CN107732172B

CN107732172B - Lithium ion battery cathode material and preparation method thereof

Info

Publication number: CN107732172B
Application number: CN201710873664.2A
Authority: CN
Inventors: 严微微
Original assignee: China Jiliang University
Current assignee: China Jiliang University
Priority date: 2017-09-25
Filing date: 2017-09-25
Publication date: 2020-10-30
Anticipated expiration: 2037-09-25
Also published as: CN107732172A

Abstract

The invention discloses a lithium ion battery cathode material and a preparation method thereof, belonging to the technical field of lithium ion batteries. The preparation process flow is copper sulfate (CuSO)₄) Preparing Cu from trisodium citrate, polyvinylpyrrolidone, sodium hydroxide and ascorbic acid₂O nanocubes and hydrolyzing in Cu by isopropyl titanate₂O surface coated with nano TiO₂To obtain nano TiO₂Clad Cu₂O nanocube material. The material of the invention has simple synthesis process, mild reaction condition, no pollution to the environment, low cost and mass production. The nano TiO of the invention₂Clad Cu₂The O nanocubes as the lithium ion battery cathode material have the advantages of obviously improved cycle stability and charge-discharge performance, and are suitable for industrial application of the lithium ion battery.

Description

Lithium ion battery cathode material and preparation method thereof

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium ion battery cathode material and a preparation method thereof.

Background

Lithium ion batteries have the advantages of high operating voltage, high specific capacity, no memory effect, environmental friendliness, and the like, and have been widely used in portable electronic devices such as mobile phones, notebook computers, and small cameras, and large electronic devices such as electric automobiles, electric bicycles, and electric tools. In recent years, intelligent electronic equipment is developed rapidly, higher requirements are put on a power supply, and the power supply is urgently required to have high energy density and power density, long cycle life and good service performance. The current commercial lithium ion battery can not completely meet the market demand, the electrochemical performance of the lithium ion battery is improved by developing high-performance electrodes and electrode materials, and the further development of the lithium ion battery is promoted, so that the lithium ion battery becomes very important work.

At present, the cathode material of the commercial lithium ion battery is mainly a graphitized carbon-based material. The carbon material with high graphitization degree has large surface anisotropy, and a passivation film formed during first charging is loose and porous, so that the co-insertion of solvated lithium ions can not be effectively prevented, and the collapse of a graphite layer can be caused. In addition, the diffusion speed of lithium ions along the ab-axis plane of the graphite crystallite is much higher than that of the c-axis direction, and lithium insertion is carried out at the boundary of the graphite layer, so that the lithium ions are diffused therein to have great kinetic barrier, and rapid charge and discharge cannot be carried out. Therefore, research and development of high-performance lithium ion battery negative electrode materials are widely regarded by researchers in various countries.

Since the first report of the excellent performance of nano transition metal oxide as a lithium ion battery anode material in Nature by j.m. Tarascon in 2000, 3d transition metal oxide (MxOy, M = Mn, Fe, Co, Ni, Cu) becomes an important candidate for a lithium battery anode material. In the above negative electrode material, the theoretical capacity of CuO is 674 mAh g^-1About 2 times that of commercial carbon cathode material, Cu₂Theoretical capacity of O372 mAh g^-1. But CuO and Cu₂The density of O is about three times that of the carbon-based material, thereby having a larger volume lithium storage density, and copper oxides (CuO, Cu)₂O or the mixture of the O and the O) is nontoxic and harmless, is easy to synthesize and store, so that the material has great development potential and application prospect as the cathode material of the lithium ion battery and is receiving more and more attention.

For copper oxides (cuprous oxide, cupric oxide), insufficient cycle stability is one of the major problems affecting its application in lithium batteries. The reason is that after the reaction of the transition metal oxide (including other transition metal oxides) and lithium, large volume expansion occurs, severe internal stress is generated, the active material is gradually pulverized in the circulation process, electrical contact with a current collector and the like is lost, and nano transition metal particles are agglomerated to form large particles, so that electrochemical activity is lost. Thus, copper oxide (CuO, Cu) is enhanced₂O) becomes the key to further use of the material. The common methods mainly comprise nanocrystallization, compounding, thin film electrode preparation and the like.

Chinese patent publication No. CN102394305B discloses a copper foam oxide/copper lithium ion battery cathode and a method for preparing the same, which mainly comprises growing a layered copper oxide in situ on the surface of a current collector copper foam, and improving the lithium battery performance of the copper oxide by in situ growth, a nano structure and a thin film structure, but this material structure does not solve the problems of volume expansion and contraction of the copper oxide and internal stress in the charge and discharge reaction, and has a limited effect on improving the cycle stability.

Disclosure of Invention

The object of the present invention is to increase Cu content₂O is used as the cycle stability and the charge and discharge performance of the lithium ion battery cathode material, and provides the lithium ion battery cathode material and the preparation method thereof.

The negative electrode material of the lithium ion battery is nano TiO₂Clad Cu₂O nanocubes, Cu₂O is in a nano cubic structure with the size of 10-500 nm, and the surface of the O is coated with a layer of amorphous TiO₂，TiO₂The layer thickness is 10-100 nm.

The nanometer TiO of the invention₂Clad Cu₂The preparation method of the O nanocube composite material comprises the following steps:

mixing copper sulfate (CuSO)₄) Sequentially dissolving trisodium citrate and polyvinylpyrrolidone (PVP) in deionized water, stirring to obtain a uniform aqueous solution, and adding CuSO₄The concentration is 0.1-5 g L^-1Trisodium citrate concentration 0.1-3 g L^-1At a PVP concentration of 1-40 gL^-1. Under stirring, dropwise adding NaOH aqueous solution (concentration 70-100 g L)^-1) After 30 min of reaction, ascorbic acid solution (with concentration of 50-150 g L) is added dropwise^-1) Stirring for reaction for 5-30 min, stopping stirring, standing for 5-20 h, centrifuging, washing the product with deionized water and anhydrous ethanol for several times, and storing in anhydrous ethanol.

Taking Cu₂Absolute ethanol solution of O (concentration 2 g L)^-1) Adding deionized water, stirring uniformly, then gradually and slowly adding isopropyl titanate, stirring and reacting for 2-5 h, washing the product for multiple times by using deionized water and absolute ethyl alcohol after centrifugal separation, and drying in vacuum at 70 ℃ to obtain the nano TiO₂Clad Cu₂An O nanocube composite.

The lithium ion battery cathode is prepared by adopting the cathode material of the invention: respectively weighing nano TiO with the mass ratio of 8:1:1₂Clad Cu₂Dissolving PVDF in a proper amount of 1-methyl-2-pyrrolidone (NMP), and stirring until the PVDF is completely dissolvedAnd adding the uniformly ground active powder and the acetylene black conductive agent into the solution, and continuously stirring to ensure that the slurry is uniformly mixed. And then uniformly coating the slurry on a disk-shaped foamed nickel current collector (the diameter is 12 mm), drying at 80 ℃ in a vacuum oven, and finally flattening by using a pressure of 10 MPa on a tabletting machine to obtain the electrode plate.

And (3) forming the prepared battery cathode, a lithium sheet and a diaphragm into the CR2025 button type lithium ion battery in a glove box filled with high-purity argon. The electrolyte is 1 mol L^-1LiPF₆The EC/DMC electrolyte of (1). And testing the charge-discharge performance and the cycle stability of the lithium ion battery by adopting a Xinwei battery testing system. Calculation of TiO according to the invention₂Clad Cu₂The specific capacity of the O material being that including TiO₂And Cu₂Total mass of O.

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

（1）Cu₂the O nanocubes have small volume and small absolute volume change in charge-discharge reaction, can reduce the internal stress of materials and have positive effect on improving the cycle stability.

(2) Nano Cu₂Small O size and large specific surface area, can provide more positions for electrochemical reaction, is favorable for reducing surface resistance and charge transfer resistance, thereby improving the activity of the electrochemical reaction, obtaining high capacity and rate capability, namely improving Cu₂O lithium battery performance.

(3) With carbon material and Cu₂Compared with O, nano TiO₂Has safer working voltage range, very small volume expansion in the charging and discharging process, stable structure and excellent cycling stability, and nano TiO₂Clad to Cu₂O-nanocube surface for effectively resisting Cu₂The volume expansion and contraction of O in the charge-discharge reaction can obviously improve the structural stability of the material, thereby improving the cycle stability.

（4）TiO₂Is close to Cu in theoretical capacity₂O, hence TiO₂The coating of (2) does not reduce the specific capacity of the whole composite material, which is an advantage that other materials such as carbon and the like do not have.

(5) TiO of the invention₂The coating of (a) is carried out by hydrolysis of isopropyl titanate, which results in the formation of TiO₂Is amorphous small crystal grains, and interconnected porous structures exist among the crystal grains, and the structural characteristics can ensure that TiO can not only be used for preparing the nano-crystalline TiO₂The material has better cycle stability and energy storage characteristic close to theoretical capacity, has small effect of obstructing permeation of electrolyte and lithium ions, and does not influence internal Cu₂And (4) performing electrochemical reaction on O.

(6) The material of the invention has simple synthesis process, mild reaction condition, no pollution to the environment, low cost, mass production and great commercial application prospect.

Drawings

FIG. 1 shows the nano TiO prepared in example 1₂Clad Cu₂SEM photograph of O nanocubes.

FIG. 2 shows the nano TiO prepared in example 1₂Clad Cu₂TEM photograph of O nanocubes after dilute hydrochloric acid treatment.

FIG. 3 shows the nano TiO prepared in example 1₂Clad Cu₂And the cyclic charge and discharge performance of the O nanocubes.

FIG. 4 shows the nano TiO prepared in example 2₂Clad Cu₂And the cyclic charge and discharge performance of the O nanocubes.

FIG. 5 shows the nano TiO prepared in example 3₂Clad Cu₂And the cyclic charge and discharge performance of the O nanocubes.

Detailed Description

The present invention is further illustrated by the following examples.

Example 1

Mixing copper sulfate (CuSO)₄) Sequentially dissolving trisodium citrate and polyvinylpyrrolidone (PVP) in deionized water, stirring to obtain a uniform aqueous solution, and adding CuSO₄Concentration 0.19 g L^-1Trisodium citrate concentration 0.6 g L^-1PVP concentration 20 g L^-1. 150 mL of the solution was added dropwise with stirring an aqueous NaOH solution (40 g L concentration)^-1) 20 mL, after 30 min of reaction, 10 mL (10 concentration) of ascorbic acid solution was added dropwise5 g L^-1) Stirring for reaction for 15 min, stopping stirring, standing for 10 h, centrifugally separating, washing the product with deionized water and absolute ethyl alcohol for multiple times, and storing in absolute ethyl alcohol.

Taking Cu ₂50 mL of absolute ethanol solution of O (concentration 2 g L)^-1) Adding deionized water, stirring uniformly, then dropwise and slowly adding 0.1 mL isopropyl titanate, stirring for reaction for 3 h, washing the product for multiple times by using deionized water and absolute ethyl alcohol after centrifugal separation, and drying in vacuum at 70 ℃ to obtain the nano TiO₂Clad Cu₂An O nanocube composite.

FIG. 1 is TiO₂Clad Cu₂And in the SEM photograph of the O nanocube, the structure of the cube is very obvious, the side length is about 200nm, the surface of the cube is rough, and a layer of substance is attached to the surface. In order to facilitate the observation of the structure of the surface coating, the composite material is dissolved with Cu inside by dilute hydrochloric acid₂TEM observation after O showed that one TiO was observed as shown in FIG. 2₂A square box with an internal dimension of about 200nm, TiO₂About 30-40 nm thick. TiO 2₂The material is composed of a plurality of fine particles, presents amorphous characteristics, has higher activity, and is different from a crystalline material synthesized by a hydrothermal method and the like.

The lithium ion battery cathode is prepared by adopting the cathode material of the invention: respectively weighing nano TiO with the mass ratio of 8:1:1₂Clad Cu₂Dissolving PVDF in a proper amount of 1-methyl-2-pyrrolidone (NMP), stirring until the PVDF is completely dissolved, adding the uniformly ground active powder and the acetylene black conductive agent into the solution, and continuously stirring to ensure that the slurry is uniformly mixed. And then uniformly coating the slurry on a disk-shaped foamed nickel current collector (the diameter is 12 mm), drying at 80 ℃ in a vacuum oven, and finally flattening by using a pressure of 10 MPa on a tabletting machine to obtain the electrode plate.

And (3) forming the prepared cathode, a metal lithium sheet (anode) and a diaphragm into the CR2025 button type lithium ion battery in a glove box filled with high-purity argon. The electrolyte is 1 mol L^-1LiPF₆The EC/DMC electrolyte of (1). And testing the charge-discharge performance and the cycle stability of the lithium ion battery by adopting a Xinwei battery testing system. The charge-discharge current is 0.1C multiplying power, and the charge-discharge voltage range is 0.01-3.0V. The specific capacity of the coating material calculated by the invention comprises TiO₂And Cu₂Total mass of O. Not coated with TiO₂Cu of (2)₂The O nanocubes were also fabricated with the same process and negative electrodes assembled into lithium ion batteries, and performance tests were performed using the same conditions for comparison.

FIG. 3 is the TiO prepared in example one₂Clad Cu₂O nanocubes and pure Cu₂Graph of cyclic performance of O nanocubes. TiO 2 cycle start₂Clad Cu₂The discharge capacity of O is very stable and is basically maintained at 370 mAh g^-1And the discharge capacity through 50 th cycle was 364 mAh g^-1And pure Cu₂The O-cube discharge capacity decreased by 42.4% from cycle 2 to cycle 20, then slowly dropped to 192 mAh g at cycle 50^-1，TiO₂Cladding pair improved Cu₂The circulation stability effect of O is obvious. 50 cycles of TiO₂Clad Cu₂The average discharge capacity of O was 380 mAh g^-1And pure Cu₂O is 250 mAhg^-1，TiO₂Cladding improves Cu₂Average discharge capacity of O52%, indicating that the TiO coating was coated₂Can improve Cu₂Charge and discharge properties of O. The result of the cyclic charge-discharge test shows that the TiO is coated₂Can obviously improve Cu₂Cyclic and charge-discharge properties of O, TiO₂Clad Cu₂The O nanocube composite material has important application value in the field of lithium ion batteries.

Example 2

Mixing copper sulfate (CuSO)₄) Sequentially dissolving trisodium citrate and polyvinylpyrrolidone (PVP) in deionized water, stirring to obtain a uniform aqueous solution, and adding CuSO₄Concentration 0.38g L^-1Trisodium citrate concentration 1.2 g L^-1PVP concentration 30 g L^-1. 150 mL of the solution was added dropwise with stirring an aqueous NaOH solution (40 g L concentration)^-1) 40 mL, after 30 min of reaction20 mL of ascorbic acid solution (concentration 105 g L) was added dropwise^-1) Stirring for reaction for 30 min, stopping stirring, standing for 15 h, centrifugally separating, washing the product with deionized water and absolute ethyl alcohol for multiple times, and storing in absolute ethyl alcohol.

Taking Cu ₂50 mL of absolute ethanol solution of O (concentration 2 g L)^-1) Adding deionized water, stirring uniformly, then gradually and slowly adding 0.2 mL isopropyl titanate drop by drop, stirring for reaction for 3 h, washing a product for multiple times by using the deionized water and absolute ethyl alcohol after centrifugal separation, and drying in vacuum at 70 ℃ to obtain the nano TiO₂Clad Cu₂An O nanocube composite.

Cu in composite material₂O still maintains the cubic structure, the side length of the cubic is about 350 nm, and the TiO is coated₂The layer is in an amorphous small crystal grain accumulation shell structure, and the thickness of the layer is 60-70 nm.

The lithium ion battery cathode is manufactured by the same process as the example 1, and assembled into the lithium ion battery, and the cycle charge and discharge test is carried out by the same equipment and conditions (0.2C multiplying power, 0.01-3.0V voltage range), and the result is shown in figure 4, and the cycle charge and discharge test result shows that the TiO coating is coated₂Can obviously improve Cu₂The cycle performance and charge-discharge performance of O.

Example 3

Mixing copper sulfate (CuSO)₄) Sequentially dissolving trisodium citrate and polyvinylpyrrolidone (PVP) in deionized water, stirring to obtain a uniform aqueous solution, and adding CuSO₄Concentration 0.76g L^-1Trisodium citrate concentration 2.4 g L^-1PVP concentration 30 g L^-1. 150 mL of the solution was added dropwise with stirring an aqueous NaOH solution (40 g L concentration)^-1) 80 mL, after 30 min of reaction, 40 mL (concentration 105 g L) of ascorbic acid solution was added dropwise^-1) Stirring for reaction for 30 min, stopping stirring, standing for 15 h, centrifugally separating, washing the product with deionized water and absolute ethyl alcohol for multiple times, and storing in absolute ethyl alcohol.

Taking Cu ₂50 mL of absolute ethanol solution of O (concentration 2 g L)^-1) Adding deionized water, stirring uniformly, then dropwise adding 0.2 mL of isopropyl titanate slowly, stirringStirring for reaction for 3 h, centrifugally separating, washing the product with deionized water and absolute ethyl alcohol for multiple times, and vacuum drying at 70 ℃ to obtain nano TiO₂Clad Cu₂An O nanocube composite.

Cu in composite material₂O still maintains the cubic structure with the side length of about 540 nm and is coated with TiO₂The layer is in an amorphous small crystal grain accumulation shell structure, and the thickness of the layer is 80-90 nm.

The lithium ion battery cathode is manufactured by the same process as the example 1, and assembled into the lithium ion battery, and the cycle charge and discharge test is carried out by the same equipment and conditions (0.2C multiplying power, 0.01-3.0V voltage range), and the result is shown in figure 5, and the cycle charge and discharge test result shows that the TiO coating is coated₂Can obviously improve Cu₂The cycle performance and charge-discharge performance of O.

Claims

1. The negative electrode material of lithium ion battery has nanometer TiO structure₂Clad Cu₂An O nanocube characterized by: cu₂O is in a nano cubic structure with the size of 10-500 nm, and the surface of the O is coated with a layer of amorphous TiO₂，TiO₂The thickness of the layer is 10-100nm, and the cathode material is prepared by the following method:

sequentially dissolving copper sulfate, trisodium citrate and polyvinylpyrrolidone in deionized water, stirring to obtain uniform water solution with copper sulfate concentration of 0.1-5 g L^-1The concentration of trisodium citrate is 0.1-3 g L^-1PVP concentration of 1-40 g L^-1(ii) a Adding dropwise 70-100 g L while stirring^-1Reacting for 30 min, and continuously dropwise adding 50-150 g L^-1Stirring the ascorbic acid solution for reaction for 5-30 min, stopping stirring, standing for 5-20 h, washing the product with deionized water and absolute ethyl alcohol for multiple times after centrifugal separation, and storing in absolute ethyl alcohol;

taking the concentration as 2 g L^-1Cu of (2)₂Adding deionized water into an absolute ethyl alcohol solution of O, stirring uniformly, then slowly adding isopropyl titanate drop by drop, stirring for reaction for 2-5 h, washing a product for multiple times with the deionized water and the absolute ethyl alcohol after centrifugal separation, and at 70 DEG CVacuum drying to obtain nano TiO₂Clad Cu₂An O nanocube composite.