Lithium-ion batteries, cells and assemblies and electric devices

Abstract

The application relates to the technical field of batteries, in particular to a lithium ion battery, a battery assembly and a power utilization device, the lithium ion battery comprising a shell and a pole core packaged in the shell; the pole core comprises a positive pole sheet, a negative pole sheet, an electrolyte and a separator; the lithium ion battery satisfies: 0.70 <= (W 负 / V+0.38) x (1.43M1+2.60M2+60W 补 / W 正 ) <= 1.65. The probability of thermal runaway and thermal diffusion of the lithium ion battery is obviously reduced, the safety is remarkably improved, and meanwhile, the lithium ion battery has higher capacity, lower internal resistance and longer cycle life.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to lithium-ion batteries, battery modules, and electrical devices. Background Technology

[0002] Lithium-ion batteries are currently widely used in electric vehicles, energy storage systems, and mobile devices, especially in power batteries, where development has been rapid. Further improving the energy density, power performance, and cycle life of lithium-ion batteries is key to enhancing industry competitiveness. Current methods for improving lithium-ion battery performance include increasing electrode areal density, introducing lithium replenishing agents, and optimizing electrolytes. While these methods can improve performance to some extent, they also introduce problems such as deteriorating battery safety and triggering thermal runaway. Therefore, lithium-ion battery technologies still require further improvement. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a lithium-ion battery and electrical device that maintains high capacity, low internal resistance, or long cycle life while significantly reducing the risk of thermal runaway.

[0004] In a first aspect, this application provides a lithium-ion battery. According to an embodiment of this application, the lithium-ion battery includes a casing and an electrode core encapsulated within the casing; the electrode core includes a positive electrode sheet, a negative electrode sheet, and an electrolyte; the positive electrode sheet includes a positive electrode coating layer, the positive electrode coating layer including a positive electrode lithium replenishing agent; the negative electrode sheet includes a negative electrode coating layer; the electrolyte contains a lithium salt, the lithium salt including at least one selected from lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI); the lithium-ion battery satisfies:

[0005] 0.70≤(W 负 / V+0.38)×(1.43M1+2.60M2+60W 补 / W 正 ≤1.65

[0006] Among them, W 负 The mass of the negative electrode dressing layer; W 补 The mass of the positive electrode lithium replenisher; W 正 M1 is the mass of the positive electrode coating layer; M2 is the molar concentration of LiPF6 in the electrolyte; M3 is the molar concentration of LiFSI in the electrolyte; V is the volume of the lithium-ion battery; where mass is in g, molar concentration is in mol / L, and volume is in cm³. 3 .

[0007] This application employs a synergistic optimization design of battery size, negative electrode coating layer quality, positive electrode lithium replenishment agent dosage, positive electrode coating layer quality, and the molar concentrations of lithium salts LiPF6 and LiFSI in the electrolyte. While maintaining high capacity, low internal resistance, and long cycle life of the lithium-ion battery, it significantly improves the safety of the lithium-ion battery. Lithium-ion batteries that meet the above conditions have a significantly reduced probability of thermal runaway or thermal diffusion, and largely avoid damage to themselves, adjacent lithium-ion batteries, or external sources caused by heat generated by the lithium-ion battery.

[0008] According to an embodiment of this application, W 补 Satisfying 0 < W 补 / W 正 ≤0.02.

[0009] According to an embodiment of this application, W 补 Satisfying 0 < W 补 / W 正 ≤0.006.

[0010] According to an embodiment of this application, M1 and M2 satisfy: 0.6≤M1+M2≤1.5.

[0011] According to an embodiment of this application, M1 and M2 satisfy: 0.8≤M1+M2≤1.2.

[0012] According to an embodiment of this application, M2 satisfies: 0 < M2 ≤ 1.5.

[0013] According to an embodiment of this application, M1 satisfies: 0 < M1 ≤ 1.5.

[0014] According to an embodiment of this application, W 负 Satisfying 0.42≤W 负 / V≤0.48.

[0015] According to an embodiment of this application, W 正 Satisfying 0.85≤W 正 / V≤1.0.

[0016] According to an embodiment of this application, W 正 With W 负 Satisfying 0.42≤W 负 / W 正 ≤0.56.

[0017] According to an embodiment of this application, the lithium-ion battery is a square battery and satisfies at least one of the following conditions:

[0018] L:H = (2~20):1;

[0019] H:D = (5~10):1;

[0020] L is 40cm to 150cm;

[0021] Wherein, L is the length of the lithium-ion battery in cm; H is the width of the lithium-ion battery in cm; and D is the thickness of the lithium-ion battery in cm.

[0022] According to embodiments of this application, the lithium-ion battery satisfies at least one of the following conditions:

[0023] The positive electrode lithium replenishing agent includes at least one of Li5FeO4, Li2O, Li2CO3 and LiNO3;

[0024] The positive electrode dressing layer includes a positive electrode active material, which includes lithium iron phosphate.

[0025] The negative electrode dressing layer includes a negative electrode active material, which includes at least one of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, and lithium titanate.

[0026] The electrolyte also includes a solvent, which includes one or more of carbonate solvents, ether solvents, and carboxylic acid ester solvents;

[0027] The electrolyte also includes additives, which include at least one of vinylene carbonate, fluoroethylene carbonate, propylene sulfite, and methylene disulfonate.

[0028] According to an embodiment of this application, the negative electrode active material includes graphite.

[0029] According to embodiments of this application, the solvent includes at least one selected from ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, and ethylene glycol dimethyl ether.

[0030] In a second aspect, this application provides a battery assembly. According to embodiments of this application, the battery and assembly include the lithium-ion battery described above. This battery assembly has high capacity, low internal resistance, and long cycle life, while also having a low risk of thermal runaway.

[0031] A third aspect of this application provides an electrical device. According to embodiments of this application, the electrical device includes the lithium-ion battery or battery assembly described above. This electrical device incorporates all the features and advantages of the lithium-ion battery or battery assembly described above, which will not be repeated here. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the heat generation caused by the breaking of numerous SF and SN bonds in LiFSI.

[0033] Figure 2 This is a schematic diagram of the structure of a lithium-ion battery according to an embodiment of this application. Detailed Implementation

[0034] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0035] This application is based on the inventor's discoveries and understanding of the following facts and problems:

[0036] With continuous technological development and advancement, increasingly higher demands are being placed on the energy density, power performance, and cycle life of lithium-ion batteries. Currently, improving energy density is mainly achieved by increasing electrode surface density and introducing positive electrode lithium replenishment agents. However, increasing electrode surface density leads to a sharp increase in battery impedance, degrading battery performance. Introducing positive electrode lithium replenishment agents to compensate for the active lithium consumed in SEI film formation can improve energy density without degrading power performance, or even improve it. However, these agents have poor thermal stability and easily release oxygen at high temperatures. Oxygen can react with the electrolyte and negative electrode active materials, leading to increased battery heat generation. Optimizing electrolyte composition can also reduce battery impedance and extend battery life, but various electrolyte components are also prone to reacting with negative electrode active materials, leading to increased battery heat generation, causing thermal runaway, and potentially resulting in serious consequences such as fire and explosion. The inventors have discovered that current lithium-ion battery designs optimize various factors independently, lacking coordinated control, making it difficult to balance the relationship between battery performance and thermal safety.

[0037] The inventors of this application considered that, for lithium-ion batteries, the heat generated during thermal runaway mainly originates from the electrolyte, the negative electrode, and the reaction between the negative electrode and the electrolyte. The high-temperature instability of the positive electrode lithium replenishment agent may exacerbate the reaction between the electrolyte and the negative electrode active material, leading to a significant increase in heat generation in the lithium-ion battery, thereby inducing thermal runaway.

[0038] In view of this, in order to improve the performance of lithium-ion batteries, it is necessary to increase the electrode surface density, introduce lithium replenishing agents, and optimize the electrolyte lithium salt, but this significantly increases the risk of thermal runaway. Based on a comprehensive consideration of the above-mentioned main factors, the inventors have rationally designed the key heat-generating factors. By controlling the amount of key heat-generating factors, the risk of battery thermal runaway or thermal diffusion is greatly reduced. At the same time, it can also make the improvement methods such as increasing the electrode surface density, introducing lithium replenishing agents, and optimizing the electrolyte lithium salt fully effective. The lithium-ion battery can maintain high capacity, low internal resistance, and long life.

[0039] A first aspect of this application provides a lithium-ion battery. According to an embodiment of this application, the lithium-ion battery includes a casing and an electrode core encapsulated within the casing; the electrode core includes a positive electrode sheet, a negative electrode sheet, and an electrolyte; the positive electrode sheet includes a positive electrode coating layer, the positive electrode coating layer including a positive electrode lithium replenishing agent; the negative electrode sheet includes a negative electrode coating layer; the electrolyte contains a lithium salt, the lithium salt including at least one selected from lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI); the lithium-ion battery satisfies:

[0040] 0.70≤A=(W 负 / V+0.38)×(1.43M1+2.60M2+60W 补 / W 正 ≤1.65

[0041] Among them, W 负 The mass of the negative electrode dressing layer; W 补 The mass of the positive electrode lithium replenisher; W 正 M1 is the mass of the positive electrode coating layer; M2 is the molar concentration of LiPF6 in the electrolyte; M3 is the molar concentration of LiFSI in the electrolyte; V is the volume of the lithium-ion battery; where mass is in g, molar concentration is in mol / L, and volume is in cm³. 3 .

[0042] This application employs a synergistic optimization design of battery size, negative electrode coating layer mass, positive electrode lithium replenishment agent dosage, positive electrode coating layer mass, and lithium salt molar concentration in the electrolyte. By controlling the negative electrode coating layer mass, positive electrode lithium replenishment agent dosage, lithium salt molar concentration, and positive electrode coating dosage per unit volume of the battery, the safety of lithium-ion batteries is significantly improved. Lithium-ion batteries meeting the above conditions have a significantly reduced probability of thermal runaway or thermal diffusion, largely avoiding damage to adjacent lithium-ion batteries or external sources caused by heat generated by the lithium-ion battery. Furthermore, these lithium-ion batteries exhibit higher capacity, lower internal resistance, and longer cycle life. In the lithium-ion batteries of this application, the thermal safety risk increases with higher A values.

[0043] As an example, A can be 0.7–1.5, 0.7–1.3, 0.7–1.2, etc.; specifically, it can be 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.65, etc. Therefore, lithium-ion batteries, while possessing high capacity, low internal resistance, and long cycle life, also exhibit significantly improved safety, with a markedly reduced probability of thermal runaway and thermal diffusion.

[0044] It is understood that the negative electrode sheet may include a negative electrode current collector and a negative electrode dressing layer disposed on at least one side of the negative electrode current collector. The negative electrode dressing layer may include a negative electrode active material, a negative electrode binder and a negative electrode conductive agent, and may also add additives with specific functions and effects, such as thickeners (e.g., sodium carboxymethyl cellulose CMC-Na), film-forming additives, flame retardants, high-temperature / low-temperature stabilizers, etc., as needed.

[0045] According to embodiments of this application, the negative electrode current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, copper foil current collectors; composite current collectors may include a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.) and a metal layer (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) formed on at least one surface of the polymer material base layer.

[0046] In some embodiments of this application, the negative electrode active material includes at least one selected from graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, and lithium titanate. In some specific examples, the negative electrode active material includes graphite. Therefore, there is less reaction between the negative electrode and the electrolyte, which can effectively reduce heat generation in the lithium-ion battery, lower the risk of thermal runaway, and simultaneously achieve higher capacity and lower internal resistance.

[0047] In some embodiments of this application, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0048] In some embodiments of this application, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0049] In some embodiments of this application, the negative electrode coating layer comprises a negative electrode active material, a conductive agent, a binder, and a thickener in a mass ratio of (90-98):(0-2):(1-5):(1-5). As an example, the negative electrode coating layer comprises graphite, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose in a mass ratio of (90-98):(0-2):(1-5):(1-5). With the above-mentioned components, the negative electrode coating layer exhibits less reaction between the negative electrode and the electrolyte, effectively reducing heat generation in the lithium-ion battery and lowering the risk of thermal runaway, while also possessing high capacity and low internal resistance.

[0050] It is understandable that for lithium-ion batteries, the reaction between the negative electrode and the electrolyte is one of the main sources of heat leading to battery thermal runaway. The amount of negative electrode coating is one of the main factors affecting the reaction between the negative electrode and the electrolyte. Therefore, by reasonably controlling the amount of negative electrode coating per unit volume of battery and coordinating it with electrolyte, the risk of battery thermal runaway can be effectively reduced.

[0051] In some embodiments of this application, W 负 Satisfying 0.42≤W 负 / V≤0.48. As an example, W 负 / V can be 0.43–0.47, 0.42–0.45, 0.43–0.48, etc., specifically 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, etc. Specifically, by controlling the mass of the negative electrode coating layer per unit volume within the above range, the capacity of lithium-ion batteries can be further improved while maintaining good safety performance.

[0052] It is understood that the positive electrode sheet may include a current collector and a positive electrode coating layer disposed on at least one side of the current collector. The positive electrode coating layer may include positive electrode active material, positive electrode lithium supplement, positive electrode conductive agent and positive electrode binder, and may also include additives with specific functions and effects, such as lithium supplement, film-forming additive, flame retardant, high temperature / low temperature stabilizer, etc., as needed.

[0053] In some embodiments, the positive current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, aluminum foil current collectors; composite current collectors may include a polymer base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.) and a metal layer (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) formed on at least one surface of the polymer base film.

[0054] In some embodiments of this application, the positive electrode active material may include at least one of the following: layered positive electrode active materials (e.g., nickel-cobalt-manganese ternary positive electrode materials, nickel-cobalt-aluminum ternary positive electrode materials, lithium nickel oxide / sodium, lithium cobalt oxide / sodium, lithium manganese oxide / sodium, lithium-rich / sodium layered and rock salt phase layered materials), olivine-type phosphate active materials (e.g., lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, etc.), and spinel-structured positive electrode active materials (e.g., spinel lithium manganese oxide, spinel lithium nickel manganese oxide, lithium-rich spinel lithium manganese oxide, and lithium nickel manganese oxide, etc.). It is understood that the above-mentioned positive electrode active materials may further include doping elements and coating layers. As a specific example, the positive electrode active material includes lithium iron phosphate. Therefore, the lithium-ion battery has better cycle stability and safety performance.

[0055] In some embodiments of this application, the specific type of positive electrode lithium replenishing agent is not particularly limited, as long as it can effectively perform the lithium replenishing function. In some embodiments, the positive electrode lithium replenishing agent includes at least one of Li5FeO4, Li2O, Li2CO3, and LiNO3. Therefore, it can fully exert the lithium replenishing function, improve the energy density and cycle life of the battery, and at the same time, it can work in conjunction with other factors to greatly reduce the risk of thermal runaway and thermal diffusion in lithium-ion batteries, thereby improving the safety performance of lithium-ion batteries.

[0056] According to embodiments of this application, the positive electrode lithium replenisher can compensate for the loss of active lithium during the first charge-discharge cycle of a lithium-ion battery, thereby increasing the energy density of the lithium-ion battery, extending its lifespan, and slowing down capacity decay. Furthermore, the decomposition products of the positive electrode lithium replenisher can participate in the formation of the negative electrode film, improving the power performance of the lithium-ion battery. However, at high temperatures, the positive electrode lithium replenisher may release oxygen, intensifying the reaction between the electrolyte and the negative electrode active material, releasing a large amount of heat, which may cause a sharp change in the self-temperature rise rate of the lithium-ion battery, thereby inducing thermal runaway.

[0057] Taking the positive electrode lithium replenishing agent Li5FeO4 as an example, it will decompose and release oxygen at high temperature. The oxygen will intensify the reaction of the electrolyte and the negative electrode active material as shown in Equations 1, 2, and 3, resulting in a significant increase in the heat generation of the lithium-ion battery, which in turn induces thermal runaway.

[0058]

[0059] 4Li + O₂ → 2lI₂o (Equation 3)

[0060] In some embodiments of this application, W 补 Satisfying 0 < W 补 / W 正 ≤0.02. In other embodiments of this application, W 补 Satisfying 0 < W 补 / W 正 ≤0.006. As an example, W 补 / W 正 It can satisfy 0 < W 补 / W 正 ≤0.01, 0.001<W 补 / W 正 ≤0.006, 0.001 < W 补 / W 正 ≤0.005, etc., W 补 / W 正Specifically, these can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, etc. W 补 / W 正 Within the aforementioned range, it can fully play its role in compensating for the loss of active lithium and participating in the formation of the negative electrode film. At the same time, it can work synergistically with other aspects of lithium-ion batteries (such as battery volume, the quality of the negative electrode coating layer, and the molar concentration of lithium salts LiPF6 and LiFSI in the electrolyte). This will not only improve the capacity of lithium-ion batteries but also enhance their thermal stability and reduce the risk of thermal runaway.

[0061] In some embodiments of this application, the positive electrode adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. This allows the positive electrode dressing layer to adhere well to the positive electrode current collector, resulting in strong adhesion and reducing the likelihood of problems such as positive electrode dressing detachment.

[0062] In some embodiments of this application, the positive electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. This effectively improves conductivity, reduces internal resistance, and enhances the electrochemical performance of lithium-ion batteries.

[0063] As mentioned earlier, although the positive electrode coating layer has relatively high stability for lithium-ion batteries, it is the main limiting factor for battery capacity. By reasonably controlling the amount of positive electrode coating layer per unit volume of battery and coordinating it with electrolyte, the battery capacity can be effectively improved.

[0064] In some embodiments of this application, W 正 Satisfying 0.85≤W 正 / V≤1.0. As an example, 0.9≤W 正 / V≤0.95、0.85≤W 正 / V≤0.9、0.9≤W 正 / V≤1.0 etc., W 正The specific values ​​for / V can be 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, etc. Specifically, by controlling the mass of the positive electrode coating layer per unit volume within the above range, lithium-ion batteries can achieve higher capacity.

[0065] In some embodiments of this application, W 正 With W 负 Satisfying 0.42≤W 负 / W 正 ≤0.56. As an example, 0.45≤W 负 / W 正 ≤0.55, 0.42≤W 负 / W 正 ≤0.5, 0.48≤W 负 / W 正 ≤0.55, etc., W 负 / W 正 Specifically, the values ​​can be 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, etc. W 负 / W 正 Within the aforementioned range, the matching degree between the positive and negative electrodes of lithium-ion batteries is higher, resulting in higher capacity of lithium-ion batteries.

[0066] According to embodiments of this application, the electrolyte may include lithium salt and solvent. Furthermore, additives with specific functions, such as film-forming additives, lithium replenishing agents, flame retardants, thermal stability additives, etc., may also be added to the electrolyte as needed.

[0067] In some embodiments of this application, the lithium salt in the electrolyte may include at least one of LiFSI and LiPF6. As an example, the lithium salt in the electrolyte may include both LiFSI and LiPF6. Specifically, LiPF6 can provide lithium ions to the lithium-ion battery, support the stability of the electrolyte and electrochemical reactions, help form a protective SEI film, improve conductivity, and enhance the safety of the lithium-ion battery. LiFSI, on the other hand, has high conductivity and excellent electrochemical stability. Using LiFSI and LiPF6 together in the electrolyte can significantly improve electrolyte conductivity, reduce viscosity, reduce battery impedance, improve the power performance of the lithium-ion battery, and extend battery life. Furthermore, LiFSI can stabilize PF5 (a decomposition product of LiPF6), reduce the HF content and dissolved iron content in the lithium-ion battery system, and extend the life of the lithium-ion battery.

[0068] Although LiFSI and LiPF6 have the aforementioned advantages, LiPF6 is prone to hygroscopic decomposition, while LiFSI may undergo a reduction reaction with the negative electrode active material at high temperatures. This reduction reaction releases a large amount of heat, and the breaking of numerous SF and SN bonds in LiFSI leads to a significant increase in heat generation (see schematic diagram of the exothermic reaction caused by SF and SN bond breaking). Figure 1 This can cause a sharp change in the self-temperature rise rate of lithium-ion batteries, which can then induce thermal runaway. Therefore, by appropriately controlling the molar concentration of [specific component], the safety of lithium-ion batteries can be improved without significantly affecting their capacity, internal resistance, and cycle life.

[0069] In some embodiments of this application, M1 satisfies: 0 < M1 ≤ 1.4. For example, 0.01 < M1 ≤ 1.4, 0.01 < M1 ≤ 1.2, 0.1 < M1 ≤ 1.0, 0.2 < M1 ≤ 1.0, etc., and M1 can specifically be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, etc. When the molar concentration of LiPF6 in the electrolyte is within the above range, it can provide lithium ions for the lithium-ion battery, support the stability of the electrolyte and electrochemical reactions, help form a protective SEI film, improve conductivity, and enhance the safety of the lithium-ion battery. Meanwhile, by coordinating with factors such as battery volume, the quality of the negative electrode coating layer, the amount of positive electrode lithium replenishing agent, the quality of the positive electrode coating layer, and the molar concentration of LiFSI in the electrolyte, the capacity of lithium-ion batteries can be increased while improving their thermal stability and reducing the risk of thermal runaway.

[0070] In some embodiments of this application, M2 satisfies: 0 < M2 ≤ 1.4. For example, 0.01 < M2 ≤ 1.4, 0.01 < M2 ≤ 1.2, 0.1 < M2 ≤ 1.0, 0.2 < M2 ≤ 1.0, etc., where M2 can specifically be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, etc. When the molar concentration of LiFSI in the electrolyte is within the above range, it can effectively improve the conductivity of the electrolyte and reduce viscosity, thereby reducing battery impedance, improving the power performance of the lithium-ion battery, and extending battery life. Simultaneously, in synergy with battery volume, the quality of the negative electrode coating layer, the amount of positive electrode lithium supplementer, the quality of the positive electrode coating layer, and the molar concentration of LiPF6 in the electrolyte, it can improve the capacity of the lithium-ion battery while simultaneously enhancing its thermal stability and reducing the risk of thermal runaway.

[0071] In some embodiments of this application, M1 and M2 satisfy the following condition: 0.6 ≤ M1 + M2 ≤ 1.4. In other embodiments of this application, M1 and M2 satisfy the following condition: 0.8 ≤ M1 + M2 ≤ 1.2. In other embodiments of this application, M1 and M2 satisfy the following condition: 0.6 ≤ M1 + M2 ≤ 1.0. In other embodiments of this application, M1 and M2 satisfy the following condition: 0.8 ≤ M1 + M2 ≤ 1.0. As an example, M1 + M2 can specifically be 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, etc. When the molar concentration of lithium salt in the electrolyte is within the above range, the electrolyte has high conductivity and low viscosity, which is beneficial for reducing the internal resistance of lithium-ion batteries. Simultaneously, it can synergistically work with other aspects of lithium-ion batteries to reduce the risk of thermal runaway and improve the thermal stability and safety performance of lithium-ion batteries.

[0072] In some embodiments of this application, the solvent in the electrolyte may include one or more of carbonate solvents, ether solvents, and carboxylic acid ester solvents. As an example, the solvent in the electrolyte may include at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, and ethylene glycol dimethyl ether.

[0073] In some embodiments of this application, the electrolyte further includes additives, including at least one selected from vinylene carbonate, fluoroethylene carbonate, propylene sulfite, and methane disulfonate. This facilitates the formation of an SEI film on the negative electrode surface, reduces side reactions, and improves the electrochemical performance of the lithium-ion battery.

[0074] According to an embodiment of this application, the lithium-ion battery further includes a separator located between the positive electrode and the negative electrode. Specifically, there is no particular limitation on the type of separator, which can be a conventional polyethylene separator, a polypropylene separator, a polyethylene-polypropylene composite separator, etc. Depending on the application requirements, a functional coating (such as a ceramic coating) can also be further provided on the above-mentioned separator.

[0075] According to embodiments of this application, the electrode core can be a wound electrode core (i.e., a electrode core is formed by winding positive electrode sheets, negative electrode sheets, and separators stacked together) or a stacked electrode core (i.e., multiple positive electrode sheets, negative electrode sheets, and separators stacked together to form an electrode core). The outer shell can be a hard shell (such as a steel shell, hard plastic shell, etc.) or a soft shell (such as an aluminum-plastic film, pouch-type soft shell, etc.). According to embodiments of this application, the shape of the lithium-ion battery is not particularly limited; it can be cylindrical, square, etc.

[0076] It is understandable that the size of a lithium-ion battery affects the internal heat transfer rate and heat output intensity. Therefore, appropriate optimization of the size of a lithium-ion battery can further improve its safety.

[0077] In some embodiments of this application, the lithium-ion battery is a square battery (see structural schematic diagram). Figure 2 The length L of the lithium-ion battery is greater than its width H, and the width H of the battery body is greater than its thickness D. Wherein, L is the length of the lithium-ion battery in cm; H is the width of the lithium-ion battery in cm; and D is the thickness of the lithium-ion battery in cm. In some embodiments, L:H = (2-20):1; H:D = (5-10):1; and L can be 40cm-150cm. As an example, L:H can be (2-15):1, (5-15):1, (5-20):1, and more specifically, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, etc.; H:D can be (6-10):1. The ratios can be (5-8):1, (6-8):1, etc., or more specifically, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.; L can be 40cm-150cm, 100cm-150cm, 80cm-150cm, 40cm-100cm, etc., or more specifically, 40cm, 60cm, 80cm, 100cm, 120cm, 140cm, 150cm, etc. Lithium-ion batteries that meet the above size requirements can dissipate heat more quickly, reducing the probability of thermal runaway and thermal diffusion. Furthermore, they can be combined with other factors to effectively improve the safety performance of lithium-ion batteries.

[0078] In a second aspect, this application provides a battery assembly. According to embodiments of this application, the battery assembly includes the lithium-ion battery described above. This battery assembly simultaneously possesses high energy density, good fast-charging performance, long cycle life, and good safety performance.

[0079] According to embodiments of this application, the specific type of battery assembly is not particularly limited, and includes, but is not limited to, battery modules and battery packs. It is understood that the specific structure of battery modules and battery packs can refer to conventional technology, and this application does not impose any particular limitations.

[0080] A third aspect of this application provides an electrical device. According to an embodiment of this application, the electrical device includes the lithium-ion battery described above. This electrical device has superior battery life, fast charging capability, and a longer service life, while also significantly improving safety performance.

[0081] According to embodiments of this application, the specific type of electrical device is not particularly limited and can be any device that uses a lithium-ion battery as a power source or energy storage unit. As examples, electrical devices include, but are not limited to, electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (e.g., mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, etc.

[0082] It is understandable that, in addition to the lithium-ion battery mentioned above, the electrical device also includes other necessary structures and components, all of which can be made with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.

[0083] The embodiments of this application are described in detail below.

[0084] Example 1

[0085] Positive electrode preparation: Following a weight ratio of lithium iron phosphate, conductive carbon black, polyvinylidene fluoride (PVDF), and positive electrode lithium supplementer of 96.7:0.8:2.4:0.1, PVDF (binder) was added to N-methylpyrrolidone (solvent) and stirred until dissolved. Then, conductive carbon black (conductive agent), lithium iron phosphate (positive electrode active material), and positive electrode lithium supplementer Li5FeO4 were added and thoroughly kneaded to obtain a positive electrode slurry. This positive electrode slurry was uniformly coated onto a current collector aluminum foil, and after baking and rolling, a positive electrode sheet was obtained.

[0086] Negative electrode preparation: The negative electrode active material graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR) and thickener CMC are mixed in a mass ratio of 93:1:4:2, and deionized water is added as solvent. The mixture is kneaded thoroughly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on the current collector copper foil, and then baked and rolled to obtain a negative electrode sheet.

[0087] Electrolyte composition: Ethyl carbonate EC, ethyl methyl carbonate EMC, and diethyl carbonate DMC were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and vinylene carbonate (VC) were added to the above mixed solvent (in Example 1, the mass percentages were 7.3% for LiPF6, 0.2% for LiFSI, and 4% for VC) to obtain the electrolyte.

[0088] Separator: Composite membrane, with a base membrane of 9mm thick polyethylene (PE) membrane, one side of the base membrane has a 1mm thick organic coating, and the other side has a 1mm thick ceramic coating.

[0089] Battery assembly process: The positive electrode, negative electrode and separator of the battery are stacked to form a cell, which is then packaged and injected with electrolyte to obtain the battery.

[0090] See Table 1 for other specific parameters.

[0091] Examples 2-30

[0092] Same as Example 1, with specific differences shown in Table 1.

[0093] Comparative Examples 1-9

[0094] Same as Example 1, with specific differences shown in Table 1.

[0095] Performance testing:

[0096] 1. Positive Electrode Coating Layer Mass: ① Disassemble the battery, separate all positive electrode sheets, and measure the weight, length, and width of the electrode sheets. Use a sheet cutter to cut 15mm diameter foil discs from the tabs, and measure the weight of the cut foil discs. Based on the weight and area of ​​the cut foil discs, as well as the length and width of the positive electrode sheets, calculate the total weight of the foil material in the positive electrode sheet. Positive electrode coating layer mass = electrode sheet weight - total weight of electrode foil material. ② Directly weigh the positive electrode coating mass (i.e., the sum of the masses of lithium iron phosphate, conductive carbon black, polyvinylidene fluoride, and positive electrode lithium supplement) during the lithium-ion battery manufacturing process.

[0097] 2. Quality of negative electrode dressing layer: Same as quality of positive electrode dressing layer.

[0098] 3. Mass of the positive electrode lithium replenisher: ① The composition of the lithium replenisher is determined by X-ray diffraction (XRD). Taking Li5FeO4 as an example, the Li, Fe, and P contents in the positive electrode are measured using ICP-OES. Since the lithium replenisher does not contain P, the mass of the lithium replenisher in the positive electrode can be calculated by the difference in the Li, Fe, and P contents. ② The amount of positive electrode lithium replenisher added is directly recorded during the lithium-ion battery manufacturing process.

[0099] 4. Molar concentrations of LiFSI and LiPF6 in the electrolyte: ① Disassemble the battery to collect the free electrolyte, and quantitatively determine PF6 using ion chromatography (IC) with a standard curve. - and FSI - The molar concentrations of LiFSI and LiPF6 in the electrolyte can be calculated based on the measured content and the volume of electrolyte extracted. ② The molar concentrations of LiFSI and LiPF6 are directly recorded during electrolyte preparation. ③ The freshly prepared electrolyte (i.e., the electrolyte before lithium-ion battery injection) is quantitatively determined using ion chromatography (IC) with a standard curve to measure PF6. - and FSI -Based on the measured content and the volume of extracted electrolyte, the molar concentrations of LiFSI and LiPF6 in the electrolyte can be calculated.

[0100] 5. Length, width, and thickness of lithium-ion batteries: Measure the length and width of lithium-ion batteries with a film ruler and measure the battery thickness with a micrometer thickness gauge.

[0101] 6. Needle Penetration Test: The test was conducted according to the method specified in GB / T 31485-2015 Safety Requirements and Test Methods for Power Batteries for Electric Vehicles. The specific needle penetration procedure was as follows: ① Charging: At room temperature, the batteries prepared in each example and comparative example were first discharged at 1C to 2.0V, rested for 5 minutes, then discharged at 0.2C to 2.0V, rested for 30 minutes, then charged at 1C to 3.65V, rested for 5 minutes, and then charged at 0.2C to 3.65V; ② Needle Penetration: A high-temperature resistant steel needle with a diameter taper of 45° was used to penetrate the lithium-ion battery from a direction perpendicular to the lithium-ion battery plate at a speed of (25±5) mm / s. The penetration position should be close to the geometric center of the pierced surface. The steel needle remained in the lithium-ion battery for 1 hour for observation. The test results are shown in Table 1.

[0102] 7. High-Temperature Cycling Test: ① Place the battery in a 60±3℃ oven for 4 hours. ② Charge the battery at 1C to 3.65V at 60±3℃, let it rest for 5 minutes, then charge it again at 0.2C to 3.65V. ③ Let the battery rest for 30 minutes at 60±3℃. ④ Discharge the battery at 1C to 2.0V at 60±3℃, let it rest for 5 minutes, then discharge it again at 0.2C to 2.0V. ⑤ Let the battery rest for 30 minutes at 60±3℃. ⑥ Cycle steps ② to ⑤ 1000 times and record the capacity retention rate of the lithium-ion battery. The test results are shown in Table 1.

[0103] 8. Capacity Test: ① Charging: At room temperature (25±3℃), charge at a constant current of 1C to 3.65V, let stand for 5 minutes, then charge at 0.2C to 3.65V, let stand for 30 minutes; ② Discharging: At room temperature (25±3℃), discharge at a constant current of 1 / 3C to 2.0V, let stand for 30 minutes; ③ Repeat the charge and discharge three times, and record the capacity of the third discharge. The test results are shown in Table 1.

[0104] 9. DC Internal Resistance Test: ① Adjusting SOC (State of Charge): At room temperature, the battery is first charged at 1C to 3.65V, left to rest for 5 minutes, then charged at 0.2C to 3.65V, left to rest for 30 minutes; then discharged at 0.5C for 90 minutes; ② Rest for 2 hours; ③ Impedance Test: The battery is discharged at 1.5C for 10 seconds; ④ Record the last voltage data from ② and ③, labeling them V1 and V2 respectively. Calculate the DCIR value using the following formula: DCIR discharge = (V1 - V2) / 1.5C capacity × 1000 (unit: mΩ). The test results are shown in Table 1.

[0105] Table 1

[0106]

[0107]

[0108]

[0109]

[0110]

[0111]

[0112] Note: A=(W in the above table 负 / V+0.38)×(1.43M1+2.60M2+60W 补 / W 正 ), V=L×H×D.

[0113] As can be seen from the test data in Table 1, when the A value is within the range of 0.70 to 1.65, the lithium-ion battery has better capacity, capacity retention rate (%) after 1000 cycles at 60℃, discharge DCIR, and nail penetration test results. If the A value is too low, the lithium-ion battery has higher capacity, capacity retention rate (%) after 1000 cycles at 60℃, and discharge DCIR. However, if the A value is too high, the battery safety is poor and it cannot pass the nail penetration test.

[0114] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0115] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a housing and an electrode core encapsulated within the housing; the electrode core includes a positive electrode, a negative electrode, and an electrolyte; The positive electrode sheet includes a positive electrode coating layer, which contains a positive electrode lithium replenishing agent; the negative electrode sheet includes a negative electrode coating layer; the electrolyte contains a lithium salt, which includes at least one of lithium hexafluorophosphate and lithium difluorosulfonylimide. The lithium-ion battery satisfies: 0.70≤(W 负 / V+0.38)×(1.43M1+2.60M2+60W 补 / IN 正 )≤1.65 Among them, W 负 The mass of the negative electrode dressing layer; W 补 The mass of the positive electrode lithium replenisher; W 正 M1 is the mass of the positive electrode coating layer; M2 is the molar concentration of lithium hexafluorophosphate in the electrolyte; M3 is the molar concentration of lithium difluorosulfonylimide in the electrolyte; V is the volume of the lithium-ion battery; wherein, the unit of mass is g, the unit of molar concentration is mol / L, and the unit of volume is cm3. 3 ; 0<W 补 / IN 正 ≤0.02; 0.6≤M1+M2≤1.5; 0＜M2≤1.5； 0＜M1≤1.5； 0.85≤W 正 / V≤1.0; 0.42≤W 负 / V≤0.48; 0.42≤W 负 / IN 正 ≤0.56; The positive electrode lithium replenishing agent includes at least one of Li5FeO4, Li2O, Li2CO3 and LiNO3; The positive electrode dressing layer includes a positive electrode active material, which includes an olivine-type phosphate active substance. The negative electrode dressing layer includes a negative electrode active material, which includes at least one of graphite, soft carbon, hard carbon, carbon fiber, and mesophase carbon microspheres. The electrolyte also includes a solvent, which includes one or more of carbonate solvents, ether solvents, and carboxylic acid ester solvents.

2. The lithium-ion battery according to claim 1, characterized in that, W 补 Satisfying 0 < W 补 / W 正 ≤0.

006.

3. The lithium-ion battery according to claim 1, characterized in that, M1 and M2 satisfy: 0.8≤M1+M2≤1.

2.

4. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery is a square battery and meets at least one of the following conditions: L:H = (2~20):1; H:D = (5~10):1; L is 40cm~150cm; Wherein, L is the length of the lithium-ion battery in cm; H is the width of the lithium-ion battery in cm; and D is the thickness of the lithium-ion battery in cm.

5. The lithium-ion battery according to claim 1, characterized in that, At least one of the following conditions must be met: The positive electrode active material includes lithium iron phosphate; The electrolyte also includes additives, which include at least one of vinylene carbonate, fluoroethylene carbonate, propylene sulfite, and methylene disulfonate.

6. The lithium-ion battery according to claim 1, characterized in that, The negative electrode active material includes graphite.

7. The lithium-ion battery according to claim 1, characterized in that, The solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, and ethylene glycol dimethyl ether.

8. A battery assembly, characterized in that, The lithium-ion battery includes any one of claims 1 to 7.

9. An electrical device, characterized in that, Includes the lithium-ion battery according to any one of claims 1 to 7 or the battery assembly according to claim 8.

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