Lithium batteries and electrical devices

Abstract

The lithium battery and electrical device are described. The lithium battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The negative electrode plate includes a current collector and a negative electrode active material layer provided on the surface of the current collector. The electrolyte includes a lithium salt, an organic solvent, and an additive, and the additive includes a fluorinated carbonate and a nitrile material. The negative electrode active material layer has a thickness D of 1 μm. The particle size corresponding to when the cumulative volume percentage of the negative electrode active material in the negative electrode active material layer reaches 50% is D. v 50 μm, and the particle size corresponding to when the cumulative volume percentage of the negative electrode active material in the negative electrode active material layer reaches 90% is D v 90 μm. Based on the total mass of the electrolyte, the mass content of the fluorinated carbonate is W0% and the mass content of the nitrile material is W1%. The lithium battery has a coefficient of performance k = (2D1 / D v 90+D v 50) / (W0+W1), where k is in the range of 0.5 to 3.

Description

[Technical Field]

[0001] Cross-reference of related applications This disclosure claims priority to China Patent Application No. 202211169554.5, titled "LITHIUM BATTERY AND ELECTRIC DEVICE," filed on 26 September 2022, which is incorporated herein by reference in its entirety.

[0002] This disclosure relates to the technology of batteries, and more particularly to lithium batteries and electrical devices. [Background technology]

[0003] Lithium-ion batteries (also known as "lithium batteries") are widely used in fields such as portable electronic devices, electric vehicles, and drones due to their characteristics such as high voltage, long lifespan, and lack of memory effect. With the continuous development of products powered by lithium-ion batteries, there is a growing demand for higher energy density, cycle performance, and safety performance of lithium-ion batteries.

[0004] During the charging and discharging processes of lithium-ion batteries, the negative electrode active material undergoes continuous lithium intercalation and deintercalation. This continuously causes cracks in the solid electrolyte interface (SEI) film on the surface of the negative electrode active material, creating new interfaces. This leads to direct contact between the negative electrode active material and the electrolyte, resulting in side reactions, loss of active lithium, and ultimately a decrease in the battery's energy density and cycle life. In addition, the stability of the SEI film formed on the negative electrode surface directly affects the stability of lithium-ion batteries tested in furnace temperature tests, which directly relates to the safety performance of lithium-ion batteries. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Currently, there are no effective technical solutions that can actually enable batteries to have superior long-cycle capability and safety performance. [Means for solving the problem]

[0006] In view of this, the present disclosure provides a lithium-ion battery and an electrical device. The lithium-ion battery is guaranteed to have a long cycle life at 130°C and excellent furnace temperature performance by defining the relative relationship between the thickness of the negative electrode active material layer, the particle size of the negative electrode active material, and the electrolyte.

[0007] This disclosure provides a lithium battery in a first embodiment. The lithium battery comprises a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The negative electrode plate comprises a current collector and a negative electrode active material layer disposed on at least one surface of the current collector. The electrolyte comprises a lithium salt, an organic solvent, and additives, the additives comprising a fluorinated carbonate and a nitrile substance. The negative electrode active material layer has a thickness D1 μm. The particle size corresponding when the volume cumulative percentage of the negative electrode active material in the negative electrode active material layer reaches 50% is D v The particle size is 50 μm, and the particle size corresponding to the point when the cumulative volume percentage of the negative electrode active material in the negative electrode active material layer reaches 90% is D v The particle size is 90 μm. Based on the total mass of the electrolyte, the mass content of fluorinated carbonate is W0%, and the mass content of nitrile material is W1%. The lithium battery is given by the following relationship, k=(2D1 / D v 90+D v It has a performance coefficient k that satisfies 50) / (W0+W1) and 0.5≦k≦3.0.

[0008] By adding fluorinated carbonate and nitrile substances as additives to the electrolyte, a stable and highly dense SEI film is formed on the negative electrode, an oxidation-resistant protective film is formed on the positive electrode, and the decomposition of the electrolyte, and thus the generation of gas on the positive electrode, is prevented. The performance coefficient k of the battery is defined by the combined action of these two additives and the quantitative relationship established between the content of the additives, the thickness of the negative electrode, and the particle size of the negative electrode active material. By controlling k within the range of 0.5 to 3, the cycle performance and oven temperature performance of the lithium battery can be improved.

[0009] In some embodiments, k is in the range of 1.0 ≦ k ≦ 2.0.

[0010] In some embodiments, W0 is in the range of 2 ≦ W0 ≦ 16.

[0011] In some embodiments, W0 is in the range of 5 ≦ W0 ≦ 10.

[0012] In some embodiments, W1 is in the range of 2 ≦ W1 ≦ 10.

[0013] In some embodiments, the ratio of W0 to W1 satisfies 0.5 ≦ W0 / W1 ≦ 4.

[0014] In some embodiments, the ratio of W0 to W1 satisfies 1.5 ≦ W0 / W1 ≦ 3.0.

[0015] In some embodiments, D1 is in the range of 30 ≦ D1 ≦ 90.

[0016] In some embodiments, D1 is in the range of 40 ≦ D1 ≦ 80.

[0017] The particle size of the negative electrode active material is, in some embodiments, 8 ≦ D v 50 < D v 90 ≦ 40 is satisfied.

[0018] D vIn some embodiments, the ratio of D1 to 90 is 1 or greater.

[0019] In some embodiments, the fluorinated carbonate includes at least one of fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5,5-tetrafluoroethylene carbonate, and 4-trifluoromethylethylene carbonate. The nitrile substance includes at least one of succinonitrile, adiposinitrile, glutalonitrile, butenedinitrile, 1,4-dicyano-2-butene, 3,3'-oxydipropionitrile, ethylene glycol diacetonitrile ether, 1,2,3-tri(2-cyanooxy)propane, 1,3,5-pentanetricarbonitride, 1,2,3-propanetricarbonitride, and 1,3,6-hexanetricarbonitride.

[0020] The organic solvent, in some embodiments, includes a carboxylate substance. The carboxylate substance includes at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl haloacetate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, and amyl halopropionate.

[0021] In some embodiments, the organic solvent further comprises a cyclic carbonate substance.

[0022] In some embodiments, the organic solvent further comprises a linear carbonate substance.

[0023] In some embodiments, the total mass content of the carboxylate substance is W2% based on the total mass of the electrolyte, and W2 / W0 ≥ 2.

[0024] In some embodiments, the ratio of W2 to W0 satisfies 2.5 ≤ W2 / W0 ≤ 8.

[0025] The additive further includes at least one of 1,3 - propane sultone, vinylene carbonate, and vinyl ethylene carbonate in some embodiments.

[0026] In a second aspect, the present disclosure provides an electrical device. The electrical device includes a lithium battery according to the first aspect of the present disclosure.

[0027] Due to the use of the above - mentioned lithium battery, the battery of the electrical device has a long battery life, excellent cycle performance, and high safety.

Brief Description of the Drawings

[0028] [Figure 1] It is a schematic structural diagram of a lithium battery according to an embodiment of the present disclosure. [Figure 2] It is a schematic structural diagram of an electrical device according to an embodiment of the present disclosure.

Modes for Carrying Out the Invention

[0029] Hereinafter, the technical solutions according to the embodiments of the present disclosure will be described in detail.

[0030] Embodiments of the present disclosure provide a lithium battery. As shown in FIG. 1, the lithium battery 10 includes a positive electrode plate 110, a negative electrode plate 120, a separator 130, and an electrolyte 140. The negative electrode plate 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector 121. The electrolyte includes a lithium salt, an organic solvent, and an additive, and the additive includes a fluorinated carbonate and a nitrile substance. The negative electrode active material layer 122 has a thickness of D1 μm. The particle size corresponding to when the volume cumulative percentage of the negative electrode active material in the negative electrode active material layer 122 reaches 50% is D v 50 μm, and the particle size corresponding to when the volume cumulative percentage of the negative electrode active material in the negative electrode active material layer 122 reaches 90% is D vThe particle size is 90 μm. Based on the total mass of electrolyte 140, the mass content of fluorinated carbonate is W0%, and the mass content of nitrile material is W1%. The lithium battery 10 has a performance coefficient k that satisfies the following relationship.

number

[0031] In some embodiments of the present disclosure, as shown in Figure 1, the positive electrode plate 110 includes a positive electrode current collector 111 and a positive electrode active material layer 112 disposed on at least one side surface of the positive electrode current collector 111.

[0032] In this disclosure, fluorinated carbonate and nitrile substances are added as additives to the electrolyte of a lithium battery. Thanks to the high affinity of fluorinated carbonate for the negative electrode active material, a stable and dense SEI film is formed on the surface of the negative electrode, which prevents continuous cracking and reforming of the SEI film, reduces electrolyte decomposition and active lithium consumption, and improves the battery's cycle performance. However, fluorinated carbonate is easily oxidized and generates gas at the positive electrode interface of the lithium battery. After the addition of nitrile substances, the nitrile substances form a complex at the positive electrode interface, forming a protective film that isolates the electrolyte from the positive electrode active material, suppresses the dissolution of metal ions from the positive electrode, reduces oxidative decomposition of the electrolyte by the positive electrode active material, and ultimately improves the battery's furnace temperature performance. Therefore, in this disclosure, fluorinated carbonate and nitrile substances are used together as additives. Due to their complementary functions, a relationship is established between the content of the two substances, the particle size of the negative electrode active material, and the thickness of the negative electrode active material layer, which defines the battery's coefficient of performance k. k is controlled within the range of 0.5 to 3, which ensures that the lithium battery can have a long cycle life and excellent furnace temperature performance.

[0033] Possible reasons inferred by the applicant after analysis are D1 / D v This is because 90 can, to some extent, reflect the degree of crushing of the negative electrode active particles during the rolling process of the negative electrode plate.v 50 reflects the overall size of the negative electrode active material particles, specifically, for example, the number of active sites on the surface of the negative electrode active material particles, and the degree of particle fracture during rolling. However, cracks in the negative electrode active material particles create more active interfaces, which increases electrolyte consumption in the conversion and cycling processes, depletes the capacity of the negative electrode active material, and allows lithium to easily deposit on the negative electrode surface during the charging process. Fluorinated carbonates can form a stable SEI film on the negative electrode that is beneficial for cycling, but they are prone to oxidation and generate gas at the positive electrode interface. Nitrile materials can form a protective film at the positive electrode interface that isolates the electrolyte from the positive electrode active material. However, the compatibility of nitrile materials with negative electrode active materials is not very good and has a certain effect on cycling performance. The influence of the above parameters on battery performance is diverse, reciprocal, and difficult to quantify. However, through a series of studies, the applicant has found that (2D1 / D v 90+D v We found that (50) / (W0+W1) can reflect the overall influence of the negative electrode plate and electrolyte on the battery's cycle performance, furnace temperature performance, and lithium deposition. (2D1 / D v 90+D v By controlling 50) / (W0+W1) within the range of 0.5 to 3, the battery's cycle performance, furnace temperature performance, lithium deposition, and other safety performance can be appropriately balanced to improve the overall performance of the battery.

[0034] In this disclosure, the negative electrode active material D v 90 and D v50 can be measured as follows: The negative electrode plate removed from the battery is immersed in dimethyl carbonate (DMC) for 1 hour, then removed and washed twice with DMC to remove any electrolyte remaining on the surface of the electrode plate, and then air-dried. The air-dried electrode plate is immersed in deionized water until the negative electrode material is separated from the current collector. The negative electrode material is then dried in an oven at 100°C to remove moisture. The dried negative electrode material is then heat-treated in a tubular furnace at 800°C under a helium atmosphere for 6 hours to remove the binder and thickener in the negative electrode material and thus obtain the negative electrode active material. Finally, the particle size distribution of the obtained negative electrode active material is tested by laser diffraction, and D v 90 and D v 50 is obtained from the resulting particle size distribution curve. The test method is found in GB / T19077-2016 / ISO13320:2009 Particle size analysis - Laser diffraction method. D v 90 and D v The instrument used to detect 50 is generally a laser particle size analyzer (such as the Malvin 3000 laser particle analyzer). The particle size D corresponds to the point when the cumulative volume percentage of the negative electrode active material reaches 50%. v 50 can also be called the "median particle size" of the material. Furthermore, W0 and W1 are obtained by analyzing the composition of the electrolyte. D1 is obtained by directly or indirectly measuring the thickness of the negative electrode active material layer and refers to the thickness of the negative electrode active material layer on only one side.

[0035] In some embodiments of this disclosure, the parameter k is in the range of 1.0 to 2.0. In this case, the lithium battery can better balance cycle performance and furnace temperature performance to have better overall performance.

[0036] In embodiments of the present disclosure, the fluorinated carbonate includes a fluorinated cyclic carbonate. Specifically, the fluorinated cyclic carbonate may include one or more of fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5,5-tetrafluoroethylene carbonate, and 4-trifluoromethylethylene carbonate.

[0037] In some embodiments of this disclosure, W0 is in the range of 2 ≤ W0 ≤ 16. In other words, the mass content of fluorinated carbonate is 2% to 16% based on the total mass of the electrolyte. Specifically, the mass content may be 2.1%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5.5%, 6%, 8%, 9%, 11%, 12%, 14%, 15%, or 15.5%. That is, W0 may specifically be 2.1, 2.5, 3, 3.5, 4, 4.5, 5.5, 6, 8, 9, 11, 12, 14, 15, or 15.5. In some embodiments, 6 ≤ W0 ≤ 12. The parameter k can be set in a preferred range of 1 to 2, which in this case allows the battery to have a low battery core expansion rate and excellent furnace temperature test results, while ensuring that the battery has a high cycle capacity retention rate. In some other embodiments, 8 ≤ W0 ≤ 10 so that the battery has a lower battery core expansion rate and better furnace temperature test results.

[0038] By controlling the fluorinated carbonate content W0 in the electrolyte to an appropriate range, a stable SEI film is formed on the surface of the negative electrode, ensuring that the battery has a long cycle capability, avoiding poor furnace temperature performance caused by an unstable SEI film, reducing gas generation due to oxidative decomposition of fluorinated carbonate at the positive electrode, avoiding significant expansion of the battery core thickness, and ensuring excellent furnace temperature performance of the battery. In some embodiments, W0 is in the range of 5 ≤ W0 ≤ 10. When W0 is within this range, lithium batteries have long cycle performance and can minimize battery expansion.

[0039] In embodiments of the present disclosure, the nitrile substance includes one or more of succinonitrile, adiposinitrile, glutalonitrile, butenedinitrile, 1,4-dicyano-2-butene, 3,3'-oxydipropionitrile, ethylene glycol diacetonitrile ether, 1,2,3-tri(2-cyanooxy)propane, 1,3,5-pentanetricarbonitride, 1,2,3-propanetricarbonitride, 1,3,6-hexanetricarbonitride, and 1,2,3-tri(2-cyanooxy)propane.

[0040] In some embodiments of this disclosure, W1 is in the range of 2 ≤ W1 ≤ 10. That is, the mass content of the nitrile substance is 2% to 10% based on the total mass of the electrolyte. Specifically, the mass content may be 2%, 2.5%, 3%, 3.3%, 4%, 4.6%, 5%, 5.5%, 6%, 7%, 8%, 9%, or 10%.

[0041] By controlling the nitrile content W1 in the electrolyte to an appropriate range, the positive electrode interface is completely protected, the electrolyte is less likely to oxidize and decompose to generate gases, and the battery has excellent furnace temperature performance and cycle performance. The electrolyte is guaranteed to have a suitable viscosity, the lithium ion conductivity is appropriate, the battery impedance does not increase significantly, lithium deposition on the negative electrode occurs almost never during the long cycle process, the battery capacity retention rate is high, and the thickness of the battery core does not increase significantly.

[0042] In some embodiments of this disclosure, the ratio of W0 to W1 satisfies 0.5 ≤ W0 / W1 ≤ 4. That is, the mass ratio of fluorinated carbonate to nitrile material is in the range of 0.5 to 4. This not only ensures that a stable and uniform SEI film is formed on the surface of the negative electrode during the cycling process, but also ensures that the positive electrode interface is effectively protected, thereby enabling the battery to have excellent cycle performance, furnace temperature performance, and the battery core to not bulge significantly. Specifically, W0 / W1 may be 0.8, 1.0, 1.2, 1.5, 1.6, 1.7, 1.8, 2.0, 2.2, 2.3, 2.5, 2.6, 2.8, 3.0, or 3.5. In some embodiments, W0 / W1 is in the range of 1.5 to 3.0. In this case, the lithium battery can have long cycle performance and excellent furnace temperature performance. W0 / W1 is further in the range of 1.5 to 2.5.

[0043] The electrolyte of the lithium battery according to this disclosure comprises a lithium salt, an organic solvent, and additives. The additives include fluorinated carbonates and nitrile substances. In some embodiments of this disclosure, the organic solvent includes a carboxylate substance. Carboxylate substances are generally linear esters that reduce the viscosity of the electrolyte, ensuring that the electrolyte has excellent fluidity, and can ensure the penetration of the electrolyte into the electrode plates and separators, as well as the low-temperature discharge performance of the battery. Carboxylate substances include one or more of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate (PP), butyl propionate, pentyl propionate, ethyl haloacetate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, and amyl halopropionate.

[0044] In some embodiments of this disclosure, the organic solvent further comprises a cyclic carbonate. That is, the organic solvent in this case comprises a carboxylate and a cyclic carbonate. The cyclic carbonate promotes the dissolution of lithium salts in the electrolyte, ensuring that the electrolyte has excellent ionic conductivity. The presence of the carboxylate lowers the viscosity of the electrolyte, improves its permeability, promotes the formation of a uniform and stable SEI film, improves ionic conductivity, and enhances the battery's rate and cycle performance. This combination facilitates maintaining the electrolyte at a low viscosity and contributes to the solubility of lithium salts in the electrolyte. The cyclic carbonate may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, haloethylene carbonate, halopropylene carbonate, and the like.

[0045] In some embodiments, the organic solvent further comprises a linear carbonate substance. That is, the organic solvent in this case comprises a carboxylate substance, a cyclic carbonate, and a linear carbonate substance. The presence of the linear carbonate substance can further reduce the viscosity of the electrolyte and ensure the permeability of the electrolyte to the electrode plates and separators. The linear carbonate substance may include at least one of the following: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate, halogenated dimethyl carbonate, halogenated ethyl methyl carbonate, halogenated diethyl carbonate, etc.

[0046] In embodiments of this disclosure, the total mass content of carboxylate material is W2% based on the total mass of the electrolyte, and W2 / W0 ≥ 2. This reduces the expansion rate of the battery during the cycle process. In some embodiments, 2.5 ≤ W2 / W0 ≤ 8. In this case, the lithium battery has excellent electrolyte permeability and excellent dynamic performance, which promotes the formation of a uniform SEI film on the surface of the negative electrode active material by fluorinated carbonate, making it easier for the battery to have a low battery core expansion rate and excellent capacity retention rate. W2 / W0 may specifically be 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.5, 4.0, 5.0, 6.0, 6.5, 7.0, 7.5, or 7.9. W2 / W0 is further in the range of 3.0 to 7.0 in some embodiments.

[0047] In some embodiments of this disclosure, the additives in the electrolyte may further include, in addition to fluorinated carbonates and nitrile substances, one or more of 1,3-propanesultone (PS), vinylene carbonate (VC), and vinylethylene carbonate (VEC). These additives promote the formation of a stable SEI film during the battery cycle process. In particular, 1,3-propanesultone is especially useful in improving high-temperature resistance, such as the furnace temperature performance of lithium batteries.

[0048] Lithium salts include one or more of the following: lithium hexafluoride phosphate (LiPF6), lithium tetraborate (LiBF4), lithium hexafluoride arsenate (LiAsF6), lithium hexafluorosilicate (Li2SiF6), lithium antimonate hexafluoride (LiSbF6), lithium perchlorate (LiClO4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), sodium bis(fluorosulfonyl)imide (LiFSI, molecular formula LiN(SO2F)2), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI, molecular formula LiN(SO2CF3)2), lithium bis(perfluoroethylsulfonyl)imide (LiN(C2F5SO2)2), lithium trifluoromethylsulfonate (LiCF3SO3), and lithium perfluorobutylsulfonate (LiC4F9SO3).

[0049] Optionally, the mass percentage of lithium salt content in the electrolyte may be 12% to 18%. In this case, it is guaranteed that the conduction resistance of lithium ions in the electrolyte will not be so high as to degrade the battery's rate performance, and that the viscosity of the electrolyte will not be so high as to affect the battery's performance by preventing effective penetration to the positive / negative electrodes.

[0050] In some embodiments of this disclosure, D1 is in the range of 30 ≤ D1 ≤ 90. That is, the thickness of the negative electrode active material layer is in the range of 30 μm to 90 μm. It should be understood that D1 refers only to the thickness of the negative electrode active material layer on one side, regardless of whether the negative electrode plate has the negative electrode active material layer on one side surface or on both sides surface. In this case, an appropriate thickness of the negative electrode active material layer facilitates the battery to have excellent room temperature cycling performance and furnace temperature performance. Specifically, a negative electrode active material layer of appropriate thickness facilitates the penetration of the electrolyte, promotes the formation of a uniform and stable SEI film on the surface of the negative electrode active material, reduces the conduction resistance of lithium ions in the negative electrode, and allows the battery to easily pass furnace temperature tests. By using a negative electrode active material layer of appropriate thickness, the increase in the thickness of the negative electrode SEI film, and consequently the consumption of active lithium, caused by the continuous decrease in electrolyte due to an incomplete SEI film during the battery cycling process, can be avoided, making it easier for the battery to maintain a high capacity retention rate. Furthermore, a negative electrode active material layer of appropriate thickness can also ensure a suitable load for the negative electrode active material of the battery and a high energy density of the battery. D1 is in the range of 40 to 80 in some embodiments.

[0051] In some embodiments of this disclosure, the particle size of the negative electrode active material is 8 ≤ D v 50 <D v The value of the negative electrode active material is D, which satisfies 90 ≤ 40. v 50 can reflect the overall particle size distribution. Preferred particle size D v 50 ensures that the negative electrode active material has a suitable specific surface area so that the electrolyte, especially the fluorinated carbonate, is not consumed too quickly during the battery cycle process, and that side reactions at the negative electrode do not become too vigorous, thereby enabling the battery to have a high capacity retention rate during long cycle processes. Suitable particle size D of the negative electrode active material v Furthermore, 50 facilitates the negative electrode active material layer having appropriate porosity, which reduces the diffusion and migration resistance of ions in the liquid, ultimately benefiting the battery's rate performance and cycle performance. In some embodiments, 8 ≤ D v50 < 36, specifically, for example, 8, 10, 12, 14, 16, 18, 20, 21, 23, 25, 27, 30, 32, 34, and 35. D v In some embodiments, 50 is in the range of 8 to 30, and preferably in the range of 8 to 20.

[0052] Particle size D of the negative electrode active material v 90 can reflect the large particles contained in the negative electrode active material. v By controlling the 90 to less than 40 μm, the negative electrode plate is easier to process, the negative electrode active material layer has excellent flatness, the negative electrode active material is rarely crushed and produces more active fracture surfaces, the consumption of electrolyte and fluorinated carbonate in the chemical conversion and cycling processes is reduced, and ultimately, the excellent cycling performance of the battery is ensured. v In some embodiments, 90 is in the range of 10 to 40, and more preferably in the range of 12 to 40, and more preferably in the range of 15 to 35. D1 is generally D v This is more than 1 / 90. This ensures that the negative electrode active material is not crushed during the rolling process of the negative electrode plate, thereby improving the stability of the negative electrode plate, improving the battery's cycle performance, and reducing the expansion of the battery core.

[0053] The negative electrode active material may include, but is not limited to, one or more of the following in embodiments of this disclosure: carbon materials, silicon-based materials, tin-based materials, and lithium titanate. Carbon materials include one or more of the following: soft carbon, hard carbon, carbon fibers, graphitized carbon microspheres, artificial graphite, and natural graphite. Silicon-based materials include one or more of the following: elemental silicon, silicon alloys, silicon oxides, silicon-carbon composites, and silicon carbide. Tin-based materials include one or more of the following: elemental tin, tin oxides, tin-based alloys, and tin-carbon compounds. If the negative electrode active material includes multiple materials (for example, both graphite and elemental silicon), D v 90 and D v 50 refers to the appropriate particle size of the mixed negative electrode active material.

[0054] In embodiments of this disclosure, the negative electrode active material layer further comprises a binder. The negative electrode active material layer may optionally further comprise a conductive agent. The binder may include, but is not limited to, one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylonitrile (PAN), polyacrylates (such as polymethyl methacrylate, polymethyl acrylate, and polyethyl acrylate), polyolefins (such as polypropylene and polyethylene), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), sodium carboxymethylcellulose (CMC-Na), and sodium alginate. The first and second conductive agents may be one or more separately selected from conductive carbon blacks (such as acetylene black, Ketjen black, Supper P, and 350G carbon black), furnace black, carbon fibers, carbon nanotubes, and graphene, but the disclosure is not limited thereto. The current collector carrying the negative electrode active material (specifically the negative electrode current collector) may include, but is not limited to, copper foil, stainless steel foil, copper alloy foil, carbon-coated copper foil, or copper plating films.

[0055] The negative electrode plate is obtained by coating a current collector with a negative electrode suspension containing a negative electrode active material, a binder, and an optional conductive agent, drying it, and rolling it. The current collector may be coated on one side or on both sides. In other words, one side of the current collector may have a negative electrode active material layer, or both opposite sides of the negative electrode current collector may have negative electrode active material layers. When the negative electrode current collector is coated on both sides, the thickness D1 μm of the negative electrode active material layer refers to the thickness of the negative electrode active material layer on one side. In this case, the thicknesses of the negative electrode active material layers on both sides of the negative electrode current collector may be the same or different, and the negative electrode active material layer on each side surface of the negative electrode current collector allows the parameter k to fall within the above range.

[0056] A lithium battery, in this disclosure, specifically includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator located between the positive and negative electrode plates. The positive electrode active material of the positive electrode plate is a material in which lithium ions can be reversibly deintercalated and intercalated. The positive electrode active material may include, but is not limited to, one or more of the following: lithium monooxides (such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide), lithium binary oxides (such as lithium nickel manganese oxide, lithium nickel cobalt oxide, and lithium cobalt manganese oxide), lithium ternary oxides (such as lithium nickel cobalt manganese oxide ternary material or lithium nickel cobalt aluminum oxide ternary material), lithium polyelement oxides, and lithium-containing phosphates (such as lithium iron phosphate and lithium manganese iron phosphate). The separator can be made of any separator material from existing batteries. The separator may include, but is not limited to, a single-layer polypropylene (PP) film, a single-layer polyethylene (PE) film, a double-layer PP / PE film, a double-layer PP / PP film, a triple-layer PP / PE / PP film, or a polymer separator such as a nonwoven fabric.

[0057] Embodiments of the present disclosure further provide an electrical device. The electrical device 1 includes a lithium battery 10 according to an embodiment of the present disclosure, as shown in Figure 2.

[0058] In this disclosure, there are no special limitations on electrical devices that use lithium batteries. Electrical devices include, but are not limited to, mobile phones, laptop computers, tablet computers, computers with stylus input, portable fax machines, portable photocopiers, portable printers, transceivers, video recorders, cameras, televisions, radios, portable audio recorders, portable CD players, MiniDiscs, e-book players, electronic organizers, wearable devices (such as smartwatches, smart bracelets, headphones, and Bluetooth headsets), portable vacuum cleaners, calculators, memory cards, emergency power supplies, vehicles, motorcycles, bicycles (such as electric-assist bicycles), lighting fixtures (such as flashlights), toys, game consoles, clocks, power tools, large household batteries, and lithium-ion capacitors.

[0059] Because they use lithium batteries, the batteries in electrical devices have a long battery life, excellent cycle performance, and high safety performance.

[0060] The technical solutions of this disclosure will be further explained below, along with specific examples.

[0061] (Example 1) A lithium-ion battery was fabricated using a process that included the following steps.

[0062] 1) Preparation of electrolyte: Various non-aqueous organic solvents were mixed in a glove box filled with argon having a water content of <1 ppm and an oxygen content of <1 ppm, according to the composition shown in Table 1. Dry lithium salt LiPF6 and additives were added to prepare an electrolyte containing 14.5% LiPF6.

[0063] 2) Fabrication of the positive electrode plate A positive electrode active material (specifically lithium cobalt oxide (LiCoO2)), a conductive agent (specifically carbon nanotubes (CNT)), and a binder (specifically polyvinylidene fluoride) were mixed in a mass ratio of 95:2:3. The mixed powder was added to a vacuum stirrer, the solvent N-methylpyrrolidone (NMP) was added, and the mixture was uniformly stirred to obtain a positive electrode suspension. The positive electrode suspension was applied to an aluminum foil positive electrode current collector, dried at 85°C, cold-rolled, sliced, cut, and dried under vacuum at 85°C for 4 hours to obtain a positive electrode plate.

[0064] 3) Fabrication of the negative electrode plate The negative electrode active material (specifically, graphite having the particle size and dimensional parameters shown in Table 1) and a binder (specifically, styrene-butadiene rubber (SBR) and sodium carboxymethylcellulose (CMC-Na) in a mass ratio of 2:3) were mixed in ionized water in a mass ratio of 95:5 and uniformly stirred in a vacuum stirrer to obtain a negative electrode suspension. Next, the negative electrode suspension was applied to two opposing sides of a copper foil negative electrode current collector, dried, cold-rolled, and cut to obtain a negative electrode plate. The negative electrode plate comprises a copper foil and negative electrode active material layers arranged on the two opposing sides of the copper foil. The thickness of each negative electrode active material layer is summarized in Table 1.

[0065] 4) Battery assembly A battery core was obtained by sequentially stacking a positive electrode plate, a polyethylene (PE) separator, and a negative electrode plate in a glove box filled with argon. The stacked battery core was wound up, placed in an aluminum-plastic film which served as the outer foil, injected with the prepared electrolyte, and then subjected to vacuum packaging, settling, chemical conversion, shaping, and other processes. In this way, the lithium battery was manufactured. The calculated performance coefficient k of the obtained lithium battery is summarized in Table 1.

[0066] It should be understood that the order in which some of the operations included in the method for fabricating lithium-ion batteries are performed is not limited to this disclosure. For example, operations 1), 2), and 3) may be performed simultaneously, or in an order different from that described herein.

[0067] (Other examples) Lithium batteries for other examples and comparative examples were fabricated according to the battery fabrication method of Example 1, using the parameters listed in Table 1. [Table 1-1] [Table 1-2]

[0068] In Examples 1-26 and 32-34, and Comparative Examples 1-5, W0 specifically represents the mass percentage of fluoroethylene carbonate in the electrolyte, and W1 specifically represents the total mass percentage of 1,3,6-hexanetricarbonate and succinonitrile in the electrolyte. In Example 27, W0 specifically represents the mass percentage of 4,5-difluoroethylene carbonate in the electrolyte. In Example 28, W0 specifically represents the mass percentage of 4,4,5,5-tetrafluoroethylene carbonate in the electrolyte. In Examples 27-28, W1 specifically represents the total mass percentage of 1,3,6-hexanetricarbonate and succinonitrile in the electrolyte. In Examples 29-31, W0 specifically represents the mass percentage of fluoroethylene carbonate in the electrolyte. In Example 29, W1 represents the total mass percentage of 1,3,6-hexanetricarbonitric acid and adiponitrile in the electrolyte. In Example 30, W1 represents the mass percentage of succinonitrile in the electrolyte. In Example 31, W1 specifically represents the mass percentage of adiponitrile in the electrolyte.

[0069] To provide strong support for the beneficial effects of this disclosure, the following electrochemical performance tests were performed on the lithium batteries of each example and comparative example. The results are summarized in Table 2 below.

[0070] 1) Room temperature cycling performance test Five test lithium batteries were charged at room temperature (25±3℃) with a constant current at a rate of 1C to a cutoff voltage of 4.48V, and then charged with a constant voltage at 4.48V to a cutoff current of 0.05C, resulting in a fully charged battery. The batteries were left to stand for 5 minutes, then discharged at a rate of 1C to 3.0V with a constant current, and left to stand for 5 minutes. This constituted a charge-discharge cycle. The capacity retention rate and thickness expansion rate were recorded after 1000 cycles at room temperature. Capacity retention rate after 1000 cycles = (Discharge capacity after 1000 cycles / Initial discharge capacity) × 100%, Battery thickness expansion rate = (Battery thickness when fully charged at 1000 cycles / Battery thickness when first fully charged) × 100%

[0071] 2) Furnace temperature performance test at 130°C Each group tested five lithium batteries. The batteries were charged at room temperature (25±3℃) with a constant current at a rate of 1C to a cutoff voltage of 4.48V, and then with a constant voltage to a cutoff current of 0.05C at 4.48V, resulting in a fully charged battery. The furnace temperature test was then performed 12-24 hours after the batteries were fully charged (Note: Fully charged batteries could not be tested immediately after being left undisturbed for more than 12 hours). Each lithium battery was heated from an initial temperature of 25±3℃ by convection or in a circulating hot air box, with the heating rate controlled at 5±2℃ / min and the heating time controlled at 25-28 minutes. The batteries were heated to 130±2℃ and maintained at this temperature for 60 minutes. The test was then completed. Each lithium battery was observed for any smoke, flame, or explosion. If the lithium battery did not exhibit any of the above, it was considered to have passed the furnace temperature test and was recorded as OK. If a lithium battery exhibited the above characteristics, it was considered to have failed the furnace temperature test and was recorded as NG. The number of batteries that passed the furnace temperature test was recorded for each group of five batteries. [Table 2-1] [Table 2-2]

[0072] As shown in Tables 1 and 2, when the additives in the electrolyte of a lithium battery contain both fluorinated carbonate and nitrile additives, and the battery composition allows the battery's coefficient of performance k to fall within the range of 0.5 to 3.0, the lithium battery exhibits excellent room-temperature cycling performance, high capacity, and a small thickness expansion rate of the battery core, and passes the furnace temperature performance test at 130°C. In particular, when k is between 1.0 and 2.0, the battery exhibits superior performance in various aspects. (2D1 / D v 90+D v If (50) / (W0+W1) (i.e., the coefficient of performance k) is less than 0.5 or greater than 3 (Comparative Examples 1-3), the long-cycle performance and furnace temperature performance of the lithium battery are insufficient and clearly inferior to that of Example 4, which has the same negative electrode plate characteristic parameters and organic solvent composition. Furthermore, if the electrolyte of the lithium battery does not contain fluorinated carbonate or additives, the battery performance is insufficient. Even when the parameter k is in the range of 0.5 to 3 (Comparative Example 5), the cycle life of the lithium battery is extremely insufficient. For example, it is difficult to reach 1000 cycles, and the pass rate for furnace temperature tests is low, or even zero.

[0073] In addition, a comparison of Examples 1-5 and 6-7 shows that, when the thickness D1 of the negative electrode active material layer varies and other conditions are the same, if k is 0.5-3, then the various performance characteristics of the battery are superior when the thickness D1 of the negative electrode active material layer is in the range of 30-90 μm (i.e., 2D1 is in the range of 60-180 μm), and especially when D1 is in the range of 30-75 μm (i.e., 2D1 is in the range of 60-150 μm).

[0074] In Examples 18-26, the thickness D1 of the negative electrode active material layer, the particle size parameter of the negative electrode active material, and the organic solvent and additive PS in the electrolyte were the same, but the fluorinated carbonate content W0 and the nitrile substance content W1 differed. A comparison of Example 18 and Example 23 shows that, under the same conditions, when the fluorinated carbonate content W0 in the system is in the range of 2-16, the battery's cycle performance and various other performances are well balanced, and in particular, its resistance to expansion is excellent. In particular, when W0 is in the range of 6-12, W0 / W1 is in the more preferable range of 1.5-3.0, and k is in the more preferable range of 1-2, the battery has excellent overall performance. Furthermore, when W2 / W0 is 2 or higher, the overall performance is even better. Furthermore, a comparison of Example 26 with Examples 4 and 24-25 shows that, under the same conditions, when the nitrile additive content W1 in the system is in the range of 2-10, the battery can maintain excellent furnace temperature performance. Furthermore, the electrolyte viscosity is appropriate, the battery impedance is low, the battery cycle performance is excellent, and the thickness expansion rate is small.

[0075] In addition, a comparison between Example 4 and Examples 33-34 shows that the inclusion of carboxylate improves the long-cycle performance of the battery compared to the pure carbonate-based organic solvent in the electrolyte (e.g., Example 34, which contains only EC, PC, and DEC). That is, the cycle performance of Examples 4 and 33 is superior to that of Example 34, which may be due to the addition of the carboxylate solvent. The addition of the carboxylate solvent lowers the viscosity of the electrolyte, improves its permeability to the negative electrode, promotes the formation of a uniform and stable SEI film, improves the capacity retention rate during the cycle process, and reduces the thickness expansion rate. Furthermore, a comparison between Example 4 and Example 32 shows that, if the additives in the electrolyte contain both fluorinated carbonate and nitrile additives of the same composition, and the parameters of the organic solvent and negative electrode plate are the same, the inclusion of the additive 1,3-propanesultone (PS) can further improve the high-temperature resistance of the battery.

[0076] While exemplary embodiments of the Disclosure have been described above, they should not be understood as limiting the scope of the Disclosure. It should be noted that several improvements and modifications can be made by those skilled in the art without departing from the principles of the Disclosure, and these will fall within the scope of the Disclosure. [Explanation of symbols]

[0077] 1. Electrical devices 10 Lithium batteries 110 Positive plate 111 Positive electrode current collector 112 Cathode active material layer 120 Negative plate 121 Negative electrode current collector 122 Negative electrode active material layer 130 Separator 140 Electrolyte

Claims

1. A lithium battery (10) comprising a positive electrode plate (110), a negative electrode plate (120), a separator (130), and an electrolytic solution (140), wherein the negative electrode plate includes a current collector and a negative electrode active material layer (122) disposed on at least one surface of the current collector, the electrolytic solution contains a lithium salt, an organic solvent, and an additive, the additive contains a fluorinated carbonate and a nitrile substance, and the negative electrode active material layer has a thickness D １ μm, and the particle size corresponding to when the volume cumulative percentage of the negative electrode active material in the negative electrode active material layer reaches 50% is D ｖ 50 μm, and the particle size corresponding to when the volume cumulative percentage of the negative electrode active material in the negative electrode active material layer reaches 90% is D ｖ 90 μm, based on the total mass of the electrolytic solution, the mass content of the fluorinated carbonate is W ０ %, and the mass content of the nitrile substance is W １ %, and the lithium battery has a performance coefficient k that satisfies the following relational expression, k = (2D １ / D ｖ 90 + D ｖ 50) / (W ０ + W １ ) and 0.5 ≤ k ≤ 3.0, a lithium battery.

2. The lithium battery according to claim 1, wherein k is in the range of 1.0 ≤ k ≤ 2.

0.

3. W ０ 2 ≤ W ０ A lithium battery according to claim 1, wherein the range is ≤ 16.

4. W ０ 5 ≤ W ０ A lithium battery according to claim 1, wherein the range is ≤ 10.

5. W １ 2 ≤ W １ A lithium battery according to claim 1, wherein the range is ≤ 10.

6. W １ W ０ The ratio is 0.5 ≤ W ０ / W １ A lithium battery according to claim 1, satisfying ≤ 4.

7. W １ W ０ The ratio is 1.5 ≤ W ０ / W １ A lithium battery according to claim 1, satisfying ≤ 3.

0.

8. D １ 30 ≤ D １ A lithium battery according to claim 1, wherein the value is in the range of ≤90.

9. D １ 40 ≤ D １ A lithium battery according to claim 1, wherein the value is in the range of ≤80.

10. The particle size of the negative electrode active material is 8 ≤ D ｖ 50 < D ｖ A lithium battery according to claim 1, satisfying 90 ≤ 40.

11. D ｖ D relative to 90 １ The lithium battery according to claim 1, wherein the ratio of is 1 or more.

12. The lithium battery according to claim 1, wherein the fluorinated carbonate comprises at least one of fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5,5-tetrafluoroethylene carbonate, and 4-trifluoromethylethylene carbonate, and the nitrile substance comprises at least one of succinonitrile, adiposinitrile, glutalonitrile, butenedinitrile, 1,4-dicyano-2-butene, 3,3'-oxydipropionitrile, ethylene glycol diacetonitrile ether, 1,2,3-tri(2-cyanooxy)propane, 1,3,5-pentanetricarbonitride, 1,2,3-propanetricarbonitride, and 1,3,6-hexanetricarbonitride.

13. The lithium battery according to claim 1, wherein the organic solvent comprises a carboxylate substance, and the carboxylate substance comprises at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl haloacetate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, and amyl halopropionate.

14. The lithium battery according to claim 13, wherein the organic solvent further comprises a cyclic carbonate.

15. The lithium battery according to claim 14, wherein the organic solvent further comprises a linear carbonate substance.

16. Based on the total mass of the electrolyte, the total mass content of the carboxylate substance is W. ２ It is a percentage, and W ２ / W ０ A lithium battery according to claim 13, wherein ≥ 2.

17. W ０ W ２ The ratio is 2.5 ≤ W ２ / W ０ A lithium battery according to claim 16, satisfying ≤ 8.

18. The lithium battery according to claim 1, wherein the additive further comprises at least one of 1,3-propanesultone, vinylene carbonate, and vinylethylene carbonate.

19. An electrical device (1) comprising a lithium battery (10) according to any one of claims 1 to 18.

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