Electrolyte, preparation method thereof, injection method and lithium ion battery

Abstract

The present invention relates to the field of lithium-ion battery technology, and more particularly to an electrolyte, a preparation method thereof, an injection method thereof, and a lithium-ion battery. The electrolyte comprises the following components in volume percentages: 15% to 30% of a first electrolyte; 70% to 85% of a second electrolyte. The first electrolyte comprises a first lithium salt, a first solvent, and an additive, and the second electrolyte comprises a second lithium salt and a second solvent, wherein the second solvent comprises at least one of an ether fluoride liquid and an alcohol fluoride liquid. By replacing easily vaporized and flammable organic solvents such as dimethyl orthocarbonate (DMC) and ethyl methyl carbonate (EMC) with an ether / alcohol fluoride liquid, the electrolyte of the present invention, when used in a lithium-ion battery, provides the lithium-ion battery with higher safety performance.

Description

Technical Field

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

[0002] Lithium-ion battery safety is currently a major concern in its application. Currently produced and used lithium-ion batteries primarily utilize liquid electrolytes, primarily containing lithium hexafluorophosphate and organic solvents such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). When the internal temperature of a lithium-ion battery is too high, thermal runaway can occur. Organic solvents such as DEC, DMC, and EMC become flammable and, at high temperatures, can easily generate flammable gases, leading to explosions and explosions.

[0003] Therefore, how to improve the safety performance of lithium-ion batteries is a technical problem that needs to be solved urgently in this technical field. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention aims to provide an electrolyte, a preparation method thereof, an injection method thereof, and a lithium-ion battery. The present invention replaces easily vaporized and flammable organic solvents such as dimethyl orthocarbonate (DMC) and ethyl methyl carbonate (EMC) with ether / alcohol fluorinated liquids, so that when the electrolyte of the present invention is used in a lithium-ion battery, the lithium-ion battery has higher safety performance.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides an electrolyte comprising the following components in percentage by volume:

[0007] The first electrolyte is 15% to 30%;

[0008] The second electrolyte is 70% to 85%;

[0009] The first electrolyte includes a first lithium salt, a first solvent and an additive, the second electrolyte includes a second lithium salt and a second solvent, and the second solvent includes at least one of an ether fluoride liquid and an alcohol fluoride liquid.

[0010] The present invention replaces easily gasified and flammable organic solvents such as dimethyl orthocarbonate DMC and ethyl methyl carbonate EMC with ether / alcohol fluorinated liquid, so that when the electrolyte of the present invention is applied to a lithium ion battery, the lithium ion battery has higher safety performance.

[0011] Furthermore, the first electrolyte includes the following components in percentage by weight: 15% to 18% of the first lithium salt, 72% to 84% of the first solvent, and 1% to 10% of the additive.

[0012] Furthermore, the first lithium salt includes at least one of lithium hexafluorophosphate and lithium fluoride;

[0013] and / or, the first solvent comprises at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate;

[0014] And / or, the first solvent comprises dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate is (2-5): (2-5): (2-5);

[0015] and / or, the additive comprises at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, vinyl sulfate, biphenyl, cyclohexylbenzene, and tert-amylbenzene;

[0016] And / or, the additive includes vinylene carbonate and vinyl sulfate, and the mass ratio of the vinylene carbonate to the vinyl sulfate is (0.5-2):1.

[0017] Furthermore, the second electrolyte includes the following components in percentage by weight: 10% to 15% of the second lithium salt and 85% to 90% of the second solvent.

[0018] Furthermore, the second lithium salt includes at least one of lithium hexafluorophosphate and lithium fluoride;

[0019] And / or, the ether fluorinated liquid includes at least one of tetrafluoroethyl tetrafluoropropyl ether, tetrafluoroethyl trifluoropropyl ether, and 1,1,1,2,2,3.3,4.4-nonafluorobutyl methyl ether;

[0020] And / or, the alcohol fluorinated liquid includes at least one of 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol, perfluorooctylethanol, 1H,1H,2H,2H-perfluorooctanol, 1H,1H,8H-perfluoro-1-octanol, tetrafluoroisopropanol, and (CF3)2CHOH.

[0021] In a second aspect, the present invention provides a method for preparing the electrolyte according to the first aspect, the preparation method comprising the following steps:

[0022] Weighing each component according to the designed ratio, and evenly mixing the weighed first solvent and the additive to obtain a first primary electrolyte; adding the first lithium salt to the first primary electrolyte, and mixing evenly to obtain the first electrolyte;

[0023] The components are weighed according to the designed ratio, and the weighed second solvent and the second lithium salt are evenly mixed to obtain the second electrolyte.

[0024] In a third aspect, the present invention provides a method for injecting the electrolyte according to the second aspect, wherein the method includes injecting once or twice;

[0025] Wherein, the one-time injection comprises the following steps:

[0026] Mixing the first electrolyte and the second electrolyte to obtain a mixed electrolyte, injecting the mixed electrolyte into the battery to be filled, performing formation after sufficient infiltration, and sealing after the formation is completed;

[0027] The two injections comprise the following steps:

[0028] All of the first electrolyte and part of the second electrolyte are mixed to obtain a first electrolyte, which is injected into the battery to be injected, and is formed after being fully infiltrated. After the formation is completed, the remaining second electrolyte is injected and the battery is packaged.

[0029] Furthermore, the volume percentage of the first-injected electrolyte to the total electrolyte is 30% to 65%.

[0030] Furthermore, the sufficient infiltration includes standing at 20 to 60° C. for 2 to 8 hours;

[0031] And / or, the formation includes charging at 55°C to 65°C at a constant current of 0.05C to 0.15C for 2h to 0.6h, then charging at a constant current of 0.15C to 0.3C for 2.6h to 1.3h, charging at a constant current of 0.3C to 0.5C for 1h to 0.6h, and finally charging at a constant current of 0.1C to 0.25C for 2h to 0.8h.

[0032] In a fourth aspect, the present invention provides a lithium-ion battery, which includes the electrolyte described in the first aspect, or is prepared using the injection method described in the third aspect.

[0033] Compared with the prior art, the present invention has at least one of the following advantages:

[0034] (1) The present invention replaces easily gasified and flammable organic solvents such as dimethyl orthocarbonate DMC and ethyl methyl carbonate EMC with ether / alcohol fluorinated liquid, so that when the electrolyte of the present invention is applied to lithium-ion batteries, the lithium-ion batteries have higher safety performance.

[0035] (2) Ether / alcohol fluorinated liquids are insoluble in water. When used as solvents for lithium hexafluorophosphate, they can more quickly infiltrate the positive electrode, negative electrode, and diaphragm, and have a drainage function.

[0036] (3) Fluorinated liquid has high voltage resistance. When used as an electrolyte solvent, it makes it possible to connect batteries in series at the core level. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0038] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0039] In a first aspect, the present invention provides an electrolyte comprising the following components in percentage by volume:

[0040] 15% to 30% of the first electrolyte (for example, 15%, 20%, 25% or 30%);

[0041] The second electrolyte is 70% to 85% (for example, 70%, 75%, 80% or 85%);

[0042] The first electrolyte includes a first lithium salt, a first solvent and an additive, the second electrolyte includes a second lithium salt and a second solvent, and the second solvent includes at least one of an ether fluoride liquid and an alcohol fluoride liquid.

[0043] The present invention replaces easily gasified and flammable organic solvents such as dimethyl orthocarbonate DMC and ethyl methyl carbonate EMC with ether / alcohol fluorinated liquid, so that when the electrolyte of the present invention is applied to a lithium ion battery, the lithium ion battery has higher safety performance.

[0044] The most critical factor affecting battery safety is high temperature:

[0045] 1. Under high temperature conditions, a large number of side reactions will occur between the positive and negative electrode materials and the electrolyte in the battery. In the present invention, the free second electrolyte is a stable ether / alcohol fluorinated liquid that will not react with the positive and negative electrode materials.

[0046] 2. Under high temperature conditions, DMC, EMC, etc. in traditional electrolytes are easily vaporized. The vaporized DMC, EMC, etc. quickly increase the internal pressure of the battery. After the battery explosion-proof valve is opened, the high-temperature and high-pressure electrolyte gas is exposed to air and is easily ignited. In the present invention, fluorinated liquid is used instead of the flammable and easily vaporized electrolyte, which can reduce the internal pressure of the battery. Even if the gasified liquid is sprayed out of the battery, it will not burn. Therefore, the sprayed fluorinated liquid quickly forms a mist after cooling, deposits around the battery and displaces the air, which has a certain fire extinguishing ability.

[0047] 3. When the battery experiences thermal runaway, a short-circuit high-temperature point will appear inside. Liquid fluoride solution can lower the temperature and prevent it from igniting when immersed in the high-temperature position.

[0048] In the present invention, the first and second electrolytes are used together. The first electrolyte ensures the integrity of the positive and negative electrodes in the battery, while the second electrolyte improves battery safety by reducing the content of flammable organic solvents and minimizing side reactions in the battery. If the volume percentage of the first electrolyte is too high, the battery safety is poor. If the volume percentage of the first electrolyte is too low, the integrity of the positive and negative electrodes in the battery cannot be guaranteed, resulting in poor electrochemical performance.

[0049] In the above-mentioned electrolyte, as an optional embodiment, the first electrolyte includes the following components in percentage by mass: 15% to 18% of the first lithium salt, 72% to 84% of the first solvent (for example, it can be 72%, 74%, 76%, 78%, 80%, 82% or 84%), and 1% to 10% of the additive (for example, it can be 1%, 3%, 5%, 7% or 10%).

[0050] In the above electrolyte, as an optional embodiment, the first lithium salt includes at least one of lithium hexafluorophosphate and lithium fluoride.

[0051] In the above electrolyte, as an optional embodiment, the first solvent includes at least two of ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, diethyl carbonate DEC, ethyl methyl carbonate EMC, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0052] In the above electrolyte, as an optional embodiment, the first solvent includes dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate is (2-5): (2-5): (2-5).

[0053] In the above electrolyte, as an optional embodiment, the additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, vinyl sulfate, biphenyl, cyclohexylbenzene, and tert-amylbenzene.

[0054] In the above electrolyte, as an optional embodiment, the additive includes vinylene carbonate and vinyl sulfate, and the mass ratio of the vinylene carbonate to the vinyl sulfate is (0.5-2):1, for example, it can be 0.5:1, 1:1, 1.5:1 or 2:1.

[0055] In the aforementioned electrolyte, as an optional embodiment, the second electrolyte comprises the following components in percentage by weight: 10% to 15% of the second lithium salt and 85% to 90% of the second solvent. Because the fluorinated solution limits the growth of the SEI film and reduces lithium ion loss, the amount of the second lithium salt in the second electrolyte is relatively low.

[0056] In the above electrolyte, as an optional embodiment, the second lithium salt includes at least one of lithium hexafluorophosphate and lithium fluoride.

[0057] In the above electrolyte, as an optional embodiment, the ether fluorinated liquid includes at least one of tetrafluoroethyl tetrafluoropropyl ether (HFE458), tetrafluoroethyl trifluoropropyl ether (HFE347), and 1,1,1,2,2,3.3,4.4-nonafluorobutyl methyl ether (HFE7100).

[0058] In the above electrolyte, as an optional embodiment, the alcohol fluorinated liquid includes 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol (C9H5F 15 O), perfluorooctylethanol, 1H,1H,2H,2H-perfluorooctanol, 1H,1H,8H-perfluoro-1-octanol, tetrafluoroisopropanol, (CF3)2CHOH).

[0059] In a second aspect, the present invention provides a method for preparing the electrolyte according to the first aspect, the preparation method comprising the following steps:

[0060] Weighing each component according to the designed ratio, and evenly mixing the weighed first solvent and the additive to obtain a first primary electrolyte; adding the first lithium salt to the first primary electrolyte, and mixing evenly to obtain the first electrolyte;

[0061] The components are weighed according to the designed ratio, and the weighed second solvent and the second lithium salt are evenly mixed to obtain the second electrolyte.

[0062] In a third aspect, the present invention provides a method for injecting the electrolyte according to the first aspect, wherein the method includes injecting once or twice;

[0063] Wherein, the one-time injection comprises the following steps:

[0064] Mixing the first electrolyte and the second electrolyte to obtain a mixed electrolyte, injecting the mixed electrolyte into the battery to be filled, performing formation after sufficient infiltration, and sealing after the formation is completed;

[0065] The two injections comprise the following steps:

[0066] All of the first electrolyte and part of the second electrolyte are mixed to obtain a first electrolyte, which is injected into the battery to be injected, and is formed after being fully infiltrated. After the formation is completed, the remaining second electrolyte is injected and the battery is packaged.

[0067] The embodiment of the present invention injects the electrolyte twice, thereby making the high and low temperature performance and rate performance of the lithium-ion battery more excellent.

[0068] During the two-step electrolyte injection process, the positive and negative electrode materials in the battery generate a stable solid electrolyte interface film (SEI film) at the negative electrode during the formation process, and an electrochemical interface film (CEI film) on the surface of the positive electrode material. After the infiltration and formation are completed, the battery is filled with the second electrolyte. After the second electrolyte is injected into the battery, due to its better fluidity, surface tension and miscibility with the first electrolyte, the second electrolyte will replace or dilute the first electrolyte that is infiltrated in the gaps between the positive and negative electrode materials. The solvent in the second electrolyte is chemically stable and does not participate in the formation of the SEI film and the CEI film. It will not come into contact with the positive and negative electrode materials to produce side reactions. Therefore, the SEI film and the CEI film will not continue to grow due to side reactions, resulting in increased resistance and consumption of lithium ions, thereby protecting the stability of the battery's electrical performance and cycle life.

[0069] In the above-mentioned electrolyte injection method, as an optional embodiment, the volume percentage of the first-injected electrolyte in the electrolyte is 30% to 65%, for example, it can be 30%, 40%, 50%, 55%, 60% or 65%, preferably 50% to 65%. The embodiment of the present invention limits the volume percentage of the first-injected electrolyte to 50% to 65% of the electrolyte, so that the positive and negative electrodes in the lithium-ion battery can be fully infiltrated, thereby improving the electrochemical performance of the lithium-ion battery.

[0070] In the above-mentioned electrolyte injection method, as an optional embodiment, the sufficient infiltration includes standing at 20-60°C (for example, 20°C, 30°C, 40°C, 50°C or 60°C) for 2-8h (for example, 2h, 4h, 6h or 8h).

[0071] In the above-mentioned electrolyte injection method, as an optional embodiment, the formation includes charging at 55°C to 65°C (for example, 55°C, 60°C or 65°C) with a constant current of 0.05C to 0.15C for 2h to 0.6h, then charging with a constant current of 0.15C to 0.3C for 2.6h to 1.3h, charging with a constant current of 0.3C to 0.5C for 1h to 0.6h, and finally charging with a constant current of 0.1C to 0.25C for 2h to 0.8h.

[0072] In a fourth aspect, the present invention provides a lithium-ion battery, which includes the electrolyte described in the first aspect, or is prepared using the injection method described in the third aspect.

[0073] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0074] Example 1: Inject the first electrolyte, the second electrolyte, and the second electrolyte twice in succession

[0075] This embodiment provides an electrolyte, which includes the following components in percentage by volume:

[0076] First electrolyte: 25%;

[0077] Second electrolyte: 75%;

[0078] The first electrolyte comprises the following components by weight: 16% lithium hexafluorophosphate, 81% first solvent, 1.8% vinylene carbonate, and 1.2% vinyl sulfate, wherein the first solvent is composed of dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate is 3:2:5;

[0079] The second electrolyte includes the following components in percentage by weight: 14% lithium hexafluorophosphate, 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol (C9H5F 15 O)86%.

[0080] The preparation method of the electrolyte provided in this embodiment includes the following steps:

[0081] Weigh each component according to the designed ratio, and in a glove box filled with inert gas (argon, nitrogen) (water content <0.1ppm, oxygen content <0.1ppm), mix dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate in a mass ratio of 3:2:5, then add 1.8% by mass of vinylene carbonate and 1.2% by mass of vinyl sulfate, mix them evenly, and then add lithium hexafluorophosphate (16% by weight of the total weight of the first electrolyte), which is recorded as the first electrolyte;

[0082] Weigh each component according to the designed ratio, and in a glove box filled with inert gas (argon, nitrogen) (water content <0.1ppm, oxygen content <0.1ppm), add the weighed 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol (C9H5F 15 O) and lithium hexafluorophosphate are uniformly mixed to obtain the second electrolyte.

[0083] This embodiment also provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, and a separator, wherein:

[0084] Positive electrode: Contains aluminum foil and active membrane layer, where the active membrane layer contains lithium iron phosphate, conductive agent (conductive carbon black (Super-P)), and binder (polyvinylidene fluoride (PVDF)), with the weight ratio of each component being 95:3:2 respectively;

[0085] Negative electrode: Contains copper foil and active membrane layer, where the active membrane layer contains artificial graphite, conductive agent (Super-P), binder (CMC and SBR), and the mass ratio of each component is 95:2:1.8:1.2 respectively;

[0086] Separator membrane: A polyethylene porous polymer membrane is used as the separator membrane.

[0087] The preparation method of the lithium ion battery comprises the following steps:

[0088] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are assembled according to the designed size and sequence so that the separator can completely isolate the positive electrode from the negative electrode sheet, and the negative electrode sheet can be completely covered to form a core, which is placed in an outer package and baked until the moisture content is qualified. Then, all of the first electrolyte and part of the second electrolyte are mixed in a volume ratio of 1:1 to obtain a first-injection electrolyte, and the first-injection electrolyte is injected into the battery to be injected (accounting for 50% of the volume percentage of the total required electrolyte). After that, after standing for 4 hours at 60°C, at 60°C, first charge at a constant current of 0.1C for 1 hour, then charge at a constant current of 0.2C for 2 hours, charge at a constant current of 0.5C for 0.6 hours, and finally charge at a constant current of 0.2C for 1 hour for formation. After formation is completed, the remaining second electrolyte is injected (accounting for 50% of the volume percentage of the total required electrolyte), and finally sealed.

[0089] Example 2: Mix thoroughly and inject once according to AB

[0090] This embodiment provides an electrolyte, which includes the following components in percentage by volume:

[0091] First electrolyte: 25%;

[0092] Second electrolyte: 75%;

[0093] The first electrolyte comprises the following components by weight: 16% lithium hexafluorophosphate, 81% first solvent, 1.8% vinylene carbonate, and 1.2% vinyl sulfate, wherein the first solvent is composed of dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate is 3:2:5;

[0094] The second electrolyte includes the following components in percentage by weight: 14% lithium hexafluorophosphate, 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol (C9H5F 15 O)86%.

[0095] The preparation method of the electrolyte provided in this embodiment includes the following steps:

[0096] Weigh each component according to the designed ratio, and in a glove box filled with inert gas (argon, nitrogen) (water content <0.1ppm, oxygen content <0.1ppm), mix dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate in a mass ratio of 3:2:5, then add 1.8% by mass of vinylene carbonate and 1.2% by mass of vinyl sulfate, mix them evenly, and then add lithium hexafluorophosphate (16% by weight of the total weight of the first electrolyte), which is recorded as the first electrolyte;

[0097] Weigh each component according to the designed ratio, and in a glove box filled with inert gas (argon, nitrogen) (water content <0.1ppm, oxygen content <0.1ppm), add the weighed 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol (C9H5F 15 O) and lithium hexafluorophosphate are uniformly mixed to obtain the second electrolyte.

[0098] This embodiment further provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet, the negative electrode sheet and the separator are the same as those in Example 1.

[0099] The preparation method of the lithium ion battery comprises the following steps:

[0100] The positive electrode sheet, separator and negative electrode sheet are assembled according to the designed size and sequence, so that the separator can completely isolate the positive electrode from the negative electrode sheet, and the negative electrode sheet can be completely covered to form a winding core, which is placed in an outer package and baked until the moisture content is qualified. Then, all the first electrolyte and all the second electrolyte are mixed to obtain a mixed electrolyte, and the mixed electrolyte is injected into the battery to be filled. After that, the battery is allowed to stand at 60°C for 4 hours, and then at 60°C, it is first charged at a constant current of 0.1C for 1 hour, then at a constant current of 0.2C for 2 hours, at a constant current of 0.5C for 0.6 hours, and finally at a constant current of 0.2C for 1 hour for formation. After formation, the battery is sealed.

[0101] Example 3: Inject the first electrolyte, the second electrolyte, and the second electrolyte twice in succession

[0102] This embodiment provides an electrolyte, which includes the following components in percentage by volume:

[0103] First electrolyte: 15%;

[0104] Second electrolyte: 85%;

[0105] The first electrolyte comprises the following components by weight: 16% lithium hexafluorophosphate, 81% first solvent, 1.8% fluoroethylene carbonate, and 1.2% cyclohexylbenzene, wherein the first solvent is composed of dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate is 3:3:3;

[0106] The second electrolyte includes the following components in percentage by mass: 10% lithium hexafluorophosphate and 90% tetrafluoroethyl trifluoropropyl ether (HFE347).

[0107] The preparation method of the electrolyte provided in this embodiment includes the following steps:

[0108] Weigh each component according to the designed ratio, and in a glove box filled with inert gas (argon, nitrogen) (water content <0.1ppm, oxygen content <0.1ppm), mix dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate in a mass ratio of 3:3:3, then add 1.8% by mass of fluoroethylene carbonate and 1.2% by mass of cyclohexylbenzene, mix well, and then add lithium hexafluorophosphate (16% by weight of the total weight of the first electrolyte), which is recorded as the first electrolyte;

[0109] The components were weighed according to the designed ratio, and tetrafluoroethyl trifluoropropyl ether (HFE347) and lithium hexafluorophosphate were mixed evenly in a glove box filled with inert gas (argon, nitrogen) (moisture content <0.1 ppm, oxygen content <0.1 ppm) to obtain the second electrolyte.

[0110] This embodiment also provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, and a separator, wherein:

[0111] Positive electrode: Contains aluminum foil and active membrane layer, where the active membrane layer contains lithium iron phosphate, conductive agent (conductive carbon black (Super-P)), and binder (polyvinylidene fluoride (PVDF)), with the weight ratio of each component being 95:3:2 respectively;

[0112] Negative electrode: Contains copper foil and active membrane layer, where the active membrane layer contains artificial graphite, conductive agent (Super-P), binder (CMC and SBR), and the mass ratio of each component is 95:2:1.8:1.2 respectively;

[0113] Separator membrane: A polyethylene porous polymer membrane is used as the separator membrane.

[0114] The preparation method of the lithium ion battery comprises the following steps:

[0115] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are assembled according to the designed size and sequence so that the separator can completely isolate the positive electrode from the negative electrode sheet, and the negative electrode sheet can be completely covered to form a core, which is placed in an outer package and baked until the moisture content is qualified. The first electrolyte and part of the second electrolyte are mixed in a volume ratio of 1:1 to obtain a first-injection electrolyte, and the first-injection electrolyte is injected into the battery to be injected (accounting for 30% of the volume percentage of the total required electrolyte). After that, after standing for 4 hours at 60°C, at 60°C, it is first charged at a constant current of 0.1C for 1 hour, then at a constant current of 0.2C for 2 hours, at a constant current of 0.5C for 0.6 hours, and finally at a constant current of 0.2C for 1 hour for formation. After formation is completed, the remaining second electrolyte is injected (accounting for 70% of the volume percentage of the total required electrolyte), and finally sealed.

[0116] Comparative Example 1

[0117] This comparative example provides an electrolyte, which includes the following components in percentage by mass: 16% lithium hexafluorophosphate, 81% of a first solvent, 1.8% of vinylene carbonate, and 1.2% of vinyl sulfate. The first solvent is composed of dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate is 3:2:5.

[0118] The electrolyte was prepared by referring to the preparation method of the electrolyte provided in Example 1.

[0119] This embodiment further provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet, the negative electrode sheet and the separator are the same as those in Example 1.

[0120] The preparation method of the lithium ion battery comprises the following steps:

[0121] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are assembled according to the designed size and sequence, so that the separator can completely isolate the positive and negative electrode sheets, and at the same time, the negative electrode sheet can be completely covered with the positive electrode to form a core, which is placed in the outer packaging. After baking until the moisture content is qualified, all the electrolyte is injected into the battery to be filled, and then it is allowed to stand at 60°C for 4 hours. At 60°C, it is first charged with a constant current of 0.1C for 1 hour, then charged with a constant current of 0.2C for 2 hours, and charged with a constant current of 0.5C for 0.6 hours. Finally, it is charged with a constant current of 0.2C for 1 hour for formation. After formation, it is sealed.

[0122] Comparative Example 2

[0123] The electrolyte provided in this comparative example is exactly the same as that in Example 1.

[0124] The electrolyte was prepared by referring to the preparation method of the improved electrolyte in Example 1.

[0125] This comparative example also provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet, the negative electrode sheet and the separator are the same as those in Example 1.

[0126] The preparation method of the lithium ion battery comprises the following steps:

[0127] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are assembled according to the designed size and sequence, so that the separator can completely isolate the positive and negative electrode sheets, and at the same time, the negative electrode sheet can be completely covered with the positive electrode to form a core. The core is placed in the outer packaging and baked until the moisture content is qualified. The first electrolyte is injected into the battery to be filled. After that, it is allowed to stand for 4 hours at 60°C, and then at 60°C, it is first charged at a constant current of 0.1C for 1 hour, then at a constant current of 0.2C for 2 hours, and at a constant current of 0.5C for 0.6 hours. Finally, it is charged at a constant current of 0.2C for 1 hour for formation. After the formation is completed, the second electrolyte is injected and finally sealed.

[0128] Performance Testing

[0129] The performance of the lithium-ion batteries provided in the examples and comparative examples was tested, and the specific testing process is as follows:

[0130] Needle penetration test (LFP battery): 1. Incubate at 25°C for 10 minutes; 2. Charge at a constant current of 1C to 3.65V, then charge at a constant voltage of 0.05C until the battery is cut off; 3. Incubate at 25°C for 2 hours; 4. Use a steel needle with a diameter of 8mm and a 45-degree angle to pierce the battery cell vertically from the large surface at a speed of 25mm / s. The needle remains in the cell for 1 hour, and the maximum temperature inside the battery and the battery status are recorded during this process. The results are shown in Table 1.

[0131] High- and Low-Temperature Discharge Performance (LFP Battery) Test: 1. Allow to stand at 25°C for 30 minutes; 2. Charge at a constant current of 1C to 3.65V, then charge at a constant voltage of 0.05C; 3. Allow to stand at 25°C for 30 minutes; 4. Discharge at a constant current of 1C to 2.5V; 5. Repeat steps 1-4 at different temperatures. Record the discharge capacity retention at different temperatures: discharge capacity retention = discharge capacity at target temperature / discharge capacity at 25°C. The results are shown in Table 2. Note: For discharge at -10°C, -20°C, and -30°C, the battery must be allowed to stand at the target temperature for 12 hours; for discharge at 0°C, 45°C, and 55°C, the battery must be allowed to stand at the target temperature for 6 hours. For example, when testing the performance at -30℃, the specific process is: 1. Place at 25℃ for 30 minutes; 2. Charge at 25℃ with a constant current of 1C to 3.65V, and charge at a constant voltage to 0.05C; 3. Place at -30℃ for 12 hours; 4. Discharge at -30℃ with a constant current of 1C to 2.5V.

[0132] Rate discharge performance (LFP battery): 1. Allow to stand at 25°C for 30 minutes; 2. Charge at a constant current of 1C to 3.65V, then charge at a constant voltage to a cutoff of 0.05C; 3. Allow to stand at 25°C for 30 minutes; 4. Discharge at a constant current of 1C to 2.5V; 5. Repeat steps 1-4, varying the discharge current in step 4 to 1 / 3C, 1 / 2C, 2C, and 3C. Record the discharge capacity retention at different currents: discharge capacity retention = discharge capacity at target current / discharge capacity at 1C. The results are shown in Table 3.

[0133] Table 1

[0134]

[0135] From Table 1, we can see at least the following points:

[0136] (1) By comparing Example 1 with Comparative Example 1, it can be seen that the present invention replaces easily vaporized and flammable organic solvents such as dimethyl orthocarbonate DMCDMC and ethyl methyl carbonate EMCEMC with ether / alcohol fluorinated liquid, so that when the electrolyte of the present invention is used in a lithium ion battery, the maximum needle puncture temperature is significantly reduced to only 71.1°C, which is far below the thermal shrinkage temperature of the diaphragm of 125°C, and no white smoke phenomenon occurs, thereby improving the safety performance of the lithium ion battery.

[0137] (2) By comparing Example 1 with Example 2 and Comparative Example 2, it can be seen that the present invention can further reduce the maximum acupuncture temperature and improve the safety performance of lithium-ion batteries by injecting the first electrolyte, the second electrolyte + the second electrolyte twice in sequence.

[0138] Table 2

[0139] Group -30℃ -20℃ -10℃ 0℃ 25℃ 45℃ 55℃ Example 1 92.42％ 95.80％ 97.34％ 98.85％ 100.00％ 100.98％ 101.02％ Example 2 87.22％ 91.41％ 94.68％ 96.84％ 100.00％ 100.16％ 99.37％ Example 3 88.21％ 90.62％ 94.37％ 97.02％ 100.00％ 100.84％ 100.10％ Comparative Example 1 82.65％ 88 37％ 93.47％ 96.58％ 100.00％ 100.53％ 99.76％ Comparative Example 2 91.01％ 93.58％ 95.62％ 97.43％ 100.00％ 100.75％ 100.11％

[0140] Table 2 shows at least the following points:

[0141] (1) By comparing Example 1 with Comparative Example 1, it can be seen that the present invention significantly improves the discharge capacity retention rate at low temperatures when the electrolyte of the present invention is applied to lithium-ion batteries by replacing the organic solvents dimethyl orthocarbonate DMCDMC and ethyl methyl carbonate EMCEMC with ether / alcohol fluorinated liquid.

[0142] (2) By comparing Example 1 with Example 2, it can be seen that the present invention can further improve the discharge capacity retention rate of the lithium-ion battery at low temperature by injecting the first electrolyte, the second electrolyte, and the second electrolyte twice in sequence.

[0143] Table 3

[0144] Group 1 / 3C 1 / 2C 1C 2C 3C Example 1 100.32％ 100.11％ 100.00％ 100.87％ 100.34％ Example 2 100.03％ 100.04％ 100.00％ 99.50％ 98.89％ Example 3 100.20％ 100.01％ 100.00％ 100.28％ 100.01％ Comparative Example 1 101.50％ 100.77％ 100.00％ 96.21％ 90.89％ Comparative Example 2 101.21％ 100.55％ 100.00％ 99.17％ 96.69％

[0145] Table 3 shows at least the following points:

[0146] (1) By comparing Example 1 with Comparative Example 1, it can be seen that the present invention replaces the dimethyl orthocarbonate DMCDMC and ethyl methyl carbonate EMCEMC organic solvents with ether / alcohol fluorinated liquids, so that when the electrolyte of the present invention is used in lithium-ion batteries, the discharge capacity retention rate at high rate is significantly improved.

[0147] (2) By comparing Example 1 with Example 2 and Comparative Example 2, it can be seen that the present invention can further improve the discharge capacity retention rate of the lithium-ion battery at high rate by injecting the first electrolyte, the second electrolyte + the second electrolyte twice in sequence.

[0148] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises the following components in volume percentage: The first electrolyte is 15%~30%; The second electrolyte is 70%~85%; The first electrolyte comprises a first lithium salt, a first solvent, and an additive; the second electrolyte comprises a second lithium salt and a second solvent; the second solvent is an alcohol fluoride liquid, and the alcohol fluoride liquid is 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol; and the second electrolyte comprises the following components in percentage by weight: 14% of the second lithium salt and 86% of the second solvent; The first solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

2. The electrolyte according to claim 1, characterized in that The first electrolyte includes the following components in percentage by weight: 15% to 18% of the first lithium salt, 72% to 84% of the first solvent, and 1% to 10% of the additive.

3. The electrolyte according to claim 1, characterized in that The first lithium salt includes at least one of lithium hexafluorophosphate and lithium fluoride; and / or, the first solvent comprises dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate is (2-5):(2-5):(2-5); and / or, the additive comprises at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, vinyl sulfate, biphenyl, cyclohexylbenzene, and tert-amylbenzene; And / or, the additive includes vinylene carbonate and vinyl sulfate, and the mass ratio of the vinylene carbonate to the vinyl sulfate is (0.5-2):

1.

4. The electrolyte according to claim 1, characterized in that The second lithium salt includes at least one of lithium hexafluorophosphate and lithium fluoride.

5. A method for preparing an electrolyte according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: Weighing each component according to the designed ratio, and evenly mixing the weighed first solvent and the additive to obtain a first primary electrolyte; adding the first lithium salt to the first primary electrolyte, and mixing evenly to obtain the first electrolyte; The components are weighed according to the designed ratio, and the weighed second solvent and the second lithium salt are evenly mixed to obtain the second electrolyte.

6. A method for injecting an electrolyte according to any one of claims 1 to 4, characterized in that: The injection method includes one injection or two injections; Wherein, the one-time injection comprises the following steps: Mixing the first electrolyte and the second electrolyte to obtain a mixed electrolyte, injecting the mixed electrolyte into the battery to be filled, performing formation after sufficient infiltration, and sealing after the formation is completed; The two injections comprise the following steps: All of the first electrolyte and part of the second electrolyte are mixed to obtain a first electrolyte, which is injected into the battery to be injected, and is formed after being fully infiltrated. After the formation is completed, the remaining second electrolyte is injected and the battery is packaged.

7. The electrolyte injection method according to claim 6, characterized in that: The volume percentage of the first-injected electrolyte to the electrolyte is 30% to 65%.

8. The electrolyte injection method according to claim 6, characterized in that: The sufficient infiltration includes standing at 20-60°C for 2-8 hours; And / or, the formation includes charging at 55°C to 65°C with a constant current of 0.05C to 0.15C for 2h to 0.6h, then charging at a constant current of 0.15C to 0.3C for 2.6h to 1.3h, charging at a constant current of 0.3C to 0.5C for 1h to 0.6h, and finally charging at a constant current of 0.1C to 0.25C for 2h to 0.8h.

9. A lithium-ion battery, characterized in that: The lithium-ion battery comprises the electrolyte according to any one of claims 1 to 4, or is prepared by the injection method according to any one of claims 6 to 8.

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