Electrolyte, battery, battery pack and electric equipment

Abstract

The invention provides an electrolyte, a battery, a battery pack and electric equipment, the electrolyte comprises a carbonic ester solvent, lithium nitrate and dimethyl sulfoxide, the mass ratio of the lithium nitrate in the electrolyte is x, the mass ratio of the dimethyl sulfoxide in the electrolyte is y, and x and y meet the following conditions: 0.2 wt% < = x < = 1.2 wt%, 0.8 wt% < = y < = 4.2 wt%, and 4 < = y / x < = 16; the mass ratio of the carbonic ester solvent in the electrolyte is greater than or equal to 80wt%. According to the invention, a small amount of dimethyl sulfoxide (DMSO) and lithium nitrate are added based on a traditional carbonate solvent, and the contents of the DMSO and the lithium nitrate are regulated, so that the problem of dissolution of the lithium nitrate in the traditional carbonate electrolyte is solved, the problem of co-intercalation of the DMSO in a graphite negative electrode is effectively inhibited, the production cost is reduced, and the graphite negative electrode is compatible; and the charging rate and / or the low-temperature performance of the lithium ion battery are / is effectively improved.

Description

An electrolyte, a battery, a battery pack, and an electrical device. Technical Field

[0001] This invention relates to the field of batteries, and more particularly to an electrolyte, a battery, a battery pack, and an electrical device. Background Technology

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and low self-discharge rate. However, with the increasing demands on battery performance in extreme environments, the low-temperature performance of existing lithium-ion batteries has become a significant bottleneck limiting their further application.

[0003] Adjusting the electrolyte composition has become a common method to improve the low-temperature performance of lithium-ion batteries. Lithium nitrate (LiNO3), as a good negative electrode film-forming agent, has attracted widespread attention from researchers. Lithium nitrate can form an SEI film (solid electrolyte interphase) with good lithium-ion conductivity on the negative electrode surface, thereby improving the lithium-ion conductivity. + This improves the transmission rate, thereby enhancing the battery's low-temperature performance. However, lithium nitrate has extremely low solubility in conventional carbonate electrolytes, making direct addition difficult. Patent CN201811276532.2 discloses an electrolyte scheme using LiNO3 as the electrolyte and a nitrogen-containing heterocyclic compound as the solvent. LiNO3 forms an SEI film on the lithium metal surface, inhibiting the growth of lithium dendrites. Patent CN201910284294.8 discloses an electrolyte using LiNO3 as the electrolyte and an amide compound as the solvent, similarly preparing an electrolyte for lithium metal batteries to inhibit lithium dendrite growth. Patent CN201910552682.X also discloses a LiNO3-containing electrolyte system. In addition to LiNO3, this electrolyte system also includes lithium bis(fluorosulfonyl) salt, which is also used in lithium metal batteries to form a stable solid electrolyte interphase (SEI) film on the lithium metal surface. As can be seen, the above schemes abandon traditional carbonate electrolytes and use novel polar solvents as the main solvent to promote the dissolution of LiNO3. The cost is high, and they are all used in lithium metal batteries, which have poor compatibility with traditional graphite anodes. Summary of the Invention

[0004] To address the technical problems existing in the background art, the present invention provides an electrolyte that is mainly composed of traditional carbonate solvents, with the addition of small amounts of dimethyl sulfoxide (DMSO) and lithium nitrate. By controlling the content of the two, not only is the dissolution problem of lithium nitrate in traditional carbonate-based electrolytes solved, but also the co-intercalation problem of DMSO in graphite anodes is effectively suppressed, thereby reducing production costs and ensuring compatibility with graphite anodes, and effectively improving the low-temperature performance of lithium-ion batteries.

[0005] The present invention also provides a battery comprising the above-described electrolyte, which, due to the inclusion of the electrolyte, has excellent low-temperature resistance.

[0006] The present invention also provides a battery pack including the above-mentioned battery, which has the advantages of high energy storage efficiency and long service life.

[0007] The present invention also provides an electrical device that, because it includes the aforementioned battery or battery pack, has good electrical performance and a long service life.

[0008] In a first aspect, the present invention provides an electrolyte comprising lithium nitrate and dimethyl sulfoxide, wherein the mass percentage of lithium nitrate in the electrolyte is x, and the mass percentage of dimethyl sulfoxide in the electrolyte is y, wherein x and y satisfy: 0.2wt%≤x≤1.2wt%, 0.8wt%≤y≤4.2wt%, and 4≤y / x≤16; and the mass percentage of the carbonate solvent in the electrolyte is greater than or equal to 80wt%.

[0009] Furthermore, 0.2% ≤ x ≤ 0.4%.

[0010] Furthermore, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butene carbonate.

[0011] Furthermore, it also includes lithium salts, said lithium salts comprising at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, lithium difluorosulfonyl imide, lithium trifluoromethanesulfonate, lithium perchlorate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium perfluorobutyl sulfonate, and lithium fluorinated fatty acids.

[0012] Furthermore, the lithium salt accounts for more than or equal to 10 wt% of the mass of the electrolyte.

[0013] Furthermore, it also includes organic film-forming additives, which include at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, methane disulfonate, or siloxane additives.

[0014] Furthermore, the organic film-forming additive has a mass percentage of less than or equal to 5 wt% in the electrolyte.

[0015] In a second aspect, the present invention provides a battery comprising a positive electrode, a negative electrode, and the electrolyte described in the first aspect; the negative electrode comprises a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, the negative electrode active material layer comprising graphite.

[0016] Thirdly, the present invention provides a battery pack comprising the battery described in the second aspect.

[0017] Fourthly, the present invention provides an electrical device comprising the battery described in the second aspect or the battery pack described in the third aspect.

[0018] This invention effectively improves the low-temperature performance of lithium-ion batteries and effectively suppresses the co-intercalation problem of DMSO in the graphite anode by simultaneously introducing LiNO3 (lithium nitrate) and dimethyl sulfoxide (DMSO) into the electrolyte and limiting their mass ratio. Specifically, DMSO is a strongly polar solvent that can effectively dissolve LiNO3. LiNO3 can form an SEI film on the anode surface before DMSO co-intercalation, effectively suppressing the co-intercalation reaction of DMSO. At low temperatures, the viscosity of the electrolyte increases and the ionic conductivity decreases. The SEI film, with its high ionic conductivity, can compensate for this defect to some extent, ensuring that lithium ions can still be effectively conducted at low temperatures. The specific ratio of lithium nitrate and dimethyl sulfoxide improves battery performance while also greatly avoiding the impact of dimethyl sulfoxide co-intercalation on the cycle performance of the graphite system. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In a first aspect, the present invention provides an electrolyte comprising lithium nitrate and dimethyl sulfoxide, wherein the mass percentage of lithium nitrate in the electrolyte is x, and the mass percentage of dimethyl sulfoxide in the electrolyte is y, wherein x and y satisfy: 0.2wt%≤x≤1.2wt%, 0.8wt%≤y≤4.2wt%, and 4≤y / x≤16; and the mass percentage of the carbonate solvent in the electrolyte is greater than or equal to 80wt%.

[0021] This invention provides a method to effectively improve the low-temperature performance of lithium-ion batteries containing graphite anodes by simultaneously introducing lithium nitrate and dimethyl sulfoxide (DMSO) into an electrolyte primarily composed of traditional carbonate solvents, and by limiting their mass ratio. The main reasons include: firstly, this electrolyte ensures the effective dissolution of lithium nitrate in carbonate electrolytes; secondly, it inhibits graphite sheet peeling caused by the co-intercalation of DMSO in the graphite anode. Specifically, DMSO is a strongly polar solvent that can effectively dissolve LiNO3; traditional film-forming agents such as vinylene carbonate (VC) have a film-forming potential of ~0.8 (V vs. Li) on the anode surface. + The film formation potential of LiNO3 on the negative electrode surface is 1.5 (V vs. Li). + / Li), while the potential for DMSO to undergo co-intercalation at the graphite anode is ~1.0 (V vs. Li). + Therefore, LiNO3 can form an SEI film on the negative electrode surface before DMSO co-intercalation, effectively inhibiting the co-intercalation reaction of DMSO. In addition, the higher the amount of DMSO added, the greater the probability of co-intercalation caused by the random movement of molecules, and its high viscosity will reduce the ionic conductivity of the electrolyte, all of which have adverse effects on battery performance. Therefore, only by limiting the amount of LiNO3 and DMSO added within a suitable range can the film-forming effect of LiNO3 be better utilized to form an SEI film with high lithium-ion conductivity on the graphite negative electrode surface, thereby improving the low-temperature performance of the battery.

[0022] For example, the LiNO3 content in the electrolyte can be tested using an ion chromatograph (IC). Specifically, using an IC-2800 ion chromatograph as an example, the experimental conditions are: anion exchange column, suppressor current 35 mA, flow rate 1 mL / min, eluent of 5 mmol / L sodium carbonate solution: acetone = 75:25, and injection volume 100 µL. First, the sample to be tested is diluted: 1 mL of electrolyte is taken, diluted with acetonitrile, and transferred to a 100 mL volumetric flask. The acetonitrile is then brought to the mark, and the solution is shaken well before testing. Next, a standard solution is prepared: 0.05 mL of a 1 mg / mL LiNO3 solution is taken... - The aqueous solution was diluted to a volumetric flask with deionized water to obtain NO3 with a concentration of 5 µg / mL. - Prepare a series of standard solutions with varying concentrations by transferring 1 mL, 2 mL, 4 mL, and 10 mL of the aqueous solution into 10 mL volumetric flasks and diluting to the mark with deionized water. Analyze the standards using NO3-. -A standard curve was established using the peak area (y) as the ordinate and the concentration of the standard sample as the abscissa (x). The curve equation and correlation coefficient were then obtained. Finally, the electrolyte to be tested was analyzed, and the LiNO3 content in the electrolyte was calculated based on the standard curve equation. The contents of other organic solvents in the electrolyte were obtained by gas chromatography-mass spectrometry (GC-MS).

[0023] In some implementations, 0.2% <x≤0.4%。

[0024] The above-described embodiments, by further limiting the mass ratio of lithium nitrate and dimethyl sulfoxide, can further improve the fast-charging performance of lithium-ion batteries containing graphite anodes. The main reason is that LiNO3 can form an SEI film with high ionic conductivity on the surface of the graphite anode. The SEI film with high ionic conductivity can more effectively conduct lithium ions and reduce the impedance of ions at the interface. This helps to achieve a higher charging rate during fast charging. Moreover, the SEI film with high ionic conductivity can reduce electrode polarization, thereby reducing the internal resistance of the battery and improving charging efficiency.

[0025] In some embodiments, the carbonate solvent includes at least one of ethylene carbonate (EC), propylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butene carbonate.

[0026] Specifically, when the mass percentage of carbonate solvent is above 80 wt%, the production cost of the electrolyte can be kept low. For example, the mass percentage of the carbonate solvent in the electrolyte is 80 wt%, 81 wt%, 82 wt%, 85 wt%, 87 wt%, 90 wt%, or any combination thereof.

[0027] In some embodiments, a lithium salt is also included, said lithium salt comprising at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, lithium difluorosulfonylimide, lithium trifluoromethanesulfonate, lithium perchlorate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium perfluorobutylsulfonate, and lithium fluorinated fatty acids.

[0028] In other embodiments, the lithium salt accounts for more than or equal to 10 wt% of the mass of the electrolyte.

[0029] For example, the lithium salt in the electrolyte has a mass percentage of 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, or any combination thereof.

[0030] In some embodiments, an organic film-forming additive is also included, said organic film-forming additive comprising at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), methylene disulfonate (MMDS), or siloxane additives.

[0031] Among them, the aforementioned organic film-forming additives have good affinity for the negative electrode surface, which can assist lithium nitrate in constructing a stable SEI film on the negative electrode surface. Compared with the inorganic SEI film formed by LiNO3, the SEI film formed by the organic film-forming additives has higher toughness and density, further protecting the negative electrode structure from solvent molecules, HF, and F in the electrolyte. - Corrosion from other impurities.

[0032] In other embodiments, the organic film-forming additive accounts for less than or equal to 5 wt% of the mass of the electrolyte.

[0033] For example, the organic film-forming additive in the electrolyte has a mass percentage of 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, etc., or any combination thereof.

[0034] In a second aspect, the present invention provides a battery comprising the electrolyte, positive electrode, and negative electrode as described in the first aspect above; wherein the active material of the negative electrode comprises graphite.

[0035] In some embodiments, the battery meets the following conditions: after being charged to 50% SOC at a constant current of 3.5C, then charged to 3.8V at a constant current of 1C, rested for a first preset time, and discharged to 2.0V at a constant current of 1C, and cycled 100 times, the battery capacity retention rate is greater than or equal to 38%; and after being charged to 3.8V at a constant current and constant voltage of 0.3C and discharged to 2.0V at a constant current of 0.3C under conditions of -8℃ to -10℃, and cycled 50 times, the battery capacity retention rate is greater than or equal to 25%.

[0036] It is understood that the purpose of the aforementioned first preset time is depolarization. Therefore, the value of the first preset time can be adjusted according to the actual situation. In some embodiments, the first preset time is 10 minutes. Exemplarily, the aforementioned negative electrode sheet includes a negative current collector and a negative active material layer located on at least one surface of the negative current collector. The negative active material layer includes the negative active material, a conductive agent, a dispersant, and a binder. The negative active material includes graphite. The conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene. The binder can be selected from at least one of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. The dispersant can be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate. The negative electrode current collector can be a conventional negative electrode current collector in this field, such as copper foil, etc. The mass fraction of the negative electrode active material in the negative electrode active layer is 90%-98%, the mass fraction of the binder is 0.5%-3%, and the mass fraction of the conductive agent is 0.5%-2.5%.

[0037] For example, the above-mentioned positive electrode sheet includes a positive current collector and a positive active material layer located on at least one surface of the positive current collector. The positive active material layer includes the positive active material, a conductive agent, a dispersant, and a binder. The above-mentioned lithium salt includes, but is not limited to, LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and Li 1+a Mn 1-b M b O2, LiCo 1-b M b O2, LiFe 1- b M b PO4, Li2Mn 1-b O4, LiNi x Co y Mn zAt least one of O2, etc., M is selected from one or more of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, 0≤a<0.2, 0≤b<1, x+y+z=1. The above conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, graphene; the binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, sodium polyacrylate; the dispersant can be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, sodium dodecyl sulfate.

[0038] The present invention does not specifically limit the thickness, areal density, and active layer thickness of the positive electrode sheet. However, in order to balance battery capacity, cycle life, and energy density, in one specific embodiment, the thickness of the positive electrode sheet is 40-130µm, specifically including but not limited to: 50µm, 60µm, 70µm, 80µm, 90µm, 100µm, 110µm, etc.; and the areal density of the positive electrode sheet is 10-35mg / cm³. 2 Specifically, including but not limited to: 10mg / cm 2 15mg / cm 2 20mg / cm 2 25mg / cm 2 30mg / cm 2 35mg / cm 2 The thickness of the active layer is 20-60µm, specifically including but not limited to: 25µm, 30µm, 35µm, 40µm, 45µm, 50µm, 55µm, etc.

[0039] The battery of the present invention can be manufactured according to conventional methods in the art. For example, the positive electrode, separator and negative electrode can be stacked in sequence and assembled into a cell by winding or stacking process. Then, after hot pressing, shaping, packaging and baking, electrolyte is injected and the battery is obtained after impregnation and other processes.

[0040] The battery described above may also include a separator. This invention does not impose any particular limitation on the material of the separator; any known porous separator with electrochemical and chemical stability can be selected. For example, it can be at least one of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP), or polyvinylidene fluoride. The separator can be single-layer or multi-layer.

[0041] Thirdly, the present invention provides a battery pack comprising the battery described in the second aspect.

[0042] Fourthly, the present invention provides an electrical device comprising the battery described in the second aspect or the battery pack described in the third aspect.

[0043] It should be noted that the above-mentioned electrical equipment can be any equipment that conventionally requires electricity, such as, but not limited to, computers, electric vehicles, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0044] The technical solution of the present invention will be further illustrated below with reference to specific embodiments. All parts, percentages and ratios recorded in the following embodiments are based on weight. All reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the embodiments are also commercially available.

[0045] Example 1

[0046] This example provides an electrolyte comprising, by mass fraction: 0.25 wt% LiNO3, 1 wt% DMSO, 84.20 wt% carbonate solvent (EC / DMC volume ratio 1:1), 2 wt% VC, and 12.55 wt% LiPF6.

[0047] Its preparation method includes the following steps:

[0048] 1) EC and DMC were mixed evenly at a volume ratio of 1:1 at room temperature to obtain a carbonate solvent;

[0049] 2) Add LiNO3, DMSO, VC and LiPF6 to the carbonate solvent in step 1) and mix evenly to obtain the electrolyte.

[0050] Examples 2-8

[0051] Basically the same as Example 1, the only difference being: changing the LiNO3 content (W) in the electrolyte. LiNO3 DMSO content (W) DMSO ), content of carbonate solvent (W) 碳酸酯溶剂 ), the content of additive VC (W) VC ) and lithium salt LiPF6 (W LiPF6 The content remains unchanged, as detailed in Table 1.

[0052] Examples 9-10

[0053] Basically the same as Example 1, the only difference being: the content of additive VC (W) VC ) and lithium salt LiPF6 (W LiPF6 The content changes, see Table 1 for details.

[0054] Comparative Example 1

[0055] It is basically the same as Example 1, except that LiNO3 and DMSO cosolvents were not added.

[0056] Comparative Example 2

[0057] It is basically the same as Example 1, except that LiNO3 and DMSO were not added, and the LiPF6 content was increased to 13.55%.

[0058] Comparative Example 3-12

[0059] The results are basically the same as in Example 1, except that the contents of LiNO3, DMSO and carbonate solvent are changed, while the contents of VC additive and LiPF6 remain unchanged. See Table 1 for details.

[0060] Application examples

[0061] This example provides a series of lithium-ion batteries, each including the electrolyte of the above embodiments or comparative examples.

[0062] 1. Positive Electrode Preparation: LiFePO4, PVDF, and carbon black were weighed in a mass ratio of 90:5:5 as the active material, binder, and conductive agent, respectively. An appropriate amount of N-methylpyrrolidone (NMP) was added as a solvent. The binder was dissolved by stirring, and all materials were thoroughly mixed to obtain the positive electrode slurry. A 13 μm thick aluminum foil was used as the current collector. The positive electrode slurry was uniformly coated onto the current collector using a coating machine. After drying and rolling, an areal density of 33 mg / cm³ was obtained. 2 A positive electrode with a coating thickness of 58 μm.

[0063] 2. Anode Preparation: Graphite, CMC+SBR (mass ratio 1:1), and carbon black were weighed at a mass ratio of 90:5:5 as the active material, binder, and conductive agent, respectively. An appropriate amount of water was added as a solvent, and the materials were mixed evenly by stirring to obtain the anode slurry. A 6 μm copper foil was used as the current collector, and the anode slurry was evenly coated onto the current collector using a coating machine. After drying and rolling, an areal density of 18 mg / cm³ was obtained. 2 A negative electrode with a coating thickness of 68 μm.

[0064] 3. Diaphragm: A single-layer PP diaphragm is used.

[0065] 4. Cell preparation: 1) The positive electrode, separator, and negative electrode are stacked using a stacking machine to obtain the battery core. The core is then placed inside the battery, and the end caps are assembled and welded. 2) An appropriate amount of the electrolyte is injected into the aluminum-cased lithium battery cell through the injection hole, and the injection hole is sealed to obtain the desired battery. 3) All batteries are left to stand at 45°C for 12 hours to allow the electrolyte to fully impregnate them. Each battery is then tested for capacity using a battery testing system at a current density of 0.1 C to obtain the battery to be tested.

[0066] Performance testing:

[0067] 1. Fast charging performance test:

[0068] Under room temperature conditions, the battery cells from Application Example 1, after being tested for capacity, were charged at a constant current of 3.5 C to 50% SOC, then charged at a constant current of 1 C to 3.8 V, left to rest for 10 min, and then discharged at a constant current of 1 C to 2.0 V. This cycle was repeated, and the ratio of the battery capacity after 100 cycles to the initial capacity of the first cycle was recorded, i.e., the capacity retention rate R. 快充 .

[0069] 2. Low-temperature performance test:

[0070] At -9℃, the battery cells from Application Example 1, after capacity testing, were charged to 3.8 V using a constant current and constant voltage of 0.3 C, and then discharged to 2.0 V using a constant current of 0.3 C. This cycle was repeated, and the capacity retention rate R was recorded after 50 cycles. 低温 The test results are shown in Table 1:

[0071] Table 1:

[0072]

[0073] As can be seen from Table 1, compared with the comparative example, the LiNO3 addition amount x in Examples 1-10 was 0.2~1.2wt%, the DMSO addition amount y was 0.8~4.2wt%, and 4≤y / x≤16; the battery had better low-temperature performance. This is because during low-temperature cycling, the SEI film, which is mainly composed of inorganic components, exhibited high ionic conductivity, which significantly suppressed low-temperature lithium plating and effectively improved the low-temperature cycling performance of the battery. Comparing Examples 1-4, 9-10 with the comparative examples, it can be seen that when the LiNO3 content is 0.2-0.4%, in addition to low-temperature performance, the fast-charging performance of the battery is further optimized. This is because an appropriate amount of LiNO3 forms a tough SEI film with high ionic conductivity on the graphite anode surface, which can adapt to the severe volume expansion effect of the graphite anode during fast charging and effectively suppress the co-intercalation reaction of DMSO. In Comparative Examples 3, 6, 8, and 10, the prepared electrolytes showed obvious precipitation of insoluble matter because their y / x ratio was too small, making it difficult for DMSO to dissolve the corresponding mass of LiNO3, thus hindering application. The main reason for the performance degradation of the batteries in Comparative Examples 4 and 5 was that the LiNO3 content was too low (<0.2wt%), failing to form an effective SEI film, and the co-intercalation of DMSO further degraded the battery performance. In Comparative Example 7, the high DMSO content led to increased electrolyte viscosity and a higher probability of co-intercalation, but it did not significantly improve the fast-charging or low-temperature performance of the battery. In Comparative Example 9, although W LiNO3While y / x meets the conditions, the excessively high mass percentage of DMSO not only increases the electrolyte viscosity but also increases the probability of DMSO co-intercalation, leading to battery performance degradation. In Comparative Example 11, when W... LiNO3 When the concentration was >1.2 wt% and y / x = 4, insoluble matter precipitation also occurred in the prepared electrolyte. This is because carbonate solvents have limited solubility for LiNO3, and the lithium salt content in the electrolyte itself was greater than 10 wt%, further limiting the solubility of LiNO3. In Comparative Example 12, both LiNO3 and DMSO were added in excess, which not only resulted in extremely poor SEI film toughness, but also led to battery performance degradation due to DMSO co-intercalation and increased electrolyte viscosity.

[0074] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises carbonate solvents, lithium nitrate, and dimethyl sulfoxide, wherein the mass percentage of lithium nitrate in the electrolyte is x, and the mass percentage of dimethyl sulfoxide in the electrolyte is y, wherein x and y satisfy: 0.2wt%≤x≤1.2wt%, 0.8wt%≤y≤4.2wt%, and 4≤y / x≤16; the mass percentage of carbonate solvent in the electrolyte is greater than or equal to 80wt%.

2. The electrolyte according to claim 1, characterized in that, 0.2wt%≤x≤0.4wt%.

3. The electrolyte according to claim 1 or 2, characterized in that, The carbonate solvents include at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and butene carbonate.

4. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte is a lithium-ion battery electrolyte.

5. The electrolyte according to any one of claims 1-4, characterized in that, It also includes lithium salts, including at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, lithium difluorosulfonylimide, lithium trifluoromethanesulfonate, lithium perchlorate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium perfluorobutyl sulfonate, and lithium fluorinated fatty acids.

6. The electrolyte according to claim 5, characterized in that, The lithium salt has a mass percentage of 10 wt% or greater in the electrolyte.

7. The electrolyte according to any one of claims 1-6, characterized in that, It also includes organic film-forming additives, which include at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, methane disulfonate, or siloxane additives.

8. The electrolyte according to claim 7, characterized in that, The organic film-forming additive has a mass percentage of less than or equal to 5 wt% in the electrolyte.

9. A battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte according to any one of claims 1-8; the negative electrode includes a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, the negative electrode active material layer including graphite.

10. A battery pack, characterized in that, Includes the battery as described in claim 9.

11. An electrical appliance, characterized in that, Includes the battery of claim 9 or the battery pack of claim 10.

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