ion battery, which differs from Embodiment 1 only in that: the flexible coating material of the positive electrode lithium supplement is different, and the flexible coating material used in Embodiment 22 is polyethylene oxide (model PEO-8000, manufacturer Sigma Aldrich) with a tensile strength of 40 MPa. The negative electrode active material is different. In terms of mass percentage, the negative electrode active material of Embodiment 22 is composed of 50% Si elemental substance and 50% graphite, wherein the particle size D50 of Si is 10 μm, and the particle size D50 of graphite is 12 μm. The core material of the positive electrode lithium supplement is different, and the core material of Embodiment 22 is Li5FeO6. The rest is the same as Embodiment 1 and will not be repeated.

[0101] Embodiment 23: This embodiment provides a lithium-ion battery, which differs from the embodiment 22 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 23 is 11 μm. The flexible coating material of the positive electrode lithium supplement is different, and the flexible coating material used in the embodiment 23 is polyethylene oxide (model PEO-10000, manufacturer Sigma Aldrich) with a tensile strength of 60 MPa. The rest is the same as the embodiment 22 and will not be repeated.

[0102] Embodiment 24: This embodiment provides a lithium ion battery, which is different from the embodiment 22 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 24 is 6.2 μm. The rest is the same as the embodiment 22 and will not be described again.

[0103] Embodiment 25: This embodiment provides a lithium ion battery, which is different from the embodiment 23 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 25 is 8 μm. The rest is the same as the embodiment 23 and will not be described again.

[0104] Embodiment 26: This embodiment provides a lithium-ion battery, which differs from Embodiment 1 only in that: the flexible coating material of the positive electrode lithium supplement is different, and the flexible coating material used in Embodiment 26 is polyethylene oxide with a tensile strength of 40 MPa (model PEO-8000, manufacturer Sigma Aldrich). The negative electrode active material is different. In terms of mass percentage, the negative electrode active material of Embodiment 26 is composed of 80% Si elemental substance and 20% graphite, wherein the particle size D50 of Si is 7 μm, and the particle size D50 of graphite is 13 μm. The core material of the positive electrode lithium supplement is different, and the core material of Embodiment 26 is Li5FeO7. The rest is the same as Embodiment 1 and will not be repeated.

[0105] Embodiment 27: This embodiment provides a lithium ion battery, which is different from the embodiment 26 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 24 is 6.2 μm. The rest is the same as the embodiment 26 and will not be described again.

[0106] Embodiment 28: This embodiment provides a lithium-ion battery, which differs from the embodiment 26 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 28 is 8 μm. The flexible coating material of the positive electrode lithium supplement is different, and the flexible coating material used in the embodiment 28 is polyethylene oxide (model PEO-10000, manufacturer Sigma Aldrich) with a tensile strength of 60 MPa. The rest is the same as the embodiment 26 and will not be repeated.

[0107] Embodiment 29: This embodiment provides a lithium ion battery, which is different from the embodiment 28 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 29 is 7.1 μm. The rest is the same as the embodiment 28 and will not be described again.

[0108] Embodiment 30: This embodiment provides a lithium ion battery, which is different from the embodiment 28 only in that the particle size D50 of Si is different, and the particle size D50 of Si in the embodiment 30 is 6.5 μm. The rest is the same as the embodiment 28 and will not be described again.

[0109] Comparative Example 1: This comparative example provides a lithium-ion battery, which differs from Example 2 in that no positive electrode lithium replenisher is added, and the remaining steps are the same.

[0110] Comparative Example 2: This comparative example provides a lithium-ion battery, which differs from Example 15 in that no positive electrode lithium replenisher is added, and the remaining steps are the same.

[0111] Comparative Example 3: This comparative example provides a lithium-ion battery, which differs from Example 22 in that no positive electrode lithium replenisher is added, and the remaining steps are the same.

[0112] Comparative Example 4: This comparative example provides a lithium-ion battery, which differs from Example 26 in that no positive electrode lithium replenisher is added, and the remaining steps are the same.

[0113] Comparative Example 5: This comparative example provides a lithium-ion battery, which differs from Example 2 in that the positive electrode lithium supplement containing the flexible coating material is replaced with an equal amount of Li5FeO4, that is, the lithium supplement of Comparative Example 5 does not contain a flexible coating material, and the remaining steps are the same.

[0114] Performance Test: The cycle performance of the lithium ion batteries of Examples 1 to 30 and Comparative Examples 1 to 5 was tested respectively, and the specific method is as follows: At room temperature 25±2℃ or high temperature 45℃±2℃, charge the divided lithium-ion battery to 3.65V (cut-off current is 0.01C) with 0.5C constant current and constant voltage, and then discharge it to 2.5V with 0.5C constant current. Record the charge and discharge capacity in the first week.

[0115] Cycle capacity retention rate (%) = (Nth cycle discharge capacity / 1st cycle discharge capacity) × 100%.

[0116] The specific composition parameters and cycle performance test results of the lithium ion batteries of Examples 1 to 30 and Comparative Examples 1 to 5 are shown in Table 1.

[0117] Table 1: Lithium-ion battery composition parameters and cycle performance test results

[0118] In the table, x0 is the mass fraction of the flexible coating material in the positive electrode lithium replenisher; x1 is the mass ratio of the positive electrode lithium replenisher / (positive electrode lithium replenisher + positive electrode active material); when the negative electrode active material is graphite, a represents the particle size D50 (μm) of graphite; when the negative electrode active material is a mixture of graphite and silicon, a represents the particle size D50 (μm) of silicon.

[0119] The above test results show that the positive electrode lithium supplement of the present invention is helpful to improve the cycle performance of lithium ion batteries and extend the battery life. The negative electrode active material is graphite, and the ratio of the tensile strength T (unit MPa) of the flexible coating material in the positive electrode lithium supplement to the particle size D50 R1 (unit μm) of the graphite is: 1≤T / R1≤4, which significantly improves the cycle performance of lithium ion batteries. The negative electrode active material is a mixture of graphite and silicon. When the mass fraction of the silicon material in the negative electrode active material is 15% to 30%, the ratio of the tensile strength T (unit MPa) of the flexible coating material in the positive electrode lithium replenisher to the particle size D50 R2 (unit μm) of silicon is 4.0 to 5.5, or, when the mass fraction of the silicon material in the negative electrode active material is greater than 30% and less than or equal to 70%, the ratio of the tensile strength T (unit MPa) of the flexible coating material in the positive electrode lithium replenisher to the particle size D50 R2 (unit μm) of silicon is 5.5 to 6.5, or, when the mass fraction of the silicon material in the negative electrode active material is greater than 70% and less than or equal to 80%, the ratio of the tensile strength T MPa of the flexible coating material in the positive electrode lithium replenisher to the particle size D50 R2 (unit μm) of silicon is 6.5 to 8.5, which significantly improves the cycle performance of the lithium-ion battery.

[0120] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A positive electrode lithium supplement, characterized in that: include: Core material, the chemical formula of the core material is Li a M b O c , wherein M is selected from at least one of Mg, Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn, and C, and 2≤a≤8, 0≤b≤6, and 1≤c≤8; A flexible covering material, the flexible covering material covers at least a portion of the outer surface of the core material, and the chemical formula of the flexible covering material is (C d Y e ) n , wherein Y is selected from one or more of H, O, N, P, and S, and 0<d<10, 0<e<50, n is the degree of polymerization, 1000≤n≤100000.

2. The positive electrode lithium supplement according to claim 1, characterized in that: In the positive electrode lithium supplement, the mass fraction of the flexible coating material is 0.5% to 8%; And / or, the flexible covering material is selected from at least one of polyethylene oxide, polypropylene, polyethylene, polystyrene, polyester, synthetic rubber, polyurethane, and polyoxymethylene.

3. A positive electrode sheet, characterized in that: The invention comprises the positive electrode lithium supplement agent as claimed in claim 1 or 2 and a positive electrode active material.

4. The positive electrode sheet according to claim 3, characterized in that: The positive electrode active material is selected from at least one of LiFePO4, LiFePO5, LiFePO6 and LiFePO7; And / or, the mass ratio of the positive electrode lithium supplement agent to the positive electrode active material is 0.1-10:90-99.

9.

5. A lithium ion battery, characterized in that: The invention comprises a negative electrode sheet and the positive electrode sheet according to claim 3 or 4, wherein the negative electrode sheet comprises a negative electrode active material.

6. The lithium-ion battery according to claim 5, characterized in that: The negative electrode active material is graphite, and the ratio of the tensile strength of the flexible coating material in the positive electrode lithium supplement to the particle size D50 of the graphite is: 1≤T / R1≤4; Wherein, T is the tensile strength of the flexible coating material in the positive electrode lithium supplement, in MPa; R1 is the particle size D50 of the graphite, in μm.

7. The lithium-ion battery according to claim 6, characterized in that: The tensile strength of the flexible coating material in the positive electrode lithium replenisher is 10-40 MPa; and / or the particle size D50 of the graphite is 10-15 μm; and / or the mass fraction of the flexible coating material in the positive electrode lithium replenisher is 1%-8%.

8. The lithium-ion battery according to claim 5, characterized in that: The negative electrode active material comprises graphite and silicon material, wherein the mass fraction of the silicon material in the negative electrode active material is 15% to 80%; The ratio of the tensile strength of the flexible coating material in the positive electrode lithium supplement to the particle size D50 of the silicon material is: 3≤T / R2≤9; Wherein, T is the tensile strength of the flexible coating material in the positive electrode lithium supplement, in MPa; R2 is the particle size D50 of the silicon material, in μm.

9. The lithium-ion battery according to claim 8, characterized in that: Satisfies at least one of the following (1)-(3): (1) The mass fraction of the flexible coating material in the positive electrode lithium supplement is 0.5% to 2%; (2) The particle size D50 of the silicon material is 3-20 μm; (3) When the mass fraction of the silicon material in the negative electrode active material is 15% to 30%, the T / R2 is 4.0 to 5.5; And / or, when the mass fraction of the silicon material in the negative electrode active material is greater than 30% and less than or equal to 70%, the T / R2 is 5.5~6.5; and / or, when the mass fraction of the silicon material in the negative electrode active material is greater than 70% and less than or equal to 80%, the T / R2 is 6.5~8.

5.

10. An electrical device, characterized in that: Comprising a lithium ion battery as described in any one of claims 5 to 9.

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