CN106410267A - Silicon-based lithium ion secondary battery with high specific energy and preparation method of lithium ion secondary battery - Google Patents

Abstract

The invention relates to a high specific energy silicon-based lithium ion secondary battery and a preparation method thereof. The battery includes a negative electrode, the negative electrode includes a negative electrode active material, a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material is silicon, silicon One or more of carbon, silicon oxide and silicon-based composite materials; the negative electrode binder is one or more of styrene-butadiene rubber, polyacrylic acid, sodium alginate, and polyimide. The high specific energy silicon-based lithium ion secondary battery and the preparation method thereof of the present invention, the prepared battery has high specific energy and excellent cycle performance.

Description

High specific energy silicon-based lithium ion secondary battery and preparation method thereof

technical field

The invention relates to a lithium ion secondary battery, in particular to a high specific energy silicon-based lithium ion secondary battery and a preparation method thereof.

Background technique

Due to its excellent performance, lithium-ion batteries have become the most important energy storage devices for various electronic products, wireless communications and electric vehicles. At present, commercial lithium-ion batteries mainly use graphite-like carbon materials as negative electrode active materials. However, due to its low specific capacity (372mAh/g) and safety issues caused by lithium deposition, carbon-based anode materials cannot meet the requirements of miniaturization of electronic equipment and high capacity and long battery life of lithium-ion batteries for vehicles. New anode materials with high energy density, high safety performance, and long cycle life that can replace carbon-based anode materials are an important factor for the breakthrough of lithium-ion batteries.

As a new lithium-ion battery anode material, silicon has become the focus of researchers because of its high theoretical specific capacity (4200mAh/g). However, its volume expansion (400%) during the charging and discharging process will cause the pulverization of active particles, which will lead to rapid capacity decay due to the loss of electrical contact, which hinders its commercialization process. To solve this problem, people have carried out a lot of exploration, including reducing the particle size of silicon particles, preparing silicon thin films and constructing silicon-based composite materials.

Contents of the invention

The object of the present invention is to provide a high specific energy silicon-based lithium ion secondary battery and a preparation method thereof, the battery has high specific energy.

In order to achieve the above object, the present invention provides a high specific energy silicon-based lithium ion secondary battery, including a negative electrode, the negative electrode includes a negative electrode active material, a negative electrode binder and a negative electrode conductive agent, it is characterized in that the negative electrode active The substance is one or more of silicon, silicon carbon, silicon oxide, and silicon-based composite materials; the negative electrode binder is one or more of styrene-butadiene rubber, polyacrylic acid, sodium alginate, and polyimide Various.

The above-mentioned high specific energy silicon-based lithium ion secondary battery, wherein the high specific energy silicon based lithium ion secondary battery further includes an electrolyte, and the electrolyte is an organic electrolyte system containing a silicon-based film-forming additive.

In the aforementioned high specific energy silicon-based lithium ion secondary battery, the silicon-based film-forming additive is one or more of fluoroethylene carbonate, vinylene carbonate, and 1,3-propane sultone.

The above-mentioned high specific energy silicon-based lithium ion secondary battery, wherein, the high specific energy silicon-based lithium ion secondary battery also includes a positive electrode, and the positive electrode includes a positive electrode active material, a positive electrode binder and a positive electrode conductor; the positive electrode The active material is one or more of high-voltage lithium cobalt oxide, lithium nickel cobalt aluminate, lithium nickel cobalt manganese oxide, and lithium-rich multi-element materials.

Another technical solution provided by the present invention is a method for preparing a high specific energy silicon-based lithium-ion secondary battery, comprising the following steps: step 1, making a positive electrode sheet; step 2, making a negative electrode sheet, wherein the negative electrode active material used It is one or more of silicon, silicon carbon, silicon oxide and silicon-based composite materials, and the negative electrode binder used is one or more of styrene-butadiene rubber, polyacrylic acid, sodium alginate, and polyimide. A kind; Step 3, make electric core by the positive electrode sheet that step 1 makes and the negative electrode sheet that step 2 makes; Step 4, put electric core into outer packaging, remove residual moisture in electric core by baking; Step 5, Add electrolyte to the outer packaging, vacuum seal, leave at room temperature for 12 hours and then turn to high temperature for 12 hours; the electrolyte is an organic electrolyte system containing silicon-based film-forming additives; step 6, the battery is formed: First, after charging to the predetermined capacity with a current below 0.1C, remove the gas in the outer packaging; then continue to charge at a current of 0.1C to a specified voltage and then discharge, and then charge to a specified voltage at a current of 0.1C and then discharge, and so on. After at least 3 times, remove the gas in the outer packaging.

The preparation method of the above-mentioned high specific energy silicon-based lithium ion secondary battery, wherein, the silicon-based film-forming additive is one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone or Various.

The above method for preparing a high specific energy silicon-based lithium ion secondary battery, wherein, in the step 5, the high-temperature standing is divided into two steps, and the last step is to install a fixture on the battery.

The above-mentioned method for preparing a silicon-based lithium-ion secondary battery with high specific energy, wherein, in the step 1, the positive electrode active material used is high-voltage lithium cobaltate, nickel-cobalt lithium aluminate, nickel-cobalt lithium manganate, lithium-rich multi-element material one or more of.

Compared with the prior art, the present invention has the following technical effects:

1) The specific energy of the lithium-ion secondary battery is significantly improved by using high specific capacity positive and negative electrode materials;

2) The negative electrode can adjust the amount of silicon-based materials added according to the specific energy requirements of the battery, and through the unique binder technology, the negative electrode sheet prepared has the advantages of high specific capacity, high compaction density, and stability to the electrolyte solvent;

3) Due to the addition of special lithium salt and silicon-based film-forming additives in the electrolyte, the electrolyte has high electrical conductivity and good wettability to the material, and at the same time enables the interface between the electrolyte and the negative electrode to form a dense solid electrolyte interface Membrane (SEI membrane), so that the battery has better cycle characteristics;

4) Due to the special static and chemical formation process, the first-time efficiency of silicon-based batteries is improved, and while ensuring the formation of a stable and dense SEI film on the negative electrode, it reduces the expansion effect of silicon-based materials during cycling.

detailed description

The high specific energy silicon-based lithium ion secondary battery of the present invention comprises a positive pole, a negative pole, a diaphragm, an electrolyte and an outer package.

The positive electrode includes a positive electrode active material (mass fraction of 80wt% to 98.3wt%), a positive electrode binder (mass fraction of 1.2wt% to 10wt%) and a positive electrode conductor (mass fraction of 0.5wt% to 10wt%); The positive electrode active material is one or more of lithium cobalt oxide (including high-voltage lithium cobalt oxide), lithium manganate, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and lithium-rich multi-element materials; The positive electrode binder is high molecular weight polyvinylidene fluoride; the positive electrode conductive agent is one or more of superconducting carbon black, flake graphite, carbon nanotubes, graphene, and carbon fibers.

In the present invention, the positive electrode active material has higher specific capacity, lower specific surface area, higher compacted density and better safety performance. The positive electrode thus prepared has the advantages of high specific capacity, high compacted density, and stability to the electrolyte. Preferably, the positive electrode active material is one or more of high-voltage lithium cobalt oxide, lithium nickel cobalt aluminate, lithium nickel cobalt manganate, and lithium-rich multi-element materials.

The negative electrode includes negative electrode active material (mass fraction is 80wt%~98wt%), negative electrode binder (mass fraction is 10wt%~2wt%) and negative electrode conductive agent (mass fraction is 10wt%~0wt%); the negative electrode The active material is one or more of silicon, silicon carbon, silicon oxide (SiO _x ) and silicon-based composite materials; the negative electrode binder is styrene-butadiene rubber, polyacrylic acid, sodium alginate, polyimide One or more of them; the negative electrode conductive agent is one or more of superconducting carbon black, carbon nanotubes, graphene, and carbon fibers.

In the present invention, the negative electrode binder has good bonding performance, can form chemical bonds with the negative electrode active material, and has excellent elasticity, and can withstand the stress changes caused by the expansion and contraction of the negative electrode during the battery charge and discharge cycle, making the battery Has excellent cycle performance.

The diaphragm is one of a ceramic diaphragm, a polyolefin diaphragm, and a non-woven diaphragm.

The electrolyte is an organic electrolyte system containing a silicon-based film-forming additive. The solvent of the electrolyte is one or a mixture of ethylene carbonate, propylene carbonate, and methyl ethyl carbonate. The electrolyte needs to add a silicon-based film-forming additive, and the silicon-based film-forming additive (mass fraction is 0.5wt%~3wt%) is fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonic acid internal One or more of the esters; the silicon-based film-forming additive can form a stable SEI film on the surface of the silicon-based negative electrode, which can ensure the cycle stability of the battery. Preferably, the electrolyte of the electrolyte is a non-aqueous electrolyte, and the electrolyte is a lithium salt of a non-aqueous solution, such as lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), and lithium dioxalate borate (LiBOB). One or more.

The preparation method of the high specific energy silicon-based lithium ion secondary battery of the present invention comprises the following steps:

Step 1, mix and stir the positive electrode binder and solvent (N-methylpyrrolidone), then add the positive electrode conductive agent and stir together, then add the positive electrode active material and stir to obtain a solid-liquid mixture, and finally apply the above solid-liquid mixture evenly on On the surface of aluminum foil, dry the positive electrode sheet;

Step 2, mix and stir the negative electrode binder and solvent (deionized water), then add the negative electrode conductive agent and stir together, then add the negative electrode active material and stir to obtain a solid-liquid mixture, and finally apply the above solid-liquid mixture evenly on the copper foil On the surface, the negative electrode sheet was dried;

Step 3: Cut the positive electrode sheet obtained in step 1 and the negative electrode sheet obtained in step 2 into several small pieces, stack the positive electrode sheet, separator, and negative electrode sheet in a "Z" shape, and then connect all the positive electrode sheets Get up and weld the aluminum sheets, connect all the negative electrode sheets and weld the nickel sheets or nickel-plated copper sheets, and finally fix the positive and negative electrode sheets with adhesive tape to make them closely contact, and then get the cell;

Step 4, put the batteries into the outer packaging, and remove the residual moisture in the batteries by baking;

Step 5, add electrolyte to the outer packaging, vacuum seal, let stand at room temperature for 12-24 hours, then turn to high temperature and stand for 12-24 hours, so that the electrolyte can fully infiltrate the electrode sheets (including positive and negative electrodes);

The high-temperature standing is divided into two steps, wherein the last step is to stand at a high temperature for 8-12 hours after the battery is placed on a fixture; the temperature of the high-temperature standing is 60°C to 80°C;

Step 6. Formation of the battery (segmented formation): first charge to the predetermined capacity with a small current (below 0.1C), then remove the gas in the outer package; then continue to charge to the specified voltage with a current of 0.1C and discharge, then Charge to a specified voltage with a current of 0.1C and then discharge. After such charge and discharge cycles go through at least 3 times, remove the gas in the outer package, and complete the preparation of the high specific energy silicon-based lithium ion secondary battery of the present invention.

The preparation method of the high specific energy silicon-based lithium-ion secondary battery of the present invention adopts unique standing (normal temperature standing and then high temperature standing) and formation process (segmented formation), which can ensure high initial efficiency of the battery, high Capacity, electrochemical stability and safety of the battery system.

The high specific energy silicon-based lithium ion secondary battery of the present invention and its preparation method are now described with specific examples.

Example 1:

Fully mix and stir 93.5 grams of N-methylpyrrolidone and 6.52 grams of polyvinylidene fluoride, stir until the viscosity of the mixed solution changes less than 3% within 10 minutes, then add 3.91 grams of dispersed conductive carbon nanotubes, and stir to 10 The viscosity change of the mixture within 1 minute is less than 3%, and finally add 250 grams of nickel-cobalt lithium aluminate material, stir until the viscosity change of the mixture within 10 minutes is less than 5%, and then coat the above mixture evenly on the aluminum foil, 100 ℃ The positive electrode sheet was obtained after vacuum drying for 24 hours.

Fully mix and stir 148.5 grams of deionized water and 2.63 grams of polyacrylic acid, and stir until the viscosity of the mixed solution changes less than 3% within 10 minutes, then add 1.05 grams of dispersed conductive carbon nanotubes, and stir until the mixture reaches a viscosity within 10 minutes. The viscosity change is less than 3%, and finally add 100 grams of silicon oxide and graphite mixed material, stir until the viscosity change of the mixture is less than 5% within 10 minutes, then apply the above mixture evenly on the copper foil, and vacuum dry at 100°C for 24 A negative electrode sheet was obtained after 1 hour.

Die the produced positive electrode and negative electrode into small pieces of a certain size to obtain several positive and negative electrode pieces. The positive electrode pieces, separators, and negative electrode pieces are stacked alternately, and aluminum strips are welded on the aluminum foil, and nickel is welded on the copper foil. Tape, and finally fixed with adhesive tape to make a battery with a capacity of 2Ah. Then, put the cell into the outer package, heat seal it, and bake it in a vacuum oven to remove the residual moisture. The baking temperature is 70°C, and the water content of the electrode sheet after baking is below 200ppm.

Cool the baked cell to room temperature in a vacuum, take it out, and inject 5.5g of silicon-based electrolyte containing three film-forming additives of FEC/VC/PS. After liquid injection, the battery is vacuum-adsorbed three times, each time for 20 minutes; after standing at room temperature for 12 hours, turn to high temperature and stand at 45°C for 12 hours.

Before the battery is formed, put the battery on the fixture, and let it stand at 60°C for 4 hours before forming. The formation temperature is 20±3°C. When charging for the first time, charge it to 10% of the battery capacity with a current of 0.02C, and discharge the generated during charging. Gas, then continue to charge to 4.2V with 0.1C current and then discharge, cycle 3 times (referring to charge to 4.2V with 0.1C current and then discharge), then extract the gas generated during the charging and discharging process of the battery and seal it.

The first-time efficiency of the silicon-based lithium-ion secondary battery prepared by this process can reach 90%, and the specific energy can reach 270Wh/Kg. The specific energy can be increased by increasing the silicon content in the negative electrode. Under the environment of 20±3℃, the battery still maintains more than 90% of the initial capacity after 200 cycles, which proves that it has good cycle performance.

Comparative example 1:

Fully mix and stir 93.5 grams of N-methylpyrrolidone and 6.52 grams of polyvinylidene fluoride, stir until the viscosity of the mixed solution changes less than 3% within 10 minutes, then add 3.91 grams of dispersed conductive carbon nanotubes, and stir to 10 The viscosity change of the mixture within 1 minute is less than 3%, and finally add 250 grams of nickel-cobalt lithium aluminate material, stir until the viscosity change of the mixture within 10 minutes is less than 5%, and then coat the above mixture evenly on the aluminum foil, 100 ℃ The positive electrode sheet was obtained after vacuum drying for 24 hours.

Fully mix and stir 148.5 grams of deionized water and 2.63 grams of polyacrylic acid, and stir until the viscosity of the mixed solution changes less than 3% within 10 minutes, then add 1.05 grams of dispersed conductive carbon nanotubes, and stir until the mixture reaches a viscosity within 10 minutes. The viscosity change is less than 3%, and finally add 100 grams of silicon oxide and graphite mixed material, stir until the viscosity change of the mixture is less than 5% within 10 minutes, then apply the above mixture evenly on the copper foil, and vacuum dry at 100°C for 24 A negative electrode sheet was obtained after 1 hour.

Die the produced positive electrode and negative electrode into small pieces of a certain size to obtain several positive and negative electrode pieces. The positive electrode pieces, separators, and negative electrode pieces are stacked alternately, and aluminum strips are welded on the aluminum foil, and nickel is welded on the copper foil. belt, and finally fixed with adhesive tape to make a battery with a capacity of 2Ah. Then, put the cell into the outer packaging, heat seal it, and bake it in a vacuum oven to remove the residual moisture. The baking temperature is 70°C, and the water content of the electrode sheet after baking is below 200ppm.

Cool the baked cell to room temperature in a vacuum, take it out, and inject 5.5 grams of common electrolyte (EC:DEC=1:1, 1.0M LiPF ₆ ), after the injection, the battery is vacuum-adsorbed three times, each time for 20 minutes; After standing at room temperature for 12 hours, turn to high temperature and stand at 45°C for 12 hours.

Before the battery is formed, put the battery on the fixture, and let it stand at 60°C for 4 hours before forming. The formation temperature is 20±3°C. When charging for the first time, charge it to 10% of the battery capacity with a current of 0.02C, and discharge the generated during charging. Gas, and then continue to charge to 4.2V with a current of 0.1C and then discharge. After 3 cycles, the gas generated during the charging and discharging process of the battery is drawn out and sealed.

The silicon-based lithium-ion secondary battery with ordinary electrolyte prepared by this process has an initial efficiency of 83%, and a specific energy of only 245Wh/Kg. Under the environment of 20±3℃, the battery only maintains 70% of the initial capacity after 100 cycles, which proves that the ordinary electrolyte cannot form the SEI film on the surface of the negative electrode well, so that its initial efficiency, specific energy and cycle performance are very good. decline to a great extent.

Comparative example 2:

Fully mix and stir 93.5 grams of N-methylpyrrolidone and 6.52 grams of polyvinylidene fluoride, stir until the viscosity of the mixed solution changes less than 3% within 10 minutes, then add 3.91 grams of dispersed conductive carbon nanotubes, and stir to 10 The viscosity change of the mixture within 1 minute is less than 3%, and finally add 250 grams of nickel-cobalt lithium aluminate material, stir until the viscosity change of the mixture within 10 minutes is less than 5%, and then coat the above mixture evenly on the aluminum foil, 100 ℃ The positive electrode sheet was obtained after vacuum drying for 24 hours.

Fully mix and stir 148.5 grams of deionized water and 2.63 grams of polyacrylic acid, and stir until the viscosity of the mixed solution changes less than 3% within 10 minutes, then add 1.05 grams of dispersed conductive carbon nanotubes, and stir until the mixture reaches a viscosity within 10 minutes. The viscosity change is less than 3%, and finally add 100 grams of silicon oxide and graphite mixed material, stir until the viscosity change of the mixture is less than 5% within 10 minutes, then apply the above mixture evenly on the copper foil, and vacuum dry at 100°C for 24 A negative electrode sheet was obtained after 1 hour.

Die the produced positive electrode and negative electrode into small pieces of a certain size respectively to obtain several positive and negative electrode pieces. Nickel tape, and finally fixed with adhesive tape, made a battery with a capacity of 2Ah. Then, put the cell into the outer package, heat seal it, and bake it in a vacuum oven to remove the residual moisture. The baking temperature is 70°C, and the water content of the electrode sheet after baking is below 200ppm.

Cool the baked cell to room temperature in a vacuum, take it out, and inject 5.5g of silicon-based electrolyte containing three film-forming additives of FEC/VC/PS. After filling the battery, let it stand at room temperature for 24 hours.

The formation temperature is 20±3°C, charge to 4.2V with a certain current and then discharge, after 3 cycles, the gas generated during the charging and discharging process of the battery is extracted and sealed.

The initial efficiency of the silicon-based lithium-ion secondary battery prepared by this process is 80%, and the specific energy can reach 240Wh/Kg. Under the environment of 20±3℃, the battery only maintains 75% of the initial capacity after 100 cycles, which proves that even if the silicon-based electrolyte is used, it cannot be prepared with a high specific energy , Long-life silicon-based lithium-ion secondary battery.

The high specific energy lithium ion secondary battery provided by the invention has the advantages of high specific energy and good cycle performance, and can be used as an alternative battery for consumer electronics, electric vehicles and energy storage batteries.

Claims (8)

1. high-energy-density silicon substrate lithium rechargeable battery, including negative pole, described negative pole includes negative electrode active material, negative electrode binder With cathode conductive agent it is characterised in that described negative electrode active material be silicon, in silicon-carbon, the sub- silicon of oxidation and silicon based composite material One or more；Described negative electrode binder be one of butadiene-styrene rubber, polyacrylic acid, sodium alginate, polyimides or Multiple.

2. high-energy-density silicon substrate lithium rechargeable battery as claimed in claim 1 is it is characterised in that described high-energy-density silicon substrate Lithium rechargeable battery also includes electrolyte, and described electrolyte is the organic electrolyte system containing silicon substrate film for additive.

3. high-energy-density silicon substrate lithium rechargeable battery as claimed in claim 2 is it is characterised in that described silicon substrate film forming is added Agent is one of fluorinated ethylene carbonate, vinylene carbonate, 1,3- propane sultone or multiple.

4. high-energy-density silicon substrate lithium rechargeable battery as claimed in claim 1 is it is characterised in that described high-energy-density silicon substrate Lithium rechargeable battery also includes positive pole, and described positive pole includes positive active material, positive electrode binder and positive conductive agent；Described Positive active material is high pressure cobalt acid lithium, nickel cobalt lithium aluminate, nickle cobalt lithium manganate, rich lithium multicomponent material one or more.

5. the preparation method of high-energy-density silicon substrate lithium rechargeable battery is it is characterised in that comprise the steps：

Step 1, makes positive plate；

Step 2, makes negative plate, and wherein, the negative electrode active material of employing is silicon, silicon-carbon, the sub- silicon of oxidation and silicon based composite material One of or multiple, the negative electrode binder of employing is butadiene-styrene rubber, in polyacrylic acid, sodium alginate, polyimides one Plant or multiple；

The negative plate that step 3, the positive plate being obtained by step 1 and step 2 are obtained makes battery core；

Step 4, battery core is put into external packing, removes the Residual water in battery core by baking；

Step 5, adds electrolyte, vacuum-pumping and sealing, normal temperature turns quiescence in high temperature 12 hours after standing 12 hours in external packing；

Described electrolyte is the organic electrolyte system containing silicon substrate film for additive；

Step 6, is melted into battery：After first below 0.1C electric current charges to predetermined volumes, remove the gas in external packing；So Continue to charge to electric discharge after given voltage with 0.1C electric current afterwards, then electric discharge after given voltage is charged to 0.1C electric current, so fill After discharge cycles at least experience 3 times, remove the gas in external packing.

6. the preparation method of high-energy-density silicon substrate lithium rechargeable battery as claimed in claim 5 is it is characterised in that described silicon Base film for additive is one of fluorinated ethylene carbonate, vinylene carbonate, 1,3- propane sultone or multiple.

7. the preparation method of high-energy-density silicon substrate lithium rechargeable battery as claimed in claim 5 is it is characterised in that described step In rapid 5, quiescence in high temperature in two steps, wherein after a step battery upper fixture.

8. the preparation method of high-energy-density silicon substrate lithium rechargeable battery as claimed in claim 5 is it is characterised in that described step In rapid 1, the positive active material of employing is high pressure cobalt acid lithium, nickel cobalt lithium aluminate, nickle cobalt lithium manganate, one kind of richness lithium multicomponent material Or it is multiple.