Electrode plate, preparation method thereof and lithium ion battery

Abstract

The invention provides an electrode plate, a preparation method thereof and a lithium ion battery, and belongs to the technical field of battery materials. The electrode pole piece comprises a current collector and an active layer arranged on the surface of at least one side of the current collector, materials of the active layer comprise an active material, a conductive agent, a fibration binder and a pore forming agent, and the pore forming agent is at least partially dispersed in micropores of the fibration binder; and the pore forming agent comprises LiFSi and / or LiPO2F2. The introduced pore-forming agent can occupy space in the active layer, at least part of the pore-forming agent can enter micropores of the fibration binder, entering of the conductive agent is reduced, more conductive agent makes contact with the active particles, when the electrode plate is wound into a roll core and then injected, the pore-forming agent can be dissolved in electrolyte, micropores are formed in the original positions, and the pore-forming agent can be dissolved in the electrolyte. The porosity of the electrode plate is increased, the infiltration of electrolyte and the transmission of lithium ions are facilitated, and the cycle and fast charge performance of the battery can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to an electrode plate and a preparation method thereof, and a lithium ion battery. Background Art

[0002] At present, lithium nickel manganese oxide is the most promising alternative to lithium iron phosphate for electric vehicles. As an electric vehicle product, the battery needs to have excellent fast charging performance. For the lithium nickel manganese oxide graphite system, it is necessary not only to optimize the positive and negative electrode systems, but also to develop targeted fast-charging electrolytes, which must not only meet the high voltage requirements of lithium nickel manganese oxide, but also have good lithium ion transmission and desolvation capabilities. However, the existing pole piece has a low porosity, which is not conducive to the transmission of lithium ions during the charging and discharging process, and is prone to cause large polarization, which is not conducive to the cycle performance of the battery. In addition, the use of dry electrodes to manufacture pole pieces will make it easy for the conductive agent to enter the fibrous binder pores, so that the amount of conductive agent in contact with the active material is less, which is not conducive to the transmission of electrons.

[0003] Therefore, how to reduce the conductive agent from entering the pores of the fiberized binder, allow more conductive agent to contact the active particles, and maximize the porosity of the electrode, increase the transfer rate of lithium ions, and improve the battery cycle performance is a technical problem that needs to be solved urgently. Summary of the invention

[0004] In view of the deficiencies of the prior art, the purpose of the present invention is to provide an electrode plate and a preparation method thereof and a lithium-ion battery. The present invention introduces LiFSi and / or LiPO2F2 as pore formers in the active layer of the electrode plate, and uses soluble solid pore formers to occupy space in the active layer in advance, and at least part of the pore formers can enter the micropores of the fiberized binder, which is conducive to reducing the entry of the conductive agent and allowing more conductive agents to contact the active particles. When the electrode plate is wound into a winding core and then injected with liquid, the pore former dissolves in the electrolyte, thereby forming micropores at the original position, maximizing the porosity of the electrode plate, facilitating the infiltration of the electrolyte and the transmission of lithium ions, and significantly improving the cycle performance and fast charging performance of the lithium-ion battery.

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

[0006] In a first aspect, the present invention provides an electrode plate, comprising a current collector and an active layer arranged on at least one side of the current collector, wherein the material of the active layer comprises an active material, a conductive agent, a fiberized binder and a pore-forming agent, and the pore-forming agent is at least partially dispersed in the micropores of the fiberized binder.

[0007] The pore former includes LiFSi and / or LiPO2F2.

[0008] The present invention introduces LiFSi and / or LiPO2F2 as pore formers in the active layer of the electrode plate, and uses soluble solid pore formers to occupy space in the active layer in advance, and at least part of the pore formers can enter the micropores of the fiberized binder, which is beneficial to reduce the conductive agent from entering the micropores of the fiberized binder, so that more conductive agents can contact the active particles; in addition, the pore formers can also form pores between the positive electrode particles, the conductive agent and the binder. When the electrode plate is wound into a winding core and then injected with liquid, the pore former dissolves in the electrolyte, thereby forming micropores at the original position, maximizing the porosity of the electrode plate, facilitating the infiltration of the electrolyte and the transmission of lithium ions, and significantly improving the cycle performance and fast charging performance of the lithium-ion battery.

[0009] In the present invention, LiFSi and / or LiPO2F2 are used as pore formers to form pores in the electrode sheet and can occupy the pores of the fiberized binder, thereby reducing the conductive agent from entering the pores of the fiberized binder and allowing more conductive agent to contact the active material.

[0010] Preferably, after the electrode plate is soaked in electrolyte, when the electrode plate is a positive electrode plate, the porosity of the positive electrode plate is 46-53%, for example, it may be 46%, 47%, 48%, 49%, 50%, 51%, 52% or 53%.

[0011] Preferably, after the electrode plate is soaked in electrolyte, when the electrode plate is a negative electrode plate, the porosity of the negative electrode plate is 42-48%, for example, it may be 42%, 43%, 44%, 45%, 46%, 47% or 48%.

[0012] Preferably, after the electrode plate is prepared into a lithium-ion battery, when the electrode plate is a positive electrode plate, the porosity of the positive electrode plate is 46-53%, for example, it can be 46%, 47%, 48%, 49%, 50%, 51%, 52% or 53%.

[0013] Preferably, after the electrode plate is prepared into a lithium-ion battery, when the electrode plate is a negative electrode plate, the porosity of the negative electrode plate is 42-48%, for example, it may be 42%, 43%, 44%, 45%, 46%, 47% or 48%.

[0014] Preferably, the pore former includes LiFSi and LiPO2F2, and the mass ratio of LiFSi to LiPO2F2 is (1-5):(5-1), and the mass ratio of the two can be any ratio that satisfies this range. For example, relatively, the mass of LiFSi can be any ratio within the range of 1-5, such as 1, 2, 3, 4 or 5, and the mass of LiPO2F2 can be any ratio within the range of 5-1, such as 1, 2, 3, 4 or 5, etc.

[0015] In the present invention, LiFSi and LiPO2F2 with a mass ratio of (1-5): (5-1) are used as pore-forming agents. LiFSi and LiPO2F2 occupy space during mixing, and dissolve to leave micropores after injection, which helps to keep the pole piece at a high porosity, and can make full use of the role of LiFSi and LiPO2F2 as electrolyte additives to improve the fast charging performance of the battery. Using LiFSi as a pore-forming agent, LiFSi is dissolved in the electrolyte, which can reduce the impedance of the battery and improve the fast charging performance of the battery. Using LiPO2F2 as a pore-forming agent, LiPO2F2 is dissolved in the electrolyte, and a passivation film can be formed on the aluminum foil, reducing the corrosion of LiFSi in the electrolyte to the aluminum foil. An appropriate amount of LiFSi and LiPO2F2 are used together as pore-forming agents, which can take into account avoiding corrosion to the aluminum foil and reducing the impedance of the battery and improving the fast charging performance of the battery.

[0016] Preferably, the electrode plate is a positive electrode plate, in which the active material includes any one of lithium nickel manganese oxide, lithium cobalt oxide or a ternary positive electrode material.

[0017] Preferably, in the positive electrode plate, the conductive agent includes a combination of any two or at least three of single-walled carbon nanotubes, conductive carbon black, conductive graphite or graphene.

[0018] Preferably, in the positive electrode plate, the fiberized binder includes any one of fiberized tetrafluoroethylene (PTFE), fiberized styrene-butadiene rubber (SBR), fiberized polyimide (PAN), fiberized nitrile rubber (NBR), fiberized polyacrylic acid (PAA), fiberized polyvinyl alcohol (PVA), fiberized polyethylene oxide (PEO) or fiberized alginate (Alginate) or a combination of at least two thereof.

[0019] Preferably, in the positive electrode sheet, the mass ratio of the total mass of the active material, the conductive agent and the fibrous binder to the pore-forming agent is 100:(1-3), for example, it can be 100:1, 100:1.2, 100:1.4, 100:1.6, 100:1.8, 100:2, 100:2.5 or 100:3, etc. Further, in the positive electrode sheet, the mass ratio of the total mass of the active material, the conductive agent and the fibrous binder to the pore-forming agent is 100:1.5.

[0020] Among them, exemplarily, the mass ratio of the active material, the conductive agent and the fiberized binder can be, for example, (94-96):(1-3):(1.5-3), the selection range of the active material "94-96" can be, for example, 94, 94.5, 95, 95.5 or 96, etc., the selection range of the conductive agent "1-3" can be, for example, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.5 or 3, etc., and the selection range of the fiberized binder "1.5-3" can be, for example, 1.5, 1.75, 2, 2.25, 2.5 or 3, etc.

[0021] In the present invention, a suitable amount of pore-forming agent is used in the positive electrode plate so that it can occupy a suitable space during mixing and dissolve to obtain sufficient micropores after injection, which helps to maintain a high porosity of the plate, enhance lithium ion transmission, improve the charge and discharge performance of the battery, and avoid corrosion of the aluminum foil causing a decrease in battery performance.

[0022] Preferably, in the positive electrode sheet, the single-sided thickness of the active layer is 50-200 μm, for example, 50 μm, 100 μm, 150 μm or 200 μm.

[0023] In the present invention, a suitable single-side thickness of the active layer can effectively improve battery performance, improve the energy density of the battery and improve the charge and discharge performance of the battery.

[0024] Preferably, the electrode plate is a negative electrode plate, in which the active material includes any one of graphite, mesophase carbon microbeads, hard carbon, soft carbon, silicon oxygen or silicon carbon.

[0025] Preferably, in the negative electrode plate, the conductive agent includes conductive carbon black and / or conductive graphite.

[0026] Preferably, in the negative electrode plate, the fiberized binder includes any one of fiberized tetrafluoroethylene, fiberized styrene-butadiene rubber, fiberized polyimide, fiberized nitrile rubber, fiberized polyacrylic acid, fiberized polyvinyl alcohol, fiberized polyethylene oxide or fiberized alginate, or a combination of at least two thereof.

[0027] Preferably, in the negative electrode sheet, the mass ratio of the total mass of the active material, the conductive agent and the fibrous binder to the pore-forming agent is 100:(1-3), for example, it can be 100:1, 100:1.2, 100:1.4, 100:1.6, 100:1.8, 100:2, 100:2.5 or 100:3, etc. Further, in the negative electrode sheet, the mass ratio of the active material, the conductive agent and the fibrous binder to the pore-forming agent is 100:1.5.

[0028] Among them, exemplarily, the mass ratio of the active material, the conductive agent and the fiberized binder can be, for example, (95-97):(1-2):(2-3), the selection range of the active material "95-97" can be, for example, 95, 95.5, 96, 96.5 or 97, etc., the selection range of the conductive agent "1-2" can be, for example, 1, 1.2, 1.4, 1.6, 1.8 or 2, etc., and the selection range of the fiberized binder "2-3" can be, for example, 2, 2.5 or 3, etc.

[0029] In the present invention, a suitable amount of pore-forming agent is used in the negative electrode plate so that it can occupy a suitable space during mixing and dissolve to obtain sufficient micropores after injection, which helps to maintain a high porosity of the negative electrode plate, enhance lithium ion transmission, improve the charge and discharge performance of the battery, and avoid corrosion of aluminum foil leading to a decrease in battery performance.

[0030] Preferably, in the negative electrode plate, the single-sided thickness of the active layer is 40-200 μm, for example, 40 μm, 50 μm, 100 μm, 150 μm or 200 μm.

[0031] In the present invention, a suitable single-side thickness of the active layer can effectively improve battery performance, improve the energy density of the battery and improve the charge and discharge performance of the battery.

[0032] In a second aspect, the present invention provides a method for preparing the electrode sheet according to the first aspect, the preparation method comprising the following steps:

[0033] The active material, the conductive agent, the binder and the pore-forming agent are mixed to obtain a mixed dry material, and then the mixed dry material is subjected to a fiberization treatment to obtain a fiberized dry material.

[0034] The fiberized dry material is compounded onto a current collector to obtain the electrode plate.

[0035] Wherein, the pore former includes LiFSi (lithium bis(fluorosulfonyl)imide) and / or LiPO2F2 (lithium difluorophosphate).

[0036] In the present invention, a method combining a dry process and a pore former is used to manufacture an electrode plate. The solid lithium salt pore former originally added to the electrolyte is added during the active material mixing process, which can not only form pores, increase the porosity of the electrode plate, and improve the transmission of lithium ions, but also occupy the micropores of the fibrous binder, which is conducive to more conductive agents contacting the active particles and increasing the electronic conductivity of the plate. In particular, when using a dry process to prepare a negative electrode plate, the use of aqueous solvents and dispersants can be avoided, which is not only conducive to increasing the proportion of negative electrode active materials, but also allows the easily hydrolyzed lithium salts LiPO2F2 and / or LiFSi to be used on the negative electrode, expanding the application range of lithium salt-type pore formers.

[0037] Preferably, the mixing method is dry mixing.

[0038] Preferably, the fiberization process is carried out in an internal mixer, and the rotation speed of the internal mixer is 20-60 rpm, for example, 20 rpm, 30 rpm, 40 rpm, 50 rpm or 60 rpm.

[0039] Preferably, the fibrosis treatment time is 0.5-1.5 h, for example, 0.5 h, 1 h or 1.5 h.

[0040] In the present invention, the appropriate fiberization treatment time helps the pore-forming agent to enter the micropores of the fiberized binder, which is beneficial for more conductive agents to contact with active particles and increase the electronic conductivity of the electrode.

[0041] Preferably, before the fiberized dry material is compounded onto the current collector, the fiberized dry material is first subjected to a hot pressing and thinning treatment to obtain a target thickness.

[0042] Preferably, the preparation method comprises the following steps:

[0043] (1) The active material and the conductive agent are premixed for 5-15 minutes (for example, 5 minutes, 10 minutes or 15 minutes, etc.), and then the fiberizing binder and the pore-forming agent are added and stirred for 20-40 minutes (for example, 20 minutes, 30 minutes or 40 minutes, etc.) to obtain a mixed dry material; wherein the mass ratio of the total mass of the active material, the conductive agent and the fiberizing binder to the mass ratio of the pore-forming agent is 100:(1-3).

[0044] Wherein, the pore former comprises LiFSi and LiPO2F2 in a mass ratio of (1-5):(5-1).

[0045] (2) Adding the mixed dry material into an internal mixer for fiberization treatment, and controlling the rotation speed to be 20-60 rpm for 0.5-1.5 h to obtain a fiberized dry material, and then using a hot press to perform a hot pressing thinning treatment on the fiberized dry material at a hot pressing temperature of 60-100° C. (for example, 60° C., 70° C., 80° C., 90° C. or 100° C., etc.) to obtain a target thickness.

[0046] (3) The dry material treated in step (2) is compounded onto the current collector foil by a hot press, the hot pressing temperature is 150-250°C (for example, it can be 150°C, 175°C, 200°C, 225°C or 250°C, etc.), and the roller speed is 1-3m / min (for example, it can be 1m / min, 1.5m / min, 2m / min, 2.5m / min or 3m / min, etc.), to obtain the electrode sheet.

[0047] In a third aspect, the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet and / or the negative electrode sheet is the electrode sheet described in the first aspect.

[0048] Preferably, the porosity of the positive electrode plate is 46-53%, for example, it may be 46%, 47%, 48%, 49%, 50%, 51%, 52% or 53%.

[0049] It should be noted that the porosity of conventional positive electrode sheets is between 40-45%. The present invention improves the porosity of the positive electrode sheets by introducing a pore-forming agent, which is beneficial to the transmission of lithium ions during the charge and discharge process of the battery, avoids battery polarization, and improves the cycle performance of the battery.

[0050] Preferably, the porosity of the negative electrode plate is 42-48%, for example, it may be 42%, 43%, 44%, 45%, 46%, 47% or 48%.

[0051] In the present invention, the porosity of the conventional negative electrode sheet is between 36-41%. The present invention improves the porosity of the negative electrode sheet by introducing a pore-forming agent, which is beneficial to the transmission of lithium ions during the charge and discharge process of the battery, avoids battery polarization, and improves the cycle performance of the battery.

[0052] Preferably, the solvent in the electrolyte includes a combination of at least three of FEC (fluoroethylene carbonate), DMC (dimethyl carbonate), DEC (diethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate).

[0053] Preferably, the solutes in the electrolyte include TAP (triallyl phosphate), TMSP (tris(trimethylsilyl) phosphate), LiPF6, LiFSi and LiPO2F2.

[0054] In the present invention, TAP is used to form a dense and stable surface film on the surface of the positive electrode, reducing the oxidative decomposition of the solvent, TMSP is used to remove water and acid in the electrolyte, LiFSi is used to reduce the desolvation impedance of the battery and improve the fast charging performance of the battery, and LiPO2F2 is used to form a passivation film on the aluminum foil, which can reduce the corrosion effect of LiFSi on the aluminum foil.

[0055] The electrolyte of the lithium-ion battery provided by the present invention contains LiFSi and LiPO2F2, which are not taken away during the battery preparation process. At the same time, LiFSi and LiPO2F2 can be dissolved in the electrolyte after injection, so that the holes formed in the positive electrode sheet are beneficial to the transportation of lithium ions in the electrolyte.

[0056] Preferably, in the electrolyte, the mass fraction of TAP is 0.5-2%, for example, it can be 0.5%, 1%, 1.5% or 2%, the mass fraction of TMSP is 0.5-2%, for example, it can be 0.5%, 1%, 1.5% or 2%, the mass fraction of LiFSi is 2-4%, for example, it can be 2%, 3% or 4%, the mass fraction of LiPO2F2 is 1.5-3%, for example, it can be 1.5%, 2%, 2.5% or 3%, and the mass fraction of LiPF6 is 12-13%, for example, it can be 12%, 12.5% ​​or 13%, etc.

[0057] In the present invention, the electrolyte components within the above range are used in combination with each other, which can significantly improve the cycle performance and fast charging performance of the lithium-ion battery.

[0058] It should be noted that the structure of the lithium-ion battery also includes a diaphragm structure, and the type of diaphragm is selected by conventional technical means, such as PE (polyethylene) film.

[0059] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] (1) The present invention introduces LiFSi and / or LiPO2F2 as pore-forming agents into the active layer of the electrode plate. The two work together to occupy space in the active layer, and part of the pore-forming agent can enter the micropores of the fiberized binder, reducing the conductive agent from entering the micropores of the fiberized binder, so that more conductive agent can contact the active particles. When the electrode plate is wound into a core and injected with liquid, LiFSi and / or LiPO2F2 dissolve in the electrolyte, and micropores are formed at the original position, thereby increasing the porosity of the electrode plate, facilitating the infiltration of the electrolyte and the transmission of lithium ions, and significantly improving the cycle performance and fast charging performance of the lithium-ion battery.

[0062] (2) The lithium-ion battery made of the electrode plate provided by the present invention can have good performance in the working range of 3.4-4.9V. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0064] Example 1

[0065] This embodiment provides a positive electrode sheet and a negative electrode sheet.

[0066] Among them, the positive electrode plate includes a current collector aluminum foil and an active layer arranged on the surface of one side of the current collector aluminum foil. The single-side thickness of the active layer is 180μm. The materials of the active layer include active materials, conductive agents, fiberized binders and pore-forming agents. The pore-forming agent is at least partially dispersed in the micropores of the fiberized binder; the pore-forming agent is a combination of LiFSi and LiPO2F2 in a mass ratio of 1:1; the fiberized binder is fiberized polytetrafluoroethylene; the active material is lithium nickel manganese oxide, and the conductive agent includes single-walled carbon nanotubes and conductive carbon black; the mass ratio of active materials, conductive agents, fiberized binders and pore-forming agents is 95.95:1.55:2.5:1.5; after the positive electrode plate is soaked in the electrolyte for 10 minutes, it is taken out and the porosity of the positive electrode plate obtained by mercury injection testing is 48%.

[0067] Among them, the negative electrode plate includes a current collector copper foil and an active layer arranged on one side surface of the current collector copper foil. The single-side thickness of the active layer is 150μm. The materials of the active layer include active materials, conductive agents, fiberized binders and pore-forming agents. The pore-forming agent is dispersed in the micropores of the fiberized binder; the pore-forming agent is a combination of LiFSi and LiPO2F2 in a mass ratio of 1:1; the fiberized binder is fiberized polytetrafluoroethylene; the active material is graphite, and the conductive agent is conductive carbon black; the mass ratio of the active material, the conductive agent, the fiberized binder and the pore-forming agent is 96:1.5:2.5:1.5; after the negative electrode plate is soaked in the electrolyte for 10 minutes, it is taken out and the porosity of the negative electrode plate is 45% tested by mercury injection method.

[0068] This embodiment also provides a method for preparing the positive electrode sheet and the negative electrode sheet, and the method for preparing the positive electrode sheet comprises the following steps:

[0069] (1) The total mass of lithium nickel manganese oxide, single-walled carbon nanotubes, conductive carbon black and fiberized polytetrafluoroethylene is 100%. Lithium nickel manganese oxide (95.95% by mass) is placed in a double planetary stirring tank, and single-walled carbon nanotubes (0.05% by mass) and conductive carbon black (1.5% by mass) are added. The mixture is stirred and premixed for 10 minutes. Then, fiberized polytetrafluoroethylene (2.5% by mass) and LiFSi (0.75% by mass and LiPO2F2) (0.75% by mass of the total mass of the powder (including lithium nickel manganese oxide, single-walled carbon nanotubes, conductive carbon black and fiberized polytetrafluoroethylene)) are added. The mixture is stirred and premixed for 30 minutes to ensure that the powder is evenly mixed to obtain a mixed dry material.

[0070] (2) The mixed dry material is added to an internal mixer for fiberization treatment, and the rotation speed is controlled to be 50 rpm for 1 hour to obtain a fiberized dry material. The fiberized dry material is then subjected to hot pressing and thinning treatment using a hot press. The hot pressing temperature is 80°C and the speed ratio of the two rollers is 1.07:1. After three rounds of hot pressing and thinning, the target thickness is obtained.

[0071] (3) The dry material after thinning in step (2) is compounded onto the current collector aluminum foil by using a hot press, the hot pressing temperature is 200° C., and the roller speed is 2 m / min, to obtain the electrode plate.

[0072] The method for preparing the negative electrode sheet comprises the following steps:

[0073] (a) The total mass of graphite, conductive carbon black and fiberized polytetrafluoroethylene is 100%, and 95% of the graphite is placed in a double planetary stirring tank. 1.25% of the conductive carbon black is added, and the mixture is stirred and premixed for 10 minutes. Then, 2.25% of the fiberized polytetrafluoroethylene is added, and 0.75% of LiFSi and 0.75% of LiPO2F2, which account for the total mass of the powder (including graphite, conductive carbon black and fiberized polytetrafluoroethylene), are added, and the mixture is stirred and mixed for 30 minutes to make the powder uniformly stirred to obtain a mixed dry material.

[0074] (b) The mixed dry material is added into an internal mixer for fiberization treatment, and the rotation speed is controlled to be 50 rpm for 1 hour to obtain a fiberized dry material, and then a hot press is used to perform hot pressing and thinning treatment on the fiberized dry material. The hot pressing temperature is 70° C. and the speed ratio of the two rollers is 1.07:1. After 3 rounds of hot pressing and thinning, the target thickness is obtained.

[0075] (c) The dry material treated in step (2) is compounded onto the current collector copper foil using a hot press at a hot pressing temperature of 180° C. and a roller speed of 2 m / min to obtain an electrode sheet.

[0076] This embodiment also provides a lithium-ion battery, comprising the positive electrode plate as described above, the negative electrode plate as described above, and an electrolyte.

[0077] The solvents of the electrolyte include FEC, DMC, DEC and EC, among which the mass fraction of FEC is 15.82%, the mass fraction of DMC is 27.9%, the mass fraction of DEC is 20.47%, and the mass fraction of EC is 15.87%.

[0078] The solutes in the electrolyte include TAP, TMSP, LiPF6, LiFSi and LiPO2F2, among which the mass fraction of TAP is 1.66%, the mass fraction of TMSP is 0.53%, the mass fraction of LiFSi is 2.79%, the mass fraction of LiPO2F2 is 2.43%, and the mass fraction of LiPF6 is 12.53%.

[0079] This embodiment also provides a method for preparing the above lithium ion battery, comprising the following steps:

[0080] (i) Providing a positive electrode sheet and a negative electrode sheet by using the above-mentioned method for preparing a positive electrode sheet and the above-mentioned method for preparing a negative electrode sheet.

[0081] (ii) Preparation of electrolyte: The total mass of the electrolyte is taken as 100%, and the mass fractions of LiFSi and LiPO2F2 are calculated on the assumption that all LiFSi and LiPO2F2 in the positive electrode sheet and the negative electrode sheet can be dissolved in the electrolyte. The mass fractions of LiFSi and LiPO2F2 are calculated as 2.5% and 2.5%, respectively. FEC, DMC, DEC and EC are mixed at mass fractions of 16%, 28%, 20% and 16%, respectively, to obtain a mixed solvent. LiPF6 is then added to the mixed solvent with a mass fraction of 13%. The mixture is stirred while being added. Then, TAP with a mass fraction of 1.5% and TMSP with a mass fraction of 0.5% are added. The mixture is stirred for 3 h to obtain an electrolyte.

[0082] (iii) The positive electrode sheet, the negative electrode sheet and the separator (the separator is a PE film with Al2O3 and PVDF coated on its surface) are formed into a core, and then the electrolyte is injected. The amount of electrolyte added is 4g / Ah. After the injection, it is left to stand for 16 hours, and then the formation, degassing and capacity separation are carried out to obtain a lithium-ion battery.

[0083] It should be noted that in lithium-ion batteries, the test methods for the porosity of the positive electrode sheet and the porosity of the negative electrode sheet are as follows:

[0084] 1. Discharge the battery to an empty state, disassemble the battery in a drying room, and separate the positive and negative electrodes.

[0085] 2. Soak the disassembled positive electrode or negative electrode in DMC solvent at room temperature for 3 times, each time for 10 minutes. Use fresh DMC solvent for each soaking.

[0086] 3. Place the soaked positive electrode or negative electrode in a vacuum drying oven for 3 hours to allow DMC to completely evaporate.

[0087] 4. Place the positive electrode or negative electrode to be tested into the mercury intrusion instrument, and perform a porosity test according to the operating procedures of the mercury intrusion instrument to obtain the porosity of the electrode.

[0088] Example 2

[0089] This embodiment provides a positive electrode sheet and a negative electrode sheet.

[0090] Among them, the positive electrode plate includes a current collector aluminum foil and an active layer arranged on the surface of one side of the current collector aluminum foil. The single-side thickness of the active layer is 180μm. The materials of the active layer include active materials, conductive agents, fiberized binders and pore-forming agents. The pore-forming agent is at least partially dispersed in the micropores of the fiberized binder; the pore-forming agent is a combination of LiFSi and LiPO2F2 in a mass ratio of 1:1; the fiberized binder is fiberized polytetrafluoroethylene; the active material is lithium nickel manganese oxide, and the conductive agent includes single-walled carbon nanotubes and conductive carbon black; the mass ratio of active materials, conductive agents, fiberized binders and pore-forming agents is 95.95:1.55:2.5:3; after the positive electrode plate is soaked in the electrolyte for 10 minutes, it is taken out and the porosity of the positive electrode plate obtained by mercury injection testing is 52%.

[0091] Among them, the negative electrode plate includes a current collector copper foil and an active layer arranged on one side of the current collector copper foil. The single-side thickness of the active layer is 150μm, and the materials of the active layer include active materials, conductive agents and fiberized binders; the fiberized binder is fiberized polytetrafluoroethylene; the active material is graphite, and the conductive agent is conductive carbon black; the mass ratio of the active material, the conductive agent and the fiberized binder is 96:1.5:2.5; after the negative electrode plate is soaked in the electrolyte for 10 minutes, the porosity of the negative electrode plate is taken out and tested by the mercury injection method, and the porosity is 37%.

[0092] This embodiment also provides a method for preparing the positive electrode sheet and the negative electrode sheet, and the method for preparing the positive electrode sheet comprises the following steps:

[0093] (1) The total mass of lithium nickel manganese oxide, single-walled carbon nanotubes, conductive carbon black and fiberized polytetrafluoroethylene is 100%. Lithium nickel manganese oxide (95.95% by mass) is placed in a double planetary stirring tank, and single-walled carbon nanotubes (0.05% by mass) and conductive carbon black (1.5% by mass) are added. The mixture is stirred and premixed for 10 minutes. Then, fiberized polytetrafluoroethylene (2.5% by mass) and LiFSi (1.5% by mass and 1.5% by mass of the total mass of the powder (including lithium nickel manganese oxide, single-walled carbon nanotubes, conductive carbon black and fiberized polytetrafluoroethylene)) are added. The mixture is stirred and premixed for 30 minutes to ensure that the powder is evenly mixed to obtain a mixed dry material.

[0094] (2) The mixed dry material is added to an internal mixer for fiberization treatment, and the rotation speed is controlled to be 50 rpm for 1 hour to obtain a fiberized dry material. The fiberized dry material is then subjected to hot pressing and thinning treatment using a hot press. The hot pressing temperature is 80°C and the speed ratio of the two rollers is 1.07:1. After three rounds of hot pressing and thinning, the target thickness is obtained.

[0095] (3) The dry material after thinning in step (2) is compounded onto the current collector aluminum foil by using a hot press, the hot pressing temperature is 200° C., and the roller speed is 2 m / min, to obtain the electrode plate.

[0096] The method for preparing the negative electrode sheet comprises the following steps:

[0097] (a) The total mass of graphite, conductive carbon black and fiberized polytetrafluoroethylene is 100%, and 96% of the graphite is placed in a double planetary stirring tank. 1.5% of the conductive carbon black is added and stirred for premixing for 10 minutes. Then, 2.5% of the fiberized polytetrafluoroethylene is added and stirred for 30 minutes to make the powders uniformly mixed to obtain a mixed dry material.

[0098] (b) The mixed dry material is added into an internal mixer for fiberization treatment, and the rotation speed is controlled to be 50 rpm for 1 hour to obtain a fiberized dry material, and then a hot press is used to perform hot pressing and thinning treatment on the fiberized dry material. The hot pressing temperature is 70° C. and the speed ratio of the two rollers is 1.07:1. After 3 rounds of hot pressing and thinning, the target thickness is obtained.

[0099] (c) The dry material treated in step (2) is compounded onto the current collector copper foil using a hot press at a hot pressing temperature of 180° C. and a roller speed of 2 m / min to obtain an electrode sheet.

[0100] This embodiment also provides a lithium-ion battery, comprising the positive electrode plate as described above, the negative electrode plate as described above, and an electrolyte.

[0101] The solvents of the electrolyte include FEC, DMC, DEC and EC, among which the mass fraction of FEC is 15.66%, the mass fraction of DMC is 27.98%, the mass fraction of DEC is 20.57%, and the mass fraction of EC is 15.97%.

[0102] The solutes in the electrolyte include TAP, TMSP, LiPF6, LiFSi and LiPO2F2, among which the mass fraction of TAP is 1.6%, the mass fraction of TMSP is 0.5%, the mass fraction of LiFSi is 2.4%, the mass fraction of LiPO2F2 is 2.85%, and the mass fraction of LiPF6 is 12.47%.

[0103] This embodiment also provides a method for preparing the above lithium ion battery, comprising the following steps:

[0104] (i) Providing a positive electrode sheet and a negative electrode sheet by using the above-mentioned method for preparing a positive electrode sheet and the above-mentioned method for preparing a negative electrode sheet.

[0105] (ii) Preparation of electrolyte: The total mass of the electrolyte is taken as 100%, and the mass fractions of LiFSi and LiPO2F2 are calculated on the assumption that all LiFSi and LiPO2F2 in the positive electrode sheet and the negative electrode sheet can be dissolved in the electrolyte. The mass fractions of LiFSi and LiPO2F2 are calculated as 2.5% and 2.5%, respectively. FEC, DMC, DEC and EC are mixed at mass fractions of 16%, 28%, 20% and 16% to obtain a mixed solvent. LiPF6 is then added to the mixed solvent with a mass fraction of 13%. The mixture is stirred while being added. Then, 1.5% of TAP and 0.5% of TMSP are added. The mixture is stirred for 3 h to obtain an electrolyte.

[0106] (iii) The positive electrode sheet, the negative electrode sheet and the separator (the separator is a PE film with Al2O3 and PVDF coated on its surface) are formed into a core, and then the electrolyte is injected. The amount of electrolyte added is 4g / Ah. After the injection, it is left to stand for 16 hours, and then the formation, degassing and capacity separation are carried out to obtain a lithium-ion battery.

[0107] Example 3

[0108] This embodiment provides a positive electrode sheet and a negative electrode sheet.

[0109] Among them, the positive electrode plate includes a current collector aluminum foil and an active layer arranged on one side of the current collector aluminum foil. The single-side thickness of the active layer is 180μm, and the materials of the active layer include active materials, conductive agents and fiberized binders; the fiberized binder is fiberized polytetrafluoroethylene; the active material is lithium nickel manganese oxide, and the conductive agent includes single-walled carbon nanotubes and conductive carbon black; the mass ratio of the active material, the conductive agent and the fiberized binder is 95.95:1.55:2.5; after the positive electrode plate is soaked in the electrolyte for 10 minutes, the porosity of the positive electrode plate is taken out and tested by mercury injection method, and the porosity is 42%.

[0110] Among them, the negative electrode plate includes a current collector copper foil and an active layer arranged on the surface of one side of the current collector copper foil. The single-side thickness of the active layer is 150μm. The materials of the active layer include active materials, conductive agents, fiberized binders and pore-forming agents. The pore-forming agent is at least partially dispersed in the micropores of the fiberized binder; the pore-forming agent is a combination of LiFSi and LiPO2F2 in a mass ratio of 1:1; the fiberized binder is fiberized polytetrafluoroethylene; the active material is graphite, and the conductive agent is conductive carbon black; the mass ratio of the active material, the conductive agent, the fiberized binder and the pore-forming agent is 96:1.5:2.5:3; after the negative electrode plate is immersed in the electrolyte for 10 minutes, it is taken out and the porosity of the negative electrode plate is 48% tested by mercury injection method.

[0111] This embodiment also provides a method for preparing the positive electrode sheet and the negative electrode sheet, and the method for preparing the positive electrode sheet comprises the following steps:

[0112] (1) The total mass of lithium nickel manganese oxide, single-walled carbon nanotubes, conductive carbon black and fiberized polytetrafluoroethylene is 100%. Lithium nickel manganese oxide (95.95% by mass) is placed in a double planetary stirring tank, and single-walled carbon nanotubes (0.05% by mass) and conductive carbon black (1.5% by mass) are added. The mixture is stirred and premixed for 10 minutes. Then, fiberized polytetrafluoroethylene (2.5% by mass) is added and stirred and mixed for 30 minutes to ensure that the powders are evenly mixed to obtain a mixed dry material.

[0113] (2) The mixed dry material is added to an internal mixer for fiberization treatment, and the rotation speed is controlled to be 50 rpm for 1 hour to obtain a fiberized dry material. The fiberized dry material is then subjected to hot pressing and thinning treatment using a hot press. The hot pressing temperature is 80°C and the speed ratio of the two rollers is 1.07:1. After three rounds of hot pressing and thinning, the target thickness is obtained.

[0114] (3) The thinned dry material in step (2) is compounded onto the current collector aluminum foil by a hot press at a hot pressing temperature of 200° C. and a roller speed of 2 m / min to obtain the electrode sheet;

[0115] The method for preparing the negative electrode sheet comprises the following steps:

[0116] (a) The total mass of graphite, conductive carbon black and fiberized polytetrafluoroethylene is 100%, and 96% of the graphite is placed in a double planetary stirring tank. 1.5% of the conductive carbon black is added and stirred for premixing for 10 minutes. Then, 2.5% of the fiberized polytetrafluoroethylene is added, and 1.5% of LiFSi and 1.5% of LiPO2F2 accounting for the total mass of the powder (including graphite, conductive carbon black and fiberized polytetrafluoroethylene) are added. The mixture is stirred and mixed for 30 minutes to make the powder uniformly stirred to obtain a mixed dry material.

[0117] (b) The mixed dry material is added into an internal mixer for fiberization treatment, and the rotation speed is controlled to be 50 rpm for 1 hour to obtain a fiberized dry material, and then a hot press is used to perform hot pressing and thinning treatment on the fiberized dry material. The hot pressing temperature is 70° C. and the speed ratio of the two rollers is 1.07:1. After 3 rounds of hot pressing and thinning, the target thickness is obtained.

[0118] (c) The dry material treated in step (2) is compounded onto the current collector copper foil using a hot press at a hot pressing temperature of 180° C. and a roller speed of 2 m / min to obtain an electrode sheet.

[0119] This embodiment also provides a lithium-ion battery, comprising the positive electrode plate as described above, the negative electrode plate as described above, and an electrolyte.

[0120] The solvents of the electrolyte include FEC, DMC, DEC and EC, among which the mass fraction of FEC is 15.95%, the mass fraction of DMC is 27.59%, the mass fraction of DEC is 20.34%, and the mass fraction of EC is 16.47%.

[0121] The solutes in the electrolyte include TAP, TMSP, LiPF6, LiFSi and LiPO2F2, among which the mass fraction of TAP is 1.57%, the mass fraction of TMSP is 0.47%, the mass fraction of LiFSi is 2.36%, the mass fraction of LiPO2F2 is 2.78%, and the mass fraction of LiPF6 is 12.47%.

[0122] This embodiment also provides a method for preparing the above lithium ion battery, comprising the following steps:

[0123] (i) Providing a positive electrode sheet and a negative electrode sheet by using the above-mentioned method for preparing a positive electrode sheet and the above-mentioned method for preparing a negative electrode sheet.

[0124] (ii) Preparation of electrolyte: The total mass of the electrolyte is taken as 100%, and the mass fractions of LiFSi and LiPO2F2 are calculated on the assumption that all LiFSi and LiPO2F2 in the positive electrode sheet and the negative electrode sheet can be dissolved in the electrolyte. The mass fractions of LiFSi and LiPO2F2 are calculated as 2.5% and 2.5%, respectively. FEC, DMC, DEC and EC are mixed at mass fractions of 16%, 28%, 20% and 16% to obtain a mixed solvent. LiPF6 is then added to the mixed solvent at a mass fraction of 13%. The mixture is stirred while being added. Then, 1.5% of TAP and 0.5% of TMSP are added. The mixture is stirred for 3 h to obtain an electrolyte.

[0125] (iii) The positive electrode sheet, the negative electrode sheet and the separator (the surface of the PE film is coated with Al2O3 and PVDF) are formed into a core, and then the electrolyte is injected. The amount of electrolyte added is 4g / Ah. After the injection, it is left to stand for 16 hours, and then the formation, degassing and capacity separation are carried out to obtain a lithium-ion battery.

[0126] Example 4

[0127] The difference between this embodiment and Embodiment 1 is that the positive electrode plate includes LiFSi and LiPO2F2 in a mass ratio of 5:1, and the negative electrode plate includes LiFSi and LiPO2F2 in a mass ratio of 5:1.

[0128] The rest of the preparation methods and parameters were the same as those in Example 1.

[0129] Example 5

[0130] The difference between this embodiment and Embodiment 1 is that the positive electrode plate includes LiFSi and LiPO2F2 in a mass ratio of 1:5, and the negative electrode plate includes LiFSi and LiPO2F2 in a mass ratio of 1:5.

[0131] The rest of the preparation methods and parameters were the same as those in Example 1.

[0132] Example 6

[0133] The difference between this embodiment and embodiment 1 is that the mass ratio of active material, conductive agent, fibrous binder and pore former in the positive electrode sheet is 95.95:1.55:2.5:0.1, and the mass ratio of active material, conductive agent, fibrous binder and pore former in the negative electrode sheet is 96:1.5:2.5:0.1. In addition, the step (ii) of preparing the electrolyte comprises: taking the total mass of the electrolyte as 100%, calculating the mass fraction of LiFSi and LiPO2F2 based on the total dissolution of LiFSi and LiPO2F2 in the positive electrode sheet and the negative electrode sheet into the electrolyte, and calculating the mass fraction of LiFSi and LiPO2F2 dissolved into the electrolyte of the positive electrode sheet and the negative electrode sheet as 0.16% and the mass fraction of LiPO2F2 as 0.16%, and adding 2.4% of LiFSi and 2.4% of LiPO2F2.

[0134] The rest of the preparation methods and parameters were the same as those in Example 1.

[0135] Example 7

[0136] The difference between this embodiment and embodiment 1 is that the mass ratio of active material, conductive agent, fiberized binder and pore-forming agent in the positive electrode sheet is 95.95:1.55:2.5:5, and the mass ratio of active material, conductive agent, fiberized binder and pore-forming agent in the negative electrode sheet is 96:1.5:2.5:5. Furthermore, (ii) the step of preparing an electrolyte comprises: calculating the mass fractions of LiFSi and LiPO2F2 based on the assumption that all of the LiFSi and LiPO2F2 in the positive electrode sheet and the negative electrode sheet can be dissolved into the electrolyte, and based on the assumption that the mass fractions of LiFSi and LiPO2F2 dissolved into the electrolyte in the positive electrode sheet and the negative electrode sheet are 8.3% and 8.3%, respectively, mixing FEC, DMC, DEC and EC at mass fractions of 16%, 28%, 20% and 16%, respectively, to obtain a mixed solvent, and then adding LiPF6 to the mixed solvent, the mass fraction of LiPF6 added being 13%, stirring while adding, and then adding TAP at a mass fraction of 1.5% and TMSP at a mass fraction of 0.5%, stirring for 3 hours to fully mix, to obtain an electrolyte.

[0137] The rest of the preparation methods and parameters were the same as those in Example 1.

[0138] Example 8

[0139] The difference between this embodiment and embodiment 1 is that the pore-forming agent is LiFSi, that is, step (1) and step (a) only add LiFSi to the powder. In addition, the step (ii) of preparing the electrolyte includes: taking the total mass of the electrolyte as 100%, calculating the mass fraction of LiFSi based on the fact that all the LiFSi in the positive electrode sheet and the negative electrode sheet can be dissolved into the electrolyte, and taking the mass fraction of LiFSi as 5%, FEC, DMC, DEC and EC are mixed at mass fractions of 16%, 28%, 20% and 16% respectively to obtain a mixed solvent, and then adding LiPF6 to the mixed solvent, the mass fraction of LiPF6 added is 13%, stirring while adding, and then adding TAP with a mass fraction of 1.5% and TMSP with a mass fraction of 0.5%, stirring for 3 hours to fully mix, to obtain an electrolyte;

[0140] The rest of the preparation methods and parameters were the same as those in Example 1.

[0141] Example 9

[0142] The difference between this embodiment and embodiment 1 is that the pore-forming agent is LiPO2F2, that is, in step (1) and step (a), only LiPO2F2 is added to the powder. In addition, the step (ii) of preparing the electrolyte includes: taking the total mass of the electrolyte as 100%, calculating the mass fraction of LiPO2F2 based on the fact that all the LiPO2F2 in the positive electrode sheet and the negative electrode sheet can be dissolved into the electrolyte, and taking the mass fraction of LiPO2F2 as 2.5%, FEC, DMC, DEC and EC are mixed at mass fractions of 16%, 28%, 20% and 16% respectively to obtain a mixed solvent, and then adding LiPF6 to the mixed solvent, the mass fraction of LiPF6 added is 13%, stirring while adding, and then adding TAP with a mass fraction of 1.5%, TMSP with a mass fraction of 0.5% and LiPO2F2 with a mass fraction of 2.5%, stirring for 3 hours to fully mix, and obtaining an electrolyte;

[0143] The rest of the preparation methods and parameters were the same as those in Example 1.

[0144] Comparative Example 1

[0145] This comparative example provides a positive electrode sheet and a negative electrode sheet.

[0146] Among them, the positive electrode plate includes a current collector aluminum foil and an active layer arranged on one side of the current collector aluminum foil. The single-side thickness of the active layer is 180μm, and the materials of the active layer include active materials, conductive agents and fiberized binders; the fiberized binder is fiberized polytetrafluoroethylene; the active material is lithium nickel manganese oxide, and the conductive agent includes single-walled carbon nanotubes and conductive carbon black; the mass ratio of the active material, the conductive agent and the fiberized binder is 95.95:1.55:2.5; after the positive electrode plate is soaked in the electrolyte for 10 minutes, the porosity of the positive electrode plate is taken out and tested by mercury injection method, and the porosity is 43%.

[0147] Among them, the negative electrode plate includes a current collector copper foil and an active layer arranged on one side of the current collector copper foil. The single-side thickness of the active layer is 150μm, and the materials of the active layer include active materials, conductive agents and fiberized binders; the fiberized binder is fiberized polytetrafluoroethylene; the active material is graphite, and the conductive agent is conductive carbon black; the mass ratio of the active material, the conductive agent and the fiberized binder is 96:1.5:2.5; after the negative electrode plate is soaked in the electrolyte for 10 minutes, the porosity of the positive electrode plate is taken out and tested by the mercury injection method, which is 37%.

[0148] This comparative example also provides a method for preparing the positive electrode sheet and the negative electrode sheet, and the method for preparing the positive electrode sheet comprises the following steps:

[0149] (1) The total mass of lithium nickel manganese oxide, single-walled carbon nanotubes, conductive carbon black and fiberized polytetrafluoroethylene is 100%. Lithium nickel manganese oxide (95.95% by mass) is placed in a double planetary stirring tank, and single-walled carbon nanotubes (0.05% by mass) and conductive carbon black (1.5% by mass) are added. The mixture is stirred and premixed for 10 minutes. Then, fiberized polytetrafluoroethylene (2.5% by mass) is added and stirred and mixed for 30 minutes to ensure that the powders are evenly mixed to obtain a mixed dry material.

[0150] (2) The mixed dry material is added to an internal mixer for fiberization treatment, and the rotation speed is controlled to be 50 rpm for 1 hour to obtain a fiberized dry material. The fiberized dry material is then subjected to hot pressing and thinning treatment using a hot press. The hot pressing temperature is 80°C and the speed ratio of the two rollers is 1.07:1. After three rounds of hot pressing and thinning, the target thickness is obtained.

[0151] (3) The dry material after thinning in step (2) is compounded onto the current collector aluminum foil by using a hot press, the hot pressing temperature is 200° C., and the roller speed is 2 m / min, to obtain the electrode plate.

[0152] The method for preparing the negative electrode sheet comprises the following steps:

[0153] (a) The total mass of graphite, conductive carbon black, and fiberized polytetrafluoroethylene is 100%, and 96% of the graphite is placed in a double planetary stirring tank. 1.5% of the conductive carbon black is added and stirred for premixing for 10 minutes. Then, 2.5% of the fiberized polytetrafluoroethylene is added and stirred for 30 minutes to make the powder material uniformly mixed to obtain a mixed dry material.

[0154] (b) The mixed dry material is added into an internal mixer for fiberization treatment, and the rotation speed is controlled to be 50 rpm for 1 hour to obtain a fiberized dry material, and then a hot press is used to perform hot pressing and thinning treatment on the fiberized dry material. The hot pressing temperature is 70° C. and the speed ratio of the two rollers is 1.07:1. After 3 rounds of hot pressing and thinning, the target thickness is obtained.

[0155] (c) The dry material treated in step (2) is compounded onto the current collector copper foil using a hot press at a hot pressing temperature of 180° C. and a roller speed of 2 m / min to obtain an electrode sheet.

[0156] This comparative example also provides a lithium-ion battery, comprising the positive electrode plate as described above, the negative electrode plate as described above, and an electrolyte.

[0157] The solvents of the electrolyte include FEC, DMC, DEC and EC, among which the mass fraction of FEC is 15.98%, the mass fraction of DMC is 27.64%, the mass fraction of DEC is 20.39%, and the mass fraction of EC is 16.54%.

[0158] The solutes in the electrolyte include TAP, TMSP, LiPF6, LiFSi and LiPO2F2, among which the mass fraction of TAP is 1.43%, the mass fraction of TMSP is 0.48%, the mass fraction of LiFSi is 2.89%, the mass fraction of LiPO2F2 is 2.28%, and the mass fraction of LiPF6 is 12.37%.

[0159] This comparative example also provides a method for preparing the above lithium ion battery, comprising the following steps:

[0160] (i) Providing a positive electrode sheet and a negative electrode sheet by using the above-mentioned method for preparing a positive electrode sheet and the above-mentioned method for preparing a negative electrode sheet.

[0161] (ii) Preparation of electrolyte: Taking the total mass of the electrolyte as 100%, FEC, DMC, DEC and EC are mixed in a mass ratio of 20:35:25:20 to obtain a mixed solvent, and then LiPF6 is added to the mixed solvent while stirring until the concentration of LiPF6 is 1 mol / L, and then 1% by mass of TAP, 0.5% by mass of TMSP, 2.3% by mass of LiFSi and 2.8% by mass of LiPO2F2 are added, and the mixture is stirred for 3 h to be thoroughly mixed to obtain an electrolyte.

[0162] (iii) The positive electrode sheet, the negative electrode sheet and the separator (the surface of the PE film is coated with Al2O3 and PVDF) are assembled into a battery cell, and then the electrolyte is injected at an amount of 4g / Ah. After the injection, the electrolyte is left to stand for 16 hours, and then the formation, degassing and capacity separation are carried out to obtain a lithium-ion battery.

[0163] The method for detecting the composition and content of the pore formers of the positive electrode sheets and the negative electrode sheets provided in the above embodiments and comparative examples includes:

[0164] The positive electrode sheet or the negative electrode sheet is immersed in DMC solvent to extract the pore-forming agent therein, and then IC is used for qualitative and quantitative testing to test the composition and content of the pore-forming agent therein. The test results are shown in Table 1.

[0165] Table 1

[0166]

[0167] Performance Testing

[0168] The positive electrode sheets and negative electrode sheets provided in the above-mentioned embodiments and comparative examples were subjected to resistance tests, and the prepared lithium-ion batteries were subjected to capacity performance and rate performance tests.

[0169] The test conditions for capacity performance are: room temperature 25°C, 3C / 1C, 900 cycles, the battery discharge cut-off voltage is 3.5V-4.90V, and the cut-off current is 0.05C; high temperature 45°C, 3C / 1C, 400 cycles, the battery discharge cut-off voltage is 3.5V-4.90V, and the cut-off current is 0.05C.

[0170] Rate performance test: 3C / 0.2C, 2C / 0.2C, 1C / 0.2C, battery discharge cut-off voltage is 3.5V-4.90V, cut-off current is 0.05C, test capacity ratio.

[0171] The test results are shown in Table 2.

[0172] Table 2

[0173]

[0174] analyze:

[0175] It can be seen from the above table that the present invention can occupy space in the active layer by introducing a pore-forming agent into the active layer of the electrode plate, and at least part of the pore-forming agent can enter the micropores of the fiberized binder, reducing the conductive agent from entering the micropores of the fiberized binder, allowing more conductive agent to contact the active particles, and when the electrode plate is wound into a core and injected with liquid, the pore-forming agent dissolves in the electrolyte, and micropores are formed at the original position, thereby increasing the porosity of the electrode plate, which is beneficial to the infiltration of the electrolyte and the transmission of lithium ions, and can significantly improve the cycle performance and fast charging performance of lithium-ion batteries.

[0176] It can be seen from Example 1 and Examples 2-3 that if a pore-forming agent is only introduced into the positive electrode sheet or the negative electrode sheet, and pores are only formed on one side of the positive and negative electrodes, it is not conducive to improving the overall performance of the battery. The performance of the battery is related to the porosity of the positive and negative electrode sheets, and improving the performance of one side is not optimal.

[0177] It can be seen from Examples 1 and 4-5 that if the mass ratio of LiFSi and LiPO2F2 in the electrode plate is too large, the excess LiFSi will easily corrode the aluminum foil, and too little LiPO2F2 cannot protect the aluminum foil well, and the contact between the aluminum foil and the active material will deteriorate, which will eventually lead to poor cycle performance of the battery; if the mass ratio of LiFSi and LiPO2F2 in the electrode plate is too small, too little LiFSi will be unfavorable for reducing the impedance of the battery and improving performance.

[0178] It can be seen from Examples 1 and 6-7 that if the content of the pore-forming agent in the electrode plate is too low, the pore-forming ability is too low, and more pores cannot be formed in the plate, which is not conducive to the transmission of lithium ions and affects the charge and discharge performance of the battery. If the content of the pore-forming agent in the electrode plate is too high, too much LiFSi will corrode the foil, resulting in a decrease in battery performance, and too much LiPO2F2 cannot be dissolved in the electrolyte, resulting in waste.

[0179] It can be seen from Example 1 and Example 8 that compared with Example 1, only one pore-forming agent LiFSi is used. Although the pore-forming agent can increase the porosity of the electrode and reduce the membrane resistance of the electrode, although LiFSi alone can improve the charging performance, it will corrode the aluminum foil. Without the protective effect of LiPO2F2 on the aluminum foil, the battery cycle performance will deteriorate, and the coordination effect of LiFSi and LiPO2F2 will not be exerted.

[0180] It can be seen from Example 1 and Example 9 that, compared with Example 1, only one pore-forming agent LiPO2F2 is used, resulting in an insufficient amount of pore-forming agent, insufficient promotion of lithium ion transmission, and ultimately poor improvement in battery performance.

[0181] It can be seen from Example 1 and Comparative Example 1 that if no pore-forming agent is introduced into the positive electrode sheet and the negative electrode sheet, there is no pore-forming ability and more pores cannot be formed in the electrode sheet, which is not conducive to the transmission of lithium ions and affects the charge and discharge performance of the battery.

[0182] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An electrode plate, characterized in that: The electrode plate comprises a current collector and an active layer disposed on at least one side of the current collector, wherein the material of the active layer comprises an active material, a conductive agent, a fibrous binder and a pore-forming agent, wherein the pore-forming agent is at least partially dispersed in the micropores of the fibrous binder; The pore former includes LiFSi and / or LiPO2F2.

2. The electrode plate according to claim 1, characterized in that: After the electrode plate is soaked in the electrolyte, when the electrode plate is a positive electrode plate, the porosity of the positive electrode plate is 46-53%; and / or when the electrode plate is a negative electrode plate, the porosity of the negative electrode plate is 42-48%; Or, after the electrode plate is prepared into a lithium-ion battery, when the electrode plate is a positive electrode plate, the porosity of the positive electrode plate is 46-53%; and / or, when the electrode plate is a negative electrode plate, the porosity of the negative electrode plate is 42-48%.

3. The electrode plate according to claim 1, characterized in that: The pore former includes LiFSi and LiPO2F2, and the mass ratio of LiFSi to LiPO2F2 is (1-5):(5-1).

4. The electrode plate according to claim 1, characterized in that: The electrode plate is a positive electrode plate, in which the active material includes any one of lithium nickel manganese oxide, lithium cobalt oxide or a ternary positive electrode material; And / or, in the positive electrode plate, the conductive agent includes a combination of any two or at least three of single-walled carbon nanotubes, conductive carbon black, conductive graphite or graphene; And / or, in the positive electrode plate, the fiberized binder includes any one of fiberized tetrafluoroethylene, fiberized styrene-butadiene rubber, fiberized polyimide, fiberized nitrile rubber, fiberized polyacrylic acid, fiberized polyvinyl alcohol, fiberized polyethylene oxide or fiberized alginate, or a combination of at least two thereof; And / or, in the positive electrode sheet, the mass ratio of the total mass of the active material, the conductive agent and the fibrous binder to the mass ratio of the pore-forming agent is 100:(1-3); And / or, in the positive electrode plate, the single-side thickness of the active layer is 50-200 μm.

5. The electrode plate according to claim 1, characterized in that: The electrode plate is a negative electrode plate, in which the active material includes any one of graphite, mesophase carbon microbeads, hard carbon, soft carbon, silicon oxygen or silicon carbon; And / or, in the negative electrode plate, the conductive agent includes conductive carbon black and / or conductive graphite; And / or, in the negative electrode plate, the fiberized binder includes any one or a combination of at least two of fiberized tetrafluoroethylene, fiberized styrene-butadiene rubber, fiberized polyimide, fiberized nitrile rubber, fiberized polyacrylic acid, fiberized polyvinyl alcohol, fiberized polyethylene oxide or fiberized alginate; And / or, in the negative electrode sheet, the mass ratio of the total mass of the active material, the conductive agent and the fibrous binder to the mass ratio of the pore-forming agent is 100:(1-3); And / or, in the negative electrode plate, the single-side thickness of the active layer is 40-200 μm.

6. A method for preparing an electrode sheet according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: The active material, the conductive agent, the binder and the pore-forming agent are mixed to obtain a mixed dry material, and then the mixed dry material is subjected to a fiberization treatment to obtain a fiberized dry material; Compounding the fiberized dry material onto a current collector to obtain the electrode sheet; Wherein, the pore former includes LiFSi and / or LiPO2F2.

7. The preparation method according to claim 6, characterized in that: The mixing method is dry mixing; And / or, the fibrosis treatment time is 0.5-1.5h; And / or, before the fiberized dry material is compounded onto the current collector, the fiberized dry material is first subjected to a heat-pressing thinning treatment to obtain a target thickness.

8. The preparation method according to claim 6, characterized in that: The preparation method comprises the following steps: (1) premixing the active material and the conductive agent for 5-15 minutes, then adding the fiberizing binder and the pore-forming agent, stirring and mixing for 20-40 minutes to obtain a mixed dry material; wherein the total mass ratio of the active material, the conductive agent and the fiberizing binder to the pore-forming agent is 100:(1-3); Wherein, the pore former comprises LiFSi and LiPO2F2 in a mass ratio of (1-5):(5-1); (2) adding the mixed dry material into an internal mixer for fiberization treatment, and controlling the speed to be 20-60 rpm for 0.5-1.5 h to obtain a fiberized dry material, and then using a hot press to perform a hot pressing thinning treatment on the fiberized dry material at a hot pressing temperature of 60-100° C. to obtain a target thickness; (3) The dry material treated in step (2) is compounded onto the current collector foil by using a hot press at a temperature of 150-250° C. and a roller speed of 1-3 m / min to obtain the electrode sheet.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, and the positive electrode sheet and / or the negative electrode sheet is the electrode sheet according to any one of claims 1 to 5.

10. The lithium ion battery according to claim 9, characterized in that: The porosity of the positive electrode sheet is 46-53%; And / or, the porosity of the negative electrode plate is 42-48%; and / or, the solvent in the electrolyte includes a combination of at least three of FEC, DMC, DEC, EMC and EC; and / or, the solute in the electrolyte includes TAP, TMSP, LiPF6, LiFSi and LiPO2F2; And / or, in the electrolyte, the mass fraction of TAP is 0.5-2%, the mass fraction of TMSP is 0.5-2%, the mass fraction of LiFSi is 2-4%, the mass fraction of LiPO2F2 is 1.5-3%, and the mass fraction of LiPF6 is 12-13%.

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