Electrochemical device and preparation method therefor, and electronic device

Abstract

The present application provides an electrochemical device and a preparation method therefor, and an electronic device. The electrochemical device comprises an electrode assembly and an electrolyte, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a selective lithium-ion permeable membrane, a positive electrode side and a negative electrode side that are independent from each other are formed on two sides of the selective lithium-ion permeable membrane, and the air permeability of the selective lithium-ion permeable membrane is greater than or equal to 4000 s / 100mL; the electrolyte comprises a positive electrolyte and a negative electrolyte, the positive electrode sheet and the positive electrolyte are accommodated on the positive electrode side, and the negative electrode sheet and the negative electrolyte are accommodated on the negative electrode side; and the positive electrolyte and the negative electrolyte are different. The aforementioned arrangement can improve the kinetics and high-temperature performance of the electrochemical device.

Description

Electrochemical device and preparation method thereof, and electronic device Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to an electrochemical device and a preparation method thereof, and an electronic device. Background Art

[0002] Electrochemical devices, such as lithium-ion batteries, have been widely used in portable electronics, electric vehicles, and smart grids due to their advantages such as high energy density, cycling stability, and low self-discharge.

[0003] Lithium-ion batteries primarily consist of four key components: the positive electrode, negative electrode, separator, and electrolyte. The positive and negative electrodes have different requirements for electrolyte. Current lithium-ion batteries often utilize a mixed electrolyte system, where both the positive and negative electrodes reside in the same electrolyte. This not only limits the electrolyte design window but also impacts the performance of the lithium-ion battery, particularly its high-temperature storage and cycling performance.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide an electrochemical device and its preparation method, and an electronic device to achieve improvements in the dynamics and high-temperature performance of the electrochemical device, wherein the high-temperature performance mainly refers to high-temperature storage performance and high-temperature cycle performance.

[0006] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides an electrochemical device, which includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a selective lithium ion permeable membrane. The selective lithium ion permeable membrane forms independent positive and negative sides on both sides. The permeability of the selective lithium ion permeable membrane is ≥4000s / 100mL. The electrolyte is divided into a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode sheet and the positive electrode electrolyte are contained on the positive electrode side, and the negative electrode sheet and the negative electrode electrolyte are contained on the negative electrode side. The positive electrode electrolyte is different from the negative electrode electrolyte. The present application selects a selective lithium ion permeable membrane with a permeability greater than or equal to 4000s / 100mL to form independent positive and negative sides on both sides of the selective lithium ion permeable membrane. The positive electrode electrolyte can be placed on the positive electrode side and the negative electrode electrolyte can be placed on the negative electrode side, so that the positive electrode electrolyte and the negative electrode electrolyte are separated. In this way, the electrolyte can be regulated separately on the positive electrode side and the negative electrode side. The difference between the positive and negative electrolytes allows for a better fit between the positive and negative electrodes, reducing the likelihood of negative electrolyte components affecting the positive and negative electrodes. This also allows for a better fit between the negative and positive electrodes, reducing the likelihood of positive electrolyte components affecting the negative electrodes. This also reduces the mutual influence between the positive and negative electrolytes, thereby broadening the selection window for the positive and negative electrolytes and fully leveraging their respective roles. This can improve the kinetics and high-temperature performance of electrochemical devices.

[0008] In one embodiment of the present application, the electrolyte includes a film-forming additive, and the film-forming additive includes at least one positive electrode film-forming additive and at least one negative electrode film-forming additive; after the electrochemical device is formed, the mass percentage of the positive electrode film-forming additive in the positive electrode electrolyte is W1, and the mass percentage of the positive electrode film-forming additive in the negative electrode electrolyte is W2, and W1 is greater than W2; and the mass percentage of the negative electrode film-forming additive in the negative electrode electrolyte is W3, and the mass percentage of the negative electrode film-forming additive in the positive electrode electrolyte is W4, and W3 is greater than W4. This indicates that after the electrochemical device is formed, the selective lithium ion permeation membrane separates the positive electrode electrolyte on the positive electrode side from the negative electrode electrolyte on the negative electrode side. The separate regulation of the positive electrode electrolyte containing more positive electrode film-forming additives on the positive electrode side and the negative electrode electrolyte containing more negative electrode additives on the negative electrode side can achieve improvements in the kinetics and high-temperature performance of the electrochemical device.

[0009] In one embodiment of the present application, the positive electrode film-forming additive includes at least one of ethanedinitrile, malononitrile, succinonitrile or glutaronitrile, and 0.1%≤W1≤10%.

[0010] In one embodiment of the present application, the negative electrode film-forming additive includes any one of fluoroethylene carbonate, vinylene carbonate, ethylene carbonate, butylene sulfite, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, vinyl sulfate, propylene sulfate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), or lithium bis(oxalatoborate), with 0.1% ≤ W3 ≤ 10%. Selecting the above-mentioned positive electrode film-forming additives and negative electrode film-forming additives and regulating their contents within the above-mentioned ranges can improve the kinetics and high-temperature performance of the electrochemical device.

[0011] In one embodiment of the present application, the negative electrode film-forming additive includes any one of fluoroethylene carbonate, vinylene carbonate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), or lithium bis(oxalatoborate). These negative electrode film-forming additives, when applied to the electrolyte, are more conducive to forming a dense and uniform film on the surfaces of the positive and negative electrode sheets, thereby further improving the kinetics and high-temperature performance of the electrochemical device.

[0012] In one embodiment of the present application, the electrolyte includes carbonate and carboxylate; after the electrochemical device is formed, the mass percentage of carbonate in the positive electrode electrolyte is W5, and the mass percentage of carbonate in the negative electrode electrolyte is W6, where W5 is greater than W6; and the mass percentage of carboxylate in the negative electrode electrolyte is W7, and the mass percentage of carboxylate in the positive electrode electrolyte is W8, where W7 is greater than W8. This indicates that after the electrochemical device is formed, the selective lithium ion permeation membrane separates the positive electrode electrolyte on the positive electrode side from the negative electrode electrolyte on the negative electrode side. The separate regulation of the positive electrode electrolyte containing more carbonate on the positive electrode side and the negative electrode electrolyte containing more carboxylate on the negative electrode side can improve the kinetics and high-temperature performance of the electrochemical device.

[0013] In one embodiment of the present application, the carbonate comprises at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or methylpropyl carbonate (MPC); the carboxylate comprises at least one of γ-butyrolactone (BL), methyl formate (MF), ethyl formate (EF), methyl acetate (MA), ethyl acetate (EA), methyl butyrate (MB), ethyl butyrate (EB), n-propyl propionate (PP), or ethyl propionate (EP); and 50%≤W5≤80%, and 50%≤W7≤80%. Selecting the above-mentioned carbonates and carboxylates, and regulating the content of the carbonate in the positive electrolyte and the content of the carboxylate in the negative electrolyte within the above-mentioned ranges, can improve the kinetics and high-temperature performance of the electrochemical device.

[0014] In one embodiment of the present application, the ionic conductivity of the selective lithium ion permeable membrane is greater than or equal to 10 -2 mS / cm. This indicates that the selective lithium ion permeable membrane has high ionic conductivity. The electrochemical device has good cycle performance on the basis of good high-temperature performance, and its kinetics are further improved.

[0015] In one embodiment of the present application, the ionic conductivity of the selective lithium ion permeable membrane is 0.1 mS / cm to 5 mS / cm. Controlling the ionic conductivity of the selective lithium ion permeable membrane within this range makes it easier to manufacture electrochemical devices while maintaining excellent high-temperature performance, cycle performance, and kinetics, thereby reducing production costs and improving production efficiency of electrochemical devices.

[0016] In one embodiment of the present application, the structure of the electrode assembly includes any one of a single-layer laminate structure, a multi-layer laminate structure, and a wound structure.

[0017] A second aspect of the present application provides a method for preparing an electrochemical device, comprising the following steps:

[0018] (1) stacking the positive electrode sheet, the selective lithium ion permeable membrane, and the negative electrode sheet in sequence to form an electrode assembly with a single-layer laminate structure, with the two sides of the selective lithium ion permeable membrane forming independent positive and negative electrode sides; or

[0019] (1') stacking the positive electrode sheet, the selective lithium ion permeable membrane, the negative electrode sheet, and the selective lithium ion permeable membrane in sequence as a structural unit, and then repeatedly stacking multiple structural units to form an electrode assembly with a multi-layer laminate structure, with the two sides of the selective lithium ion permeable membrane forming independent positive and negative electrode sides; or

[0020] (1") stacking the positive electrode sheet, the selective lithium ion permeable membrane, and the negative electrode sheet in sequence, wherein the selective lithium ion permeable membrane forms a cavity with an opening on one side and the positive electrode sheet is accommodated in the cavity, and the negative electrode sheet is wound along the outside of the cavity to form an electrode assembly with a wound structure, and the two sides of the selective lithium ion permeable membrane respectively form independent positive and negative electrode sides; or

[0021] (1') stacking the positive electrode sheet, the selective lithium ion permeable membrane, and the negative electrode sheet in sequence, wherein the selective lithium ion permeable membrane forms a cavity with an opening on one side and the negative electrode sheet is accommodated in the cavity, and the positive electrode sheet is wound along the outside of the cavity to form an electrode assembly with a wound structure, and the two sides of the selective lithium ion permeable membrane respectively form independent negative and positive electrode sides;

[0022] (2) The electrode assembly is placed in an outer package, a positive electrode electrolyte is injected into the positive electrode side, and a negative electrode electrolyte is injected into the negative electrode side, and after packaging, an electrochemical device according to any of the aforementioned embodiments is obtained.

[0023] The preparation method of the electrochemical device provided in the present application can produce an electrochemical device containing electrode assemblies with different structures. The preparation method is simple, easy to operate by those skilled in the art, and can be widely used in industrial production.

[0024] A third aspect of the present application provides an electronic device, wherein the electronic device comprises the electrochemical device described in any of the aforementioned embodiments. Therefore, the electronic device has good performance.

[0025] Beneficial effects of this application:

[0026] The present application provides an electrochemical device and an electronic device, wherein the electrochemical device forms an independent positive electrode side and negative electrode side on both sides of the selective lithium ion permeable membrane by selecting a selective lithium ion permeable membrane with an air permeability greater than or equal to 4000s / 100mL, and can place the positive electrode electrolyte on the positive electrode side and the negative electrode electrolyte on the negative electrode side, so that the positive electrode electrolyte and the negative electrode electrolyte are separated. In this way, the electrolyte can be regulated separately in the positive electrode side and the negative electrode side. The difference between the positive electrode electrolyte and the negative electrode electrolyte makes the positive electrode electrolyte more compatible with the positive electrode sheet, reduces the possibility of the components in the negative electrode electrolyte affecting the positive electrode sheet, and also makes the negative electrode electrolyte more compatible with the negative electrode sheet, reduces the possibility of the components in the positive electrode electrolyte affecting the negative electrode sheet, and reduces the mutual influence between the positive electrode electrolyte and the negative electrode electrolyte, thereby widening the selection window of the positive electrode electrolyte and the negative electrode electrolyte, and giving full play to the respective roles of the positive electrode electrolyte and the negative electrode electrolyte. This can improve the kinetics and high-temperature performance of electrochemical devices. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions, and advantages of this application more clearly understood, the following examples are given to further describe this application in detail. Obviously, the described examples are only some examples of this application, rather than all examples. All other examples obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] It should be noted that, in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0029] In existing electrochemical devices, there is no distinction between the positive and negative sides, and a mixed electrolyte system is often used, so that the positive and negative electrodes are in the same electrolyte. In order to meet the film formation requirements of the positive and negative electrodes at the same time, the electrolyte will add positive and negative electrode film-forming additives. The coexistence of positive and negative electrode film-forming additives will cause the two to affect each other. For example, some positive electrode film-forming additives will form a film on the surface of the negative electrode, consuming the positive electrode film-forming additives and reducing the protection of the positive electrode. At the same time, the film formation of the positive electrode additives on the negative electrode will also affect the stability of the film formation of the negative electrode itself. It will be necessary to add more negative electrode film-forming additives to form a film on the negative electrode itself. However, the addition of more film-forming additives will reduce the kinetics and high-temperature performance of the electrochemical device. At the same time, some negative electrode film-forming additives will also undergo oxidation reactions on the positive electrode, which will not only affect the film formation of the negative electrode, but also affect the stability of the film formation of the positive electrode. In addition, some byproducts of the positive and negative electrode film formation process will affect the corresponding electrode performance. In addition to additives, the electrolyte solvent will also be selective between the positive and negative electrodes. The stability of the positive electrode sheet is the key to high-temperature performance, requiring more stable carbonates. The dynamics of the negative electrode sheet is the key to the dynamics of the electrochemical device, requiring more carboxylates to meet the kinetic performance. Therefore, there will be selectivity differences in the solvents of the positive and negative electrodes to simultaneously meet the kinetic performance and high-temperature stability of the electrochemical device.

[0030] The first aspect of the present application provides an electrochemical device, wherein the electrochemical device includes an electrode assembly and an electrolyte, and the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a selective lithium ion permeable membrane. The selective lithium ion permeable membrane forms independent positive and negative sides on both sides, and the positive and negative sides are independent cavities. The permeability of the selective lithium ion permeable membrane is ≥4000s / 100mL. The electrolyte is divided into a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode sheet and the positive electrode electrolyte are accommodated on the positive electrode side, and the negative electrode sheet and the negative electrode electrolyte are accommodated on the negative electrode side. The positive electrode electrolyte is different from the negative electrode electrolyte.

[0031] When the air permeability of the selective lithium ion permeable membrane is ≥4000s / 100mL, lithium ions can shuttle back and forth between the positive electrode side and the negative electrode side through the selective lithium ion permeable membrane to form a charge and discharge circuit. However, the probability of solvent molecules shuttling back and forth between the positive electrode side and the negative electrode side through the selective lithium ion permeable membrane is very low, so the two sides of the selective ion permeable membrane can form independent positive electrode side and negative electrode side, and the positive electrode side and the negative electrode side are independent cavities, that is, there is a good isolation effect between the positive electrode side and the negative electrode side. When the air permeability of the selective lithium ion permeable membrane is less than 4000s / 100mL, some solvent molecules can pass through the isolation membrane and isolation cannot be achieved. The present application selects a selective lithium ion permeable membrane with an air permeability greater than or equal to 4000s / 100mL to form independent positive electrode side and negative electrode side on both sides of the selective lithium ion permeable membrane, and can place the positive electrode electrolyte on the positive electrode side and the negative electrode electrolyte on the negative electrode side, so that the positive electrode electrolyte and the negative electrode electrolyte are separated. In this way, the electrolyte can be regulated separately on the positive and negative electrode sides. The difference between the positive and negative electrolytes makes the positive electrolyte and the positive electrode sheet more compatible, reducing the possibility of the components in the negative electrolyte affecting the positive electrode sheet, and also makes the negative electrolyte and the negative electrode sheet more compatible, reducing the possibility of the components in the positive electrolyte affecting the negative electrode sheet, and also reducing the mutual influence between the positive and negative electrolytes, thereby widening the selection window of the positive and negative electrolytes, and giving full play to the respective roles of the positive and negative electrolytes. In this way, it is possible to achieve improvements in the kinetics and high-temperature performance of the electrochemical device.

[0032] In this application, high temperature refers to a temperature greater than or equal to 45°C.

[0033] In one embodiment of the present application, the permeability of the selective lithium ion permeable membrane is 4000s / 100mL to 16000s / 100mL. For example, the permeability of the selective lithium ion permeable membrane is 4000s / 100mL, 5000s / 100mL, 6000s / 100mL, 7000s / 100mL, 8000s / 100mL, 9000s / 100mL, 10000s / 100mL, 11000s / 100mL, 13000s / 100mL, 16000s / 100mL or any value between any two of the above numerical ranges. Selective ion permeable membranes with a permeability within the above range are easier to obtain and have lower production costs. Selective lithium ion permeable membranes with a permeability within the above range can reduce the production cost of electrochemical devices while improving the kinetics and high-temperature performance of electrochemical devices.

[0034] In one embodiment of the present application, the electrolyte includes a film-forming additive, wherein the film-forming additive includes at least one positive electrode film-forming additive and at least one negative electrode film-forming additive. After the electrochemical device is formed, the mass percentage of the positive electrode film-forming additive in the positive electrode electrolyte is W1, and the mass percentage of the positive electrode film-forming additive in the negative electrode electrolyte is W2, where W1 is greater than W2; and the mass percentage of the negative electrode film-forming additive in the negative electrode electrolyte is W3, and the mass percentage of the negative electrode film-forming additive in the positive electrode electrolyte is W4, where W3 is greater than W4. After the electrochemical device is formed, the mass percentage content W1 of the positive electrode film-forming additive in the positive electrode electrolyte is greater than the mass percentage content W2 of the positive electrode film-forming additive in the negative electrode electrolyte, and the mass percentage content W3 of the negative electrode film-forming additive in the negative electrode electrolyte is greater than the mass percentage content W4 of the negative electrode film-forming additive in the positive electrode electrolyte, indicating that after the electrochemical device is formed, the positive electrode film-forming additive in the positive electrode electrolyte on the positive electrode side does not flow freely between the positive electrode side and the negative electrode side, and the negative electrode film-forming additive in the negative electrode electrolyte on the negative electrode side does not flow freely between the negative electrode side and the positive electrode side, that is, the selective lithium ion permeation membrane separates the positive electrode electrolyte on the positive electrode side from the negative electrode electrolyte on the negative electrode side. When preparing the electrolyte, the positive electrode film-forming additive is added to the positive electrode electrolyte, and the negative electrode film-forming additive is added to the negative electrode electrolyte. In this way, the positive electrode electrolyte and the negative electrode electrolyte can be regulated separately on the positive electrode side and the negative electrode side. Separate regulation of the positive electrode electrolyte containing more positive electrode film-forming additives on the positive electrode side and the negative electrode electrolyte containing more negative electrode additives on the negative electrode side can, on the one hand, reduce the mutual influence of the positive electrode film-forming additives and the negative electrode film-forming additives, reduce the influence of the positive electrode film-forming additives on the film-forming stability of the negative electrode sheet itself, thereby reducing the content of the negative electrode film-forming additives in the electrolyte, and achieving improvements in the kinetics and high-temperature performance of the electrochemical device; on the other hand, it can reduce the influence of the reduction products generated by the negative electrode film-forming additives on the stability of the positive electrode sheet, thereby improving the high-temperature performance of the electrochemical device; on the other hand, it can also reduce the probability of some film-forming additives being unable to be used due to redox window problems. For example, lithium bis(trifluoromethanesulfonyl imide) has kinetic advantages, but cannot be used in a mixed electrolyte system because it is not resistant to high voltage and corrodes aluminum foil. However, in this application, it can be used as a negative electrode film-forming additive to improve the kinetics of the electrochemical device. In this way, improvements in the kinetics and high-temperature performance of the electrochemical device can be achieved.

[0035] In this application, the above-mentioned "formation" refers to the process of charging the electrochemical device under the conditions of 80°C and 1MPa to form a solid electrolyte interface film (SEI). The specific process parameters are: charging the electrochemical device to 75% SOC (state of charge) at 1C under the conditions of 80°C and 1MPa.

[0036] In one embodiment of the present application, the positive electrode film-forming additive includes any one of ethanedinitrile, malononitrile, succinonitrile or glutaronitrile, and 0.1%≤W1≤10%. In one embodiment of the present application, the negative electrode film-forming additive includes any one of fluoroethylene carbonate (FEC), vinylene carbonate, vinyl ethylene carbonate, butylene sulfite, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, vinyl sulfate, propylene sulfate, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(oxalatoborate) (LiBOB), and 0.1%≤W3≤10%. For example, W1 is 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value between any two of the above numerical ranges. For example, W3 is 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value between any two of the above numerical ranges. The positive electrode film-forming additives of the above types and content ranges are applied to the positive electrode electrolyte on the positive electrode side, which is conducive to the formation of a dense and uniform positive electrode electrolyte interface (CEI) film on the surface of the positive electrode plate, which is used to stabilize the positive electrode active material and reduce the occurrence of side reactions; the negative electrode film-forming additives of the above types and content ranges are applied to the negative electrode electrolyte on the negative electrode side, which is conducive to the formation of a dense and uniform solid electrolyte interface (SEI) film on the surface of the negative electrode plate, which is used to stabilize the negative electrode active material, reduce further reduction process, and reduce the consumption of negative electrode electrolyte. By selecting the above types of positive electrode film-forming additives and negative electrode film-forming additives, and regulating the content within the above ranges respectively, extremely stable CEI films and SEI films can be formed at the positive and negative electrodes respectively, while reducing the mutual influence of the positive and negative electrode film formation, thereby improving the kinetics and high-temperature performance of the electrochemical device.

[0037] There is no particular limitation on W2 and W4 in this application, as long as W1 is greater than W2 and W3 is greater than W4, the purpose of this application can be achieved. For example, 0% ≤ W2 < 10%, 0% ≤ W4 < 10%.

[0038] The present application does not particularly limit the method for regulating W1, W2, W3, and W4, as long as the purpose of the present application can be achieved. For example, this can be achieved by regulating at least one of the permeability of the selective lithium ion permeable membrane or the content of the membrane-forming additive.

[0039] In one embodiment of the present application, the negative electrode film-forming additive includes any one of FEC, vinylene carbonate, LiTFSI, LiFSI, or LiBOB. These negative electrode film-forming additives, when applied to the electrolyte, are more conducive to forming a dense and uniform film on the surfaces of the positive and negative electrode plates, thereby further improving the kinetics and high-temperature performance of the electrochemical device.

[0040] In one embodiment of the present application, the electrolyte includes carbonate and carboxylate; after the electrochemical device is formed, the mass percentage of carbonate in the positive electrode electrolyte is W5, and the mass percentage of carbonate in the negative electrode electrolyte is W6, and W5 is greater than W6; and the mass percentage of carboxylate in the negative electrode electrolyte is W7, and the mass percentage of carboxylate in the positive electrode electrolyte is W8, and W7 is greater than W8. After the electrochemical device is formed, the mass percentage of carbonate in the positive electrode electrolyte, W5, is greater than the mass percentage of carbonate in the negative electrode electrolyte, W6, and the mass percentage of carboxylate in the negative electrode electrolyte, W7, is greater than the mass percentage of carboxylate in the positive electrode electrolyte, W8. This indicates that after the electrochemical device is formed, the carbonate in the positive electrode electrolyte on the positive electrode side does not flow freely between the positive and negative electrode sides, and the carboxylate in the negative electrode electrolyte on the negative electrode side does not flow freely between the negative and positive electrode sides. In other words, the selective lithium ion permeability membrane separates the positive electrode electrolyte on the positive electrode side from the negative electrode electrolyte on the negative electrode side. When preparing the electrolyte, carbonate is added to the positive electrode electrolyte and carboxylate is added to the negative electrode electrolyte. In this way, the positive electrode electrolyte and negative electrode electrolyte can be controlled separately on the positive and negative electrode sides. Separate regulation of the positive electrode electrolyte containing more carbonates on the positive electrode side and the negative electrode electrolyte containing more carboxylates on the negative electrode side can, on the one hand, reduce the mutual influence of carbonates and carboxylates, reduce the carbonate content on the negative electrode side, and improve the kinetics of the negative electrode sheet. At the same time, the carbonate content on the positive electrode side is not reduced, and while improving the kinetic performance, it will not affect the high-temperature performance of the electrochemical device; at the same time, reducing the carboxylate content on the positive electrode side can improve the high-temperature performance of the electrochemical device. At the same time, the carboxylate content on the negative electrode side is not reduced, and the kinetic performance of the electrochemical device is not affected. Thus, the kinetics and high-temperature performance of the electrochemical device can be improved.

[0041] In one embodiment of the present application, the carbonate comprises at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or methylpropyl carbonate (MPC); the carboxylate comprises at least one of γ-butyrolactone (BL), methyl formate (MF), ethyl formate (EF), methyl acetate (MA), ethyl acetate (EA), methyl butyrate (MB), ethyl butyrate (EB), n-propyl propionate (PP), or ethyl propionate (EP); and 50%≤W5≤80%, and 50%≤W7≤80%. For example, W5 is 50%, 54%, 60%, 63%, 70%, 75%, 78%, 80%, or any value between any two of the above numerical ranges. For example, W7 is 50%, 53%, 61%, 63%, 67%, 72%, 78%, 80%, or any value between any two of the above numerical ranges. The carbonates of the above types and content ranges are applied to the positive electrode electrolyte on the positive electrode side, which is beneficial for improving the kinetic performance of the electrochemical device while not affecting its high-temperature performance; the carboxylates of the above types and content ranges are applied to the negative electrode electrolyte on the negative electrode side, which is beneficial for improving the high-temperature performance of the electrochemical device while not affecting its kinetic performance. Therefore, by selecting the above types of carbonates and carboxylates, and regulating the content of the carbonates in the positive electrode electrolyte and the content of the carboxylates in the negative electrode electrolyte within the above ranges, the kinetic and high-temperature performance of the electrochemical device can be improved.

[0042] There is no particular limitation on W6 and W8 in this application. As long as W5 is greater than W6 and W7 is greater than W8, the purpose of this application can be achieved. For example, W6 is 0% to 50% and W8 is 0% to 50%.

[0043] The present application does not particularly limit the method for regulating W5, W6, W7, and W8, as long as the purpose of the present application can be achieved. For example, this can be achieved by regulating the permeability of the selective lithium ion permeation membrane or at least one of the content of carbonate and carboxylate.

[0044] In one embodiment of the present application, the ionic conductivity of the selective lithium ion permeable membrane is greater than or equal to 10 -2 mS / cm. This indicates that the selective lithium-ion permeable membrane has a high ionic conductivity, which facilitates a high lithium ion transmission rate, further improving the kinetics of the electrochemical device and enabling good cycling performance. As a result, the electrochemical device not only has good high-temperature performance but also good cycling performance, and its kinetics are further improved.

[0045] In one embodiment of the present application, the ionic conductivity of the selective lithium ion permeable membrane is 0.1 mS / cm to 5 mS / cm. For example, the ionic conductivity of the selective lithium ion permeable membrane is 0.1 mS / cm, 0.6 mS / cm, 1 mS / cm, 1.4 mS / cm, 2 mS / cm, 2.4 mS / cm, 3 mS / cm, 3.5 mS / cm, 4 mS / cm, 4.7 mS / cm, 5 mS / cm, or any value between any two of the above numerical ranges. A selective lithium ion permeable membrane having an ionic conductivity within the above range makes it easier to obtain an electrochemical device while having good high-temperature performance, cycle performance, and kinetics, which is beneficial to reducing the production cost of the electrochemical device and improving the production efficiency of the electrochemical device.

[0046] The present application does not particularly limit the method for regulating the permeability and ionic conductivity of the selective lithium ion permeable membrane, as long as the purpose of the present application can be achieved. For example, this can be achieved by adjusting the type of selective lithium ion permeable membrane.

[0047] This application does not specifically limit the preparation method of a selective lithium-ion permeable membrane, as long as the objectives of this application can be achieved. For example, the preparation method of a selective lithium-ion permeable membrane includes, but is not limited to, the following steps: coating a mixed slurry of lithium aluminum titanium phosphate (LATP) and a binder on one surface of a PP / PE base membrane (denoted as surface A), drying the mixture, and performing a reduction reaction using a lithium replenishment device. After the reaction, a separator layer is formed, thereby obtaining a selective lithium-ion permeable membrane. Furthermore, when the reduction reaction is performed using the lithium replenishment device, surface A faces the negative electrode of the lithium replenishment device. The above-mentioned "PP / PE base membrane" refers to a base membrane for a separator formed by mixing polyethylene and polypropylene, which is well known in the art. Those skilled in the art can select the appropriate one based on actual conditions, as long as the objectives of this application can be achieved. This application is not limited to this. This application does not specifically limit the mass ratio of LATP to binder in the mixed slurry, as long as the objectives of this application can be achieved. For example, it can be (75-85):(15-25). This application does not specifically limit the type of the above-mentioned binder, as long as the objectives of this application can be achieved. The present application does not place any particular restrictions on the reaction temperature of the above-mentioned "reduction reaction", as long as the purpose of the present application can be achieved. For example, the reaction temperature of the reduction reaction is 45°C to 80°C. The present application does not place any particular restrictions on the thickness of the isolation layer, as long as the purpose of the present application can be achieved. For example, the thickness of the isolation layer can be 0.01μm to 3μm. In some embodiments, the ionic conductivity of the selective lithium ion permeable membrane can be regulated by regulating the thickness of the isolation layer. Generally, the thicker the isolation layer, the smaller the ionic conductivity of the selective lithium ion permeable membrane; the thinner the isolation layer, the greater the ionic conductivity of the selective lithium ion permeable membrane. In other embodiments, the permeability of the selective lithium ion permeable membrane can be regulated by regulating the reaction temperature of the above-mentioned reduction reaction.

[0048] In one embodiment of the present application, the structure of the electrode assembly includes any one of a single-layer laminate structure, a multi-layer laminate structure, or a wound structure. In some embodiments, the structure of the electrode assembly is a single-layer laminate structure. It is understood that the electrode assembly of the single-layer laminate structure includes a positive electrode sheet, a negative electrode sheet, and a selective lithium ion permeable membrane. The selective lithium ion permeable membrane is located between the positive electrode sheet and the negative electrode sheet to separate the positive electrode sheet and the negative electrode sheet. The selective lithium ion permeable membrane is connected to the outer packaging. Independent cavities are formed on both sides of the selective lithium ion permeable membrane, namely the positive electrode side and the negative electrode side. The positive electrode sheet is accommodated on the positive electrode side, and the negative electrode sheet is accommodated on the negative electrode side. In other embodiments, the structure of the electrode assembly is a multi-layer laminate structure, and the electrode assembly of the multi-layer laminate structure includes a multi-layer positive electrode sheet, a multi-layer negative electrode sheet and a multi-layer selective lithium ion permeable membrane. The selective lithium ion permeable membrane is located between the positive electrode sheet and the negative electrode sheet, separating the positive electrode sheet and the negative electrode sheet, and the two adjacent selective lithium ion permeable membranes are each connected to the outer packaging, and independent cavities are formed on both sides of the selective lithium ion permeable membrane, namely the positive electrode side and the negative electrode side, respectively. The positive electrode sheet is accommodated on the positive electrode side, and the negative electrode sheet is accommodated on the negative electrode side. This application does not particularly limit the number of layers in the above-mentioned "multi-layer". Those skilled in the art can choose according to actual needs as long as the purpose of this application can be achieved. For example, the multi-layer is at least two layers. In some other embodiments, the structure of the electrode assembly is a wound structure. It should be noted that during the preparation process, the selective lithium ion permeable membrane first forms a cavity with an opening on one side, and then the positive electrode sheet or the negative electrode sheet is placed in the cavity, and then the negative electrode sheet or the positive electrode sheet is wound along the outside of the cavity to obtain an electrode assembly with a wound structure. It can be understood that one of the positive electrode sheet and the negative electrode sheet is located in the cavity formed by the selective lithium ion permeable membrane, and the other is located outside the cavity formed by the selective lithium ion permeable membrane.

[0049] In one embodiment of the present application, the positive electrode electrolyte includes a positive electrode film-forming additive, a lithium salt and an organic solvent, and the negative electrode electrolyte includes a negative electrode film-forming additive, a lithium salt and an organic solvent. After the electrochemical device is formed, based on the mass of the positive electrode electrolyte, the mass percentage of the positive electrode film-forming additive is 0.1% to 10%, the mass percentage of the lithium salt is 10% to 17%, and the mass percentage of the organic solvent is 73% to 89.9%. After the electrochemical device is formed, based on the mass of the negative electrode electrolyte, the mass percentage of the negative electrode film-forming additive is 0.1% to 10%, the mass percentage of the lithium salt is 10% to 17%, and the mass percentage of the organic solvent is 73% to 89.9%. This application does not particularly limit the above-mentioned organic solvents, as long as the purpose of this application can be achieved. For example, it can include carbonates, carboxylates and other organic solvents of this application.

[0050] In one embodiment of the present application, the positive electrode electrolyte includes a carbonate ester, and the negative electrode electrolyte includes a carboxylate ester. After the electrochemical device is formed, based on the mass of the positive electrode electrolyte, the mass percentage of the carbonate ester is 50% to 80%, the mass percentage of the lithium salt is 10% to 17%, and the mass percentage of other organic solvents and additives is 3% to 40%. After the electrochemical device is formed, based on the mass of the negative electrode electrolyte, the mass percentage of the carboxylate ester is 50% to 80%, the mass percentage of the lithium salt is 10% to 17%, and the mass percentage of other organic solvents and additives is 3% to 40%. The present application does not specifically limit the lithium salt in this embodiment, as long as it can achieve the objectives of the present application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBCl6, LiSO3CF3, LiBF4, or LiCF3SO3. The present application does not specifically limit the types of the above-mentioned additives, and electrolyte additives known in the art can be selected, as long as they can achieve the objectives of the present application.

[0051] In one embodiment of the present application, the positive electrode electrolyte includes a positive electrode film-forming additive and a carbonate, and the negative electrode electrolyte includes a negative electrode film-forming additive and a carboxylate. After the electrochemical device is formed, based on the mass of the positive electrode electrolyte, the mass percentage of the positive electrode film-forming additive is 0.1% to 10%, the mass percentage of the carbonate is 50% to 80%, the mass percentage of the lithium salt is 10% to 17%, and the mass percentage of other organic solvents is 0% to 40%. After the electrochemical device is formed, based on the mass of the negative electrode electrolyte, the mass percentage of the negative electrode film-forming additive is 0.1% to 10%, the mass percentage of the carboxylate is 50% to 80%, the mass percentage of the lithium salt is 10% to 17%, and the mass percentage of other organic solvents is 0% to 40%. This application does not specifically limit the types of other organic solvents. Those skilled in the art can select organic solvents other than the carbonates and carboxylates specified in this application according to actual needs, as long as the purpose of this application can be achieved.

[0052] In one embodiment of the present application, the electrolyte further comprises other organic solvents. The present application does not particularly limit the types of other organic solvents, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), vinyl ethylene carbonate (VEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, methyl formate, acetic acid At least one of propyl ester, tert-butyl acetate, methyl propionate, propyl propionate, decanoic acid lactone, valerolactone, mevalonolactone, caprolactone, dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphate ester.

[0053] This application does not specifically limit the positive electrode sheet, as long as it can achieve the objectives of this application. In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is disposed on one or both surfaces of the positive electrode current collector. The "surface" mentioned above can be a portion of the surface of the positive electrode current collector or the entire surface of the positive electrode current collector. This application does not specifically limit the positive electrode current collector, as long as it can achieve the objectives of this application. For example, the positive electrode current collector can include aluminum foil or aluminum alloy foil. The positive electrode active material layer of this application includes positive electrode active material. This application does not specifically limit the type of positive electrode active material, as long as it can achieve the objectives of this application. For example, the positive electrode active material can include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate. In this application, the positive electrode active material may also include non-metallic elements. The non-metallic elements may include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. These elements can further improve the stability of the positive electrode active material. In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm, preferably 6μm to 18μm. The thickness of the single-sided positive electrode active material layer is 30μm to 300μm. Optionally, the positive electrode active material layer may also include at least one of a positive electrode conductive agent or a binder. The present application does not particularly limit the types of positive electrode conductive agents and binders in the positive electrode active material layer, as long as the purpose of the present application can be achieved. The present application does not particularly limit the mass ratio of the positive electrode active material, positive electrode conductive agent, and binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. For example, the mass ratio of the positive electrode active material, positive electrode conductive agent, and binder in the positive electrode active material layer is (97.5~97.9):(0.8~1.7):(1.0~2.0).

[0054] The present application has no special restrictions on the negative electrode plate, as long as the purpose of the present application can be achieved. In one embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is arranged on one surface or two surfaces of the negative electrode current collector. The above-mentioned "surface" can be a partial surface of the negative electrode current collector or the entire surface of the negative electrode current collector. The present application has no special restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel or foam copper, etc. The negative electrode active material layer of the present application contains negative electrode active material. The present application has no special restrictions on the type of negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiOx (0 < x < 2), at least one of Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 、Li-Al alloy or metallic lithium. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the object of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode active material layer is 30 μm to 400 μm. Optionally, the negative electrode active material layer may further include at least one of a negative electrode conductive agent, a dispersant or a binder. This application has no particular limitation on the types of the negative electrode conductive agent, the dispersant and the binder in the negative electrode active material layer, as long as the object of this application can be achieved. This application has no particular limitation on the mass ratio of the negative electrode active material, the negative electrode conductive agent, the dispersant and the binder in the negative electrode active material layer, as long as the object of this application can be achieved. For example, the mass ratio of the negative electrode active material, the negative electrode conductive agent, the dispersant and the binder in the negative electrode active material layer is (97 - 98):(0.5 - 1.5):(0 - 1.5):(1.0 - 2.0).

[0055] The electrochemical device of this application further includes an outer package. This application has no particular limitation on the outer package, and any type well-known in the art can be selected, as long as the object of this application can be achieved.

[0056] This application has no particular limitation on the type of the electrochemical device, and it may include any device that undergoes an electrochemical reaction. For example, the electrochemical device may include, but is not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), sodium ion secondary batteries (sodium ion batteries), lithium polymer secondary batteries, lithium ion polymer secondary batteries (lithium ion polymer batteries).

[0057] The second aspect of this application provides a method for preparing an electrochemical device, including the following steps:

[0058] (1) Stack the positive electrode sheet, the selective lithium ion permeable membrane, and the negative electrode sheet in sequence to form an electrode assembly with a single-layer laminated structure, and independent positive and negative sides are formed on both sides of the selective lithium ion permeable membrane; or,

[0059] (1’) Stack the positive electrode sheet, the selective lithium ion permeable membrane, the negative electrode sheet, and the selective lithium ion permeable membrane in sequence and use them as a structural unit, and then stack multiple structural units repeatedly to form an electrode assembly with a multi-layer laminated structure. The selective lithium ion permeable membrane is connected to the outer package, and independent positive and negative sides are formed on both sides of the selective lithium ion permeable membrane; or,

[0060] (1") The positive electrode sheet, the selective lithium ion permeable membrane, and the negative electrode sheet are stacked in sequence, the selective lithium ion permeable membrane forms a cavity with an opening on one side and the positive electrode sheet is accommodated in the cavity, and the negative electrode sheet is wound along the outside of the cavity to form an electrode assembly with a wound structure, and independent positive and negative electrode sides are formed on both sides of the selective lithium ion permeable membrane, i.e., inside and outside the cavity; or

[0061] (1') stacking the positive electrode sheet, the selective lithium ion permeable membrane, and the negative electrode sheet in sequence, wherein the selective lithium ion permeable membrane forms a cavity with an opening on one side and the negative electrode sheet is accommodated in the cavity, and the positive electrode sheet is wound along the outside of the cavity to form an electrode assembly with a wound structure, and forming independent negative and positive electrode sides on both sides of the selective lithium ion permeable membrane, i.e., inside and outside the cavity, respectively;

[0062] (2) Injecting a positive electrode electrolyte into the positive electrode side and a negative electrode electrolyte into the negative electrode side, and then encapsulating the electrochemical device to obtain any of the aforementioned embodiments.

[0063] In one embodiment of the present application, a method for preparing an electrochemical device comprises the following steps: (1) stacking a positive electrode sheet, a selective lithium ion permeable membrane, and a negative electrode sheet in sequence to form an electrode assembly with a single-layer laminate structure, placing the electrode assembly in an outer package, connecting the selective lithium ion permeable membrane to the outer package, and forming independent positive and negative electrode sides on both sides of the selective lithium ion permeable membrane; (2) injecting a positive electrode electrolyte into the positive electrode side and a negative electrode electrolyte into the negative electrode side, and encapsulating the outer package to obtain the electrochemical device.

[0064] In one embodiment of the present application, a method for preparing an electrochemical device comprises the following steps: (1') stacking a positive electrode sheet, a selective lithium ion permeable membrane, a negative electrode sheet, and a selective lithium ion permeable membrane in sequence as a structural unit, and then repeatedly stacking a plurality of said structural units to form an electrode assembly with a multilayer laminate structure, placing the electrode assembly in an outer package, and bonding the selective lithium ion permeable membrane by heat treatment, so as to form independent cavities on both sides of the selective lithium ion permeable membrane, i.e., a positive electrode side and a negative electrode side; (2) injecting a positive electrode electrolyte into the positive electrode side and a negative electrode electrolyte into the negative electrode side, and then encapsulating the outer package to obtain an electrochemical device. It is understood that the above-mentioned "repeated stacking" means that the "positive electrode sheet, selective lithium ion permeable membrane, negative electrode sheet, and selective lithium ion permeable membrane" are regarded as a structural unit. After the stacking of the first structural unit is completed, the stacking of the second structural unit is repeated, and so on. The number of repetitions is selected according to the number of layers of the multilayer laminate structure, thereby completing the arrangement of the electrode assembly with a multilayer laminate structure.

[0065] In one embodiment of the present application, a method for preparing an electrochemical device comprises the following steps: (1") stacking a positive electrode sheet, a selective lithium ion permeable membrane, and a negative electrode sheet in sequence, wherein the selective lithium ion permeable membrane forms a cavity with an opening on one side and the positive electrode sheet is accommodated in the cavity, and the negative electrode sheet is wound along the outside of the cavity to form an electrode assembly with a wound structure, wherein independent positive and negative electrode sides are formed on both sides of the selective lithium ion permeable membrane, i.e., inside and outside the cavity, respectively; (2) placing the electrode assembly in an outer package, injecting a positive electrode electrolyte into the positive electrode side and a negative electrode electrolyte into the negative electrode side, and sealing the outer package to obtain the electrochemical device.

[0066] In one embodiment of the present application, a method for preparing an electrochemical device comprises the following steps: (1) stacking a positive electrode sheet, a selective lithium ion permeable membrane, and a negative electrode sheet in sequence, wherein the selective lithium ion permeable membrane forms a cavity with an opening on one side and the negative electrode sheet is accommodated in the cavity, and the positive electrode sheet is wound along the outside of the cavity to form an electrode assembly with a wound structure, and independent negative and positive electrode sides are formed on both sides of the selective lithium ion permeable membrane, i.e., inside and outside the cavity, respectively; (2) placing the electrode assembly in an outer package, injecting a positive electrode electrolyte into the positive electrode side and a negative electrode electrolyte into the negative electrode side, and sealing the outer package to obtain the electrochemical device.

[0067] The present application does not particularly limit the preparation method of the above-mentioned "selective lithium ion permeable membrane forming a cavity with an opening on one side", and those skilled in the art can make a selection based on actual conditions as long as the purpose of the present application can be achieved.

[0068] The preparation method of the electrochemical device provided in the present application can produce an electrochemical device containing electrode assemblies with different structures. The preparation method is simple, easy to operate by those skilled in the art, and can be widely used in industrial production.

[0069] A third aspect of the present application provides an electronic device, wherein the electronic device comprises the electrochemical device described in any of the aforementioned embodiments. Therefore, the electronic device has good performance.

[0070] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0071] Example

[0072] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

[0073] Test methods and equipment:

[0074] Permeability test of selective lithium ion permeable membrane:

[0075] In a laboratory setting, the selective lithium-ion permeable membrane to be tested is placed between two gas chambers. Gas is passed from one chamber to the other through the membrane at a pressure differential of 1.21 kPa. The time required for 100 mL of test gas to pass through the membrane is recorded. (For this test method, the gas used is air, and the membrane to be tested is 40 mm x 40 mm in size.)

[0076] Tests for W1, W2, W3, W4, W5, W6, W7, and W8:

[0077] The lithium-ion battery was disassembled to remove the positive and negative electrodes. The positive and negative electrodes were placed in centrifuge tubes and centrifuged to obtain the positive and negative electrolytes, respectively. If no electrolyte was obtained by centrifugation, the positive and negative electrodes were soaked in acetonitrile for 0.5 hours to obtain the positive and negative electrolytes. The positive and negative electrolytes were injected into a gas chromatograph (Agilent 7890B) for component testing and content comparison. The type and content of the lithium salt were determined by ion chromatography; the type and content of the film-forming additive, carbonate, and carboxylate were determined by gas chromatography.

[0078] Test of ionic conductivity of selective lithium ion permeation membrane:

[0079] It should be noted that when testing the Examples, Comparative Example 1-1, and Comparative Example 2-1, the following separator is a selective lithium ion permeable membrane.

[0080] (1) Preparation of isolation membrane: The isolation membrane to be tested was cut into the same size (45.3 mm × 33.7 mm), dried at 60°C for 4 h, and then transferred to a glove box for use;

[0081] (2) Preparation of symmetrical lithium-ion battery outer packaging: Use copper foil to assemble blank symmetrical lithium-ion battery outer packaging without a separator. Before use, the outer packaging needs to be dried at 60°C for 4 hours and then transferred to a glove box for use;

[0082] (3) Assembly of symmetrical lithium-ion batteries: Assemble symmetrical lithium-ion batteries with negative electrode sheets against negative electrode sheets in the outer packaging of the symmetrical lithium-ion batteries, and assemble different layers (1, 2, 3, 4 layers) of separators in situ in the middle of the symmetrical electrodes in a glove box to form symmetrical lithium-ion batteries (5 parallel samples of symmetrical lithium-ion batteries with each layer number are assembled); use a simple packaging machine to seal the outer packaging side, use a pipette to inject electrolyte (300 μL), and then seal the bottom;

[0083] (4) Loading the symmetrical lithium-ion battery into the fixture: Load the assembled symmetrical lithium-ion battery into the fixture and then place it in the glove box for 12 hours to allow the electrolyte to fully infiltrate the isolation membrane;

[0084] (5) Electrochemical Impedance Spectroscopy (EIS) Test: Before the EIS test, symmetrical lithium-ion batteries with different numbers of separator layers were placed in a temperature chamber at 25°C for half an hour. The EIS test was performed at the set temperature. During the EIS test, the frequency was set to 1 kHz and the perturbation voltage was set to 5 mV. The conductivity S of the separator was calculated based on the test results.

[0085] (6) Calculation of the conductivity S of the isolation membrane:

[0086] The resistance value obtained from symmetrical lithium-ion batteries with different numbers of isolation membrane layers is used as the vertical coordinate, and the number of layers n is used as the horizontal coordinate. A scatter plot is made, and then a linear fit is performed. The slope is the resistance value of the isolation membrane. The conductivity S of the isolation membrane is calculated according to the following formula.

[0087] The conductivity S of the isolation membrane = the thickness of the isolation membrane / (the resistance of the isolation membrane × the effective area of ​​the isolation membrane that can transmit ions when the impedance is tested);

[0088] Among them, the effective area of ​​the isolation membrane that can transmit ions when testing impedance is 153.86mm 2 The negative electrode sheet and electrolyte used in the EIS test are the same as those in Example 1-1.

[0089] 80℃ storage performance test:

[0090] After the lithium-ion battery is charged to 4.5 V and reaches a fully charged state, its thickness is measured and recorded as the initial thickness.

[0091] The fully charged lithium-ion battery obtained above was placed in a high-low temperature box at 80°C for storage, and the thickness of the lithium-ion battery after storage for 24 hours was recorded as the final thickness. The thickness of the lithium-ion battery was tested using a PPG thickness gauge with a thickness measurement pressure of 300g.

[0092] Lithium-ion battery thickness expansion rate (%) = (final thickness - initial thickness) / initial thickness × 100%. The smaller the thickness expansion rate, the better the 80°C storage performance.

[0093] 45℃ cycle performance test:

[0094] Place the lithium-ion battery in a 45°C high and low temperature chamber, charge it to 4.5V at a constant current of 1C, charge it to 0.05V at a constant voltage of 4.5V, and then discharge it to 3.0V at 1C. Repeat this charge and discharge cycle. The number of cycles required for the capacity to decay to 80% indicates the 45°C cycling performance. The more cycles, the better the 45°C cycling performance.

[0095] Lithium deposition window test:

[0096] The lithium-ion batteries of each embodiment and comparative example were charged and discharged at 25°C according to the following steps: discharging at a constant current of 0.2C to 3.0V; then charging at a constant current of 1.5C to 4.5V; and then charging at a constant voltage of 4.5V to 0.05C (at this point, fully charged); this constitutes one charge-discharge cycle. After 10 cycles of this charge-discharge cycle, the fully charged lithium-ion battery was disassembled and the negative electrode plate was inspected for lithium deposition. If white or gray lithium appeared on the surface of the negative electrode plate, lithium deposition was confirmed; otherwise, lithium deposition was confirmed.

[0097] If lithium deposition does not occur, the lithium-ion battery prepared in the same embodiment or comparative example is taken and the charging rate is gradually increased by 0.1C while other charge and discharge parameters remain unchanged, and the above steps are repeated until lithium deposition occurs on the negative electrode.

[0098] The maximum charge rate at which the negative electrode does not release lithium is defined as the maximum charge rate without lithium deposition, also known as the lithium deposition window. The maximum charge rate without lithium deposition is used to characterize the lithium deposition window of a lithium-ion battery. A larger charge rate without lithium deposition indicates better kinetics.

[0099] Example 1-1

[0100] <Preparation of Selective Lithium Ion Permeable Membrane>

[0101] LATP and binder polyacrylic acid (PAA, weight-average molecular weight 70W) were mixed in a mass ratio of 80:20, added to water and stirred evenly to obtain a mixed slurry with a solid content of 30 wt%;

[0102] After coating the mixed slurry on one surface of a 5 μm thick PP / PE base film (denoted as surface A), drying it, and using a lithium replenishing device to carry out a reduction reaction at a reaction temperature of 80°C to form an isolation layer with a thickness of 1 μm, thus obtaining a selective lithium ion permeable membrane.

[0103] <Preparation of Electrolyte>

[0104] Preparation of electrolyte A: Under an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and an organic solvent (EC:PC:EA:DEC=1:1:1:1, mass ratio) were prepared to prepare electrolyte A.

[0105] Preparation of the positive electrode electrolyte: Malononitrile, a positive electrode film-forming additive, was added to electrolyte A and mixed thoroughly to obtain the positive electrode electrolyte. Based on the mass of the positive electrode electrolyte, the mass percentage of malononitrile was 5%, the mass percentage of LiPF6 was 12.5%, and the balance was an organic solvent.

[0106] Preparation of the negative electrode electrolyte: Add the negative electrode film-forming additive FEC to electrolyte A and mix thoroughly to obtain the negative electrode electrolyte. Based on the mass of the negative electrode electrolyte, the mass percentage of FEC is 6%, the mass percentage of LiPF6 is 12.4%, and the balance is organic solvent.

[0107] <Preparation of positive electrode sheet>

[0108] The positive electrode active material lithium cobalt oxide (LCO), the positive electrode conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF, weight-average molecular weight 300,000) were dissolved in an N-methylpyrrolidone (NMP) solution at a mass ratio of 97.6:1.1:1.3 to form a positive electrode slurry. The LCO has a D50 of 13 μm, a D10 of 3 μm, and a D99 of 18 μm. The positive electrode slurry was evenly coated on one surface of a 10 μm thick positive electrode current collector aluminum foil and dried at 85°C to obtain a positive electrode sheet coated with a positive electrode active material layer on one side. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. After cold pressing and slitting, a positive electrode sheet with a length × width = 1500 mm × 80 mm was obtained for use. The single-sided coating weight of the positive electrode active material layer was 229 mg / 1540.25 mm. 2 .

[0109] <Preparation of negative electrode sheet>

[0110] The negative electrode active material artificial graphite, the negative electrode conductive agent conductive carbon and the binder styrene-butadiene rubber are dissolved in deionized water in a mass ratio of 97.5:0.5:2 to form a negative electrode slurry. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8μm, and dried at 85°C to obtain a negative electrode sheet coated with a negative electrode active material layer on one side. Thereafter, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. After cold pressing and slitting, a negative electrode sheet with a length × width = 1505mm × 82mm is obtained for standby use. The single-sided coating weight of the negative electrode active material layer is 120mg / 1540.25mm 2 .

[0111] <Preparation of lithium-ion batteries>

[0112] The selective lithium-ion permeable membrane, the positive electrode sheet, and the selective lithium-ion permeable membrane are stacked, with the selective lithium-ion permeable membrane forming a cavity with an open side. The positive electrode sheet is located within the cavity, and the negative electrode sheet is located outside the cavity, forming a stacked structure. The stacked structure is then wound along the length of the cavity to form a wound electrode assembly, with the inner side of the cavity forming the positive electrode side and the outer side of the cavity forming the negative electrode side. The electrode assembly is placed in an outer packaging aluminum-plastic film, dehydrated at 80°C, and the prepared positive and negative electrolytes are injected into the positive and negative electrode sides, respectively, before packaging. The lithium-ion battery is then produced through a formation, degassing, and trimming process.

[0113] The formation steps are: charging the lithium-ion battery at a constant current of 1C to 75% SOC under the conditions of 80°C and 1 MPa.

[0114] Since the malononitrile in the positive electrode electrolyte participates in the positive electrode film formation during the formation process and will be partially consumed, Table 1 lists the mass percentage content of malononitrile in the positive electrode electrolyte after the formation process (W1). The same meaning applies to the mass percentage content of FEC in the negative electrode electrolyte (W3). In Table 1, W1 and W2 are the mass percentage contents of the positive electrode film-forming additive in the positive electrode electrolyte and the negative electrode electrolyte, respectively, after the lithium-ion battery has undergone the formation process. In Table 1, W3 and W4 are the mass percentage contents of the negative electrode film-forming additive in the positive electrode electrolyte and the negative electrode electrolyte, respectively, after the lithium-ion battery has undergone the formation process.

[0115] Example 1-2

[0116] The process was the same as in Example 1-1 except that the thickness of the separator was adjusted to 3 μm in the preparation of a selective lithium ion permeable membrane.

[0117] Examples 1-3

[0118] The process was the same as in Example 1-1 except that the thickness of the separator was adjusted to 2 μm in the step <Preparation of Selective Lithium Ion Permeable Membrane>.

[0119] Examples 1-4

[0120] The process was the same as in Example 1-1 except that the thickness of the separator was adjusted to 0.5 μm in the step <Preparation of Selective Lithium Ion Permeable Membrane>.

[0121] Example 1-5 and Example 1-6

[0122] Except for adjusting the type of the positive electrode film-forming additive according to Table 1, the rest is the same as Example 1-1.

[0123] Example 1-7 to Example 1-10

[0124] Except for adjusting the type of negative electrode film-forming additive according to Table 1, the rest is the same as Example 1-1.

[0125] Example 1-11 to Example 1-20

[0126] Except for adjusting the relevant parameters according to Table 1, the rest is the same as Example 1-1.

[0127] Among them, the change of W1 is achieved by adjusting the mass percentage of the positive electrode film-forming additive in the positive electrode electrolyte during the preparation of the positive electrode electrolyte (that is, adjusting the initial addition amount before the formation process). When the mass percentage of the positive electrode film-forming additive in the positive electrode electrolyte changes, the mass percentage of the organic solvent in the positive electrode electrolyte changes accordingly, the mass percentage of the lithium salt in the positive electrode electrolyte remains unchanged, and the mass ratio of EC, PA, EA and DEC in the organic solvent remains unchanged; the change of W3 is achieved by adjusting the mass percentage of the negative electrode film-forming additive in the negative electrode electrolyte during the preparation of the negative electrode electrolyte. When the mass percentage of the negative electrode film-forming additive in the negative electrode electrolyte changes, the mass percentage of the organic solvent in the negative electrode electrolyte changes accordingly, the mass percentage of the lithium salt in the positive electrode electrolyte remains unchanged, and the mass ratio of EC, PA, EA and DEC in the organic solvent remains unchanged.

[0128] Example 1-21 and Example 1-22

[0129] The process was the same as Example 1-1 except that the reaction temperature was adjusted in the step of "Preparation of Selective Lithium Ion Permeable Membrane" so that the air permeability of the selective lithium ion permeable membrane was as shown in Table 1.

[0130] Example 2-1

[0131] <Preparation of Electrolyte>

[0132] Preparation of the positive electrolyte: LiPF6 was added to carbonate (EC:EMC = 3:7, mass ratio), mixed evenly, and then FEC and malononitrile were added and mixed evenly to obtain the positive electrolyte. Based on the mass of the positive electrolyte, the mass percentage of FEC was 4%, the mass percentage of malononitrile was 4%, the mass percentage of carbonate was 80%, and the balance was LiPF6.

[0133] Preparation of the negative electrode electrolyte: LiPF6 was added to a carboxylate (EA:MF = 1:1, mass ratio), mixed evenly, and then EC, FEC, and malononitrile were added and mixed evenly to obtain the negative electrode electrolyte. Based on the mass of the negative electrode electrolyte, the mass percentage of FEC was 4%, the mass percentage of malononitrile was 4%, the mass percentage of carboxylate was 70%, the mass percentage of EC was 10%, and the balance was LiPF6.

[0134] The rest is the same as Example 1-1.

[0135] Example 2-2

[0136] Except that the selective lithium ion permeable membrane is the same as that in Example 1-2, the rest is the same as that in Example 2-1.

[0137] Example 2-3

[0138] Except that the selective lithium ion permeable membrane is the same as that in Example 1-3, the rest is the same as that in Example 2-1.

[0139] Examples 2-4

[0140] Except that the selective lithium ion permeable membrane is the same as that in Example 1-4, the rest is the same as that in Example 2-1.

[0141] Examples 2-5

[0142] Preparation of the positive electrode electrolyte: LiPF6 was added to carbonate (EC:EMC=3:7, mass ratio), mixed evenly, and then EA, FEC, and malononitrile were added and mixed evenly to obtain the positive electrode electrolyte. Based on the mass of the positive electrode electrolyte, the mass percentage of FEC was 4%, the mass percentage of malononitrile was 4%, the mass percentage of carbonate was 70%, the mass percentage of EA was 10%, and the balance was LiPF6.

[0143] Except for the preparation of the positive electrode electrolyte, the rest is the same as Example 2-1.

[0144] Example 2-6 to Example 2-7

[0145] Except for adjusting the relevant parameters according to Table 2, the rest is the same as Example 2-1.

[0146] Among them, the change of W5 is achieved by adjusting the mass percentage of carbonate in the positive electrode electrolyte during the preparation of the positive electrode electrolyte. When the mass percentage of carbonate in the positive electrode electrolyte changes, the mass percentage of EA in the positive electrode electrolyte changes accordingly. The mass percentages of FEC, malononitrile and lithium salt in the positive electrode electrolyte remain unchanged. The sum of the mass percentages of carbonate and EA in the positive electrode electrolyte is 80%, and the sum of the mass percentages of carbonate, EA, FEC, malononitrile and lithium salt in the positive electrode electrolyte is 10. 0%; the change of W7 is achieved by adjusting the mass percentage of carboxylate in the negative electrode electrolyte during the preparation of the negative electrode electrolyte. When the mass percentage of carboxylate in the negative electrode electrolyte changes, the mass percentage of EC in the negative electrode electrolyte changes accordingly, and the contents of FEC, malononitrile and lithium salt in the negative electrode electrolyte change accordingly. The sum of the mass percentages of carboxylate and EC in the positive electrode electrolyte is 80%, and the sum of the mass percentages of carboxylate, EC, FEC, malononitrile and lithium salt in the positive electrode electrolyte is 100%.

[0147] Example 2-8 to Example 2-10

[0148] Except for adjusting the type of carbonate in the positive electrode electrolyte as shown in Table 2 in <Preparation of Electrolyte>, the rest was the same as Example 2-1.

[0149] Example 2-11 and Example 2-12

[0150] Except for adjusting the type of carboxylic acid ester in the negative electrode electrolyte as shown in Table 2 in <Preparation of Electrolyte>, the rest was the same as Example 2-1.

[0151] Example 2-13

[0152] Except that the selective lithium ion permeable membrane is the same as that in Example 1-21, the rest is the same as that in Example 2-1.

[0153] Examples 2-14

[0154] Except that the selective lithium ion permeable membrane is the same as that in Example 1-22, the rest is the same as that in Example 2-1.

[0155] Example 3-1

[0156] <Preparation of Electrolyte>

[0157] Preparation of the positive electrolyte: Mix the carbonate EC:EMC in a mass ratio of 3:7, then add LiPF6 and the cathode film-forming additive malononitrile to prepare the positive electrolyte. Based on the mass of the positive electrolyte, the mass percentage of carbonate is 80%, the mass percentage of malononitrile is 5%, and the balance is LiPF6.

[0158] Preparation of the negative electrode electrolyte: Carboxylate EA:MF = 1:1 (mass ratio) was mixed uniformly, and then carbonate EC, LiPF6, and the negative electrode film-forming additive FEC were added to obtain the negative electrode electrolyte. Based on the mass of the negative electrode electrolyte, the mass percentage of carboxylate was 70%, the mass percentage of EC was 10%, the mass percentage of FEC was 6%, and the balance was LiPF6.

[0159] The rest is the same as Example 1-1.

[0160] Example 3-2 to Example 3-6

[0161] Except for adjusting the relevant parameters according to Table 3, the rest is the same as Example 3-1.

[0162] Among them, the change of W1 is achieved by adjusting the mass percentage of the positive electrode film-forming additive in the positive electrode electrolyte during the preparation of the positive electrode electrolyte. When the mass percentage of the positive electrode film-forming additive in the positive electrode electrolyte changes, the mass percentage of the lithium salt in the positive electrode electrolyte changes accordingly, the mass percentage of the carbonate in the positive electrode electrolyte does not change much, and can be regarded as basically unchanged, and the mass ratio of EC and EMA in the carbonate remains unchanged; the change of W3 is achieved by adjusting the mass percentage of the negative electrode film-forming additive in the negative electrode electrolyte during the preparation of the negative electrode electrolyte. When the mass percentage of the negative electrode film-forming additive in the negative electrode electrolyte changes, the mass percentage of the lithium salt in the negative electrode electrolyte changes accordingly, the mass percentage of the carboxylate in the negative electrode electrolyte does not change much, and can be regarded as basically unchanged, and the mass ratio of EA and MF in the carboxylate remains unchanged. The change of W5 is achieved by adjusting the mass percentage of carbonate in the positive electrode electrolyte during the preparation of the positive electrode electrolyte. When the mass percentage of carbonate in the positive electrode electrolyte changes, the mass percentage of lithium salt in the positive electrode electrolyte changes accordingly. The mass ratio of EC and EMA in carbonate remains unchanged, and the mass percentage of positive electrode film-forming additive in the positive electrode electrolyte does not change much and can be regarded as basically unchanged; the change of W7 is achieved by adjusting the mass percentage of carboxylate in the negative electrode electrolyte during the preparation of the negative electrode electrolyte. When the mass percentage of carboxylate in the negative electrode electrolyte changes, the mass percentage of lithium salt in the negative electrode electrolyte changes accordingly. The mass ratio of EA and MF in carboxylate remains unchanged, and the mass percentage of EC and negative electrode film-forming additive in the negative electrode electrolyte remains unchanged.

[0163] Comparative Example 1-1

[0164] The process was the same as Example 1-1 except that the reaction temperature was adjusted in the step of "Preparation of Selective Lithium Ion Permeable Membrane" so that the air permeability of the selective lithium ion permeable membrane was as shown in Table 1.

[0165] Comparative Example 1-2

[0166] Except that the selective lithium ion permeable membrane is replaced by a separator, and the separator selected is Celgard 2325, the rest is the same as Example 1-1.

[0167] Comparative Examples 1-3 to 1-7

[0168] Except for adjusting the type of the positive electrode film-forming additive or the negative electrode film-forming additive according to Table 1, the rest is the same as Comparative Example 1-2.

[0169] Comparative Examples 1-8

[0170] Preparation of electrolyte: Under an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and an organic solvent (EC:PC:EA:DEC=1:1:1:1, mass ratio) were prepared to prepare electrolyte A.

[0171] Preparation of the positive electrode electrolyte: Malononitrile, a positive electrode film-forming additive, was added to Electrolyte A and mixed thoroughly to obtain the positive electrode electrolyte. Based on the mass of the positive electrode electrolyte, the mass percentage of malononitrile was 0.5%, the mass percentage of LiPF6 was 12.5%, and the balance was an organic solvent.

[0172] Preparation of the negative electrode electrolyte: Add the negative electrode film-forming additive FEC to electrolyte A and mix thoroughly to obtain the negative electrode electrolyte. Based on the mass of the negative electrode electrolyte, the mass percentage of FEC is 1%, the mass percentage of LiPF6 is 12.4%, and the balance is organic solvent.

[0173] The rest is the same as Comparative Example 1-2.

[0174] Comparative Example 2-1

[0175] Except that the selective lithium ion permeable membrane is the same as that of Comparative Example 1-1, the rest is the same as that of Example 2-1.

[0176] Comparative Example 2-2

[0177] Except that the selective lithium ion permeable membrane is the same as that of Comparative Example 1-2, the rest is the same as that of Example 2-1.

[0178] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0179] Table 1

[0180] From Examples 1-1, 1-21, and 1-22, and Comparative Examples 1-1 and 1-2, it can be seen that in the lithium-ion batteries of the examples, by selecting a selective lithium-ion permeable membrane with an air permeability of ≥4000s / 100mL and including a film-forming additive in the electrolyte, after formation, the mass percentage W1 of the positive electrode film-forming additive in the positive electrode electrolyte is greater than the mass percentage W2 of the positive electrode film-forming additive in the negative electrode electrolyte, and the mass percentage W3 of the negative electrode film-forming additive in the negative electrode electrolyte is greater than the mass percentage W4 of the negative electrode film-forming additive in the positive electrode electrolyte, indicating that the positive electrode electrolyte and the negative electrode electrolyte on the positive and negative electrode sides of the selective lithium-ion permeable membrane, respectively, are separated. The lithium-ion batteries of the examples have a larger maximum non-lithium precipitation rate at 25°C, a lower expansion rate at 85°C, and a higher number of cycles at 45°C, indicating that the dynamics and high-temperature performance of the lithium-ion batteries have been improved. The comparative lithium-ion battery, however, employed a selective lithium-ion permeable membrane with an air permeability of less than 4000s / 100mL or a conventional separator. After formation, the mass percentage (W1) of the positive electrode film-forming additive in the positive electrolyte failed to exceed the mass percentage (W2) of the positive electrode film-forming additive in the negative electrolyte, and the mass percentage (W3) of the negative electrode film-forming additive in the negative electrolyte failed to exceed the mass percentage (W4) of the negative electrode film-forming additive in the positive electrolyte, indicating that the positive and negative electrolytes on the positive and negative sides of the selective lithium-ion permeable membrane, respectively, failed to separate. The comparative lithium-ion battery exhibited a lower maximum non-lithium deposition rate at 25°C, a higher expansion rate at 85°C, and a lower number of cycles at 45°C, indicating poor kinetic and high-temperature performance. It will be understood by those skilled in the art that different electrolyte systems have a greater impact on the performance of lithium-ion batteries. Therefore, the performance comparison should be made under similar electrolyte system designs. If there are significant differences in the substance or content of the electrolyte itself, the performance cannot be compared on a year-on-year basis. For example, when comparing Example 1-1, Example 1-21 and Example 1-22, and Comparative Example 1-1 and Comparative Example 1-2, Example 1-11 and Example 1-12 have different electrolyte systems because the difference in the content of the positive electrode film-forming additive is greater than that between Example 1-1, Example 1-21 and Example 1-22, and Comparative Example 1-1 and Comparative Example 1-2. Therefore, the performance is not comparable.

[0181] When the positive electrolyte contains a positive film-forming additive and the negative electrolyte contains a negative film-forming additive, the ionic conductivity of the selective lithium-ion permeable membrane generally affects the kinetics and high-temperature performance of the lithium-ion battery. As shown in Examples 1-1 to 1-4, using a selective lithium-ion permeable membrane with an ionic conductivity within the range of this application demonstrates a lower maximum non-lithium deposition rate at 25°C, a higher expansion ratio at 85°C, and a lower number of cycles at 45°C, indicating that the lithium-ion battery has good kinetics and high-temperature performance.

[0182] The types of positive and negative electrode film-forming additives generally affect the kinetics and high-temperature performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-6, and 1-10, selective lithium-ion permeable membranes using positive and negative electrode film-forming additives within the scope of this application exhibit a lower maximum non-lithium deposition rate at 25°C, a higher expansion rate at 85°C, and a lower number of cycles at 45°C, indicating that lithium-ion batteries have good kinetics and high-temperature performance.

[0183] After lithium-ion batteries are formed, the mass percentage of the positive electrode film-forming additive in the positive electrode electrolyte and the mass percentage of the negative electrode film-forming additive in the negative electrode electrolyte generally affect the kinetics and high-temperature performance of the lithium-ion battery. As can be seen from Examples 1-1, 1-11, and 1-20, a selective lithium-ion permeable membrane having a mass percentage of the positive electrode film-forming additive in the positive electrode electrolyte and a mass percentage of the negative electrode film-forming additive in the negative electrode electrolyte within the ranges of this application exhibits a smaller maximum non-lithium deposition rate at 25°C, a higher expansion rate at 85°C, and a lower number of cycles at 45°C, indicating that the lithium-ion battery has good kinetics and high-temperature performance.

[0184] Table 2

[0185] As can be seen from Examples 2-1, 2-13, 2-14, Comparative Examples 2-1, and 2-2, in the lithium-ion batteries of the Examples, when a selective lithium-ion permeable membrane with an air permeability of ≥4000 s / 100 mL is selected and the electrolyte includes carbonate and carboxylate, after formation, the mass percentage of carbonate in the positive electrolyte (W5) is greater than the mass percentage of carbonate in the negative electrolyte (W6), and the mass percentage of carboxylate in the negative electrolyte (W7) is greater than the mass percentage of carboxylate in the positive electrolyte (W8), indicating that the positive and negative electrolytes on the positive and negative sides of the selective lithium-ion permeable membrane, respectively, are separated. The lithium-ion batteries of the Examples have a greater maximum non-lithium deposition rate at 25°C, a lower expansion rate at 85°C, and a greater number of cycles at 45°C, indicating that the dynamics and high-temperature performance of the lithium-ion batteries have been improved. In contrast, the lithium-ion batteries in the comparative examples employed a selective lithium-ion permeable membrane or conventional separator with an air permeability of less than 4000 s / 100 mL. After formation, the mass percentage of carbonate in the positive electrolyte (W5) failed to exceed the mass percentage of carbonate in the negative electrolyte (W6), and the mass percentage of carboxylate in the negative electrolyte (W7) failed to exceed the mass percentage of carboxylate in the positive electrolyte (W8), indicating that the positive and negative electrolytes on the positive and negative sides of the selective lithium-ion permeable membrane, respectively, failed to separate. While the positive and negative electrolytes on the positive and negative sides of Comparative Examples 2-1 and 2-2 ultimately achieved homogeneity, due to the different air permeabilities of the corresponding selective lithium-ion permeable membranes / conventional separators, the time required to achieve homogeneity varied, with Comparative Example 2-1 taking longer than Comparative Example 2-2. The comparative lithium-ion battery has a smaller maximum non-lithiation rate at 25°C, a higher expansion rate at 85°C, and fewer cycles at 45°C, indicating that the lithium-ion battery has poor kinetics and high-temperature performance.

[0186] When the positive electrolyte contains carbonates and the negative electrolyte contains carboxylates, the ionic conductivity of the selective lithium-ion permeable membrane typically affects the kinetics and high-temperature performance of the lithium-ion battery. Examples 2-1 to 2-4 show that using a selective lithium-ion permeable membrane with an ionic conductivity within the range of this application results in a smaller maximum non-lithium deposition rate at 25°C, a higher expansion rate at 85°C, and a lower number of cycles at 45°C, indicating that the lithium-ion battery has good kinetics and high-temperature performance.

[0187] After formation, the mass percentage of carbonate in the positive electrolyte and the mass percentage of carboxylate in the negative electrolyte typically affect the kinetics and high-temperature performance of lithium-ion batteries. Examples 2-1, 2-5, and 2-7 show that using a selective lithium-ion permeable membrane with a carbonate mass percentage in the positive electrolyte and a carboxylate mass percentage in the negative electrolyte within the ranges of this application results in a smaller maximum non-lithium deposition rate at 25°C, a higher expansion rate at 85°C, and a lower number of cycles at 45°C, indicating that the lithium-ion battery exhibits good kinetics and high-temperature performance.

[0188] The types of carbonate and carboxylate esters generally affect the dynamics and high-temperature performance of lithium-ion batteries. As can be seen from Examples 2-1, 2-8, and 2-12, selective lithium-ion permeable membranes using positive and negative electrode film-forming additives within the scope of this application exhibit a low maximum non-lithium deposition rate at 25°C, a high expansion rate at 85°C, and a low number of cycles at 45°C, demonstrating good dynamics and high-temperature performance for lithium-ion batteries.

[0189] Table 3

[0190] It can be seen from Examples 3-1 to 3-6 that the lithium-ion batteries in the examples, by selecting a selective lithium ion permeable membrane with a permeability of ≥4000s / 100mL and the electrolyte including a film-forming additive, a carbonate and a carboxylate, after the lithium-ion battery is formed, the mass percentage W1 of the positive electrode film-forming additive in the positive electrode electrolyte is greater than the mass percentage W2 of the positive electrode film-forming additive in the negative electrode electrolyte, and the mass percentage W3 of the negative electrode film-forming additive in the negative electrode electrolyte is greater than the mass percentage W4 of the negative electrode film-forming additive in the positive electrode electrolyte, the mass percentage W5 of the carbonate in the positive electrode electrolyte is greater than the mass percentage W6 of the carbonate in the negative electrode electrolyte, and the mass percentage W7 of the carboxylate in the negative electrode electrolyte is greater than the mass percentage W8 of the carboxylate in the positive electrode electrolyte, indicating that the positive electrode electrolyte and the negative electrode electrolyte on the positive electrode side and the negative electrode side on both sides of the selective lithium ion permeable membrane, respectively, are separated. The lithium-ion battery of the embodiment has a larger maximum non-lithium precipitation rate at 25°C, a lower expansion rate at 85°C, and a larger number of cycles at 45°C, indicating that the dynamics and high-temperature performance of the lithium-ion battery are improved.

[0191] After formation, the mass percentages of the positive electrode film-forming additive and carbonate in the positive electrode electrolyte, and the mass percentages of the negative electrode film-forming additive and carboxylate in the negative electrode electrolyte, typically affect the kinetics and high-temperature performance of the lithium-ion battery. Examples 3-1 to 3-6 show that selective lithium-ion permeable membranes with mass percentages of the positive electrode film-forming additive and carbonate in the positive electrode electrolyte, and mass percentages of the negative electrode film-forming additive and carboxylate in the negative electrode electrolyte, within the ranges of this application exhibit a smaller maximum non-lithium deposition rate at 25°C, a higher expansion rate at 85°C, and a lower number of cycles at 45°C, indicating that the lithium-ion battery exhibits good kinetics and high-temperature performance.

[0192] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0193] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0194] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device, comprising an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a selective lithium ion permeable membrane. Independent positive and negative sides are formed on both sides of the selective lithium ion permeable membrane. The air permeability of the selective lithium ion permeable membrane is ≥4000 s / 100 mL. The electrolyte is divided into a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode sheet and the positive electrode electrolyte are accommodated on the positive side, and the negative electrode sheet and the negative electrode electrolyte are accommodated on the negative side; The positive electrode electrolyte is different from the negative electrode electrolyte.

2. The electrochemical device according to claim 1, wherein, The electrolyte includes a film-forming additive, and the film-forming additive includes at least one positive electrode film-forming additive and at least one negative electrode film-forming additive; After the electrochemical device is formed, the mass percentage content of the positive electrode film-forming additive in the positive electrode electrolyte is W1, and the mass percentage content of the positive electrode film-forming additive in the negative electrode electrolyte is W2. W1 is greater than W2; And the mass percentage content of the negative electrode film-forming additive in the negative electrode electrolyte is W3, and the mass percentage content of the negative electrode film-forming additive in the positive electrode electrolyte is W4. W3 is greater than W4.

3. The electrochemical device according to claim 2, wherein The positive electrode film-forming additive includes at least one of acetonitrile, propionitrile, butyronitrile, or valeronitrile, and 0.1% ≤ W1 ≤ 10%.

4. The electrochemical device according to claim 2, wherein, The negative electrode film-forming additive includes at least one of fluoroethylene carbonate, vinylene carbonate, ethylene vinylene carbonate, butene sulfite, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sulfonic acid lactone, ethylene sulfate, propylene sulfate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium bis(oxalato)borate, and 0.1% ≤ W3 ≤ 10%.

5. The electrochemical device according to claim 4, wherein, The negative electrode film-forming additive includes any one of fluoroethylene carbonate, vinylene carbonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium bis(oxalato)borate.

6. The electrochemical device according to claim 1, wherein, The electrolyte includes a carbonate and a carboxylate; After the electrochemical device is formed, the mass percentage content of the carbonate in the positive electrode electrolyte is W5, and the mass percentage content of the carbonate in the negative electrode electrolyte is W6. W5 is greater than W6; and the mass percentage content of the carboxylate in the negative electrode electrolyte is W7, and the mass percentage content of the carboxylate in the positive electrode electrolyte is W8. W7 is greater than W8.

7. The electrochemical device according to claim 6, wherein, The carbonate includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or methyl propyl carbonate; The carboxylate includes at least one of γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, methyl butyrate, ethyl butyrate, n-propyl propionate, or ethyl propionate; And, 50% ≤ W5 ≤ 80%, 50% ≤ W7 ≤ 80%.

8. The electrochemical device according to claim 1, wherein, The ionic conductivity of the selective lithium ion permeable membrane is greater than or equal to 10 -2 mS / cm.

9. The electrochemical device according to claim 8, wherein, The ionic conductivity of the selective lithium ion permeable membrane is 0.1 mS / cm to 5 mS / cm.

10. The electrochemical device according to claim 1, wherein, The structure of the electrode assembly includes any one of a single-layer laminated structure, a multi-layer laminated structure, or a wound structure.

11. An electronic device, wherein, The electronic device includes the electrochemical device according to any one of claims 1 to 10.

12. A method for preparing an electrochemical device, comprising the following steps: (1) Stacking a positive electrode sheet, a selective lithium ion permeable membrane, and a negative electrode sheet in sequence to form an electrode assembly with a single-layer laminated structure, where independent positive and negative sides are formed on both sides of the selective lithium ion permeable membrane; or, (1’) Stacking a positive electrode sheet, a selective lithium ion permeable membrane, a negative electrode sheet, and the selective lithium ion permeable membrane in sequence as a structural unit, and then repeatedly stacking multiple said structural units to form an electrode assembly with a multi-layer laminated structure, where independent positive and negative sides are formed on both sides of the selective lithium ion permeable membrane; or, (1”) Stacking a positive electrode sheet, a selective lithium ion permeable membrane, and a negative electrode sheet in sequence, where the selective lithium ion permeable membrane forms a cavity with an opening on one side and houses the positive electrode sheet within the cavity, and the negative electrode sheet is wound around the outside of the cavity to form a wound-structured electrode assembly, where independent positive and negative sides are respectively formed on both sides of the selective lithium ion permeable membrane; or, (1”’) Stacking a positive electrode sheet, a selective lithium ion permeable membrane, and a negative electrode sheet in sequence, where the selective lithium ion permeable membrane forms a cavity with an opening on one side and houses the negative electrode sheet within the cavity, and the positive electrode sheet is wound around the outside of the cavity to form a wound-structured electrode assembly, where independent negative and positive sides are respectively formed on both sides of the selective lithium ion permeable membrane; (2) Injecting a positive electrode electrolyte into the positive side and a negative electrode electrolyte into the negative side, and obtaining the electrochemical device according to any one of claims 1 to 10 after encapsulating with an outer package.

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