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

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to an electrolyte, a preparation method of the electrolyte, a liquid injection method of the electrolyte and a lithium ion battery. 70%-85% of a second electrolyte; wherein 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, and the second solvent comprises at least one of an ether fluorinated solution and an alcohol fluorinated solution. Easily gasified and flammable organic solvents such as DMC (dimethyl orthocarbonate) and EMC (ethyl methyl carbonate) are replaced with the ether / alcohol fluorinated solution, so that the lithium ion battery has high safety performance when the electrolyte is applied to the lithium ion battery.

Description

Technical Field

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

[0002] At present, the safety of lithium-ion batteries has become the most important focus of application. The lithium-ion batteries currently produced and used mainly use liquid electrolytes, which mainly contain lithium hexafluorophosphate and organic solvents such as diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. When the internal temperature of the lithium-ion battery is too high, thermal runaway is prone to occur. DEC, DMC, EMC, etc., which are organic solvents, become combustibles and easily form combustible gases at high temperatures, causing explosions and other phenomena.

[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 object of the present invention is to provide an electrolyte and a preparation method thereof, a liquid injection method and a lithium ion battery. The present invention replaces easily gasified 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 applied to 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, wherein the electrolyte comprises the following components in volume percentage:

[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 uses ether / alcohol fluorinated liquid to replace easily gasified and flammable organic solvents such as dimethyl orthocarbonate DMC and ethyl methyl carbonate EMC, 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 includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl vinyl 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 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol, perfluorooctylethanol, 1H,1H,2H,2H-perfluorooctanol, 1H,1H,8H-perfluoro-1-octanol, tetrafluoroisopropanol, (CF 3 ) 2 At least one of CHOH.

[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] Weigh each component according to the designed ratio, and mix the weighed first solvent and the additive evenly to obtain a first primary electrolyte; add the first lithium salt to the first primary electrolyte, and mix 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 as described in the second aspect, wherein the method comprises injecting once or injecting twice;

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

[0026] The first electrolyte and the second electrolyte are mixed to obtain a mixed electrolyte, the mixed electrolyte is injected into the battery to be filled, and chemical formation is performed after sufficient infiltration, and sealing is completed after the chemical formation is completed;

[0027] The two-step injection comprises the following steps:

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

[0029] Furthermore, the volume percentage of the first-injected electrolyte to the 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 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.

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

[0033] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0034] (1) The present invention replaces easily gasifiable 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.

[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 sheet, negative electrode sheet, and separator, and have a drainage function.

[0036] (3) Fluorinated liquid has the ability to withstand high voltage. 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 scheme and advantages of the present invention clearer, the technical scheme in the embodiment 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 only 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 ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0038] The endpoints and any values ​​of the ranges disclosed in the present invention 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 endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

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

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

[0041] The second electrolyte is 70% to 85% (for example, it can be 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 uses ether / alcohol fluorinated liquid to replace easily gasified and flammable organic solvents such as dimethyl orthocarbonate DMC and ethyl methyl carbonate EMC, 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 causing battery safety is high temperature:

[0045] 1. Under high temperature environment, 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 fluoride liquid, which will not have side reactions with the positive and negative electrode materials;

[0046] 2. In a high temperature environment, DMC, EMC, etc. in a traditional electrolyte are very easy to vaporize. The vaporized DMC, EMC, etc. quickly increase the internal pressure of the battery. After the explosion-proof valve of the battery is opened, it contacts the air, and the high-temperature and high-pressure electrolyte gas is very easy to be 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 it is sprayed out of the battery after vaporization, it will not burn. Therefore, the sprayed fluorinated liquid quickly forms a mist after cooling down and deposits around the battery to squeeze out 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. When the liquid fluoride liquid is immersed in the high-temperature position, the temperature can be lowered and it will not be ignited.

[0048] In the present invention, the first electrolyte and the second electrolyte are used in combination, the first electrolyte is based on ensuring the integrity of the positive and negative electrode structures in the battery, and the second electrolyte improves the safety performance of the battery by reducing the content of flammable organic solvents and reducing side reactions in the battery. If the volume percentage of the first electrolyte is too high, the safety of the battery is poor, and if the volume percentage of the first electrolyte is too low, the integrity of the positive and negative electrode structures in the battery cannot be ensured, resulting in poor electrochemical performance of the battery.

[0049] In the above-mentioned electrolyte, as an optional embodiment, 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 (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 implementation, the first lithium salt includes at least one of lithium hexafluorophosphate and lithium fluoride.

[0051] In the above-mentioned 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 vinyl 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 above electrolyte, as an optional embodiment, 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. Because the fluoride solution limits the growth of the SEI film and reduces the loss of lithium ions, the amount of the second lithium salt in the second electrolyte is relatively low.

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

[0057] In the above-mentioned 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 (C 9 H 5 F 15 O), perfluorooctylethanol, 1H,1H,2H,2H-perfluorooctanol, 1H,1H,8H-perfluoro-1-octanol, tetrafluoroisopropanol, (CF 3 ) 2 CHOH).

[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] Weigh each component according to the designed ratio, and mix the weighed first solvent and the additive evenly to obtain a first primary electrolyte; add the first lithium salt to the first primary electrolyte, and mix 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 as described in the first aspect, wherein the method comprises injecting once or injecting twice;

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

[0064] The first electrolyte and the second electrolyte are mixed to obtain a mixed electrolyte, the mixed electrolyte is injected into the battery to be filled, and chemical formation is performed after sufficient infiltration, and sealing is completed after the chemical formation is completed;

[0065] The two-step injection comprises the following steps:

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

[0067] The embodiment of the present invention injects the electrolyte twice, so that the high and low temperature performance and rate performance of the lithium-ion battery can be made better.

[0068] In the process of injecting electrolyte twice, 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 generate 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, it has better fluidity, surface tension and can be miscible with the first electrolyte, so the second electrolyte will replace or dilute the first electrolyte infiltrated in the gap between the positive and negative electrode materials. The solvent in the second electrolyte is chemically stable, does not participate in the formation of SEI film and CEI film, and will not contact with the positive and negative electrode materials to produce side reactions. Therefore, the SEI film and 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 implementation mode, the volume percentage of the first-injected electrolyte to 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 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.

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

[0073] The present invention will be further described in detail below with reference to specific embodiments 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 volume percentage:

[0076] First electrolyte: 25%;

[0077] Second electrolyte: 75%;

[0078] Wherein, the first electrolyte comprises the following components in percentage 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, vinyl carbonate, and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, vinyl 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 (C 9 H 5 F 15 O)86%.

[0080] The preparation method of the electrolyte provided in this embodiment comprises 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 fraction of vinylene carbonate and 1.2% by mass fraction of vinyl sulfate, mix them evenly, and then add 16% by mass of lithium hexafluorophosphate 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), weigh 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol (C 9 H 5 F 15 O) and lithium hexafluorophosphate are evenly 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 sheet: contains aluminum foil and active membrane layer, wherein the active membrane layer contains lithium iron phosphate, conductive agent (conductive carbon black (Super-P)), binder (polyvinylidene fluoride (PVDF)), and the mass ratio of each component is 95:3:2 respectively;

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

[0086] Separation membrane: A polyethylene porous polymer membrane is used as the separation membrane.

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

[0088] The positive electrode sheet, the separator, and the negative electrode sheet are assembled according to the designed size and order, 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 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 total required electrolyte volume percentage), and then left to stand for 4 hours at 60°C, and then at 60°C, first charged at a constant current of 0.1C for 1 hour, then charged at a constant current of 0.2C for 2 hours, and charged at a constant current of 0.5C for 0.6 hours, and finally charged at a constant current of 0.2C for 1 hour for formation. After the formation is completed, the remaining second electrolyte is injected (accounting for 50% of the total required electrolyte volume percentage), 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 volume percentage:

[0091] First electrolyte: 25%;

[0092] Second electrolyte: 75%;

[0093] Wherein, the first electrolyte comprises the following components in percentage 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, vinyl carbonate, and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, vinyl 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 (C 9 H 5 F 15 O)86%.

[0095] The preparation method of the electrolyte provided in this embodiment comprises 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 fraction of vinylene carbonate and 1.2% by mass fraction of vinyl sulfate, mix them evenly, and then add 16% by mass of lithium hexafluorophosphate 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), weigh 1H,1H,2H,2H-perfluoro-7-methyloctan-1-ol (C 9 H 5 F 15 O) and lithium hexafluorophosphate are evenly mixed to obtain the second electrolyte.

[0098] This embodiment 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 Embodiment 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 separate 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, and 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, and then allowed to stand for 4 hours at 60°C, and then charged at a constant current of 0.1C for 1 hour at 60°C, and then charged at a constant current of 0.2C for 2 hours, and then charged at a constant current of 0.5C for 0.6 hours, and finally charged at a constant current of 0.2C for 1 hour for formation, and sealed after the formation is completed.

[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 volume percentage:

[0103] First electrolyte: 15%;

[0104] Second electrolyte: 85%;

[0105] Wherein, the first electrolyte comprises the following components in percentage 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 comprises 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 fraction of fluoroethylene carbonate and 1.2% by mass fraction of cyclohexylbenzene, mix them evenly, and then add 16% by mass of lithium hexafluorophosphate of the total weight of the first electrolyte, which is recorded as the first electrolyte;

[0109] Weigh each component according to the designed ratio, and mix the weighed tetrafluoroethyl trifluoropropyl ether (HFE347) and lithium hexafluorophosphate evenly in a glove box filled with inert gas (argon, nitrogen) (water content <0.1ppm, oxygen content <0.1ppm) 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 sheet: contains aluminum foil and active membrane layer, wherein the active membrane layer contains lithium iron phosphate, conductive agent (conductive carbon black (Super-P)), binder (polyvinylidene fluoride (PVDF)), and the mass ratio of each component is 95:3:2 respectively;

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

[0113] Separation membrane: A polyethylene porous polymer membrane is used as the separation membrane.

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

[0115] The positive electrode sheet, the separator, and the 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. 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 total required electrolyte by volume), and then allowed to stand for 4 hours at 60°C, and then at 60°C, first charged at a constant current of 0.1C for 1 hour, then charged at a constant current of 0.2C for 2 hours, and charged at a constant current of 0.5C for 0.6 hours, and finally charged at a constant current of 0.2C for 1 hour for formation. After the formation is completed, the remaining second electrolyte is injected (accounting for 70% of the total required electrolyte by volume), 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% first solvent, 1.8% vinylene carbonate, and 1.2% vinyl sulfate, wherein the first solvent is composed of dimethyl carbonate, vinyl carbonate, and ethyl methyl carbonate, and the mass ratio of dimethyl carbonate, vinyl carbonate, and ethyl methyl carbonate is 3:2:5.

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

[0119] This embodiment 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 Embodiment 1.

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

[0121] The positive electrode sheet, separator and negative electrode sheet are assembled according to the designed size and sequence, so that the separator can completely separate 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 electrolyte is injected into the battery to be filled, and then it 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, and sealed after formation.

[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 positive electrode sheet, separator and negative electrode sheet are assembled according to the designed size and sequence, so that the separator can completely separate 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. The first electrolyte is injected into the battery to be filled, and then 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, 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 the formation is completed, the second electrolyte is injected, and finally the sealing is completed.

[0128] Performance Testing

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

[0130] Puncture test (LFP battery): 1. Place at 25℃ for 10min; 2. Charge at 1C constant current to 3.65V, and charge at constant voltage to 0.05C; 3. Place at 25℃ for 2h; 4. Use a steel needle with a diameter of 8mm and a needle tip of 45° to pierce the battery cell vertically from the large surface at a speed of 25mm / s. The steel needle stays in the battery cell and is observed for 1h. The maximum temperature inside the battery and the battery status during the process are recorded. The results are shown in Table 1.

[0131] High and low temperature discharge performance (LFP battery) test: 1. Place at 25℃ for 30min; 2. Charge at 1C constant current to 3.65V, and charge at constant voltage to 0.05C cut-off; 3. Place at 25℃ for 30min; 4. Discharge at 1C constant current to 2.5V; 5. Repeat steps 1 to 4 at different temperatures. Record the discharge capacity retention rate at different temperatures, discharge capacity retention rate = discharge capacity at target temperature / discharge capacity at 25℃, the results are shown in Table 2. Note: Before discharging at -10℃, -20℃, and -30℃, place at the target temperature for 12h, and before discharging at 0℃, 45℃, and 55℃, place at the target temperature for 6h. 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 cutoff; 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. Place at 25℃ for 30min; 2. Charge at 1C constant current to 3.65V, and charge at constant voltage to 0.05C cut-off; 3. Place at 25℃ for 30min; 4. Discharge at 1C constant current to 2.5V; 5. Repeat steps 1 to 4 above, and change the discharge current in step 4 to 1 / 3C, 1 / 2C, 2C, and 3C. Record the discharge capacity retention rate at different currents, discharge capacity retention rate = discharge capacity at target current / discharge capacity at 1C, and 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 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, and 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] From Table 2, we can at least see the following points:

[0141] (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 low temperatures is significantly improved.

[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] From Table 3, we can at least see 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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 includes the following components in volume percentage: The first electrolyte is 15% to 30%; The second electrolyte is 70% to 85%; 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.

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 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; 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 includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl vinyl 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 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.

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

6. A method for preparing an electrolyte according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: Weigh each component according to the designed ratio, and mix the weighed first solvent and the additive evenly to obtain a first primary electrolyte; add the first lithium salt to the first primary electrolyte, and mix 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.

7. A method for injecting an electrolyte according to any one of claims 1 to 5, characterized in that: The injection method includes one-time injection or two-time injection; Wherein, the one-time injection comprises the following steps: The first electrolyte and the second electrolyte are mixed to obtain a mixed electrolyte, the mixed electrolyte is injected into the battery to be filled, and chemical formation is performed after sufficient infiltration, and sealing is completed after the chemical formation is completed; The two-step injection comprises the following steps: All of the first electrolyte and part of the second electrolyte are mixed to obtain a first electrolyte, and the first electrolyte is injected into the battery to be injected, and is formed after sufficient infiltration. After the formation is completed, the remaining second electrolyte is injected and packaged.

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

9. The electrolyte injection method according to claim 7, characterized in that: The sufficient infiltration includes standing at 20 to 60° C. for 2 to 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.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte described in any one of claims 1 to 5, or is prepared by the injection method described in any one of claims 7 to 9.

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