CN110224112B

CN110224112B - Secondary pore-forming method for lithium ion battery

Info

Publication number: CN110224112B
Application number: CN201811320937.1A
Authority: CN
Inventors: 张学全; 周伟; 孙先富; 杨行; 陈云鹏; 孙世界; 吕文东; 兰海侠
Original assignee: Shandong Huayi Bico New Energy Co ltd
Current assignee: Shandong Huayi Bico New Energy Co ltd
Priority date: 2018-11-07
Filing date: 2018-11-07
Publication date: 2022-02-22
Anticipated expiration: 2038-11-07
Also published as: CN110224112A

Abstract

The invention discloses a secondary pore-forming method for a lithium ion battery, which comprises the following steps: s1: heating the pore-forming agent to form a molten liquid; s2: adding a molten liquid soaking or spraying box body at the tail of the coating machine, wherein the soaking box adopts the molten liquid; s3: uniformly coating the prepared positive and negative electrode slurry on a current collector substrate, drying, and then passing through a spray box or a soaking box; s4: coiling the pole piece after curing the pore-forming agent into a coil stock, and performing roll forming by a roll squeezer according to a normal flow; s5: the rolled pole pieces are extracted by an extraction box and then dried by an oven, or the rolled pole pieces are sprayed by hot air into the oven and then are subjected to heat treatment by a high-temperature nitrogen atmosphere oven.

Description

Secondary pore-forming method for lithium ion battery

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a secondary pore-forming method for a lithium ion battery.

Background

Lithium ion batteries have the advantages of high energy density, long service life, high voltage and the like, and are not only rapidly developed in consumer markets such as mobile phones, mobile power supplies, digital cameras, notebooks and the like, but also widely applied in power markets such as electric automobiles, electric bicycles, electric tools and the like, and emerging markets such as energy storage markets and the like.

In these emerging market areas, particularly automotive power applications, both market demand and national policy oriented, higher demands are placed on the power cell capacity density. Therefore, the energy density of each enterprise and each research institution is improved by replacing the anode and cathode materials, reducing the thickness of the diaphragm, improving the charging voltage and the like, but the methods for improving the energy density have advantages and disadvantages, and leave great hidden dangers in the aspect of battery safety.

For the most core positive and negative pole pieces of the power battery, many enterprises adopt higher compaction density to improve the capacity density, for example, lithium iron phosphate is improved from 1.8g/cm3 in 2011 to 2.5-2.6g/cm3 in 2017, graphite is gradually improved from 1.35-1.5g/cm3 to 1.6-1.65g/cm3, and the purpose of improving the energy density of the power battery under the condition of not affecting the safety performance as much as possible is achieved. However, the higher the compaction density, the more porous the electrode sheet, and the higher the compaction density, the more closed surface pores are generated. The pole piece is theoretically pressed downwards in the rolling process, but the diameter of the steel rod of the current rolling machine is generally 600-1200mm, and the horizontal deformation cannot be realized. Meanwhile, the pole piece is pressed up and down, the thickness of the active material on two sides is 80-180 micrometers due to the fact that the current collector is arranged in the middle, the active material looks thin, but active material particles adopted in the industry are generally 0.5-30 micrometers, therefore, a plurality of layers of active material particles are stacked together, deformation of the surface layer is large during rolling, deformation close to the base material layer is small, through crystal section detection and SEM amplification, the difference of the porosity of the inner layer and the porosity of the outer layer can be calculated to be large, the average porosity after rolling is about 30-40%, the porosity of the inner layer is generally 45-55%, and the porosity of the outer layer is generally 20-30%. The porosity of the outer layer is obviously reduced by a mercury pressing method compared with that of the outer layer without rolling, the tortuosity is increased (mercury withdrawing time is long, and mercury residues are more), namely, when the rolling compaction density is increased, a large amount of closed pores are generated, the pore diameter of the surface layer is sharply reduced, and the adverse effects of reduction of battery multiplying power, reduction of low-temperature performance, easiness in lithium precipitation, reduction of battery cycle life and the like are caused.

Therefore, a new pore-forming process is created in the industry, which is to add pore-forming agent in various forms, and then to heat pore-forming after rolling, such as: CN104157827A, CN106848148A and CN 103515607A. The CN104157827A patent adopts the method that a liquid pore-forming agent is added into slurry, more pores are formed during coating and baking, but the thickness of a pole piece is improved, the pores generated in the subsequent rolling process also have the phenomena of pore closing and pore reduction, the ratio of the pore reduction and the pore closing is larger than that of the normal pole piece, because the pole piece is not integral pores but pores on the surface layer, more actually obtained pore closing holes are formed by the pore-forming method, and the difference of the pores on the inner layer and the outer layer is larger. The CN103515607A patent mentions that solid pore-forming agent is added to prepare slurry, and after the pole piece is rolled, the pore-forming agent is decomposed at high temperature to generate more pores. The battery performance can be improved only to a certain extent, and the improvement effect on the energy density is limited. The CN106848148A patent proposes that the pole piece just sprays pore-forming agent when not dry after the coating, enter the baking oven of coating machine and bake, let the pore-forming agent disperse to pole piece thick liquids top layer, it is more to form pores on the pole piece top layer after the stoving, heating decomposition pore-forming after the roll-in, but this kind of scheme also has a very obvious problem, though pore-forming agent is in top layer pole piece inside, pore-forming also can lead to pole piece thickness to bounce, though it is good to the pore re-opening of closed, but do not help to the little hole of compression, the other of production can directly discharge through these apertures, some holes of production, still many need communicate with each other with the external world through the hole that reduces, have certain effect to reducing surface polarization, but still can't solve to keep improving really useful porosity under the high compaction condition of pole piece.

Aiming at the problems, the invention provides a method which can carry out pore-forming on the middle layer and the surface layer to different degrees under high compaction density, achieves more pore-forming on the surface layer and less pore-forming on the middle layer by controlling the pore-forming agent adding process, and does not influence the rebound of a pole piece. The proportion and degree of reducing the hole on the surface layer become light during rolling, so that the pressure is uniformly dispersed to the inner layer of the pole piece, the deformation of the inner layer becomes large, the deformation of the outer layer is reduced, and the proportion and degree of reducing the rolling closed hole and the hole are reduced. By secondary pore forming, the reduced pores are directionally expanded and the closed pores are opened. The method can not only keep the pole piece high in compaction and improve the energy density of the battery, but also improve the uniformity of the pole piece of the battery and ensure the performances of multiplying power, circulation, low temperature and the like.

Disclosure of Invention

The invention aims to provide a method for improving the energy density of a battery by keeping the pole piece high in compaction and improving the uniformity of the pole piece of the battery to ensure the performances of multiplying power, circulation, low temperature and the like. The method can ensure that the surface layer of the pole piece has uniform and large quantity of pores under the condition of further improving the compacted density of the pole piece, the proportion of closed pores and shrinkage cavities can be greatly reduced, and the effective porosity of the pole piece is improved so as to solve the problems in the background technology.

In order to achieve the purpose, the invention provides the following technical scheme: a secondary pore-forming method for a lithium ion battery comprises the following steps:

s1: heating the pore-forming agent to 40-120 ℃ to form a molten liquid;

s2: adding a molten liquid into a soaking box or a spraying box body at the tail of the coating machine, wherein the atomizing pressure in the spraying box is 0.1-100 KPa, the atomizing temperature is 60-130 ℃, and the soaking box adopts the molten liquid at the temperature of 40-120 ℃;

s3: uniformly coating the prepared positive and negative electrode slurry on a current collector substrate, drying, passing through a spray box at the speed of 0.01-5 m/s or a soaking box at the speed of 1-60 m/s, cooling the box body, and ensuring that the pole piece is atomized for 1-300 seconds or soaked for 0.1-30 seconds, wherein the time of the cooling box is based on cooling until the pore-forming agent is completely solidified;

s4: coiling the pole piece after curing the pore-forming agent into a coil stock, and performing roll forming by a roll squeezer according to a normal flow, and keeping the humidity of a roll-in environment within a range that the pore-forming agent does not absorb water;

s5: extracting the rolled pole piece for 1-300 seconds through an extraction box, and drying the extractant through an oven, wherein the extractant is condensed and recycled; or the rolled pole piece is treated by a hot air spraying oven at the temperature of 80-150 ℃ for 1-300 seconds, most of the molten pore-forming agent liquid is blown out for recycling, the pole piece is treated by a high-temperature nitrogen atmosphere oven at the temperature of 5-10 ℃ higher than the boiling point of the pore-forming agent, most of the residual pore-forming agent adsorbed into the capillary pore is evaporated out in a high-temperature boiling mode, the residue is reduced as much as possible, the pore-forming agent can be recycled by more than 99.9%, the oven is provided with a condensation recovery device, and the heat treatment time is 1-30 minutes;

s6: transferring the prepared pole piece to a subsequent process for production according to the production flow;

s7: taking the pole pieces obtained in the fifth step, recording the pole pieces as 1-1 and 1-2 of atomization and extraction meters, 1-3 and 1-4 of atomization and heating treatment meters, 1-5 and 1-6 of soaking and extraction meters, 1-7 and 1-8 of soaking and heating treatment meters, testing the porosity and the tortuosity by a mercury intrusion method, recording, performing section analysis on the pole pieces, performing statistical analysis on the porosity of the upper layer, the middle layer and the lower layer by adopting a low-power SEM (scanning electron microscope), and recording;

s8: randomly taking 2 batteries, recording the number of the batteries as 1-1 and 1-2 by atomization and extraction respectively, recording the number of the batteries as 1-3 and 1-4 by atomization and heating treatment, recording the number of the batteries as 1-5 and 1-6 by soaking and extraction and recording the number of the batteries as 1-7 and 1-8 by soaking and heating treatment, calculating the energy density after capacity grading, well recording, and testing the multiplying power of the obtained batteries and the discharge recording capacity at the temperature of-20 ℃.

Preferably, the pore-forming agent in step S1 is any one of EC, DPC, paraffin, FEC, TCA, dibenzoic acid, oxybenzone, forty alkane, 2-chlorobenzonitrile, and 2, 3-butanediol, but is not limited thereto.

Preferably, the extracting agents corresponding to the EC, DPC, 2, 3-butanediol and forty-alkane are DMC, carbon disulfide, ethanol and dimethyl ammonium formate, respectively, but are not limited to these kinds of solvents.

Preferably, in the step S2, the pressure value of the atomization inside the spray box is preferably 1 to 10KPa, the temperature of the atomization is preferably 80 to 120 ℃, the temperature of the molten liquid adopted by the soaking box is preferably 60 to 100 ℃, and the viscosity of the molten liquid is less than 100mPa · S.

Preferably, the time for receiving the spraying in the step S3 is 5 to 180 seconds or the soaking time is 0.5 to 5 seconds, the surface of the soaked pole piece is blown and showered by nitrogen, the excessive pore-forming agent melt on the surface is remained on the surface of the pole piece as little as possible, and the pole piece is fully cooled until the pore-forming agent is completely solidified.

Preferably, the step S4 is carried out in a roller press, the pole piece and the environmental moisture of the equipment are adopted to control and tighten to be less than 2% RH, the calendering condition is 0.5-3.0 MPa, the calendering speed is 10-40 m/min, the thickness of the formed pole piece is 90-190 um, and the compaction density is as follows: graphite cathode 1.6-1.68 g/cm³2.7-2.8 g/cm of positive lithium iron phosphate³3.6-3.75 g/cm ternary positive electrode³3.1-3.2 g/cm of positive lithium manganate³But are not limited to these thicknesses and compacted densities.

Preferably, in the step S5, the time value of extraction through the extraction box is 10 to 120 seconds, the viscosity of the treated molten liquid is less than 50mPa · S, the treatment time is 10 to 180 seconds, the oven is provided with a condensation recovery device, and the heat treatment time is 3 to 20 minutes.

The method provided by the invention is essentially different from the comparative patent in that the method is characterized in that after the pole piece is dried, the pore-forming agent is added, the pore-forming agent is transversely and uniformly added into pores on the surface layer of the pole piece, and is longitudinally and non-uniformly added into the surface layer, the middle layer and the inner layer of the pole piece.

The pore-forming agent is solid at normal temperature, is liquid in a molten state at 40-80 ℃, passes through the molten liquid through the pole piece, and is soaked and adsorbed in the pores of the pole piece. But not limited to, the mode of soaking adsorption is similar to that of the same family patents of the company, and the spraying mode is also adopted for adding, and the difference is that the spraying is not a solution of the pore-forming agent, but the pore-forming agent is in a liquid state, and the details are not repeated here.

After the pore-forming agent is added into the pores of the pole piece, the pole piece is cooled, rolled, extracted by a corresponding solvent or blown by hot air, and dried by a high-temperature oven.

The selected pore-forming agent has little residue and has no influence on the performance of the battery.

The pore-forming agent of the invention can effectively and basically fill the pores of the surface layer and partially fill the pores of the middle layer after entering the pores of the surface layer of the pole piece and being cooled, thereby artificially manufacturing a high-density surface layer, a medium-density middle layer and a low-density inner layer. The pole piece inner layer can be conducted with pressure during roll-in, and the pole piece top layer that has low porosity and is difficult to compress is artificially made before roll-in promptly, conducts pressure to the inlayer, forms a transition layer including the middle and middle layer three-layer, and the pore-forming agent content on top layer is the most, and is difficult to compress, and middle level pore-forming agent is few, and is difficult to compress than, and the inlayer does not have the pore-forming agent, easily compresses. Through the adjustment of the compression difficulty, the problems that the surface layer is high in pressure and the inner layer is small in pressure in the common pore-forming or rolling process are solved, and the pressure is effectively transmitted to the inner layer of the pole piece. Although the outer layer is stressed greatly during rolling, the outer layer is difficult to compress, the inner layer is stressed slightly less, but the inner layer is easy to compress, so that the deformation of the inner layer and the outer layer which can be finally obtained by adjusting the proportion of the rolling agent and the pore-forming agent is very close to each other, and the problem of the compression ratio of the inner layer and the outer layer is solved to a great extent. The invention is a range with good effect obtained by hundreds of related addition processes and rolling matching tests. It is not obvious to a person skilled in the art to consider how more holes are made or how holes are made again after compression. Other approaches reduce the amount of surface deformation such as: the roller press with larger diameter is used to lead the force to be close to the rolling in the vertical direction, and a mode of coating for multiple times and rolling for multiple times is also adopted, but the front and back coating process of the mode has great difficulty, the surface density control is very difficult, but the problem of deformation of the inner layer and the outer layer can not be effectively solved. The invention solves the contradiction fundamentally by controlling the compression ratio of the inner layer and the outer layer through the process, reducing the deformation amount of the outer layer and improving the porosity of the outer layer.

The pore-forming agent is distributed in original pores generated in coating and baking in different degrees, the problems of blind holes and closed holes of pore-forming after rolling in the traditional patent do not exist, and the thickness of a pole piece cannot rebound due to decomposition of the pore-forming agent. The pore-forming agent is directionally adsorbed into the original pores, so that the original pores during baking are released during pore-forming during extraction or hot air showering or thermal decomposition, closed pores can be changed into through pores, and the reduced pores are enlarged, rather than the pores formed everywhere or randomly in the prior patent.

The invention realizes the directional pore-forming, lays a foundation for pole pieces with higher compaction density, and realizes the performance which can not be achieved by the prior art. When the porosity of the pole piece in the prior art is about 30-40%, the surface is closed or shrunk, the problem of large difference of the porosities of the inner layer and the outer layer cannot be solved, so that the whole porosity is large, but the actually available porosity is only the surface (the inner layer and the outer layer are in a large number of series-parallel connection modes), even if the overall porosity is 30-40%, the actual effective porosity is only 20-30% (the surface porosity is generally about 25-28%), when the average porosity of the pole piece is 25-30%, the effective porosity can reach 23% -28%, which means that under the condition of the same effective porosity, the positive and negative pole pieces treated by the method can be coated with materials (accounting for about 12 percent of the space of the active substances) accounting for about 8 percent of the space, namely, the active substance of the dressing is increased by about 12 percent, and the energy density is improved by at least 12 percent.

The invention provides a pole piece (porous electrode) before rolling, which comprises an active material, a binder, a solvent and a pore-forming agent, wherein the pore-forming agent can be one or more of organic compounds with the melting point of 40-80 ℃. The pore-forming agent of the invention can be selected from EC ethylene carbonate, DPC, paraffin and the like, and the corresponding extracting agents are respectively DMC, carbon disulfide and the like, but is not limited to the pore-forming agents and the extracting agents.

The second purpose of the invention is to provide a lithium ion battery, which is prepared from the above pole piece through the processes of heat treatment, sheet preparation, assembly, liquid injection and the like, wherein the average porosity of the pole piece is 25% -30%, the effective porosity is 23% -28%, the low-temperature, rate and cycle performance are the same as those of a battery with low compaction density, and the energy density is improved by 6% -12% (about 6% for single electrode treatment, about 12% for both positive and negative electrodes).

A third object of the present invention is to provide a lithium ion battery comprising a battery case, and an electrode group and an electrolyte sealed in the battery case; the electrode group comprises a positive electrode, a negative electrode and a diaphragm positioned between the positive electrode and the negative electrode, and the lithium ion battery is provided. This object is a well-known technique in the industry that can be achieved by those skilled in the art and will not be described in detail herein.

Compared with the prior art, the invention has the beneficial effects that: the method can not only keep the pole piece highly compacted to improve the energy density of the battery, but also improve the uniformity of the pole piece of the battery and ensure the performances of multiplying power, circulation, low temperature and the like. The method can ensure that the surface layer of the pole piece has uniform and large quantity of pores under the condition of further improving the compaction density of the pole piece, the proportion of closed pores and shrinkage cavities can be greatly reduced, and the effective porosity of the pole piece is improved.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The positive and negative electrode active materials are not particularly limited, and may be any commercially available positive and negative electrode active materials in the prior art, and all commercially available positive electrode active materials may be used, such as LiFePO4, Li3V2(PO4)3, LiMn2O4, LiMnO2, LiNiO2, LiCoO2, LiVPO4F, and LiFeO 2; or ternary system Li1 plus aL1-b-cMbNcO2, wherein a, b and c respectively represent mole numbers, wherein a is more than or equal to-0.1 and less than or equal to 0.2, b is more than or equal to 0 and less than or equal to 1, c is more than or equal to 0 and less than or equal to 1, b plus c is more than or equal to 0 and less than or equal to 1.0, and L, M, N is one or more of Co, Mn, Ni, Al, Mg, Ga, Sc, Ti, V, Cr, Fe, Cu and Zn. All negative electrode active materials that are commercially available, such as artificial graphite, natural graphite, a silicon carbon material, lithium titanate, and the like, may be used.

The types of the positive and negative electrode current collectors are well known to those skilled in the art, and may be selected from, for example, aluminum foil, copper foil, punched foil, and the like. In a specific embodiment of the present invention, an aluminum foil is used as the positive electrode current collector, and a copper foil is used as the negative electrode current collector.

The present invention has no special requirements for the preparation method of the lithium ion battery, and can be performed with reference to the prior art, generally speaking, the positive electrode and the negative electrode are wound and separated by a separator to form an electrode group, the electrode group is placed in a battery case, an electrolyte is added, and then the battery case is sealed, wherein the winding and sealing method is well known to those skilled in the art. The amount of the electrolyte is the conventional amount. Thus obtaining the lithium ion battery provided by the invention. The subsequent conventional steps of aging, formation and the like are also carried out, and are not described again.

The invention only relates to the improvement of the pole piece processing technology of the lithium ion secondary battery in the prior art, so that other compositions and structures of the lithium ion secondary battery are not particularly limited. For example, the positive electrode, the separator, and the electrolyte of the battery are not particularly limited, and all types of positive electrodes, separators, and electrolytes that can be used in lithium ion secondary batteries can be used. The person skilled in the art can easily select and prepare the positive electrode, the separator and the electrolyte of the lithium ion secondary battery according to the present invention based on the teaching of the prior art, and prepare the lithium ion secondary battery according to the present invention from the positive electrode, the negative electrode, the separator and the electrolyte, which will not be described in detail herein.

Example 1:

a secondary pore-forming method for a lithium ion battery comprises the following steps:

s1: firstly, heating a pore-forming agent EC to form a molten liquid, wherein the corresponding extracting agents DMC respectively;

s2: adding a molten liquid at the tail of the coating machine, and soaking the molten liquid in a spraying box body, wherein the internal atomization pressure of the spraying box is 1KPa, the atomization temperature is 100 ℃, and the soaking box adopts 80 ℃;

s3: uniformly coating the prepared negative graphite slurry on a current collector substrate, drying, passing through a spray box at the speed of 2 m/s or a soaking box at the speed of 40m/min, spraying for 5 s or soaking for 0.5 s, blowing nitrogen on the surface of the soaked pole piece, and fully cooling the pole piece until the pore-forming agent is completely solidified;

s4: the pole piece after curing the pore-forming agent is rolled into a coil stock, and is rolled and formed by a roll squeezer according to the normal flow,keeping the humidity of the rolling environment within the range of non-water absorption of the pore-forming agent, adopting a pole piece and equipment environment to control the moisture to be tighter to less than 2 percent RH, and realizing the compaction density of the graphite cathode to be 1.68g/cm³；

S5: extracting the rolled pole piece for 60 seconds by an extraction box, and drying the extractant by an oven, wherein the extractant is condensed and recycled; or the rolled pole piece passes through a hot nitrogen air shower oven, the hot nitrogen air shower treatment temperature is 150 ℃, the treatment time is 120 seconds, most of the melted pore-forming agent liquid is blown out by hot nitrogen for recycling, the pole piece is subjected to heat treatment at 255 ℃ by a high-temperature nitrogen atmosphere oven, and the heat treatment time is 20 minutes;

s6: transferring the prepared pole piece to the subsequent process for production according to the production flow, using a ternary manganese-doped positive electrode, and adjusting the surface density to reach a reasonable excess ratio to prepare the battery;

s7: taking the pole pieces obtained in the fifth step, recording the pole pieces as 1-1 and 1-2 of atomization and extraction meters, 1-3 and 1-4 of atomization and heating treatment meters, 1-5 and 1-6 of soaking and extraction meters, 1-7 and 1-8 of soaking and heating treatment meters, testing the porosity and the tortuosity by a mercury intrusion method, recording, performing section analysis on the pole pieces, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by adopting a low-power SEM (scanning electron microscope), and recording;

s8: randomly taking 2 batteries, recording the number of the batteries as 1-1 and 1-2 by atomization and extraction respectively, recording the number of the batteries as 1-3 and 1-4 by atomization and heating treatment, recording the number of the batteries as 1-5 and 1-6 by soaking and extraction and recording the number of the batteries as 1-7 and 1-8 by soaking and heating treatment, calculating the energy density (under the same shell condition) after capacity grading, well recording, and testing the multiplying power of the obtained batteries and discharging recording capacity at-20 ℃.

Example 2:

s1: heating a pore-forming agent which is forty-alkane to form molten liquid, wherein the corresponding extracting agents are dimethyl ammonium formate respectively;

s2: adding a molten liquid at the tail of the coating machine to soak or spray a box body, wherein the atomization pressure in the spray box is 10KPa, the atomization temperature is 120 ℃, and the soaking box adopts 100 ℃;

s3: uniformly coating the prepared negative graphite slurry on a current collector substrate, drying, passing through a spray box at the speed of 0.05 m/s or a soaking box at the speed of 6 m/min, spraying for 180 seconds or soaking for 5 seconds, blowing nitrogen on the surface of the soaked pole piece, and fully cooling the pole piece until the pore-forming agent is completely solidified;

s4: the pole piece after the pore-forming agent is solidified is rolled into a coil stock, the coil stock is rolled and formed by a rolling machine according to a normal flow, the humidity of the rolling environment is kept within the range that the pore-forming agent does not absorb water, the moisture of the environment of the pole piece and equipment is controlled and tightened to be less than 2 percent RH, and the compaction density of the graphite cathode is 1.60g/cm³；

S5: extracting the rolled pole piece for 120 seconds by an extraction box, and drying the extractant by an oven, wherein the extractant is condensed and recycled; or the rolled pole piece passes through a hot nitrogen air shower oven, the hot nitrogen air shower treatment temperature is 120 ℃, the treatment time is 180 seconds, most of the melted pore-forming agent liquid is blown out by hot nitrogen for recycling, and the pole piece is subjected to heat treatment at the temperature of 155 ℃ for 5 minutes by a high-temperature nitrogen atmosphere oven;

s6: and transferring the prepared pole piece to the subsequent process for production according to the production flow. Using a ternary manganese-doped anode, preparing a ternary manganese-doped battery in the same workshop according to a formula, and adjusting the surface density to reach a reasonable excess ratio to obtain the battery;

s7: taking the pole pieces obtained in the fifth step, recording the pole pieces as 2-1 and 2-2 by atomization and extraction meters, 2-3 and 2-4 by atomization and heating treatment meters, 2-5 and 2-6 by soaking and extraction meters, 2-7 and 2-8 by soaking and heating treatment meters, testing the porosity and the tortuosity by a mercury intrusion method, recording, performing section analysis on the pole pieces, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by adopting a low-power SEM (scanning electron microscope), and recording;

s8: randomly taking 2 batteries, recording the number of the batteries as 2-1 and 2-2 respectively by atomization and extraction, recording the number of the atomization and extraction as 2-3 and 2-4 by atomization and heating treatment, recording the number of the soaking and extraction as 2-5 and 2-6 by soaking and heating treatment as 2-7 and 2-8 by soaking and heating treatment, calculating the energy density (under the same shell condition) after capacity grading, well recording, and testing multiplying power of the obtained batteries and discharging recording capacity at-20 ℃.

Example 3:

s1: heating a pore-forming agent which is 2-chlorobenzonitrile to form molten liquid, wherein the corresponding extracting agents are respectively ethanol;

s2: adding a molten liquid at the tail of the coating machine to soak or spray a box body, wherein the atomization pressure in the spray box is 5KPa, the atomization temperature is 80 ℃, and the soaking box adopts 60 ℃;

s3: uniformly coating the prepared positive lithium iron phosphate slurry on a current collector substrate, drying, passing through a spray box at the speed of 0.5 m/s or a soaking box at the speed of 25 m/min, spraying for 30 seconds or soaking for 1 second, blowing nitrogen on the surface of the soaked pole piece, and fully cooling the pole piece until the pore-forming agent is completely solidified;

s4: the pole piece after the pore-forming agent is solidified is rolled into a coil stock, the coil stock is rolled and formed by a roll squeezer according to a normal flow, the humidity of the rolling environment is kept within the range that the pore-forming agent does not absorb water, the moisture of the pole piece and the environment of equipment is controlled and tightened to be less than 2 percent RH, and the compaction density of the positive lithium iron phosphate positive pole is 2.7g/cm³；

S5: extracting the rolled pole piece for 10 seconds by an extraction box, and drying the extractant by an oven, wherein the extractant is condensed and recycled; or the rolled pole piece passes through a hot nitrogen air shower oven, the hot nitrogen air shower treatment temperature is 80 ℃, the treatment time is 60 seconds, most of the melted pore-forming agent liquid is blown out by hot nitrogen for recycling, the pole piece is subjected to heat treatment at 240 ℃ by a high-temperature nitrogen atmosphere oven, and the heat treatment time is 3 minutes;

s6: and transferring the well-made pole piece to the subsequent process for production according to the production flow known in the industry. Using a common graphite cathode, adjusting the surface density to reach a reasonable excess ratio, and preparing a battery;

s7: taking the pole pieces obtained in the fifth step, recording the pole pieces as 3-1 and 3-2 of atomization and extraction meters, 3-3 and 3-4 of atomization and heating treatment meters, 3-5 and 3-6 of soaking and extraction meters, 3-7 and 3-8 of soaking and heating treatment meters, testing the porosity and the tortuosity by a mercury intrusion method, recording, performing section analysis on the pole pieces, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by adopting a low-power SEM (scanning electron microscope), and recording;

s8: randomly taking 2 batteries, recording the number of the batteries as 3-1 and 3-2 by atomization and extraction, the number of atomization and heating treatment as 3-3 and 3-4 by atomization and extraction, the number of immersion and extraction as 3-5 and 3-6 by immersion and heating treatment as 3-7 and 3-8 by immersion and heating treatment, calculating energy density (under the same shell condition) after capacity grading, well recording, and testing multiplying power and discharging recording capacity at-20 ℃.

Example 4:

s1: heating the pore-forming agent which is 2-butanediol or 3-butanediol to form molten liquid, wherein the corresponding extracting agents are respectively ethanol;

s2: adding a molten liquid at the tail of the coating machine to soak or spray a box body, wherein the atomization pressure in the spray box is 2KPa, the atomization temperature is 110 ℃, and the soaking box adopts 80 ℃;

s3: uniformly coating the prepared positive lithium iron phosphate slurry on a current collector substrate, drying, passing through a spray box at the speed of 1.5 m/s or a soaking box at the speed of 35 m/min, spraying for 30 seconds or soaking for 3 seconds, blowing nitrogen on the surface of the soaked pole piece, and fully cooling the pole piece until the pore-forming agent is completely solidified;

s4: the pole piece after the pore-forming agent is solidified is rolled into a coil stock, the coil stock is rolled and formed by a roll squeezer according to a normal flow, the humidity of the rolling environment is kept within the range that the pore-forming agent does not absorb water, the moisture of the pole piece and the environment of equipment is controlled and tightened to be less than 2 percent RH, and the compaction density of the positive lithium iron phosphate positive pole is 2.6g/cm³；

S5: extracting the rolled pole piece for 60 seconds by an extraction box, and drying the extractant by an oven, wherein the extractant is condensed and recycled; or the rolled pole piece passes through a hot nitrogen air shower oven, the hot nitrogen air shower treatment temperature is 150 ℃, the treatment time is 20 seconds, most of the melted pore-forming agent liquid is blown out by hot nitrogen for recycling, the pole piece is subjected to heat treatment at 188 ℃ by a high-temperature nitrogen atmosphere oven, and the heat treatment time is 15 minutes;

s6: the prepared pole piece is transferred to the subsequent process for production according to the production flow, and a common graphite cathode is used for adjusting the surface density to reach a reasonable excess ratio to prepare a battery;

s7: taking the pole pieces obtained in the fifth step, recording the pole pieces as 4-1 and 4-2 by atomization and extraction, 4-3 and 4-4 by atomization and heating treatment, 4-5 and 4-6 by soaking and extraction, 4-7 and 4-8 by soaking and heating treatment, testing the porosity and the tortuosity by a mercury intrusion method, recording, performing section analysis on the pole pieces, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by adopting a low-power SEM (scanning electron microscope), and recording;

s8: randomly taking 2 batteries, recording the number of the batteries as 4-1 and 4-2 by atomization and extraction, the number of atomization and heating treatment as 4-3 and 4-4, the number of immersion and extraction as 4-5 and 4-6, and the number of immersion and heating treatment as 3-7 and 3-8, calculating the energy density (under the same shell condition) after capacity grading, well recording, and testing the multiplying power of the batteries and the discharge recording capacity at the temperature of-20 ℃.

Example 5:

s1: firstly, heating a pore-forming agent which is 2-butanediol and 3-butanediol to form molten liquid, wherein the corresponding extracting agents are respectively ethanol;

s2: adding a molten liquid at the tail of the coating machine to soak or spray a box body, wherein the atomization pressure in the spray box is 2KPa, the atomization temperature is 100 ℃, and the soaking box adopts 70 ℃;

s3: uniformly coating the prepared positive lithium iron phosphate slurry on a current collector substrate, drying, passing through a spray box at the speed of 0.2 m/s or a soaking box at the speed of 15 m/min, spraying for 100 seconds or soaking for 5 seconds, blowing nitrogen on the surface of the soaked pole piece, and fully cooling the pole piece until the pore-forming agent is completely solidified;

s4: rolling the pole piece after curing the pore-forming agent into a coil stock, performing roll forming by a roll squeezer according to a normal flow, keeping the humidity of a roll-in environment within a range that the pore-forming agent does not absorb water, controlling and tightening the moisture of the pole piece and the environment of equipment to be less than 2 percent RH, and adopting the rolling conditions commonly used in the field to realize the ternary positive electrode compacted density of 3.75g/cm³；

S5: extracting the rolled pole piece for 100 seconds by an extraction box, and drying the extractant by an oven, wherein the extractant is condensed and recycled; or the rolled pole piece passes through a hot nitrogen air shower oven, the hot nitrogen air shower treatment temperature is 100 ℃, the treatment time is 150 seconds, most of the melted pore-forming agent liquid is blown out by hot nitrogen for recycling, the pole piece is subjected to heat treatment at 188 ℃ by a high-temperature nitrogen atmosphere oven, and the heat treatment time is 5 minutes;

s7: taking the pole pieces obtained in the fifth step, recording the pole pieces as 5-1 and 5-2 of atomization and extraction meters, 5-3 and 5-4 of atomization and heating treatment meters, 5-5 and 5-6 of soaking and extraction meters, 5-7 and 5-8 of soaking and heating treatment meters, testing the porosity and the tortuosity by a mercury intrusion method, recording, performing section analysis on the pole pieces, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by adopting a low-power SEM (scanning electron microscope), and recording;

s8: randomly taking 2 batteries, recording the number of the batteries as 5-1 and 5-2 by atomization and extraction, recording the number of the batteries as 5-3 and 5-4 by atomization and heating treatment, recording the number of the batteries as 5-5 and 5-6 by soaking and extraction, recording the number of the batteries as 5-7 and 5-8 by soaking and heating treatment, calculating the energy density (under the same shell condition) after capacity grading, and recording the test multiplying power and the discharge recording capacity at the temperature of-20 ℃.

Example 6:

s1: heating a pore-forming agent EC to form a molten liquid, wherein the corresponding extracting agents are DMC respectively;

s2: adding a molten liquid at the tail of the coating machine to soak or spray a box body, wherein the atomization pressure in the spray box is 5KPa, the atomization temperature is 110 ℃, and the soaking box adopts 90 ℃;

s3: uniformly coating the prepared positive lithium iron phosphate slurry on a current collector substrate, drying, passing through a spray box at the speed of 0.5 m/s or a soaking box at the speed of 30 m/min, spraying for 30 s or soaking for 3 s, blowing nitrogen on the surface of the soaked pole piece, and fully cooling the pole piece until the pore-forming agent is completely solidified;

s4: rolling the pole piece after curing the pore-forming agent into a coil stock, performing roll forming by a roll squeezer according to a normal flow, keeping the humidity of a roll-in environment within a range that the pore-forming agent does not absorb water, controlling and tightening the moisture of the pole piece and the environment of equipment to be less than 2 percent RH, and adopting the rolling conditions commonly used in the field to realize the ternary positive electrode compacted density of 3.6g/cm³；

S5: extracting the rolled pole piece for 120 seconds by an extraction box, and drying the extractant by an oven, wherein the extractant is condensed and recycled; or the rolled pole piece passes through a hot nitrogen air shower oven, the hot nitrogen air shower treatment temperature is 120 ℃, the treatment time is 120 seconds, most of the melted pore-forming agent liquid is blown out by hot nitrogen for recycling, and the pole piece is subjected to heat treatment for 15 minutes by a high-temperature nitrogen atmosphere oven at 253 ℃;

s6: and transferring the prepared pole piece to the subsequent process for production according to the production flow. Using a common graphite cathode, adjusting the surface density to reach a reasonable excess ratio, and preparing a battery;

s7: taking the pole pieces obtained in the fifth step, recording the pole pieces as 6-1 and 6-2 by atomization and extraction, 6-3 and 6-4 by atomization and heating treatment, 6-5 and 6-6 by soaking and extraction, 6-7 and 6-8 by soaking and heating treatment, testing the porosity and the tortuosity by a mercury pressing method, recording, performing section analysis on the pole pieces, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by adopting a low-power SEM (scanning electron microscope), and recording;

s8: randomly taking 2 batteries, recording the number of the batteries as 6-1 and 6-2 by atomization and extraction, the number of atomization and heating treatment as 6-3 and 6-4 by atomization and extraction, the number of immersion and extraction as 6-5 and 6-6 by immersion and heating treatment as 6-7 and 6-8 by immersion and heating treatment, calculating energy density (under the same shell condition) after capacity grading, well recording, and testing multiplying power and discharging recording capacity at-20 ℃.

Example 7:

s3: uniformly coating the prepared positive lithium iron phosphate slurry on a current collector substrate, drying, passing through a spray box at the speed of 0.1 m/s or a soaking box at the speed of 10 m/min, spraying for 150 seconds or soaking for 5 seconds, blowing nitrogen on the surface of the soaked pole piece, and fully cooling the pole piece until the pore-forming agent is completely solidified;

s4: rolling the pole piece after curing the pore-forming agent into a coil stock, performing roll forming by a roll squeezer according to a normal flow, keeping the humidity of a roll-in environment within a range that the pore-forming agent does not absorb water, controlling and tightening the moisture of the pole piece and the environment of equipment to be less than 2 percent RH, and adopting the rolling conditions commonly used in the field to make the compaction density of the lithium manganate positive pole to be 3.2g/cm³；

S5: extracting the rolled pole piece for 100 seconds by an extraction box, and drying the extractant by an oven, wherein the extractant is condensed and recycled; or the rolled pole piece passes through a hot nitrogen air shower oven, the hot nitrogen air shower treatment temperature is 130 ℃, the treatment time is 30 seconds, most of the melted pore-forming agent liquid is blown out by hot nitrogen for recycling, the pole piece is subjected to heat treatment at 256 ℃ for 5 minutes by a high-temperature nitrogen atmosphere oven;

s7: taking the pole pieces obtained in the fifth step, recording the pole pieces as 7-1 and 7-2 by atomization and extraction meters, 7-3 and 7-4 by atomization and heating treatment meters, 7-5 and 7-6 by soaking and extraction meters, 7-7 and 7-8 by soaking and heating treatment meters, testing the porosity and the tortuosity by a mercury intrusion method, recording, performing section analysis on the pole pieces, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by adopting a low-power SEM (scanning electron microscope), and recording;

s8: 2 batteries are randomly selected, and are recorded as 7-1 and 7-2 of atomization and extraction respectively, 7-3 and 7-4 of atomization heating treatment, 7-5 and 7-6 of soaking and extraction respectively, 7-7 and 7-8 of soaking and heating treatment respectively, after capacity grading, energy density (under the same shell condition) is calculated, recording is well made, and the obtained battery is tested for multiplying power and discharging recording capacity at-20 ℃.

Example 8:

s1: heating a pore-forming agent which is forty-alkane to form molten liquid, wherein the corresponding extracting agents are respectively dodecane;

s2: adding a molten liquid at the tail of the coating machine to soak or spray a box body, wherein the atomization pressure in the spray box is 1KPa, the atomization temperature is 110 ℃, and the soaking box adopts 100 ℃;

s3: uniformly coating the prepared positive lithium iron phosphate slurry on a current collector substrate, drying, passing through a spray box at the speed of 0.3 m/s or a soaking box at the speed of 30 m/min, spraying for 60 seconds or soaking for 3 seconds, blowing nitrogen on the surface of the soaked pole piece, and fully cooling the pole piece until the pore-forming agent is completely solidified;

s4: the pole piece after the pore-forming agent is solidified is rolled into a coil stock, the coil stock is rolled and formed by a roller press according to a normal flow, the humidity of the rolling environment is kept within the range that the pore-forming agent does not absorb water, the moisture of the environment of the pole piece and equipment is controlled and tightened to be less than 2 percent RH, and the compaction density of the lithium manganate anode is 3.1g/cm³；

S5: extracting the rolled pole piece for 90 seconds by an extraction box, and drying the extractant by an oven, wherein the extractant is condensed and recycled; or the rolled pole piece passes through a hot nitrogen air shower oven, the hot nitrogen air shower treatment temperature is 140 ℃, the treatment time is 160 seconds, and most of the melted pore-forming agent liquid is blown out by hot nitrogen for recycling. The pole piece is subjected to heat treatment at 160 ℃ for 15 minutes by a high-temperature nitrogen atmosphere oven;

s7: taking the pole pieces obtained in the fifth step, recording the pole pieces as 8-1 and 8-2 by atomization and extraction meters, 8-3 and 8-4 by atomization and heating treatment meters, 8-5 and 8-6 by soaking and extraction meters, 8-7 and 8-8 by soaking and heating treatment meters, testing the porosity and the tortuosity by a mercury intrusion method, recording, performing section analysis on the pole pieces, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by adopting a low-power SEM (scanning electron microscope), and recording;

s8: randomly taking 2 batteries, recording the number of the batteries as 7-1 and 7-2 by atomization and extraction, 7-3 and 7-4 by atomization and heating treatment, 7-5 and 7-6 by soaking and extraction, 7-7 and 7-8 by soaking and heating treatment, calculating the energy density (under the same shell condition) after capacity grading, well recording, and testing the multiplying power of the batteries and discharging recording capacity at-20 ℃.

Comparative example 1:

and manufacturing the battery according to a normal production flow. The ternary manganese-doped positive electrode used in examples 1 and 2 was used as the positive electrode, the positive electrode and the negative electrode were prepared according to the same formulation and the areal density was adjusted to match accordingly, and 18650 cells were prepared.

Taking a normal negative plate (the compaction density is 1.55 g/cm)³) The porosity and tortuosity were measured by mercury intrusion method and recorded. And (3) performing section analysis on the pole piece, adopting a low-power SEM, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by using software, and recording.

After the capacity of the prepared battery is divided, the energy density is calculated (under the same shell condition), and the record is prepared. The resulting cell was tested for rate and recording capacity at-20 ℃.

Comparative example 2:

and manufacturing the battery according to a normal production flow. The positive electrode adopts a lithium iron phosphate positive electrode, the proportion of the positive electrode and the negative electrode in the examples 3 and 4 is the same, and the negative electrode is 1.55g/cm according to the common negative electrode³The surface density is adjusted to match, and the 18650 battery is made.

Taking the positive plate (compacted density is 2.35 g/cm)³) The porosity and tortuosity were measured by mercury intrusion method and recorded. And (3) performing section analysis on the pole piece, adopting a low-power SEM, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by using software, and recording.

Comparative example 3:

and manufacturing the battery according to a normal production flow. The anode adopts a ternary anode, the anode with the same proportion as the examples 5 and 6 is used, and the cathode adopts a common cathode of 1.55g/cm³The surface density is adjusted to match, and the 18650 battery is made.

Taking the positive plate (compacted density is 3.45 g/cm)³) The porosity and tortuosity were measured by mercury intrusion method and recorded. And (3) performing section analysis on the pole piece, adopting a low-power SEM, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by using software, and recording.

Comparative example 4:

and manufacturing the battery according to a normal production flow. The positive electrode adopts lithium manganate, the same proportion of the positive electrodes in the examples 7 and 8 is used, and the negative electrode adopts a common negative electrode of 1.55g/cm³The surface density is adjusted to match, and the 18650 battery is made.

Taking a positive plate (compacted density is 2.9 g/cm)³) The porosity and tortuosity were measured by mercury intrusion method and recorded. The pole piece is subjected to section analysis, a low-power SEM is adopted, the porosity (3 equal-part thickness) of the upper layer, the middle layer and the lower layer is statistically analyzed by software, and recording is well performedAnd (5) recording.

Comparative example 5:

and (4) manufacturing the pole piece and the battery according to the CN106848148A scheme. The positive electrode adopts the ternary manganese-doped positive electrode used in the embodiment 1, the positive electrode and the negative electrode in the same proportion are treated according to the patent, and the surface density is correspondingly adjusted to be matched to prepare the 18650 battery.

Taking the obtained negative plate (the compacted density is 1.55 g/cm)³) The porosity and tortuosity were measured by mercury intrusion method and recorded. And (3) performing section analysis on the pole piece, adopting a low-power SEM, performing statistical analysis on the porosity (3 equal parts of thickness) of the upper layer, the middle layer and the lower layer by using software, and recording.

Comparative example 6:

and (4) manufacturing the pole piece and the battery according to the CN103515607A scheme. The positive electrode adopts the ternary manganese-doped positive electrode used in the embodiment 1, the positive electrode and the negative electrode in the same proportion are treated according to the patent, and the surface density is correspondingly adjusted to be matched to prepare the 18650 battery.

Comparative example 7:

the pole piece and the battery are manufactured according to the CN104157827A scheme, the ternary manganese-doped anode used in the embodiment 1 is adopted as the anode, the anode and the cathode in the same proportion are processed according to the patent, and the surface density is correspondingly adjusted to be matched to manufacture the 18650 battery.

Performance detection

(1) Detecting the porosity of the pole piece:

and (3) testing the porosity: the open porosity of the pole piece samples prepared in examples 1-8 above was tested using a fully automatic mercury porosimeter, with the maximum pressure of 30000PSI and the porosity of the pole piece samples of comparative examples 1-4 tested using the same method. Characterized by the porosity of the through-hole, the ratio of pore volumes that can be directly connected to the surface of the pole piece.

Calculating the porosity: 1-material true density volume/porous electrode volume measurement, wherein the porous electrode volume is dressing thickness x dressing area, and the true density of the material is calculated according to the formula and the true density of the corresponding material to obtain the true solid volume in the porous electrode. All porosities (including blind and closed pores) of the pole pieces were characterized.

Tortuosity, the length of the pore calculated by mercury intrusion curve simulation is the thickness. The length from the communicating hole to the surface of the pole piece is represented, and the shorter the length is, the better the subsequent ionic conductivity is, the fewer the closed holes are, and the more the surface holes are. The structural coefficient phi is tested in a mercury intrusion method, the difference between a real core and a hypothetical parallel tube columnar capillary bundle model with equal length and equal sectional area is represented, and the value of the difference is the measurement of various factors influencing the difference. The structural coefficient phi represents the tortuous degree of the seepage of fluid in the pores, and the larger the structural coefficient is, the stronger the tortuous degree of the pores is.

The test results of the pole piece mercury intrusion method are shown in the table 1: the test results are shown in table 1:

as can be seen from Table 1, the compacted densities of the negative electrodes of examples 1 and 2 were 1.68g/cm³And 1.6g/cm³The negative pole of the porosity of the through hole is between 27.2 and 28.8 percent, and the compaction density of the through hole and the normal process of a workshop is 1.55g/cm³The porosity of the through hole is 28.5-29.9%, the difference is not large, and the pore-forming effect of the invention on the negative electrode is obvious.

The difference between the calculated porosity and the porosity of the test via is: the difference between examples 1-8 is about 2% to 4% and between comparisons 1-7 is 10.6%, 9.4%, 10.0%, 11.8%, 8.6%, 9.5%, 13.1%, respectively, indicating that the comparative examples have a significant proportion of pores that are not filled with mercury, i.e., some have a high tortuosity or a high proportion of blind pores.

Structural coefficient phi: the examples are generally between 4 and 5, and comparative examples 1 to 7 are: 7.4, 7.3, 8.2, 6.7, 6.6 and 8.6, which shows that the comparative example has slower mercury removal and higher pore proportion with large tortuosity, and also laterally proves that the pole piece has less pores on the surface and small pore diameter on the surface.

(2) Energy density of battery

The batteries prepared by the invention are 18650 batteries, the energy density of the batteries is compared by adopting batteries with uniform volume, and the detailed table of each embodiment and the calculation table of the comparative energy density is shown in a table 2:

it can be seen from table 2 that the batteries of examples 1 and 2 and comparative examples 1, 5, 6 and 7 are all positive electrode ternary manganese-doped batteries, the proportion of positive electrode is the same, the negative electrode is graphite, the treatment process of the negative electrode is different, the energy density of the weight of examples 1 and 2 is 186Wh/Kg and 183Wh/Kg, and the energy density of comparative examples 1, 5, 6 and 7 is 170Wh/Kg, 174Wh/Kg, 173Wh/Kg and 169Wh/Kg respectively, which shows that the method of the invention plays a significant role in improving the energy density, and the comparative patent also has a certain promotion, but the space is not large.

In examples 3 and 4, examples 4 and 6, and examples 7 and 8, compared with comparative examples 2, 3 and 4, respectively, the energy density is generally higher than 6% -9%, which is still the result of processing only one of the positive electrode and the negative electrode, if the positive electrode and the negative electrode are processed in this way, the energy density can be improved, and calculated according to the existing data, the energy density can be improved by about 12% compared with the industry mainstream level.

(3) And testing the low-temperature discharge performance of the battery at the temperature of minus 20 ℃ and the rate performance of the battery at normal temperature.

The batteries prepared in examples 1 to 8 and comparative examples 1 to 7 were charged at a constant current and a constant voltage of 0.5C to 3.65 (lithium iron phosphate battery)/4.2V (lithium ternary and lithium manganate battery), respectively, at a normal temperature of 25C, and 0.5C was discharged to 1.5V (lithium iron phosphate battery)/2.5V (ternary and lithium manganate battery) after being left at-20℃ for 48 hours, and the discharge capacities were recorded, and the test results are shown in table 3.

The batteries prepared in examples 1 to 8 and comparative examples 1 to 7 were charged at a constant current and a constant voltage of 0.5C to 3.65 (lithium iron phosphate battery)/4.2V (lithium ternary and lithium manganate batteries), respectively, at a normal temperature of 25 ℃, and 0.5C/1C/3C was discharged to 2.0V (lithium iron phosphate battery)/2.75V (ternary and lithium manganate batteries) after being left for 10 minutes, and the discharge capacities were recorded, and the results of the discharge at a low temperature of-20 ℃ and the discharge test at a different rate at a normal temperature for each of the examples and comparative examples are shown in table 3:

as can be seen from Table 3, the discharge capacity retention rates at-20 ℃ are significantly different between examples 1 and 2 as compared with comparative examples 1 to 7: the retention rates of the examples 1 and 2 are 76% -79%, and the comparative examples 1, 5, 6 and 7 are 71% -72%, 74% -75%, 73% -74% and 68% -72%, respectively, so that the retention rates are high, the consistency is improved, the consistency of the comparative examples 2 and 3 is higher, the capacity at relatively low temperature is obviously improved, and the comparative examples 2 and 3 have certain effects and are also obvious in improvement of the battery performance. Compared with comparative examples 2, 3 and 4 corresponding to the retention rates of examples 3 to 8, the low-temperature and rate performance of the battery is improved by 5 to 10 percent under the condition of higher energy density, and the effect is obvious. From the view of different multiplying power discharge, the discharge capacity retention rate is similar to that at the temperature of-20 ℃, the scheme of the embodiment is obviously improved, and better multiplying power discharge performance can be ensured under the condition of improving the energy density.

In summary, the following steps: the method can not only keep the pole piece highly compacted to improve the energy density of the battery, but also improve the uniformity of the pole piece of the battery and ensure the performances of multiplying power, circulation, low temperature and the like. The method can ensure that the surface layer of the pole piece has uniform and large quantity of pores under the condition of further improving the compaction density of the pole piece, the proportion of closed pores and shrinkage cavities can be greatly reduced, and the effective porosity of the pole piece is improved.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims

1. A secondary pore-forming method for a lithium ion battery is characterized by comprising the following steps: the method comprises the following steps:

s1: heating the pore-forming agent to 40-120 ℃ to form a molten liquid;

2. The secondary pore-forming method for the lithium ion battery according to claim 1, characterized in that: the pore-forming agent in the step S1 is any one of EC, DPC, paraffin, FEC, TCA, dibenzoic acid, oxybenzone, forty alkane, 2-chlorobenzonitrile, and 2, 3-butanediol.

3. The secondary pore-forming method for the lithium ion battery according to claim 2, characterized in that: the extracting agents respectively corresponding to the EC, the DPC, the 2, 3-butanediol and the forty-alkane are respectively DMC, carbon disulfide, ethanol and dimethyl ammonium formate.

4. The secondary pore-forming method for the lithium ion battery according to claim 1, characterized in that: in the step S2, the atomization pressure value in the spray box is 1-10 KPa, the atomization optimal temperature is 80-120 ℃, the temperature of the molten liquid adopted by the soaking box is 60-100 ℃, and the viscosity of the molten liquid is less than 100mPa & S.

5. The secondary pore-forming method for the lithium ion battery according to claim 1, characterized in that: and in the step S3, the spraying time is 5-180 seconds or the soaking time is 0.5-5 seconds, the surface of the soaked pole piece is sprayed by nitrogen, the redundant pore-forming agent solution on the surface is remained on the surface of the pole piece as little as possible, and the pole piece is fully cooled until the pore-forming agent is completely solidified.

6. The secondary pore-forming method for the lithium ion battery according to claim 1, characterized in that: step S4 is carried out in a roller press, pole pieces and equipment environment moisture are adopted to control and tighten to be less than 2% RH, the calendering condition is 0.5-3.0 MPa, the calendering speed is 10-40 m/min, the thickness of the formed pole pieces is 90-190 um, and the compaction density is as follows: graphite cathode 1.6-1.68 g/cm³2.7-2.8 g/cm of positive lithium iron phosphate³3.6-3.75 g/cm ternary positive electrode³3.1-3.2 g/cm of positive lithium manganate³。

7. The secondary pore-forming method for the lithium ion battery according to claim 1, characterized in that: in the step S5, the time value of extraction through the extraction box is 10-120 seconds, the viscosity of the treated molten liquid is less than 50mPa · S, the treatment time is 10-180 seconds, the oven is provided with a condensation recovery device, and the heat treatment time is 3-20 minutes.