CN111554895A - A kind of solid polymer lithium ion battery positive electrode and its preparation method and application - Google Patents

Abstract

The invention relates to a solid polymer lithium ion battery, in particular to a solid polymer lithium ion battery anode and a preparation method and application thereof; the solid polymer lithium ion battery positive electrode comprises an active material, a binder and conductive carbon, wherein the active material is lithium cobaltate or high nickel cobalt lithium manganate; the binder is selected from one or a mixture of more of sodium carboxymethylcellulose, lithium carboxymethylcellulose, sodium alginate and lithium alginate; the positive electrode comprises, by mass, 70-95% of an active material, 2-15% of a binder and 3-15% of conductive carbon. The anode material has better cycling stability, longer service life and higher energy density under the voltage of 4 volts and above 4 volts. In addition, the preparation process of the solid polymer lithium ion battery is simple, easy to amplify and environment-friendly; is beneficial to promoting the development of solid-state high-energy-density lithium batteries.

Description

A kind of solid polymer lithium ion battery positive electrode and its preparation method and application

technical field

The invention relates to a solid polymer lithium ion battery, in particular to a solid polymer lithium ion battery positive electrode and a preparation method and application thereof.

Background technique

As a rechargeable energy storage device, lithium-ion batteries have the advantages of green and pollution-free, high energy density, and stable charging and discharging for multiple times. The above advantages make lithium-ion batteries have the prospect of replacing fossil fuels in the transportation industry. However, at present, lithium-ion batteries are mainly used in small devices such as mobile phones, cameras, and laptop computers, as well as in small electric vehicles. To further apply lithium-ion batteries to the field of electric transportation and replace fuel vehicles, it is also necessary to solve the safety of lithium-ion batteries. sexuality and energy density. Compared with traditional liquid batteries, solid-state lithium-ion batteries have higher energy density, and solid-state lithium-ion batteries do not use any organic solvents in the preparation process, which can effectively avoid potential dangers such as fire and leakage during use. Lithium-ion batteries have better safety and energy density than traditional lithium-ion batteries.

At this stage, the most promising solid-state lithium-ion battery is the solid-state polymer lithium-ion battery; the solid-state polymer lithium-ion battery uses a solid-state polymer electrolyte. Solid polymer electrolytes have the advantages of low price, environmental friendliness, high ionic conductivity, and low interfacial impedance. At present, the most widely used solid polymer electrolytes are polyethylene oxide (PEO) polymer solid electrolytes, and its derivatives contain EO. Branched polymer electrolytes have also been extensively studied. The Bolloré Bluecar, an electric car used in Paris, France, is a solid-state polymer lithium-ion battery. The solid-state polymer lithium-ion battery uses a polyethylene oxide analog as a solid electrolyte, lithium metal as a negative electrode, and lithium iron phosphate as a positive electrode; However, the energy density of the solid-state polymer lithium-ion battery is too low, so that the mileage of the electric vehicle is too short.

In order to improve the energy density of solid-state polymer lithium-ion batteries, it is necessary to use high-voltage or high-capacity cathode materials; although lithium iron phosphate has a relatively high specific capacity, its discharge voltage platform is relatively low, resulting in low energy density; phase Compared with lithium iron phosphate, lithium cobalt oxide and high nickel cobalt lithium manganate and other cathode active materials, they have the advantages of high specific capacity and high voltage platform, so they can provide higher energy density for solid-state polymer lithium-ion batteries. However, polyethylene oxide-based solid polymer electrolytes will decompose violently at charge and discharge voltages of 4 volts and above, resulting in poor cycle performance of solid polymer lithium-ion batteries such as lithium cobalt oxide and high nickel cobalt manganese oxide. poor and cannot meet the practical application.

In the prior art, the method for improving the cycle performance of solid-state polymer lithium ion batteries at voltages of 4 volts and above is mainly achieved by coating electrode particles; for example, materials such as alumina and lithium phosphate have been reported for Coating lithium cobalt oxide particles to improve the stability of solid-state polymer lithium-ion batteries (Chem.Mater.2005,17,23,5603-5605, Chem.Mater.2005,17,8,2041-2045); another example, Lithium cobalt oxide coated with polymer PECA has also been tried to be used in solid-state polymer lithium-ion batteries to improve the stability of the battery. Although the above-mentioned coating technical solution can significantly improve the cycle stability of solid-state polymer lithium-ion batteries, the improvement is limited and cannot meet the requirements of practical applications. In addition, in the prior art, there is also a method for improving the stability of solid-state polymer lithium ion batteries at a voltage of 4 volts and above by using a double-layer electrolyte. The method is specifically to use a layer of negative electrode stable PEO polymer electrolyte, On the positive side, a layer of high-voltage stable poly-N-methylmalonamide (PMA)-based polymer electrolyte (Adv. Mater. 2019, 31, 1805574) is used; the solid-state polymer lithium-ion battery with the above-mentioned double-layer structure It exhibits excellent cycling performance when matched with lithium cobalt oxide cathodes, but this double-layer electrolyte approach increases the mass of the electrolyte layer and reduces the energy density of solid-state batteries.

In view of this, the present invention is proposed.

SUMMARY OF THE INVENTION

In view of the shortcomings of the prior art, the present application provides a solid-state polymer lithium-ion battery positive electrode; the solid-state polymer lithium-ion battery including the positive electrode has very excellent cycle stability under voltage conditions of 4 volts and above and energy density.

Specifically, the positive electrode includes an active material, a binder and conductive carbon, and the active material is lithium cobalt oxide or high-nickel cobalt lithium manganese oxide; the binder is selected from sodium carboxymethyl cellulose, carboxymethyl cellulose One or more mixtures of lithium cellulose, sodium alginate and lithium alginate;

Wherein, in terms of mass percentage, the positive electrode comprises 70-95% of active material, 2-15% of binder, and 3-15% of conductive carbon.

As an important component of the positive electrode material of the battery, the binder needs to have a certain mechanical strength, can disperse the active material and conductive carbon, and has a good bonding effect, so that the positive electrode material does not fall off or separate during the battery cycle; The present invention finds that the stability of cathode materials composed of different binders varies significantly under high voltage conditions, especially in solid-state polymer lithium-ion batteries. For example, the PEO binder or the polymer binder containing EO branch chains often used in the prior art is used to prepare the positive electrode. Although the above-mentioned binder can effectively improve the ion conductivity of the positive electrode, thereby effectively improving the rate performance of the battery, it contains the above The positive electrode of the binder is prone to electrochemical decomposition of the binder at a voltage of 4 volts and above, resulting in poor battery performance. Further, the present invention finds that selecting a specific binder, an active material, and a battery positive electrode composed of conductive carbon will not cause an electrochemical decomposition reaction at a voltage of 4 volts and above, thereby obtaining a solid state with excellent cycle stability. Positive electrode for polymer lithium ion battery.

Preferably, the active material is lithium cobaltate; the binder is sodium carboxymethyl cellulose or sodium alginate; the conductive carbon is acetylene black; the active material, the binder and the The mass ratio of the conductive carbon is 8-9:0.5-1:0.5-1.

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

(1) mixing the active material, the binder and the conductive carbon in a solvent to obtain a slurry;

(2) Coating the slurry on the surface of the current collector and drying.

Preferably, the current collector is a carbon-coated aluminum foil.

The present invention also provides the application of the above positive electrode in the solid polymer lithium ion battery.

The present invention also provides a solid-state polymer lithium ion battery, comprising the above-mentioned positive electrode, a negative electrode and a solid-state polymer electrolyte; the negative electrode is one of lithium metal, graphite, silicon material, and silicon-carbon composite material; the solid-state polymer The electrolyte is a polyoxyethylene solid polymer electrolyte or a solid polymer electrolyte containing EO branches.

Preferably, the solid polymer electrolyte is prepared by a method comprising the following steps: after mixing polyethylene oxide or a polymer containing EO branches with a lithium salt in a solvent, casting is performed to form a film.

Preferably, the lithium salt is selected from lithium perchlorate (LiClO ₄ ), lithium bis(trifluoromethanesulfonyl)imide (LITFIS), lithium bisfluorosulfonimide (LIFSI), lithium bis(oxalate)borate ( A mixture of one or more of LIBOB).

Further, the lithium salt is lithium perchlorate or lithium bis(trifluoromethanesulfonyl)imide.

Preferably, the molar ratio of the EO group in the polyethylene oxide or the polymer containing the EO branch to the Li ⁺ ion in the lithium salt is 6:1-20:1; preferably 16:1-20 :1.

Preferably, in the preparation process of the solid polymer electrolyte, a metal oxide additive or an inorganic solid electrolyte filler is also added to the mixing;

The metal oxide additive is selected from one or more mixtures of alumina, silicon oxide and titanium oxide; the inorganic solid electrolyte filler is selected from garnet type lithium lanthanum zirconium oxygen, NASICON type lithium aluminum titanium phosphate, One or several mixtures of lithium aluminum germanium phosphate.

In the present invention, in the preparation process of the solid polymer electrolyte, an appropriate amount of metal oxide additives or inorganic solid electrolyte fillers can also be added in the mixing to improve the lithium ion conductivity of the polymer and its mechanical strength.

In the present invention, the preparation method of the battery is a conventional method in the field, which is not limited herein.

Beneficial effects of the present invention:

By selecting a specific binder, active material and conductive carbon in the present invention, when the obtained material is used as a positive electrode of a solid polymer lithium ion battery, the battery has very excellent cycle stability at a voltage of 4 volts and above; compared with the existing The positive electrode of the solid polymer lithium ion battery in the technology, the positive electrode material of the present invention has better cycle stability, longer service life and higher energy density at voltages of 4 volts and above. In addition, the preparation process of the solid-state polymer lithium ion battery of the present invention is simple, easy to scale up, and environmentally friendly; it is beneficial to promote the development of a solid-state high-energy-density lithium battery.

Description of drawings

Fig. 1 is the X-ray spectrum of the solid polymer lithium ion battery positive electrode of Examples 1-2 and Comparative Examples 1-2;

2 is a scanning electron microscope image of the positive electrode of the solid polymer lithium ion battery of Examples 1-2 and Comparative Examples 1-2;

FIG. 3 is a comparison diagram of the cycle stability of solid polymer lithium ion batteries made from the solid polymer lithium ion battery positive electrodes of Examples 1 to 2 and Comparative Examples 1 to 2 under the condition of 2.7 to 4.2 V;

FIG. 4 is a comparison diagram of the cycle stability of solid polymer lithium ion batteries made from the solid polymer lithium ion battery positive electrodes of Examples 1 to 2 and Comparative Examples 1 to 2 under the condition of 2.7 to 4.3 V.

Detailed ways

The following examples are intended to illustrate the present invention, but not to limit the scope of the present invention.

Example 1

This embodiment provides a solid polymer lithium ion battery positive electrode, the battery positive electrode is composed of lithium cobalt oxide, sodium alginate, and acetylene black in a mass ratio of 8:1:1.

The preparation method of the positive electrode comprises the following steps:

(1) obtaining slurry after mixing lithium cobaltate, sodium alginate and acetylene black in water;

(2) Coating the slurry on the surface of the carbon-coated aluminum foil, drying in a vacuum oven at 80° C. to remove water, and obtaining a solid polymer lithium ion battery positive electrode.

The X-ray spectrum of the solid-state polymer lithium ion battery positive electrode is shown in FIG. 1 , and the scanning electron microscope image is shown in FIG. 2 .

Example 2

This embodiment provides a solid polymer lithium ion battery positive electrode, the battery positive electrode is composed of lithium cobalt oxide, sodium carboxymethyl cellulose, and acetylene black in a mass ratio of 8:1:1.

The preparation method of the positive electrode comprises the following steps:

(1) obtain slurry after mixing lithium cobaltate, sodium carboxymethyl cellulose and acetylene black in water;

(2) Coating the slurry on the surface of the carbon-coated aluminum foil, drying in a vacuum oven at 80° C. to remove water, and obtaining a solid polymer lithium ion battery positive electrode.

The X-ray spectrum of the solid-state polymer lithium ion battery positive electrode is shown in FIG. 1 , and the scanning electron microscope image is shown in FIG. 2 .

Comparative Example 1

This comparative example provides a solid-state polymer lithium ion battery positive electrode, which is different from the embodiment 1 only in that sodium alginate is replaced with polyethylene oxide (PEO), and the water solvent is replaced with acetonitrile.

The X-ray spectrum of the solid-state polymer lithium ion battery positive electrode is shown in FIG. 1 , and the scanning electron microscope image is shown in FIG. 2 .

Comparative Example 2

This comparative example provides a solid-state polymer lithium-ion battery positive electrode, which is different from Example 1 only in that sodium alginate is replaced by polyvinylidene fluoride (PVDF), and the water solvent is replaced by N-methyl-2 - Pyrrolidone.

The X-ray spectrum of the solid-state polymer lithium ion battery positive electrode is shown in FIG. 1 , and the scanning electron microscope image is shown in FIG. 2 .

Test Example 1

In this test example, the positive electrodes of Examples 1-2 and Comparative Examples 1-2 are respectively assembled into solid polymer lithium ion batteries; the negative electrodes of the solid polymer lithium ion batteries are lithium metal, and the electrolyte is polyoxyethylene solid polymer electrolyte;

The preparation method of the polyoxyethylene solid-state polymer electrolyte is as follows:

After mixing polyethylene oxide with a molar ratio of EO:Li ⁺ of 16:1 and lithium perchlorate in acetonitrile, casting is performed to form a film to obtain a solid polymer electrolyte film;

The preparation method of the solid-state polymer lithium ion battery is as follows:

(1) Cut the positive electrode into circular or square pieces;

(2) cutting the solid polymer electrolyte film into a round or square piece slightly larger than the positive electrode;

(3) Cut the lithium metal negative electrode into a round or square piece as large as the positive electrode;

(4) The positive electrode in step (1), the electrolyte in step (2), and the negative electrode in step (3) are sequentially stacked into a sandwich structure to form a solid-state polymer lithium ion battery, and no liquid is added during the entire operation.

The electrochemical performance of each solid-state polymer lithium-ion battery was tested at 60°C, and the test results were shown in Figures 3 and 4; it can be seen from Figures 3 and 4 that the solid-state polymer lithium-ion batteries containing the positive electrodes of Examples 1 to 2 were Higher cycle stability and higher energy density at 4 V and above.

Although the present invention has been described in detail above with general description, specific embodiments and tests, some modifications or improvements can be made on the basis of the present invention, which is obvious to those skilled in the art . Therefore, these modifications or improvements made without departing from the spirit of the present invention fall within the scope of the claimed protection of the present invention.

Claims (10)

1. The solid polymer lithium ion battery anode comprises an active material, a binder and conductive carbon, and is characterized in that the active material is lithium cobaltate or high nickel cobalt lithium manganate; the binder is selected from one or a mixture of more of sodium carboxymethylcellulose, lithium carboxymethylcellulose, sodium alginate and lithium alginate;

the positive electrode comprises, by mass, 70-95% of an active material, 2-15% of a binder and 3-15% of conductive carbon.

2. The positive electrode according to claim 1, wherein the active material is lithium cobaltate; the binder is sodium carboxymethyl cellulose or sodium alginate; the conductive carbon is acetylene black; the mass ratio of the active material to the binder to the conductive carbon is 8-9: 0.5-1: 0.5 to 1.

3. The method for producing a positive electrode according to claim 1 or 2, comprising the steps of:

(1) mixing an active material, a binder and conductive carbon in a solvent to obtain slurry;

(2) and coating the slurry on the surface of a current collector, and drying.

4. The method of manufacturing according to claim 3, wherein the current collector is a carbon-coated aluminum foil.

5. Use of the positive electrode according to claim 1 or 2 in a solid polymer lithium ion battery.

6. A solid polymer lithium ion battery comprising the positive electrode of claim 1 or 2, a negative electrode, and a solid polymer electrolyte; the negative electrode is one of lithium metal, graphite, silicon material and silicon-carbon composite material; the solid polymer electrolyte is a polyoxyethylene-based solid polymer electrolyte or a solid polymer electrolyte containing EO branches.

7. The battery of claim 6, wherein the solid polymer electrolyte is prepared by a method comprising: polyethylene oxide or a polymer having EO branches is mixed with a lithium salt in a solvent, and then cast into a film.

8. The battery according to claim 7, wherein the lithium salt is selected from one or more of lithium perchlorate, lithium bis (trifluoromethanesulfonyl) imide, lithium bis (fluorosulfonyl) imide, and lithium bis (oxalato) borate; lithium perchlorate or lithium bis (trifluoromethanesulfonyl) imide are preferred.

9. The cell of claim 7 or 8, wherein the EO groups of the polyethylene oxide or EO-branched polymer and Li in the lithium salt⁺The molar ratio of the ions is 6: 1-20: 1; preferably 16:1 to 20: 1.

10. The battery according to any one of claims 7 to 9, wherein a metal oxide additive or an inorganic solid electrolyte filler is further added to the mixture during the preparation of the solid polymer electrolyte;

the metal oxide additive is selected from one or a mixture of more of aluminum oxide, silicon oxide and titanium oxide; the inorganic solid electrolyte filler is selected from one or a mixture of more of garnet type lithium lanthanum zirconium oxide, NASICON type lithium aluminum titanium phosphate and lithium aluminum germanium phosphate.

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