Electrolyte and preparation method therefor, lithium battery and electric device

Abstract

Provided are an electrolyte and a preparation method therefor, a lithium battery and an electric device. The electrolyte comprises a lithium salt, a solvent and a film-forming additive, wherein the solvent comprises a low-viscosity solvent having a viscosity of 0.50 mPa·s or less. The electrolyte satisfies the following: by taking the mass of the solvent as 100%, the mass fraction value of the low-viscosity solvent in the solvent is W, with the unit thereof being wt%; and the ratio of the mass of the film-forming additive in the electrolyte to the total mass of the lithium salt and the solvent is Add. For positive electrode sheets having different compaction densities, the contents of the low-viscosity solvent and the film-forming additive in the matched electrolyte can be obtained by means of calculation, thereby obtaining the matched electrolyte; and after a lithium battery is prepared from the positive electrode sheets and the matched electrolyte, the electrolyte not only has good wettability on the positive electrode sheets, but also has excellent cycling stability.

Description

An electrolyte and its preparation method, a lithium battery and an electric device

[0001] This application claims priority to Chinese Patent Application No. 202510742268.0, filed with the Chinese Patent Office on June 4, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of battery technology and relates to an electrolyte, specifically an electrolyte and its preparation method, lithium batteries and electric devices. Background Technology

[0003] Increasing the compaction density of lithium manganese iron phosphate (LMP) cathode sheets is an important technical means to improve battery energy density. However, increasing the compaction density of LMP cathode sheets significantly increases the difficulty of electrolyte wetting of the electrode. Moreover, the porosity of the cathode material in LMP cathode sheets with increased compaction density decreases and the pore structure becomes more compact. The penetration path of electrolyte inside LMP cathode sheets becomes more complex, and conventional electrolyte solvents with high surface tension often cannot fully wet the three-dimensional network structure formed by the active material and conductive agent.

[0004] Therefore, introducing ethyl acetate (EA), with its lower viscosity, into the electrolyte as a co-solvent reduces the dynamic viscosity of the electrolyte system. Ethyl acetate has low surface tension, significantly improving the wettability of the electrolyte on the high-pressure lithium manganese iron phosphate cathode, effectively avoiding the defects of increased interfacial impedance and deteriorated lithium-ion transport performance caused by insufficient wetting. However, ethyl acetate decomposes at high temperatures to generate acidic substances, which can damage the CEI film of the cathode and the SEI film of the anode, leading to battery cycle degradation. Therefore, it is necessary to add suitable film-forming additives to the electrolyte to form more stable CEI and SEI films to improve high-temperature cycle performance.

[0005] CN119230914A discloses a lithium iron phosphate battery. The lithium iron phosphate battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The main material of the positive electrode is lithium iron phosphate, and the main material of the negative electrode includes graphite and silicon-based materials; the areal density of the positive electrode is ≥23 mg / cm³. 2 The areal density of the negative electrode is ≥7.8 mg / cm³. 2 The electrolyte consists of lithium salts, solvents, and additives. The solvents mainly include ethylene carbonate and small-molecule linear solvents. The additives include FEC and negative electrode film-forming additives. The negative electrode film-forming agents include vinylene carbonate and lithium salt additives. The mass fraction of the small-molecule linear solvent is 35%–60%, the mass fraction of fluoroethylene carbonate is M, the mass fraction of silicon in the negative electrode layer is W1, 2% ≤ M ≤ 2 × W1, and the mass fraction of the negative electrode film-forming agent is 4%–6%.

[0006] CN116259834A discloses a 12V auxiliary battery and its electrolyte. The electrolyte comprises lithium salt, organic solvent, and additives. The lithium salt accounts for 14% to 20% by weight and is composed of lithium hexafluorophosphate and lithium difluorosulfonylimide, with a molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide of 0.5:1 to 2.0. The organic solvent is composed of at least one of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. The additives are composed of at least one of lithium difluorooxalate phosphate, lithium difluorophosphate, and vinylene carbonate, with a weight percentage of 0.2% to 2.5%. Technical issues

[0007] However, the disclosed technical solutions in related technologies are difficult to match electrolytes with appropriate amounts of film-forming additives and low-viscosity solvents to positive electrode sheets with different compaction densities. This makes it difficult to ensure good wettability of the electrolyte on the positive electrode sheet, thus avoiding increased interfacial impedance and deterioration of lithium-ion transport performance, while simultaneously improving the high-temperature cycle stability of the battery. Therefore, this paper aims to develop a novel electrolyte, its preparation method, a lithium battery, and an electric device. Technical solutions

[0008] This application provides an electrolyte and its preparation method, a lithium battery, and an electric device. The electrolyte provided in this application satisfies the following requirements: For positive electrode sheets with different compaction densities, the content of low-viscosity solvent and film-forming additives in the matching electrolyte can be calculated to obtain a matching electrolyte. After preparing a lithium battery with the positive electrode sheet and the matching electrolyte, not only does the electrolyte have good wettability to the positive electrode sheet, that is, the lithium battery has low interfacial impedance and good lithium-ion transport performance, but the lithium battery also has excellent high-temperature cycle stability.

[0009] In a first aspect, this application provides an electrolyte comprising a lithium salt, a solvent, and a film-forming additive, wherein the solvent comprises a low-viscosity solvent with a viscosity of less than 0.50 mPa·s;

[0010] The electrolyte meets the following requirements. Wherein, PD is 2.1 to 2.6, and PD is the compaction density value of the positive electrode sheet in the lithium battery that is paired with the electrolyte. The unit of compaction density is g / cm³. 3 ;

[0011] The mass fraction of the low-viscosity solvent in the solvent is W, expressed as wt%, with the mass of the film-forming additive in the electrolyte being the ratio of the mass of the lithium salt and the total mass of the solvent to A. dd .

[0012] The electrolyte provided in this application satisfies the following conditions: This application controls the content of low-viscosity solvents and film-forming additives in the electrolyte. When used in lithium batteries, especially lithium batteries with high-density positive electrode sheets, the electrolyte has good wettability on the positive electrode sheet, resulting in lithium batteries with low interfacial impedance, good lithium-ion transport performance, and excellent high-temperature cycle stability.

[0013] Optionally, the electrolyte satisfies

[0014] Optionally, 0.087≤PD:W≤0.420, or 0.100≤PD:W≤0.220.

[0015] Optionally, 0.0014 ≤ A dd W≤0.0062, can be selected as 0.0016≤A dd W≤0.0033.

[0016] Optionally, PD is 2.2 to 2.5.

[0017] Optionally, W can be 5 to 30, or 10 to 25.

[0018] Optionally, A dd The range is 0.031 to 0.041, and can be selected as 0.033 to 0.039.

[0019] Optionally, the lithium salt includes LiPF6 and LiFSI.

[0020] Optionally, the concentration of LiPF6 in the electrolyte is 0.3–1 mol / L, and the concentration of LiFSI is 0.3–1 mol / L.

[0021] Optionally, the film-forming additive includes vinylene carbonate.

[0022] Optionally, the film-forming additive may further include any one or a combination of at least two of fluoroethylene carbonate, lithium difluorooxalate borate, and ethylene sulfate.

[0023] Optionally, based on the mass of the film-forming additive, the film-forming additive contains 46.5% to 100% vinylene carbonate, no more than 18.6 wt% fluoroethylene carbonate, no more than 11.6 wt% lithium difluorooxalate borate, and no more than 23.3 wt% vinyl sulfate.

[0024] Optionally, the viscosity of the low-viscosity solvent is 0.40 to 0.50 mPa·s.

[0025] Optionally, the low-viscosity solvent includes any one or a combination of at least two of ethyl acetate, methyl propionate, or ethyl propionate.

[0026] Optionally, the solvent may further include a main solvent, which may include ethylene carbonate.

[0027] Optionally, the main solvent may further include any one or a combination of at least two of propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0028] Optionally, based on the mass of the main solvent, the mass fraction of ethylene carbonate in the main solvent is 18.2 to 100 wt%, the mass fraction of propylene carbonate is not higher than 9.0 wt%, the mass fraction of methyl ethyl carbonate is not higher than 36.4 wt%, and the mass fraction of dimethyl carbonate is not higher than 36.4 wt%.

[0029] Secondly, this application provides a method for preparing the electrolyte described in the first aspect, the method comprising:

[0030] An electrolyte is obtained by mixing lithium salt, low-viscosity solvent, main solvent and film-forming additive.

[0031] Optionally, the preparation method includes: first mixing a low-viscosity solvent with a main solvent to obtain a solvent; second mixing the obtained solvent with a lithium salt to obtain a pre-electrolyte; and third mixing the obtained pre-electrolyte with a film-forming additive to obtain an electrolyte.

[0032] Thirdly, this application provides a lithium battery, the lithium battery comprising the electrolyte described in the first aspect;

[0033] The electrolyte meets the following requirements.

[0034] This application provides an electrolyte for lithium batteries that meets the following requirements: For positive electrode sheets with different compaction densities, the content of low-viscosity solvent and film-forming additives in the matching electrolyte can be calculated to obtain a matching electrolyte. After preparing a lithium battery with the positive electrode sheet and the matching electrolyte, not only does the electrolyte have good wettability to the positive electrode sheet, that is, the lithium battery has low interfacial impedance and good lithium-ion transport performance, but the lithium battery also has excellent high-temperature cycle stability.

[0035] Optionally, the positive electrode active material in the positive electrode sheet includes lithium manganese iron phosphate, and the areal density of the positive electrode sheet on one side is 200-260 g / m³. 2 The option is 210-250 g / m³. 2 .

[0036] Optionally, the negative electrode of the electrolyte comprises a graphite negative electrode, wherein the compaction density of the graphite negative electrode is 1.55–1.75 g / cm³. 3 The surface density of a single surface is 80–110 g / m³. 2 .

[0037] Optionally, the electrolyte injection coefficient is 3.0 to 5.0 g / Ah, and can be 3.5 to 4.5 g / Ah.

[0038] Fourthly, this application provides an electric device comprising the lithium battery described in the third aspect.

[0039] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range. Beneficial effects

[0040] Compared with related technologies, this application has the following advantages:

[0041] (1) The electrolyte provided in this application satisfies the following conditions: This application controls the content of low-viscosity solvents and film-forming additives in the electrolyte and uses it in lithium batteries, especially lithium batteries with high-density positive electrode sheets. The electrolyte has good wettability on the positive electrode sheet, which makes the lithium battery have low interfacial impedance, good lithium-ion transport performance and excellent high-temperature cycle stability.

[0042] (2) The electrolyte for the lithium battery provided in this application meets the requirements. For positive electrode sheets with different compaction densities, the content of low-viscosity solvent and film-forming additives in the matching electrolyte can be calculated to obtain a matching electrolyte. After preparing a lithium battery with the positive electrode sheet and the matching electrolyte, not only does the electrolyte have good wettability to the positive electrode sheet, that is, the lithium battery has low interfacial impedance and good lithium-ion transport performance, but the lithium battery also has excellent high-temperature cycle stability.

[0043] After reading and understanding the detailed description, other aspects can be understood. Embodiments of the present invention

[0044] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0045] In one embodiment, this application provides an electrolyte comprising a lithium salt, a solvent, and a film-forming additive, wherein the solvent comprises a low-viscosity solvent with a viscosity of less than 0.50 mPa·s;

[0046] The electrolyte meets the following requirements. Wherein, PD is 2.1 to 2.6, and PD is the compaction density value of the positive electrode sheet in the lithium battery that is paired with the electrolyte. The unit of compaction density is g / cm³. 3 ;

[0047] The mass fraction of the low-viscosity solvent in the solvent is W, expressed as wt%, with the mass of the film-forming additive in the electrolyte being the ratio of the mass of the lithium salt and the total mass of the solvent to A. dd .

[0048] The low-viscosity solvent mentioned in this application refers to an organic solvent (including ethyl acetate, methyl propionate, and ethyl propionate, etc.) with low viscosity in the electrolyte. Low-viscosity solvents can reduce the overall viscosity of the electrolyte, improve lithium-ion mobility and electrolyte permeability, thereby improving the electrochemical performance of lithium batteries.

[0049] The electrolyte provided in this application satisfies For example, it can be 0.35, 0.40, 0.45, 0.50, 0.60, 0.70, 0.80, 0.90, 1.00, 1.10, 1.20 or 1.30, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] In this application, PD is 2.1 to 2.6, for example, it can be 2.1, 2.15, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45, 2.5, 2.55 or 2.6, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] The electrolyte provided in this application satisfies the following conditions: This application controls the content of low-viscosity solvents and film-forming additives in the electrolyte. When used in lithium batteries, especially lithium batteries with high-density positive electrode sheets, the electrolyte has good wettability on the positive electrode sheet, resulting in lithium batteries with low interfacial impedance, good lithium-ion transport performance, and excellent high-temperature cycle stability.

[0052] In some embodiments, the electrolyte satisfies For example, the values ​​could be 0.39, 0.42, 0.45, 0.48, 0.51, 0.54, 0.57, 0.60, 0.63, 0.66, 0.69, 0.72, or 0.73, but are not limited to the listed values; other unlisted values ​​within this range also apply.

[0053] In some implementations, 0.087 ≤ PD:W ≤ 0.420, where PD:W can be, for example, 0.087, 0.100, 0.120, 0.150, 0.180, 0.200, 0.220, 0.250, 0.280, 0.300, 0.320, 0.350, 0.380, 0.400, or 0.420, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, such as 0.100 ≤ PD:W ≤ 0.220.

[0054] In this application, when 0.087 ≤ PD:W, excessive use of low-viscosity solvent is avoided, which would lead to a decrease in the dissociation ability of lithium salt due to the low dielectric constant of the low-viscosity solvent, and a decrease in the oxidation decomposition of high-molecular-weight lithium due to the weak antioxidant capacity of the low-viscosity solvent. When PD:W ≤ 0.420, the low-viscosity solvent is ensured to sufficiently reduce the viscosity of the electrolyte, thereby improving the wetting effect of the electrolyte on the positive electrode, reducing the interfacial impedance in the electrolyte, and improving the lithium-ion transport performance.

[0055] In some implementations, 0.0014 ≤ A dd W≤0.0062, A dd For example, W can be 0.0013, 0.0015, 0.0020, 0.0025, 0.0030, 0.0035, 0.0040, 0.0045, 0.0050, 0.0055, 0.0060, or 0.0062, but is not limited to the listed values; other unlisted values ​​within this range also apply. It can be selected as 0.0016 ≤ A. dd W≤0.0033.

[0056] In this application, when 0.0014 ≤ A dd When W ≤ 0.0062, the electrolyte exhibits superior cycle performance, which is due to A dd When the value of W is within this range, the film-forming additive has an appropriate addition amount, which can not only form a more stable CEI film and SEI film to improve high-temperature cycling performance, but also ensure that the CEI film and SEI film have an appropriate thickness to ensure that the electrolyte has good lithium-ion transport performance, and also reduce the production cost of the electrolyte.

[0057] In some implementations, PD is 2.2 to 2.5, for example, it can be 2.2, 2.22, 2.24, 2.26, 2.28, 2.3, 2.32, 2.34, 2.36, 2.38, 2.4, 2.42, 2.44, 2.46, 2.48 or 2.5, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0058] In some implementations, W is 5 to 30, for example, it can be 5, 6, 8, 10, 12, 15, 18, 20, 22, 25, 28 or 30, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, and can be 10 to 25.

[0059] In some implementation schemes, A dd The range is 0.031 to 0.041, for example, it can be 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039, 0.040 or 0.041, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, and can be selected from 0.033 to 0.039.

[0060] In some embodiments, the lithium salt includes LiPF6 and LiFSI;

[0061] In some embodiments, the concentration of LiPF6 in the electrolyte is 0.3–1 mol / L, and the concentration of LiFSI is 0.3–1 mol / L.

[0062] The concentration of LiPF6 in the electrolyte described in this application is 0.3 to 1 mol / L, for example, it can be 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L.

[0063] The concentration of LiFSI in the electrolyte described in this application is 0.3 to 1 mol / L, for example, it can be 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L.

[0064] In some embodiments, the film-forming additive includes vinylene carbonate.

[0065] In some embodiments, the film-forming additive further includes any one or a combination of at least two of fluoroethylene carbonate, lithium difluorooxalate borate, and vinyl sulfate. Typical but non-limiting combinations include combinations of fluoroethylene carbonate and lithium difluorooxalate borate, combinations of lithium difluorooxalate borate and vinyl sulfate, combinations of fluoroethylene carbonate and vinyl sulfate, or combinations of fluoroethylene carbonate, lithium difluorooxalate borate, and vinyl sulfate.

[0066] In some embodiments, the film-forming additive contains, by mass percentage, 46.5% to 100% vinylene carbonate, no more than 18.6 wt% fluoroethylene carbonate, no more than 11.6 wt% lithium difluorooxalate borate, and no more than 23.3 wt% vinyl sulfate.

[0067] In this application, the mass of the film-forming additive is taken as 100%. The mass fraction of vinylene carbonate in the film-forming additive is 46.5% to 100%, for example, it can be 46.5%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0068] In this application, the mass of the film-forming additive is taken as 100%. The mass fraction of fluoroethylene carbonate in the film-forming additive is not higher than 18.6 wt%, for example, it can be 0.1 wt%, 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 18.6 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0069] In this application, the mass of the film-forming additive is taken as 100%. The mass fraction of lithium difluorooxalate borate in the film-forming additive is not higher than 11.6 wt%, for example, it can be 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 10 wt%, 11 wt%, or 11.6 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0070] In this application, the mass of the film-forming additive is taken as 100%. The mass fraction of vinyl sulfate in the film-forming additive is not higher than 23.3 wt%, for example, it can be 0.1 wt%, 2 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, or 23.3 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0071] In some embodiments, the viscosity of the low-viscosity solvent is 0.40 to 0.50 mPa·s, for example, 0.40 mPa·s, 0.41 mPa·s, 0.42 mPa·s, 0.43 mPa·s, 0.44 mPa·s, 0.45 mPa·s, 0.46 mPa·s, 0.47 mPa·s, 0.48 mPa·s, 0.49 mPa·s, or 0.50 mPa·s, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0072] In this application, when the low-viscosity solvent has a viscosity of 0.40 to 0.50 mPa·s, by optimizing ion transport, interfacial wettability and solvation structure, a balance between high ionic conductivity, low interfacial impedance and wide temperature range stability of the electrolyte is achieved, ultimately improving the rate performance and high-temperature cycling performance of the battery; this viscosity range is the optimal window for kinetic and thermodynamic equilibrium.

[0073] In some embodiments, the low-viscosity solvent includes any one or a combination of at least two of ethyl acetate, methyl propionate, or ethyl propionate. Typical but non-limiting combinations include combinations of ethyl acetate and methyl propionate, methyl propionate and ethyl propionate, ethyl acetate and ethyl propionate, or ethyl acetate, methyl propionate, and ethyl propionate.

[0074] In some embodiments, the solvent further includes a main solvent, which includes ethylene carbonate.

[0075] In some embodiments, the main solvent further includes any one or a combination of at least two of propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. Typical but non-limiting combinations include combinations of propylene carbonate and ethyl methyl carbonate, combinations of ethyl methyl carbonate and dimethyl carbonate, combinations of propylene carbonate and dimethyl carbonate, or combinations of propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0076] In some embodiments, the main solvent contains 18.2 to 100 wt% ethylene carbonate, no more than 9.0 wt% propylene carbonate, no more than 36.4 wt% methyl ethyl carbonate, and no more than 36.4 wt% dimethyl carbonate, based on the mass of the main solvent.

[0077] In this application, the solvent is defined as a percentage by mass, and the mass fraction of ethylene carbonate in the solvent is 18.2 to 100 wt%, for example, it can be 18.2 wt%, 20 wt%, 25 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, or 100 wt%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0078] In this application, the mass of the solvent is taken as 100%. The mass fraction of propylene carbonate in the solvent is not higher than 9.0 wt%, for example, it can be 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, or 9 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0079] In this application, the mass of the solvent is taken as 100%. The mass fraction of methyl ethyl carbonate in the solvent is not higher than 36.4 wt%, for example, it can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 36.4 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0080] In this application, the mass of the solvent is taken as 100%. The mass fraction of dimethyl carbonate in the solvent is not higher than 36.4 wt%, for example, it can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 36.4 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0081] In another embodiment, this application provides a method for preparing the above-mentioned electrolyte, the method comprising:

[0082] An electrolyte is obtained by mixing lithium salt, low-viscosity solvent, main solvent and film-forming additive.

[0083] In some embodiments, the preparation method includes: first mixing a low-viscosity solvent with a main solvent to obtain a solvent; second mixing the obtained solvent with a lithium salt to obtain a pre-electrolyte; and third mixing the obtained pre-electrolyte with a film-forming additive to obtain an electrolyte.

[0084] In another embodiment, this application provides a lithium battery comprising the electrolyte described above;

[0085] The electrolyte meets the following requirements.

[0086] This application provides an electrolyte for lithium batteries that meets the following requirements: For positive electrode sheets with different compaction densities, the content of low-viscosity solvent and film-forming additives in the matching electrolyte can be calculated to obtain a matching electrolyte. After preparing a lithium battery with the positive electrode sheet and the matching electrolyte, not only does the electrolyte have good wettability to the positive electrode sheet, that is, the lithium battery has low interfacial impedance and good lithium-ion transport performance, but the lithium battery also has excellent high-temperature cycle stability.

[0087] In some embodiments, the positive electrode active material in the positive electrode sheet includes lithium manganese iron phosphate, and the areal density of the positive electrode sheet on one side is 200-260 g / m³. 2 For example, it could be 200g / m 2 205g / m 2 210g / m 2 215g / m 2 220g / m 2 225g / m 2 230g / m 2 235g / m 2 240g / m 2 245g / m 2 250g / m 2 255g / m 2 Or 260g / m 2 However, this is not limited to the listed values; other unlisted values ​​within this range are also applicable, and can be selected as 210–250 g / m³. 2 .

[0088] In some embodiments, the negative electrode of the lithium battery comprises a graphite negative electrode with a compaction density of 1.55–1.75 g / cm³. 3 For example, it could be 1.55 g / cm³ 3 1.58g / cm 3 1.60g / cm 3 1.62g / cm 3 1.65g / cm 3 1.68g / cm 3 1.70g / cm 3 1.72g / cm 3 Or 1.75g / cm 3 However, this is not limited to the listed values; other unlisted values ​​within this range also apply. The surface density of a single surface is 80–110 g / m². 2 .

[0089] In some embodiments, the electrolyte injection coefficient in the lithium battery is 3.0 to 5.0 g / Ah, for example, it can be 3.0 g / Ah, 3.2 g / Ah, 3.5 g / Ah, 3.8 g / Ah, 4.0 g / Ah, 4.2 g / Ah, 4.5 g / Ah, 4.8 g / Ah or 5.0 g / Ah, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, and can be selected as 3.5 to 4.5 g / Ah.

[0090] The lithium battery described in this application includes a positive electrode, a negative electrode, a separator, and an electrolyte. During the charging and discharging process of the lithium battery, lithium ions repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, serves to conduct active ions.

[0091] In some embodiments, the positive electrode of a lithium battery includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector. The compaction density of the positive electrode sheet has a meaning known in the art and can be tested using equipment and methods known in the art. The compaction density of the positive electrode sheet = areal density of the positive electrode film layer / thickness of the positive electrode film layer on one side. The areal density of the positive electrode sheet has a meaning known in the art and can be tested using equipment and methods known in the art. For example, take a positive electrode sheet that is single-sided coated and cold-pressed (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), cut it into small discs, and weigh them; then wipe off the positive electrode film layer of the weighed positive electrode sheet and weigh the current collector. The areal density of the positive electrode sheet = (weight of the small disc - weight of the current collector) / area of ​​the small disc.

[0092] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent; as an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0093] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0094] In some embodiments, the positive current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene.

[0095] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone, but is not limited to it.

[0096] In some implementations, the negative electrode of a lithium battery includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector.

[0097] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent; as an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include styrene-butadiene rubber, water-soluble unsaturated resin, and waterborne acrylic resin (e.g., at least one of polyacrylic acid, polymethacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan).

[0099] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene.

[0100] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone or deionized water, but is not limited to these.

[0101] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet also includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In some embodiments, the negative electrode sheet of this application also includes a protective layer covering the surface of the negative electrode film layer.

[0102] In the lithium battery described in this application, there are no particular restrictions on the type of separator used; any known porous separator with good chemical and mechanical stability can be selected.

[0103] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0104] In some implementations, the positive electrode, the separator, the negative electrode, and the electrolyte can be used to make a lithium battery.

[0105] In some implementations, the outer packaging of the lithium battery can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the individual battery cells can also be a soft pack, such as a pouch-type soft pack. The soft pack material can be plastic, such as at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0106] In another embodiment, this application provides an electric device comprising the electrolyte described above.

[0107] Example 1

[0108] This embodiment provides an electrolyte comprising a lithium salt, a solvent, and a film-forming additive. The solvent is composed of a low-viscosity solvent (ethyl acetate) with a viscosity of 0.45 mPa·s and a main solvent.

[0109] The electrolyte meets the following requirements.

[0110] Wherein, PD is the compaction density of the positive electrode sheet in the lithium battery, and the unit of compaction density is g / cm³. 3The mass fraction of the low-viscosity solvent (ethyl acetate) in the solvent is W, expressed as wt%, with the solvent mass as 100%. The ratio of the mass of the film-forming additive in the electrolyte to the total mass of the lithium salt and solvent is A. dd ;

[0111] PD is 2.3; W is 18; A dd =0.036; PD: W = 0.128; A dd W = 0.0020;

[0112] The lithium salt comprises LiPF6 at a concentration of 0.6 mol / L and LiFSI at a concentration of 0.6 mol / L;

[0113] The film-forming additive includes vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, and vinyl sulfate; based on the mass of the film-forming additive, the mass fraction of vinylene carbonate is 60%, the mass fraction of fluoroethylene carbonate is 10 wt%, the mass fraction of lithium difluorooxalate borate is 10 wt%, and the mass fraction of vinyl sulfate is 20 wt%.

[0114] The main solvent includes ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate. Based on the mass of the main solvent, the main solvent contains 60 wt% ethylene carbonate, 5 wt% propylene carbonate, 20 wt% methyl ethyl carbonate, and 15 wt% dimethyl carbonate.

[0115] This embodiment also provides a lithium battery containing the above-mentioned electrolyte, wherein the positive electrode active material in the positive electrode sheet of the lithium battery includes lithium manganese iron phosphate, and the single-sided areal density of the positive electrode sheet is 230 g / m². 2 ;

[0116] The electrolyte meets the following requirements.

[0117] The negative electrode of the lithium battery includes a graphite negative electrode with a compaction density of 1.65 g / cm³. 3 The surface density of a single side is 95 g / m³. 2 ;

[0118] The electrolyte injection coefficient of the lithium battery is 4 g / Ah.

[0119] Example 2

[0120] This embodiment provides an electrolyte comprising a lithium salt, a solvent, and a film-forming additive. The solvent is composed of a low-viscosity solvent (ethyl acetate) with a viscosity of 0.45 mPa·s and a main solvent.

[0121] The electrolyte meets the following requirements.

[0122] Wherein, PD is the compaction density of the positive electrode sheet in the lithium battery, and the unit of compaction density is g / cm³. 3 The mass fraction of the low-viscosity solvent (ethyl acetate) in the solvent is W, expressed as wt%, with the solvent mass as 100%. The ratio of the mass of the film-forming additive in the electrolyte to the total mass of the lithium salt and solvent is A. dd ;

[0123] PD is 2.5; W is 25; A dd =0.039; PD: W = 0.100; A dd W = 0.0016;

[0124] The lithium salt comprises LiPF6 at a concentration of 0.4 mol / L and LiFSI at a concentration of 0.8 mol / L;

[0125] The film-forming additive includes vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, and vinyl sulfate; based on the mass of the film-forming additive, the mass fraction of vinylene carbonate is 70%, the mass fraction of fluoroethylene carbonate is 10 wt%, the mass fraction of lithium difluorooxalate borate is 10 wt%, and the mass fraction of vinyl sulfate is 10 wt%.

[0126] The main solvent includes ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate. Based on the mass of the main solvent, the main solvent contains 40 wt% ethylene carbonate, 6 wt% propylene carbonate, no more than 24 wt% methyl ethyl carbonate, and 30 wt% dimethyl carbonate.

[0127] This embodiment also provides a lithium battery containing the above-mentioned electrolyte, wherein the positive electrode active material in the positive electrode sheet of the lithium battery includes lithium manganese iron phosphate, and the single-sided areal density of the positive electrode sheet is 250 g / m². 2 ;

[0128] The electrolyte meets the following requirements.

[0129] The negative electrode of the lithium battery includes a graphite negative electrode with a compaction density of 1.60 g / cm³. 3 The surface density of a single side is 90 g / m³. 2 ;

[0130] The electrolyte of the lithium battery has an injection coefficient of 3.5 g / Ah.

[0131] Example 3

[0132] This embodiment provides an electrolyte comprising a lithium salt, a solvent, and a film-forming additive. The solvent is composed of a low-viscosity solvent (ethyl acetate) with a viscosity of 0.45 mPa·s and a main solvent.

[0133] The electrolyte meets the following requirements.

[0134] Wherein, PD is the compaction density of the positive electrode sheet in the lithium battery, and the unit of compaction density is g / cm³. 3 The mass fraction of the low-viscosity solvent (ethyl acetate) in the solvent is W, expressed as wt%, with the solvent mass as 100%. The ratio of the mass of the film-forming additive in the electrolyte to the total mass of the lithium salt and solvent is A. dd ;

[0135] PD is 2.2; W is 10; A dd =0.033; PD: W = 0.220; A dd W = 0.0033;

[0136] The lithium salt comprises LiPF6 at a concentration of 0.8 mol / L and LiFSI at a concentration of 0.4 mol / L;

[0137] The film-forming additive includes vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, and vinyl sulfate; based on the mass of the film-forming additive, the mass fraction of vinylene carbonate is 50%, the mass fraction of fluoroethylene carbonate is not higher than 18 wt%, the mass fraction of lithium difluorooxalate borate is 10 wt%, and the mass fraction of vinyl sulfate is 22 wt%.

[0138] The main solvent includes ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate. Based on the mass of the main solvent, the main solvent contains 30 wt% ethylene carbonate, 9.0 wt% propylene carbonate, no more than 30 wt% methyl ethyl carbonate, and 31 wt% dimethyl carbonate.

[0139] This embodiment also provides a lithium battery containing the above-mentioned electrolyte, wherein the positive electrode active material in the positive electrode sheet of the lithium battery includes lithium manganese iron phosphate, and the single-sided areal density of the positive electrode sheet is 210 g / m². 2 ;

[0140] The electrolyte meets the following requirements.

[0141] The negative electrode of the lithium battery includes a graphite negative electrode with a compaction density of 1.70 g / cm³. 3 The surface density of a single side is 100 g / m³. 2 ;

[0142] The electrolyte injection coefficient of the lithium battery is 4.5 g / Ah.

[0143] Example 4

[0144] This embodiment provides an electrolyte comprising a lithium salt, a solvent, and a film-forming additive. The solvent is composed of a low-viscosity solvent (ethyl propionate) with a viscosity of 0.40 mPa·s and a main solvent.

[0145] The electrolyte meets the following requirements.

[0146] Wherein, PD is the compaction density of the positive electrode sheet in the lithium battery, and the unit of compaction density is g / cm³. 3 The mass fraction of the low-viscosity solvent (ethyl propionate) in the solvent, expressed as W (wt%), is given by weight as 100%. The ratio of the mass of the film-forming additive in the electrolyte to the total mass of the lithium salt and solvent is A. dd ;

[0147] PD is 2.1; W is 5; A dd =0.031; PD: W = 0.420; A dd W = 0.0062;

[0148] The lithium salt comprises LiPF6 at a concentration of 1 mol / L and LiFSI at a concentration of 0.3 mol / L;

[0149] The film-forming additive includes vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, and vinyl sulfate; based on the mass percentage of the film-forming additive, the mass fraction of vinylene carbonate is 46.5%, the mass fraction of fluoroethylene carbonate is 18.6 wt%, the mass fraction of lithium difluorooxalate borate is 11.6 wt%, and the mass fraction of vinyl sulfate is 23.3 wt%.

[0150] The main solvent includes ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate. Based on the mass of the main solvent, the main solvent contains 80 wt% ethylene carbonate, 2 wt% propylene carbonate, 10 wt% methyl ethyl carbonate, and 8 wt% dimethyl carbonate.

[0151] This embodiment also provides a lithium battery containing the above-mentioned electrolyte, wherein the positive electrode active material in the positive electrode sheet of the lithium battery includes lithium manganese iron phosphate, and the single-sided areal density of the positive electrode sheet is 200 g / m². 2 ;

[0152] The electrolyte meets the following requirements.

[0153] The negative electrode of the lithium battery includes a graphite negative electrode with a compaction density of 1.55 g / cm³. 3 The surface density of a single side is 80 g / m³. 2 ;

[0154] The electrolyte injection coefficient of the lithium battery is 5.0 g / Ah.

[0155] Example 5

[0156] This embodiment provides an electrolyte comprising lithium salt, solvent and film-forming additive, wherein the solvent is composed of a low-viscosity solvent (methyl propionate) with a viscosity of 0.50 mPa·s and a main solvent;

[0157] The electrolyte meets the following requirements.

[0158] Wherein, PD is the compaction density of the positive electrode sheet in the lithium battery, and the unit of compaction density is g / cm³. 3 The mass fraction of the low-viscosity solvent (methyl propionate) in the solvent, expressed as W (wt%), is given by weight as 100% of the solvent's mass. The ratio of the mass of the film-forming additive in the electrolyte to the total mass of the lithium salt and solvent is A. dd ;

[0159] PD is 2.6; W is 30; A dd =0.041; PD: W = 0.087; A dd W = 0.0014;

[0160] The lithium salt comprises LiPF6 at a concentration of 0.3 mol / L and LiFSI at a concentration of 1 mol / L;

[0161] The film-forming additive includes vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, and vinyl sulfate; based on the mass of the film-forming additive, the mass fraction of vinylene carbonate is 60%, the mass fraction of fluoroethylene carbonate is 10 wt%, the mass fraction of lithium difluorooxalate borate is 10 wt%, and the mass fraction of vinyl sulfate is 20 wt%.

[0162] The main solvent includes ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate. Based on the mass of the main solvent, the main solvent contains 18.2 wt% ethylene carbonate, 9.0 wt% propylene carbonate, 36.4 wt% methyl ethyl carbonate, and 36.4 wt% dimethyl carbonate.

[0163] This embodiment also provides a lithium battery containing the above-mentioned electrolyte, wherein the positive electrode active material in the positive electrode sheet of the lithium battery includes lithium manganese iron phosphate, and the single-sided areal density of the positive electrode sheet is 260 g / m². 2 ;

[0164] The electrolyte meets the following requirements.

[0165] The negative electrode of the lithium battery includes a graphite negative electrode with a compaction density of 1.75 g / cm³. 3 The surface density of a single side is 110 g / m³. 2 ;

[0166] The electrolyte injection coefficient of the lithium battery is 3.0 g / Ah.

[0167] Example 6

[0168] This embodiment provides an electrolyte with PD of 2.3, W = 28, and A dd =0.056, PD:W = 0.082, A dd W = 0.0020 Except for the above, everything else is the same as in Example 1.

[0169] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0170] Example 7

[0171] This embodiment provides an electrolyte with PD of 2.3, W = 5.1, and A dd =0.010, PD:W = 0.45, A dd W = 0.0020 Except for the above, everything else is the same as in Example 1.

[0172] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0173] Example 8

[0174] This embodiment provides an electrolyte with a PD of 2.95, W = 23, and A...dd =0.028, PD:W = 0.128, A dd W = 0.0012, Except for the above, everything else is the same as in Example 1.

[0175] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0176] Example 9

[0177] This embodiment provides an electrolyte, except that PD is 2, W = 16, and A... dd =0.102, PD:W = 0.128, A dd W = 0.0064 Except for the above, everything else is the same as in Example 1.

[0178] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0179] Example 10

[0180] This embodiment provides an electrolyte, which is the same as in Example 1, except that the low-viscosity solvent is ethyl formate with a viscosity of 0.30 mPa·s.

[0181] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0182] Comparative Example 1

[0183] This example provides an electrolyte with PD of 2.3, W = 18, and A dd =0.0252, PD:W = 0.128, A dd W = 0.0014 Except for the above, everything else is the same as in Example 1.

[0184] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0185] Comparative Example 2

[0186] This embodiment provides an electrolyte with PD of 2.3, W = 18, and A dd =0.106, PD:W = 0.128, A dd W = 0.0059 Except for the above, everything else is the same as in Example 1.

[0187] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0188] Comparative Example 3

[0189] This embodiment provides an electrolyte with PD of 2.3, W = 15, and A dd =0.011, PD:W = 0.153, A dd W = 0.0007 Except for the above, everything else is the same as in Example 1.

[0190] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0191] Comparative Example 4

[0192] This embodiment provides an electrolyte that is identical to that in Example 1, except that the low-viscosity solvent (ethyl acetate) is omitted and replaced with an equal mass of the main solvent.

[0193] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0194] Comparative Example 5

[0195] This embodiment provides an electrolyte, which is the same as in Example 1, except that the low-viscosity solvent is methyl propyl carbonate with a viscosity of 0.60 mPa·s.

[0196] This embodiment also provides a lithium battery, which is the same as that in Embodiment 1 except that the electrolyte of the lithium battery is the same as that in this embodiment.

[0197] The lithium batteries provided in the above embodiments and comparative examples were subjected to rate performance testing, current resistance testing, and high-temperature cycle stability testing.

[0198] The method for rate performance testing is as follows: Under conditions of 25℃, the battery is fully charged and discharged. The test steps are as follows: the battery is left to rest for 30 minutes; then constant current and constant voltage charging is performed with a current of 0.33C, a constant voltage of 4.2V, and a cutoff current of 0.05C (C is the battery design capacity), and the cycle is repeated three times. The capacity of the last cycle is recorded as the calibrated capacity Q; the battery is left to rest for 1 hour, and then constant current and constant voltage charging is performed again with a current of 0.33Q, a constant voltage of 4.2V, and a cutoff current of 0.05Q; the battery is left to rest for 30 minutes, and then the constant current discharge capacity of 3Q is recorded as Q1. The 3C discharge rate performance Q1 / Q of the lithium battery is shown in Table 1.

[0199] The method for testing DC resistance is as follows: Under conditions of 25℃, the battery is fully charged and discharged. The test steps are as follows: let the battery rest for 30 minutes; then perform constant current and constant voltage charging with a current of 0.33C, a constant voltage of 4.2V, and a cutoff current of 0.05C (C is the battery design capacity), cycle three times, and record the capacity of the last cycle as Q, the rated capacity; let it rest for 1 hour, then perform constant current and constant voltage charging with a current of 0.33Q, a constant voltage of 4.2V, and a cutoff current of 0.05Q; let the battery rest for another 30 minutes, then discharge it at a constant current of 0.33Q to 50% of its SOC capacity; let the battery rest for another hour, then discharge it at a constant current of 1Q for 30 seconds. The DC resistance (DCR) of the battery is measured and is shown in Table 1.

[0200] The method for high-temperature cycle stability testing is as follows: The battery is fully charged and discharged at 45℃. The test steps are: The battery is left to rest for 30 minutes; then constant current and constant voltage charging is performed at a current of 0.33C, a constant voltage of 4.2V, and a cutoff current of 0.05C (C is the battery's design capacity), for three cycles, and the capacity of the last cycle is recorded as Q (calibrated capacity); the battery is then left to rest for 1 hour, and then constant current and constant voltage charging is performed again at a current of 1Q, a constant voltage of 4.2V, and a cutoff current of 0.05Q; the battery is then left to rest for 1 hour; then constant current discharge is performed at a current of 1Q, for 1000 cycles. The capacity retention rate after 1000 cycles at 45℃ is shown in Table 1.

[0201] Table 1

[0202] From Table 1, we can obtain:

[0203] (1) The lithium batteries provided in Examples 1 to 3 of this application have low DC resistance, high 3C rate performance and strong high temperature cycle stability;

[0204] (2) By comparing Examples 1-3 with Examples 4 and 5, it can be seen that the lithium battery meets the requirements. 0.100≤PD: W≤0.220, 0.0016≤A dd W≤0.0033, PD is 2.2~2.5, W is 10~25, A dd When the selectable value is 0.033 to 0.039, lithium batteries exhibit superior electrochemical performance;

[0205] (3) By comparing Example 1 with Examples 6 and 7, it can be seen that when 0.087≤PD:W≤0.420, the electrolyte has better cycle performance. This is because when 0.087≤PD:W, too much low viscosity solvent is avoided, which leads to poor dissociation ability of lithium salt due to the low dielectric constant of low viscosity solvent, and high oxidation decomposition due to the weak antioxidant capacity of low viscosity solvent. When PD:W≤0.420, it is ensured that the low viscosity solvent can fully reduce the viscosity of the electrolyte, thereby improving the wetting effect of the electrolyte on the positive electrode, reducing the interfacial impedance in the lithium battery, and improving the lithium ion transport performance.

[0206] (4) By comparing Example 1 with Examples 8 and 9, it can be seen that 0.0014≤A dd When W ≤ 0.0062, lithium batteries exhibit superior cycle performance, which is due to A dd When the value of W is within this range, the film-forming additive has an appropriate addition amount, which can not only form a more stable CEI film and SEI film to improve high-temperature cycling performance, but also ensure that the CEI film and SEI film have an appropriate thickness to ensure that the lithium battery has good lithium-ion transport performance, and also reduce the production cost of lithium battery.

[0207] (5) By comparing Example 1 and Example 10, it can be seen that the viscosity of the low-viscosity solvent in this application affects the performance of the lithium battery. When the viscosity of the low-viscosity solvent is 0.40 to 0.50 mPa·s, by optimizing ion transport, interfacial wettability and solvation structure, the high ionic conductivity, low interfacial impedance and wide temperature range stability of the electrolyte are achieved, which ultimately improves the rate performance and high temperature cycling performance of the battery. This viscosity range is the best window for kinetic and thermodynamic balance.

[0208] (6) As can be seen from the comparison between Example 1 and Comparative Examples 1-4, the electrolyte in the lithium battery provided in this application meets the requirements. For positive electrode sheets with different compaction densities, the content of low-viscosity solvent and film-forming additives in the matching electrolyte can be calculated to obtain a matching electrolyte. After preparing a lithium battery with the positive electrode sheet and the matching electrolyte, not only does the electrolyte have good wettability to the positive electrode sheet, that is, the lithium battery has low interfacial impedance and good lithium-ion transport performance, but the lithium battery also has excellent high-temperature cycle stability.

Claims

1. An electrolyte comprising a lithium salt, a solvent, and a film-forming additive, wherein the solvent comprises a low-viscosity solvent with a viscosity of less than 0.50 mPa·s; The electrolyte satisfies wherein PD is 2.1-2.6, PD is the value of the compacted density of the positive electrode sheet in combination with the electrolyte in the lithium battery, and the unit of the compacted density is g / cm 3 ; The value of the mass fraction of the low viscosity solvent in the solvent is W, in wt%, based on 100% by mass of the solvent; the ratio of the mass of the film-forming additive in the electrolyte to the total mass of the lithium salt and the solvent is A dd .

2. The electrolyte of claim 1, wherein, The electrolyte satisfies 3. The electrolyte of claim 1, wherein, 0.087≤PD:W≤0.420, can be selected as 0.100≤PD:W≤0.

220.

4. The electrolyte of claim 1, wherein, 0.0014≤A dd : W≤0.0062, optionally 0.0016≤A dd : W≤0.0033.

5. The electrolyte of claim 1, wherein, PD is 2.2–2.5; Optionally, W is 5 to 30, or optionally 10 to 25; Optionally, A dd is 0.031 to 0.041, optionally 0.033 to 0.

039.

6. The electrolyte of claim 1, wherein, The lithium salts include LiPF6 and LiFSI; Optionally, the concentration of LiPF6 in the electrolyte is 0.3–1 mol / L, and the concentration of LiFSI is 0.3–1 mol / L.

7. The electrolyte of claim 1, wherein, The film-forming additive includes vinylene carbonate.

8. The electrolyte of claim 1, wherein, The viscosity of the low-viscosity solvent is 0.40–0.50 mPa·s; Optionally, the low-viscosity solvent includes any one or a combination of at least two of ethyl acetate, methyl propionate, or ethyl propionate.

9. A method for preparing the electrolyte according to any one of claims 1-8, comprising: An electrolyte is obtained by mixing lithium salt, low-viscosity solvent, main solvent and film-forming additive.

10. The production method according to claim 9, wherein The preparation method includes: first mixing a low-viscosity solvent with a main solvent to obtain a solvent; second mixing the obtained solvent with a lithium salt to obtain a pre-electrolyte; and third mixing the obtained pre-electrolyte with a film-forming additive to obtain an electrolyte.

11. A lithium battery wherein, The lithium battery includes the electrolyte according to any one of claims 1-8; The electrolyte satisfies 12. The lithium battery of claim 11, wherein, The positive electrode active material in the positive electrode sheet of the lithium battery includes lithium manganese iron phosphate, and the areal density of the positive electrode sheet is 200-260 g / m². 2 The option is 210-250 g / m³. 2 .

13. The lithium battery of claim 11, wherein, The negative electrode of the lithium battery includes a graphite negative electrode with a compaction density of 1.55–1.75 g / cm³. 3 The surface density of a single surface is 80–110 g / m³. 2 .

14. The lithium battery of claim 11, wherein, The electrolyte of the lithium battery has an injection coefficient of 3.0 to 5.0 g / Ah, which can be selected as 3.5 to 4.5 g / Ah.

15. An electrically powered device, wherein, The electric device includes the lithium battery as described in any one of claims 11-14.

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