A pole piece and a battery

Abstract

The present invention relates to the technical field of lithium batteries and provides a pole piece and a battery. The pole piece comprises: a current collector, an active material layer, and a cellulose layer; the active material layer is disposed on at least one surface of the current collector; the cellulose layer is disposed on a surface of the active material layer distal from the current collector; the cellulose layer comprises nanocellulose having a crystallinity greater than 85%. This pole piece exhibits a lower wrinkle rate and higher processing yield during processing, improves the battery's furnace temperature pass rate, and enhances battery safety.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a pole piece and a battery containing the pole piece. Background Art

[0002] Currently, conventional lithium-ion batteries are produced in a laminated or wound structure of diaphragm / positive electrode / diaphragm / negative electrode, requiring two separate layers of separators to separate the positive and negative electrodes. Since the diaphragms (separators) currently used are made of polyolefin materials such as PE or PP, the melting points of these materials are in the range of 130-155°C. When the battery is in the above temperature range, the diaphragm will shrink due to continuous heating. The thermal shrinkage causes the positive and negative electrodes to be exposed at the top and bottom of the battery cell, resulting in a short circuit between the positive and negative electrodes. The lithium-ion battery will continue to release heat and continue to decompose the SEI film and electrolyte, aggravating thermal runaway, resulting in open flames and combustion caused by the short circuit in the lithium-ion battery, and then violent combustion or explosion.

[0003] In addition, during the winding process of the battery cell, there is internal tension in the diaphragm when it is wound or stacked, which causes the diaphragm to rebound during the subsequent processes (hot pressing, baking), resulting in wrinkles on the electrode, and the defective rate of the electrode processing is relatively high.

[0004] Therefore, it is of great value to develop a lithium battery with low electrode wrinkle rate, high electrode processing yield and high safety. Summary of the Invention

[0005] The present invention aims to overcome the above-mentioned problems existing in the prior art and to provide a pole piece and a battery containing the pole piece. The pole piece has a lower pole piece wrinkle rate during processing, a higher processing yield, an improved furnace temperature pass rate of the battery, and better battery safety performance.

[0006] The inventors of this invention have discovered that coating a cellulose layer on a pole piece allows it to function as both a pole piece and a separator, eliminating the need for a traditional separator. On the one hand, the nanocellulose in the cellulose layer has a high melting point. When the battery is exposed to high temperatures, the cellulose layer is able to resist thermal contraction and is less likely to rebound and deform, thus preventing short circuits between the positive and negative pole pieces. This improves the battery's furnace temperature test pass rate and enhances battery safety. On the other hand, the nanocellulose in the cellulose layer has good flexibility, which increases the flexibility of the pole piece and imparts good ductility to the pole piece. This reduces the pole piece wrinkle rate during processing, improves the processing yield, and improves the pass rate of heavy object impact.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a pole piece, which comprises:

[0008] current collector;

[0009] an active material layer disposed on at least one surface of the current collector;

[0010] a cellulose layer disposed on a surface of the active material layer away from the current collector;

[0011] Wherein, the cellulose layer comprises nanocellulose, and the crystallinity of the nanocellulose is greater than 85%.

[0012] A second aspect of the present invention provides a battery, which includes the electrode described in the first aspect of the present invention.

[0013] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0014] (1) The electrode provided by the present invention has the functions of both an electrode and a diaphragm, making the electrode directly processable;

[0015] (2) The electrode provided by the present invention has good ductility, which reduces the electrode wrinkle rate and improves the processing yield in the electrode processing process, while also improving the pass rate of heavy object impact;

[0016] (3) The battery provided by the present invention is less likely to have short circuits on the positive and negative electrodes, thereby improving the furnace temperature passing rate of the battery and improving the safety performance of the battery.

[0017] The endpoints of the ranges and any values 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 FIG. 1 is a schematic structural diagram of a negative electrode sheet in an embodiment of the present invention.

[0019] Figure 2 Shown is a schematic structural diagram of ceramic particles in one embodiment of the present invention.

[0020] Description of Reference Numerals

[0021] 1: negative electrode current collector; 2: active material layer; 3: cellulose layer. DETAILED DESCRIPTION

[0022] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0023] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0024] A first aspect of the present invention provides a pole piece, comprising:

[0025] current collector;

[0026] an active material layer disposed on at least one surface of the current collector;

[0027] a cellulose layer disposed on a surface of the active material layer away from the current collector;

[0028] Wherein, the cellulose layer comprises nanocellulose, and the crystallinity of the nanocellulose is greater than 85%.

[0029] In one example, the crystallinity of the nanocellulose is greater than 85%, for example, the crystallinity may be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, or 95%.

[0030] In a preferred embodiment, the crystallinity of the nanocellulose is greater than 90%.

[0031] The inventors of the present invention found that when the crystallinity of nanocellulose is greater than 85%, the melting point of nanocellulose is greater than 180°C. When the battery is at high temperature (for example, the furnace temperature test is within the range of 130-150°C), the cellulose layer has better resistance to thermal shrinkage and is not easy to rebound and deform, thus avoiding the problem of short circuit of the positive electrode.

[0032] In one example, Figure 1 As shown, the electrode sheet is a negative electrode sheet, which includes a negative electrode current collector 1, a negative electrode active material layer 2 and a cellulose layer 3. The negative electrode active material layer 2 is coated on two opposite surfaces of the negative electrode current collector 1, and the cellulose layer 3 is coated on the surface of the negative electrode active material layer 2 away from the negative electrode current collector 1.

[0033] In one embodiment, the electrode sheet is a positive electrode sheet, comprising a positive electrode current collector, a positive electrode active material layer, and a cellulose layer. The positive electrode active material layer is coated on two opposing surfaces of the positive electrode current collector, and the cellulose layer is coated on a surface of the positive electrode active material layer away from the positive electrode current collector.

[0034] In one example, the cellulose layer further includes ceramic particles.

[0035] Illustratively, the ceramic particles are selected from at least one of metal oxides, inorganic metal salts, metal nitrides, and inorganic ceramic solid electrolytes.

[0036] Illustratively, the metal oxide includes, but is not limited to, aluminum oxide, magnesium oxide, calcium oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, boehmite, and zinc oxide.

[0037] Illustratively, the inorganic metal salt includes, but is not limited to, barium sulfate, calcium carbonate, and magnesium sulfate.

[0038] Illustratively, metal nitrides include, but are not limited to, tungsten nitride, silicon carbide, boron nitride, aluminum nitride, titanium nitride, and magnesium nitride.

[0039] Illustratively, the inorganic ceramic solid electrolyte includes, but is not limited to, at least one of solid electrolyte particles having a NASICON structure, a perovskite structure, an antiperovskite structure, a thio-LISICON structure, and a garnet structure.

[0040] In one embodiment, the average particle size of the ceramic particles is in the range of 0.1 μm to 10 μm, preferably 0.3 μm to 3 μm, and the morphological structure of the particle size is not specifically limited.

[0041] In the present invention, reference is made to Figure 2 The term "particle size" refers to the average of the minimum length (R2) and / or maximum length (R1) of a single particle. When expressed as a range, it means that the particle size of particles of the same material all fall within the range. The present invention also allows for a certain degree of error; that is, if the particle size of less than 5% of the total number of particles is outside the required range, the requirement is considered met. The particle size of the ceramic particles in the present invention is measured by transmission electron microscopy.

[0042] In one example, the aspect ratio of the ceramic particles is 0.5-5.

[0043] like Figure 2 As shown in the structural schematic diagram of the ceramic particles, the ratio of the length of R1 to the length of R2 is recorded as the aspect ratio of the ceramic particles. For example, the aspect ratio of the ceramic particles can be 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, or 8. The preferred aspect ratio is 1.5-4, and the more preferred aspect ratio is 2.5-3.5.

[0044] In one example, based on the total mass of the cellulose layer, the content of the ceramic particles is 2-14 wt%, for example, 2 wt%, 5 wt%, 6 wt%, 7 wt%, 10 wt%, 12 wt%, or 14 wt%.

[0045] In a preferred embodiment, based on the total mass of the cellulose layer, the content of the ceramic particles is 4-8 wt %.

[0046] The inventors of the present invention have further studied and found that by adding ceramic particles to the cellulose layer and limiting the amount of ceramic particles added, and preferably having a long columnar structure, this type of ceramic has a good specific surface area and can complement the structure of nanocellulose. The formed coating has a clear pore structure, which is beneficial to Li + The transmission of heat is also beneficial to structural stability and heat evacuation, thereby improving the pass rate of battery furnace temperature test.

[0047] In one example, the cellulose layer further includes a polymer; the polymer includes at least one of a homopolymer or a copolymer of an olefinic monomer, a halogen-substituted olefinic monomer, and a styrenic monomer.

[0048] Illustratively, the olefin monomers include, but are not limited to, butadiene, ethylene, propylene and acrylonitrile.

[0049] For example, the halogen-substituted olefin monomers include, but are not limited to, vinylidene fluoride, hexafluoropropylene, difluoroethylene, tetrafluoroethylene, and trichloroethylene.

[0050] For example, the styrene monomers include but are not limited to styrene and methylstyrene.

[0051] In one example, the polymer is at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride-hexafluoropropylene (P(VDF-HFP)).

[0052] In one example, based on the total mass of the cellulose layer, the content of the polymer is 2-10 wt%, for example, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, or 8 wt%.

[0053] In a preferred embodiment, based on the total mass of the cellulose layer, the content of the polymer is 4-7 wt%.

[0054] The inventors of the present invention further discovered that when the electrode is a negative electrode, in an aqueous negative electrode slurry, the polymer is in a first state (powder particle state, without bonding properties) at room temperature, and changes from the first state to a second state (powder particle state converted to a swollen state, with bonding properties) under high temperature and high pressure (such as the battery formation stage), which can increase the adhesion of the electrode, thereby improving the adhesion of the positive and negative electrode sheets during battery operation and ensuring better cycle performance of the battery.

[0055] The inventors of the present invention further discovered that when the electrode is a positive electrode, the polymer is dissolved in an organic solvent in an oily positive electrode slurry. During the slurry drying process, the polymer can bond the cellulose layer and the active material layer, and can play a bonding role without the need for a high temperature and high pressure environment.

[0056] In one embodiment, the molecular formula of the nanocellulose is:

[0057]

[0058] Wherein, R1, R2, R3, and R4 are independently selected from any one of hydroxyl (-OH), carboxyl (-COOH), aldehyde (-CHO), amide (-CONH2), amino (-NH2) and carbonyl (-C=O); and n is any integer between 8000 and 15000.

[0059] In one embodiment, the molecular formula of the nanocellulose is:

[0060]

[0061] Wherein, R1, R2, and R3 are independently selected from any one of hydroxyl (-OH), carboxyl (-COOH), aldehyde (-CHO), amide (-CONH2), amino (-NH2) and carbonyl (-C=O); and n is any integer between 9000 and 12000.

[0062] In one embodiment, the molecular formula of the nanocellulose is: n is any integer between 9000 and 12000.

[0063] In one embodiment, the nanocellulose is a modified nanofiber obtained by modifying the modified nanocellulose with an organic polymer. The organic polymer is not particularly limited, and can be a homopolymer and / or copolymer of an organic monomer that can be used in the art to improve the properties of nanocellulose.

[0064] In one embodiment, the organic polymer is selected from polypropylene (PPE) and / or modified styrene-based copolymer (SBS).

[0065] In one example, the nanocellulose is modified with polypropylene (PPE) and styrene-based copolymer (SBS) to obtain the modified nanocellulose shown in Formula I-2, wherein the molecular weight of SBS is 80,000-120,000:

[0066] Among them, a is 270-400, b is 230-300, c is 230-300, d is 270-400, m is 35-80, and n is 8000-15000.

[0067] The inventors of this invention have discovered that PPE-modified nanocellulose can increase the system's glass transition temperature (Tg) by 10-20°C, reducing the system's water absorption. SBS-modified nanocellulose exhibits improved processability, excellent low-temperature performance, enhanced adhesion, and superior electrical properties, reducing the amount of adhesive used in electrode preparation.

[0068] In one example, based on the total mass of the cellulose layer, the content of the nanocellulose is 15-45wt%, and illustratively can be 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 35wt%, 38wt%, 40wt%, or 45wt%.

[0069] In a preferred embodiment, based on the total mass of the cellulose layer, the content of the nanocellulose is 28-32 wt %.

[0070] In one example, the diameter of the nanocellulose is 1 nm-30 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 15 nm, or 30 nm.

[0071] In a preferred embodiment, the diameter of the nanocellulose is 2 nm-10 nm.

[0072] In one example, the length of the nanocellulose is 20 μm-150 μm, for example, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, or 150 μm.

[0073] In a preferred embodiment, the length of the nanocellulose is 30 μm-100 μm.

[0074] Optimizing the diameter and length of nanocellulose can make the skeleton structure of the nanofiber layer more stable and more flexible, thereby improving the flexibility of the electrode, lowering the electrode wrinkle rate and increasing the processing yield during the electrode processing process.

[0075] In one example, the width of the cellulose layer is not less than the width of the electrode piece.

[0076] In one example, the thickness of the cellulose layer is 3 μm-30 μm, for example, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, or 30 μm.

[0077] In a preferred embodiment, the thickness of the cellulose layer is 5 μm-25 μm, more preferably 5 μm-15 μm.

[0078] Control the thickness of the cellulose layer to avoid the cellulose layer being too thin, which will reduce the electrode's resistance to thermal shrinkage and affect the safety performance of the battery; and avoid the cellulose layer being too thick, which will occupy the electrode thickness and reduce the energy density of the battery.

[0079] In one example, the width of the cellulose layer is greater than the width of the electrode not coated with the cellulose layer by 1 mm to 3 mm.

[0080] In one embodiment, the electrode is a negative electrode. Figure 1 As shown, the negative electrode sheet includes a negative electrode current collector 1 , a negative electrode active material layer 2 and a cellulose layer 3 .

[0081] Since the negative electrode sheet is usually larger than the positive electrode sheet, coating the negative electrode sheet with a cellulose layer can more effectively avoid the problem of short circuit between the positive and negative electrode sheets.

[0082] A second aspect of the present invention provides a battery, which includes the electrode described in the first aspect of the present invention.

[0083] In the present invention, the battery is a lithium-ion battery.

[0084] In a preferred embodiment, the battery comprises the negative electrode sheet described in the first aspect of the present invention, a conventional positive electrode sheet and an electrolyte.

[0085] In one example, the negative electrode sheet includes a negative electrode current collector, a negative electrode active material layer, and a cellulose layer.

[0086] Illustratively, the negative electrode current collector is a material that has conductivity and does not cause adverse chemical changes in the secondary battery, and can be selected from copper, stainless steel, aluminum, nickel, titanium, carbon cloth, or a composite of these materials.

[0087] The negative electrode active material layer includes a negative electrode active material, a negative electrode conductor, and a negative electrode binder. There is no particular limitation on the negative electrode active material, and any common negative electrode active material in the art can be used, for example, at least one of graphite, lithium titanate, and silicon-based negative electrodes.

[0088] In one embodiment, the battery comprises the positive electrode sheet according to the first aspect of the present invention, a conventional negative electrode sheet and an electrolyte.

[0089] In one embodiment, the positive electrode sheet includes a positive electrode current collector, a positive electrode active material layer, and a cellulose layer.

[0090] Illustratively, the positive electrode current collector is a material that has electrical conductivity and does not cause adverse chemical changes in the secondary battery, including but not limited to aluminum, aluminum alloy, nickel, nickel alloy, titanium, and titanium alloy.

[0091] The positive electrode active material layer includes a positive electrode active material, a positive electrode conductor, and a positive electrode binder. There are no particular limitations on the positive electrode active material, and any commonly used positive electrode active material in the art can be used, such as at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium nickel cobalt manganese oxide lithium iron phosphate.

[0092] In one example, the positive electrode conductive agent and the negative electrode conductive agent are independently selected from at least one of conductive graphite, ultrafine graphite, acetylene black, conductive carbon black SP, superconducting carbon black, carbon nanotubes, and conductive carbon fibers.

[0093] In one example, the positive electrode binder and the negative electrode binder are independently selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, polyvinyl alcohol, polyvinylidene fluoride, and a copolymer of vinylidene fluoride and fluorinated olefin.

[0094] The electrolyte can be any commonly used electrolyte in the art and is not specifically limited here.

[0095] The battery provided by the present invention has a higher furnace temperature passing rate and better battery safety performance.

[0096] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0097] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0098] The present invention will be described in detail below with reference to specific embodiments. These embodiments are intended to help you understand the present invention but are not intended to limit it.

[0099] Example 1

[0100] A lithium-ion battery, comprising the following preparation method:

[0101] 1. Preparation of negative electrode sheet

[0102] (1) Preparation of cellulose layer slurry

[0103] Nanocellulose: Molecular formula: n is 10000, crystallinity is about 95%, diameter is 8nm, length is 80μm, and content is 30wt%;

[0104] Polymer: PVDF, content 5wt%;

[0105] Ceramic particles: Al2O3, aspect ratio 3, content 6wt%;

[0106] Wetting agent: AEO-09, content 1.0wt%;

[0107] Binder: 8508D, content 0.5wt%;

[0108] Dispersant: T-31, content 2.5%wt%;

[0109] Deionized water: content 55wt%;

[0110] The slurry is prepared according to the above ratio to form an aqueous slurry with a solid content of about 45%.

[0111] (2) The negative electrode current collector is made of high-strength copper foil with a thickness of 5 μm; the negative electrode active material layer includes: the negative electrode active material is mesophase carbon microspheres, accounting for 96.50 wt%; the conductive agent is carbon nanotubes, accounting for 0.90 wt%; the binder is SBR, accounting for 1.30 wt%; the dispersant is sodium carboxymethyl cellulose / CMC, accounting for 1.30 wt%;

[0112] (3) The slurry obtained in step (1) was extrusion-transfer coated to prepare a negative electrode sheet, with a cellulose layer thickness of 10 μm.

[0113] 2. Preparation of positive electrode

[0114] The positive electrode current collector is made of aluminum foil with a thickness of 9 μm; the positive electrode active coating includes: the positive electrode active material is LiCoO2, accounting for 98.0wt%; the conductive agent is conductive carbon black, accounting for 1.0wt%; the binder is polyvinylidene fluoride, accounting for 1.0wt%.

[0115] 3. Preparation of batteries

[0116] The negative electrode sheet and the positive electrode sheet obtained in the above steps are used together to obtain a coil core, which is then packaged, injected with liquid (EC:EMC:DEC=3:5:2, LiPF6 molar ratio 1.2 mol / L), formed, re-sealed, sorted, and OCV is performed to obtain a battery for electrical performance testing.

[0117] Example 2

[0118] The method is carried out with reference to Example 1, except that:

[0119] 1. Preparation of negative electrode sheet

[0120] (1) Preparation of cellulose layer slurry

[0121] Nanocellulose: Molecular formula: n is 9000, crystallinity is 93%, diameter is 6 nm, length is 100 μm, and content is 28 wt%;

[0122] Polymer: PTFE, content 6wt%;

[0123] Ceramic particles: SiO2, aspect ratio 3.5, content 7wt%;

[0124] Wetting agent: AEO-09, content 1.0wt%;

[0125] Binder: 8508D, content 0.5wt%;

[0126] Dispersant: T-31, content 2.5%wt%;

[0127] Deionized water: content 55wt%;

[0128] The slurry is prepared according to the above ratio to form an aqueous slurry with a solid content of about 45%.

[0129] The thickness of the cellulose layer was 15 μm.

[0130] Example 3

[0131] The method is carried out with reference to Example 1, except that:

[0132] 1. Preparation of negative electrode sheet

[0133] (1) Preparation of cellulose layer slurry

[0134] Nanocellulose: Molecular formula: n is 12000, crystallinity is 90%, diameter is 10nm, length is 60μm, and content is 32wt%;

[0135] Polymer: P(VDF-HFP), content 4wt%;

[0136] Ceramic particles: titanium dioxide, aspect ratio 4.5, content 5wt%

[0137] Wetting agent: AEO-09, content 1.0wt%;

[0138] Binder: 8508D, content 0.5wt%;

[0139] Dispersant: T-31, content 2.5%wt%;

[0140] Deionized water: content 55wt%;

[0141] The slurry is prepared according to the above ratio to form an aqueous slurry with a solid content of about 45%.

[0142] The thickness of the cellulose layer was 13 μm.

[0143] Example 4 Group

[0144] This set of examples is used to illustrate the effect of cellulose layer thickness on battery performance.

[0145] This group of examples was carried out in accordance with Example 1, except that the thickness of the cellulose layer was changed respectively, specifically:

[0146] Example 4a: The thickness of the cellulose layer is 3 μm;

[0147] Example 4b: The thickness of the cellulose layer is 5 μm;

[0148] Example 4c: The thickness of the cellulose layer is 25 μm.

[0149] Example 5 group

[0150] This group of examples is used to illustrate the effect of the nanocellulose content in the cellulose layer on battery performance.

[0151] This group of examples was carried out in accordance with Example 1, except that the nanocellulose content in the cellulose layer was changed and the content of deionized water was adjusted to keep the total amount of the cellulose layer unchanged. Specifically:

[0152] Example 5a: The content of nanocellulose is 15 wt%;

[0153] Example 5b: The content of nanocellulose is 45 wt%.

[0154] Example 6

[0155] The process was carried out with reference to Example 1, except that the aspect ratio of the ceramic particles was 2.

[0156] Example 7

[0157] The method is carried out with reference to Example 1, except that the nanocellulose is modified cellulose, and its molecular formula is Wherein, a is 300, b is 250, c is 250, d is 300, m is 60, n is 10000, the content of the polymer is 2 wt%, and the content of deionized water is 58 wt%.

[0158] Example 8

[0159] The process was carried out with reference to Example 1, except that no ceramic particles and polymer were added to the cellulose layer.

[0160] Example 9

[0161] The process was carried out with reference to Example 1, except that no polymer was added to the cellulose layer.

[0162] Example 10

[0163] The process was carried out with reference to Example 1, except that no ceramic particles were added to the cellulose layer.

[0164] Comparative Example 1

[0165] The method is carried out with reference to Example 1, except that: the negative electrode sheet does not contain a cellulose layer, the battery assembly uses a diaphragm to separate the positive and negative electrode sheets, and the diaphragm is a normal PE base film: the coating structure is 1+7+2+1, where 1 indicates a 1 μm thick adhesive layer (PVDF adhesive) on both sides, 2 indicates a 2 μm ceramic coating on one side, and the ceramic uses a normal Al2O3 coating, and 7 indicates that the base film is a 7 μm PE base film.

[0166] Comparative Example 2

[0167] The process was carried out with reference to Example 1, except that the crystallinity of the nanocellulose was 80%.

[0168] Experimental example

[0169] The batteries obtained from the above examples and comparative examples were subjected to the following performance tests:

[0170] (1) Furnace temperature test

[0171] The temperature is raised from room temperature (25°C) at a rate of 5°C / min to a specified temperature (usually 130°C / 135°C / 140°C / 145°C) for a specific period of time (usually 30 minutes / 60 minutes / 240 minutes). After the time is up, the thermostat is opened and the battery is inspected. If the battery does not catch fire or explode, it is considered to have passed the oven temperature test.

[0172] (2) Pole wrinkle test

[0173] The electrode wrinkles can be identified by simply disassembling the battery and checking whether there is a tortuous surface shape on the single-sided area of the copper foil of the battery.

[0174] (3) Heavy object impact test

[0175] Place the battery cell on a platform. Place a metal rod with a diameter of 15.8mm ± 0.2mm horizontally above the geometric center of the cell. A weight of 9.1kg ± 0.1kg is dropped from a height of 610mm ± 25mm to impact the surface of the cell with the metal rod. Observe for 6 hours. Perform the impact test on the wide surface. Only one impact test is performed on each sample. The battery is considered to have passed the heavy object impact test if there is no fire or explosion.

[0176] (4) Self-discharge test

[0177] In an environment of 25+ / -3℃, the battery voltage V1 is tested at t1, and the voltage V2 of the same battery is tested at t2. Self-discharge = (V1-V2) / (t2-t1).

[0178] (5) Volume energy density test

[0179] Battery energy density test method: The battery width is a cm, the height is b cm, the thickness is c cm, the battery platform voltage is 3.85V, the battery capacity is Q Ah, and the volume energy density = Q*3.85 / a / b / c can be obtained

[0180] (6) Capacity retention rate

[0181] Perform simulated cycling at a rate of 1C / 1C in a constant temperature room at 45°C. Take the maximum capacity of the first three times as Cmax. Continue cycling at a rate of 1C at 45°C until the capacity of the battery tested after 700T is recorded as C700T. The capacity retention rate = C700T / Cmax*100%.

[0182] (7) Thickness expansion rate

[0183] Perform simulated cycling at a rate of 1C / 1C in a constant temperature room at 45°C, record the thickness at 50% SOC as Tinitial, and continue cycling at a rate of 1C at 45°C until 700T, then test the fully charged battery thickness as T700T. Thickness expansion rate = (T700T-Tinitial) / Tinitial*100%.

[0184] Battery full charge system: constant current charging at a certain rate (0.7C) in a constant temperature room at 25℃. When the voltage reaches the cut-off voltage, it will jump to constant voltage mode for charging and end when the cut-off current (generally 0.02C) is reached.

[0185] The results of the above tests are recorded in Table 1.

[0186] Table 1

[0187]

[0188] From the results in Table 1, it can be seen that when the cellulose coating in the battery contains nanocellulose, ceramic particles and polymers, the furnace temperature test pass rate of the battery cell is significantly improved, the heat resistance of the battery is increased from 130°C to 150°C, the heavy object impact pass rate of the battery is increased from 30% to 100%, the number of wrinkles in the battery pole piece is effectively suppressed, and the self-discharge capacity of the battery can reach a level comparable to that of a normal diaphragm. The effective thickness of the cellulose layer is closely related to the improvement of battery performance. When the thickness of the cellulose layer of the pole piece is reduced to below 5μm (Example 4a), the furnace temperature effective pass rate of the battery is significantly reduced, and the self-discharge capacity of the battery becomes larger; however, when the thickness of the cellulose layer reaches 25μm, the self-discharge of the battery can be effectively suppressed, but compared to the normal diaphragm, the overall thickness is occupied by the cellulose layer, resulting in a significant decrease in the energy density of the battery cell.

[0189] Furthermore, when the cellulose coating in the battery contains nanocellulose, ceramic particles, and a polymer, the battery performs at a comparable level to the separator of Comparative Example 1 in terms of high-temperature cycling at 45°C. However, the results of Examples 8 and 9 show that using nanocellulose alone only improves battery safety; during long-term battery cycling, a certain degree of adhesion between the electrodes is required to maintain subsequent cycling.

[0190] Therefore, the present invention coats a cellulose layer containing nanocellulose, ceramic particles and polymer on the electrode, which can replace the traditional isolation membrane, so that the electrode has the functions of both the electrode and the membrane, and can replace the existence of the membrane layer in practical applications.

[0191] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A battery, characterized in that: The battery comprises a pole piece and an electrolyte, but does not include a diaphragm; the pole piece comprises: current collector; an active material layer disposed on at least one surface of the current collector; a cellulose layer disposed on a surface of the active material layer away from the current collector; The cellulose layer comprises nanocellulose, ceramic particles and a polymer, wherein the crystallinity of the nanocellulose is 85%-95%; the content of the nanocellulose is 15-45wt% based on the total mass of the cellulose layer; the aspect ratio of the ceramic particles is 2.5-5; the content of the polymer is 2-10wt% based on the total mass of the cellulose layer; and the polymer comprises at least one of a homopolymer or a copolymer of an olefin monomer, a halogen-substituted olefin monomer and a styrene monomer; The molecular formula of the nanocellulose includes: At least one of; In formula I-1, R1, R2, and R3 are independently selected from any one of hydroxyl (-OH), carboxyl (-COOH), aldehyde (-CHO), amide (-CONH2), amino (-NH2), and carbonyl (-C=O); n is any integer from 9000 to 12000; In formula I-2, a is 270-400, b is 230-300, c is 230-300, d is 270-400, m is 35-80, and n is 8000-15000.

2. The battery according to claim 1, wherein Based on the total mass of the cellulose layer, the content of the ceramic particles is 2-14 wt%.

3. The battery according to claim 1 or 2, wherein The diameter of the nanocellulose is 1 nm to 30 nm; and / or, The length of the nanocellulose is 20 μm-150 μm.

4. The battery according to claim 1 or 2, wherein The diameter of the nanocellulose is 2nm-10nm.

5. The battery according to claim 1 or 2, wherein The length of the nanocellulose is 30 μm-100 μm.

6. The battery according to claim 1 or 2, wherein The width of the cellulose layer is not less than the width of the electrode piece; and / or, The thickness of the cellulose layer is 3 μm to 30 μm; and / or, The width of the cellulose layer is greater than the width of the electrode not coated with the cellulose layer by more than 1 mm to 3 mm.

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