阅读说明：本技术 用于固态电池的低孔隙率正极极片及其制备方法 (Low-porosity positive pole piece for solid-state battery and preparation method thereof ) 是由 卢灿生 陈邦义 于 2021-01-29 设计创作，主要内容包括：本发明公开了一种用于固态电池的低孔隙率正极极片,包括质量百分比为：70-90％的正极活性物质、3-10％混合导体添加剂、3-10％柔性填充剂、0.5-2％管状导电剂、3.5-10％无机锂盐、0.5-2.5％粘接剂。本申请方法制备的正极极片具有较低的孔隙率,显著改善界面接触性能,且内阻低、循环性能好；使用本申请正极极片制作的固态电池能量密度密度高,循环性能稳定,能满足多种固态电池使用的需要。(The invention discloses a low-porosity positive pole piece for a solid-state battery, which comprises the following components in percentage by mass: 70-90% of positive active material, 3-10% of mixed conductor additive, 3-10% of flexible filler, 0.5-2% of tubular conductive agent, 3.5-10% of inorganic lithium salt and 0.5-2.5% of adhesive. The positive pole piece prepared by the method has lower porosity, obviously improves the interface contact performance, and has low internal resistance and good cycle performance; the solid-state battery manufactured by the positive pole piece has high energy density and stable cycle performance, and can meet the use requirements of various solid-state batteries.)

1. A low porosity positive pole piece for a solid state battery, characterized in that: comprises the following components in percentage by mass: 70-90% of positive active material, 3-10% of mixed conductive additive, 3-10% of flexible filler, 0.5-2% of tubular conductive agent, 3.5-10% of inorganic lithium salt and 0.5-2.5% of adhesive.

2. The low porosity positive electrode sheet for solid state battery of claim 1, wherein: the positive active material is one or more of lithium cobaltate and lithium nickel cobalt manganese oxide;

the ratio of nickel, cobalt and manganese in the nickel, cobalt and lithium manganate is 7:1:2 or 8:1: 1.

3. The low porosity positive electrode sheet for solid state battery of claim 1, wherein: the mixed conductor additive is TiO₂、TiS₂、Cu₂S, or WO₃One or more of (a).

4. The low porosity positive electrode sheet for solid state battery of claim 1, wherein: the flexible filler is one or more of polyvinyl alcohol, polyethylene oxide, polypropylene oxide, polyethylene and polypropylene.

5. The low porosity positive electrode sheet for solid state battery of claim 1, wherein: the tubular conductive agent is one or more of carbon nanotubes or carbon fibers.

6. The low porosity positive electrode sheet for solid state battery of claim 1, wherein: the adhesive is PVDF, and the inorganic lithium salt is Li₃PO₄、Li₂SO₄、Li₄SiO₄Or LiBF₄One or more of (a).

7. A method of making, characterized by: the preparation method of the low-porosity positive pole piece for the solid-state battery of any one of claims 1 to 6 comprises the following specific steps:

s1, preparing a positive glue solution, weighing a binder in proportion, and preparing the positive glue solution with the concentration of 2-8% by adopting NMP as a solvent;

s2, mixing, namely weighing the positive active substance, the mixed conductive additive, the flexible filler, the tubular conductive agent and the inorganic lithium salt in proportion, and uniformly mixing the substances to obtain a solid particle mixture;

s3, preparing slurry, namely adding the prepared positive pole glue solution into the mixed particle mixture in the S2 step by step, and preparing the positive pole slurry through a vacuum stirring process;

s4, coating, namely coating the positive electrode slurry on one or two surfaces of the metal foil, and drying to obtain a positive electrode piece;

s5, hot pressing: and (3) preparing the positive pole piece with low porosity by a hot pressing process.

8. The method of claim 7, wherein: in the hot pressing process in the step S5, the pressure is 50 +/-5 MPa, the temperature is 60-90 ℃, and the rolling speed is 5-20 m/S.

9. The method of claim 7, wherein: in the step S3, the stirring speed revolves at 15-30 rpm, the rotation speed is 1500-2500 rpm, the stirring temperature is 25-35 ℃, and the stirring time is 4-8 h.

10. The method of claim 7, wherein: the positive electrode slurry prepared in the step S3 has the viscosity of 4000-8000 cP and the solid content of 65-75%.

Technical Field

The invention relates to the field of lithium batteries, in particular to a low-porosity positive pole piece for a solid-state battery and a preparation method thereof.

Background

A "lithium battery" is a type of battery using a nonaqueous electrolyte solution with lithium metal or a lithium alloy as a negative electrode material. Lithium metal batteries were first proposed and studied by Gilbert n.lewis in 1912. In the 70 s of the 20 th century, m.s.whitetingham proposed and began to study lithium ion batteries. Because the chemical characteristics of lithium metal are very active, the requirements on the environment for processing, storing and using the lithium metal are very high. Since the beginning of the 90 s in the 20 th century, with the advent of the japanese sony corporation that uses carbon materials instead of lithium metal materials as negative electrode materials to improve the safety of lithium batteries, lithium ion batteries have gained wide use due to their advantages of high energy density, high power density, long life, and the like, and have become mainstream energy storage and conversion devices in the fields of portable digital electronics, electric vehicles, and the like.

Currently, the mainstream lithium ion battery uses a liquid electrolyte. The liquid electrolyte has the advantages of high ionic conductivity, relatively wide use temperature range, low cost and the like. However, in the liquid electrolyte, because the solvent uses organic compounds with relatively low ignition points, such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc., in the occasions of overcharge, internal short circuit or collision, etc., the liquid electrolyte causes fire and explosion due to factors such as temperature rise, existence of combustion improver, etc., and causes safety accidents, thereby causing great loss. In particular, in recent years, in the case where electric vehicles are increasingly driven on roads, safety accidents such as fire frequently occur. For this reason, solid-state batteries that do not use a liquid electrolyte have drawn more attention in the industry due to good safety performance and higher energy density.

At present, the industry is going to research solid electrolyte and solid electrolyte membrane deeply, and develops inorganic, organic and composite solid electrolyte and solid electrolyte membrane with promising application prospect. In the test of assembling the solid-state battery, the common positive pole piece manufacturing mode of the commercial lithium ion battery is adopted, the porosity of the pole piece is large, the interface contact is poor, the internal resistance is relatively high, in addition, in the circulation process, the active particles are dropped into the pores of the pole piece due to the volume change of the positive pole piece, the electric contact is lost, and the circulation performance is rapidly degraded.

In order to solve the above problems, patent CN110380111 proposes a double in-situ polymerization method, which refers to the method of gel polymer battery cell, and performs core fabrication in a conventional liquid lithium ion battery manner, and introduces an initiator into a liquid electrolyte during liquid injection to initiate polymerization reaction to prepare an all-solid battery. The method still uses the manufacturing mode of the liquid battery on the manufacturing process of the battery core, and the transmission of lithium ions between the anode and the cathode is limited by the existence of the conventional diaphragm; meanwhile, the porosity of the positive plate is high, and the energy density of the positive plate is influenced.

Disclosure of Invention

Aiming at the problems, the invention aims to provide a low-porosity positive pole piece for a solid-state battery and a preparation method thereof, wherein the low-porosity positive pole piece is used for improving the interface contact performance, reducing the internal resistance and improving the energy density.

In order to realize the technical purpose, the scheme of the invention is as follows: a low-porosity positive pole piece for a solid-state battery comprises the following components in percentage by mass: 70-90% of positive active material, 3-10% of mixed conductive additive, 3-10% of flexible filler, 0.5-2% of tubular conductive agent, 3.5-10% of inorganic lithium salt and 0.5-2.5% of adhesive.

Preferably, the positive electrode active material is one or more of lithium cobaltate and lithium nickel cobalt manganese oxide;

the ratio of nickel, cobalt and manganese in the nickel, cobalt and lithium manganate is 7:1:2 or 8:1: 1.

Preferably, the mixed conductor additive is TiO₂、TiS₂、Cu₂S, or WO₃One or more of (a).

Preferably, the flexible filler is one or more of polyvinyl alcohol, polyethylene oxide, polypropylene oxide, polyethylene and polypropylene.

Preferably, the tubular conductive agent is one or more of carbon nanotubes or carbon fibers.

Preferably, the binder is PVDF, and the inorganic lithium salt is Li₃PO₄、Li₂SO₄、Li₄SiO₄Or LiBF₄One or more of (a).

A preparation method for preparing a low-porosity positive pole piece for a solid-state battery comprises the following specific steps:

s1, preparing a positive glue solution, weighing a binder in proportion, and preparing the positive glue solution with the concentration of 2-8% by adopting NMP as a solvent;

s2, mixing, namely weighing the positive active substance, the mixed conductive additive, the flexible filler, the tubular conductive agent and the inorganic lithium salt in proportion, and uniformly mixing the substances to obtain a solid particle mixture;

s3, preparing slurry, namely adding the prepared positive pole glue solution into the mixed particle mixture in the S2 step by step, and preparing the positive pole slurry through a vacuum stirring process;

s4, coating, namely coating the positive electrode slurry on one or two surfaces of the metal foil, and drying to obtain a positive electrode piece;

s5, hot pressing: and (3) preparing the positive pole piece with low porosity by a hot pressing process.

Preferably, in the hot pressing process in the step S5, the pressure is 50 +/-5 MPa, the temperature is 60-90 ℃, and the rolling speed is 5-20 m/S.

Preferably, in the step S3, the stirring speed revolves at 15-30 rpm, the rotation speed is 1500-2500 rpm, the stirring temperature is 25-35 ℃, and the stirring time is 4-8 h.

Preferably, the positive electrode slurry prepared in the step S3 has the viscosity of 4000-8000 cP and the solid content of 65-75%.

The positive pole piece prepared by the method has low porosity, interface contact performance is obviously improved, internal resistance is low, and cycle performance is stable; the solid-state battery manufactured by the positive pole piece has high energy density and can meet the use requirements of various solid-state batteries.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

The specific embodiment of the invention is a low-porosity positive pole piece for a solid-state battery, which comprises the following components in percentage by mass: 70-90% of positive active material, 3-10% of mixed conductive additive, 3-10% of flexible filler, 0.5-2% of tubular conductive agent, 3.5-10% of inorganic lithium salt and 0.5-2.5% of adhesive.

The positive active material is one or more of lithium cobaltate and lithium nickel cobalt manganese (the ratio of nickel cobalt to manganese is 7:1:2 or 8:1: 1). The mixed conductive additive is TiO₂、TiS₂、Cu₂S、WO₃One or more of (a). The above-mentionedThe flexible filler is one or more of polyvinyl alcohol, polypropylene oxide, polyethylene, polypropylene and the like. The tubular conductive agent is one or more of carbon nano tubes and carbon fibers. The adhesive is PVDF (polyvinylidene fluoride), and the inorganic lithium salt is Li₃PO₄、Li₂SO₄、Li₄SiO₄、LiBF₄One or more of (a). Lithium salt with a certain concentration is added into the electrolyte of the liquid lithium ion battery, and the solid lithium ion battery also needs to be introduced with the lithium salt to conduct lithium ions more quickly.

The known preparation method of the low-porosity solid-state battery positive pole piece usually adopts a mode of deposition on a current collector, and sintering is required to be carried out at high temperature subsequently, so that the production efficiency is low, the cost is high, and the method is not suitable for industrial mass production. And the mode of in-situ polymerization is adopted, one more liquid electrolyte injection process is needed, the efficiency is influenced, and the equipment investment (liquid injection equipment and a dehumidifier unit added for keeping the low humidity of the liquid injection environment) is increased. The preparation method adopted by the application is compatible with the existing positive pole piece manufacturing mode, a liquid injection process is not needed, the production is more efficient, and the preparation cost is lower.

A preparation method for preparing a low-porosity positive pole piece for a solid-state battery comprises the following specific steps:

s1, preparing a positive glue solution, weighing PVDF (polyvinylidene fluoride) as a binder in proportion, and preparing the positive glue solution with the concentration of 2-8% by adopting NMP (N-methyl pyrrolidone) as a solvent;

s2, mixing, namely weighing the positive active substance, the mixed conductor additive, the flexible filler, the tubular conductive agent and the inorganic lithium salt in proportion, and stirring and mixing the substances to obtain a particle mixture;

s3, preparing slurry, namely adding the prepared positive pole glue solution into the mixed particle mixture obtained in the step S2 step by step, and preparing the positive pole slurry through a vacuum stirring process; the stirring speed is 15-30 rpm in revolution, the rotation speed is 1500-2500 rpm, the stirring temperature is 25-35 ℃, and the stirring time is 4-8 h. The obtained positive electrode slurry has the viscosity of 4000-8000 cP and the solid content of 65-75%.

S4, coating, namely coating the positive electrode slurry on one or two surfaces of the metal foil, and drying to obtain a positive electrode piece;

s5, hot pressing: the positive pole piece with low porosity is prepared by a hot pressing process, wherein the pressure in the hot pressing process is 50 +/-5 MPa, the temperature is 60-80 ℃, and the rolling speed is 5-20 m/s. In the step S3

The conventional liquid lithium ion battery positive electrode generally has a porosity of 20-40%, and the porosity is used for absorbing electrolyte to conduct lithium ions. The solid-state lithium ion battery anode has poor contact among particles due to the existence of pores, so that internal resistance is increased, and performance is influenced. Therefore, the preparation method can effectively reduce the porosity and is greatly helpful for improving the contact of the solid-state battery. The preparation method is low in cost and easy to operate, and the porosity of the positive pole piece can be greatly reduced. The flexible filler can fill the pores, so that the positive active particles, the lithium ion conductor, the electronic conductor and the binder are ensured to be fully contacted; due to the adoption of the flexible filler, when the volume of the lithium battery anode material is changed due to the release and the insertion of lithium in the charging and discharging processes, the flexible substance can well absorb and buffer the volume change. In addition, the pole piece is manufactured in a conventional pole piece manufacturing mode, and the flexible fillers cannot effectively occupy pores in the pole piece; this application introduces the mode of hot pressing and carries out the roll-in of pole piece, and the flexible filler that this application chose for use simultaneously has relatively lower softening point, owing to be heated the softening in the hot pressing process, for the relative slip creation condition between the positive pole granule of rigidity to effectively discharge remaining gas in the pole piece, further reduced the porosity.

Meanwhile, a lithium ion electron mixed conductor is introduced into the positive pole piece of the solid lithium battery, so that the conductivity can be better realized; a quantity of tubular carbon material is also introduced to form a conductive sub-network. On one hand, reversible lithium ions in the positive electrode particles can be fully utilized to ensure the capacity and the energy density, and on the other hand, the lithium ions can be ensured to be transferred and diffused at a higher speed to ensure the multiplying power performance.

The first embodiment is as follows:

positive electrodeThe parts ratio of the formula is as follows: lithium nickel cobalt manganese (nickel cobalt manganese ratio 8:1:1) TiS₂Polyethylene oxide: polyethylene: CNT (carbon nanotube): Li₃PO₄:PVDF＝82:3:4:4:1:5:1；

The negative electrode is lithium metal foil or lithium alloy foil, and the sulfide electrolyte and polymer electrolyte composite membrane is used as an isolating layer between the positive electrode and the negative electrode.

Preparing the anode slurry according to the mixture ratio, wherein the stirring speed is 20rpm in revolution, the rotation speed is 2000rpm, the stirring time is 6 hours, the discharging temperature is 25 ℃, the solid content is 68 percent, and the viscosity is 4500 cP. And after the slurry is demagnetized, pumping the slurry to a coating machine head for coating, wherein the current collector is an aluminum foil, the thickness is 14 mu m, the coating surface density is 16mg/cm2 on one side, the temperature of a positive coating and baking area is between 60 and 120 ℃, and the coating speed is 15 m/min. And rolling the coated positive pole piece at 80 ℃, pressing at 50MPa and at the speed of 10m/s, slitting and punching to obtain the positive pole piece, laminating the positive pole piece with the negative pole and the electrolyte membrane to form a single-layer or multi-layer pole group, pressing and molding, filling the single-layer or multi-layer pole group into an aluminum plastic film package which is punched and molded in a mold, and sealing to obtain the all-solid-state lithium battery cell of the first embodiment.

Compared with the conventional liquid lithium ion battery, the lithium metal is used as the negative electrode, and the high-capacity lithium nickel cobalt manganese oxide (the ratio of nickel cobalt to manganese is 8:1:1) is used as the positive electrode, so that higher energy density can be obtained.

The all-solid-state battery cell prepared in the embodiment is tested at 60 ℃ and 0.1C, and has the first efficiency of 85%, the gram capacity of 178mAh/g, the capacity retention rate of 92.5% after 50 cycles and the capacity retention rate of 86% after 200 cycles.

Example two:

the parts of the positive electrode formula are as follows: LiCoO₂:TiS₂Polyethylene oxide: polyethylene: CNT (carbon nanotube): Li₃PO₄:PVDF＝84:3:4:3:1:4:1；

The negative electrode is lithium metal foil or lithium alloy foil, and the sulfide electrolyte and polymer electrolyte composite membrane is used as an isolating layer between the positive electrode and the negative electrode.

Preparing the anode slurry according to the mixture ratio, wherein the stirring speed is 20rpm in revolution, the rotation speed is 2000rpm, the stirring time is 6 hours, the discharging temperature is 25 ℃, the solid content is 71 percent, and the viscosity is 5000 cP. And after the slurry is demagnetized, pumping the slurry to a coating head for coating, wherein the current collector is an aluminum foil, the thickness is 14 mu m, the density of the coated surface is single-sided 20mg/cm2, the temperature of a coating and baking area of the anode is between 60 and 120 ℃, and the coating speed is 15 m/min. And rolling the coated positive pole piece at 80 ℃, pressing at 50MPa and at the speed of 10m/s, slitting and punching to obtain the positive pole piece, laminating the positive pole piece with the negative pole and the electrolyte membrane to form a single-layer or multi-layer pole group, pressing and molding, filling the single-layer or multi-layer pole group into an aluminum plastic film package which is punched and molded in a mold, and sealing to obtain the all-solid-state lithium battery cell of the second embodiment.

Compared with the conventional liquid lithium ion battery, the solid lithium battery core adopting the positive plate has the advantages that the negative electrode adopts metal lithium, and the positive electrode adopts high-capacity lithium cobalt oxide, so that higher energy density can be obtained.

The all-solid-state battery cell prepared in the embodiment is tested at 60 ℃ and 0.1C, and has the first efficiency of 94%, the gram capacity of 141mAh/g, the capacity retention rate of 90.5% after 50 cycles and the capacity retention rate of 82.2% after 200 cycles.

The solid lithium cell adopting the positive pole piece has higher energy density than the traditional liquid lithium cell, and has remarkable advantages compared with the existing solid lithium cell; meanwhile, the cycle retention rate of 50 weeks is more than 90 percent, which is superior to that of a common solid lithium cell; the cycle retention rate of 200 weeks is more than 80%, which is superior to that of a common solid lithium cell.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any minor modifications, equivalent replacements and improvements made to the above embodiment according to the technical spirit of the present invention should be included in the protection scope of the technical solution of the present invention.