Battery cell and lithium ion battery

Abstract

The invention provides a battery cell. The battery cell comprises a positive plate, a diaphragm and a negative plate, the positive plate comprises a positive current collector and a positive active material layer; the positive electrode active material layer comprises a positive electrode active material, the positive electrode active material comprises lithium cobalt oxide, the particle size of the lithium cobalt oxide is d1, the unit is [mu] m, and the value range of the d1 is that 0 [mu] m < d1 < = 2 [mu] m; the negative plate comprises a negative current collector and a negative active material layer coated on the surface of the negative current collector; the thickness of the negative current collector is 7-11 [mu] m; the negative active material layer comprises a second binder, and the second binder comprises a CMC compound; the lithium cobalt oxide particles with the particle size of 0-2 microns are introduced into the positive plate, the negative electrode current collector with the thickness of 7-11 microns is adopted, and meanwhile, the CMC compound is adopted in the negative electrode active material layer, so that the direct-current internal resistance of the battery can be relatively small, heat generated in the circulation process can be reduced, byproducts caused by temperature rise can be relatively reduced, and the service life of the battery is prolonged. Therefore, the long cycle performance of the battery cell is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a battery cell and a lithium ion battery. Background Art With the rapid development of applications such as electric vehicles, portable electronic devices and energy storage systems, the requirements for the performance of lithium-ion batteries are getting higher and higher. DC internal resistance (DCIR) is a key parameter to measure the internal resistance of lithium-ion batteries, which directly affects the battery's charging and discharging efficiency, power output capacity and thermal management; the initial internal resistance in the existing technology is large and cannot meet the demand for low DC internal resistance; therefore, how to overcome the above-mentioned technical problems and defects has become a key issue that needs to be solved. Summary of the invention

[0002] In order to solve the problem that the initial DC internal resistance of the battery is relatively large, the present invention provides a battery cell and a lithium ion battery.

[0003] The technical solution adopted by the present invention to solve the above technical problems is as follows: In one aspect, the present invention provides a battery cell, comprising a positive electrode sheet, a separator and a negative electrode sheet; the positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, and the battery cell is formed by winding or laminating; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode active material, a first conductive agent and a first binder, the positive electrode active material comprises lithium cobalt oxide, the particle size of the lithium cobalt oxide is d1, the unit is μm, and the value range of d1 is 0μm<d1≤2μm; The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on the surface of the negative electrode current collector; The thickness of the negative electrode current collector is 7 μm-11 μm; The negative electrode active material layer includes a negative electrode active material, a second conductive agent, and a second binder, wherein the second binder includes a CMC-based compound.

[0004] Optionally, the value range of d1 is 0.1 μm≤d1≤1 μm.

[0005] Optionally, the positive electrode active material, the first conductive agent and the first binder are mixed to form a positive electrode slurry, and the positive electrode slurry forms the positive electrode active material layer on the surface of the positive electrode collector. The lithium cobalt oxide agglomerates when forming the positive electrode slurry, and the particle size of the lithium cobalt oxide after agglomeration is d2, in μm, and the value range of d2 is 3μm≤d2≤4.5μm.

[0006] Optionally, based on the total mass of the positive electrode active material being 100%, the mass percentage of the agglomerated lithium cobalt oxide particles in the positive electrode active material is 15%-25%.

[0007] Optionally, the thickness of the negative electrode current collector is 8-10 μm.

[0008] Optionally, the CMC-based compound includes one or more of CMC-Na and CMC-Li.

[0009] Optionally, the double-sided surface density of the positive electrode active material layer is 240-360 g / m 2 .

[0010] Optionally, the compaction density of the positive electrode active material layer is 4.0 to 4.3 g / cm 3 .

[0011] Optionally, the double-sided surface density of the negative electrode active material layer is 94-174 g / m 2 .

[0012] Optionally, the compaction density of the negative electrode active material layer is 1.6 to 1.8 g / cm 3 .

[0013] Optionally, taking the total mass of the positive electrode active material layer as 100%, the mass percentage of the positive electrode active material in the positive electrode active material layer is 97%-99%; the mass percentage of the first conductive agent in the positive electrode active material layer is 0.1%-1%; and the mass percentage of the first binder in the positive electrode active material layer is 0.5%-1.5%.

[0014] Optionally, the positive electrode active material further comprises one or more of lithium iron phosphate and NCM; and / or, The first conductive agent includes one or more of carbon nanotubes and acetylene black; and / or, The first binder includes PVDF.

[0015] Optionally, taking the total mass of the negative electrode active material layer as 100%, the mass percentage of the negative electrode active material in the negative electrode active material layer is 95%-97%; the mass percentage of the second conductive agent in the negative electrode active material layer is 2%-3%; and the mass percentage of the second binder in the negative electrode active material layer is 0.5%-2.5%.

[0016] Optionally, the negative electrode active material includes graphite; and / or, The second conductive agent includes acetylene black; and / or, The second binder also includes SBR.

[0017] Another aspect of the present invention provides a lithium-ion battery, comprising a battery housing, an electrolyte and the above-mentioned battery core, wherein the battery core is placed in the battery housing, the electrolyte is injected into the battery housing, and the lithium-ion battery is formed through packaging.

[0018] According to the battery cell provided by the present invention, lithium cobalt oxide particles with a particle size of 0-2 μm are introduced into the positive electrode sheet, which have small particle size, high surface energy and more active chemical properties, so that small particles of lithium cobalt oxide are driven to agglomerate, so the transmission speed is faster, thereby reducing the DC internal resistance of the battery; a negative electrode current collector with a thickness of 7 μm-11 μm is adopted, and the thicker negative electrode current collector provides a larger electron transmission path, reduces the internal resistance of the negative electrode current collector itself, thereby reducing the overall internal resistance of the battery; at the same time, CMC compounds are used in the negative electrode active material layer. CMC compounds are thickeners, which can improve the rheological properties of the negative electrode slurry and improve the interface characteristics between the negative electrode sheet and the electrolyte, thereby reducing the internal resistance of the battery, and the heat generation during the cycle will be reduced, so that the by-products caused by temperature rise can be relatively reduced, thereby ensuring the long cycle performance of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 It is a DCR (25°C cycle) test graph of Example 20 and Examples 23-24 at 25°C and 80% SOC; Figure 2 It is a DCR (45°C cycle) test graph of Example 20 and Examples 23-24 at 45°C and 80% SOC; Figure 3 It is a battery cycle performance test diagram of Example 20 and Examples 23-24 at 25°C; Figure 4 It is a battery cycle performance test diagram of Example 20 and Examples 23-24 at 45°C; DETAILED DESCRIPTION In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0022] In one embodiment, the present invention provides a battery cell, including a positive electrode sheet, a separator and a negative electrode sheet; the positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence and wound or laminated to form a battery cell; The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector; the positive electrode active material layer includes a positive electrode active material, a first conductive agent and a first binder, the positive electrode active material includes lithium cobalt oxide, the particle size of the lithium cobalt oxide is d1, the unit is μm, and the value range of d1 is 0μm<d1≤2μm; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the surface of the negative electrode current collector; The thickness of the negative electrode current collector is 7μm-11μm; The negative electrode active material layer includes a negative electrode active material, a second conductive agent and a second binder, and the second binder includes a CMC-based compound.

[0023] Specifically, the value range of d1 is any point value among 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm or 2μm, or a range consisting of any two point values; When the value range of d1 is 0μm<d1≤2μm, the lithium cobalt oxide particles have small particle size and high surface energy. The higher the energy, the more active the chemical properties of the lithium cobalt oxide particles are and the faster the energy transfer is. Therefore, small particles of lithium cobalt oxide tend to agglomerate, driving the overall energy to decrease in order to achieve a stable state. Therefore, the particle size of lithium cobalt oxide particles is small, the particle transfer speed will be faster, and the DC internal resistance of the battery will be smaller. When the value range of d1 is greater than 2μm, the surface energy of the lithium cobalt oxide particles will be reduced, and the transfer speed of the lithium cobalt oxide particles will be reduced, thereby making the DC internal resistance of the battery larger.

[0024] Specifically, the thickness of the negative electrode current collector is any value of 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm or 11 μm, or a range consisting of any two values.

[0025] When the thickness of the negative electrode current collector is 7μm-11μm, the DC internal resistance of the battery is small; when the thickness of the negative electrode current collector is less than 7μm, the DC internal resistance of the battery will be larger; when the thickness of the negative electrode current collector is greater than 11μm, the volume of the battery occupied by the copper foil will increase, the battery thickness will increase, and the practicality of the battery will become weaker.

[0026] The negative electrode current collector is selected from a metal material that can conduct electrons. Preferably, the negative electrode current collector includes one or more of Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0027] By using CMC compounds in the negative electrode active material layer, the rheological properties of the slurry are improved, the interface characteristics between the electrode and the electrolyte are improved, and thus the stability and integrity of the electrode structure are enhanced.

[0028] Specifically, the present application introduces lithium cobalt oxide particles with a particle size of 0-2μm into the positive electrode sheet. The particles have a small particle size, high surface energy, and more active chemical properties, which drives the small particles of lithium cobalt oxide to agglomerate, so the transmission speed is faster, thereby reducing the DC internal resistance of the battery; a 7μm-11μm thick negative electrode current collector is used. The thicker negative electrode current collector provides a larger electron transmission path, reduces the internal resistance of the negative electrode current collector itself, and thus reduces the overall internal resistance of the battery; at the same time, CMC compounds are used in the negative electrode active material layer. CMC compounds are thickeners, which can improve the rheology of the negative electrode slurry and the interface characteristics between the negative electrode sheet and the electrolyte, thereby reducing the internal resistance of the battery, and the heat generation during the cycle will be reduced, thereby relatively reducing the by-products caused by temperature rise, thereby ensuring the long cycle performance of the battery cell.

[0029] In one embodiment, the value range of d1 is 0.1 μm≤d1≤1 μm.

[0030] When the value range of d1 is 0.1μm≤d1≤1μm, the lithium cobalt oxide particles have higher surface energy, the chemical properties of the lithium cobalt oxide particles are more active, and the energy transfer is faster, thereby reducing the DC internal resistance of the battery.

[0031] In one embodiment, the positive electrode active material, the first conductive agent and the first binder are mixed to form a positive electrode slurry, and the positive electrode slurry forms a positive electrode active material layer on the surface of the positive electrode collector. The lithium cobalt oxide agglomerates when forming the positive electrode slurry. The particle size of the lithium cobalt oxide after agglomeration is d2, in μm, and the value range of d2 is 3μm≤d2≤4.5μm.

[0032] Specifically, the value range of d2 is any point value among 3μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4μm, 4.1μm, 4.2μm, 4.3μm, 4.4μm or 4.5μm, or a range value consisting of any two point values; Since the particle size of lithium cobalt oxide is 0μm<d1≤2μm, the particle size of lithium cobalt oxide is small, the specific surface energy is large, and the overall energy of lithium cobalt oxide particles is high. The higher the energy, the more active the chemical properties of lithium cobalt oxide particles. Therefore, small particles of lithium cobalt oxide tend to agglomerate, driving the overall energy to decrease in order to achieve a stable state. Therefore, the particle size of lithium cobalt oxide particles is small, the particle transfer speed will be faster, and the DC internal resistance of the battery will be smaller.

[0033] In one embodiment, based on the total mass of the positive electrode active material being 100%, the mass percentage of the agglomerated lithium cobalt oxide particles in the positive electrode active material is 15%-25%.

[0034] Specifically, the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is any point value among 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, or a range value consisting of any two point values; in a preferred embodiment, the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is 18%-22%.

[0035] When the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is 15%-25%, the comprehensive performance and stability of the battery can be significantly improved, which is helpful to improve the rate and extend the cycle life; when the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is less than 15%, the diffusion path of lithium ions will increase, resulting in poor rate performance; during the charge and discharge process, the agglomerated lithium cobalt oxide particles are more likely to undergo volume changes and disperse stress. When the number of agglomerated lithium cobalt oxide particles decreases, it is not conducive to the stability of the structure; when the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is greater than 25%, the positive electrode material structure will be unstable, easy to pulverize or rupture, affecting the electron transmission path, and instead reducing the rate performance and shortening the cycle life of the battery.

[0036] In a preferred embodiment, the thickness of the negative electrode current collector is 8-10 μm.

[0037] When the thickness of the negative electrode current collector is 8-10 μm, the DC internal resistance of the battery is small.

[0038] In one embodiment, the CMC-based compound includes one or more of CMC-Na and CMC-Li.

[0039] By using one or more of CMC-Na and CMC-Li as a binder, the rheological properties of the negative electrode slurry are improved, the interface characteristics between the negative electrode sheet and the electrolyte are improved, and thus the stability and integrity of the electrode structure are enhanced.

[0040] In one embodiment, the double-sided surface density of the positive electrode active material layer is 240-360 g / m 2 .

[0041] Specifically, the double-sided surface density of the positive electrode active material layer is 240 g / m 2 , 250g / m 2 , 260g / m 2 , 270g / m 2 , 280g / m 2 , 290g / m 2 , 300g / m 2 , 310g / m 2 , 320g / m 2 , 330g / m 2 , 340g / m 2 , 350g / m 2 or 360g / m 2 In a preferred embodiment, the double-sided surface density of the positive electrode active material layer is 270-330 g / m 2 .

[0042] When the double-sided surface density of the positive electrode active material layer is 240~360 g / m 2 When the double-sided surface density of the positive electrode active material layer is less than 240 g / m 2 When the double-sided surface density of the positive electrode sheet is too low, it will have a negative impact on the energy density, electrochemical performance, manufacturing cost, safety and mechanical properties of the battery, and limit its applicability in specific application scenarios; when the double-sided surface density of the positive electrode active material layer is greater than 360 g / m 2 When the battery is too close together, it will cause the electrode structure to be too tight, hinder the diffusion path of lithium ions in the active material, increase the transmission resistance, reduce the rate, shorten the cycle life, make heat dissipation difficult, and increase the risk of thermal runaway of the battery.

[0043] In one embodiment, the compaction density of the positive electrode active material layer is 4.0-4.3 g / cm 3 .

[0044] Specifically, the compaction density of the positive electrode active material layer is 4.0 g / cm 3 , 4.1g / cm 3, 4.2g / cm 3 or 4.3g / cm 3 In a preferred embodiment, the compaction density of the positive electrode active material layer is 4.1-4.2 g / cm 3 .

[0045] When the compaction density of the positive electrode active material layer is 4.0-4.3 g / cm 3 When the compacted density of the positive electrode active material layer is less than 4.0 g / cm, the electrode structure can be made neither too loose nor too tight, ensuring a good transmission path for lithium ions and electrons, improving the rate performance of the battery, making the electrode structure more stable, reducing material pulverization and shedding caused by volume change, helping to disperse stress, reduce local stress concentration, reduce the risk of material cracking, and further improve structural stability. This will extend the cycle life of the battery; when the compacted density of the positive electrode active material layer is less than 4.0 g / cm 3 When the compaction density of the positive electrode active material layer is greater than 4.3 g / cm 3 When the compaction density is too high, the electrode structure is too tight, which hinders the diffusion path of lithium ions in the active material and increases the transmission resistance, thereby reducing the rate performance of the battery. During the charge and discharge process, the active material will undergo volume changes. Excessive compaction density will aggravate this change, causing material structure damage and pulverization, accelerating capacity decay, and shortening the cycle life of the battery.

[0046] In one embodiment, the double-sided surface density of the negative electrode active material layer is 94-174 g / m 2 .

[0047] Specifically, the double-sided surface density of the negative electrode active material layer is 94 g / m 2 , 104g / m 2 , 114g / m 2 , 1 2 4g / m 2 , 134g / m 2 , 144g / m 2 , 154g / m 2 , 164g / m 2 or 174g / m 2 In a preferred embodiment, the double-sided surface density of the negative electrode active material layer is 114-154 g / m 2 .

[0048] When the double-sided surface density of the negative electrode active material layer is 94~174 g / m 2When the double-sided surface density of the negative electrode active material layer is less than 94 g / m 2 When the double-sided surface density of the negative electrode sheet is too low, it will have a negative impact on the energy density, electrochemical performance, manufacturing cost, safety and mechanical properties of the battery, and limit its applicability in specific application scenarios; when the double-sided surface density of the negative electrode active material layer is greater than 174 g / m 2 When the battery is too close together, it will cause the electrode structure to be too tight, hinder the diffusion path of lithium ions in the active material, increase the transmission resistance, reduce the rate, shorten the cycle life, make heat dissipation difficult, and increase the risk of thermal runaway of the battery.

[0049] In one embodiment, the compaction density of the negative electrode active material layer is 1.6-1.8 g / cm 3 .

[0050] Specifically, the compaction density of the negative electrode active material layer is 1.6 g / cm 3 , 1.65g / cm 3 , 1.7g / cm 3 , 1.75g / cm 3 or 1.8 g / cm 3 In a preferred embodiment, the compaction density of the negative electrode active material layer is 1.65-1.75 g / cm 3 .

[0051] When the compaction density of the negative electrode active material layer is 1.6-1.8 g / cm 3 When the electrode structure is neither too loose nor too tight, the electrode structure can be made more stable, ensuring a good transmission path for lithium ions and electrons, improving the rate performance of the battery, reducing material pulverization and shedding caused by volume change, helping to disperse stress, reduce local stress concentration, reduce the risk of material cracking, and further improve structural stability; it helps to form a uniform and stable solid electrolyte interface (SEI) film, reduce its rupture and repair frequency, and thus extend the cycle life of the battery; when the compaction density of the negative electrode active material layer is less than 1.6 g / cm 3 When the battery has a certain volume, the amount of electricity stored in the battery is reduced; it may also cause the electrode structure to be too loose, increase the internal resistance, reduce the rate performance, and shorten the cycle life; moreover, the loose electrode structure makes the heat conduction path longer, the heat dissipation effect is poor, and it is easy to cause local overheating and increase the risk of thermal runaway; when the compaction density of the negative electrode active material layer is greater than 1.8g / cm 3When the compaction density is too high, the electrode structure is too tight, which hinders the diffusion path of lithium ions in the active material and increases the transmission resistance, thereby reducing the rate performance of the battery. During the charge and discharge process, the active material will undergo volume changes. Excessive compaction density will aggravate this change, leading to material structure damage and pulverization, accelerating capacity decay and shortening the cycle life of the battery. It is easy to cause local stress concentration, increase the risk of material cracking, and reduce the overall mechanical strength of the electrode. Increase the risk of thermal runaway.

[0052] In one embodiment, taking the total mass of the positive electrode active material layer as 100%, the mass percentage of the positive electrode active material in the positive electrode active material layer is 97%-99%; the mass percentage of the first conductive agent in the positive electrode active material layer is 0.1%-1%; and the mass percentage of the first binder in the positive electrode active material layer is 0.5%-1.5%.

[0053] Specifically, the mass percentage of the positive electrode active material in the positive electrode active material layer is 97%, 97.2%, 97.4%, 97.6%, 97.8%, 98%, 98.2%, 98.4%, 98.6%, 98.8% or 99%, or a range value consisting of any two points; in a preferred embodiment, the mass percentage of the positive electrode active material in the positive electrode active material layer is 97.6% to 98.4%.

[0054] Specifically, the mass percentage of the first conductive agent in the positive electrode active material layer is any point value among 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, or a range value consisting of any two point values; in a preferred embodiment, the mass percentage of the first conductive agent in the positive electrode active material layer is 0.3%-0.8%.

[0055] Specifically, the first binder accounts for any point value among 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5% of the positive electrode active material layer, or a range value consisting of any two point values; in a preferred embodiment, the first binder accounts for 0.8%-1.2% of the positive electrode active material layer.

[0056] When the mass proportions of various materials in the positive electrode active material layer are within the above range, the positive electrode sheet can have a higher lithium removal and lithium insertion capacity, and the battery can have a higher capacity.

[0057] In one embodiment, the positive electrode active material further comprises one or more of lithium iron phosphate and NCM; and / or, The first conductive agent includes one or more of carbon nanotubes and acetylene black; and / or, The first binder includes PVDF.

[0058] Specifically, the positive electrode active material also includes but is not limited to one or more of lithium iron phosphate (LFP), lithium iron manganese phosphate (LMFP), lithium manganese oxide (LMO), lithium nickel oxide (LNO), ternary material (NCA), lithium manganese-rich base (LMR), lithium nickel manganese oxide (LNMO), and lithium vanadium phosphate (Li3V2(PO4)3, LiVOPO4).

[0059] In some embodiments, the first conductive agent further includes, but is not limited to, one or more of graphite, superconducting carbon, carbon black, graphene, carbon nanofibers, metal powders, metal fibers, and polyphenylene derivatives.

[0060] In some embodiments, the first binder further includes but is not limited to one or more of polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic resin.

[0061] In some embodiments, the positive electrode current collector is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector includes one or more of aluminum, nickel, tin, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0062] The thickness of the positive electrode current collector is 10 μm-14 μm.

[0063] The positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive electrode active material layer is usually prepared by coating a positive electrode slurry made of a positive electrode active material, a first conductive agent, a first binder and any other components on a positive electrode current collector, followed by drying and cold pressing. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0064] In one embodiment, taking the total mass of the negative electrode active material layer as 100%, the mass percentage of the negative electrode active material in the negative electrode active material layer is 95%-97%; the mass percentage of the second conductive agent in the negative electrode active material layer is 2%-3%; and the mass percentage of the second binder in the negative electrode active material layer is 0.5%-2.5%.

[0065] Specifically, the mass percentage of the negative electrode active material in the negative electrode active material layer is 95%, 95.2%, 95.4%, 95.6%, 95.8%, 96%, 96.2%, 96.4%, 96.6%, 96.8% or 97%, or a range value consisting of any two points; in a preferred embodiment, the mass percentage of the negative electrode active material in the negative electrode active material layer is 95.6% to 96.4%.

[0066] Specifically, the mass percentage of the second conductive agent in the negative electrode active material layer is 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9% or 3%, or a range of any two points; in a preferred embodiment, the mass percentage of the second conductive agent in the negative electrode active material layer is 2.2%-2.8%.

[0067] Specifically, the second binder accounts for any point value among 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4% or 2.5% of the negative electrode active material layer, or a range value consisting of any two point values; in a preferred embodiment, the second binder accounts for 1%-2% of the negative electrode active material layer.

[0068] When the mass proportions of various materials in the negative electrode active material layer are within the above range, the battery can have excellent long cycle performance both at room temperature and at high temperature.

[0069] In one embodiment, the negative electrode active material comprises graphite; and / or, The second conductive agent includes acetylene black; and / or, The second binder also includes SBR.

[0070] In one embodiment, the negative electrode active material also includes but is not limited to one or more of silicon-oxygen negative electrode materials, silicon-carbon negative electrode materials, silicon negative electrode materials, tin negative electrode materials, tin oxide negative electrode materials, tin alloy negative electrode materials (Sn-Fe, Sn-Co, Sn-Cu, etc.), lithium metal negative electrode materials, lithium alloy negative electrode materials (Li-Ag, Li-Al, Li-Sn, Li-Mg, Li-Zn, Li-In, Li-Ga, etc.), and lithium-free negative electrode materials.

[0071] In some embodiments, the second conductive agent further includes, but is not limited to, one or more of graphite, superconducting carbon, carbon black, carbon nanotubes, graphene, carbon nanofibers, metal powders, metal fibers, and polyphenylene derivatives.

[0072] In some embodiments, the second binder further includes, but is not limited to, one or more of polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and polymethacrylic acid.

[0073] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the negative electrode active material layer is usually prepared by coating a negative electrode slurry made of a negative electrode active material, a second conductive agent, a second binder and any other components on a negative electrode current collector, followed by drying and cold pressing. The solvent can be an aqueous solvent, but is not limited thereto.

[0074] Another aspect of the present invention provides a lithium ion battery, comprising a battery housing, an electrolyte and the above-mentioned battery core, wherein the battery core is placed in the battery housing, the electrolyte is injected into the battery housing, and the lithium ion battery is formed through packaging.

[0075] The lithium ion battery of the present invention introduces lithium cobalt oxide particles with a particle size of 0-2 μm into the positive electrode sheet. The lithium cobalt oxide particles are small in particle size and high in surface energy, so they are more active. The energy drives the small particles to deagglomerate, so the transmission speed is faster, thereby reducing the DC internal resistance; a negative electrode current collector with a thickness of 7 μm-11 μm is adopted, and the thicker copper foil provides a larger electron transmission path, reduces the internal resistance of the current collector itself, and thus reduces the overall internal resistance of the battery; at the same time, CMC compounds are adopted in the negative electrode active material layer. The CMC compounds are thickeners, which can improve the rheology of the slurry and the interface characteristics of the electrode and the electrolyte, thereby reducing the internal resistance of the battery. The initial DC internal resistance of the battery is small, and the heat generation during the cycle will be reduced, thereby relatively reducing the byproducts caused by the temperature rise, thereby ensuring the long cycle performance of the battery core.

[0076] The beneficial effects of the present invention are further illustrated below in conjunction with embodiments.

[0077] In order to make the invention purpose, technical scheme and beneficial technical effect of the present invention clearer, the present invention is further described in detail below in conjunction with examples. However, it should be understood that the examples of the present invention are only for explaining the present invention, not for limiting the present invention, and the examples of the present invention are not limited to the examples given in the specification. The specific experimental conditions or operating conditions not specified in the examples are made under conventional conditions, or are made under the conditions recommended by the material supplier.

[0078] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0079] In the following examples, the reagents, materials and instruments used, unless otherwise specified, can be purchased commercially or obtained by synthetic methods known in the art.

[0080] Table 1 Design of the battery cells of Examples 1-32 and Comparative Examples 1-4; Embodiment 1: This embodiment is used to illustrate the battery cell and battery disclosed in the present invention; it includes the following operating steps: Preparation of positive electrode: The positive electrode active material lithium cobalt oxide, the first conductive agent CNT, SP, and the first binder PVDF are fully stirred and mixed in an NMP solvent at a mass ratio of 98.3:0.4:0.5:0.8 to form a uniform positive electrode slurry.

[0081] The slurry was coated on both sides of the 12 μm thick positive electrode current collector aluminum foil at a pressure of 240 g / m 2 The double-sided coating surface density is coated, and the roller pressing is based on a compaction density of 4.0g / cm 3 Roll-press and then cut into strips to obtain positive electrode sheets of appropriate size.

[0082] Preparation of negative electrode: Graphite, a second binder sodium carboxymethyl cellulose CMC2200, styrene-butadiene rubber SBR, and a second conductive agent SP were fully stirred and mixed in deionized water at a mass ratio of 96.3:1.2:1.5%:1.0 to form a uniform negative electrode slurry.

[0083] The negative electrode slurry was coated on both sides of the 7 μm thick negative electrode current collector copper foil at a pressure of 94 g / m 2 The double-sided coating surface density is coated, and the roller pressing is based on a compaction density of 1.6g / cm 3 The negative electrode sheets are rolled and then cut into strips to obtain negative electrode sheets of appropriate size.

[0084] Preparation of diaphragm: PE porous polymer film is used as the diaphragm substrate; Battery production: The positive electrode sheet, separator and negative electrode sheet are stacked in order, and the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. The stacked electrode sheet and separator are then wound into an aluminum-plastic film bag that has been punched and formed. The electrolyte is injected into the baked and dried battery cell. After vacuum packaging, standing, formation and other processes, a lithium-ion battery is obtained.

[0085] Example 2-32 Examples 2-32 are used to illustrate the battery cells and batteries disclosed in the present invention, and include most of the operating steps in Example 1, except that: The parameters of the positive electrode sheet and the negative electrode sheet shown in Table 1 were used.

[0086] Comparative Examples 1-4 Comparative Examples 1-4 are used to illustrate the battery cells and batteries disclosed in the present invention, and include most of the operating steps in Example 1, except that: The parameters of the positive electrode sheet and the negative electrode sheet shown in Table 1 were used. Performance Testing The following performance tests were performed on three groups of batteries prepared in the above Examples 1 to 32 and Comparative Examples 1 to 4: Normal temperature performance test: After the initial DC internal resistance performance test of 3 groups of batteries at 25°C, a long cycle test was carried out at 25°C to test the DC internal resistance performance during the normal temperature cycle and its long-life normal temperature cycle performance.

[0087] High temperature performance test: After the initial DC internal resistance performance test of the three groups of batteries at 25°C, a long cycle test was carried out at 45°C to test the DC internal resistance performance at room temperature during the high temperature cycle and its long-life high temperature cycle performance; The test results are shown in Table 2.

[0088] Table 2 Electrochemical performance of lithium-ion batteries Table 2 and Figure 1-4 It can be seen that compared with Examples 1-3, when the value range of d1 is 0μm<d1≤2μm, the lithium cobalt oxide particles have a small particle size, high surface energy, more active chemical properties, and faster energy transfer, thereby making the battery DC internal resistance smaller and the cycle life longer; when the value range of d1 is greater than 2μm, the surface energy of the lithium cobalt oxide particles will be reduced, and the energy transfer of the lithium cobalt oxide particles will be slower, thereby making the battery DC internal resistance larger and shortening the cycle life.

[0089] Compared with Example 2 and Examples 4-7, when the particle size of the lithium cobalt oxide after agglomeration is 3μm-4.5μm, the transmission speed is faster, thereby reducing the DC internal resistance of the battery; when the particle size of the lithium cobalt oxide after agglomeration is less than 3μm, the initial DC internal resistance will increase, and the capacity retention rate will remain almost unchanged; when the particle size of the lithium cobalt oxide after agglomeration is greater than 4.5μm, the initial DC internal resistance will increase, and the battery capacity retention rate will remain almost unchanged.

[0090] Compared with Example 4 and Examples 8-11, when the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is 15%-25%, the internal resistance of the battery is small and the cycle life is long; when the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is less than 15%, the cycle life of the battery will be shortened. This is because when the agglomerated lithium cobalt oxide particles decrease, the diffusion path of lithium ions increases, resulting in poor rate performance; during the charge and discharge process, the agglomerated lithium cobalt oxide particles are more likely to undergo volume changes, disperse stress, and are not conducive to structural stability; when the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is greater than 25%, the cycle life of the battery will be shortened. This is because when the agglomerated lithium cobalt oxide particles increase, the structure of the positive electrode material will be unstable, easy to pulverize or rupture, affecting the electron transmission path, and reducing the rate performance.

[0091] Compared with Example 8 and Examples 12-15, when the double-sided surface density of the positive electrode active material layer is 240-360 g / m 2 When the double-sided surface density of the positive electrode active material layer is less than 240 g / m 2 When the double-sided surface density of the positive electrode layer is greater than 360 g / m 2 When the battery is too close together, it will cause the electrode structure to be too tight, hinder the diffusion path of lithium ions in the active material, increase the transmission resistance, reduce the rate, shorten the cycle life, make heat dissipation difficult, and increase the risk of thermal runaway of the battery.

[0092] Compared with Example 12 and Examples 16-19, when the compaction density of the positive electrode active material layer is 4.0-4.3 g / cm 3 When the positive electrode active material layer is compacted, the positive electrode active material layer is less than 4.0 g / cm2, which can ensure a good transmission path for lithium ions and electrons, improve the rate performance of the battery, make the electrode structure more stable, reduce material pulverization and shedding caused by volume change, help disperse stress, reduce local stress concentration, reduce the risk of material cracking, and further improve structural stability; thereby extending the cycle life of the battery; when the compaction density of the positive electrode active material layer is less than 4.0 g / cm2 ... 3 When the compaction density of the positive electrode active material layer is greater than 4.3 g / cm 3When the density is too high, the electrode structure will be too tight, which will hinder the diffusion path of lithium ions in the active material and increase the transmission resistance, thus reducing the rate performance of the battery. During the charge and discharge process, the active material will undergo volume changes. Excessive compaction density will aggravate this change, leading to material structure damage and pulverization, accelerating capacity decay and shortening the cycle life of the battery.

[0093] Compared with Comparative Example 16, Examples 20-23 and Comparative Examples 2-3, when the thickness of the negative electrode current collector is 7μm-11μm, the DC internal resistance of the battery is small; when the thickness of the negative electrode current collector is less than 7μm, the DC internal resistance of the battery will be large, shortening the cycle life; when the thickness of the negative electrode current collector is greater than 11μm, the DC internal resistance of the battery is small, and the cycle life is long, but it will cause the volume of the battery occupied by the copper foil to increase, the battery thickness to increase, and the practicality of the battery to become weakened.

[0094] Compared with Example 21 and Example 24, Comparative Example 4 uses CMC compounds in the negative electrode active material layer, which improves the rheology of the slurry and the interface characteristics between the electrode and the electrolyte, thereby enhancing the stability and integrity of the electrode structure, and the battery has a small DC internal resistance and a long cycle life. When CMC compounds are not used, the battery internal resistance increases, and the heat generation during the cycle increases, which increases the byproducts caused by the temperature rise and shortens the cycle life of the battery. Compared with Examples 24-28, when the double-sided surface density of the negative electrode active material layer is 94-174 g / m 2 When the double-sided surface density of the negative electrode active material layer is less than 94 g / m 2 When the double-sided surface density of the negative electrode sheet is too low, it will have a negative impact on the energy density, electrochemical performance, manufacturing cost, safety and mechanical properties of the battery, and limit its applicability in specific application scenarios; when the double-sided surface density of the negative electrode active material layer is greater than 174 g / m 2 When the battery is too close together, it will cause the electrode structure to be too tight, hinder the diffusion path of lithium ions in the active material, increase the transmission resistance, reduce the rate, shorten the cycle life, make heat dissipation difficult, and increase the risk of thermal runaway of the battery.

[0095] Comparative Example 25 Compared with Examples 29-33, when the compaction density of the negative electrode active material layer is 1.6-1.8 g / cm 3When the electrode structure is neither too loose nor too tight, the electrode structure can be made more stable, ensuring a good transmission path for lithium ions and electrons, improving the rate performance of the battery, reducing material pulverization and shedding caused by volume change, helping to disperse stress, reduce local stress concentration, reduce the risk of material cracking, and further improve structural stability; it helps to form a uniform and stable solid electrolyte interface (SEI) film, reduce its rupture and repair frequency, thereby reducing the battery's DC internal resistance and extending the battery's cycle life; when the compaction density of the negative electrode active material layer is less than 1.6 g / cm 3 When the density of the negative electrode active material layer is greater than 1.8 g / cm, the amount of electricity stored in the battery at the same volume is reduced; it may also cause the electrode structure to be too loose, increase the internal resistance, reduce the rate performance, and shorten the cycle life; moreover, the loose electrode structure makes the heat conduction path longer, the heat dissipation effect is poor, and it is easy to cause local overheating and increase the risk of thermal runaway; when the compaction density of the negative electrode active material layer is greater than 1.8 g / cm 3 When the compaction density is too high, the electrode structure is too tight, which hinders the diffusion path of lithium ions in the active material and increases the transmission resistance, thereby reducing the rate performance of the battery. During the charge and discharge process, the active material will undergo volume changes. Excessive compaction density will aggravate this change, leading to material structure damage and pulverization, accelerating capacity decay and shortening the cycle life of the battery. It is easy to cause local stress concentration, increase the risk of material cracking, reduce the overall mechanical strength of the electrode, and increase the risk of thermal runaway.

[0096] 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A battery cell, characterized in that: It comprises a positive electrode sheet, a separator and a negative electrode sheet; the positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, and the battery core is formed by winding or laminating; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode active material, a first conductive agent and a first binder, the positive electrode active material comprises lithium cobalt oxide, the particle size of the lithium cobalt oxide is d1, the unit is μm, and the value range of d1 is 0μm<d1≤2μm; The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on the surface of the negative electrode current collector; The thickness of the negative electrode current collector is 7 μm-11 μm; The negative electrode active material layer includes a negative electrode active material, a second conductive agent, and a second binder, wherein the second binder includes a CMC-based compound.

2. The battery cell according to claim 1, characterized in that: The value range of d1 is 0.1 μm≤d1≤1 μm.

3. The battery cell according to claim 1, characterized in that: The positive electrode active material, the first conductive agent and the first binder are mixed to form a positive electrode slurry, and the positive electrode slurry forms the positive electrode active material layer on the surface of the positive electrode collector. The lithium cobalt oxide agglomerates when forming the positive electrode slurry, and the particle size of the lithium cobalt oxide after agglomeration is d2, in μm, and the value range of d2 is 3μm≤d2≤4.5μm.

4. The battery cell according to claim 3, characterized in that: Taking the total mass of the positive electrode active material as 100%, the mass percentage of the agglomerated lithium cobalt oxide particles in the positive electrode active material is 15%-25%.

5. The battery cell according to claim 1, characterized in that: The thickness of the negative electrode current collector is 8-10 μm.

6. The battery cell according to claim 1, characterized in that: The CMC-based compounds include one or more of CMC-Na and CMC-Li.

7. The battery cell according to claim 1, characterized in that: The double-sided surface density of the positive electrode active material layer is 240-360 g / m 2 .

8. The battery cell according to claim 1, characterized in that: The compaction density of the positive electrode active material layer is 4.0 to 4.3 g / cm 3 .

9. The battery cell according to claim 1, characterized in that: The double-sided surface density of the negative electrode active material layer is 94-174 g / m 2 .

10. The battery cell according to claim 1, characterized in that: The compaction density of the negative electrode active material layer is 1.6 to 1.8 g / cm 3 .

11. The battery cell according to claim 1, characterized in that: Taking the total mass of the positive electrode active material layer as 100%, the mass percentage of the positive electrode active material in the positive electrode active material layer is 97%-99%; the mass percentage of the first conductive agent in the positive electrode active material layer is 0.1%-1%; and the mass percentage of the first binder in the positive electrode active material layer is 0.5%-1.5%.

12. The battery cell according to claim 1, characterized in that: The positive electrode active material further comprises one or more of lithium iron phosphate and NCM; and / or, The first conductive agent includes one or more of carbon nanotubes and acetylene black; and / or, The first binder includes PVDF.

13. The battery cell according to claim 1, characterized in that: Taking the total mass of the negative electrode active material layer as 100%, the mass percentage of the negative electrode active material in the negative electrode active material layer is 95%-97%; the mass percentage of the second conductive agent in the negative electrode active material layer is 2%-3%; and the mass percentage of the second binder in the negative electrode active material layer is 0.5%-2.5%.

14. The battery cell according to claim 1, characterized in that: The negative electrode active material includes graphite; and / or, The second conductive agent includes acetylene black; and / or, The second binder also includes SBR.

15. A lithium ion battery, characterized in that: The invention comprises a battery casing, an electrolyte and a battery core as claimed in any one of claims 1 to 14, wherein the battery core is placed in the battery casing, the electrolyte is injected into the battery casing, and the lithium-ion battery is formed through packaging.

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