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 TO RELATED APPLICATIONS This disclosure claims priority to Chinese Patent Application No. 202211169554.5, filed on September 26, 2022, entitled "LITHIUM BATTERY AND ELECTRIC DEVICE," which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to the technical field of batteries, and in particular 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 life, and no memory effect. With the continuous development of products powered by lithium-ion batteries, higher requirements are being placed on the energy density, cycle performance, and safety performance of lithium-ion batteries.

[0004] During the charge and discharge process of a lithium-ion battery, the negative electrode active material undergoes continuous lithium intercalation and deintercalation, which continuously cracks the solid electrolyte interface (SEI) film on the surface of the negative electrode active material and creates a new interface. This leads to direct contact of the negative electrode active material with the electrolyte and the occurrence of side reactions, resulting in the 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 surface of the negative electrode directly affects the stability of lithium-ion batteries tested in oven temperature tests, which is directly related to the safety performance of lithium-ion batteries. Summary of the Invention [Problem to be solved by the invention]

[0005] At present, there is no effective technical solution that can make batteries have excellent long cycle capability and safety performance in practice. [Means for solving the problem]

[0006] In view of this, the present disclosure provides a lithium-ion battery and an electric device, which are guaranteed to have a long cycle life at 130°C and excellent furnace temperature performance by specifying 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] In a first aspect, the present disclosure provides a lithium battery. 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 disposed on at least one surface of the current collector. The electrolyte includes a lithium salt, an organic solvent, and an additive, the additive including 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 is calculated using the following formula: k = (2D1 / D v 90+D v 50) / (W0+W1) and has a coefficient of performance k such that 0.5≦k≦3.0.

[0008] The addition of fluorinated carbonate and nitrile materials to the electrolyte as additives forms a stable and dense SEI film on the negative electrode and an oxidation-resistant protective film on the positive electrode, preventing electrolyte decomposition and ultimately gas generation on the positive electrode. The synergistic effect of these two additives, along with the quantitative relationship established between the additive content, negative electrode thickness, and particle size of the negative electrode active material, determines the battery's coefficient of performance (k). Controlling k within the range of 0.5 to 3 can achieve the goal of improving the cycle performance and furnace temperature performance of lithium batteries.

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

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

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

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

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

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

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

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

[0019] In some embodiments, the fluorinated carbonate comprises at least one of fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5,5-tetrafluoroethylene carbonate, and 4-trifluoromethylethylene carbonate. The nitrile material comprises at least one of succinonitrile, adipoditrile, glutaronitrile, butenedinitrile, 1,4-dicyano-2-butene, 3,3'-oxydipropionitrile, ethylene glycol diacetonitrile ether, 1,2,3-tri(2-cyanooxy)propane, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, and 1,3,6-hexanetricarbonitrile.

[0020] The organic solvent, in some embodiments, comprises a carboxylate material, which 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.

[0021] The organic solvent, in some embodiments, further comprises a cyclic carbonate material.

[0022] The organic solvent, in some embodiments, further comprises a linear carbonate material.

[0023] In some embodiments, the total mass content of the carboxylate material 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, in some embodiments, further comprises at least one of 1,3-propane sultone, vinylene carbonate, and vinyl ethylene carbonate.

[0026] In a second aspect, the present disclosure provides an electric device comprising a lithium battery according to the first aspect of the 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 explanation of the drawings]

[0028] [Figure 1] 1 is a schematic structural diagram of a lithium battery according to an embodiment of the present disclosure; FIG. [Figure 2] 1 is a schematic structural diagram of an electrical device according to an embodiment of the present disclosure; DETAILED DESCRIPTION OF THE INVENTION

[0029] The technical solutions according to the embodiments of the present disclosure are described in detail below.

[0030] An embodiment of the present disclosure provides 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 material. The negative electrode active material layer 122 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 122 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 122 reaches 90% is D v90 μm. Based on the total mass of the electrolyte 140, the mass content of the fluorinated carbonate is W0%, and the mass content of the nitrile material is W1%. The lithium battery 10 has a coefficient of performance k that satisfies the following relationship:

number

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

[0032] In this disclosure, a fluorinated carbonate and a nitrile material are added as additives to a lithium battery electrolyte. The fluorinated carbonate's high affinity for the negative electrode active material allows the formation of a stable and dense SEI film on the surface of the negative electrode, preventing continuous cracking and reformation of the SEI film, reducing electrolyte decomposition and active lithium consumption, and improving the battery's cycle performance. However, fluorinated carbonates are easily oxidized, generating gas at the positive electrode interface of lithium batteries. After the nitrile material is added, it forms a complex at the positive electrode interface, forming a protective film that isolates the electrolyte from the positive electrode active material, suppressing metal ion dissolution from the positive electrode, reducing oxidative decomposition of the electrolyte by the positive electrode active material, and ultimately improving the battery's oven temperature performance. Therefore, in this disclosure, a fluorinated carbonate and a nitrile material are used in combination as additives. Their complementary functions establish a relationship between the content of the two materials, the particle size of the negative electrode active material, and the thickness of the negative electrode active material layer, thereby determining the battery's coefficient of performance (k). k is controlled in 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] The possible reasons speculated by the applicant after the analysis are: D1 / D v This is because the value of 90 can reflect to some extent the degree of crushing of the negative electrode active particles during the rolling process of the negative electrode plate.v The 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 crushing during rolling. However, cracks in the negative electrode active particles result in more active interfaces, which increases the consumption of electrolyte during the formation and cycling processes, causes the capacity loss of the negative electrode active material, and facilitates lithium deposition on the surface of the negative electrode during the charging process. Fluorinated carbonates can form a stable SEI film on the negative electrode, which 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, which has a certain impact on cycling performance. The effects of the above parameters on battery performance are diverse and interactive, making them difficult to quantify. However, through a series of studies, the applicant has found that (2D1 / D v 90+D v It was found that the ratio (2D1 / D 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. v 90+D v By controlling (50) / (W0+W1) in the range of 0.5 to 3, the cycle performance, furnace temperature performance, lithium precipitation, and other safety performance of the battery can be properly balanced to improve the overall performance of the battery.

[0034] In this disclosure, the negative electrode active material D v 90 and D vThe D 50 can be measured as follows: The negative electrode plate removed from the battery is immersed in dimethyl carbonate (DMC) for 1 hour, then removed, washed twice with DMC to remove the remaining electrolyte on the surface of the electrode plate, and 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 the 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 method, and the D v 90 and D v 50 is obtained from the particle size distribution curve obtained. The test method can be found in GB / T19077-2016 / ISO13320:2009 Particle size analysis - Laser diffraction method. v 90 and D v The device used to detect 50 is typically a laser particle size analyzer (such as a Malvin 3000 laser particle analyzer). The particle size D corresponding to the volume cumulative percentage of the negative electrode active material reaching 50% is v 50 can also be referred to as 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 only one side of the negative electrode active material layer.

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

[0036] In embodiments of the present disclosure, the fluorinated carbonate includes a fluorinated cyclic carbonate, which may specifically 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 the present disclosure, W0 is in the range of 2≦W0≦16. In other words, the mass content of the 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 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. In this case, the parameter k can be set in the preferred range of 1 to 2, which allows the battery to have a low battery core expansion rate and excellent oven temperature test results while ensuring a high cycle capacity retention rate. In other embodiments, 8≦W0≦10 so that the battery has a lower battery core expansion rate and better oven temperature test results.

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

[0039] The nitrile material, in embodiments of the present disclosure, includes one or more of succinonitrile, adipodinitrile, glutaronitrile, butenedinitrile, 1,4-dicyano-2-butene, 3,3′-oxydipropionitrile, ethylene glycol diacetonitrile ether, 1,2,3-tri(2-cyanooxy)propane, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, and 1,2,3-tri(2-cyanooxy)propane.

[0040] In some embodiments of the present disclosure, W1 is in the range of 2≦W1≦10. That is, the mass content of the nitrile material 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 within an appropriate range, the positive electrode interface is fully protected and the electrolyte is less likely to oxidize and decompose, generating gas. This results in batteries with excellent furnace temperature and cycle performance. The electrolyte has an appropriate viscosity, adequate lithium ion conductivity, no significant increase in battery impedance, almost no lithium deposition on the negative electrode during long cycles, high battery capacity retention, and no significant increase in battery core thickness.

[0042] In some embodiments of the present disclosure, the ratio of W0 to W1 satisfies 0.5≦W0 / W1≦4. That is, the mass ratio of the fluorinated carbonate to the nitrile material is in the range of 0.5 to 4. This not only ensures the formation of a stable and uniform SEI film on the surface of the negative electrode during cycling, but also ensures effective protection of the positive electrode interface, thereby enabling the battery to have excellent cycle performance and oven temperature performance without significant battery core expansion. 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 oven temperature performance. W0 / W1 may also be in the range of 1.5 to 2.5.

[0043] The electrolyte for a lithium battery according to the present disclosure includes a lithium salt, an organic solvent, and an additive. The additive includes a fluorinated carbonate and a nitrile material. In some embodiments of the present disclosure, the organic solvent includes a carboxylate material. The carboxylate material is generally a linear ester and reduces the viscosity of the electrolyte, ensuring excellent fluidity of the electrolyte and ensuring the electrolyte's penetration into the electrode plates and separator, as well as the low-temperature discharge performance of the battery. The carboxylate material includes 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 the present disclosure, the organic solvent further includes a cyclic carbonate. That is, the organic solvent in this case includes a carboxylate material and a cyclic carbonate. The cyclic carbonate promotes dissolution of the lithium salt in the electrolyte and ensures that the electrolyte has excellent ionic conductivity. The presence of the carboxylate material reduces the viscosity of the electrolyte, improves the permeability of the electrolyte, promotes the formation of a uniform and stable SEI film, improves ionic conductivity, and improves the rate and cycle performance of the battery. This combination of the two facilitates maintaining a low viscosity of the electrolyte and contributes to the solubility of the lithium salt in the electrolyte. The cyclic carbonate may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, haloethylene carbonate, halopropylene carbonate, etc.

[0045] In some embodiments, the organic solvent further includes a linear carbonate material. That is, the organic solvent in this case includes a carboxylate material, a cyclic carbonate, and a linear carbonate material. The presence of the linear carbonate material further reduces the viscosity of the electrolyte solution and ensures the electrolyte solution's permeability into the electrode plates and separator. The linear carbonate material may include at least one of 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 the present disclosure, the total mass content of the carboxylate material is W2% based on the total mass of the electrolyte, and W2 / W0 is greater than or equal to 2. This reduces the battery's expansion rate during cycling. In some embodiments, 2.5≦W2 / W0≦8. In this case, the lithium battery has excellent electrolyte permeability and excellent dynamic performance. This promotes the formation of a uniform SEI film on the surface of the negative electrode active material by the fluorinated carbonate, facilitating the battery's low battery core expansion rate and excellent capacity retention. Specifically, W2 / W0 may 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. In some embodiments, W2 / W0 is in the range of 3.0 to 7.0.

[0047] In some embodiments of the present disclosure, the additives in the electrolyte may further include one or more of 1,3-propane sultone (PS), vinylene carbonate (VC), and vinyl ethylene carbonate (VEC) in addition to the fluorinated carbonate and nitrile materials. These additives promote the formation of a stable SEI film during the battery cycling process. In particular, 1,3-propane sultone is particularly useful for improving the high-temperature resistance, such as the oven-temperature performance, of lithium batteries.

[0048] The lithium salts include one or more of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoroarsenate (LiAsF), lithium hexafluorosilicate (LiSiF), lithium hexafluoroantimonate (LiSbF), lithium perchlorate (LiClO), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), sodium bis(fluorosulfonyl)imide (LiFSI, molecular formula LiN(SOF)), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI, molecular formula LiN(SOCF)), lithium bis(perfluoroethylsulfonyl)imide (LiN(CFSO)), lithium trifluoromethylsulfonate (LiCFSO), and lithium perfluorobutylsulfonate (LiCFSO).

[0049] Optionally, the mass percentage of the lithium salt content in the electrolyte may be 12% to 18%, which ensures that the conduction resistance of lithium ions in the electrolyte is not so large as to deteriorate the rate performance of the battery, and that the viscosity of the electrolyte is not so large as to prevent effective penetration into the positive and negative electrodes, thereby affecting the performance of the battery.

[0050] In some embodiments of the present 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 to the thickness of the negative electrode active material layer on only one side of the negative electrode plate, regardless of whether the negative electrode active material layer is disposed on one surface or both surfaces. In this case, the thickness of the negative electrode active material layer is appropriate, facilitating the battery to have excellent room temperature cycling performance and oven 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 within the negative electrode, and enables the battery to easily pass oven temperature tests. Using a negative electrode active material layer of appropriate thickness avoids the increase in the thickness of the negative electrode SEI film, which is caused by the continuous reduction of the electrolyte due to an incomplete SEI film during the battery cycling process, and thus the consumption of active lithium, thereby facilitating the battery to maintain a high capacity retention rate. Furthermore, a negative electrode active material layer of appropriate thickness can also ensure suitable loading of the negative electrode active material of the battery and high energy density of the battery. D1 is in the range of 40 to 80 in some embodiments.

[0051] In some embodiments of the present disclosure, the particle size of the negative electrode active material is 8≦D v 50 <D v 90≦40. Particle size D of negative electrode active material v 50 can reflect the overall particle size distribution. v The particle size D of the negative electrode active material can ensure 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 cycle process of the battery, and side reactions at the negative electrode are not too violent, thereby enabling the battery to have a high capacity retention rate during a long cycle process. v 50 also facilitates the negative electrode active material layer to have an appropriate porosity, which reduces the resistance to ion diffusion and migration in the liquid, ultimately benefiting the rate and cycle performance of the battery. 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 negative electrode active material v 90 may reflect the large particles contained in the negative electrode active material. v By controlling the thickness of the negative electrode to less than 40 μm, the negative electrode plate is easy to process, the negative electrode active material layer has excellent flatness, the negative electrode active material is hardly crushed to produce more active fracture surfaces, the consumption of electrolyte and fluorinated carbonate in the formation and cycling processes is reduced, and ultimately the excellent cycling performance of the battery is ensured. v In some embodiments, D90 is in the range of 10 to 40, more preferably in the range of 12 to 40, and more preferably in the range of 15 to 35. D1 is approximately D v 90 times or more. 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 cycle performance of the battery, and reducing the expansion of the battery core.

[0053] In embodiments of the present disclosure, the negative electrode active material may include, but is not limited to, one or more of a carbon material, a silicon-based material, a tin-based material, and lithium titanate. Carbon materials include one or more of soft carbon, hard carbon, carbon fiber, graphitized carbon microspheres, artificial graphite, and natural graphite. Silicon-based materials include one or more of elemental silicon, silicon alloys, silicon oxides, silicon-carbon composites, silicon carbide, and the like. Tin-based materials include one or more of elemental tin, tin oxides, tin-based alloys, tin-carbon compounds, and the like. When the negative electrode active material includes multiple materials (e.g., 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 an embodiment of the present disclosure, the negative electrode active material layer further includes a binder. The negative electrode active material layer may further include a conductive agent in some cases. The binder may include, but is not limited to, one or more of 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), carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), and sodium alginate. The first conductive agent and the second conductive agent may be one or more independently selected from conductive carbon black (such as acetylene black, ketjen black, Supper P, and 350G carbon black), furnace black, carbon fiber, carbon nanotubes, and graphene. However, the present disclosure is not limited thereto. The current collector (specifically, the negative electrode current collector) carrying the negative electrode active material may include, but is not limited to, copper foil, stainless steel foil, copper alloy foil, carbon-coated copper foil, or copper-plated film.

[0055] A negative electrode plate is obtained by applying a negative electrode suspension containing a negative electrode active material, a binder, and an optional conductive agent to a current collector, drying the suspension, and rolling the current collector. The current collector may be coated on one or both surfaces. In other words, the negative electrode active material layer may be formed on one surface of the current collector, or on both surfaces facing opposite to each other. When the negative electrode current collector is coated on both surfaces, the thickness D1 μm of the negative electrode active material layer refers to the thickness of the negative electrode active material layer on one surface. 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, as long as the thickness of the negative electrode active material layers on each side of the negative electrode current collector allows the parameter k to fall within the above range.

[0056] In this disclosure, a lithium battery specifically includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator located between the positive and negative electrodes. The positive electrode active material of the positive electrode plate is a material through which lithium ions can be reversibly deintercalated and intercalated. In the case of a lithium battery, the positive electrode active material may include, but is not limited to, one or more of lithium monoxides (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 materials or lithium nickel cobalt aluminum oxide ternary materials), lithium multi-element oxides, and lithium-containing phosphates (such as lithium iron phosphate and lithium manganese iron phosphate). The separator can be made of any separator material used in existing batteries. The separator may include, by way of example and not limitation, a polymer separator such as a monolayer polypropylene (PP) film, a monolayer polyethylene (PE) film, a two-layer PP / PE film, a two-layer PP / PP film, and a three-layer PP / PE / PP film, or a nonwoven fabric.

[0057] An embodiment of the present disclosure further provides an electric device 1, which includes a lithium battery 10 according to an embodiment of the present disclosure, as shown in FIG.

[0058] In the present disclosure, there is no particular limitation on electrical devices that use lithium batteries, including, but not limited to, mobile phones, laptops, tablet computers, computers with stylus input, portable fax machines, portable copiers, portable printers, walkie-talkies, video recorders, cameras, televisions, radios, portable audio recorders, portable CD players, minidiscs, e-book players, electronic organizers, wearable devices (such as smart watches, smart bracelets, headphones, and Bluetooth headsets), portable vacuum cleaners, calculators, memory cards, emergency power supplies, vehicles, motorcycles, bicycles (such as electrically assisted bicycles), lighting equipment (such as flashlights), toys, game consoles, watches, power tools, large household batteries, and lithium ion capacitors.

[0059] Due to the use of lithium batteries, the batteries of the electrical devices have a long battery life, excellent cycle performance, and high safety performance.

[0060] Hereinafter, the technical solutions of the present disclosure are further illustrated with specific examples.

[0061] Example 1 The lithium-ion battery was fabricated by a process that included the following steps:

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

[0063] 2) Preparation of the positive electrode plate The positive electrode active material (specifically, lithium cobalt oxide (LiCoO)), conductive agent (specifically, carbon nanotubes (CNTs)), and binder (specifically, polyvinylidene fluoride) were mixed in a mass ratio of 95:2:3. The mixed powder was placed in a vacuum mixer, and the solvent N-methylpyrrolidone (NMP) was added and stirred uniformly 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) Preparation of the negative electrode plate A 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 carboxymethyl cellulose sodium (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 mixer to obtain a negative electrode suspension. The negative electrode suspension was then applied to two opposing sides of a negative electrode current collector, which was copper foil, dried, cold-rolled, and cut to obtain a negative electrode plate. The negative electrode plate included copper foil and negative electrode active material layers disposed 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 In an argon-filled glove box, a positive electrode plate, a polyethylene (PE) separator, and a negative electrode plate were stacked in this order to obtain a battery core. The stacked battery core was then wound and placed inside an aluminum-plastic foil exterior foil. The prepared electrolyte was then injected, followed by vacuum packaging, standing, chemical formation, shaping, and other processes. In this way, the fabrication of the lithium battery was completed. The calculated performance coefficient k of the obtained lithium battery is also summarized in Table 1.

[0066] It should be understood that the order in which the various operations in the method for fabricating a lithium-ion battery are performed is not limited to the present disclosure. For example, operations 1), 2), and 3) may be performed simultaneously or in a different order than described herein.

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

[0068] In Examples 1 to 26 and 32 to 34 and Comparative Examples 1 to 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-hexanetricarbonitrile 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 and 28, W1 specifically represents the total mass percentage of 1,3,6-hexanetricarbonitrile and succinonitrile in the electrolyte. In Examples 29 to 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-hexanetricarbonitrile 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 evidence of the beneficial effects of the present disclosure, the lithium batteries of each example and comparative example were tested for the following electrochemical performance, and the results are summarized in Table 2 below.

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

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

[0072] As shown in Tables 1 and 2, when the additive in the electrolyte of a lithium battery contains both a fluorinated carbonate and a nitrile additive, and the battery composition allows the battery's performance coefficient k to fall within the range of 0.5 to 3.0, the lithium battery has excellent room temperature cycle performance, high capacity, and a small thickness expansion coefficient of the battery core, and passes the oven temperature performance test at 130°C. In particular, when k is 1.0 to 2.0, the battery's various performance characteristics are excellent. (2D1 / D v 90+D v When the coefficient of performance k (k) is less than 0.5 or greater than 3 (Comparative Examples 1 to 3), the long-cycle performance and oven-temperature performance of the lithium battery are insufficient, clearly inferior to that of Example 4, which has the same negative plate characteristic parameters and organic solvent composition. Furthermore, when the electrolyte of the lithium battery does not contain either a fluorinated carbonate or an additive, 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 1,000 cycles, and the pass rate of the oven-temperature test is low, at 0.

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

[0074] In Examples 18 to 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 material content W1 were different. A comparison of Example 18 with Example 23 reveals that, under the same conditions, when the fluorinated carbonate content W0 in the system is in the range of 2 to 16, the battery's cycle performance and other performance characteristics are well balanced, with excellent expansion resistance in particular. In particular, when W0 is in the range of 6 to 12, W0 / W1 is in the more preferred range of 1.5 to 3.0, and k is in the more preferred range of 1 to 2, the battery exhibits excellent overall performance. Furthermore, when W2 / W0 is 2 or greater, the overall performance is even better. Furthermore, a comparison of Example 26 with Examples 4 and 24 to 25 reveals that, under the same conditions, when the nitrile additive content W1 in the system is in the range of 2 to 10, the battery maintains excellent furnace temperature performance. In addition, the viscosity of the electrolyte is appropriate, the battery impedance is small, the battery cycle performance is excellent, and the thickness expansion rate is small.

[0075] Additionally, a comparison of Example 4 with Examples 33 and 34 indicates that the incorporation of a carboxylate solvent improves the long-term cycling performance of the battery compared to a pure carbonate-based electrolyte containing an organic solvent (e.g., Example 34, which contains only EC, PC, and DEC). The cycling performance of Examples 4 and 33 is superior to that of Example 34, which may be due to the addition of a carboxylate solvent. The addition of a carboxylate solvent reduces the viscosity of the electrolyte, improves its permeability to the negative electrode, promotes the formation of a uniform and stable SEI film, improves capacity retention during cycling, and reduces thickness expansion. Furthermore, a comparison of Example 4 with Example 32 indicates that when the electrolyte contains both a fluorinated carbonate and a nitrile additive with the same composition, and the organic solvent and negative plate parameters are the same, the incorporation of the additive 1,3-propane sultone (PS) can further improve the high-temperature resistance of the battery.

[0076] Although the exemplary embodiments of the present disclosure have been described above, they should not be understood as limiting the scope of the present disclosure. It should be noted that, without departing from the principle of the present disclosure, some improvements and modifications may be made by those skilled in the art, and they shall fall within the protection scope of the present disclosure. [Explanation of symbols]

[0077] 1 Electrical Devices 10. Lithium battery 110 Positive electrode plate 111 Positive electrode current collector 112 Cathode active material layer 120 negative electrode 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 electrolyte (140), wherein the negative electrode plate comprises a current collector and a negative electrode active material layer (122) disposed on at least one surface of the current collector, the electrolyte comprising a lithium salt, an organic solvent, and an additive, the additive comprising a fluorinated carbonate and a nitrile material, and the negative electrode active material layer has a thickness D １ The particle size 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, and the mass content of the fluorinated carbonate is W based on the total mass of the electrolyte solution. ０ %, and the mass content of the nitrile material is W １ %, and the lithium battery satisfies the following relationship: k=(2D １ / D ｖ 90+D ｖ 50) / (W ０ +W １ ) and has a coefficient of performance k such that 0.5≦k≦3.

0.

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

0.

3. W ０ 2≦W ０ 3. The lithium battery of claim 1, wherein the .alpha.-methyl-.alpha.-methyl-.alpha.-methyl.beta ...

4. W ０ 5≦W ０ 3. The lithium battery of claim 1, wherein the R is in the range of ≦10.

5. W １ 2≦W １ 5. The lithium battery of claim 1, wherein the R is in the range of ≦10.

6. W １ W against ０ The ratio is 0.5≦W ０ / W １ 3. The lithium battery according to claim 1, wherein the .lambda.

7. W １ W against ０ The ratio of 1.5≦W ０ / W １ 3. The lithium battery according to claim 1 or 2, wherein the .lambda. / .lambda. ratio satisfies .ltoreq.3.

0.

8. D １ is 30≦D １ 8. The lithium battery of claim 1, wherein the .DELTA..times ...

9. D １ is 40≦D １ 8. The lithium battery of claim 1, wherein the .DELTA..times ...

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

11. D ｖ D against 90 １ 8. The lithium battery of claim 1, wherein the ratio of

12. 12. The lithium battery of 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 material includes at least one of succinonitrile, adipoditrile, glutaronitrile, butenedinitrile, 1,4-dicyano-2-butene, 3,3′-oxydipropionitrile, ethylene glycol diacetonitrile ether, 1,2,3-tri(2-cyanooxy)propane, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, and 1,3,6-hexanetricarbonitrile.

13. 13. The lithium battery of claim 1, wherein the organic solvent comprises a carboxylate material, the carboxylate material including 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. 14. The lithium battery of claim 13, wherein the organic solvent further comprises a cyclic carbonate.

15. 15. The lithium battery of claim 14, wherein the organic solvent further comprises a linear carbonate material.

16. The total mass content of the carboxylate material is W based on the total mass of the electrolyte solution. ２ %, and W ２ / W ０ 16. The lithium battery of claim 13, wherein R is ≧2.

17. W ０ W against ２ The ratio of W ２ / W ０ 17. The lithium battery of claim 16, wherein:

18. 18. The lithium battery of claim 1, wherein the additive further comprises at least one of 1,3-propane sultone, vinylene carbonate, and vinyl ethylene carbonate.

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

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