Electrolyte, battery, battery pack, and electric device

Abstract

The application provides an electrolyte, a battery, a battery pack and an electric device. The electrolyte comprises a carbonic acid ester solvent, a nitrate and a dimethyl ether compound. The electrolyte satisfies 3<=y / x<=4 and 0<y<1%, wherein x is a mass ratio of the nitrate in the electrolyte, and y is a mass ratio of the dimethyl ether compound in the electrolyte. The application can improve the fast charging and high-temperature cycle stability of the battery.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and particularly to an electrolyte, a battery, a battery pack, and an electrical device. Background Art

[0002] Batteries are common electrochemical energy storage devices with wide applications. For example, lithium-ion batteries are widely used in fields such as 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 demand for fast charging and the requirements for battery performance under extreme environments such as high temperature, the defects of existing batteries, such as poor fast charge cycle performance and high temperature cycle performance, are important factors limiting their further applications. Summary of the Invention

[0003] The present invention provides an electrolyte, a battery, a battery pack, and an electrical device, which can balance the improvement of the fast charge cycle performance and high temperature cycle performance of the battery, and effectively overcome the defects existing in the prior art.

[0004] In one aspect of the present invention, there is provided an electrolyte including a carbonate solvent, a nitrate, and a dimethyl ether compound, and the electrolyte satisfies 3 ≤ y / x ≤ 4, 0 < y < 1%, where x is the mass ratio of the nitrate in the electrolyte, and y is the mass ratio of the dimethyl ether compound in the electrolyte.

[0005] According to an embodiment of the present invention, 0.15% ≤ y ≤ 0.9%.

[0006] According to an embodiment of the present invention, 0 < x < 0.3%; preferably 0.15 < x < 25%.

[0007] According to an embodiment of the present invention, the mass ratio of the carbonate solvent in the electrolyte is greater than or equal to 80%.

[0008] According to an embodiment of the present invention, the dimethyl ether compound includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0009] According to an embodiment of the present invention, the carbonate solvent includes one or more of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0010] According to an embodiment of the present invention, the nitrate includes lithium nitrate.

[0011] According to one embodiment of the present invention, the electrolyte further includes other lithium salts besides lithium nitrate, including one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, and lithium difluorophosphate.

[0012] According to one embodiment of the present invention, the electrolyte further includes a film-forming additive, which includes one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, methane disulfonate, or siloxane additives.

[0013] In another aspect, the present invention provides a battery comprising the above-described electrolyte.

[0014] According to one embodiment of the present invention, the battery further includes a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material, the negative electrode active material comprising graphite.

[0015] According to one embodiment of the present invention, the battery is a lithium-ion battery.

[0016] In another aspect, the present invention provides a battery pack including the battery described above.

[0017] In another aspect, the present invention provides an electrical device comprising the aforementioned battery or battery pack.

[0018] The electrolyte provided by this invention uses a carbonate solvent, and introduces nitrate and dimethyl ether compounds into the carbonate solvent system. The mass ratio x of nitrate and the mass ratio y of dimethyl ether compounds in the electrolyte are synergistically controlled to satisfy 3≤y / x≤4 and 0<y<1%. This can improve the fast-charging cycle performance of the battery and enhance its cycle stability under high-temperature conditions, thereby increasing the cycle life of the battery under fast-charging and high-temperature conditions and facilitating the industrial application of the battery. 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] Existing batteries generally suffer from defects such as poor fast charging performance and poor high-temperature cycle performance, which urgently need to be addressed.

[0021] According to the inventors' research, a battery typically includes a cell and an electrolyte that wets the cell. The cell includes a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. During charging and discharging, active ions (such as lithium ions in a lithium-ion battery) are transported between the positive and negative electrodes through the electrolyte and undergo corresponding extraction / intercalation. During charging and discharging, solvents, additives, and lithium salts in the electrolyte undergo a reduction reaction on the surface of the negative electrode, generating an SEI film (solid electrolyte interphase). The SEI film conducts ions but not electrons, thus inhibiting further reduction and consumption of the electrolyte. However, the SEI film formed by carbonate electrolytes has poor ionic conductivity, hindering the absorption of lithium ions (Li). + The insertion / extraction process of active ions such as ions affects the performance of fast charging.

[0022] According to further research by the inventors of this application, using carbonate solvents and adding nitrates (such as lithium nitrate (LiNO3)) to the electrolyte can form an SEI film with high ionic conductivity, improving the fast-charging performance of the battery. However, nitrates have extremely low solubility in carbonate solvents, requiring the introduction of polar co-solvents to increase their solubility in the electrolyte. However, polar co-solvents and other components in the electrolyte are prone to side reactions with the electrode materials, affecting the performance of the electrode materials and consequently impacting the battery's fast-charging and cycle stability.

[0023] Specifically, graphite anodes are commonly used (i.e., graphite is used as the active material of the anode). Polar co-solvents in the electrolyte are prone to co-intercalation reactions in graphite anodes. In particular, the severe volume expansion effect of graphite under fast charging conditions and the thermal motion of solvent molecules under high temperature conditions have aggravated the co-intercalation reaction of polar co-solvents in graphite, leading to problems such as graphite anode stripping, which in turn affects the fast charging and high temperature cycle stability of the battery.

[0024] Specifically, under fast charging conditions, the graphite anode undergoes severe volume expansion, causing the SEI film to continuously rupture / repair. This process increases nitrate consumption and the severity of polar co-intercalation in the graphite anode, significantly impacting its fast-charging cycle stability. Similarly, at high temperatures, accelerated molecular thermal motion also exacerbates the co-intercalation problem of polar co-solvents in the graphite anode. Therefore, fast charging and high-temperature conditions intensify the co-intercalation reaction of polar co-solvents in the graphite anode, leading to a decrease in the battery's fast-charging and cycle stability. How to improve battery performance while avoiding these problems, thereby achieving a balance between improving fast-charging and cycle stability, remains a challenging problem to overcome.

[0025] In view of this, embodiments of the present invention provide an electrolyte comprising a carbonate solvent, a nitrate, and a dimethyl ether compound, wherein the electrolyte satisfies 3≤y / x≤4, 0<y<1%, x is the mass ratio of lithium nitrate to the electrolyte, and y is the mass ratio of the dimethyl ether compound to the electrolyte.

[0026] According to the inventors' research, by using carbonate solvents and simultaneously introducing nitrates and dimethyl ether compounds, and synergistically controlling the content of nitrates and dimethyl ether compounds to satisfy 3≤y / x≤4 and 0<y<1%, it is possible to improve both the fast-charging performance and high-temperature cycle stability of the battery. The reason for this is that, under the above electrolyte composition system, dimethyl ether compounds can act as a co-solvent to promote the solution of nitrates in the electrolyte. The nitrates dissolved in the electrolyte can act as a film-forming agent to form a high ionic conductivity SEI film on the electrode surface. At the same time, the formation of this SEI film on the electrode surface can also prevent the co-intercalation reaction of dimethyl ether compounds and other components in the electrolyte in graphite, effectively suppressing the co-intercalation reaction of dimethyl ether compounds on the graphite negative electrode under fast charging and high-temperature conditions, thereby improving the cycle stability of the battery under fast charging and high-temperature conditions. In the aforementioned electrolyte system, the content of dimethyl ether compounds (y) is less than 1%. This promotes the dissolution of nitrates in the electrode solution while further preventing the co-intercalation reaction of dimethyl ether compounds with graphite, thereby ensuring the function of the graphite anode and improving the battery's fast charging and high-temperature cycle stability. Therefore, this invention not only solves the problem of nitrate dissolution in electrolytes using carbonate solvents but also significantly suppresses the co-intercalation of dimethyl ether compounds in the graphite anode under fast charging and high-temperature conditions. This results in the formation of a high-ionic-conductivity SEI film on the electrode surface while simultaneously improving the battery's fast charging and high-temperature cycle stability.

[0027] For example, y / x can be a range consisting of 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any two of them.

[0028] For example, y can be a range of 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, or any combination thereof.

[0029] In some embodiments, 0.15% ≤ y ≤ 0.9%, by further controlling the nitrate content y in the electrolyte within this range, it is beneficial to promote nitrate dissolution while further avoiding the co-intercalation reaction of dimethyl ether compounds with graphite, thereby better balancing the improvement of battery fast charging performance and high-temperature performance.

[0030] In some embodiments, 0 < x < 0.3%, where x can be, for example, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.27%, or any range composed of any two of them. Preferably, 0.15 < x < 0.25%. By further regulating the amount of nitrate in the electrolyte to meet the above range, it is beneficial for its dissolution in the electrolyte and the formation of a SEI film with high ionic conductivity and stability on the electrode surface, thus being more conducive to simultaneously improving the fast charging performance and high-temperature performance of the battery.

[0031] In some embodiments, the mass ratio of the carbonate solvent in the electrolyte is greater than or equal to 80%, such as 85%, 90%, 95%, or any range composed of any two of them. The electrolyte is mainly composed of carbonate solvents, that is, the electrolyte belongs to carbonate-based electrolytes. Introducing the above-mentioned ratio of nitrate and dimethyl ether compounds is beneficial for simultaneously improving the fast charging and high-temperature cycle stability of the battery. At the same time, it is also beneficial for the preparation of the electrolyte, with advantages such as low production cost, and is more conducive to practical industrial application.

[0032] In some embodiments, the carbonate solvent can include one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), which is beneficial for the better dissolution of nitrate in the carbonate solvent under the solubilizing effect of the dimethyl ether compound, and is beneficial for the formation of a SEI film with high ionic conductivity and stability on the electrode surface, simultaneously improving the fast charging and high-temperature cycle stability of the battery.

[0033] In some embodiments, the above-mentioned dimethyl ether compound can include one or more of dimethyl glycol ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. This dimethyl ether compound is beneficial for promoting the dissolution of nitrate in the electrolyte, forming a SEI film with high ionic conductivity on the electrode surface, and at the same time, it can also reduce its co-insertion reaction with graphite, thereby further simultaneously improving the fast charging performance and high-temperature cycle stability of the battery.

[0034] In some embodiments, the nitrate can include lithium nitrate, which is more conducive to matching with the dimethyl ether compound. In the above-mentioned electrolyte, in the coexistence system of lithium nitrate and the dimethyl ether compound, the dimethyl ether compound can increase the solubility of lithium nitrate in the electrolyte. When applying the electrolyte to a lithium-ion battery, it is more conducive to forming a SEI film with high lithium-ion conductivity and stability on the electrode surface, simultaneously improving the fast charging performance and high-temperature cycle stability of the lithium-ion battery.

[0035] In this embodiment of the invention, the electrolyte may also include other electrolyte salts besides nitrates. Other electrolyte salts may include one or more of the following: hexafluorophosphate, bis(fluorosulfonyl)imide salt, bis(trifluoromethanesulfonyl)imide salt, trifluoromethanesulfonate, tetrafluoroborate, hexafluoroarsenate, perchlorate, bis(oxalate)borate, difluorooxalateborate, and difluorophosphate.

[0036] Generally, the metal ions in nitrates are the same as those in other electrolyte salts. For example, when the nitrate is lithium nitrate (i.e., the metal ion in the nitrate is lithium ion), the other electrolyte salts are other types of lithium salts besides lithium nitrate.

[0037] In some embodiments, the electrolyte further includes lithium salts other than nitrates. These other lithium salts include one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiOTf), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bis(oxalateborate)borate (LiBOB), lithium difluorooxalateborate (LiDFOB), and lithium difluorophosphate (LiDFP). These lithium salts are beneficial for further improving the wetting ability and ion diffusion rate of the electrolyte, reducing the internal resistance of the battery, and improving the cycle life and other performance characteristics of the battery.

[0038] Specifically, the other lithium salts mentioned above may account for 10% or more of the electrolyte by mass, for example, 10% to 15%, such as 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof.

[0039] In this embodiment of the invention, the electrolyte may further include film-forming additives, which may include one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), methane disulfonate (MMDS), or siloxane additives. By introducing film-forming additives into the electrolyte, it is more conducive to the formation of an SEI film on the negative electrode surface. At the same time, the combination with components such as nitrates and dimethyl ether compounds can improve the ionic conductivity and stability of the SEI film, thereby improving both the fast charging performance and high-temperature performance of the battery.

[0040] Generally, the above-mentioned film-forming additives account for less than or equal to 5% of the mass of the electrolyte, for example, 1% to 5%, such as 1%, 2%, 3%, 4%, 5%, or any combination thereof.

[0041] This invention also provides a battery comprising the above-described electrolyte, which has advantages corresponding to the electrolyte described above, and will not be elaborated further.

[0042] The battery in this embodiment of the invention can specifically be a lithium-ion battery.

[0043] Generally, a battery includes a cell and a casing that encapsulates the cell. Electrolyte is injected into the cell inside the casing. The cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode.

[0044] Specifically, the positive electrode sheet includes a positive current collector and a positive electrode coating located on at least one side surface of the positive current collector. Specifically, the positive electrode coating may be provided on one side surface of the positive current collector, or the positive electrode coating may be provided on both sides of the positive current collector in the thickness direction.

[0045] Specifically, the positive electrode coating (positive electrode active material layer) may include a positive electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the positive electrode active material may include one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary cathode materials. The ternary cathode materials may include nickel-cobalt-manganese ternary materials and / or nickel-cobalt-aluminum ternary materials. The conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fiber. The binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0046] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0047] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder, and other components used to form the positive electrode coating can be dispersed in a positive electrode solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0048] Specifically, the negative electrode sheet includes a negative current collector and a negative electrode coating located on at least one side surface of the negative current collector. Specifically, the negative electrode coating may be provided on one side surface of the negative current collector, or negative electrode coatings may be provided on both opposite sides of the negative current collector in the thickness direction.

[0049] Specifically, the negative electrode coating (negative electrode active material layer) may include a negative electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the negative electrode active material may include one or more of graphite, silicon, silicon oxide, and lithium metal; the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; and the binder may include one or more 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.

[0050] In some embodiments, the negative electrode active material includes graphite, that is, the negative electrode sheet is a graphite negative electrode. By using the above-mentioned electrolyte, it is beneficial to form a SEI film with high ionic conductivity and stability on the surface of the graphite negative electrode, and to avoid the co-intercalation reaction of dimethyl ether compounds on graphite, thereby improving the battery's fast charging cycle stability and high temperature cycle stability.

[0051] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0052] In this embodiment of the invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode coating, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a negative electrode solvent, such as water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0053] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. The separator in this embodiment of the invention can be a conventional separator in the art, for example, the separator includes a polypropylene membrane (PP membrane), but is not limited thereto.

[0054] In this embodiment of the invention, conventional housing materials in the art can be used to encapsulate the battery cell. The housing may include, for example, soft packaging materials such as aluminum-plastic film (in which case the battery is a soft-pack battery), but it is not limited to this.

[0055] The embodiments of the present invention can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in an alternating manner to obtain a stacked cell (or wound into a wound cell); then the cell is placed in a casing and subjected to conventional processes such as electrolyte injection (i.e., injection of electrolyte) and formation to obtain a battery.

[0056] In this embodiment of the invention, ion chromatography (IC) and gas chromatography-mass spectrometry (GC-MS) can be used to detect the components and their contents, such as nitrates (e.g., lithium nitrate) and organic solvents, in the electrolyte. For example, the content of nitrates (e.g., lithium nitrate) in the electrolyte can be measured by IC, and the content of organic solvents can be measured by GC-MS.

[0057] For example, the content of nitrates (such as lithium nitrate) in electrolyte can be tested using an ion chromatograph (IC). Taking the IC-2800 ion chromatograph as an example, the test conditions are as follows: anion exchange column, suppressor current 35mA, flow rate 1mL / min, eluent 5mmol / L sodium carbonate solution: acetone = 75:25, injection volume 100μL; the test process is as follows: (1) First, dilute the sample to be tested: take 1mL of electrolyte, dilute with acetonitrile and transfer to a 100mL volumetric flask, dilute with acetonitrile to the mark, shake well and test; (2) Next, prepare the standard solution: take 0.05mL of NO3 with a concentration of 1mg / mL. - An aqueous solution (prepared using nitrates such as lithium nitrate) is diluted to a volumetric flask with deionized water to obtain NO3 with a concentration of 5 μg / mL. - (2) Prepare a series of standard solutions with varying concentration gradients by taking 1 mL, 2 mL, 4 mL, and 10 mL of the solution into a 10 mL volumetric flask and diluting to the mark with deionized water; (3) Analyze the standard samples: using NO3 - The peak area (y) is used as the vertical axis and the concentration of the standard sample is used as the horizontal axis (x). A standard curve is established, and the curve equation and correlation coefficient are obtained. (4) Finally, the electrolyte to be tested is tested, and the measured NO3 is used as the vertical axis. - Substituting the peak area into the standard curve equation, the content of nitrates (such as lithium nitrate) in the electrolyte is calculated.

[0058] This invention also provides a battery pack including the battery described above, which has advantages corresponding to the negative electrode sheet described above, and will not be described in detail here.

[0059] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0060] This invention also provides an electrical device, including the battery or battery pack described above. This electrical device has advantages corresponding to the negative electrode sheet described above, which will not be elaborated further.

[0061] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations.

[0062] The present invention will be further described below through specific embodiments.

[0063] Example 1

[0064] 1. Preparation of electrolyte

[0065] LiNO3, DME, carbonate solvent, VC, and LiPF6 were uniformly mixed in a mass ratio of 0.05:0.16:85.24:2:12.55 to obtain the electrolyte. The carbonate solvent consisted of EC and DMC in a 1:1 volume ratio. The mass ratio of LiNO3 in the electrolyte was x = 0.05 wt%, the mass ratio of DME in the electrolyte was y = 0.16 wt%, and the mass ratio of carbonate solvent in the electrolyte was 85.24 wt%.

[0066] 2. Battery manufacturing

[0067] (1) Preparation of positive electrode

[0068] LiFePO4, carbon black, and PVDF were mixed in a mass ratio of 8:1:1, and NMP was added. The mixture was stirred until homogeneous to prepare a positive electrode slurry.

[0069] The positive electrode slurry is coated on both sides of the aluminum foil. After drying and rolling, a positive electrode coating is formed on both sides of the aluminum foil, thus producing a positive electrode sheet.

[0070] (2) Preparation of negative electrode

[0071] Graphite, SBR, CMC, and carbon black were mixed in a mass ratio of 8:0.5:0.5:1, and deionized water was added. The mixture was stirred evenly to prepare a negative electrode slurry.

[0072] The negative electrode slurry is coated on both the front and back surfaces of a copper foil. After drying and rolling, a negative electrode coating is formed on both the front and back surfaces of the copper foil, thus producing a negative electrode sheet.

[0073] (3) Preparation of lithium-ion batteries

[0074] The positive electrode, separator (PP film) and negative electrode are alternately stacked to assemble a stacked cell; the cell is encapsulated with aluminum-plastic film and electrolyte is injected into it, and then processed through formation and other processes to obtain a lithium-ion battery.

[0075] The difference between Examples 2-13, Comparative Examples 1-10 and Example 1 lies in the content of LiNO3 (x), DME (y), and carbonate solvent (W) in the electrolyte. 碳酸酯溶剂 The conditions differ in terms of the types of dimethyl ether compounds, as detailed in Table 1. Except for the differences shown in Table 1, the other conditions are the same.

[0076] The performance of the lithium-ion batteries in each embodiment and comparative example was tested using the following process, and the results are shown in Table 1:

[0077] 1. Fast charging cycle stability test: At 35℃, the lithium-ion battery is charged at a constant current of 4C to 50% SOC, then charged at a constant current of 1C to 3.8V, rested for 10 minutes, and then discharged at a constant current of 1C to 2.0V. This cycle is repeated, and the ratio of the battery discharge capacity after 100 cycles to the initial capacity of the first cycle is recorded. This is the capacity retention rate R of the fast charging cycle. 快充 .

[0078] 2. High-Temperature Cycling Stability Test: At 60℃, the lithium-ion battery is subjected to constant current charge-discharge test at a current density of 1C between 2.0 and 3.8V. The ratio of the battery's discharge capacity after 100 cycles to the initial capacity of the first cycle is recorded, which is the capacity retention rate R during high-temperature cycling. 高温 .

[0079] Table 1

[0080]

[0081] As shown in Table 1, the electrolyte in Comparative Example 8, which did not contain lithium nitrate or dimethyl ether compounds, exhibited poor fast-charging and high-temperature cycling stability. Comparative Example 9, which only added lithium nitrate without dimethyl ether compounds, showed poor solubility of lithium nitrate, leading to the precipitation of insoluble substances. Comparative Example 10, which did not add lithium nitrate but only dimethyl ether compounds, showed severe deterioration in fast-charging and high-temperature cycling performance. For Comparative Examples 1 and 2, y / x < 3, indicating that the amount of dimethyl ether compounds relative to lithium nitrate was too small, limiting the doping potential due to the solubility of lithium nitrate. Insoluble substances precipitated during electrolyte preparation, making it difficult to apply. In Comparative Examples 3 and 4, y / x > 4, indicating an excessive amount of dimethyl ether compounds relative to lithium nitrate, meaning the lithium nitrate content was relatively low. The resulting SEI film was insufficient to suppress the co-intercalation reaction of dimethyl ether compounds on the graphite anode, leading to a deterioration in the cycle performance of the lithium-ion battery under fast charging and high-temperature conditions. In Comparative Examples 5–7, y > 1%, indicating an excessively high content of dimethyl ether compounds in the electrolyte, which intensified the co-intercalation reaction on the graphite anode, also resulting in a decrease in battery cycle stability.

[0082] Compared with Comparative Examples 1 to 10, in Examples 1 to 13, by using a carbonate solvent, doping lithium nitrate and a dimethyl ether compound therein, and making the mass ratio x of lithium nitrate in the electrolyte and the mass ratio y of the dimethyl ether compound satisfy 3≤y / x≤4 and 0<y<1%, the fast charge cycle stability and high-temperature cycle stability of the battery can be significantly improved.

[0083] Furthermore, it can be seen from Example 2 and Example 10 that, compared with Example 10, on the premise of satisfying 3≤y / x≤4 and 0<y<1%, by further controlling 0.15<x<25% in Example 2, while improving the high-temperature cycle stability of the battery, the fast charge cycle stability of the battery can be more significantly improved.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that, It includes a carbonate solvent, a nitrate, and a dimethyl ether compound. The electrolyte satisfies 3 ≤ y / x ≤ 4, 0 < y < 1%, where x is the mass ratio of the nitrate in the electrolyte, and y is the mass ratio of the dimethyl ether compound in the electrolyte.

2. The electrolyte according to claim 1, characterized in that, 0.15％≤y≤0.9％。 3. The electrolyte according to claim 1, characterized in that, 0 < x < 0.3%; preferably 0.15 < x < 25%.

4. The electrolyte according to claim 1, characterized in that, The mass ratio of the carbonate solvent in the electrolyte is greater than or equal to 80%.

5. The electrolyte according to claim 1, characterized in that, The dimethyl ether compound includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

6. The electrolyte according to any one of claims 1-5, characterized in that, The carbonate solvent includes one or more of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

7. The electrolyte according to any one of claims 1-5, characterized in that, The nitrate includes lithium nitrate.

8. The electrolyte according to claim 7, characterized in that, The electrolyte further includes other lithium salts other than lithium nitrate. The other lithium salts include one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium difluorophosphate.

9. The electrolyte according to any one of claims 1-5, characterized in that, The electrolyte further includes a film-forming additive. The film-forming additive includes one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, methylene methanedisulfonate, or a siloxane additive.

10. A battery, characterized in that, It includes the electrolyte according to any one of claims 1-9.

11. The battery according to claim 10, characterized in that, The battery further includes a negative electrode sheet, and the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes graphite.

12. The battery according to claim 10, characterized in that, The battery is a lithium-ion battery.

13. A battery pack, characterized in that, It includes the battery according to any one of claims 10-12.

14. An electrical appliance, characterized in that, It includes the battery according to any one of claims 10-12 or the battery pack according to claim 13.

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