Battery cell and lithium ion battery

Abstract

The application provides a battery cell, which comprises a positive electrode sheet, a separator and a negative electrode sheet; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer; the positive electrode active material layer comprises a positive electrode active material, the positive electrode active material comprises lithium cobaltate, the particle size of the lithium cobaltate is d1, the unit is mu m, and the value range of d1 is 0 mu m < d1 <= 2 mu m; 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 mu m-11 mu m; the negative electrode active material layer comprises a second binder, and the second binder comprises a CMC compound; by introducing lithium cobaltate particles with a particle size of 0-2 mu m into the positive electrode sheet, adopting a negative electrode current collector with a thickness of 7 mu m-11 mu m, and simultaneously adopting a CMC compound in the negative electrode active material layer, the direct current resistance of the battery can be small, the heat generation in the cycle process can be reduced, the by-products caused by temperature rise can be relatively reduced, and the long cycle performance of the battery cell can be ensured.

Description

A battery cell and a lithium-ion battery Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a battery cell and a lithium-ion battery. Background Technology

[0002] With the rapid development of applications such as electric vehicles, portable electronic devices, and energy storage systems, the performance requirements for lithium-ion batteries are becoming increasingly stringent. DC internal resistance (DCIR) is a key parameter measuring the internal resistance of a lithium-ion battery, directly affecting its charge / discharge efficiency, power output, and thermal management. Current technologies exhibit relatively high initial internal resistance, failing to meet the requirements for low DC internal resistance. Therefore, overcoming these technical problems and shortcomings has become a crucial issue that needs to be addressed. Summary of the Invention

[0003] To address the problem of high initial DC internal resistance in batteries, this invention provides a battery cell and a lithium-ion battery.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0005] The present invention provides a battery cell, comprising a positive electrode, a separator, and a negative electrode; the positive electrode, the separator, and the negative electrode are sequentially stacked and formed by winding or stacking.

[0006] The positive electrode sheet includes a positive current collector and a positive active material layer coated on the surface of the positive current collector; the positive active material layer includes a positive active material, a first conductive agent and a first binder, the positive active material includes lithium cobalt oxide, the particle size of the lithium cobalt oxide is d1, the unit is μm, and the value of d1 is 0μm<d1≤2μm;

[0007] 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;

[0008] The thickness of the negative electrode current collector is 7μm-11μm;

[0009] 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-type compound.

[0010] Optionally, the value of d1 is in the range of 0.1μm≤d1≤1μm.

[0011] Optionally, the positive electrode active material, the first conductive agent, and the first binder are mixed to form a positive electrode slurry. The positive electrode slurry forms the positive electrode active material layer on the surface of the positive electrode current collector. The lithium cobalt oxide agglomerates during the formation of the positive electrode slurry. The particle size of the agglomerated lithium cobalt oxide is d2, in μm, and the value of d2 ranges from 3μm to 4.5μm.

[0012] Optionally, the mass percentage of agglomerated lithium cobalt oxide particles is 15%-25% of the total mass of the positive electrode active material, which is 100% of the total mass of the positive electrode active material.

[0013] Optionally, the thickness of the negative electrode current collector is 8-10 μm.

[0014] Optionally, the CMC-type compounds include one or more of CMC-Na and CMC-Li.

[0015] Optionally, the areal density of the positive electrode active material layer is 240~360 g / m². 2 .

[0016] Optionally, the compaction density of the positive electrode active material layer is 4.0–4.3 g / cm³. 3 .

[0017] Optionally, the areal density of the negative electrode active material layer is 94~174 g / m². 2 .

[0018] Optionally, the compaction density of the negative electrode active material layer is 1.6–1.8 g / cm³. 3 .

[0019] Optionally, based on the total mass of the positive electrode active material layer as 100%, the positive electrode active material accounts for 97%-99% of the mass of the positive electrode active material layer; the first conductive agent accounts for 0.1%-1% of the mass of the positive electrode active material layer; and the first binder accounts for 0.5%-1.5% of the mass of the positive electrode active material layer.

[0020] Optionally, the positive electrode active material further includes one or more of lithium iron phosphate and NCM; and / or,

[0021] The first conductive agent includes one or more of carbon nanotubes and acetylene black; and / or,

[0022] The first adhesive comprises PVDF.

[0023] Optionally, based on the total mass of the negative electrode active material layer as 100%, the negative electrode active material accounts for 95%-97% of the mass of the negative electrode active material layer; the second conductive agent accounts for 2%-3% of the mass of the negative electrode active material layer; and the second binder accounts for 0.5%-2.5% of the mass of the negative electrode active material layer.

[0024] Optionally, the negative electrode active material includes graphite; and / or,

[0025] The second conductive agent includes acetylene black; and / or,

[0026] The second adhesive also includes SBR.

[0027] Another aspect of the present invention provides a lithium-ion battery, comprising a battery casing, an electrolyte, and the aforementioned battery cell, wherein the battery cell is placed inside the battery casing, the electrolyte is injected into the battery casing, and the battery is encapsulated to form the lithium-ion battery.

[0028] According to the battery cell provided by the present invention, the introduction of lithium cobalt oxide particles with a particle size of 0-2μm into the positive electrode sheet has the advantages of small particle size, high surface energy, and more active chemical properties, which drives the small lithium cobalt oxide particles to agglomerate, thus resulting in faster transfer speed and reducing the DC internal resistance of the battery. The use of a 7μm-11μm thick negative electrode current collector provides a larger electron transport path and reduces the internal resistance of the negative electrode current collector itself, thereby reducing the overall internal resistance of the battery. At the same time, the use of CMC-type compounds in the negative electrode active material layer, which are thickeners, can improve the rheology of the negative electrode slurry and improve the interfacial characteristics between the negative electrode sheet and the electrolyte, thereby reducing the internal resistance of the battery. Moreover, the heat generation during cycling is reduced, which can relatively reduce the by-products caused by temperature rise, thus ensuring the long-cycle performance of the battery cell. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 shows the DCR (25°C cycling) test results of Examples 20 and 23-24 at 25°C and 80% SOC.

[0031] Figure 2 shows the DCR (45°C cycling) test results of Examples 20 and 23-24 at 45°C and 80% SOC;

[0032] Figure 3 shows the battery cycle performance test results of Examples 20 and 23-24 at 25°C.

[0033] Figure 4 shows the battery cycle performance test results of Examples 20 and 23-24 at 45°C. Detailed Implementation

[0034] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0036] In one embodiment, the present invention provides a battery cell, including a positive electrode, a separator, and a negative electrode; the positive electrode, the separator, and the negative electrode are sequentially stacked and formed into a battery cell by winding or stacking.

[0037] The positive electrode sheet includes a positive current collector and a positive active material layer coated on the surface of the positive current collector; the positive active material layer includes a positive active material, a first conductive agent and a first binder, the positive active material includes lithium cobalt oxide, the particle size of lithium cobalt oxide is d1, the unit is μm, and the value range of d1 is 0μm<d1≤2μm;

[0038] 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;

[0039] The thickness of the negative electrode current collector is 7μm-11μm;

[0040] The negative electrode active material layer includes a negative electrode active material, a second conductive agent, and a second binder. The second binder includes CMC-type compounds.

[0041] Specifically, the value of d1 can be any single value or a range of any two values ​​from 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.

[0042] When the value of d1 is in the range of 0μm < d1 ≤ 2μm, the lithium cobalt oxide particles have small particle size, high surface energy, and higher energy, which leads to more active chemical properties and faster energy transfer. Therefore, small lithium cobalt oxide particles tend to aggregate, driving down the overall energy to achieve a stable state. Thus, the smaller the particle size of lithium cobalt oxide particles, the faster the particle transfer speed and the lower the DC internal resistance of the battery. When the value of d1 is greater than 2μm, it will lead to a decrease in the surface energy of lithium cobalt oxide particles and a decrease in the transfer speed of lithium cobalt oxide particles, resulting in a larger DC internal resistance of the battery.

[0043] Specifically, the thickness of the negative electrode current collector is any one value or any two values ​​from 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm or 11μm.

[0044] When the thickness of the negative electrode current collector is 7μm-11μm, the battery's DC internal resistance is relatively small; when the thickness of the negative electrode current collector is less than 7μm, the battery's DC internal resistance will be relatively large; when the thickness of the negative electrode current collector is greater than 11μm, the copper foil will occupy more battery volume, increasing the battery thickness and weakening the battery's practicality.

[0045] The negative electrode current collector is selected from a metallic 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.

[0046] By using CMC-type compounds in the negative electrode active material layer, the technical effects of improving the slurry rheology and the interfacial properties between the electrode and the electrolyte are enhanced, thereby improving the stability and integrity of the electrode structure.

[0047] Specifically, this application introduces lithium cobalt oxide particles with a particle size of 0-2μm into the positive electrode. These particles have small size, high surface energy, and more active chemical properties, driving the aggregation of small lithium cobalt oxide particles, thus increasing the transfer speed and reducing the DC internal resistance of the battery. A negative electrode current collector with a thickness of 7μm-11μm is used. The thicker negative electrode current collector provides a larger electron transport path, reducing the internal resistance of the negative electrode current collector itself, thereby reducing the overall internal resistance of the battery. At the same time, CMC-type compounds are used in the negative electrode active material layer. CMC-type compounds are thickeners that can improve the rheology of the negative electrode slurry and improve the interfacial characteristics between the negative electrode and the electrolyte, thereby reducing the internal resistance of the battery. Moreover, heat generation during cycling is reduced, which can relatively reduce the by-products caused by temperature rise, thus ensuring the long-cycle performance of the cell.

[0048] In one embodiment, the value of d1 is in the range of 0.1μm≤d1≤1μm.

[0049] When the value of d1 is in the range of 0.1μm≤d1≤1μm, lithium cobalt oxide particles have higher surface energy, more active chemical properties, and faster energy transfer, thus resulting in lower DC internal resistance of the battery.

[0050] In one embodiment, a positive electrode active material, a first conductive agent and a first binder are mixed to form a positive electrode slurry. The positive electrode slurry forms a positive electrode active material layer on the surface of the positive electrode current collector. Lithium cobalt oxide agglomerates during the formation of the positive electrode slurry. The particle size of the agglomerated lithium cobalt oxide is d2, in μm, and the value of d2 is in the range of 3μm≤d2≤4.5μm.

[0051] Specifically, the value of d2 can be any single value or a range of any two values ​​from 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.

[0052] Since the particle size of lithium cobalt oxide is 0μm < d1 ≤ 2μm, the small particle size of lithium cobalt oxide results in a large specific surface energy and a high overall energy of lithium cobalt oxide particles. The higher the energy, the more chemically active the lithium cobalt oxide particles become. Therefore, small lithium cobalt oxide particles tend to aggregate, driving the overall energy down to achieve a stable state. As a result, the small particle size of lithium cobalt oxide particles leads to faster particle transport speed and lower DC internal resistance of the battery.

[0053] In one embodiment, the aggregated lithium cobalt oxide particles account for 15%-25% of the total mass of the positive electrode active material, which is 100% of the total mass of the positive electrode active material.

[0054] Specifically, the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is any one or any two of the following values: 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%; in a preferred embodiment, the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is 18%-22%.

[0055] When the mass percentage of aggregated lithium cobalt oxide particles in the positive electrode active material is 15%-25%, it can significantly improve the overall performance and stability of the battery, helping to increase the rate capability and extend cycle life. When the mass percentage of aggregated lithium cobalt oxide particles in the positive electrode active material is less than 15%, it increases the diffusion path of lithium ions, leading to a deterioration in rate performance. During charge and discharge, aggregated lithium cobalt oxide particles are more prone to volume changes and stress dispersion. When the number of aggregated lithium cobalt oxide particles decreases, it is detrimental to structural stability. When the mass percentage of aggregated lithium cobalt oxide particles in the positive electrode active material is greater than 25%, it leads to unstable positive electrode material structure, making it prone to pulverization or breakage, affecting electron transport paths, thus reducing rate performance and shortening the battery's cycle life.

[0056] In a preferred embodiment, the thickness of the negative electrode current collector is 8-10 μm.

[0057] When the thickness of the negative electrode current collector is 8-10μm, the DC internal resistance of the battery is relatively small.

[0058] In one embodiment, the CMC-type compound includes one or more of CMC-Na and CMC-Li.

[0059] By using one or more of CMC-Na and CMC-Li as binders, the technical effect of improving the rheological properties of the negative electrode slurry and the interfacial characteristics between the negative electrode sheet and the electrolyte is achieved, thereby enhancing the stability and integrity of the electrode structure.

[0060] In one embodiment, the double-sided areal density of the positive electrode active material layer is 240~360 g / m². 2 .

[0061] Specifically, the areal density of the positive electrode active material layer is 240 g / m². 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 The value of any one point or a range of any two points; in a preferred embodiment, the double-sided areal density of the positive electrode active material layer is 270~330 g / m². 2 .

[0062] When the double-sided areal density of the positive electrode active material layer is 240~360 g / m 2 This ensures the electrode structure is neither too porous nor too dense, guaranteeing a good transport path for lithium ions and electrons, improving the battery's rate performance, and extending cycle life; when the double-sided areal density of the positive electrode active material layer is less than 240 g / m², 2 When the areal density of the positive electrode coating is too low, it will negatively affect the battery's energy density, electrochemical performance, manufacturing cost, safety, and mechanical properties, and limit its applicability in specific application scenarios; when the areal density of the positive electrode active material layer is greater than 360 g / m², it will negatively affect the battery's energy density, electrochemical performance, manufacturing cost, safety, and mechanical properties, and limit its applicability in specific application scenarios. 2 When this happens, the electrode structure becomes too dense, hindering the diffusion path of lithium ions in the active material, increasing transport resistance, reducing rate capability, shortening cycle life, making heat dissipation difficult, and increasing the risk of battery thermal runaway.

[0063] In one embodiment, the compaction density of the positive electrode active material layer is 4.0–4.3 g / cm³. 3 .

[0064] Specifically, the compaction density of the positive electrode active material layer is 4.0 g / cm³. 3 4.1g / cm 3 4.2g / cm 3 Or 4.3g / cm 3 The value is any one point value or a range of any two point values; in a preferred embodiment, the compaction density of the positive electrode active material layer is 4.1–4.2 g / cm³. 3 .

[0065] When the compaction density of the positive electrode active material layer is 4.0–4.3 g / cm³ 3 This allows the electrode structure to be neither too loose nor too dense, ensuring a good transport path for lithium ions and electrons, improving the battery's rate performance, making the electrode structure more stable, reducing material pulverization and shedding caused by volume changes, helping to disperse stress, reducing local stress concentration, lowering the risk of material cracking, and further improving structural stability. This extends the battery's cycle life; when the compaction density of the positive electrode active material layer is less than 4.0 g / cm³... 3 When the battery's capacity is reduced within the same volume, it may lead to an overly porous electrode structure, increasing internal resistance, reducing rate performance, and shortening cycle life. Furthermore, when the compaction density of the positive electrode active material layer exceeds 4.3 g / cm³... 3 Excessive compaction leads to an overly dense electrode structure, hindering the diffusion path of lithium ions in the active material, increasing transport resistance, and thus reducing the battery's rate performance. During charge and discharge, the active material undergoes volume changes, and excessively high compaction density exacerbates these changes, causing material structure damage and pulverization, accelerating capacity decay, and shortening the battery's cycle life.

[0066] In one embodiment, the double-sided areal density of the negative electrode active material layer is 94~174 g / m². 2 .

[0067] Specifically, the double-sided areal density of the negative electrode active material layer is 94 g / m². 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 The value of any one point or a range of any two points; in a preferred embodiment, the double-sided areal density of the negative electrode active material layer is 114~154 g / m³. 2 .

[0068] When the double-sided areal density of the negative electrode active material layer is 94~174 g / m 2 This ensures the electrode structure is neither too porous nor too dense, guaranteeing a good transport path for lithium ions and electrons, improving the battery's rate performance, and extending cycle life; when the double-sided areal density of the negative electrode active material layer is less than 94 g / m², 2 When the areal density of the negative electrode coating is too low, it will negatively affect the battery's energy density, electrochemical performance, manufacturing cost, safety, and mechanical properties, and limit its applicability in specific application scenarios; when the areal density of the negative electrode active material layer is greater than 174 g / m², it will negatively affect the battery's energy density, electrochemical performance, manufacturing cost, safety, and mechanical properties, and limit its applicability in specific application scenarios. 2 When this happens, the electrode structure becomes too dense, hindering the diffusion path of lithium ions in the active material, increasing transport resistance, reducing rate capability, shortening cycle life, making heat dissipation difficult, and increasing the risk of battery thermal runaway.

[0069] In one embodiment, the compaction density of the negative electrode active material layer is 1.6–1.8 g / cm³. 3 .

[0070] Specifically, the compaction density of the negative electrode active material layer is 1.6 g / cm³. 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 Or 1.8g / cm 3 The value is any one point value or a range of any two point values; in a preferred embodiment, the compaction density of the negative electrode active material layer is 1.65–1.75 g / cm³. 3 .

[0071] When the compaction density of the negative electrode active material layer is 1.6–1.8 g / cm³ 3 This design ensures the electrode structure is neither too loose nor too dense, resulting in greater stability, guaranteeing a good transport path for lithium ions and electrons, improving battery rate performance, reducing material pulverization and shedding caused by volume changes, helping to disperse stress, reducing local stress concentration, lowering the risk of material cracking, and further improving structural stability; it also helps to form a uniform and stable solid electrolyte interphase (SEI) film, reducing its cracking and repair frequency, thereby extending the battery's cycle life; when the compaction density of the negative electrode active material layer is less than 1.6 g / cm³... 3 At this time, the amount of electricity stored in the battery within the same volume is reduced; it may also lead to an overly porous electrode structure, increasing internal resistance, reducing rate performance, and shortening cycle life; moreover, a porous electrode structure results in a longer heat conduction path, poor heat dissipation, and a tendency to cause localized overheating, increasing the risk of thermal runaway; when the compaction density of the negative electrode active material layer is greater than 1.8 g / cm³... 3 Excessive compaction density leads to an overly dense electrode structure, hindering the diffusion path of lithium ions in the active material, increasing transport resistance, and thus reducing the battery's rate performance. During charge and discharge, the active material undergoes volume changes; excessively high compaction density exacerbates these changes, causing material structure damage and pulverization, accelerating capacity decay, and shortening the battery's cycle life. It also easily leads to localized stress concentration, increasing the risk of material cracking and reducing the overall mechanical strength of the electrode. Furthermore, it increases the risk of thermal runaway.

[0072] In one embodiment, the positive electrode active material layer accounts for 97%-99% of the total mass of the positive electrode active material layer, with the first conductive agent accounting for 0.1%-1% of the mass of the positive electrode active material layer and the first binder accounting for 0.5%-1.5% of the mass of the positive electrode active material layer.

[0073] Specifically, the mass percentage of the positive electrode active material in the positive electrode active material layer is any one value or a range of any two values ​​from 97%, 97.2%, 97.4%, 97.6%, 97.8%, 98%, 98.2%, 98.4%, 98.6%, 98.8%, or 99%; 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%.

[0074] Specifically, the mass percentage of the first conductive agent in the positive electrode active material layer is any one value or a range of any two values ​​from 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%; in a preferred embodiment, the mass percentage of the first conductive agent in the positive electrode active material layer is 0.3%-0.8%.

[0075] Specifically, the first binder accounts for any one value or any two values ​​within the range of 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; in a preferred embodiment, the first binder accounts for 0.8%-1.2% of the positive electrode active material layer.

[0076] When the mass ratio of various materials in the positive electrode active material layer is within the above range, the positive electrode sheet can have a high lithium delithiation and lithium insertion capacity, thus enabling the battery to have a high capacity.

[0077] In one embodiment, the positive electrode active material further includes one or more of lithium iron phosphate and NCM; and / or,

[0078] The first conductive agent includes one or more of carbon nanotubes and acetylene black; and / or

[0079] The first adhesive includes PVDF.

[0080] Specifically, positive electrode active materials include, but are not limited to, one or more of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium manganese oxide (LMO), lithium nickel oxide (LNO), ternary materials (NCA), lithium-rich manganese-based materials (LMR), lithium nickel manganese oxide (LNMO), and lithium vanadium oxide phosphate (Li3V2(PO4)3, LiVOPO4).

[0081] In some embodiments, the first conductive agent includes, but is not limited to, one or more of graphite, superconducting carbon, carbon black, graphene, carbon nanofibers, metal powder, metal fibers, and polyphenylene derivatives.

[0082] In some embodiments, the first adhesive may include, but is not limited to, one or more of polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0083] In some embodiments, the positive current collector is selected from a metallic material that can conduct electrons. Preferably, the positive current collector includes one or more of aluminum, nickel, tin, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0084] The thickness of the positive electrode current collector is 10μm-14μm.

[0085] The positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive electrode active material layer is typically formed by coating a positive electrode slurry, consisting of a positive electrode active material, a first conductive agent, a first binder, and any other components, onto a positive electrode current collector, followed by drying and cold pressing. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0086] In one embodiment, the total mass of the negative electrode active material layer is 100%, the negative electrode active material accounts for 95%-97% of the mass of the negative electrode active material layer; the second conductive agent accounts for 2%-3% of the mass of the negative electrode active material layer; and the second binder accounts for 0.5%-2.5% of the mass of the negative electrode active material layer.

[0087] Specifically, the mass percentage of the negative electrode active material in the negative electrode active material layer is any one value or a range of any two values ​​selected from 95%, 95.2%, 95.4%, 95.6%, 95.8%, 96%, 96.2%, 96.4%, 96.6%, 96.8%, or 97%; 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%.

[0088] Specifically, the second conductive agent accounts for any one or any two values ​​within the mass percentage of the negative electrode active material layer, which is 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3%; in a preferred embodiment, the second conductive agent accounts for 2.2%-2.8% of the mass percentage of the negative electrode active material layer.

[0089] Specifically, the second binder accounts for any one or a range of any two values ​​from 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; in a preferred embodiment, the second binder accounts for 1%-2% of the negative electrode active material layer.

[0090] When the mass ratio of various materials in the negative electrode active material layer is within the above range, the battery can have excellent long-cycle performance under both normal and high-temperature environments.

[0091] In one embodiment, the negative electrode active material includes graphite; and / or,

[0092] The second conductive agent includes acetylene black; and / or,

[0093] The second adhesive also includes SBR.

[0094] In one embodiment, the negative electrode active material includes, but is not limited to, one or more of the following: silicon-oxygen negative electrode material, silicon-carbon negative electrode material, silicon negative electrode material, tin negative electrode material, tin oxide negative electrode material, tin alloy negative electrode material (Sn-Fe, Sn-Co, Sn-Cu, etc.), lithium metal negative electrode material, lithium alloy negative electrode material (Li-Ag, Li-Al, Li-Sn, Li-Mg, Li-Zn, Li-In, Li-Ga, etc.), and lithium-free negative electrode material.

[0095] In some embodiments, the second conductive agent includes, but is not limited to, one or more of graphite, superconducting carbon, carbon black, carbon nanotubes, graphene, carbon nanofibers, metal powder, metal fibers, and polyphenylene derivatives.

[0096] In some embodiments, the second adhesive includes, but is not limited to, one or more of polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and polymethacrylic acid.

[0097] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the negative electrode active material layer is typically formed by coating a negative electrode slurry, consisting of a negative electrode active material, a second conductive agent, a second binder, and any other components, onto a negative electrode current collector, followed by drying and cold pressing. The solvent can be an aqueous solvent, but is not limited to it.

[0098] Another aspect of the present invention provides a lithium-ion battery, comprising a battery casing, an electrolyte, and the aforementioned battery cell, wherein the battery cell is placed inside the battery casing, the electrolyte is injected into the battery casing, and the battery is encapsulated to form a lithium-ion battery.

[0099] The lithium-ion battery of this invention introduces lithium cobalt oxide particles with a particle size of 0-2 μm into the positive electrode. The small particle size and high surface energy of the lithium cobalt oxide particles make them more active, and the energy drives the small particles to aggregate, resulting in faster energy transfer and reduced DC internal resistance. A 7 μm-11 μm thick negative electrode current collector is used; the thicker copper foil provides a larger electron transport path, reducing the internal resistance of the current collector itself and thus reducing the overall internal resistance of the battery. Simultaneously, CMC compounds are used in the negative electrode active material layer. CMC compounds are thickeners that improve the rheology of the slurry and the interfacial characteristics between the electrode and electrolyte, thereby reducing the battery's internal resistance. The initial DC internal resistance of the battery is relatively low, and heat generation during cycling is reduced, thus relatively reducing byproducts caused by temperature rise and ensuring the long-cycle performance of the cell.

[0100] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0101] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Unless otherwise specified, specific experimental or operational conditions in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0102] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0103] In the following embodiments, the reagents, materials and instruments used, unless otherwise specified, are commercially available or can be obtained through synthesis methods known in the art.

[0104] Table 1. Design of battery cells in Examples 1-32 and Comparative Examples 1-4;

[0105]

[0106]

[0107] Example 1:

[0108] This embodiment illustrates the battery cell and battery disclosed in this invention; it includes the following operation steps:

[0109] Preparation of positive electrode:

[0110] The positive electrode active material lithium cobalt oxide, the first conductive agent CNT, SP, and the first binder PVDF are thoroughly mixed in NMP solvent at a mass ratio of 98.3:0.4:0.5:0.8 to form a uniform positive electrode slurry.

[0111] This slurry was coated onto both sides of a 12μm thick positive electrode current collector aluminum foil, at a ratio of 240g / m². 2The coating is applied to both sides with a specific surface density, and the roller is pressed to achieve a compaction density of 4.0 g / cm³. 3 The material is rolled and then slit to obtain positive electrode sheets of suitable size.

[0112] Preparation of negative electrode:

[0113] Graphite, sodium carboxymethyl cellulose (CMC2200) as the second binder, styrene-butadiene rubber (SBR), and the second conductive agent (SP) were thoroughly mixed in deionized water at a mass ratio of 96.3:1.2:1.5%:1.0 to form a uniform negative electrode slurry.

[0114] The negative electrode slurry was coated on both sides of a 7μm thick negative electrode current collector copper foil, at a ratio of 94g / m 2 The coating is applied to both sides with a specific surface density, and the roller is pressed to achieve a compaction density of 1.6 g / cm³. 3 The plates are rolled and then slit to obtain negative electrode sheets of suitable size.

[0115] Membrane fabrication: PE porous polymer film is used as the membrane substrate;

[0116] Battery making:

[0117] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The stacked electrodes and separator are then wound and placed in a pre-formed aluminum-plastic film bag. Electrolyte is injected into the baked and dried cell. After vacuum sealing, settling, and formation processes, a lithium-ion battery is obtained.

[0118] Example 2-32

[0119] Examples 2-32 illustrate the battery cell and battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences:

[0120] The parameters of the positive and negative electrodes shown in Table 1 are used.

[0121] Comparative Examples 1-4

[0122] Comparative Examples 1-4 are used to illustrate the battery cell and battery disclosed in this invention, including most of the operating steps in Example 1, the difference being:

[0123] The parameters of the positive and negative electrodes shown in Table 1 are used.

[0124] Performance testing

[0125] The following performance tests were performed on three groups of batteries prepared in Examples 1-32 and Comparative Examples 1-4:

[0126] Room temperature performance test: After initial DC internal resistance performance test of 3 groups of batteries at 25℃, long cycle test was carried out at 25℃ to test DC internal resistance performance and long-life room temperature cycle performance during room temperature cycling.

[0127] High-temperature performance test: After initial DC internal resistance performance test of 3 groups of batteries at 25℃, long-term cycle test was carried out at 45℃ to test the DC internal resistance performance under normal temperature conditions during high-temperature cycle and its long-life high-temperature cycle performance.

[0128] The test results are shown in Table 2.

[0129] Table 2 Electrochemical performance of lithium-ion batteries

[0130]

[0131]

[0132] As shown in Table 2 and Figures 1-4, compared with Examples 1-3, when the value of d1 is in the range of 0μm < d1 ≤ 2μm, the lithium cobalt oxide particles have small particle size, high surface energy, and more active chemical properties, resulting in faster energy transfer and thus lower DC internal resistance and longer cycle life of the battery. When the value of d1 is greater than 2μm, the surface energy of the lithium cobalt oxide particles decreases, the energy transfer of the lithium cobalt oxide particles is slower, resulting in higher DC internal resistance and shorter cycle life of the battery.

[0133] Compared with Examples 2 and 4-7, when the particle size of lithium cobalt oxide after agglomeration is 3μm-4.5μm, the transfer speed is faster, thereby reducing the DC internal resistance of the battery; when the particle size of lithium cobalt oxide after agglomeration is less than 3μm, the initial DC internal resistance increases, and the capacity retention rate remains almost unchanged; when the particle size of lithium cobalt oxide after agglomeration is greater than 4.5μm, the initial DC internal resistance increases, and the battery capacity retention rate remains almost unchanged.

[0134] Compared with Examples 4 and 8-11, when the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is 15%-25%, the battery has a lower internal resistance and a longer cycle life. When the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is less than 15%, the battery's cycle life is shortened. This is because a decrease in agglomerated lithium cobalt oxide particles increases the diffusion path of lithium ions, leading to a deterioration in rate performance. During charge and discharge, agglomerated lithium cobalt oxide particles are more prone to volume changes, dispersing stress and negatively impacting structural stability. When the mass percentage of agglomerated lithium cobalt oxide particles in the positive electrode active material is greater than 25%, the battery's cycle life is shortened. This is because an increase in agglomerated lithium cobalt oxide particles leads to an unstable positive electrode material structure, making it prone to pulverization or breakage, affecting electron transport paths and thus reducing rate performance.

[0135] Compared with Examples 8 and 12-15, when the double-sided areal density of the positive electrode active material layer is 240~360 g / m² 2 This ensures the electrode structure is neither too porous nor too dense, guaranteeing a good transport path for lithium ions and electrons, improving the battery's rate performance, and extending cycle life; when the double-sided areal density of the positive electrode active material layer is less than 240 g / m², 2 When the surface density of the positive electrode coating is too low, it will negatively affect the battery's energy density, electrochemical performance, manufacturing cost, safety, and mechanical properties, and limit its applicability in specific applications; when the surface density of the positive electrode active material layer is greater than 360 g / m², it will negatively affect the battery's energy density, electrochemical performance, manufacturing cost, safety, and mechanical properties, and limit its applicability in specific applications. 2 When this happens, the electrode structure becomes too dense, hindering the diffusion path of lithium ions in the active material, increasing transport resistance, reducing rate capability, shortening cycle life, making heat dissipation difficult, and increasing the risk of battery thermal runaway.

[0136] Compared with Examples 16-19, when the compaction density of the positive electrode active material layer is 4.0–4.3 g / cm³, the results show that… 3 Ensuring a good transport path for lithium ions and electrons improves the battery's rate performance, makes the electrode structure more stable, reduces material pulverization and shedding caused by volume changes, helps disperse stress, reduces local stress concentration, lowers the risk of material cracking, and further improves structural stability; thus extending the battery's cycle life; when the compaction density of the positive electrode active material layer is less than 4.0 g / cm³. 3 When this occurs, it can lead to a reduction in the amount of electricity stored in the battery within the same volume; it may also result in an overly porous electrode structure, increasing internal resistance, reducing rate performance, and shortening cycle life; when the compaction density of the positive electrode active material layer exceeds 4.3 g / cm³... 3Excessive compaction can lead to an overly dense electrode structure, hindering the diffusion path of lithium ions in the active material, increasing transport resistance, and thus reducing the battery's rate performance. During charge and discharge, the active material undergoes volume changes, and excessively high compaction density exacerbates these changes, leading to material structure damage and pulverization, accelerating capacity decay, and shortening the battery's cycle life.

[0137] Compared with Comparative Examples 16, 20-23 and 2-3, when the thickness of the negative electrode current collector is 7μm-11μm, the DC internal resistance of the battery is relatively small; when the thickness of the negative electrode current collector is less than 7μm, the DC internal resistance of the battery is relatively large, which shortens the cycle life; when the thickness of the negative electrode current collector is greater than 11μm, the DC internal resistance of the battery is relatively small and the cycle life is relatively long, but it will lead to an increase in the volume occupied by the copper foil in the battery, an increase in the battery thickness, and a decrease in the practicality of the battery.

[0138] Compared with Examples 21 and 24, Comparative Example 4 shows that by using CMC-type compounds in the negative electrode active material layer, the slurry rheology and the interfacial characteristics between the electrode and the electrolyte are improved, thereby enhancing the stability and integrity of the electrode structure, resulting in a lower DC internal resistance and a longer cycle life. When CMC-type compounds are not used, the battery internal resistance increases, and heat generation during cycling increases, leading to increased byproducts caused by temperature rise and a shorter cycle life.

[0139] Compared to Examples 24-28, when the double-sided areal density of the negative electrode active material layer is 94~174 g / m² 2 This ensures the electrode structure is neither too porous nor too dense, guaranteeing a good transport path for lithium ions and electrons, improving the battery's rate performance, reducing DC internal resistance, and extending cycle life; when the double-sided areal density of the negative electrode active material layer is less than 94 g / m², the battery's rate performance is improved. 2 When the areal density of the negative electrode coating is too low, it will negatively affect the battery's energy density, electrochemical performance, manufacturing cost, safety, and mechanical properties, and limit its applicability in specific application scenarios; when the areal density of the negative electrode active material layer is greater than 174 g / m², it will negatively affect the battery's energy density, electrochemical performance, manufacturing cost, safety, and mechanical properties, and limit its applicability in specific application scenarios. 2 When this happens, the electrode structure becomes too dense, hindering the diffusion path of lithium ions in the active material, increasing transport resistance, reducing rate capability, shortening cycle life, making heat dissipation difficult, and increasing the risk of battery thermal runaway.

[0140] Compared with Examples 29-33, Example 25 shows that when the compaction density of the negative electrode active material layer is 1.6–1.8 g / cm³, the results are more satisfactory. 3At this point, the electrode structure is neither too loose nor too dense, which makes the electrode structure more stable, ensures a good transport path for lithium ions and electrons, improves the rate performance of the battery, reduces material pulverization and shedding caused by volume changes, helps to disperse stress, reduces local stress concentration, lowers the risk of material cracking, and further improves structural stability; it also helps to form a uniform and stable solid electrolyte interface (SEI) film, reducing its cracking 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 / cm³... 3 At this time, the amount of electricity stored in the battery within the same volume decreases; it may also lead to an overly porous electrode structure, increasing internal resistance, reducing rate performance, and shortening cycle life; moreover, a porous electrode structure results in a longer heat conduction path, poor heat dissipation, and a tendency to cause localized overheating, increasing the risk of thermal runaway; when the compaction density of the negative electrode active material layer is greater than 1.8 g / cm³... 3 Excessive compaction density leads to an overly dense electrode structure, hindering the diffusion path of lithium ions in the active material, increasing transport resistance, and thus reducing the battery's rate performance. During charge and discharge, the active material undergoes volume changes; excessively high compaction density exacerbates these changes, causing material structure damage and pulverization, accelerating capacity decay, and shortening the battery's cycle life. It also easily leads to localized stress concentration, increasing the risk of material cracking, reducing the overall mechanical strength of the electrode, and increasing the risk of thermal runaway.

[0141] 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 within the protection scope of the present invention.

Claims

1. A battery cell, characterized in that: The battery cell comprises a positive electrode, a separator, and a negative electrode; the positive electrode, the separator, and the negative electrode are sequentially stacked and formed by winding or stacking; the positive electrode includes a positive current collector and a positive active material layer coated on the surface of the positive current collector; the positive active material layer includes a positive active material, a first conductive agent, and a first binder, wherein the positive active material includes lithium cobalt oxide, the particle size of which is d1 in μm, and the value of d1 ranges from 0 μm to 2 μm; the negative electrode includes 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 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-type compound; 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 current collector; the lithium cobalt oxide agglomerates during the formation of the positive electrode slurry, and the particle size of the agglomerated lithium cobalt oxide is d2, in μm, and the value of d2 ranges from 3μm to 4.5μm; based on the total mass of the positive electrode active material as 100%, the agglomerated lithium cobalt oxide particles account for 15%-25% of the mass of the positive electrode active material.

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

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

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

5. The battery cell according to claim 1, characterized in that: The double-sided areal density of the positive electrode active material layer is 240~360 g / m². 2 .

6. The battery cell according to claim 1, characterized in that: The compaction density of the positive electrode active material layer is 4.0–4.3 g / cm³. 3 .

7. The battery cell according to claim 1, characterized in that: The double-sided areal density of the negative electrode active material layer is 94~174 g / m². 2 .

8. The battery cell according to claim 1, characterized in that: The compaction density of the negative electrode active material layer is 1.6–1.8 g / cm³. 3 .

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

10. The battery cell according to claim 1, characterized in that: The positive electrode active material further includes 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.

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

12. 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 further includes SBR.

13. A lithium-ion battery, characterized in that: The battery includes a battery casing, an electrolyte, and a battery cell as described in any one of claims 1-12, wherein the battery cell is placed inside the battery casing, the electrolyte is injected into the battery casing, and the battery is encapsulated to form the lithium-ion battery.

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