A non-aqueous electrolyte, a lithium ion battery and an electric device

Abstract

The application discloses a non-aqueous electrolyte, a lithium ion battery and an electric device, and belongs to the technical field of batteries.The non-aqueous electrolyte comprises a lithium salt and an electrolyte; the electrolyte comprises 86wt%-90.5wt% of a solvent, 9wt%-12.5wt% of a film-forming additive and 0.5wt%-1.5wt% of a lithium salt additive according to the mass percentage.The solvent comprises methyl acetate, and the content of the methyl acetate in the electrolyte is 2wt%-15wt%; the film-forming additive comprises at least one of fluoroethylene carbonate and vinylene carbonate; and the lithium salt additive comprises at least two of lithium difluorophosphate, lithium bisoxalate borate and lithium difluoro oxalate borate.The non-aqueous electrolyte realizes the SEI stability and the cycle life superior to an ethyl acetate system through the low swelling characteristics of the methyl acetate, the compounding effect of the film-forming additive and the multiple lithium salt.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a non-aqueous electrolyte, a lithium-ion battery, and an electrical device. Background Technology

[0002] The solid electrolyte interphase (SEI) film is a passivation film formed on the surface of the negative electrode of a lithium-ion battery during the first charge and discharge process. It is mainly composed of electrolyte decomposition products (polycarbonates, LiF, Li₂CO₃, etc.). The integrity and stability of the SEI film directly affect the battery's cycle life, safety performance, and high-rate performance. During battery cycling, organic solvent molecules in the electrolyte continuously interact with the SEI film, penetrating, swelling, and even dissolving the organic components of the SEI film, leading to continuous thickening and reconstruction of the SEI film. This process not only consumes the active components in the electrolyte but also causes a continuous increase in interfacial impedance, ultimately resulting in capacity decay and deterioration of power performance.

[0003] Linear carboxylic acid ester solvents, such as ethyl acetate, ethyl propionate, and methyl acetate, are often used to improve the low-temperature and rate performance of lithium-ion battery electrolytes due to their low viscosity. However, it is generally recognized in the art that low molecular weight esters, such as ethyl acetate and methyl acetate, form an SEI film with excessively high resistance and insufficient protection on the negative electrode, while ethyl propionate and ethyl butyrate exhibit superior SEI performance. In other words, it has long been generally accepted in the art that low molecular weight esters are detrimental to SEI.

[0004] Therefore, how to improve rate performance using low-viscosity linear carboxylic esters while avoiding their adverse effects on SEI film stability is a technical problem that urgently needs to be solved in this field.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a non-aqueous electrolyte, a lithium-ion battery, and an electrical device to solve or improve the above-mentioned technical problems.

[0007] This invention can be implemented as follows: In a first aspect, the present invention provides a non-aqueous electrolyte comprising a lithium salt and an electrolyte; the electrolyte comprises, by mass percentage, 86wt% to 90.5wt% of a solvent, 9wt% to 12.5wt% of a film-forming additive, and 0.5wt% to 1.5wt% of a lithium salt additive. The solvent includes methyl acetate, and the content of methyl acetate in the electrolyte is 2wt%~15wt%. Film-forming additives include at least one of fluoroethylene carbonate and vinylene carbonate; The lithium salt additives include at least two of lithium difluorophosphate, lithium bis(oxalate)borate, and lithium difluorooxalateborate.

[0008] In optional embodiments, the solvent further includes dimethyl carbonate and ethylene carbonate; The content of dimethyl carbonate in the electrolyte is 59wt%~68.5wt%, and the content of ethylene carbonate in the electrolyte is 12wt%~18wt%.

[0009] In an optional embodiment, the film-forming additive includes both fluoroethylene carbonate and vinylene carbonate. The content of fluoroethylene carbonate in the electrolyte is 8wt%~15wt%, and the content of vinylene carbonate in the electrolyte is 0.1wt%~1wt%.

[0010] In an optional embodiment, the content of fluoroethylene carbonate in the electrolyte is 8wt% to 12wt%, and the content of vinylene carbonate in the electrolyte is 0.5wt% to 1wt%.

[0011] In an optional embodiment, the mass ratio of methyl acetate to fluoroethylene carbonate is 1:(0.5~7.5).

[0012] In an optional embodiment, the lithium salt additive contains at least lithium difluorophosphate and lithium bis(oxalato)borate. The content of lithium difluorophosphate in the electrolyte is 0.3wt%~0.8wt%, and the content of lithium bis(oxalato)borate in the electrolyte is 0.2wt%~0.4wt%.

[0013] In an optional embodiment, the lithium salt content in the non-aqueous electrolyte is 0.8 mol / L to 1.2 mol / L.

[0014] In an optional implementation, the lithium salt includes lithium hexafluorophosphate.

[0015] In a second aspect, the present invention provides a lithium-ion battery comprising the non-aqueous electrolyte of any of the foregoing embodiments.

[0016] In an optional embodiment, the lithium-ion battery has at least one of the following characteristics: Feature 1: The swelling ratio of the SEI film on the surface of the negative electrode of the lithium-ion battery does not exceed 3.1%; Feature 2: The thickness increase rate of the SEI film on the surface of the lithium-ion battery negative electrode after 300 cycles does not exceed 28.5%; Feature 3: The capacity retention rate of the lithium-ion battery after 300 cycles of being charged to 4.2V at 1C constant current and then discharged to 2.8V at 1C constant current is no less than 89.5%. Feature 4: The CID trigger temperature of the lithium-ion battery does not exceed 77°C during the 0.2C / 6V overcharge test; Feature 5: The DC internal resistance of lithium-ion batteries does not increase by more than 14.5% after 300 cycles; Feature 6: The diameter of the lithium-ion battery is 20.8mm~21.2mm, the height is 64.5mm~70.5mm, and the cell energy density is ≥270Wh / kg.

[0017] Thirdly, the present invention provides an electrical device comprising a lithium-ion battery according to any of the foregoing embodiments.

[0018] The beneficial effects of this invention include: This invention creatively utilizes a non-aqueous electrolyte with a specific formulation for lithium-ion batteries, significantly reducing the swelling rate of the SEI film, slowing down the growth of SEI impedance, and improving the cycle retention rate, DCR stability, and overcharge safety of lithium ions compared to existing technologies. Specifically, by combining the low swelling characteristics of methyl acetate with the synergistic effect of film-forming additives and multiple lithium salts, it achieves superior SEI stability and cycle life compared to the ethyl acetate system, overcoming the long-held perception in the art that methyl acetate SEI films have excessively high resistance and insufficient protection, thus achieving SEI performance superior to the ethyl acetate system. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a lithium-ion battery provided by the present invention; Figure 2 This is a schematic diagram of the structure of the battery core provided by the present invention.

[0021] Icons: 10-Wound cell; 20-Casing; 31-Positive terminal; 32-Negative terminal; 1-Positive electrode plate; 2-Negative electrode plate; 3-Separator. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] The non-aqueous electrolyte, lithium-ion battery, and power device provided by this invention will be described in detail below.

[0024] The present invention provides a non-aqueous electrolyte comprising a lithium salt and an electrolyte.

[0025] In some alternative embodiments, the lithium salt content in the non-aqueous electrolyte is 0.8 mol / L to 1.2 mol / L, such as 0.8 mol / L, 1 mol / L, or 1.2 mol / L, or other values ​​within the range of 0.8 mol / L to 1.2 mol / L.

[0026] The lithium salt may, by way of example, include lithium hexafluorophosphate (LiPF6).

[0027] In this invention, the electrolyte comprises, by mass percentage, 86wt% to 90.5wt% of solvent, 9wt% to 12.5wt% of film-forming additives, and 0.5wt% to 1.5wt% of lithium salt additives.

[0028] In some optional embodiments, the solvent content in the electrolyte can be 86wt%, 86.5wt%, 87wt%, 87.5wt%, 88wt%, 88.5wt%, 89wt%, 89.5wt%, 90wt%, or 90.5wt%, or other values ​​in the range of 86wt% to 90.5wt%.

[0029] The content of film-forming additives in the electrolyte can be 9wt%, 9.5wt%, 10wt%, 10.5wt%, 11wt%, 11.5wt%, 12wt%, or 12.5wt%, or other values ​​within the range of 9wt% to 12.5wt%.

[0030] The lithium salt additive in the electrolyte can be 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, or 1.5wt%, or other values ​​within the range of 0.5wt% to 1.5wt%.

[0031] In this invention, the solvent includes methyl acetate (MA), and the content of methyl acetate in the non-aqueous electrolyte is 2wt% to 15wt%, such as 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt%, etc., or other values ​​within the range of 2wt% to 15wt%.

[0032] If the content of methyl acetate in the non-aqueous electrolyte is less than 2wt%, it is not conducive to significantly reducing the overall viscosity of the electrolyte system, making it difficult to effectively improve the ion transport rate under low temperature conditions. In other words, the improvement in low temperature performance is not obvious, and the film-forming modification effect is small. If the content of methyl acetate in the non-aqueous electrolyte is higher than 15wt%, it is not conducive to maintaining the thermal stability of the electrolyte and the oxidation resistance under high pressure. It is also easy to cause the battery's high-temperature storage performance to deteriorate. Specifically, it is easy to cause high-temperature gas generation and gas expansion, and the battery's high-temperature tolerance will decrease. In addition, it may also lead to a decrease in the electrolyte flash point and safety hazards.

[0033] In addition to methyl acetate, solvents may also include dimethyl carbonate (DMC) and ethylene carbonate (EC).

[0034] The content of dimethyl carbonate in the electrolyte can be 59wt% to 68.5wt%, such as 59wt%, 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, or 68.5wt%, or other values ​​within the range of 59wt% to 68.5wt%.

[0035] The content of ethylene carbonate in the electrolyte can be 12wt% to 18wt%, such as 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, or 18wt%, or other values ​​within the range of 12wt% to 18wt%.

[0036] It should be noted that the electrolyte of this invention does not contain ethyl acetate or other low molecular weight linear carboxylic acid ester solvents.

[0037] In this invention, the film-forming additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

[0038] In some alternative embodiments, the film-forming additive includes both fluoroethylene carbonate (FEC) and vinylene carbonate (VC). In this invention, under the same dosage of film-forming additive, the presence of both fluoroethylene carbonate and vinylene carbonate in the film-forming additive is superior to the presence of only one of them.

[0039] The content of fluoroethylene carbonate in the electrolyte can be 8wt% to 15wt%, such as 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt%, or other values ​​within the range of 8wt% to 15wt%. In some typical embodiments, the content of fluoroethylene carbonate in the electrolyte is 8wt% to 12wt%.

[0040] If the content of fluoroethylene carbonate in the electrolyte is less than 8 wt%, it is not conducive to building a sufficiently strong and dense fluorinated SEI film on the surface of the silicon-carbon high-volume expansion negative electrode. This makes it difficult to effectively suppress capacity decay and interfacial side reactions during battery cycling, meaning there is insufficient buffering for the volume expansion of the silicon-carbon negative electrode and limited protection of the high-voltage positive electrode interface. If the content of fluoroethylene carbonate in the electrolyte is greater than 15 wt%, it is not conducive to maintaining the ionic conductivity and low-temperature transport performance of the electrolyte, and it is prone to causing serious gas generation and swelling problems, damaging the safety and cycle life of the battery. In other words, it easily leads to the deterioration of the battery's low-temperature performance and ion transport, as well as causing severe gas generation and swelling.

[0041] Preferably, the mass ratio of methyl acetate to fluoroethylene carbonate can be 1:(0.5~7.5), such as 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7 or 1:7.5, or other values ​​within the range of 1:(0.5~7.5). In some typical embodiments, the mass ratio of methyl acetate to fluoroethylene carbonate is 1:(0.8~6).

[0042] The content of vinylene carbonate in the electrolyte can be 0.1wt% to 1wt%, such as 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, or 1wt%, or other values ​​within the range of 0.1wt% to 1wt%. In some typical embodiments, the content of vinylene carbonate in the electrolyte is 0.5wt% to 1wt%.

[0043] If the content of vinylene carbonate in the electrolyte is less than 0.1 wt%, it is not conducive to the formation of a complete and dense SEI protective film on the negative electrode surface, making it difficult to effectively suppress the continuous decomposition and side reactions of the electrolyte. If the content of vinylene carbonate in the electrolyte is greater than 1 wt%, it is not conducive to maintaining the low-temperature charge-discharge performance and rate performance of the battery, and it is also likely to lead to a significant increase in the battery's internal resistance.

[0044] In this invention, the lithium salt additive includes at least two of lithium difluorophosphate (LiDFP), lithium bis(oxalate-borate) (LiBOB), and lithium difluorooxalate-borate (LiODFB).

[0045] In some optional embodiments, the lithium salt additive contains at least both lithium difluorophosphate and lithium bis(oxalato)borate. In this invention, under the same dosage of lithium salt additive, the presence of both lithium difluorophosphate and lithium bis(oxalato)borate in the lithium salt additive is more effective than the presence of only one of them.

[0046] The content of lithium difluorophosphate in the electrolyte can be 0.3wt% to 0.8wt%, such as 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, or 0.8wt%, or other values ​​within the range of 0.3wt% to 0.8wt%.

[0047] If the content of lithium difluorophosphate in the electrolyte is less than 0.3 wt%, it is not conducive to building a sufficiently dense, smooth and stable interface protective film on the electrode surface, making it difficult to effectively play its role in improving the battery dynamic performance. If the content of lithium difluorophosphate in the electrolyte is greater than 0.8 wt%, it is not conducive to maintaining the high ionic conductivity of the electrolyte, and it is easy to cause excessive passivation of the electrode surface, which seriously damages the dynamic performance and safety of the battery.

[0048] The content of lithium bis(oxalate)borate in the electrolyte can be 0.2wt% to 0.4wt%, such as 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt% or 0.4wt%, or other values ​​within the range of 0.2wt% to 0.4wt%.

[0049] If the content of lithium bis(oxalato)borate in the electrolyte is less than 0.2 wt%, it is not conducive to the formation of a sufficiently dense and stable interfacial protective film on the positive and negative electrode surfaces, making it difficult to effectively improve the battery's high-temperature performance and cycle life. If the content of lithium bis(oxalato)borate in the electrolyte is greater than 0.4 wt%, it is not conducive to maintaining the battery's low impedance and good kinetic performance, and it is likely to lead to a significant increase in the battery's internal resistance, deteriorating the battery's cycle and rate performance.

[0050] Furthermore, the lithium salt additive may also include lithium difluorooxalate borate, and the content of lithium difluorooxalate borate in the electrolyte may be 0.2wt% to 0.4wt%, such as 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, or 0.4wt%, or other values ​​within the range of 0.2wt% to 0.4wt%.

[0051] Accordingly, the present invention also provides a lithium-ion battery comprising the above-mentioned non-aqueous electrolyte.

[0052] like Figure 1 and Figure 2 As shown, the lithium-ion battery includes a casing 20, an electrolyte, and a wound cell 10. The wound cell 10 is formed by stacking and winding a negative electrode 2, a separator 3, and a positive electrode 1. The wound cell 10 is encapsulated in the casing 20, and the electrolyte is injected into the space within the wound cell 10 enclosed by the casing 20, thus forming opposing positive and negative terminals 31 and 32 in the lithium-ion battery.

[0053] In some alternative embodiments, the swelling ratio of the SEI film on the surface of the lithium-ion battery negative electrode does not exceed 3.1 wt%, such as 2.5 wt% to 3.1 wt%.

[0054] In some alternative implementations, the thickness growth rate of the SEI film on the surface of the lithium-ion battery anode after 300 cycles does not exceed 28.5%, such as 27.1% to 28.3%.

[0055] In some optional implementations, the capacity retention rate of the lithium-ion battery after 300 cycles of being charged to 4.2V at 1C constant current and then discharged to 2.8V at 1C constant current is not less than 89.5%, such as 89.5% to 92%.

[0056] In some alternative implementations, the CID trigger temperature of the lithium-ion battery does not exceed 77°C during the 0.2C / 6V overcharge test, such as 70°C to 77°C.

[0057] In some alternative implementations, the DC internal resistance of the lithium-ion battery increases by no more than 14.5% after 300 cycles, such as 11% to 14.5%.

[0058] In some alternative implementations, the lithium-ion battery can have a diameter of 20.8 mm to 21.2 mm, a height of 64.5 mm to 70.5 mm, and a cell energy density of ≥270 Wh / kg.

[0059] In addition, the present invention also provides an electrical device comprising the aforementioned lithium-ion battery.

[0060] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0061] Table 1 Electrolyte Composition (wt%)

[0062] Example 1 This embodiment provides a non-aqueous electrolyte, which is composed of lithium salt and electrolyte. The lithium salt content in the non-aqueous electrolyte is 1 mol / L. As shown in Table 1, by mass percentage, the electrolyte contains: 89.1 wt% solvent (methyl acetate 5 wt%, dimethyl carbonate 68.1 wt%, and ethylene carbonate 16 wt%), 10.3 wt% film-forming additive (fluoroethylene carbonate 10 wt%, vinylene carbonate 0.3 wt%), and 0.6 wt% lithium salt additive (lithium difluorophosphate 0.3 wt%, lithium bis(oxalato)borate 0.3 wt%).

[0063] The electrolyte is prepared as follows: In a glove box (H2O and O2 both below 0.1 ppm, room temperature), ethylene carbonate and dimethyl carbonate are mixed in a set ratio, methyl acetate is added, and the mixture is stirred until homogeneous. Lithium hexafluorophosphate is slowly added until the concentration reaches 1.0 mol / L, followed by the addition of film-forming additives and lithium salt additives, and the mixture is stirred for 1 hour until completely dissolved.

[0064] Example 2 As shown in Table 1, the difference between this embodiment and Example 1 is that, by mass percentage, the electrolyte contains: 90.2 wt% solvent (10 wt% methyl acetate, 65.2 wt% dimethyl carbonate and 15 wt% ethylene carbonate), 9 wt% film-forming additives (8 wt% fluoroethylene carbonate and 1 wt% vinylene carbonate), and 0.8 wt% lithium salt additives (0.5 wt% lithium difluorophosphate and 0.3 wt% lithium bis(oxalato)borate).

[0065] Example 3 As shown in Table 1, the difference between this embodiment and Example 1 is that, by mass percentage, the electrolyte contains: 86.1 wt% solvent (methyl acetate 15 wt%, dimethyl carbonate 59.1 wt%, ethylene carbonate 12 wt%), 12.5 wt% film-forming additive (fluoroethylene carbonate 12 wt%, vinylene carbonate 0.5 wt%), and 1.4 wt% lithium salt additive (lithium difluorophosphate 0.8 wt%, lithium bis(oxalato)borate 0.3 wt%, lithium difluorooxalato)borate 0.3 wt%.

[0066] Example 4 As shown in Table 1, the difference between this embodiment and Example 1 is that, by mass percentage, the electrolyte contains: 86.9 wt% solvent (8 wt% methyl acetate, 61.9 wt% dimethyl carbonate, and 17 wt% ethylene carbonate), 12.5 wt% film-forming additive (12 wt% fluoroethylene carbonate and 0.5 wt% vinylene carbonate), and 0.6 wt% lithium salt additive (0.3 wt% lithium difluorophosphate and 0.3 wt% lithium bis(oxalato)borate).

[0067] Example 5 As shown in Table 1, the difference between this embodiment and Example 1 is that, by mass percentage, the electrolyte contains: 86.9 wt% solvent (methyl acetate 2 wt%, dimethyl carbonate 66.9 wt%, ethylene carbonate 18 wt%), 12.5 wt% film-forming additive (fluoroethylene carbonate 12 wt%, vinylene carbonate 0.5 wt%), and 0.6 wt% lithium salt additive (lithium difluorophosphate 0.3 wt%, lithium bis(oxalato)borate 0.3 wt%).

[0068] Comparative Example 1 As shown in Table 1, the difference between this comparative example and Example 2 is that ethyl acetate is used instead of methyl acetate.

[0069] Comparative Example 2 As shown in Table 1, the difference between this comparative example and Example 2 is that the total amount of film-forming additive remains unchanged, and all film-forming additives are fluoroethylene carbonate, without vinylene carbonate.

[0070] Comparative Example 3 As shown in Table 1, the difference between this comparative example and Example 2 is that the total amount of film-forming additive remains unchanged, and all film-forming additives are vinylene carbonate, without fluorinated vinyl carbonate.

[0071] Comparative Example 4 As shown in Table 1, the difference between this comparative example and Example 2 is that the total amount of lithium salt additive remains unchanged, and all lithium salt additives are lithium difluorophosphate, without lithium bis(oxalate-borate).

[0072] Test case The non-aqueous electrolytes from Examples 1-5 and Comparative Examples 1-4 were used in lithium-ion batteries, and the battery assembly method was as follows: the positive electrode used NCM811 ternary material with an areal loading of 3.5 mAh / cm³. 2 The negative electrode uses artificial graphite with an areal loading of 3.85 mAh / cm³. 2 The N / P ratio (capacity ratio of negative electrode to positive electrode) is 1.1. The separator is a PP / PE / PP three-layer composite separator with a thickness of 16μm. The positive electrode, separator, and negative electrode are stacked and then placed into an aluminum-plastic film casing, electrolyte is injected, and the casing is sealed. The battery is designed to have a capacity of 2.5Ah. The formation process is as follows: constant current charging at 0.1C to 4.2V, followed by aging at 60°C for 24 hours.

[0073] The assembled lithium-ion batteries were subjected to the following tests, and the results are shown in Tables 2 and 3.

[0074] (1) SEI swelling rate test: The simulated SEI film, i.e. polyvinyl carbonate film, is prepared as a standard sample, immersed in the electrolyte, and kept at 60°C for 24 hours. After taking it out, the surface electrolyte is wiped dry, and the swelling rate (which can also be understood as liquid absorption) is calculated by weighing.

[0075] (2) AC impedance test: The test was conducted at 4.2V under full charge, with a frequency range of 0.1Hz to 100kHz and an amplitude of 10mV. The SEI film impedance R was extracted by equivalent circuit fitting. SEI .

[0076] (3) DC internal resistance test: Under 50% SOC, discharge at 12A for 10s and 24A for 10s respectively, and calculate the ratio of voltage difference to current difference under the two discharge conditions.

[0077] (4) Cyclic test: Charge to 4.2V with 1C constant current, then discharge to 2.8V with 1C constant current, repeat 300 cycles, and record the discharge capacity of each cycle.

[0078] (5) Overcharge test: Charge the battery to 6V with a constant current of 0.2C, monitor the temperature change, and record the temperature value at the CID trigger moment.

[0079] Table 2 Comparison of SEI swelling ratio and impedance

[0080] Table 3 Comparison of Cycle Retention Rate and Overcharge Performance

[0081] As shown in Table 1, the SEI swelling rates of Examples 1-5 are all significantly lower than those of Comparative Example 1. Examples 2 and Comparative Example 1 demonstrate that the SEI swelling rate of methyl acetate can be reduced by more than 50% compared to ethyl acetate. Combined with Examples 1-5, it can be seen that the low swelling characteristics of methyl acetate for SEI remain stable over a wide range of 2wt% to 15wt%.

[0082] From the perspective of SEI impedance growth, R after 300 cycles corresponds to Examples 1-5. SEI The growth rates were all below 28.3%, while the R of the comparative ratio 1 was... SEI The growth rate was as high as 86.7%, a difference of more than 3 times.

[0083] As can be seen from Comparative Examples 2-4 and Example 2, the combination of fluoroethylene carbonate, vinylene carbonate, and bis-lithium salts (lithium difluorophosphate and lithium bis(oxalato)borate) synergistically contributes to the low impedance of SEI.

[0084] As shown in Table 2, the cycle retention rate of Examples 1-5 after 300 cycles was not less than 89.5%, which was about 8% to 10% higher than that of Comparative Example 1. Furthermore, even Example 5, which only added 2 wt% methyl acetate, achieved a cycle retention rate of 89.5%, which was significantly better than that of Comparative Example 1, which added 10 wt% ethyl acetate.

[0085] Based on the above results, this invention achieves SEI stability and cycle life superior to the ethyl acetate system by combining the low swelling characteristics of methyl acetate with the synergistic effect of film-forming additives and multiple lithium salts. This overcomes the long-standing perception in the field that methyl acetate SEI film has excessively high resistance and insufficient protection. The synergistic effect of film-forming additives and multiple lithium salts achieves SEI performance superior to the ethyl acetate system.

[0086] In summary, this invention creatively uses a non-aqueous electrolyte with a specific formulation for lithium-ion batteries, which significantly reduces the swelling rate of the SEI film, slows down the growth of SEI impedance, and improves the cycle retention rate, DCR stability, and overcharge safety of lithium ions compared to existing technologies.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that, It includes lithium salt and electrolyte; by mass percentage, the electrolyte includes 86wt% to 90.5wt% solvent, 9wt% to 12.5wt% film-forming additive and 0.5wt% to 1.5wt% lithium salt additive. The solvent includes methyl acetate, and the content of methyl acetate in the electrolyte is 2wt%~15wt%. The film-forming additive includes at least one of fluoroethylene carbonate and vinylene carbonate; The lithium salt additive includes at least two of lithium difluorophosphate, lithium bis(oxalate)borate, and lithium difluorooxalateborate.

2. The non-aqueous electrolyte according to claim 1, characterized in that, The solvent also includes dimethyl carbonate and ethylene carbonate; The dimethyl carbonate content in the electrolyte is 59wt%~68.5wt%, and the ethylene carbonate content in the electrolyte is 12wt%~18wt%.

3. The non-aqueous electrolyte according to claim 1 or 2, characterized in that, The film-forming additive includes both fluoroethylene carbonate and vinylene carbonate. The fluoroethylene carbonate content in the electrolyte is 8wt%~15wt%, and the vinylene carbonate content in the electrolyte is 0.1wt%~1wt%.

4. The non-aqueous electrolyte according to claim 3, characterized in that, The content of the fluoroethylene carbonate in the electrolyte is 8wt%~12wt%, and the content of the vinylene carbonate in the electrolyte is 0.5wt%~1wt%.

5. The non-aqueous electrolyte according to claim 3, characterized in that, The mass ratio of methyl acetate to fluoroethylene carbonate is 1:(0.5~7.5).

6. The non-aqueous electrolyte according to claim 1, characterized in that, The lithium salt additive contains at least lithium difluorophosphate and lithium bis(oxalate-borate) simultaneously. The lithium difluorophosphate content in the electrolyte is 0.3wt%~0.8wt%, and the lithium bis(oxalato)borate content in the electrolyte is 0.2wt%~0.4wt%.

7. The non-aqueous electrolyte according to claim 1, characterized in that, The lithium salt content in the non-aqueous electrolyte is 0.8 mol / L to 1.2 mol / L; Preferably, the lithium salt comprises lithium hexafluorophosphate.

8. A lithium-ion battery, characterized in that, Includes the non-aqueous electrolyte as described in any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that, The lithium-ion battery has at least one of the following characteristics: Feature 1: The swelling ratio of the SEI film on the surface of the lithium-ion battery negative electrode does not exceed 3.1 wt%; Feature 2: The thickness increase rate of the SEI film on the surface of the lithium-ion battery negative electrode after 300 cycles does not exceed 28.5%; Feature 3: The lithium-ion battery retains no less than 89.5% of its capacity after being charged to 4.2V at 1C constant current and then discharged to 2.8V at 1C constant current for 300 cycles. Feature 4: The CID trigger temperature of the lithium-ion battery does not exceed 77°C during the 0.2C / 6V overcharge test; Feature 5: The DC internal resistance of the lithium-ion battery increases by no more than 14.5% after 300 cycles; Feature 6: The lithium-ion battery has a diameter of 20.8mm~21.2mm, a height of 64.5mm~70.5mm, and a cell energy density of ≥270Wh / kg.

10. An electrical device, characterized in that, Including the lithium-ion battery as described in claim 8 or 9.

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