HK1142172B

HK1142172B - Preparation method for gel polymeric lithium ion battery

Info

Publication number: HK1142172B
Application number: HK10108375.6A
Authority: HK
Inventors: 陈向魁; 黄东
Original assignee: 深圳市比克动力电池有限公司
Filing date: 2010-09-03
Publication date: 2015-01-23

Abstract

The invention discloses a preparation method of gel polymer lithium ion battery,Dissolve P (VDF-HFP) in an organic solvent,And inorganic ultrafine powder was added by in-situ hydrolysis method,Prepare a P (VDF-HFP) - TiO2 mixed solution,Then apply the mixed solution onto the positive and negative electrode plates of the battery,Evaporate the solvent,Forming a composite porous membrane on the positive and negative electrode plates,Then assemble the electrode sheet containing the composite porous membrane with the membrane,And inject liquid electrolyte into the assembled battery cells,Heating and baking the battery cells,Make the composite porous membrane and electrolyte form gel,Gel polymer battery was made.The process of producing polymer batteries using this method is simple, the cost is reduced, and the production process is widely applicable; The composite porous membrane produced has high liquid absorption rate, high porosity, stable structure, and good battery cycling performance and conductivity.

Description

Preparation method of gel polymer lithium ion battery

Technical Field

The invention relates to the field of battery manufacturing, in particular to a preparation method of a gel polymer lithium ion battery.

Background

The traditional lithium ion battery adopts liquid electrolyte, and the liquid electrolyte is formed by dissolving lithium salt in organic solvents such as carbonates and the like. For liquid electrolytes, the applicable negative electrode materials are limited; the liquid electrolyte is easy to decompose to generate gas and form overlarge vapor pressure in the discharging process. In addition, the liquid electrolyte is easy to corrode the cell shell, causing leakage and the like. And the polymer lithium ion battery is a novel green and environment-friendly chemical energy source appearing in 90 s of the 20 th century. It has the advantages of high voltage, large specific energy, stable discharge voltage, good cycle performance, good safety performance, long storage life and the like.

A method for preparing polymer electrolyte is disclosed in 1994 by the American Bell communication research institute (BELLCORE) (U.S. Pat. No. 5,96318). The production process of BELLCORE technology includes dissolving polyvinylidene fluoride-hexafluoropropylene P (VDF-HFP), adding great amount of dibutyl phthalate (DBP) as plasticizer and silica particle, coating the mixture onto substrate to form P (VDF-HFP) film, extracting plasticizer with great amount of low boiling point solvent (methanol) to obtain microporous film, rolling and compounding the microporous film and the electrode layer, and injecting liquid electrolyte to activate the film in drying room to obtain the polymer lithium ion battery. The biggest defects of the technology are that the technology is too complex, the cost is high, the extraction process of the plasticizer is complex and difficult to control, and the thermal compounding process is easy to generate micro short circuit, so that the yield of the battery is reduced.

Disclosure of Invention

The invention aims to provide a preparation method of a polymer lithium ion battery, which realizes complete gelation of electrolyte, does not contain free liquid electrolyte and has simple preparation process.

The purpose of the invention is realized by the following technical scheme.

The preparation method of the gel polymer lithium ion battery is characterized by comprising the following steps:

a) fully dissolving P (VDF-HFP) powder in an organic solvent to prepare a P (VDF-HFP) solution, wherein the organic solvent is one or a combination of any several of dimethylformamide, dimethyl sulfoxide, acetone, N-methyl pyrrolidone and tetrahydrofuran, and in the P (VDF-HFP) powder, the mass ratio of HFP to VDF is 6-20: 100, respectively;

b) fully mixing and stirring tetrabutyl titanate, a tetrabutyl titanate solvent and a complexing agent to prepare a precursor solution, wherein the mass ratio of tetrabutyl titanate to the complexing agent is 1.7-6.8: 1, wherein the complexing agent is acetylacetone; the tetrabutyl titanate solvent is n-butyl alcohol, ethylene glycol or toluene;

c) uniformly mixing the P (VDF-HFP) solution and the precursor solution, adding a mixed solution of an organic solvent and 5-25% hydrochloric acid, uniformly stirring, and aging to prepare the P (VDF-HFP) -TiO₂Mixed solution of P (VDF-HFP) -TiO₂In the mixed solution, the mass concentration of P (VDF-HFP) is 1-20%, and the organic solvent is one or the combination of any more of dimethylformamide, dimethyl sulfoxide, acetone, N-methylpyrrolidone and tetrahydrofuran;

d) the P (VDF-HFP) -TiO obtained in step c) is added₂Coating the mixed solution on the surface layers of active substances of the positive plate and the negative plate of the battery to volatilize the solvent and form a composite porous membrane on the polar plate;

e) assembling the positive and negative pole pieces obtained in the step d) and the diaphragm, injecting liquid electrolyte into the assembled battery core, heating and baking the battery core to enable the composite porous membrane and the electrolyte to form gel, and then carrying out pre-charging and grading processes on the battery core to prepare the gelA polymer battery. The electrolyte is conventional liquid electrolyte, and the lithium salt is LiFP₆And LiBOB, etc., and the organic solvent is PC, DEC, EC, DME, EMC, etc.

The preparation method of the gel polymer lithium ion battery is further realized by the following technical scheme.

In the step a), the dissolving process is heated, and the heating temperature is 30-85 ℃.

The mass ratio of P (VDF-HFP) to the organic solvent in the step a) is 2-25: 100.

in the step c), the temperature is kept between 15 ℃ and 40 ℃ for standing for 5h to 30h during aging.

The thickness of the composite porous membrane layer coated on the positive electrode sheet and the negative electrode sheet cumulatively in the step d) is 8-30 μm.

In the step e), the battery cell is pre-charged, then the battery cell is heated and baked to form gel, and then the gel is divided into different volumes.

In the step e), the battery cell is pre-charged and subjected to capacity grading, and then the battery cell is heated and baked to form gel.

And e), performing the process of heating and baking the battery cell to form the gel in the step e) in a segmented manner, and performing the process in a staggered manner with the process of pre-charging and grading the battery cell.

And c) pressurizing the interior of the battery cell when the battery cell is heated and baked in the step e) so as to be beneficial to forming gel.

And the pressure for pressurizing the inside of the battery cell in the step e) is 0.01 MPa-0.2 MPa.

In the step e), the heating temperature for heating and baking the battery cell is 60-140 ℃, and the total heating time is 0.5-7 h.

The invention adopts P (VDF-HFP) copolymer as the surface film of the microporous gel electrolyte, and the PVDF has good anodic oxidation resistance and mechanical strength and also has a larger dielectric constant (epsilon is 8.4), which is beneficial to the dissociation of lithium salt, thereby improving the concentration of carriers in the polymer electrolyte. The introduction of HFP into PVDF can reduce the crystallinity of PVDF and improve the capacity of PVDF to adsorb electrolyte solution.

The organic solvent of P (VDF-HFP) is selected according to the following principle: the polymer is compatible with the solvent with similar polarity and solubility parameter. The solubility parameter is 23.2MPa^1/2. Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, N-methyl pyrrolidone (NMP) and Tetrahydrofuran (THF) with solubility parameter of 20.3-26.7, and good compatibility with P (VDF-HFP).

Adding inorganic superfine powder TiO by adopting in-situ hydrolysis method₂. Tetrabutyl titanate Ti (OC)₄H₉) (TBT for short) has a large hydrolysis rate (hydrolysis rate constant Kh of 10)^-3mol·L^-1·s^-1) The complexing agent acetylacetone CH is used₃COCH₂COCH₃(AcAc for short) to control the rate of hydrolysis. The solvent water in the hydrochloric acid solution generates hydrolysis reaction with TBT, the added acid is favorable for inhibiting the hydrolysis of alkoxide, and in addition, the-OC in the TBT is caused₄H₉The groups are protonated, thereby imparting a positive charge to the colloidal particles, preventing agglomeration of the micelles. The hydrochloric acid solution was mixed with acetone in order to dilute the added water and avoid severe hydrolysis.

The TBT hydrolysis reaction is as follows:

Ti(OC₄H₉)₄+nH₂O→Ti(OC₄H₉)_4-n(OH)_n+nC₄H₉OH(n＝1，2，3，4)

aging is the process by which hydrolysis and condensation of TBT occurs. The polycondensation reaction is as follows:

2(OC₄H₉)₃Ti—OH→(OC₄H₉)₃Ti—O—Ti(OC₄H₉)₃+H₂O

Ti(OC₄H₉)₄+(OC₄H₉)₃Ti-OH→(OC₄H₉)₃Ti-O-Ti(OC₄H₉)₃+C₄H₉OH

later in sol-gelation, TiO formed₂Further condensation polymerization between sol molecules and H removal₂O molecules or alcohol molecules, and further forming a network of- (TiO)₂)_n-a structure.

When coating and volatilizing, separating by using two solvents, wherein the mixed solution comprises a solvent and a non-solvent of P (VDF-HFP), adding the solvent as a solvent of TBT and n-butanol C generated by reaction₄H₉OH is a non-solvent for P (VDF-HFP) and has a boiling point of 117.7 ℃ higher (56.48 ℃) than the acetone solvent for P (VDF-HFP), which is favorable for the formation of micropores in the composite gel electrolyte layer. After the mixed solvent is coated on the positive and negative electrode sheets, the boiling point difference between the solvent and the non-solvent is utilized (>-30 ℃), the organic solution begins to phase separate as the low boiling point solvent evaporates at the surface layer of the polymer microporous membrane, i.e. rich and poor phases of the organic polymer are produced. The polymer is precipitated to form a film skeleton when the solvent content in the rich phase is low, while the solvent content in the lean phase distributed in the skeleton is still high, and when the solvent is slowly volatilized, a small amount of polymer in the lean phase solution is crystallized and shrunk to be attached to the skeleton, so that micropores are generated. After the solvent was evaporated, P (VDF-HFP) formed a uniform film. The mechanical strength of the film is poor, the positive and negative pole pieces can be used as attachments to play a supporting role, and the conventional polyolefin diaphragm is used as a positive and negative pole partition.

After the composite porous membrane is formed on the pole piece, liquid electrolyte is injected, and the microporous structure on the composite porous pole piece absorbs a large amount of liquid electrolyte and keeps the electrolyte in the micropores. The organic solvent portion of the liquid electrolyte dissolves or swells the P (VDF-HFP) microporous scaffold by heating. After cooling, the high molecular swelling system formed by the solvent and the insoluble crosslinked polymer solid is gel. In addition, the heat and the pressure can cause the P (VDF-HFP) of the microporous polymer electrolyte membrane and the adhesive on the pole piece to generate physical or chemical crosslinking, so that the internal structure of the cell is more compact. The thermal gelation may be performed before the battery is precharged, after the battery is precharged, or after the battery is divided. Or the three steps of pre-filling gel, pre-filling gel and partial volume gel are combined in pairs or all three steps are subjected to gelation treatment. Under the conditions of the temperature and the pressure, the total heating and pressurizing time is not more than 8H generally. The gel polymer lithium ion battery manufactured by the method has better performance no matter gel before pre-charging, gel after pre-charging and gel after capacity grading.

Compared with the prior art, the invention has the advantages that:

1. the gel polymer battery manufactured by the method does not contain free liquid electrolyte, so that the problems of battery cell failure and the like caused by battery leakage and the like are greatly reduced, and the battery has high performance; the process is simple, the cost is reduced, no plasticizer is required to be added, and the extraction process of the plasticizer is omitted; the manufactured composite porous membrane has high liquid absorption rate and high porosity. The production process has wide application range, and the assembling mode of the battery core can adopt a laminated type or a winding type.

2. The technology of adding inorganic superfine powder by in-situ hydrolysis is adopted, so that the porosity and the structural stability of the composite porous membrane are improved. Firstly, the inorganic superfine powder has higher surface energy and is easy to agglomerate in the solution, so that the superfine powder can be dispersed in the solution more uniformly. And the particle size of the produced ultrafine powder can be controlled by controlling the reaction conditions. Secondly, the uniformly added superfine powder enhances the mechanical property of the inorganic-organic composite material. Because the added inorganic powder and polymer molecular chains form a three-dimensional network structure through Van der Waals force, electrostatic attraction or hydrogen bond action, the combination is tighter, and the polymer matrix has toughening and reinforcing effects. And thirdly, the uniform addition of the inorganic powder is beneficial to ion conduction, and the conductivity of the composite gel polymer electrolyte is improved. Due to the addition of the inorganic superfine powder, the randomness of the system is increased, the crystallinity of a polymer matrix is reduced, the activity of a polymer chain is improved, and the ionic conduction is facilitated. And the inorganic powder is uniformly added, so that the stability of the interface between the composite gel polymer electrolyte membrane and the electrode is further improved, and the safety of the polymer battery is further enhanced. This is because the inorganic ultrafine powder has affinity for moisture or an excessive solvent, and can adsorb these impurities. So that it does not react with the electrode surface.

3. Compared with liquid electrolyte, the composite gel electrolyte has greatly reduced reactivity with the surface of the electrode. So that the polymer battery can not generate gas due to the reaction and decomposition of the electrolyte and the surface of the electrode in the heating process to cause the battery to swell. The resulting rupture of the battery drum can be avoided.

Because of strong cohesiveness between the electrode and the composite gel electrolyte, the internal structure of the battery core is firmer and more stable. The anti-falling, anti-impact and anti-vibration capabilities of the battery core are greatly improved. The traditional battery core is easy to cause short circuit in the dislocation of the pole pieces in the processes of falling, impacting and vibrating, and even causes fire, explosion and the like.

Due to the complete combination between the electrode and the composite gel polymer electrolyte membrane, the increase of interface impedance caused by uneven surface and poor surface contact is reduced. Thereby ensuring the stability and safety of circulation.

The composite gel electrolyte membrane can meet the diversified requirements of the shapes of the battery cores, and can be cut into any shape to be assembled with positive and negative levels because the polymer electrolyte does not contain free liquid electrolyte. The composite gel electrolyte membrane is particularly suitable for the requirements of light weight and thin layer of the battery at present, and can be prepared into a thin-film battery through the hot pressing of the anode, the cathode and the composite gel electrolyte membrane.

The gel electrolyte membrane of the composite gel polymer lithium ion battery can effectively prevent the lithium dendrite from piercing the diaphragm to cause internal short circuit in the charging process of the battery. Because the diaphragm adopted by the liquid lithium ion battery is provided with the through micropores, the growth of the lithium dendrite can be connected with the anode and the cathode through the through micropores to cause short circuit. The micro-pores formed by the polymer support structure of the composite gel polymer electrolyte membrane have high bending rate, so that the internal short circuit of the positive electrode and the negative electrode cannot be caused even if dendritic crystals are generated.

The traditional liquid lithium ion battery inevitably does not consume electrolyte in the charging and discharging circulation process, so that the capacity retention capacity is reduced due to insufficient electrolyte in the later circulation stage. The gel polymer electrolyte layer in the composite gel polymer lithium ion battery has strong electrolyte reserving capability, thereby greatly reducing the consumption of electrolyte and increasing the cycle performance of the battery.

Drawings

FIG. 1 is a flow chart illustrating the fabrication of an embodiment;

FIG. 2 is a graph illustrating battery cycle life test results according to an embodiment;

fig. 3 is a graph showing the results of the battery discharge characteristic test according to the embodiment.

Detailed Description

The preparation process of the gel polymer lithium ion battery is shown in figure 1, and the gel polymer lithium ion battery comprises the following materials and components:

positive electrode, LiCoO₂: acetylene black conductive agent: PVDF binder (mass ratio) 96: 1.6: 2.4; the positive current collector is aluminum foil.

Negative electrode, 96% artificial graphite: SBR binder: sodium carboxymethylcellulose (mass ratio) 96: 2.5: 1.5; the negative current collector is copper foil.

Separator, 39.5% porosity polyolefin separator, thickness 12 μm.

Liquid electrolyte, EC: DEC: PC (mass ratio) 1: 1: 0.2, LiFP₆＝1M。

Solution of P (VDF-HFP), P (VDF-HFP): acetone (mass ratio) 1: 13.

TBT precursor solution (amount of P (VDF-HFP) is 1), TBT: AcAc: n-butanol (mass ratio) 0.34: 0.1: 4.

catalyst (in TBT 1), HCl: h₂O: acetone (mass ratio) 0.1: 2: 10.

preparing liquid electrolyte, P (VDF-HFP) solution, TBT precursor solution and catalyst according to the above proportion, mixing the above solutions uniformly, adding catalyst, stirring uniformly, aging to obtain P (VDF-HFP) -TiO₂The solution was mixed. And coating the prepared mixed solution on a positive electrode plate and a negative electrode plate, and volatilizing to form the composite porous electrode plate.

And winding the positive and negative composite porous pole pieces and the diaphragm and putting the wound pole pieces and the diaphragm into a shell. 1.2g of liquid electrolyte was injected. And adopting a scheme of gelation before pre-priming, and baking the battery cell after liquid injection for 3 hours at 80 ℃. And then pre-charging and grading.

According to the method, a group of composite gel polymer batteries are prepared, and the basic parameters are as follows: the aluminum plastic film is adopted for packaging, and L multiplied by W multiplied by H is 52mm multiplied by 30mm multiplied by 2.5mm, the capacity is 350mAh, and the internal resistance is 60m omega.

The following tests were performed on the batteries.

And (3) a cycle life test is shown in figure 2, and the cycle performance of the battery is improved.

And (5) carrying out 3C/5V overcharge test on the battery. The test conditions and procedures were as follows: first, the battery was discharged to 2.75V, and then charged with a constant current of 3C, and when the battery voltage reached 5V, the constant current charging was changed to the constant voltage charging, and the 5V voltage was maintained for 2 hours. And (3) testing results: the battery has no leakage, no smoke, no fire and no explosion. The battery overcharge performance is qualified.

And (3) performing hot plate baking test at 250 ℃ in a full electric state. The test conditions and procedures were as follows: first, the battery was charged to 4.2V, and then the battery was placed on an iron plate at 250 ℃ for baking, and the phenomenon of the battery during the baking at 250 ℃ was observed and recorded. And (3) testing results: the battery does not catch fire or explode. The test result of the hot plate baking at 250 ℃ under the full electric state is qualified.

And (5) testing the discharge characteristics. The test results are shown in fig. 3, in which curve 1 represents the capacity at 0.2C discharge, curve 2 represents the capacity at 0.5C discharge, and curve 3 represents the capacity at 1C discharge. When the 0.2C discharge capacity is taken as a standard, the 0.5C discharge capacity is close to 100%, and the 1C discharge capacity is 99.19%, and it can be seen that the gel polymer lithium ion battery shows good rate discharge characteristics.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims

1. The preparation method of the gel polymer lithium ion battery is characterized by comprising the following steps of:

a) dissolving P (VDF-HFP) powder in an organic solvent to prepare a P (VDF-HFP) solution, wherein the organic solvent is one or a combination of any several of dimethylformamide, dimethyl sulfoxide, acetone, N-methyl pyrrolidone and tetrahydrofuran, and in the P (VDF-HFP) powder, the mass ratio of HFP to VDF is 6-20: 100, respectively;

d) the P (VDF-HFP) -TiO obtained in step c) is added₂Coating the mixed solution on the surface layers of active substances of the positive plate and the negative plate of the battery to volatilize the solvent, and forming a composite porous membrane on the polar plate, wherein the thickness of the composite porous membrane layer coated on the positive plate and the negative plate in an accumulated mode is 30 micrometers;

e) assembling the positive and negative pole pieces obtained in the step d) and the diaphragm, injecting liquid electrolyte into the assembled battery core, heating and baking the battery core to enable the composite porous membrane and the electrolyte to form gel, and then carrying out pre-charging and grading processes on the battery core to prepare the gel polymer battery.

2. The method of claim 1, wherein the gel polymer lithium ion battery comprises: the mass ratio of P (VDF-HFP) to the organic solvent in the step a) is 2-25: 100.

3. the method of claim 1, wherein the gel polymer lithium ion battery comprises: in the step c), the temperature is kept between 15 ℃ and 40 ℃ for standing for 5h to 30h during aging.

4. The preparation method of the gel polymer lithium ion battery is characterized by comprising the following steps of:

e) assembling the positive and negative pole pieces obtained in the step d) and the diaphragm, injecting liquid electrolyte into the assembled battery core, pre-charging the battery core, heating and baking the battery core to form gel, and grading.

5. The preparation method of the gel polymer lithium ion battery is characterized by comprising the following steps of:

e) assembling the positive and negative pole pieces obtained in the step d) and the diaphragm, injecting liquid electrolyte into the assembled battery core, pre-charging and grading the battery core, and then heating and baking the battery core to form gel.

6. The preparation method of the gel polymer lithium ion battery is characterized by comprising the following steps of:

c) mixing the above P (VDF-HFP) solution and precursor solutionUniformly mixing, adding a mixed solution of an organic solvent and 5-25% hydrochloric acid, uniformly stirring, and aging to prepare P (VDF-HFP) -TiO₂Mixed solution of P (VDF-HFP) -TiO₂In the mixed solution, the mass concentration of P (VDF-HFP) is 1-20%, and the organic solvent is one or the combination of any more of dimethylformamide, dimethyl sulfoxide, acetone, N-methylpyrrolidone and tetrahydrofuran;

e) assembling the positive and negative pole pieces obtained in the step d) with a diaphragm, injecting liquid electrolyte into the assembled battery core, heating and baking the battery core to form gel, and performing the process in a segmented manner, and alternately performing the processes of pre-charging and grading the battery core.

7. The method of any of claims 1 to 6, wherein: and c) pressurizing the interior of the battery cell when the battery cell is heated and baked in the step e) so as to be beneficial to forming gel.

8. The method of claim 7, wherein the gel polymer lithium ion battery comprises: and the pressure for pressurizing the inside of the battery cell in the step e) is 0.01 MPa-0.2 MPa.

9. The method of any of claims 1 to 6, wherein: in the step e), the heating temperature for heating and baking the battery cell is 60-140 ℃, and the total heating time is 0.5-7 h.