CN107634226B

CN107634226B - Synthesis and application of lithium ion battery cathode material taking coordination polymer as template

Info

Publication number: CN107634226B
Application number: CN201710830917.8A
Authority: CN
Inventors: 师唯; 杜佳; 程鹏
Original assignee: Nankai University
Current assignee: Nankai University
Priority date: 2017-09-15
Filing date: 2017-09-15
Publication date: 2020-01-14
Anticipated expiration: 2037-09-15
Also published as: CN107634226A

Abstract

A synthesis and application of a lithium ion battery cathode material using a coordination polymer as a template belong to the technical field of lithium ion batteries, and particularly relate to [ Co (OH-BDC) (H)₂O)₃]_n(wherein OH-BDC is 5-hydroxyisophthalic acid) complex, and preparation and electrochemical performance characterization of the lithium ion battery negative electrode material. The complex is synthesized by dissolving cobalt acetate and 5-hydroxyisophthalic acid in a solvent and heating and reacting for 3 days under a hydrothermal condition. The electrode plate is prepared by uniformly mixing the complex, the conductive agent and the binder, adding N-methyl pyrrolidone serving as a solvent, and blending into slurry. And assembling the prepared electrode plate into a lithium ion battery and testing. Compared with the prior art, the invention directly applies the synthesized coordination polymer to the lithium ion battery cathode material and shows good electrochemical performance.

Description

Synthesis and application of lithium ion battery cathode material taking coordination polymer as template

Technical Field

The invention relates to the field of application of a lithium ion battery cathode material, in particular to preparation and application of a lithium ion battery cathode material taking a coordination polymer as a template.

Background

The energy crisis has gradually become an important issue hindering social development and threatening human survival. Electrochemical energy storage has received much attention due to its high energy conversion efficiency and clean energy system. The lithium ion battery has the characteristics of high energy density, light weight, high output voltage, no memory effect, no environmental pollution and the like, and is widely applied to mobile phones, computers, portable electronic equipment, environment-friendly electric or hybrid electric vehicles and the like. Since the chair type lithium ion battery was put into practical use by sony corporation in 1990, the lithium ion battery has led to the development of the electronic device industry and is still leading. A complete lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte. With positive electrode LiCoO₂Negative electrode graphite is briefly introduced as an example, and lithium ions are derived from LiCoO upon charging₂And the graphite layer falls off and is embedded into the graphite layer through the electrolyte. Electrons flow from the external circuit from the cathode to the anode. During discharge, lithium ions are extracted from the graphite interlayer and enter LiCoO through the electrolyte₂The electron flow paths are reversed. The materials currently applied to the negative electrode of the lithium ion battery can be classified into three types according to the mechanism of lithium ion deintercalation: firstly, toGraphene is a representative insertion type material, and is characterized in that lithium ions can be reversibly deintercalated between graphite layers, and the material stability is good, but the common problem of the materials is that the specific capacity is not high. The second type is a transition type material, mainly oxides, sulfides, halides, etc. of metals. In the discharging process, the oxidation state metal is converted into a metal simple substance, and the original state is returned during charging. Such materials generally have higher capacities, but the higher oxidation-reduction potential and the huge volume expansion generated during the reaction are bottlenecks that limit further practical development. The third type is an alloy type material. Mainly represented by germanium, tin and oxides thereof. It is characterized in that metal and lithium spontaneously form alloy in the electrode reaction process. Since the alloying process is generally carried out at a lower redox potential, the advantages of this material are a low electrode potential and a high capacity, but the consequent large volume expansion is also a problem to be solved.

Coordination polymers formed by metal ions or metal clusters and organic ligands through a self-assembly mode are widely concerned due to abundant and changeable chemical structures and excellent performances. The coordination polymer can be used for gas storage and separation, heterogeneous catalysis, fluorescence sensors, magnetic materials, proton conduction, drug delivery, biological imaging and the like. Based on the diversity of the combination of ligands and metal ions, the structural diversity and controllable physicochemical properties of the material make it widely applicable to lithium ion batteries, and research in this field is receiving much attention. However, among the materials reported at present, poor conductivity and low specific capacity are the key points for limiting practical applications, and the search for stable electrode materials with high capacity is urgent.

Disclosure of Invention

The invention aims to overcome the problems of low specific capacity and poor stability of the existing complex applied to the lithium ion battery, provides a coordination polymer which is simple to synthesize and low in cost, and applies the coordination polymer as a battery cathode material to the lithium ion battery.

The invention is realized by the following technical scheme:

a method for synthesizing a lithium ion battery negative electrode material by taking a coordination polymer as a template comprises the following steps:

(1) synthesizing a complex: the molar ratio of the raw materials is 1:1, dissolving cobalt acetate tetrahydrate and 5-hydroxyisophthalic acid in water, adding triethylamine to adjust the pH value of the solution to 5, heating the solution to 120 ℃ in a reaction kettle for reaction for 3 days, and cooling the solution to room temperature at a cooling rate of 2 ℃ per minute after the reaction is finished to obtain a complex [ Co (OH-BDC) (H-BDC)₂O)₃]_nWherein OH-BDC is 5-hydroxyisophthalic acid, and n is a natural number more than or equal to 1.

(2) The purity of the complex is characterized. Collecting a large amount of the complex synthesized in the step (1), filtering and drying to obtain a mauve flaky crystal. The collected crystals were subjected to PXRD testing. The experimental result is fitted with a simulated PXRD value reported in the literature, and the experimental data is well consistent with the simulated value, which shows that the synthesized crystal phase has high purity.

Complex [ Co (OH-BDC) (H)₂O)₃]_nApplication of negative electrode material in preparation of lithium ion battery

Step 1, preparing an electrode material. Weighing the complex [ Co (OH-BDC) (H) according to the mass ratio of 6:3:1₂O)₃]_nGrinding and uniformly mixing a conductive agent (ketjen black) and a binder (polyvinylidene fluoride), mixing into slurry by using a solvent (N-methylpyrrolidone), coating the slurry on a copper foil, drying for 12 hours at the temperature of 80 ℃ in vacuum, and slicing to obtain the round electrode plate.

And 2, assembling the lithium ion battery. Using lithium plate as counter electrode, Celgard 2400 membrane as diaphragm, 1mol/L lithium hexafluorophosphate (LiPF)₆) And (3) assembling a lithium ion button battery by taking the circular electrode plate obtained in the step (1) as a negative electrode, wherein the volume ratio of Ethylene Carbonate (EC) to diethyl carbonate (DEC) to electrolyte is 1:1, and the battery model is CR 2032.

And 3, testing the electrochemical performance. The temperature is room temperature during testing, the voltage range in constant current charge and discharge testing is 0.01-3V, the number of charge and discharge cycles in cycle performance testing is 100, the current density is 200mA/g, constant current charge and discharge are respectively tested under the current densities of 100mA/g, 200mA/g, 500mA/g, 1000mA/g, 2000mA/g and 100mA/g in multiplying power performance testing, and the number of cycles is 10 under each multiplying power.

The invention has the advantages and beneficial effects that:

compared with the prior art, the coordination polymer is synthesized and directly used as the negative electrode material of the lithium battery as the lithium ion battery. The obtained complex presents a one-dimensional chain structure in the structure and is stacked into a three-dimensional structure through the action of hydrogen bonds among chains. The complex has the advantages of simple synthesis method, cheap and easily obtained raw materials, high yield and convenient characterization. The prepared negative electrode material has good electrochemical performance, when the charge-discharge current density is 200mA/g, the specific capacity is maintained at 1041mAh/g after 100 times of circulation, and meanwhile, in a test of large current 2A/g, the specific capacity is maintained at 600mA/g after 700 weeks of circulation. The electrochemical material also shows good stability and excellent electrochemical performance in a rate test.

Drawings

FIG. 1 is a diagram of the minimum structural unit of a complex material;

FIG. 2(a) shows a ligand consisting of Co²⁺A one-dimensional chain diagram constructed by ions, and (b) a three-dimensional framework diagram of the compound;

FIG. 3 is a powder diffraction pattern of a complex material;

FIG. 4 is a constant current charge-discharge diagram of a lithium ion battery prepared from the lithium battery negative electrode material of the invention when the current density is 200 mA/g;

FIG. 5 is a charge-discharge cycle chart of a lithium ion battery prepared from the negative electrode material of the lithium battery of the present invention at a current density of 200 mA/g;

FIG. 6 is a charge-discharge cycle chart of a lithium ion battery prepared from the negative electrode material of the lithium battery according to the present invention, when the current density is 2A/g;

FIG. 7 is a graph of rate performance of a lithium ion battery prepared from the lithium battery negative electrode material of the present invention.

Detailed Description

To further clarify the technical means and effects of the present invention adopted to achieve the intended purpose, the following detailed description will be given of specific embodiments of the synthesis and application of a lithium ion battery anode material using a coordination polymer as a template according to the present invention with reference to the examples and the accompanying drawings.

Example 1 Synthesis of coordination Polymer

(1) synthesizing a complex: cobalt acetate tetrahydrate Co (OAc) was weighed out separately₂·4H₂Dissolving O (125mg, 0.5mmol) and 5-hydroxyisophthalic acid (OH-BDC) (105mg, 0.5mmol) in water (10mL), adding triethylamine (0.53mmol), heating in a reaction kettle at 120 ℃ for reaction for 3 days, wherein the cooling rate is 2 ℃ per minute, and cooling to room temperature at the cooling rate of 2 ℃ per minute after the reaction is finished to obtain mauve flaky crystals to obtain a complex [ Co (OH-BDC) (H) with the shape of purple sheets₂O)₃]_nWherein OH-BDC is 5-hydroxyisophthalic acid.

(2) Collecting a large amount of the complex synthesized in (1), filtering and drying. The collected crystals were subjected to PXRD testing. The experimental results are fitted with simulated PXRD values reported in the literature, the peak values completely accord with each other, and the chemical formula of the complex is proved to be [ [ Co (OH-BDC) (H)₂O)₃]_nWherein OH-BDC is 5-hydroxyisophthalic acid. Referring to fig. 1, a coordination environment diagram of divalent cobalt ions in a complex material. The divalent cobalt ion assumes a hexa-coordinated configuration in a distorted octahedral configuration, coordinating with three oxygens from the pentahydroxyisophthalic acid and three oxygens from the water, respectively. Referring to FIG. 2(a), each 5-hydroxyisophthalic ligand bridges two Co ions in a three-way mode to form a zigzag chain of the polymer, while the chains are stacked into a three-dimensional structure by hydrogen bonding, as shown in FIG. 2 (b). See FIG. 3 for powder diffraction of the complex.

Example 2 preparation of lithium ion batteries

Use of the lithium ion battery negative electrode material prepared in example 1 for the preparation of a lithium ion battery. The preparation method comprises the steps of mixing the negative electrode material of the lithium battery prepared in example 1, conductive carbon black and a binder according to the mass ratio of 6:3:1, using N-methyl pyrrolidone as a solvent to prepare slurry, using a coater to coat the slurry on copper foil, and drying the copper foil in a vacuum drying oven at 80 ℃ for 12 hours. And (4) punching the electrode plate into a circular electrode plate with the diameter of 12mm by using a punching machine, and weighing for later use.

1mol/L lithium hexafluorophosphate (LiPF) is added into the electrode plate, Celgard 2400 membrane is used as a diaphragm₆) The lithium ion battery is a lithium ion battery with the assembled battery model CR2032, wherein the electrolyte is Ethylene Carbonate (EC), diethyl carbonate (DEC) and 1:1 in volume ratio are solvents, the lithium sheet is a counter electrode.

And testing the assembled lithium ion battery on a blue battery testing system.

Please refer to fig. 4, which is a constant current charging/discharging curve of a lithium ion battery prepared by using the negative electrode material of the lithium battery of the present invention. As can be seen from the figure, the charge and discharge platform of the lithium ion battery prepared from the lithium battery negative electrode material is below 1V, and has a relatively low charge and discharge platform, which shows that the material obtained by the invention has good electrochemical performance. The current density is 200mA/g, the first-week discharge capacity is 2700mAh/g, the charge capacity is 1143mAh/g, the capacity is still 1041mAh/g after 100-week circulation, and the coulombic efficiency is as high as 99%. Showing good cycling stability. Please refer to fig. 5, which is a cycle chart of the material cycling for 100 weeks. Meanwhile, the cycling stability of the material under a large current of 2A/g is tested, and the capacity of the material is still as high as 600mAh/g after 700 weeks of cycling, so that the structure of the material is stable, and the good electrochemical performance is still maintained under the large current, please refer to FIG. 6. FIG. 7 shows a graph of the rate performance of the complex at different circuit densities. The capacity values were about 1200, 1050, 900, 750, 600mAh/g at 100, 200, 500, 1000, 2000, 100mA/g for 10 cycles, respectively, at current densities, which is consistent with the cycle stability test results. When the current density returns to 100mA/g, the capacity of the battery is increased to about 1200mAh/g, the circulation stability and the rate capability of the complex are reflected, and meanwhile, the material has a stable structure under a large current and has a good application prospect.

Claims

1. A method for synthesizing a lithium ion battery negative electrode material by taking a coordination polymer as a template is characterized by comprising the following steps:

synthesizing a complex, wherein the molar ratio is 1:1, dissolving cobalt acetate tetrahydrate and 5-hydroxyisophthalic acid in water, adding triethylamine to adjust the pH value of the solution to 5, heating the solution to 120 ℃ in a reaction kettle for reaction for 3 days, and cooling the solution to room temperature at a cooling rate of 2 ℃ per minute after the reaction is finished to obtain a mauve flaky crystal, namely a complex [ Co (OH-BDC) (H)₂O)₃]_nWherein OH-BDC is 5-hydroxyisophthalic acid and n is a natural number greater than or equal to 1.

2. The method for synthesizing the lithium ion battery anode material by using the coordination polymer as the template according to claim 1, wherein the method comprises the following specific operations: cobalt acetate tetrahydrate Co (OAc) was weighed out separately₂·4H₂O0.5mmol, 0.5mmol of 5-hydroxyisophthalic acid (OH-BDC), dissolving in 10mL of water, adding 0.53mmol of triethylamine, adjusting the pH value of the solution to 5, heating in a 23mL reaction kettle at 120 ℃ for reaction for 3 days, and cooling to room temperature at a cooling rate of 2 ℃ per minute after the reaction is finished to obtain the mauve flaky crystal.

3. The method for synthesizing the lithium ion battery anode material by using the coordination polymer as the template according to claim 1, wherein the complex [ Co (OH-BDC) (H)₂O)₃]_nThe purity is characterized by collecting a large amount of the complex synthesized in claim 1, filtering and drying, carrying out PXRD test on the collected crystals, fitting the experimental result with a simulated PXRD value reported in the literature, and confirming that the purity of the synthesized material is high and the structural formula of the complex is [ Co (OH-BDC) (H-BDC) ]₂O)₃]_nAnd simultaneously, drawing the structure by using diamond drawing software.

4. Coordination polymer [ Co (OH-BDC) (H) synthesized by the method of claim 1₂O)₃]_nThe application of the lithium ion battery negative electrode material is characterized by comprising the following steps:

step 1, preparing an electrode sheet, namely preparing the coordination polymer [ Co (OH-BDC) (H) prepared in the claim 1₂O)₃]_nGrinding and mixing the conductive agent ketjen black and the adhesive polyvinylidene fluoride uniformly according to the mass ratio of 6:3:1, mixing the mixture into slurry by using solvent N-methyl pyrrolidone, coating the slurry on copper foil, drying the copper foil for 12 hours at the temperature of 80 ℃ in vacuum, punching the copper foil into an electrode slice with the diameter of 12mm by using a punching machine, and weighing the electrode slice for later use;

step 2, assembling the lithium ion battery; lithium sheet as counter electrode, Celgard 2400 membrane as separator, 1mol/L lithium hexafluorophosphate (LiPF)₆) And (3) assembling a lithium ion button battery by taking the circular electrode plate obtained in the step (1) as a negative electrode, wherein the volume ratio of Ethylene Carbonate (EC) to diethyl carbonate (DEC) to electrolyte is 1:1, and the battery model is CR 2032.

5. The application of claim 4, wherein the lithium ion battery prepared by the application has the following electrochemical performance test method: the temperature is room temperature during testing, and the voltage range in constant current charge and discharge testing is 0.01-3V; in the cycle performance test, the charge-discharge cycle times are 100 times when the current density is 200mA/g, and 700 times are cycled under the current density of 2A/g; in the multiplying power performance test, constant current charging and discharging are respectively carried out under the current densities of 100mA/g, 200mA/g, 500mA/g, 1000mA/g, 2000mA/g and 100mA/g, and the cycle number is 10 times under each multiplying power.