Lithium ion battery electrolyte and lithium ion battery

Abstract

The invention provides a lithium ion battery electrolyte and a lithium ion battery, and belongs to the technical field of lithium batteries. The lithium ion battery electrolyte comprises the following components in percentage by weight: 10-15% of lithium salt, 80-90% of organic solvent and 0-5% (not 0) of additive, the additive comprises a functional additive A, and the structure of the functional additive A is shown as a formula I: in # imgabs0, R1, R2, R3 and R4 are the same or different and are respectively and independently hydrogen, halogen, straight-chain alkyl or alkoxy of C1 to C10, and branched-chain alkyl or alkoxy of C1 to C10; "." represents a common electron pair of a nitrogen atom and a boron atom. According to the invention, by correspondingly adjusting the components of the electrolyte and introducing the functional additive A, the lithium salt and the organic solvent for synergistic effect, the phenomenon of relatively fast capacitance attenuation or voltage attenuation in the charge-discharge cycle process of the lithium ion battery can be obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium ion battery electrolyte and a lithium ion battery. Background Art

[0002] The continuous development of computers, communications and consumer electronics has brought about the rapid development of the lithium-ion battery industry. In particular, the rise of new energy vehicles in recent years has not only promoted the development of power lithium-ion batteries, but also put forward higher energy density and safety performance. The endurance of electric vehicles has become one of the performance indicators that consumers pay most attention to, and the energy density of the battery determines the single mileage of the electric vehicle. How to improve the energy density of the battery under limited space and weight has become a hot topic in this field.

[0003] At present, increasing the working voltage of cathode materials is the main way to increase the energy density of lithium-ion batteries; high-voltage cathode materials such as LNMO, high-voltage ternary materials, high-voltage lithium cobalt oxide, layered lithium-rich oxide (LLO), etc. have become research hotspots. However, as the voltage of lithium-ion batteries continues to increase, cathode materials will have higher electrode potentials, and the oxidation decomposition of electrolytes at the cathode and the cathode interface reactions will become more intense; as the battery charge and discharge cycles continue, the internal resistance of the battery gradually increases, which in turn affects the battery performance and even causes failure.

[0004] To address the above problems, researchers mainly overcome these defects by modifying the positive electrode materials, such as surface coating, material microstructure design, element doping, etc.; among them, the material modification method has complex processes and high costs, while the use of suitable additives to improve the composition of the electrolyte is simple to operate and has obvious effects, which is conducive to industrial applications. Summary of the invention

[0005] The main purpose of the present invention is to provide a lithium ion battery electrolyte and a lithium ion battery to solve the problem of serious deterioration of electrochemical performance during battery cycling under high voltage in the prior art.

[0006] In order to achieve the above object, according to one aspect of the present invention, a lithium ion battery electrolyte is provided, which comprises the following components in weight percentage:

[0007] Lithium salt 10% to 15%, organic solvent 80% to 90%, additive 0 to 5% and not 0;

[0008] The additive includes a functional additive A, and the structure of the functional additive A is shown in Formula I:

[0009]

[0010] In Formula I, R1, R2, R3 and R4 are the same or different and are independently hydrogen, halogen, C1-C 10 Straight chain alkyl or alkoxy, C1~C 10 A branched alkyl or alkoxy group;

[0011] “..” represents the shared electron pair between the nitrogen atom and the boron atom.

[0012] Furthermore, in Formula I, R1, R2, R3 and R4 are each independently hydrogen, halogen, C1-C4 straight-chain alkyl or alkoxy, C1-C4 branched alkyl or alkoxy.

[0013] Further, R1, R2, R3 and R4 are all the same and are hydrogen; or, R1, R3 and R4 are all the same and are hydrogen, and R2 is methyl; or, R1, R3 and R4 are all the same and are hydrogen, and R2 is halogen, and more preferably R2 is chlorine; or, R1, R3 and R4 are all the same and are hydrogen, and R2 is a straight-chain alkoxy group of C1 to C4, and more preferably R2 is methoxy.

[0014] Furthermore, the weight percentage of the lithium salt in the electrolyte is 10% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 0.5 to 5%.

[0015] Furthermore, the weight percentage of the lithium salt in the electrolyte is 10% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 2% to 5%.

[0016] Furthermore, the weight percentage of the lithium salt in the electrolyte is 13% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 3% to 4%.

[0017] Furthermore, the weight percentage of the functional additive A in the electrolyte is 0.3% to 1%, preferably 0.5% to 1%.

[0018] Furthermore, the preparation method of the functional additive A comprises the following steps:

[0019] Step S1: mixing and reacting boron trifluoride etherate and a pyrrole compound in an inert atmosphere to obtain a reaction mixture;

[0020] Step S2: The reaction mixture is subjected to crystal growth to obtain a solid product, namely, functional additive A.

[0021] Furthermore, in step S1, the molar ratio of boron trifluoride etherate to the pyrrole compound is (1-1.2):1.

[0022] Furthermore, the pyrrole compound is selected from pyrrole, 3-methylpyrrole, 3-methoxypyrrole or 3-chloropyrrole.

[0023] Furthermore, in step S1, the reaction temperature is 25°C to 35°C, and the reaction time is 0.5 to 1 h.

[0024] Furthermore, in step S2, the temperature during crystal growth is -15°C to -25°C, and the crystal growth time is 2 to 3 hours.

[0025] Furthermore, in step S2, the solid product is dried in a vacuum environment at 90°C to 100°C to obtain functional additive A.

[0026] Furthermore, the additives include one or more of film-forming additives, lithium salt additives and sulfur-containing additives.

[0027] Furthermore, the film-forming additive is selected from vinylene carbonate and / or fluoroethylene carbonate.

[0028] Furthermore, the lithium salt additive is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalatoborate) and lithium difluorobis(oxalatophosphate).

[0029] Further, the sulfur-containing additive is selected from one or more of 1,3-propane sultone, 1,3-propylene sultone and ethylene sulfate.

[0030] Furthermore, the additives also include vinylene carbonate, lithium difluorophosphate and 1,3-propane sultone.

[0031] Furthermore, the weight percentage of vinylene carbonate in the electrolyte is 0.1% to 1%, preferably 0.5% to 1%.

[0032] Furthermore, the weight percentage of lithium difluorophosphate in the electrolyte is 0.5% to 1%.

[0033] Furthermore, the weight percentage of 1,3-propane sultone in the electrolyte is 0.5% to 3%, preferably 1% to 3%, and more preferably 2% to 3%.

[0034] Furthermore, the lithium salt is selected from lithium hexafluorophosphate.

[0035] Furthermore, the organic solvent is selected from one or more of cyclic carbonates, chain carbonates and chain carboxylates.

[0036] Furthermore, the mass ratio of the cyclic carbonate, the chain carbonate and the chain carboxylic acid ester is (1-15):(20-70):(5-20).

[0037] Further, the organic solvent includes fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate and diethyl carbonate.

[0038] Furthermore, the weight percentage of fluoroethylene carbonate in the organic solvent is 10% to 12%; the weight percentage of ethylene carbonate in the organic solvent is 8% to 12%, the weight percentage of ethyl difluoroacetate in the organic solvent is 12 to 18%, and the weight percentage of diethyl carbonate in the organic solvent is 60% to 70%, totaling 100%.

[0039] According to a second aspect of the present invention, a method for preparing the above-mentioned lithium ion battery electrolyte is provided, comprising: adding a formulated amount of additives to an organic solvent under an argon atmosphere, then adding an electrolyte lithium salt, and stirring and mixing at a temperature of 5 to 15° C. to obtain a lithium ion battery electrolyte.

[0040] According to a third aspect of the present invention, there is provided a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; the electrolyte is the above-mentioned lithium-ion battery electrolyte.

[0041] By applying the technical solution of the present invention, a lithium ion battery electrolyte is provided. By adjusting the electrolyte components accordingly and introducing a functional additive A, since the functional additive A contains unsaturated functional groups in its structure, it is easy to oxidize to form a dense and uniform CEI film, which effectively inhibits the dissolution of TMs metal ions and the release of oxygen, and at the same time reduces the acidic substances in the electrolyte and the LiF content in the SEI film, thereby reducing the interface side reactions and improving the film-forming quality of the negative electrode SEI film, thereby improving the high-voltage cycle process. DETAILED DESCRIPTION

[0042] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0043] In order to solve the problem of serious attenuation of electrochemical performance of lithium ion batteries in high voltage charge and discharge cycles, especially serious attenuation of battery cycle capacity and voltage, the present invention provides a lithium ion battery electrolyte, the electrolyte comprising the following components in weight percentage: 10% to 15% of lithium salt, 80% to 90% of organic solvent, and 0% to 5% of additives (not 0);

[0044] The additive includes a functional additive A, and the structure of the functional additive A is shown in Formula I:

[0045]

[0046] In Formula I, R1, R2, R3 and R4 are the same or different and are independently hydrogen, halogen, C1-C 10Straight chain alkyl or alkoxy, C1~C 10 A branched alkyl or alkoxy group;

[0047] “··” indicates the shared electron pair between the nitrogen atom and the boron atom.

[0048] In the electrolyte of the present invention, the lithium salt is selected from any value among 10%, 11%, 12%, 13%, 14%, 15%, or any range value between two thereof; the organic solvent is selected from any value among 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or any range value between two thereof; the content of the additive is not 0, for example, any value among 0.001%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range value between two thereof.

[0049] The present invention adjusts the electrolyte components accordingly and uses additives to form a film to protect the positive electrode interface, which can effectively reduce the side reactions at the electrolyte and positive electrode interface, and in situ regulates the physical structure and chemical composition of CEI through additives and solvents, providing a simple and effective method for improving battery performance.

[0050] In particular, a new functional additive A is introduced into the electrolyte of the present invention, which is characterized in that the functional additive A contains unsaturated functional groups in its structure and is easily oxidized to form a dense and uniform CEI film; the dissolution of TMs metal ions and the release of oxygen are effectively inhibited, and at the same time, the acidic substances in the electrolyte are reduced, and the LiF content in the SEI film is reduced, thereby reducing the interface side reactions and improving the film formation quality of the negative electrode SEI film, thereby improving the high-voltage cycle process.

[0051] As a specific embodiment, in Formula I, R1, R2, R3 and R4 are each independently hydrogen, halogen, C1-C4 straight-chain alkyl or alkoxy, C1-C4 branched alkyl or alkoxy.

[0052] As a specific embodiment, in Formula I, R1, R2, R3 and R4 are the same and independently hydrogen, and the chemical structure thereof is shown in Formula I-1:

[0053]

[0054] As a specific embodiment, in Formula I, R1, R3 and R4 are the same and independently hydrogen, R2 is methyl, and its structure is shown in Formula I-2:

[0055]

[0056] As a specific embodiment, in Formula I, R1, R3 and R4 are the same and independently hydrogen, R2 is halogen, preferably, R2 is chlorine, and its chemical structure is shown in Formula I-3:

[0057]

[0058] As a specific embodiment, in Formula I, R1, R3 and R4 are the same and independently hydrogen, R2 is an alkoxy group, preferably, R2 is a methoxy group, and its structure is shown in Formula I-4:

[0059]

[0060] As a preferred embodiment, the weight percentage of lithium salt in the electrolyte is 10% to 15%, the weight percentage of organic solvent in the electrolyte is 80% to 85%, and the weight percentage of additives in the electrolyte is 0.5 to 5%.

[0061] As a preferred embodiment, the weight percentage of lithium salt in the electrolyte is 10% to 15%, the weight percentage of organic solvent in the electrolyte is 80% to 85%, and the weight percentage of additives in the electrolyte is 2% to 5%.

[0062] As a preferred embodiment, the weight percentage of lithium salt in the electrolyte is 13% to 15%, the weight percentage of organic solvent in the electrolyte is 80% to 85%, and the weight percentage of additives in the electrolyte is 3% to 4%.

[0063] As a preferred embodiment, the weight percentage of functional additive A in the electrolyte is 0.3% to 1%, preferably 0.5% to 1%; its percentage range can be selected from any value among 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any range between two values.

[0064] As a specific embodiment, the present invention also provides a method for preparing the functional additive A, which comprises the following steps:

[0065] Step S1: mixing and reacting boron trifluoride etherate and a pyrrole compound in an inert atmosphere to obtain a reaction mixture;

[0066] Step S2: The reaction mixture is subjected to crystal growth to obtain a solid product, namely, functional additive A.

[0067] As a preferred embodiment, in step S1, the molar ratio of boron trifluoride etherate to the pyrrole compound is (1-1.2):1, preferably 1:1.

[0068] As a preferred embodiment, the pyrrole compound includes pyrrole, methyl-substituted pyrrole, methoxy-substituted pyrrole or halogen-substituted pyrrole; wherein the halogen-substituted pyrrole is preferably chlorine-substituted pyrrole.

[0069] As a preferred embodiment, in step S1, the reaction temperature is 25°C to 35°C, and the reaction time is 0.5 to 1 h.

[0070] As a preferred embodiment, in step S2, the temperature for growing the crystal is -15°C to -25°C, preferably -20°C, and the time for growing the crystal is 2 to 3 hours.

[0071] As a preferred embodiment, in step S2, the solid product is dried in a vacuum environment at 90°C to 100°C to obtain the functional additive A. The specific drying process is to place the solid product in a vacuum oven and dry it overnight.

[0072] As a preferred embodiment, the additive further includes one or more of a film-forming additive, a lithium salt additive and a sulfur-containing additive.

[0073] The present invention adds the functional additive A having a positive electrode film-forming effect in combination with the three different types of additives. On the one hand, the additive A forms a uniform and dense CEI film at the positive electrode, inhibits the dissolution of TMs metal ions and the release of oxygen, and inhibits its reduction on the negative electrode surface, thereby reducing the interface side reactions; on the other hand, pyrrole can also neutralize acidic substances in the electrolyte, such as PF5, HF and CO2; BF3 is a boron Lewis acid, which can dissolve LiF as an anion receptor, reduce the interface impedance, and improve the film-forming quality of the positive and negative SEI films, thereby improving the high-voltage cycle process and significantly slowing down the attenuation of the battery cycle capacity and voltage attenuation during high-voltage charging and discharging.

[0074] As a specific embodiment, the film-forming additive is selected from vinylene carbonate and / or fluoroethylene carbonate.

[0075] As a specific embodiment, the lithium salt additive is selected from one or more of lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiBOB) and lithium difluorobis(oxalatophosphate) (LiODFP).

[0076] As a specific embodiment, the sulfur-containing additive is selected from one or more of 1,3-propane sultone (PS), 1,3-propylene sultone (PST) and diethylene sulfate (DTD).

[0077] As a preferred embodiment, the additive specifically includes vinylene carbonate, lithium difluorophosphate and 1,3-propane sultone.

[0078] As a preferred embodiment, the weight percentage of vinylene carbonate in the electrolyte is 0.1% to 1%, preferably 0.5% to 1%.

[0079] As a preferred embodiment, the weight percentage of lithium difluorophosphate in the electrolyte is 0.5% to 1%.

[0080] As a preferred embodiment, the weight percentage of 1,3-propane sultone in the electrolyte is 0.5% to 3%, preferably 2% to 3%.

[0081] The vinylene carbonate (VC) of the present invention forms a film at the negative electrode. If the addition amount is too small, a dense SEI film cannot be formed. If the addition amount is too large, the impedance will be too large and high-temperature gas production will occur. 1,3-Propane sultone (PS) assists in film formation at the positive and negative electrodes and has high thermal stability. If the addition amount is too small, a dense SEI film cannot be formed at the negative electrode. If the addition amount is too large, the film impedance will be large, resulting in decreased cycle performance. Lithium difluorophosphate (LiPO2F2) participates in the film formation of the positive and negative electrodes. If the addition amount is too small, a dense SEI film cannot be formed. If the addition amount is too large, it cannot be completely dissolved. Functional additive A has a positive and negative electrode film-forming effect.

[0082] As a specific implementation, the lithium salt in the electrolyte of the present invention is selected from lithium hexafluorophosphate, and other types of lithium salt electrolytes can also be selected according to actual needs.

[0083] As a specific embodiment, the organic solvent is selected from one or more of cyclic carbonates, chain carbonates and chain carboxylates; preferably, the organic solvent comprises a mixture of a cyclic carbonate, a chain carbonate and a chain carboxylate.

[0084] As a specific implementation, the mass ratio of cyclic carbonate, chain carbonate and chain carboxylic acid ester is (1-15): (20-70): (5-20).

[0085] As a specific implementation, the organic solvent includes fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate and diethyl carbonate.

[0086] As a specific implementation manner, the weight percentage of fluoroethylene carbonate in the organic solvent is 10% to 12%; the weight percentage of ethylene carbonate in the organic solvent is 8% to 12%, the weight percentage of ethyl difluoroacetate in the organic solvent is 12 to 18%, and the weight percentage of diethyl carbonate in the organic solvent is 60% to 70%, totaling 100%.

[0087] In addition to using additives to form a film to protect the positive electrode interface, the electrolyte of the present invention can also effectively reduce side reactions at the electrolyte and positive electrode interface, and in situ regulate the physical structure and chemical composition of CEI through additives and solvents, thereby improving battery performance.

[0088] The present invention selects suitable organic solvents for compounding and limits the specific proportions of various organic solvents. The organic solvents, additives and lithium salts have good synergistic effects, which can further solve the problem of rapid battery performance degradation during high-voltage cycles and extend the battery life.

[0089] The present invention also provides a method for preparing the above-mentioned lithium ion battery electrolyte, comprising: adding a formulated amount of additives to an organic solvent under an inert atmosphere, then adding an electrolyte lithium salt, stirring and mixing at a temperature of 5 to 15° C., preferably at 10° C., to obtain a lithium ion battery electrolyte. The above-mentioned inert atmosphere can be selected from argon and other gases, and other suitable inert gases can be selected according to actual conditions.

[0090] The present invention further provides a lithium ion battery, comprising a positive electrode plate, a negative electrode plate, a separator, and an electrolyte; the electrolyte is the above-mentioned novel lithium ion battery electrolyte developed by the present invention.

[0091] As a specific embodiment, the preparation method of the above-mentioned negative electrode plate is as follows: the negative electrode material graphite, the conductive agent acetylene black and the binder CMC and SBR are prepared into a slurry in a mass percentage of 94:1:2:3, coated on the copper foil current collector, and vacuum dried to obtain the negative electrode plate.

[0092] As a specific embodiment, the preparation method of the positive electrode sheet is as follows: the positive electrode material 0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2, conductive agent acetylene black and binder PVDF are prepared into a slurry in a mass ratio of 94:3:3, coated on an aluminum foil current collector, and vacuum dried to obtain a positive electrode sheet.

[0093] As a specific embodiment, the above-mentioned diaphragm is a Celgard2400 diaphragm.

[0094] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0095] Example 1

[0096] The synthesis method comprises the following steps: adding boron trifluoride etherate and pyrrole in a molar ratio of 1:1 to a dry reaction bottle in an inert atmosphere for reaction, the reaction time is 0.5-1h, and the product is white or colorless crystalline precipitate; when no further precipitation is observed, it indicates that the basic reaction is finished; then transferring the reaction mixture in the sealed reaction bottle to a -20°C refrigerator to grow crystals, the growth time is 2-3h, collecting the solid product and transferring it to a vacuum oven, vacuum drying at 90°C-100°C overnight, and obtaining the product by vacuum drying in the form of white powder, which is recorded as compound 1. After detection and analysis, it has the structure shown in formula I-1:

[0097]

[0098] Example 2

[0099] The synthesis method comprises the following steps: adding boron trifluoride etherate and 3-methylpyrrole in a molar ratio of 1:1 to a dry reaction bottle in an inert atmosphere for reaction, the reaction time is 0.5-1h, and the product is white or colorless crystalline precipitate; when no further precipitation is observed, it indicates that the basic reaction is finished; then transferring the reaction mixture in the sealed reaction bottle to a -20°C refrigerator to grow crystals, the growth time is 2-3h, collecting the solid product and transferring it to a vacuum oven, vacuum drying at 90°C-100°C overnight, and obtaining the product by vacuum drying in the form of white powder, which is recorded as compound 2. After detection and analysis, it has the structure shown in formula I-2:

[0100]

[0101] Example 3

[0102] The synthesis method comprises the following steps: adding boron trifluoride etherate and 3-chloropyrrole in a molar ratio of 1:1 to a dry reaction bottle in an inert atmosphere for reaction, the reaction time is 0.5-1h, and the product is white or colorless crystalline precipitate; when no further precipitation is observed, it indicates that the basic reaction is completed; then the reaction mixture in the sealed reaction bottle is transferred to a -20°C refrigerator to grow crystals, the growth time is 2-3h, the solid product is collected and transferred to a vacuum oven, and vacuum dried at 90°C-100°C overnight, and the product is obtained by vacuum drying in the form of white powder, which is recorded as compound 3. After detection and analysis, it has a structure shown in formula I-3:

[0103]

[0104] Example 4

[0105] The synthesis method comprises the following steps: adding boron trifluoride etherate and 3-methoxypyrrole in a molar ratio of 1:1 to a dry reaction bottle in an inert atmosphere for reaction, the reaction time is 0.5-1h, and the product is white or colorless crystalline precipitate; when no further precipitation is observed, it indicates that the basic reaction is completed; then the reaction mixture in the sealed reaction bottle is transferred to a -20°C refrigerator to grow crystals, the growth time is 2-3h, the solid product is collected and transferred to a vacuum oven, and vacuum dried at 90°C-100°C overnight, and the product is obtained by vacuum drying in the form of white powder, which is recorded as compound 4. After detection and analysis, it has a structure shown in formula I-4:

[0106]

[0107] Example 5

[0108] Step S1: The lithium-ion battery electrolyte includes the following components in weight percentage:

[0109] 15% lithium hexafluorophosphate, 81.5% organic solvent (based on 100% by weight of the organic solvent, the organic solvent includes: 10% fluoroethylene carbonate, 10% ethylene carbonate, 15% ethyl difluoroacetate, 65% diethyl carbonate), 0.5% vinylene carbonate (VC), 0.5% lithium difluorophosphate (LiPO2F2), 2% 1,3-propane sultone (PS), 0.5% functional additive A (compound 1 of Example 1);

[0110] Step S2: Under an argon atmosphere, VC, PS, LiPO2F2 and functional additive A are added to an organic solvent according to a ratio, and then an electrolyte lithium salt is added, and the mixture is stirred and mixed at a temperature of 10° C. to obtain an electrolyte 1.

[0111] Example 6

[0112] Step S1: The lithium-ion battery electrolyte includes the following components in weight percentage:

[0113] 10% lithium hexafluorophosphate, 85% organic solvent (based on 100% by weight of the organic solvent, the organic solvent includes: 12% fluoroethylene carbonate, 12% ethylene carbonate, 12% ethyl difluoroacetate, 64% diethyl carbonate), 1% vinylene carbonate (VC), 1% lithium difluorophosphate (LiPO2F2), 2% 1,3-propane sultone (PS), 1% functional additive A (Compound 2 of Example 2);

[0114] Step S2: Under an argon atmosphere, VC, PS, LiPO2F2 and functional additive A are added to the organic solvent according to the ratio, and then electrolyte lithium salt is added, and the mixture is stirred and mixed at a temperature of 10° C. to obtain electrolyte 2.

[0115] Example 7

[0116] Step S1: The lithium-ion battery electrolyte includes the following components in weight percentage:

[0117] 13% lithium hexafluorophosphate, 83% organic solvent (based on 100% by weight of the organic solvent, the organic solvent includes: 10% fluoroethylene carbonate, 10% ethylene carbonate, 12% ethyl difluoroacetate, 68% diethyl carbonate), 0.8% vinylene carbonate (VC), 0.8% lithium difluorophosphate (LiPO2F2), 1.6% 1,3-propane sultone (PS), 0.8% functional additive A (compound 3 of Example 3);

[0118] Step S2: Under an argon atmosphere, VC, PS, LiPO2F2 and functional additive A are added to the organic solvent according to the ratio, and then electrolyte lithium salt is added, and the mixture is stirred and mixed at a temperature of 10° C. to obtain electrolyte 3.

[0119] Example 8

[0120] Step S1: The lithium-ion battery electrolyte includes the following components in weight percentage:

[0121] 10% lithium hexafluorophosphate, 88% organic solvent (based on 100% by weight of the organic solvent, the organic solvent includes: 10% fluoroethylene carbonate, 10% ethylene carbonate, 15% ethyl difluoroacetate, 65% diethyl carbonate), 0.5% vinylene carbonate (VC), 0.5% lithium difluorophosphate (LiPO2F2), 0.5% 1,3-propane sultone (PS), 0.5% functional additive A (compound 4 of Example 4);

[0122] Step S2: Under an argon atmosphere, VC, PS, LiPO2F2 and functional additive A are added to the organic solvent according to the ratio, and then electrolyte lithium salt is added, and the mixture is stirred and mixed at a temperature of 10° C. to obtain electrolyte 4.

[0123] Comparative Example 1

[0124] The difference between Comparative Example 1 and Example 5 is that the functional additive A is not added to the electrolyte.

[0125] Comparative Example 2

[0126] The difference between Comparative Example 2 and Example 5 is that a film-forming additive, succinonitrile (SN), is added to the electrolyte.

[0127] Comparative Example 3

[0128] The difference between Comparative Example 3 and Example 5 is that pyrrole is added to the electrolyte as a film-forming additive.

[0129] Comparative Example 4

[0130] The difference between Comparative Example 4 and Example 5 is that BF3 is added to the electrolyte as a film-forming additive.

[0131] Application Examples

[0132] The electrolyte provided in each embodiment and comparative example was applied to a lithium ion battery, and the performance test was carried out using the lithium ion battery.

[0133] The specific preparation method of the lithium-ion battery used for the test includes: preparing a negative electrode material graphite, a conductive agent acetylene black and a binder CMC and SBR in a mass percentage of 94:1:2:3 into a slurry, coating it on a copper foil current collector, and vacuum drying to obtain a negative electrode sheet; preparing a positive electrode material 0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2, conductive agent acetylene black and binder PVDF were prepared into a slurry in a mass ratio of 94:3:3, coated on an aluminum foil current collector, and vacuum dried to obtain a positive electrode sheet; the positive electrode sheet, the negative electrode sheet, the Celgard2400 separator and the electrolyte prepared in Examples 5 to 8 or Comparative Examples 1 to 4 were respectively assembled into soft-pack batteries to obtain samples 1 to 4 and comparative samples 1 to 4, respectively; electrochemical tests were carried out using a Xinwei charge and discharge test cabinet, and the test results are shown in Table 1.

[0134] Test method:

[0135] (1) Normal temperature cycle performance test:

[0136] At 25°C, the lithium-ion battery is charged at a constant current of 0.5C (nominal capacity) to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current ≤ 0.05C, left for 10 minutes, and then discharged at a constant current of 1C to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium-ion battery is charged and discharged 1000 times at 25°C under the above conditions.

[0137] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0138] The average voltage (V) of a lithium-ion battery after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, where N is the number of cycles of the lithium-ion battery.

[0139] (2) High temperature cycle performance test:

[0140] At 45°C, the lithium-ion battery is charged at a constant current of 1.0C (nominal capacity) to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current ≤ 0.05C, left for 10 minutes, and then discharged at a constant current of 1C to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium-ion battery is subjected to 800 charge and discharge cycles at 45°C under the above conditions.

[0141] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0142] The average voltage (V) of a lithium-ion battery after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, where N is the number of cycles of the lithium-ion battery.

[0143] Table 1

[0144]

[0145] It can be seen from the test results in Table 1 that in the normal temperature (25°C) cycle test, the lithium ion batteries assembled using the electrolytes of Examples 5 to 8 showed a capacity retention rate of more than 86% and an average voltage of more than 3.6800V; while the capacity retention rate of Comparative Example 1 was 68.0% and the average voltage was 3.6103V; it is obvious that Examples 5 to 8 of the present invention are significantly higher than the capacity retention rate of the lithium ion battery after 1000 cycles at room temperature, which is increased from the original 68% to 86.5%, and the average voltage is increased from the original 3.6103V to 3.6830V; This shows that the present invention can significantly improve the serious problem of capacity attenuation and voltage attenuation in the high-voltage battery cycle by adding functional additive A to the electrolyte.

[0146] In the high temperature (45°C) cycle test, the lithium ion batteries assembled with the electrolytes of Examples 5 to 8 showed a capacity retention rate of more than 84% and an average voltage of more than 3.6300V; while the capacity retention rate of Comparative Example 1 was 62.4% and the average voltage was 3.5998V; it is obvious that Examples 5 to 8 of the present invention significantly improve the capacity retention rate of the lithium ion battery after 800 cycles at high temperature, from the original 62.4% to 84.4%, and the average voltage is increased from the original 3.5998V to 3.6360V; this shows that the present invention can significantly improve the serious problem of capacity attenuation and voltage attenuation in the high voltage battery cycle by adding the functional additive A to the electrolyte.

[0147] Compared with Comparative Example 2, although positive electrode film-forming additives are also added in Comparative Example 2, the effect of improving capacity decay and voltage decay in high-voltage battery cycles is not as good as that of the present invention. The present invention introduces a new type of compound as a film-forming additive to significantly improve the performance decay problem of high-voltage batteries, and combines the optimized ratio of the components in the lithium-ion battery electrolyte of the present invention to achieve mutual synergy between the components and jointly promote the electrochemical performance of the lithium-ion battery.

[0148] Compared with comparative examples 3 and 4, although the structures of embodiments 5 to 8 of the present invention are similar, their effects in improving capacity decay and voltage decay in high-voltage battery cycles are not as good as those of the present invention, indicating that the effects of the two substances in comparative examples 3 and 4 are not good when acting alone. The above technical problems of the present invention can only be solved by using the new functional additive A selected by the present invention.

[0149] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: The electrolyte comprises the following components in weight percentage: Lithium salt 10% to 15%, organic solvent 80% to 90%, additive 0 to 5% and not 0; Wherein, the additive includes a functional additive A, and the structure of the functional additive A is shown in Formula I: In Formula I, R1, R2, R3 and R4 are the same or different and are independently hydrogen, halogen, C1-C 10 Straight chain alkyl or alkoxy, C1~C 10 A branched alkyl or alkoxy group; "··" represents the shared electron pair between the nitrogen atom and the boron atom.

2. The lithium ion battery electrolyte according to claim 1, characterized in that: In formula I, R1, R2, R3 and R4 are each independently hydrogen, halogen, C1-C4 straight-chain alkyl or alkoxy, C1-C4 branched-chain alkyl or alkoxy; Preferably, R1, R2, R3 and R4 are the same and are hydrogen; or, R1, R3 and R4 are all the same and are hydrogen, R2 is methyl; or, R1, R3 and R4 are all the same and are hydrogen, R2 is halogen, more preferably R2 is chlorine; or, R1, R3 and R4 are all the same and are hydrogen, R2 is a C1-C4 straight-chain alkoxy group, and more preferably R2 is a methoxy group.

3. The lithium ion battery electrolyte according to claim 1 or 2, characterized in that: The weight percentage of the lithium salt in the electrolyte is 10% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 0.5 to 5%; Preferably, the weight percentage of the lithium salt in the electrolyte is 13% to 15%, the weight percentage of the organic solvent in the electrolyte is 80% to 85%, and the weight percentage of the additive in the electrolyte is 2% to 5%; Preferably, the weight percentage of the functional additive A in the electrolyte is 0.3% to 1%, and more preferably 0.5% to 1%.

4. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that The preparation method of the functional additive A comprises the following steps: Step S1: mixing and reacting boron trifluoride etherate and a pyrrole compound in an inert atmosphere to obtain a reaction mixture; Step S2: The reaction mixture is subjected to crystal growth to obtain a solid product, namely the functional additive A.

5. The lithium ion battery electrolyte according to claim 4, characterized in that: In step S1, the molar ratio of the boron trifluoride etherate to the pyrrole compound is (1-1.2):1; and / or, the pyrrole compound is selected from pyrrole, 3-methylpyrrole, 3-methoxypyrrole or 3-chloropyrrole; And / or, in step S1, the reaction temperature is 25°C to 35°C, and the reaction time is 0.5 to 1 h; And / or, in step S2, the temperature during the crystal growth is -15°C to -25°C, and the crystal growth time is 2 to 3 hours; And / or, in step S2, the solid product is dried in a vacuum environment at 90° C. to 100° C. to obtain the functional additive A.

6. The lithium ion battery electrolyte according to any one of claims 1 to 5, characterized in that: The additives also include one or more of a film-forming additive, a lithium salt additive, and a sulfur-containing additive; Preferably, the film-forming additive is selected from vinylene carbonate and / or fluoroethylene carbonate; Preferably, the lithium salt additive is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium dioxalatoborate and lithium difluorodioxalatophosphate; Preferably, the sulfur-containing additive is selected from one or more of 1,3-propane sultone, 1,3-propylene sultone and ethylene sulfate.

7. The lithium ion battery electrolyte according to any one of claims 1 to 6, characterized in that: The additives also include vinylene carbonate, lithium difluorophosphate and 1,3-propane sultone; Preferably, the weight percentage of vinylene carbonate in the electrolyte is 0.1% to 1%, preferably 0.5% to 1%; Preferably, the weight percentage of the lithium difluorophosphate in the electrolyte is 0.5% to 1%; Preferably, the weight percentage of the 1,3-propane sultone in the electrolyte is 0.5% to 3%, preferably 2% to 3%.

8. The lithium ion battery electrolyte according to any one of claims 1 to 7, characterized in that: The lithium salt is selected from lithium hexafluorophosphate; and / or, the organic solvent is selected from one or more of cyclic carbonates, chain carbonates and chain carboxylates; Preferably, the mass ratio of the cyclic carbonate, the chain carbonate and the chain carboxylic acid ester is (1-15): (20-70): (5-20); Preferably, the organic solvent comprises fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate and diethyl carbonate; Preferably, the weight percentage of the fluoroethylene carbonate in the organic solvent is 10% to 12%; the weight percentage of the ethylene carbonate in the organic solvent is 8% to 12%, the weight percentage of the ethyl difluoroacetate in the organic solvent is 12 to 18%, and the weight percentage of the diethyl carbonate in the organic solvent is 60% to 70%, totaling 100%.

9. The method for preparing a lithium ion battery electrolyte according to any one of claims 1 to 8, characterized in that: The method comprises: adding a formulated amount of additives and electrolyte lithium salt into an organic solvent under an inert atmosphere, mixing at a temperature of 5 to 15° C., and obtaining a lithium ion battery electrolyte.

10. A lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; characterized in that: The electrolyte is the lithium ion battery electrolyte according to any one of claims 1 to 8 or the electrolyte prepared by the method according to claim 9.

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