Electrolyte, lithium ion battery and preparation method of electrolyte

Abstract

The invention provides an electrolyte, a lithium ion battery and a preparation method of the electrolyte, and relates to the technical field of batteries. The electrolyte is applied to the lithium ion battery and comprises a lithium salt, a carbonic ester solvent, a film-forming additive and an overcharge safener. Wherein the film-forming additive comprises unsaturated double bonds. The overcharge safener comprises an O-O bond. According to the electrolyte provided by the embodiment of the invention, when the lithium ion battery is in an overcharge state, an O-O bond is thermally decomposed to generate a free radical, and the free radical and an unsaturated double bond are subjected to an addition reaction to generate a polymer, so that the possibility of fire catching caused by thermal runaway due to overcharge in the charging process of the lithium battery can be reduced; and the use safety of the lithium ion battery is ensured.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrolyte, a lithium-ion battery, and a method for preparing the electrolyte. Background Art

[0002] A battery is a device that can convert chemical energy into electrical energy. It can provide electrical energy to many electrical devices, keeping them in working order. Batteries can work with different electrical devices and other structures to form different power systems.

[0003] Take lithium-ion batteries as an example. They are widely used in consumer electronics, new energy electric vehicles, energy storage, smart grids, aviation and other fields. With the continuous development of materials and continuous improvement of process technology by scientific researchers, the energy density of lithium-ion batteries continues to increase, which can meet people's demand for long battery life. This brings about the safety issues of lithium-ion batteries. In the process of using lithium-ion batteries, thermal runaway of lithium-ion batteries often occurs due to improper use.

[0004] Therefore, there is an urgent need for a lithium-ion battery with higher safety in the market. Summary of the invention

[0005] The present application provides an electrolyte, a lithium-ion battery, and a method for preparing the electrolyte, which can reduce the possibility of thermal runaway and subsequent fire due to overcharging during the charging process of the lithium battery, thereby ensuring the safety of the lithium-ion battery.

[0006] In a first aspect, the present application provides an electrolyte, the electrolyte is applied to a lithium ion battery, the electrolyte comprises a lithium salt, a carbonate solvent, a film-forming additive and an overcharge safety agent, wherein the film-forming additive comprises an unsaturated double bond, and the overcharge safety agent comprises an OO bond.

[0007] In the example of this application, the film-forming additive may contain an unsaturated double bond, and the overcharge safety agent may contain an OO bond. When the lithium-ion battery is in an overcharged state, the OO bond can be decomposed into multiple free radicals by heat, and the multiple free radicals can react with the unsaturated double bonds to form polymers. Compared with the case where there is no polymer in the electrolyte, lithium ions can move directly from the positive electrode to the negative electrode. When a polymer is generated in a lithium-ion battery, the lithium ions need to pass through the polymer to move from the positive electrode to the negative electrode, which prolongs the path for lithium ions to move from the positive electrode to the negative electrode, reduces the charging efficiency of the lithium-ion battery in the case of overcharge, and reduces the possibility of thermal runaway of the lithium-ion battery.

[0008] The polymer attached to the surface of the positive electrode can reduce the probability of lithium ions moving from the positive electrode to the negative electrode, thereby reducing the charging efficiency of the lithium-ion battery in the overcharge state, reducing the possibility of thermal runaway of the lithium-ion battery, and ensuring the safety of lithium-ion batteries.

[0009] In addition, lithium metal will be deposited on the negative electrode surface due to overcharging of lithium-ion batteries. When the lithium-ion battery is in an overcharged state, the overcharge safety agent and the film-forming additive can cooperate to undergo an addition reaction to form a polymer, which can cover the positive electrode surface and the negative electrode surface, and can reduce the possibility of reduction reaction between the electrolyte and the lithium metal on the negative electrode surface, thereby reducing the heat generated during the reduction reaction.

[0010] Compared with the prior art, by using new phase change materials and efficient heat dissipation structural design, the example of the present application does not use new phase change materials and efficient heat dissipation structural design. The polymer formed by the addition reaction of the film-forming additive and the overcharge safety agent in the overcharge state can reduce the heat generated by the lithium-ion battery in the overcharge state, reducing the heat generated by the lithium-ion battery in the overcharge state, making the structure of the lithium-ion battery simpler and the manufacturing cost lower.

[0011] In some possible implementations, the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, and alkyl nitrile compounds.

[0012] In some possible implementations, the mass ratio of the film-forming additive in the electrolyte is in the range of 1% to 5%.

[0013] In the example of this application, by controlling the mass ratio of the film-forming additive in the electrolyte, the manufacturing cost of the electrolyte can be controlled and the possibility of wasting the film-forming additive can be reduced. And by controlling the mass ratio of the film-forming additive in the electrolyte, a certain concentration of unsaturated double bonds can be provided in the electrolyte, and the unsaturated double bonds can react with the OO bonds in the overcharge safety agent to reduce the possibility of thermal runaway of the lithium-ion battery in the overcharge state.

[0014] In some possible implementations, the overcharge safety agent includes at least one of dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide.

[0015] In some possible implementations, the mass ratio of the overcharge safety agent in the electrolyte ranges from 0.2% to 5%.

[0016] In the example of this application, by controlling the mass ratio of the overcharge safety agent in the electrolyte, the manufacturing cost of the electrolyte can be controlled and the possibility of overcharge safety agent waste can be reduced. And by controlling the mass ratio of the overcharge safety agent in the electrolyte, a certain concentration of OO bonds can be provided in the electrolyte, and the OO bonds can react with the unsaturated double bonds in the film-forming additive to reduce the possibility of thermal runaway of the lithium-ion battery in the overcharge state.

[0017] In some possible implementations, the sum of the mass ratios of the film-forming additive and the overcharge safety agent in the electrolyte is in a range of 2% to 10%.

[0018] In the example of this application, the mass ratio of the film-forming additive to the overcharge safety agent in the electrolyte can be adjusted according to the range of the sum of the mass ratios of the film-forming additive and the overcharge safety agent in the electrolyte being 2% to 10%, to ensure that the film-forming additive and the overcharge safety agent can react to form a polymer, and the possibility of thermal runaway of the lithium-ion battery in an overcharge state is reduced by the polymer, thereby reducing the manufacturing cost of the electrolyte.

[0019] In some possible implementations, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorooxalatoborate.

[0020] In some possible implementations, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0021] In a second aspect, the present application provides a lithium-ion battery, wherein the lithium-ion battery includes the electrolyte provided in the first aspect and any possible implementation of the first aspect.

[0022] The beneficial effects of the electrolyte provided in the above-mentioned second aspect and each possible design of the above-mentioned second aspect can be referred to the beneficial effects brought about by the above-mentioned first aspect and each possible implementation method of the first aspect, and will not be repeated here.

[0023] In a third aspect, the present application provides a method for preparing an electrolyte, the electrolyte being suitable for lithium-ion batteries, the method comprising the following steps: adding a lithium salt to a carbonate solvent and stirring the solution thoroughly to form a solution; adding a film-forming additive and an overcharge safety agent to the solution and dissolving the solution thoroughly to form an electrolyte.

[0024] The film-forming additive contains an unsaturated double bond, and the overcharge safety agent contains an OO bond. When the lithium-ion battery is in an overcharged state, the OO bond decomposes under heat to generate free radicals, and the free radicals react with the unsaturated double bond to generate a polymer.

[0025] The beneficial effects of the electrolyte provided in the third aspect and each possible design of the third aspect can be referred to the beneficial effects brought about by the first aspect and each possible implementation method of the first aspect, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a process for preparing an electrolyte provided as an example in this application. DETAILED DESCRIPTION

[0027] In order to make the application purpose, technical scheme and beneficial technical effects of the present application clearer, the present application is further described in detail below in combination with examples and comparative examples. It should be understood that the embodiments described in this specification are only for explaining the present application, not for limiting the present application, and the formulas, proportions, etc. of the embodiments can be selected according to local conditions without substantial impact on the results.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification, claims and drawings of this application are intended to cover non-exclusive inclusions.

[0029] In the description of the present application, unless otherwise specified, "plurality" means more than two (including two), and similarly, "multiple groups" means more than two groups (including two).

[0030] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase "embodiments" in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0031] For simplicity, only some numerical ranges are clearly disclosed herein. However, any lower limit can be combined with any upper limit to form a range that is not clearly recorded. And any lower limit can be combined with other lower limits to form a range that is not clearly recorded, and similarly, any upper limit can be combined with any other upper limit to form a range that is not clearly recorded. In addition, although not clearly recorded, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value or with other lower limits or upper limits as its own lower limit or upper limit to form a range that is not clearly recorded.

[0032] The foregoing of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of embodiments, which can be used in various combinations. In each example and, enumeration is only as a representative group and should not be interpreted as exhaustive.

[0033] A battery is a device that can convert chemical energy into electrical energy. It can provide electrical energy to many electrical devices, keeping them in working order. Batteries can work with different electrical devices and other structures to form different power systems.

[0034] Take lithium-ion batteries as an example. They are widely used in consumer electronics, new energy electric vehicles, energy storage, smart grids, aviation and other fields. With the continuous development of materials and continuous improvement of process technology by scientific researchers, the energy density of lithium-ion batteries continues to increase, which can meet people's demand for long battery life. This brings about the safety issues of lithium-ion batteries. In the process of using lithium-ion batteries, thermal runaway of lithium-ion batteries often occurs due to improper use.

[0035] In some related technologies, by using new phase change materials and efficient heat dissipation structure design in the design and manufacturing process of lithium-ion batteries, lithium-ion batteries can quickly absorb and dissipate heat when they are overcharged, reducing the possibility of thermal runaway of lithium-ion batteries. However, the lithium-ion battery structure provided by this method is relatively complex and the manufacturing cost is relatively high.

[0036] Based on the above, the present application provides an electrolyte, a lithium-ion battery, and a method for preparing the electrolyte.

[0037] In order to enable those skilled in the art to better understand the present application, the electrolyte, lithium-ion battery and method for preparing the electrolyte provided by the example of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0038] Exemplarily, the present application provides a lithium-ion battery.

[0039] The lithium-ion battery can be in a discharging state or in a charging state. Please refer to the following description for the specific structure of the lithium-ion battery.

[0040] The lithium-ion battery includes an electrolyte. The lithium-ion battery may also include a positive electrode, a negative electrode and a separator. The specific composition of the electrolyte can be found in the following description, and the present application example will not be described in detail here.

[0041] The positive electrode can be made of lithium cobalt oxide (LiCoO 2 ), lithium manganese oxide (LiMn 2 O4 ), lithium iron phosphate (LiFePO 4 ), ternary materials, such as nickel cobalt lithium manganese oxide and other materials.

[0042] The negative electrode can be made of graphite, central phase carbon microspheres, lithium titanate (Li 4 Ti 5 O 12 ) and other materials.

[0043] The separator is a specially formed polymer film disposed between the positive electrode and the negative electrode, and has a microporous structure through which lithium ions can pass. The separator can be made of at least one of materials such as polyethylene (PE) and polypropylene (PP).

[0044] During the charging process of lithium-ion batteries, lithium ions are deintercalated from the positive electrode, flow through the electrolyte through the diaphragm to the negative electrode and are embedded in the negative electrode, and the electrons in the positive electrode flow to the negative electrode through the external circuit. During the discharge process, lithium ions are deintercalated from the negative electrode, flow through the electrolyte through the diaphragm to the positive electrode and are embedded in the positive electrode. As the lithium ions are deintercalated, the potential of the negative electrode gradually increases, and the potential of the positive electrode continues to decrease, causing the battery voltage to continue to decrease. The electrons in the negative electrode also flow to the positive electrode through the external circuit until the discharge cut-off voltage is reached.

[0045] During the discharge process of a lithium-ion battery, the lithium ions in the positive electrode are reduced and electrons are released. In the negative electrode, the lithium metal or lithium alloy previously inserted into the negative electrode structure is oxidized and lithium ions are released.

[0046] Next, the electrolyte mentioned in the above lithium-ion battery is described in detail.

[0047] The present application provides an electrolyte for lithium-ion batteries. The electrolyte may include lithium salt, carbonate solvent, film-forming additive and overcharge safety agent. The film-forming additive contains unsaturated double bonds. The overcharge safety agent contains OO bonds.

[0048] When a lithium-ion battery is in an overcharged state, the OO bond decomposes due to heat to generate free radicals, which react with unsaturated double bonds to generate polymers.

[0049] The unsaturated double bonds mentioned in the present application mainly exist in olefin monomers containing unsaturated double bonds.

[0050] Lithium salts can provide lithium ions during the working process of lithium-ion batteries, and realize the movement of lithium ions between the positive and negative electrodes during the charging and discharging processes of lithium-ion batteries, thereby realizing the conversion between electrical energy and chemical energy.

[0051] Lithium salts can also maintain the charge balance inside lithium-ion batteries. During the charging process, lithium ions can be deintercalated from the positive electrode and flow to the negative electrode through the electrolyte, while electrons flow from the external circuit to the negative electrode, maintaining the electrical neutrality of the entire lithium-ion battery system. During the discharge process, lithium ions are deintercalated from the negative electrode and flow to the positive electrode through the electrolyte, also maintaining electrical neutrality.

[0052] Carbonate solvents can provide solvents for lithium salts and dissolve lithium salts. Carbonate solvents can form a tightly ordered lithium ion solvation configuration with lithium ions through solvation, thereby improving the stability of the electrolyte.

[0053] The film-forming additive may contain unsaturated double bonds, and the overcharge safety agent may contain OO bonds. When the lithium-ion battery is in an overcharged state, the temperature inside the lithium-ion battery will change. Exemplarily, the temperature inside the lithium-ion battery can reach 80 to 120°C. The OO bond can be decomposed into at least one free radical when heated, and the free radical can react with the unsaturated double bond to form a polymer. Based on the different implementation methods of the overcharge safety agent and the film-forming additive, the free radical corresponding to the overcharge safety agent and the unsaturated double bond corresponding to the film-forming additive will change accordingly, and the generated polymer will also change accordingly. The following description will exemplify the generated polymer based on different overcharge safety agents and film-forming additives.

[0054] The polymer may be present on at least one of the surface of the negative electrode, the surface of the positive electrode, and the electrolyte.

[0055] In the example of this application, the lithium salt can realize the movement of lithium ions between the positive electrode and the negative electrode during the charging and discharging process of the lithium-ion battery, and maintain the charge balance inside the lithium-ion battery. In addition, the lithium salt can react with carbonate solvents and film-forming additives to protect the positive electrode material and the negative electrode material, thereby improving the cycle life and safety of the lithium-ion battery.

[0056] The film-forming additive may contain an unsaturated double bond, and the overcharge safety agent may contain an OO bond. When the lithium-ion battery is in an overcharged state, the OO bond can be decomposed into at least one free radical by heat, and the free radical can react with the unsaturated double bond to form a polymer. Compared with the case where there is no polymer in the electrolyte, lithium ions can move directly from the positive electrode to the negative electrode. When a polymer is generated in a lithium-ion battery, the lithium ions need to pass through the polymer to move from the positive electrode to the negative electrode, which extends the path for lithium ions to move from the positive electrode to the negative electrode, reduces the charging efficiency of the lithium-ion battery in the case of overcharge, and reduces the possibility of thermal runaway of the lithium-ion battery, thereby ensuring the safety of lithium-ion batteries.

[0057] The polymer attached to the surface of the positive electrode can reduce the probability of lithium ions moving between the positive electrode and the negative electrode, thereby reducing the charging efficiency of the lithium-ion battery under overcharge conditions and reducing the possibility of thermal runaway of the lithium-ion battery.

[0058] In addition, lithium metal will be deposited on the surface of the negative electrode due to overcharging of the lithium-ion battery. When the lithium-ion battery is in an overcharged state, the polymer can cover the surface of the negative electrode, reducing the possibility of reduction reaction between the electrolyte and the lithium metal on the surface of the negative electrode, and reducing the heat generated during the reduction reaction. And the polymer covering the surface of the negative electrode can also reduce the probability of lithium ions moving between the positive and negative electrodes, thereby reducing the charging efficiency of the lithium-ion battery in the overcharge state and reducing the possibility of thermal runaway of the lithium-ion battery.

[0059] Compared with the prior art, by using new phase change materials and efficient heat dissipation structural design, the example of the present application does not use new phase change materials and efficient heat dissipation structural design. The polymer formed by the addition reaction of the film-forming additive and the overcharge safety agent in the overcharge state can reduce the heat generated by the lithium-ion battery in the overcharge state, thereby reducing the heat generated by the lithium-ion battery in the overcharge state, making the structure of the lithium-ion battery simpler and the manufacturing cost lower.

[0060] Based on the electrolyte provided in the above example, the film-forming additive may include at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate and alkyl nitrile compounds.

[0061] The alkyl nitrile compounds may include, but are not limited to, acetonitrile, propionitrile, benzyl cyanide, adiponitrile, acrylonitrile, n-octanonitrile and cyclohexanecarbonitrile, and the present application does not impose any specific limitation on this.

[0062] The film-forming additive may also be other compounds containing unsaturated double bonds, as long as it is ensured that when the lithium-ion battery is in an overcharged state, the film-forming additive can undergo an addition reaction with the overcharge protection agent to generate a polymer.

[0063] Based on the electrolyte provided in the above example, the mass ratio of the film-forming additive in the electrolyte ranges from 1% to 5%.

[0064] For example, the mass ratio of the film-forming additive in the electrolyte may be 1%, 3%, or 5%. Of course, the mass ratio of the film-forming additive in the electrolyte may also be any other value between 1% and 5%.

[0065] Here, the mass ratio of the film-forming additive in the electrolyte refers to the mass percentage of all the film-forming additives in the electrolyte provided in the examples of the present application.

[0066] In the example of this application, by controlling the mass ratio of the film-forming additive in the electrolyte, the manufacturing cost of the electrolyte can be controlled and the possibility of wasting the film-forming additive can be reduced. And by controlling the mass ratio of the film-forming additive in the electrolyte, a certain concentration of unsaturated double bonds can be provided in the electrolyte, and the unsaturated double bonds can react with the OO bonds in the overcharge safety agent to reduce the possibility of thermal runaway of the lithium-ion battery in the overcharge state.

[0067] In addition, the example of the present application controls the mass ratio of the film-forming additive in the electrolyte to be in the range of 1% to 5%, thereby reducing the possibility of rapid material loss due to the reduction reaction between the electrolyte and other materials caused by the mass ratio of the film-forming additive in the electrolyte being lower than 1%.

[0068] On this basis, the possibility of the internal resistance of the lithium-ion battery being high due to the mass ratio of the film-forming additive in the electrolyte being higher than 5% and thus affecting the performance of the lithium-ion battery can also be reduced.

[0069] Based on the electrolyte provided in the above example, the overcharge safety agent may include at least one of dicumyl peroxide, benzoyl peroxide and di-tert-butyl peroxide.

[0070] The overcharge safety agent may also be other compounds, as long as it contains an OO bond and can react with the film-forming additive to form a polymer when the lithium-ion battery is in an overcharged state.

[0071] Depending on the overcharge safety agent, the temperature at which the OO bond in the overcharge safety agent decomposes under heat is different, and the corresponding addition reaction and product are also different. In this application example, the operator can select different overcharge safety agents and film-forming additives according to the use scenario of the lithium-ion battery and customer needs.

[0072] For example, at a temperature greater than or equal to 120° C., the OO bond in dicumyl peroxide will decompose into two cumene oxide free radicals, which will react with the double bond in vinyl carbonate to form a free radical addition reaction. The added free radicals will continue to react with other vinyl carbonate molecules to form a polymer chain. As the reaction proceeds, coupling reactions or disproportionation reactions may occur between the free radicals, terminating the polymerization reaction and forming high molecular weight polyvinylene carbonate.

[0073] The polyvinylene carbonate may be present on at least one of the positive electrode surface and the negative electrode surface electrolyte.

[0074] Polyvinyl carbonate attached to the surface of the positive electrode can reduce the rate at which lithium ions move from the positive electrode to the negative electrode, thereby reducing the charging efficiency of the lithium-ion battery in an overcharged state. Polyvinyl carbonate attached to the surface of the negative electrode reduces the possibility of reduction reaction between the electrolyte and the lithium metal deposited on the surface of the negative electrode.

[0075] In addition, compared with the case where there is no polyvinyl carbonate in the electrolyte, lithium ions can move directly from the positive electrode to the negative electrode. When polyvinyl carbonate is generated in the lithium-ion battery, lithium ions need to pass through polyvinyl carbonate to move from the positive electrode to the negative electrode, which prolongs the path for lithium ions to move from the positive electrode to the negative electrode, reduces the charging efficiency of the lithium-ion battery under overcharge conditions, and thus ensures the safety of lithium-ion batteries.

[0076] For example, at a temperature greater than or equal to 100° C., the OO bond in benzoyl peroxide decomposes into benzoyl peroxide and benzoyl radicals. In this example, the process of the addition reaction of benzoyl radicals with vinylene carbonate is similar, and the effects are similar, so this example will not be described in detail.

[0077] For example, when the temperature is greater than or equal to 100° C., the OO bond in di-tert-butyl peroxide decomposes into tert-butyl radicals and butanone radicals. In this example, the processes of the addition reaction of tert-butyl radicals and butanone radicals with vinylene carbonate are similar, and the effects are similar, so this application example will not be described in detail here.

[0078] Based on the electrolyte provided in the above example, the mass ratio of the overcharge safety agent in the electrolyte ranges from 0.2% to 5%.

[0079] For example, the mass ratio of the overcharge safety agent in the electrolyte may be 0.2%, 1%, 2%, or 5%. Of course, the mass ratio of the overcharge safety agent in the electrolyte may also be any other value between 0.2% and 5%.

[0080] Here, the mass ratio of the overcharge safety agent in the electrolyte refers to the mass percentage of all overcharge safety agents in the electrolyte provided in the example of this application.

[0081] In the example of this application, by controlling the mass ratio of the overcharge safety agent in the electrolyte, the manufacturing cost of the electrolyte can be controlled and the possibility of overcharge safety agent waste can be reduced. And by controlling the mass ratio of the overcharge safety agent in the electrolyte, a certain concentration of OO bonds can be provided in the electrolyte, and the OO bonds react with the unsaturated double bonds in the film-forming additive to reduce the possibility of thermal runaway of the lithium-ion battery in the overcharge state.

[0082] In addition, the example of the present application sets the mass ratio of the overcharge safety agent in the electrolyte to a range of 0.2% to 5%, which can reduce the possibility of no significant improvement in the safety of lithium-ion batteries due to the mass ratio of the overcharge safety agent in the electrolyte being lower than 0.2%, thereby resulting in a lower concentration of polymers generated by the overcharge safety agent and the film-forming additive.

[0083] It can also reduce the possibility that the mass ratio of the overcharge safety agent in the electrolyte is higher than 5%, which affects the kinetic properties of the electrolyte and further affects the performance of the lithium-ion battery.

[0084] Based on the electrolyte provided in the above example, the sum of the mass ratios of the film-forming additive and the overcharge safety agent in the electrolyte ranges from 2% to 10%.

[0085] For example, the mass ratio of the film-forming additive in the electrolyte may be 1%, and in this case, the mass ratio of the overcharge safety agent in the electrolyte may be 2%.

[0086] For example, the mass ratio of the film-forming additive in the electrolyte may be 3%, and at this time, the mass ratio of the overcharge safety agent in the electrolyte may be 2%.

[0087] For example, the mass ratio of the film-forming additive in the electrolyte may be 3%, and in this case, the mass ratio of the overcharge safety agent in the electrolyte may be 5%.

[0088] The examples in this application do not impose specific restrictions on the mass ratio of the film-forming additive and the overcharge protection agent in the electrolyte. The above only exemplifies the mass ratio of the film-forming additive and the overcharge protection agent in the electrolyte.

[0089] In the example of this application, the mass ratio of the film-forming additive to the overcharge safety agent in the electrolyte can be adjusted according to the sum of the mass ratios of the film-forming additive and the overcharge safety agent in the electrolyte being 2% to 10%, to ensure that the film-forming additive and the overcharge safety agent can react to form a polymer, and the possibility of thermal runaway of the lithium-ion battery in an overcharge state is reduced by the polymer, thereby reducing the manufacturing cost of the electrolyte.

[0090] Based on the electrolyte provided in the above example, the lithium salt may include lithium hexafluorophosphate (LiPF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF 4 ), lithium borate oxalate (LiBOB), lithium borate difluorooxalate (LiDFOB). The lithium salt may also be other compounds that can enable lithium ions to move between the positive electrode and the negative electrode. The specific selection of the lithium salt can be selected according to the use scenario of the lithium-ion battery. The example of this application does not limit the specific type of the lithium salt.

[0091] The content of lithium salt in the solution may range from 0.8 to 1.2 mol / L.

[0092] Illustratively, the content of lithium salt may be 0.8 mol / L, 1 mol / L, 1.2 mol / L or other values.

[0093] In the example of the present application, the content of lithium salt in the electrolyte is set in the range of 0.8 to 1.2 mol / L, which is beneficial to improving the performance of the lithium-ion battery and ensuring the safety of the electrolyte.

[0094] Based on the electrolyte provided in the above example, the carbonate solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DC).

[0095] In the examples of the present application, ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate can be combined in any combination.

[0096] Exemplarily, the carbonate solvent may include ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate, and the volume percentage ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate may be 25:35:40. The example of the present application does not limit the specific composition of the carbonate solvent, as long as the carbonate solvent can dissolve lithium salts and ensure the normal use of lithium-ion batteries.

[0097] Exemplarily, the present application provides a method for preparing an electrolyte, the electrolyte being suitable for lithium-ion batteries, Figure 1 For a schematic diagram of a method for preparing an electrolyte provided as an example in this application, please refer to Figure 1 , the preparation method of the electrolyte comprises the following steps:

[0098] S100, adding lithium salt to a carbonate solvent and stirring thoroughly to form a solution.

[0099] The lithium salt may be at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorooxalatoborate. The content of the lithium salt in the solution may be controlled at 0.8 to 1.2 mol / L.

[0100] The carbonate solvent may be at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Taking the carbonate solvent including ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate as an example, the volume percentage ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate may be 25:35:40. In the example of the present application, it is sufficient to ensure that the carbonate solvent can dissolve the lithium salt and keep the content of the lithium salt in the solution at 0.8 to 1.2 mol / L.

[0101] S200, adding a film-forming additive and an overcharge safety agent into the solution, and fully dissolving them to form an electrolyte.

[0102] The film-forming additive contains an unsaturated double bond, and the overcharge safety agent contains an OO bond. When the lithium-ion battery is in an overcharged state, the temperature inside the lithium-ion battery can reach 80-120°C. The OO bond can be decomposed by heat to generate free radicals, and the free radicals react with the unsaturated double bond to generate a polymer.

[0103] Adding film-forming additives and overcharge safety agents to the solution and fully dissolving them to form an electrolyte means that the film-forming additives and overcharge safety agents as solutes reach the maximum solubility in the solution. Under certain temperature and pressure conditions, the film-forming additives and overcharge safety agents have been completely dissolved in the solution to form a uniform mixture without any remaining solid or liquid solutes.

[0104] The film-forming additive may be at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, alkyl nitrile compounds, and the like.

[0105] The overcharge safety agent may be at least one of organic peroxides such as dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide.

[0106] The specific description of the addition reaction can be found in the above related records, and the example of this application will not be described in detail here.

[0107] The following describes the different ratios of the above film-forming additives and overcharge protection agents and their effects on the overcharge safety of lithium-ion batteries through multiple groups of examples and comparative examples.

[0108] The following examples describe the disclosure of the present application in more detail, and these examples are only used for illustrative purposes, because it is obvious to those skilled in the art that various modifications and variations are made within the scope of the disclosure of the present application. Unless otherwise stated, all mass ratios, contents, volume percentages, and mass percentages mentioned in the following examples are based on weight, and all reagents used in the examples are commercially available and can be used directly without further processing.

[0109] Comparative Example 1

[0110] Electrolyte formula 1: 1.2M LiPF 6 +EC:EMC:DMC (25:35:40 vol%)+1 wt% vinylene carbonate.

[0111] Corresponding electrolyte preparation method:

[0112] S110, LiPF 6 Add to a solution with a solvent ratio of EC:EMC:DMC (25:35:40 vol%) and stir thoroughly to form LiPF 6 The content of solution 1 is 1.2 mol / L.

[0113] S210, adding vinylene carbonate to the above solution 1 to fully dissolve it to form an electrolyte 1 with a mass ratio of vinylene carbonate of 1 wt%.

[0114] For example, solution 1 is a solution in which the solute is LiPF 6 The solvent is a mixture of EC, EMC and DMC, and in solution 1, the volume percentage ratio of EC:EMC:DMC is 25:35:40. The solute and solvent are fully dissolved to form LiPF 6 The content of solution 1 is 1.2 mol / L.

[0115] Vinylene carbonate was added to solution 1 and fully dissolved to form electrolyte 1 with a mass ratio of vinylene carbonate of 1 wt %.

[0116] Comparative Example 2

[0117] Electrolyte formula 2: 1.2M LiPF 6 +EC:EMC:DMC (25:35:40 vol%) +2wt% dicumyl peroxide.

[0118] Corresponding electrolyte preparation method:

[0119] S120, LiPF 6 Add to a solution with a solvent ratio of EC:EMC:DMC (25:35:40 vol%) and stir thoroughly to form LiPF 6 The content of solution 2 is 1.2 mol / L.

[0120] S220, adding dicumyl peroxide to solution 2 to fully dissolve it to form an electrolyte 2 with a mass ratio of dicumyl peroxide of 2 wt%.

[0121] For example, solution 2 is a solution in which the solute is LiPF 6The solvent is a mixture of EC, EMC and DMC, and in solution 2, the volume percentage ratio of EC:EMC:DMC is 25:35:40. The solute and solvent are fully dissolved to form LiPF 6 The content of solution 2 is 1.2 mol / L.

[0122] Dicumyl peroxide was added to solution 2 and fully dissolved to form electrolyte 2 with a mass ratio of 2 wt % of dicumyl peroxide.

[0123] Example 1

[0124] Electrolyte formula 3: 1.2M LiPF 6 +EC:EMC:DMC (25:35:40 vol%)+1 wt% vinylene carbonate+2 wt% diisopropylbenzene peroxide.

[0125] Corresponding electrolyte preparation method:

[0126] S130, LiPF 6 Add to a solution with a solvent ratio of EC:EMC:DMC (25:35:40 vol%) and stir thoroughly to form LiPF 6 The content of the solution is 1.2 mol / L 3.

[0127] S230, adding vinylene carbonate and dicumyl peroxide to the above solution 3, and fully dissolving them to form an electrolyte 3 with a mass ratio of 1 wt% of vinylene carbonate and a mass ratio of 2 wt% of dicumyl peroxide.

[0128] For example, solution 3 is a solution in which the solute is LiPF 6 The solvent is a mixture of EC, EMC and DMC, and in solution 3, the volume percentage ratio of EC:EMC:DMC is 25:35:40. The solute and solvent are fully dissolved to form LiPF 6 The content of the solution is 1.2 mol / L 3.

[0129] Vinylene carbonate and dicumyl peroxide were added to the solution 3 and fully dissolved to form an electrolyte 3 in which the mass ratio of vinylene carbonate was 1 wt % and the mass ratio of dicumyl peroxide was 2 wt %.

[0130] Example 2

[0131] Electrolyte formula 4: 1.2M LiPF 6 +EC:EMC:DMC (25:35:40 vol%) +1 wt% vinylene carbonate +1 wt% diisopropylbenzene peroxide.

[0132] Corresponding electrolyte preparation method:

[0133] S140, LiPF 6 Add to a solution with a solvent ratio of EC:EMC:DMC (25:35:40 vol%) and stir thoroughly to form LiPF 6 The content of the solution is 1.2 mol / L 4.

[0134] S240, adding vinylene carbonate and dicumyl peroxide to the solution 4, and fully dissolving them to form an electrolyte 4 with a mass ratio of 1 wt % of vinylene carbonate and a mass ratio of 1 wt % of dicumyl peroxide.

[0135] For example, solution 4 is a solution in which the solute is LiPF 6 The solvent is a mixture of EC, EMC and DMC, and in solution 4, the volume percentage ratio of EC:EMC:DMC is 25:35:40. The solute and solvent are fully dissolved to form LiPF 6 The content of the solution is 1.2 mol / L 4.

[0136] Vinylene carbonate and dicumyl peroxide were added to the solution 4 and fully dissolved to form an electrolyte 4 with a mass ratio of 1 wt % of vinylene carbonate and a mass ratio of 1 wt % of dicumyl peroxide.

[0137] Example 3

[0138] Electrolyte formula 5: 1.2M LiPF 6 +EC:EMC:DMC (25:35:40 vol%) +3wt% vinylene carbonate +2wt% diisopropylbenzene peroxide.

[0139] Corresponding electrolyte preparation method:

[0140] S150, LiPF 6 Add to a solution with a solvent ratio of EC:EMC:DMC (25:35:40 vol%) and stir thoroughly to form LiPF 6 The content of the solution is 1.2 mol / L 5.

[0141] S250, adding vinylene carbonate and dicumyl peroxide into the solution 5, and fully dissolving them to form an electrolyte 5 with a mass ratio of 3 wt % of vinylene carbonate and a mass ratio of 2 wt % of dicumyl peroxide.

[0142] For example, solution 5 is a solution in which the solute is LiPF 6The solvent is a mixture of EC, EMC and DMC, and in solution 5, the volume percentage ratio of EC:EMC:DMC is 25:35:40. The solute and solvent are fully dissolved to form LiPF 6 The content of the solution is 1.2 mol / L 5.

[0143] Vinylene carbonate and dicumyl peroxide were added to the solution 5 and fully dissolved to form an electrolyte 5 in which the mass ratio of vinylene carbonate was 3 wt % and the mass ratio of dicumyl peroxide was 2 wt %.

[0144] Example 4

[0145] Electrolyte formula 6: 1.2M LiPF 6 +EC:EMC:DMC (25:35:40 vol%) +5wt% vinylene carbonate +2wt% diisopropylbenzene peroxide.

[0146] Corresponding electrolyte preparation method:

[0147] S160, LiPF 6 Add to a solution with a solvent ratio of EC:EMC:DMC (25:35:40 vol%) and stir thoroughly to form LiPF 6 The content of the solution is 1.2 mol / L 6.

[0148] S260, adding vinylene carbonate and dicumyl peroxide to the solution 6, and fully dissolving them to form an electrolyte 6 with a mass ratio of 5 wt% of vinylene carbonate and a mass ratio of 2 wt% of dicumyl peroxide.

[0149] For example, solution 6 is a solution in which the solute is LiPF 6 The solvent is a mixture of EC, EMC and DMC, and in solution 6, the volume percentage ratio of EC:EMC:DMC is 25:35:40. The solute and solvent are fully dissolved to form LiPF 6 The content of the solution is 1.2 mol / L 6.

[0150] Vinylene carbonate and dicumyl peroxide were added to the solution 6 and fully dissolved to form an electrolyte 6 with a mass ratio of 5 wt % of vinylene carbonate and a mass ratio of 2 wt % of dicumyl peroxide.

[0151] Example 5

[0152] Electrolyte formula 7: 1.2M LiPF 6 +EC:EMC:DMC (25:35:40 vol%) +3 wt% vinylene carbonate +0.2 wt% diisopropylbenzene peroxide.

[0153] Corresponding electrolyte preparation method:

[0154] S170, LiPF 6 Add to a solution with a solvent ratio of EC:EMC:DMC (25:35:40 vol%) and stir thoroughly to form LiPF 6 The content of the solution is 1.2 mol / L 7.

[0155] S270, adding vinylene carbonate and dicumyl peroxide to the solution 7, and fully dissolving them to form an electrolyte 7 with a mass ratio of 3 wt % of vinylene carbonate and a mass ratio of 0.2 wt % of dicumyl peroxide.

[0156] For example, solution 7 is a solution in which the solute is LiPF 6 The solvent is a mixture of EC, EMC and DMC, and in solution 7, the volume percentage ratio of EC:EMC:DMC is 25:35:40. The solute and solvent are fully dissolved to form LiPF 6 The content of the solution is 1.2 mol / L 7.

[0157] Vinylene carbonate and dicumyl peroxide were added to solution 7 and fully dissolved to form a mass ratio of 3 wt % of vinylene carbonate and 0.2 wt % of dicumyl peroxide.

[0158] Example 6

[0159] Electrolyte formula 8: 1.2M LiPF 6 +EC:EMC:DMC (25:35:40 vol%) +3wt% vinylene carbonate +5wt% diisopropylbenzene peroxide.

[0160] Corresponding electrolyte preparation method:

[0161] S180, LiPF 6 Add to a solution with a solvent ratio of EC:EMC:DMC (25:35:40 vol%) and stir thoroughly to form LiPF 6 The content of the solution is 1.2 mol / L 8.

[0162] S280, adding vinylene carbonate and dicumyl peroxide to the solution 8, and fully dissolving them to form an electrolyte 8 with a mass ratio of 3 wt % of vinylene carbonate and a mass ratio of 5 wt % of dicumyl peroxide.

[0163] For example, solution 8 is a solution in which the solute is LiPF 6The solvent is a mixture of EC, EMC and DMC, and in solution 8, the volume percentage ratio of EC:EMC:DMC is 25:35:40. The solute and solvent are fully dissolved to form LiPF 6 The content of the solution is 1.2 mol / L 8.

[0164] Vinylene carbonate and dicumyl peroxide were added to the solution 8 and fully dissolved to form an electrolyte 8 in which the mass ratio of vinylene carbonate was 3 wt % and the mass ratio of dicumyl peroxide was 5 wt %.

[0165] The relevant data of different electrolytes when the lithium-ion battery is in an overcharge state are recorded in Table 1 below, and only the volume percentage ratio of EC:EMC:DMC is 25:35:40, the film-forming additive is vinylene carbonate, and the overcharge safety agent is diisopropylbenzene peroxide is compared as an example.

[0166] Table 1

[0167]

[0168] According to Comparative Examples 1 and 2, the electrolyte corresponding to Comparative Example 1 contains no overcharge safety agent, i.e., no OO bond. Therefore, when the lithium-ion battery is in an overcharged state, there is no OO bond in the electrolyte that can be decomposed into free radicals by heat, and then react with the unsaturated double bonds in the film-forming additive to undergo addition reaction.

[0169] The electrolyte of Comparative Example 2 contains no film-forming additive, i.e., no unsaturated double bonds. Therefore, when the lithium-ion battery is in an overcharged state, the OO bonds in the overcharge safety agent can be decomposed into multiple free radicals by heat, but the free radicals cannot undergo addition reaction with the unsaturated double bonds.

[0170] In summary, both Comparative Examples 1 and 2 do not meet the requirement for addition reaction between the overcharge safety agent and the film-forming additive. The large surface temperature of the lithium-ion battery in Comparative Example 1 reaches 750°C, and the large surface temperature of the lithium-ion battery in Comparative Example 2 reaches 620°C. Both of them experience thermal runaway and fire, resulting in poor safety of lithium-ion batteries.

[0171] Compared with Comparative Example 1 and Comparative Example 2, the electrolytes corresponding to Examples 1 to 6 all contain film-forming additives and overcharge safety agents, that is, the electrolytes all contain OO bonds and unsaturated double bonds. The OO bonds can be decomposed into free radicals when the lithium-ion battery is in an overcharged state. The free radicals can react with the unsaturated double bonds to form polymers. The polymers can reduce the charging efficiency of the lithium-ion battery in an overcharged state, thereby reducing the possibility of thermal runaway of the lithium-ion battery and ensuring the safety of the lithium-ion battery.

[0172] Compared with Example 1, Example 2 has the same mass ratio of the film-forming additive in the electrolyte. Compared with Example 1, the mass ratio of diisopropyl peroxide in the electrolyte is 1wt%, and the mass ratio of diisopropyl peroxide in the electrolyte is 2wt% in Example 2. Example 2 can reach the charging cut-off condition faster, and the corresponding overcharge time is shorter, the overcharge SOC (State of Charge, battery state of charge) is lower, and the temperature of the large surface of the battery cell is lower, which means that compared with Example 1, Example 2 has a lower probability of thermal runaway and fire, and is safer to use.

[0173] In summary, in the example of the present application, it is ensured that the electrolyte contains both an overcharge safety agent containing an OO bond and a film-forming additive containing an unsaturated double bond, so that the OO bond can be thermally decomposed into free radicals when the lithium-ion battery is overcharged, and the free radicals can undergo addition reactions with the unsaturated double bonds to form polymers. The polymer reduces the charging efficiency of the lithium-ion battery in the overcharge state, reduces the possibility of thermal runaway, fire, etc. of the lithium-ion battery due to overcharging, and ensures the safety of the lithium-ion battery.

[0174] According to Examples 1, 3, and 4, when the parameters such as lithium salt content and overcharge safety agent mass ratio are the same, when the mass ratio of the film-forming additive is adjusted from 1wt% to 3wt%, the overcharge SOC of the lithium-ion battery is reduced by 7%, the overcharge time is shortened by 504 seconds, and the temperature of the large surface of the battery cell is reduced by 38°C; when the mass ratio of the film-forming additive is adjusted from 3wt% to 5wt%, the overcharge SOC of the lithium-ion battery is reduced by 2%, the overcharge time is shortened by 144 seconds, and the temperature of the large surface of the battery cell is reduced by 2°C.

[0175] It can be seen that when the mass ratio of the film-forming additive is 1wt% to 3wt%, the mass ratio of the film-forming additive changes, and the effect of reducing accidents such as thermal runaway and fire in lithium-ion batteries under overcharging conditions changes significantly.

[0176] According to Examples 3, 5, and 6, when the parameters such as lithium salt content and mass ratio of film-forming additives are the same, when the mass ratio of the overcharge safety agent is adjusted from 0.2wt% to 2wt%, the overcharge SOC of the lithium-ion battery is reduced by 8%, the overcharge time is shortened by 576 seconds, and the temperature of the large surface of the battery cell is reduced by 58°C; when the mass ratio of the film-forming additive is adjusted from 2wt% to 5wt%, the overcharge SOC of the lithium-ion battery is reduced by 1%, the overcharge time is shortened by 72 seconds, and the temperature of the large surface of the battery cell is reduced by 1°C.

[0177] It can be seen that when the mass ratio of the film-forming additive is 0.2wt% to 2wt%, the mass ratio of the film-forming additive changes, and the effect of reducing accidents such as thermal runaway and fire in lithium-ion batteries under overcharging conditions changes significantly.

[0178] Finally, it should be noted that the above embodiments are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An electrolyte, characterized in that: Applied to lithium-ion batteries, the electrolyte comprises: Lithium salts; Carbonate solvents; Film-forming additives containing unsaturated double bonds; Overcharge safety agent, containing OO bond.

2. The electrolyte according to claim 1, characterized in that The film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate and alkyl nitrile compounds.

3. The electrolyte according to claim 2, characterized in that The mass ratio of the film-forming additive in the electrolyte is in the range of 1% to 5%.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The overcharge safety agent includes at least one of dicumyl peroxide, benzoyl peroxide and di-tert-butyl peroxide.

5. The electrolyte according to claim 4, characterized in that The mass ratio of the overcharge safety agent in the electrolyte is in the range of 0.2% to 5%.

6. The electrolyte according to claim 5, characterized in that The sum of the mass ratios of the film-forming additive and the overcharge safety agent in the electrolyte is in the range of 2% to 10%.

7. The electrolyte according to any one of claims 1 to 3, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorooxalatoborate.

8. The electrolyte according to any one of claims 1 to 3, characterized in that The carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

9. A lithium ion battery, characterized in that: The electrolyte comprises the electrolyte described in any one of claims 1 to 8.

10. A method for preparing an electrolyte, characterized in that: The method is used to prepare the electrolyte according to any one of claims 1 to 8, wherein the electrolyte is suitable for lithium-ion batteries, and the method comprises: Take lithium salt and add carbonate solvent, stir thoroughly to form a solution; A film-forming additive and an overcharge safety agent are added to the solution and fully dissolved to form an electrolyte.

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