CN114765277A - Lithium battery and preparation method thereof - Google Patents

Abstract

In order to overcome the problems of poor safety performance of a common liquid electrolyte lithium battery, insufficient charge and discharge performance and high cost of a gel or solid electrolyte lithium battery in the prior art, the invention provides a lithium battery, which comprises a battery shell, and a positive plate, a negative plate, an isolator and an electrolyte which are positioned in the shell; the electrolyte comprises a polymer lithium salt and an electrolyte solution; at least one of the positive electrode plate, the negative electrode plate and the separator contains a Lewis acid and the polymer lithium salt; the polymer lithium salt comprises a polymer chain segment, and anions and cations connected with the polymer chain segment; the anion contains one or more of carboxylate, sulfonate, phosphate and sulfate; the positive ions are lithium ions; the Lewis acid can be dissolved in the electrolyte, and the mass concentration of the Lewis acid in the electrolyte is less than 0.5 percent. Meanwhile, the invention also provides a preparation method of the lithium battery. The lithium battery provided by the invention can greatly improve the safety, does not reduce the charge-discharge performance and has low cost.

Description

A kind of lithium battery and preparation method thereof

technical field

The invention relates to a lithium battery, in particular to a solid-liquid mixed electrolyte lithium battery.

Background technique

Lithium-ion batteries have the advantages of high energy density, long cycle life, and high energy storage efficiency. They have been widely used in various portable electronic products, and have been gradually applied to electric vehicles, energy storage and other fields. However, the organic electrolytes used in commercial lithium-ion batteries contain a large amount of low-boiling and low-flash-point organic solvents (about 50% of the electrolyte weight), which are prone to combustion under the condition of thermal runaway of the battery. ,explode. Adding flame retardants (such as fluorophosphate and fluorophosphazene) to the electrolyte can inhibit the combustion of the above-mentioned low-boiling and low-flash-point organic solvents to a certain extent, but it will increase the internal resistance of the battery and reduce the battery's performance. Power characteristics and low temperature characteristics. The high-concentration electrolytes that have appeared in recent years can reduce the amount of organic solvents to a certain extent. At the same time, most of the solvents in the high-concentration electrolytes are complexed with lithium ions, which can significantly reduce the vapor pressure of organic solvents and improve the safety of lithium-ion batteries. Very helpful. However, this high-concentration electrolyte has high viscosity, poor wettability to electrodes and separators, and is difficult to enter into the tiny pores of electrodes and separators.

On the other hand, the use of polymer electrolytes to replace liquid electrolytes for lithium batteries has a long history. The most typical polymer electrolytes are a class of polyether polymers represented by polyethylene oxide (PEO) and small molecular lithium The polymer solid electrolyte formed by salt compounding has the problem of low conductivity. Although it has undergone a series of modifications, its room temperature conductivity can only reach the order of 10 ^-4 S/cm, which is still lower than that of liquid electrolytes. more than an order of magnitude. The anion in the lithium salt is fixedly connected to the polymer backbone to limit the migration of the anion, and a so-called single-ion conductor (polymer lithium salt) can be obtained, which can increase the lithium ion migration number to a level close to 1, which can effectively prevent The phenomenon of concentration polarization of the electrolyte caused by the migration of anions during the charging and discharging process is beneficial to improve the rate characteristics of the battery. Usually this kind of polymer lithium salt needs to add a certain amount of organic solvent to complex with lithium ions, so as to dissociate a certain amount of free lithium ions, but to dissociate enough free lithium ions, this kind of polymer lithium salt Generally, the anion must be a large anion containing a strong electron withdrawing group, such as an anion containing a fluoroalkylsulfonyl group as shown in the table below, or an anion with a complex structure centered on a boron atom (wherein R ₁ , R ₂ are hydrocarbon groups, R _f is fluorohydrocarbyl).

Due to the complex structure and difficult synthesis of such polymer lithium salts, the cost is high and it is difficult to achieve mass production applications. In particular, although polymer lithium salts containing fluorohydrocarbon groups have excellent performance, their high cost seriously hinders their mass production applications.

In order to greatly improve the safety of the lithium ion battery without reducing the charge and discharge performance of the lithium battery, the present invention proposes a new lithium battery and a preparation method thereof, which ensure that the lithium battery has excellent charge and discharge performance and safety. performance.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a new lithium battery, which greatly improves the safety of the lithium battery, does not reduce the charge and discharge performance of the lithium battery, and has the characteristics of low cost.

The technical scheme adopted by the present invention to solve the above-mentioned technical problems is as follows:

A lithium battery is provided, comprising a battery case, a positive electrode plate, a negative electrode plate, a separator and an electrolyte in the battery case; the electrolyte includes a polymer lithium salt and an electrolyte; the positive electrode plate, the negative electrode plate and the separator At least one of the bodies contains both a Lewis acid and the polymer lithium salt; the polymer lithium salt includes a polymer segment, an anion and a cation connected to the polymer segment; the anion contains carboxylate, sulfonate, One or more of phosphate and sulfate; the cation is lithium ion; the Lewis acid is soluble in the electrolyte, and the mass concentration of the Lewis acid in the electrolyte is 0.5% the following.

Meanwhile, the present invention also provides a method for preparing the above-mentioned lithium battery, comprising the following steps:

1) preparing a positive electrode plate, a negative electrode plate, and a separator, and at least one of the positive electrode plate, the negative electrode plate, and the separator contains the polymer lithium salt;

2) assembling the positive plate, the negative plate and the separator into a dry cell;

3) The Lewis acid is mixed with the electrolyte and injected into the dry cell.

The polymer lithium salt used in the lithium battery provided by the present invention has the characteristics of simple structure and low cost, and the polymer lithium salt can usually only dissociate a few free lithium ions in an organic solvent. Therefore, the present invention adopts a Lewis acid to combine with the anion in the lithium polymer salt to disperse the negative charge on the anion and significantly promote the dissociation of the lithium ion. In this way, the concentration of free lithium ions in the electrolyte can be greatly increased, the vapor pressure of the organic solvent in the electrolyte can also be greatly reduced, and the safety of the battery is greatly improved. At the same time, the increase of the free lithium ion concentration in the electrolyte is beneficial to the transport of lithium ions, and the anions on the polymer lithium salt are difficult to migrate under the action of the electric field, thus greatly improving the lithium ion migration number and ensuring the lithium battery. Has excellent charge and discharge performance.

However, since the Lewis acid is easily decomposed during the battery production process, the inventor creatively added the Lewis acid to the electrolyte and injected it into the dry cell together with the electrolyte, so that the Lewis acid was combined with the polymer lithium salt in the cell. , so as to effectively avoid the decomposition of Lewis acid and ensure the performance of the battery.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The lithium battery provided by the present invention includes a battery case and a positive electrode plate, a negative electrode plate, a separator and an electrolyte located in the battery case; the electrolyte includes a polymer lithium salt and an electrolyte; the positive electrode plate, the negative electrode plate and the separator At least one of the bodies contains both a Lewis acid and the polymer lithium salt; the polymer lithium salt includes a polymer segment, an anion and a cation connected to the polymer segment; the anion contains carboxylate, sulfonate, One or more of phosphate and sulfate; the cation is lithium ion; the Lewis acid is soluble in the electrolyte, and the mass concentration of the Lewis acid in the electrolyte is 0.5% the following.

The battery housing and the cells located within the battery housing are conventional configurations of lithium batteries. The cell usually includes a positive plate, a negative plate, and a separator.

The positive electrode plate usually includes a positive electrode current collector and a positive electrode material located on the surface of the positive electrode current collector, and the positive electrode material contains a positive electrode active material. In the present invention, there is no limitation on the types of positive electrode active materials, and various existing positive electrode active materials can be used. Preferably, the positive electrode active materials include lithium cobalt oxide, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, One or more of spinel lithium manganate and lithium iron phosphate. Usually, in order to improve the conductivity, the positive electrode material also includes a positive electrode conductive agent. Similarly, the present invention does not have any special restrictions on the positive electrode conductive agent. Preferably, the positive electrode conductive agent includes carbon black, carbon nanotubes, and graphene. one or more of.

The negative plate generally includes a negative electrode current collector and a negative electrode material located on the surface of the negative electrode current collector, and the negative electrode material contains a negative electrode active material. In the present invention, there is no limitation on the types of negative electrode active materials, and various existing negative electrode active materials can be used. Preferably, the negative electrode active materials include graphite, hard carbon, soft carbon, silicon carbon composite material, silicon oxycarbon One or more of composite materials, metallic lithium, and metallic lithium alloys. Usually, in order to improve the conductivity, the negative electrode material also includes a negative electrode conductive agent. Similarly, the present invention does not have any special restrictions on the negative electrode conductive agent. Preferably, the negative electrode conductive agent includes carbon black, carbon nanotubes, and graphene. one or more of.

In the present invention, the separator can be an existing conventional separator, that is, a polyolefin-based porous membrane. Preferably, the separator further comprises a ceramic and/or inorganic solid electrolyte coating. Besides, the separator may also include one or more of non-woven fabrics, fiber coatings, ceramic coatings, and inorganic solid electrolyte coatings. For example, the separator can be formed by coating a non-woven fabric with a fiber coating, a ceramic coating or an inorganic solid electrolyte coating, or even a fiber coating, ceramic coating directly formed on the surface of the positive electrode or negative electrode layer or inorganic solid electrolyte coating.

According to the present invention, the distribution form of the above-mentioned polymer lithium salt in the battery is not particularly limited. Preferably, the above-mentioned polymer lithium salt is dispersed in at least one of the positive electrode, the separator and the negative electrode. It can be understood that when the polymer lithium salt is dispersed in the positive electrode, the polymer lithium salt is dispersed in the positive electrode material. Specifically, the above-mentioned polymer lithium salt can be added when the positive electrode slurry is prepared, and then coated, baked and rolled. Ready to be positive. Similarly, when the above-mentioned polymer lithium salt is dispersed in the negative electrode, the polymer lithium salt is dispersed in the negative electrode material and can be added when preparing the negative electrode slurry. When the above-mentioned polymer lithium salt is dispersed in the separator, the polymer lithium salt is dispersed in the separator and can be added during the preparation of the separator.

Preferably, polymer lithium salts are dispersed in two or three of the positive electrode, separator and negative electrode. Most preferably, polymer lithium salts are dispersed in the positive electrode, separator and negative electrode.

In order for the polymer lithium salt to exert a significant effect, the weight percentage of the polymer lithium salt contained in at least one of the positive electrode material, the negative electrode material and the separator is 5% or more.

In the present invention, the above-mentioned polymer lithium salt specifically includes a polymer segment, an anion and a cation connected to the polymer segment; the anion contains one or more of carboxylate, sulfonate, sulfate, and phosphate; The cations are lithium ions.

Preferably, the anion contains a fluorohydrocarbon group, or the anion is linked to a fluorohydrocarbon group.

Further preferably, the lithium polymer salt includes one or more structures of the following structural formulas 1-3:

Wherein, R ₁ is a hydrocarbon group or a substituted hydrocarbon group optionally containing oxygen or fluorine, and R ₁ is connected to the polymer segment;

R ₂ is a fluorine atom, a hydrocarbon group or a substituted hydrocarbon group optionally containing oxygen or fluorine elements, R ₂ is connected to the polymer segment or not; R ₁ and R ₂ are connected to form a cyclic structure or not connected to form a cyclic structure.

It can be understood that the structure shown in the above structural formula 1-3 is the part connected to the polymer chain segment in the lithium polymer salt (that is, connected to the polymer chain segment through R ₁ , while R ₂ is independently connected to the polymer chain segment. connected or unconnected), rather than the complete structure of the polymer lithium salt.

For polymer lithium salts, the repeating units of the polymer segment can be various existing ones, such as polyolefins (such as structural formula 4), polyethers (such as structural formula 5), polyesters (such as structural formula 4) containing various substituents as structure

formula 6, structural formula 7), polyamide (such as structural formula 8, structural formula 9), polyurethane (such as structural formula 10) and the like.

wherein R ₁₁ and R ₁₂ are hydrocarbon groups or substituted hydrocarbon groups optionally containing oxygen, fluorine and nitrogen elements.

In the present invention, the polymer lithium salt with the above structure can be obtained by various existing methods, such as commercial purchase or self-preparation.

In the lithium battery provided by the present invention, at least one of the positive electrode plate, the negative electrode plate and the separator contains both the Lewis acid and the polymer lithium salt.

The above Lewis acid whiskers are soluble in the electrolyte. In addition, in the electrolyte solution, the mass concentration of the Lewis acid is 0.5% or less. It is preferably 0.001%-0.5%.

Further, the molar ratio of the Lewis acid to the anion in the lithium polymer salt is 0.5-1.1.

Theoretically, in order to make the Lewis acid and the anion on the polymer lithium salt fully combine and play the best effect, the mole number of Lewis acid should be equal to the mole number of the anion in the polymer lithium salt. When the number of moles of Lewis acid is lower than the number of moles of anions on the lithium polymer salt, a part of the anions on the lithium polymer salt will not be able to combine with the Lewis acid, which is not conducive to the sufficient dissociation of lithium ions in the lithium polymer salt. When the number of moles of Lewis acid is higher than the number of moles of anions on the lithium polymer salt, a part of the Lewis acid will be free in the electrolyte, and the effect of the Lewis acid free in the electrolyte on the battery performance varies with the type of Lewis acid. . In the lithium battery of the present invention, the molar ratio of the Lewis acid to the anion on the lithium polymer salt is between 0.5-1.1, preferably between 0.7-1.1, and more preferably between 0.9-1.1.

In order to prevent possible adverse effects of the free Lewis acid in the electrolyte on the battery performance, in the lithium battery of the present invention, the content of the free Lewis acid in the electrolyte is controlled within 0.5% by weight. That is to say, most of the Lewis acid in the electrolyte is combined with the polymer lithium salt after the liquid injection, so that the weight percentage of the free Lewis acid in the electrolyte is less than 0.5%.

The content of free Lewis acid in the electrolyte after the liquid injection can be obtained by the following method: the electrolyte in the battery after the liquid injection is taken out and then used for gas chromatography (GC), liquid chromatography (LC), nuclear magnetic resonance (NMR) ) and other methods for detection and quantification.

In the present invention, the Lewis acid includes a central atom and a ligand combined with the central atom; the central atom is boron or phosphorus, and the ligand contains one or more of oxygen or fluorine. Preferably, the Lewis acid includes one or more of boron trifluoride, phosphorus pentafluoride, triphenyl borate, tripentafluorophenyl boron, and tripentafluorophenyl phosphine.

As mentioned above, in the lithium battery provided by the present invention, the electrolyte includes an electrolyte in addition to the above-mentioned polymer lithium salt. Further, the electrolyte contains an organic solvent and a small molecule lithium salt. Preferably, based on the total weight of the electrolyte, the content of the polymer lithium salt is more than 10%, and the content of the organic solvent is less than 60%; the concentration of lithium ions in the electrolyte is not less than 1.5% mol/L.

The lithium battery provided by the present invention contains the above-mentioned specific content of polymer lithium salt, organic solvent and small molecule lithium salt. In this combination, the polymer lithium salt provides a part of lithium ions on the one hand, which increases the concentration of lithium ions. It is beneficial to improve the ion transport performance of the electrolyte. On the other hand, the movement of anions in the polymer lithium salt is greatly restricted, and it is difficult to migrate directionally under the action of an electric field. It can significantly improve the lithium ion migration number of the electrolyte and reduce the charge and discharge process of the electrolyte. The concentration polarization in the electrolyte has a very favorable effect on the ion transport properties of the electrolyte. Although, like other polymers, the presence of polymer lithium salts increases the viscosity of the electrolyte and has a detrimental effect on the migration of lithium ions, the above-mentioned beneficial effects are sufficient to offset the detrimental effects of increased viscosity. In addition, the presence of polymer lithium salts provides a basis for reducing the content of organic solvents, and the interaction between polymer lithium salts and organic solvents can significantly reduce the vapor pressure of organic solvents, which can greatly improve the safety of lithium batteries. sex. Therefore, the combination of the polymer lithium salt, the organic solvent and the small molecule lithium salt used in the present invention can make the lithium battery have excellent charge-discharge characteristics and safety performance at the same time.

Generally speaking, in the lithium battery provided by the present invention, based on the total weight of the electrolyte including the polymer lithium salt, the organic solvent and the small molecular lithium salt, the content of the polymer lithium salt is more than 10%, more preferably 20% or more, more preferably 30% or more. At the same time, in the above electrolyte, as mentioned above, when the content of polymer lithium salt is too high, the viscosity of the electrolyte is too high, which is not conducive to the migration of lithium ions, and the content of polymer lithium salt may be less than 50%.

Electrolytes exist in multiple locations in lithium batteries, including positive and negative electrodes and separators, and in voids outside positive and negative electrodes and separators. The composition of electrolytes at different locations can be different, but the polymer lithium salts and The total weight percentage of the organic solvent only needs to meet the above requirements.

According to the present invention, the electrolyte in the casing of the lithium battery further contains an organic solvent. It is important that in the electrolyte, the weight percent of organic solvent is 60% or less, preferably, the weight percent of organic solvent is 50% or less, and more preferably, the weight percent of organic solvent is 40% or less. Meanwhile, based on the actual usage, the weight percent of the organic solvent is more than 20%.

In the present invention, the organic solvent in the above-mentioned electrolyte can be various known in the art, for example, the organic solvent includes cyclic carbonate, cyclic carboxylate, chain carbonate, chain carboxylate, fluorine One or more of substituted cyclic carbonate, fluorinated cyclic carboxylate, fluorinated chain carbonate and fluorinated chain carboxylate.

Usually, in order to reduce the viscosity and ensure a sufficiently high conductivity, a large amount of organic solvents with a flash point lower than 30 °C are used in the electrolyte of ordinary lithium-ion batteries, such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate The weight percentage of isochain carbonate and chain carboxylates such as ethyl acetate, ethyl propionate, propyl acetate, and propyl propionate usually needs to reach more than 50%. The electrolyte of the present invention may contain the above-mentioned organic solvent with a flash point lower than 30°C. In the electrolyte, the content of the organic solvent with a flash point lower than 30°C is 40% or less of the total weight of the electrolyte, more preferably 30% or less. , more preferably 20% or less.

According to the present invention, the electrolyte in the casing of the lithium battery further comprises a small molecular lithium salt. The specific types of the above-mentioned small-molecule lithium salts are various lithium salts known in the art that are suitable for electrolytes. Preferably, the small-molecule lithium salts include lithium tetrafluoroborate, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, One of lithium bis(trifluoromethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methyl, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalate) borate, lithium difluorooxalate borate or more.

According to the present invention, through the joint action of the above-mentioned specific content of polymer lithium salt and small molecule lithium salt, the concentration of lithium ions in the electrolyte can be increased, which is beneficial to improve the ion transport performance, and the high concentration of lithium ions can reduce the amount of unreacted lithium ions in the electrolyte. The free organic solvent complexed by lithium ions is beneficial to improve the safety of the battery and also to improve the electrochemical stability of the electrolyte.

The content of small-molecule lithium salt can be changed within a certain range, as long as the lithium ion concentration in the electrolyte exceeds 1.5mol/L together with the polymer lithium salt, which can not only ensure sufficient electrical conductivity, but also significantly reduce the electrolyte. free organic solvent that is not complexed with lithium ions, thereby significantly improving the safety of the battery.

It should be noted that, in the lithium battery provided by the present invention, the concentration of lithium ions in the electrolyte is not less than 1.5 mol/L. As mentioned earlier, the above electrolytes may exist in multiple locations in a lithium battery, such as in the positive and negative electrodes and the separator and in the voids outside the positive and negative electrodes and the separator, and the composition of the electrolyte at different locations may be different. In the present invention, the above-mentioned lithium ion concentration is the average concentration calculated by all lithium ions including polymer lithium salts and small molecular lithium salts relative to the total volume of the electrolyte.

As existing, in order to improve the cycle performance, high temperature storage performance, low temperature performance and other properties of lithium batteries, various additives are usually added to the liquid electrolyte, and the above various additives can also be used in the lithium battery provided by the present invention. electrolyte. For example, the electrolyte further includes additives selected from vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfite, vinyl sulfate, difluorophosphoric acid One or more of lithium, lithium oxalate tetrafluorophosphate, lithium dioxalate difluorophosphate, and lithium trioxalate phosphate. The content of the above-mentioned various additives is also well known to those skilled in the art. For example, the content of the above-mentioned various additives in the electrolyte can be adjusted in the range of 0.01-10% according to actual performance requirements.

The present invention also provides a method for preparing the above-mentioned lithium battery, comprising the following steps:

1) preparing a positive electrode plate, a negative electrode plate, and a separator, and at least one of the positive electrode plate, the negative electrode plate, and the separator contains the polymer lithium salt;

2) assembling the positive plate, the negative plate and the separator into a dry cell;

3) The Lewis acid is mixed with the electrolyte and injected into the dry cell.

The specific methods and processes in the above steps are conventional and will not be repeated here.

In the above method, the polymer lithium salt can be added during the manufacturing process of the positive electrode plate, the negative electrode plate and the separator, and the Lewis acid can be added and injected into the electrolyte. When the electrolyte is injected into the dry cell, the Lewis will penetrate into the positive electrode material of the positive electrode plate/the negative electrode material/separator of the negative electrode plate with the electrolyte, and combine with the polymer lithium salt. Through the above method, in the lithium battery provided by the present invention, the mass concentration of the Lewis acid in the electrolyte is 0.5% or less. As mentioned above, if the Lewis acid is combined with the lithium polymer salt before preparing the lithium battery, the Lewis acid will be decomposed during the preparation of the lithium battery, so that the object of the present invention cannot be achieved.

According to the present invention, in order to ensure that the electrolyte can smoothly penetrate into the pores of the positive electrode, the negative electrode, and the separator, the concentration of the small-molecule lithium salt in the electrolyte needs to be controlled between 0.8 mol/L and 1.5 mol/L. between mol/L. When the concentration of small-molecule lithium salt in the electrolyte is too low, in order to make the lithium ion concentration in the electrolyte meet the requirements, the content of polymer lithium salt must be increased, but an excessively high content of polymer lithium salt will make the electrolyte viscosity. Too high is not conducive to ion transport. When the concentration of the small-molecule lithium salt in the electrolyte is too high, the viscosity of the electrolyte is too high, and it is difficult to fully penetrate into the pores of the positive electrode plate, the negative electrode plate, and the separator.

The present invention will be further illustrated by the following examples.

Example 1

This embodiment is used to illustrate the lithium battery disclosed in the present invention.

(1) Preparation of polymer lithium salt

Acrylic acid (AA) was dissolved in methanol, an equimolar amount of lithium hydroxide (LiOH) was added, and after stirring for 2 hr, the temperature was raised to 75 °C, and the methanol solution of azobisisobutyronitrile (AIBN) was added dropwise, and the reaction was stirred for 4 hr. After that, the precipitate of polyacrylate lithium (PAALi) was formed, which was filtered, washed and dried to obtain polymer lithium salt 1 (PAALi).

(2) Preparation of positive plate

Li)、PVDF粘结剂(

5130)、聚合物锂盐1(PAALi)按重量比91.5:1.5:2:5混合后投入双行星搅拌机，加入N-甲基吡咯烷酮(NMP)，充分搅拌均匀后经过滤网过滤获得浆料，浆料的固含量为65％。然后用挤压式涂布机将浆料涂布到厚度为12μm的铝箔的两面上，经烘烤、热辊压后得到正极板，正极板单面涂层的面密度为19.5mg/cm²，单面涂层厚度为57μm。The positive electrode active material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , carbon black conductive agent (Super

Li), PVDF binder (

5130), polymer lithium salt 1 (PAALi) were mixed in a weight ratio of 91.5:1.5:2:5, put into a double planetary mixer, added N-methylpyrrolidone (NMP), fully stirred and filtered through a filter to obtain a slurry, The solids content of the slurry was 65%. Then, the slurry was coated on both sides of the aluminum foil with a thickness of 12 μm by an extrusion coater, and the positive plate was obtained after baking and hot rolling. The surface density of the single-sided coating of the positive plate was 19.5 mg/cm ² , the single-sided coating thickness is 57 μm.

(3) Preparation of negative plate

Li)、聚合物锂盐1(PAALi)按重量比93.5:1.5:5混合后投入双行星搅拌机，加入去离子水(DIW)，充分搅拌均匀后再加入占固形物总重1％的固含量为50％的丁苯橡胶乳液(SBR)，继续搅拌均匀后经过滤网过滤获得浆料，浆料的固含量为45％。然后用挤压式涂布机将浆料涂布到厚度为6μm的铜箔的两面上，经烘烤、热辊压后得到负极板，负极板单面涂层的面密度为13.0mg/cm²，单面涂层厚度为79μm。The negative active material artificial graphite, carbon black conductive agent (Super

Li) and polymer lithium salt 1 (PAALi) were mixed in a weight ratio of 93.5:1.5:5, put into a double planetary mixer, added deionized water (DIW), fully stirred and then added a solid content of 1% of the total solid weight It is a 50% styrene-butadiene rubber latex (SBR), which is continuously stirred evenly and filtered through a filter to obtain a slurry, and the solid content of the slurry is 45%. Then, the slurry was coated on both sides of the copper foil with a thickness of 6 μm by an extrusion coater, and the negative plate was obtained after baking and hot rolling. The surface density of the coating on one side of the negative plate was 13.0 mg/cm ² , the thickness of the single-sided coating is 79 μm.

(4) Preparation of separator

Alumina powder (D50 is 1.5μm) and polymer lithium salt 1 (PAALi) were mixed in a weight ratio of 95:5, put into deionized water (DIW), and stirred and ground in a stirring mill until the particle size of alumina was 2μm Next, transfer it into a stirring tank, add styrene-butadiene rubber latex (SBR) with a solid content of 50%, which accounts for 1.2% of the total solid weight, and stir evenly, and filter through a filter to obtain a slurry. 10%. Then, the slurry was coated on one surface of a polyethylene porous film with a thickness of 9 μm (porosity 45%) by gravure printing, and this step was repeated to coat the slurry on the other surface of the polyethylene porous film. After drying, a composite porous separator with a single-sided inorganic coating thickness of 3 μm was obtained. The total thickness of the composite porous separator was 15 μm.

(5) Preparation of dry cell

Cut the above-mentioned positive electrode plate, the above-mentioned negative electrode plate, and the above-mentioned separator into a certain shape, wherein the size of the active material region on the positive electrode plate is 20cm×12cm, the size of the active material region on the negative electrode plate is 20.1cm×12.1cm, and the size of the separator It is 20.5cm×12.5cm, and the current collector lead-out parts are left on the positive plate and the negative plate respectively; then they are stacked layer by layer in the manner of negative plate, separator, positive plate, separator, negative plate, ..., a total of 26 pieces The positive plate and 27 negative plates, the outermost layer is the negative plate; then the current collectors of the positive plates are welded together with an ultrasonic welder, and the positive lugs are welded, and the current collectors of the negative plates are drawn out with an ultrasonic welder. Welded together, and welded the negative lug to get the lamination.

Put the above-mentioned laminated body into a packaging bag made of two pieces of aluminum-plastic film after punching, and fuse the hot-melt glue on the tab with the packaging bag by hot-melting, and the tab is drawn out of the packaging bag. , leaving an airbag and a liquid injection port on one side of the packaging bag, thus obtaining a dry cell. The weight of the polymer lithium salt 1 in the dry cell can be calculated from the weight of the positive electrode plate, the negative electrode plate, the separator and the content of the polymer lithium salt 1 therein.

(6) Preparation of electrolyte

The Lewis acid used was boron trifluoride (BF ₃ ), and in order to add it to the electrolyte, a complex of boron trifluoride and ethyl methyl carbonate (BF ₃ .EMC) was used. Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), boron trifluoride/ethyl methyl carbonate complex (BF ₃ . In the mixture of EMC), the weight percentage is LiPF ₆ :EC:EMC:BF ₃ .EMC=13.8:22.6:5.3:58.3, and then add 1.5% of vinylene carbonate (VC), 1.5% of the weight of the whole electrolyte 1,3-propane sultone (1,3-PS) was used as an additive to obtain the desired electrolyte.

(7) Preparation of batteries

Put the dry cell at 60°C under vacuum for more than 24 hours, and then pour the above electrolyte into the dry cell from the injection port in a glove box with a dew point lower than -40°C. The sealing machine seals the liquid injection port outside the airbag, and at the same time draws out the gas in the cell, so that the unformed cell is obtained. The weight of the unformed cell was weighed, and the weight of the injected electrolyte was obtained by subtracting the weight of the dry cell.

(8) Detection of free Lewis acid content in battery electrolyte

Cut the battery after liquid injection, apply pressure to the battery to make the electrolyte seep out, collect a sample of the seepage electrolyte, detect and quantify BF ₃ by gas chromatography, and obtain the free Lewis acid content. The results are shown in Table 1.

(9) Formation of batteries

The battery is formed with a charging and discharging device, firstly charged to 3.6V with a constant current of 0.05C, then vacuumed and exhausted with a vacuum heat sealer and cut off the airbag, and then charged with a constant current of 0.2C to 4.2V V, and then charge at constant voltage until the current drops to 0.05C, and then discharge to 3.0V at a constant current of 0.2C, that is, a good battery is obtained.

(10) Battery test

The formed battery was charged to 4.2V at a constant current of 1C at room temperature, and then charged at a constant voltage until the current dropped to 0.05C, and then discharged to 3.0V at a constant current of 1C to obtain the discharge capacity (Ah) and energy density. (Wh/kg). Then, the battery was charged to 4.2V with a constant current of 1C at room temperature, and then charged with a constant voltage until the current dropped to 0.05C, and then discharged to 3.0V with a constant current of 3C to obtain the discharge capacity and calculate the rate discharge performance 3C /1C. Finally, the battery was charged to 4.2V with a constant current of 1C at room temperature, and then charged with a constant voltage until the current dropped to 0.05C, and then discharged to 3.0V with a constant current of 1C. This cycle was performed for 1000 cycles to obtain the discharge capacity retention rate. .

According to GB/T 31485-2015, the battery needling safety test was carried out. A steel needle with a diameter of 8 mm was used to penetrate the battery in the direction perpendicular to the polar plate at a speed of 25 mm/s and stayed in it for 1 hr.

The parameters related to the polymer lithium salt and electrolyte in the battery are shown in Table 1, and the test results of the battery are shown in Table 2.

Example 2

This embodiment is used to illustrate the lithium battery disclosed in the present invention.

Except that the polymer lithium salt used is polymer lithium salt 2, and the components other than the additives in the electrolyte are adjusted by weight percentage as LiPF ₆ :EC:EMC:BF ₃ .EMC=15.2:26.6:31.5:26.7 Others are the same as in Example 1. The parameters related to polymer lithium salt and electrolyte in the battery are shown in Table 1, and the battery test results are shown in Table 2.

Preparation of polymer lithium salt 2

Acrylic acid (AA) was dissolved in methanol, equimolar lithium hydroxide (LiOH) was added, and after stirring for 2 hr, equimolar butyl acrylate (BA) was added, the temperature was raised to 75°C, and azobisisobutyronitrile was added dropwise. (AIBN) methanol solution, after stirring and reacting for 4 hr, the precipitation of the copolymer of lithium acrylate and butyl acrylate (P(AALi-BA)) was formed, and the polymer lithium salt 2 (P(AALi-BA) was obtained after filtration, washing and drying. BA), the molar ratio of the two monomers is 1:1).

Example 3

This embodiment is used to illustrate the lithium battery disclosed in the present invention.

Except that the polymer lithium salt used is polymer lithium salt 3, and the components other than additives in the electrolyte are adjusted by weight percentage as LiPF ₆ :EC:EMC:BF ₃ .EMC=14.1:23.6:11.5:50.8 Others are the same as in Example 1. The parameters related to polymer lithium salt and electrolyte in the battery are shown in Table 1, and the battery test results are shown in Table 2.

Preparation of polymer lithium salt 3

Lithium polyvinylsulfonate (PVSLi) was synthesized as polymer lithium salt 3 with reference to the literature Polymer Bulletin 57, 115-120 (2006).

Example 4

This embodiment is used to illustrate the lithium battery disclosed in the present invention.

Except that the polymer lithium salt used is polymer lithium salt 4, the Lewis acid adopts tripentafluorophenyl boron (TPFPB), and the components other than the additives in the electrolyte are LiPF ₆ :EC:EMC:TPFPB by weight percentage =13.1:18.4:33.0:35.5 was adjusted, and the rest was the same as in Example 1. The parameters related to polymer lithium salt and electrolyte in the battery are shown in Table 1, and the battery test results are shown in Table 2.

Preparation of polymer lithium salt 4

Dissolve acrylic acid (AA) in methanol, add equimolar lithium hydroxide (LiOH), stir and react for 2 hr, add butyl acrylate (BA) whose mole number is twice the mole number of acrylic acid, heat up to 75°C, and add dropwise. The methanol solution of azobisisobutyronitrile (AIBN) was stirred and reacted for 4 hr to form the precipitation of the copolymer of lithium acrylate and butyl acrylate (P(AALi-2BA)), which was filtered, washed and dried to obtain lithium polymer salt 4 (P(AALi-2BA), the molar ratio of the two monomers is 1:2).

Comparative Example 1

This comparative example is used to compare and illustrate the lithium battery disclosed in the present invention.

Except that there is no polymer lithium salt and Lewis acid, and the electrolyte is to dissolve 1 mol/L LiPF ₆ in an EC/EMC mixed solvent with a volume ratio of 3/7, and add 2% by weight of VC and 2% by weight of Except for 2% of 1,3-PS, the rest was the same as in Example 1. The parameters related to the electrolyte in the battery are shown in Table 1, and the battery test results are shown in Table 2.

Comparative Example 2

This comparative example is used to compare and illustrate the lithium battery disclosed in the present invention.

Except that there is no Lewis acid, and the electrolyte is to dissolve 1.2mol/L LiPF ₆ in an EC/EMC mixed solvent with a volume ratio of 3/7, and add 1.5% by weight of VC and 1.5% by weight of 1 , 3-PS, other is the same as Example 1. The parameters related to polymer lithium salt and electrolyte in the battery are shown in Table 1, and the battery test results are shown in Table 2.

Comparative Example 3

This comparative example is used to compare and illustrate the lithium battery disclosed in the present invention.

Except that the content of Lewis acid in the electrolyte is increased, that is, the components other than additives in the electrolyte are adjusted by weight percentage as LiPF ₆ :EC:EMC:BF ₃ .EMC=15.0:25.9:27.1:32.0, other Same as Example 1. The parameters related to polymer lithium salt and electrolyte in the battery are shown in Table 1, and the battery test results are shown in Table 2.

Table 1

The obtained test results are shown in Table 2.

It can be seen from the test results of the battery shown in Table 2 that the solution provided by the present invention adopts polymer lithium salt and Lewis acid, and the molar ratio of the two is controlled within a suitable range, so that the battery electrolyte after liquid injection The free Lewis acid weight percentage is less than 0.5%, which can ensure that the battery has excellent rate discharge performance and cycle performance, and can pass the acupuncture test with good safety. For comparison, Comparative Example 1, which did not use polymer lithium salt and Lewis acid, could not pass the acupuncture test, and the safety was not good; Comparative Example 2, which used polymer lithium salt (PAALi) but did not use Lewis acid, had good safety. , but because the polymer lithium salt itself cannot dissociate more free lithium ions, the rate discharge performance of the battery is poor; in Comparative Example 3, which uses polymer lithium salt and Lewis acid, but the content of Lewis acid is high, due to The weight percentage of free Lewis acid in the battery after liquid injection significantly exceeds 0.5%, which has a certain negative impact on the cycle performance of the battery.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (12)

1. A lithium battery comprising a battery case, and a positive electrode plate, a negative electrode plate, a separator, and an electrolyte disposed in the battery case; the electrolyte comprises a polymer lithium salt and an electrolyte solution;

at least one of the positive plate, the negative plate and the separator contains Lewis acid and the polymer lithium salt;

the polymer lithium salt comprises a polymer chain segment, and anions and cations connected with the polymer chain segment; the anion contains one or more of carboxylate, sulfonate, phosphate and sulfate; the cation is lithium ion;

the Lewis acid is soluble in the electrolyte, and the mass concentration of the Lewis acid in the electrolyte is less than 0.5 percent.

2. The lithium battery of claim 1, wherein the polymeric lithium salt comprises a structure according to one or more of the following formulas 1-3:

wherein R is₁Is a hydrocarbon group or a substituted hydrocarbon group which may contain an oxygen or fluorine element, and R₁Is connected with the polymer chain segment;

R₂is a fluorine atom, a hydrocarbon group or a substituted hydrocarbon group which may contain oxygen or fluorine, R₂With or without a polymer segment; r₁、R₂Connected to form a ring structure or not connected to form a ring structure.

3. A lithium battery as claimed in claim 1 or 2, characterized in that the lewis acid comprises a central atom and a ligand bound to the central atom;

the central atom is boron or phosphorus, and the ligand contains one or more of oxygen or fluorine.

4. A lithium battery as claimed in claim 3, characterized in that the lewis acid comprises one or more of boron trifluoride, phosphorus pentafluoride, triphenyl borate, trifluoropenta-phenyl boron, trifluoropenta-phenyl phosphine.

5. The lithium battery of claim 1, wherein the positive plate includes a positive current collector and a positive material on a surface of the positive current collector, and the negative plate includes a negative current collector and a negative material on a surface of the negative current collector;

the weight percentage of the polymer lithium salt contained in at least one of the positive electrode material, the negative electrode material and the separator is more than 5%.

6. The lithium battery of claim 1 wherein the molar ratio of the lewis acid to the anion in the lithium salt of the polymer is from 0.5 to 1.1.

7. The lithium battery of any one of claims 1, 2, 4-6, wherein the electrolyte comprises an organic solvent and a small molecule lithium salt;

the content of the polymer lithium salt is more than 10% and the content of the organic solvent is less than 60% by taking the total weight of the electrolyte as a reference;

the concentration of lithium ions in the electrolyte is not less than 1.5 mol/L.

8. The lithium battery according to claim 7, wherein the organic solvent comprises an organic solvent having a flash point of less than 30 ℃, and the content of the organic solvent having a flash point of less than 30 ℃ is 40% or less of the total weight of the electrolyte.

9. The lithium battery according to claim 8, wherein the organic solvent comprises one or more of cyclic carbonate, cyclic carboxylic ester, chain carbonate, chain carboxylic ester, fluorinated cyclic carbonate, fluorinated cyclic carboxylic ester, fluorinated chain carbonate, and fluorinated chain carboxylic ester;

the organic solvent with the flash point lower than 30 ℃ comprises one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, propyl acetate and propyl propionate.

10. The lithium battery of claim 7, wherein the small molecule lithium salt comprises one or more of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium trifluoromethylsulfonate, lithium bis (trifluoromethylsulfonyl) imide, lithium tris (trifluoromethylsulfonyl) methide, lithium bis-fluorosulfonylimide, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate.

11. The lithium battery of claim 1, further comprising an additive selected from one or more of vinylene carbonate, fluoroethylene carbonate, 1, 3-propane sultone, ethylene sulfite, vinyl sulfate, lithium difluorophosphate, lithium tetrafluorophosphate oxalate, lithium difluorophosphate, and lithium trioxalato phosphate.

12. A method of manufacturing a lithium battery as claimed in any one of claims 1 to 11, characterized in that it comprises the following steps:

1) preparing a positive electrode plate, a negative electrode plate, and a separator, and at least one of the positive electrode plate, the negative electrode plate, and the separator contains the polymer lithium salt;

2) assembling the positive plate, the negative plate, and the separator into a dry cell;

3) and mixing the Lewis acid with the electrolyte and injecting the mixture into the dry battery cell.