Use of a lithium-rich polymer containing sulfur atoms as a cathode material for lithium-ion batteries

Abstract

The application belongs to the field of lithium ion batteries, and particularly relates to application of a lithium-rich polymer containing sulfur atoms as a positive electrode material of a lithium ion battery. The organic lithium-rich polymer is synthesized by using a conjugated benzene ring derivative as a monomer and sulfur atoms for bridging, so as to synthesize the organic polymer lithium-rich polymer positive electrode material containing sulfur atoms. The positive electrode material has certain air stability, is beneficial to large-scale production, has a reduced solubility in an organic electrolyte by polymerization to expand a molecular chain, improves the cycle performance of the battery, can be matched with a graphite negative electrode by pre-embedding lithium ions in the structure through a chemical reaction, is more safe, has a relatively high discharge voltage (about 3.0 V), and is beneficial to development of a high-energy-density secondary battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion batteries, and particularly relates to application of a lithium-rich polymer containing sulfur atoms as a positive electrode material of a lithium ion battery. BACKGROUND

[0002] Lithium secondary batteries have been widely used in mobile electronic products. However, with the increase in population and the optimization of energy structure, it is currently an important task to develop lithium ion batteries that are safer, cheaper and have higher energy density. At present, commercial lithium ion batteries mainly use inorganic positive electrode materials (such as LiCoO2, LiFePO4, LiMn2O4, etc.). The related inorganic positive electrode materials have a relatively low actual specific capacity (100-170 mAh / g), and have encountered a bottleneck in realizing high energy density. In addition, the metal raw materials used in the electrode materials belong to non-renewable energy sources, and organic electrode materials that are environmentally friendly and renewable and have a high theoretical specific capacity are expected to realize the development of secondary batteries with higher energy density.

[0003] Unlike the principle of intercalation and deintercalation of inorganic electrode materials, organic electrode materials adopt a redox mechanism, which endows the organic electrode materials with unique advantages: (1) light elements such as C, N and H can participate in multi-electron redox reactions, and high specific capacity of the battery can be achieved; (2) the structure of organic compounds is strong in designability, and the voltage can be adjusted; (3) the cost of organic compounds is low, and the raw materials are abundant, which is conducive to large-scale production. Therefore, organic positive electrode materials have great development prospects.

[0004] However, most organic materials, especially small molecular compounds, are easily dissolved in electrolyte, resulting in poor cycle stability and hindering the realization of long-life batteries. Secondly, since the material itself does not contain lithium, it needs to be matched with a lithium metal negative electrode or a pre-lithiated graphite positive electrode, and cannot be compatible with the existing lithium ion battery production process. Moreover, the discharge voltage of the organic positive electrode material is low, which is not conducive to the construction of high specific energy lithium ion batteries.

[0005] In view of the higher requirements for the energy density, cycle life and resource reserves of the current rechargeable secondary batteries, and the fact that inorganic positive electrodes have reached the upper limit of energy density, the application aims to solve the problems of easy dissolution, non-lithium and low voltage of organic compounds, and to obtain an organic polymer lithium-rich polymer positive electrode material containing sulfur atoms with high voltage, high capacity and high cycle stability through functional molecular structure design. The graphite can be used as a negative electrode to assemble high energy density lithium ion secondary batteries. SUMMARY

[0006] The application aims to overcome the shortcomings of the prior art, and provides an application of a lithium-rich polymer containing sulfur atoms as a positive electrode material of a lithium ion battery, which solves the problem of dissolution from the perspective of molecular design, uses a one-step polymerization strategy, bridges monomer molecules through sulfur atoms, expands the molecular chain, and reduces the solubility of the compound, and pre-introduces lithium ions in the structure through a chemical reaction to form an organic polymer lithium-rich polymer positive electrode material, which has the characteristics of high voltage and high capacity, can match a graphite negative electrode, and can be assembled into a safer lithium ion battery.

[0007] The technical scheme for solving the technical problems of the application is as follows:

[0008] The application provides an application of a lithium-rich polymer containing sulfur atoms as a positive electrode material of a lithium ion battery, and the lithium-rich polymer containing sulfur atoms has the following structural formula, wherein -X is -OLi or =N-OLi, n=(2)-(5),

[0009]

[0010] Further, the preparation method of the lithium-rich polymer containing sulfur atoms is as follows: under an inert atmosphere, a conjugated benzene ring derivative and lithium sulfide are uniformly mixed in a solvent at a molar ratio of 1:1-3, stirring reaction is carried out at 140 DEG C-180 DEG C for 12-24 h, a precipitate is generated, and the lithium-rich polymer containing sulfur atoms is obtained through vacuum filtration, washing and drying, the conjugated benzene ring derivative is 2,5,-dichloro-1,4-benzenediol or 2,5-dichloro-1,4-benzene dioxime.

[0011] Further, the inert atmosphere is nitrogen or argon.

[0012] Further, the solvent is N-methylpyrrolidone or N,N-dimethylformamide.

[0013] Further, the lithium-rich polymer containing sulfur atoms is mixed with conductive carbon material, and then is pressed on a current collector as a positive electrode sheet, lithium sheet is used as a negative electrode, 1.0M LiTFSIDOL / DME (1.0M lithium bisfluorosulfonylimide salt is a solute, and volume ratio of ethylene carbonate and diethyl carbonate is 1:1) is used as an electrolyte, and a lithium ion battery is assembled.

[0014] The application has the following advantages and beneficial effects:

[0015] (1) The organic lithium-rich polymer positive electrode material of the present application is a conjugated benzene ring derivative as a monomer, bridged by sulfur atoms, and expanded by polymerization to reduce the solubility in organic electrolyte and improve the cycle performance of the battery.

[0016] (2) The organic lithium-rich polymer positive electrode material provided by the present application can match graphite as a negative electrode by introducing lithium ions in the structure in advance through chemical reaction, and can be assembled into an organic lithium ion secondary battery, which is more secure.

[0017] (3) The organic lithium-rich polymer positive electrode material provided by the present application has a high discharge voltage (about 3.0V), has a certain air stability, and is beneficial to the development of high-energy-density secondary batteries.

[0018] (4) The organic lithium-rich polymer positive electrode material provided by the present application has mild conditions, low toxicity, and can be synthesized in one step. It has batch production potential and broad application prospects in the fields of power batteries, intermittent renewable energy utilization, and large-scale energy storage. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The infrared spectrum of the organic lithium-rich polymer prepared in Example 1;

[0020] Figure 2 The infrared spectrum of the organic lithium-rich polymer prepared in Example 2;

[0021] Figure 3 The mass spectrum of the organic lithium-rich polymer prepared in Example 1;

[0022] Figure 4 The mass spectrum of the organic lithium-rich polymer prepared in Example 2;

[0023] Figure 5 The lithium ion battery assembled with the organic lithium-rich polymer prepared in Example 1 as a positive electrode material has a constant current charge-discharge curve at 0.33C for the first three cycles. As can be seen from the figure, the discharge voltage of the synthesized organic lithium-rich polymer is about 2.75V;

[0024] Figure 6 The lithium ion battery assembled with the organic lithium-rich polymer prepared in Example 1 as a positive electrode material has a cycle curve at 0.33C. As can be seen from the figure, the capacity of the synthesized organic lithium-rich polymer does not decrease significantly after 350 cycles, and the cycle stability is good;

[0025] Figure 7 The lithium ion battery assembled with the organic lithium-rich polymer prepared in Example 2 as a positive electrode material has a constant current charge-discharge curve at 0.33C for the first three cycles;

[0026] Figure 8The specific capacity and coulombic efficiency of long cycle at 0.33C of the lithium ion battery assembled with the organic lithium-rich polymer prepared in Example 2 as the positive electrode material;

[0027] Figure 9 The first constant current charge-discharge curve at 0.33C of the lithium ion battery assembled with graphite as the negative electrode. DETAILED DESCRIPTION

[0028] The application will be further described in the following specific examples, which are only illustrative and not restrictive, and cannot limit the protection scope of the application.

[0029] Example 1:

[0030] Under an argon atmosphere, 2,5-dichloro-1,4-benzenediol (0.19 g, 1 mmol) and lithium sulfide (0.092) were added to 20 ml N-methylpyrrolidone, and stirred at 160°C for 12 h. Filtration, dimethyl sulfoxide washing, ethyl acetate washing, and drying at 80°C for 12 h to obtain the organic lithium-rich polymer.

[0031] Figure 1 The infrared spectrum of the organic lithium-rich polymer of Example 1, from which it can be seen that the -OH peak of the starting material disappears, and is converted into -OLi structure. -1 The above -OH peak disappears, thereby being converted into -OLi structure.

[0032] Figure 3 The mass spectrum of the organic lithium-rich polymer of Example 1, from which it can be seen that the polymerization degree of the synthesized organic lithium-rich material is 3.

[0033] The organic lithium-rich polymer of Example 1 was uniformly ground with conductive carbon material (ketjen black) at a mass ratio of 5:5, 1 mg of the above mixture was added in a demoldable infrared tablet pressing mold, a 10 mm current collector stainless steel mesh current collector, and the active material and conductive carbon were pressed on the stainless steel mesh as the positive electrode sheet at a pressure of 15 MPa. In an argon glove box, a metal lithium sheet was used as the negative electrode, a 1.0 M lithium bisfluorosulfonylimide salt was used as the solute, a volume ratio of 1:1 of ethylene carbonate and diethyl carbonate was used as the solvent, and Celgard 2325 was used as the separator, to assemble a button lithium battery for electrochemical performance test.

[0034] Figure 5 The first constant current charge-discharge curve at 0.33C of the lithium ion battery assembled with the organic lithium-rich polymer prepared in Example 1 as the positive electrode material; from the figure, it can be seen that the discharge voltage of the synthesized organic lithium-rich polymer is ~2.75V.

[0035] Figure 6The lithium-rich organic polymer prepared in Example 1 was used as a positive electrode material to assemble a lithium ion battery, and the cycle curve at 0.33 C was plotted. As can be seen from the figure, the capacity of the synthesized lithium-rich organic polymer did not decrease significantly after 350 cycles, and the cycle stability was good.

[0036] Example 2:

[0037] Under an argon atmosphere, 2,5-dichloro-1,4-benzenediol (0.21 g, 1 mmol) and lithium sulfide (0.092 g, 2 mmol) were added to 20 ml of N,N-dimethylformamide, and the reaction was stirred at 140°C for 12 h. Filtration, methanol washing, ethyl acetate washing, and drying at 80°C for 12 h yielded a lithium-rich organic polymer.

[0038] Figure 2 The infrared spectrum of the lithium-rich organic polymer of Example 2. As can be seen from the figure, the -NOH peak of the synthesized lithium-rich organic polymer disappeared, and was converted into a -NOLi structure. -1 The above -NOH peak disappeared, thereby being converted into a -NOLi structure.

[0039] Figure 4 The mass spectrum of the lithium-rich organic polymer of Example 2. As can be seen from the figure, the polymerization degree of the synthesized lithium-rich organic material was 3.

[0040] The lithium-rich organic polymer of Example 2 was uniformly ground with a conductive carbon material (ketjen black) at a mass ratio of 5:5, 1 mg of the above mixture was added to a demoldable infrared tablet pressing mold, a 10 mm current collector stainless steel mesh current collector was used, and the active material and conductive carbon were pressed on the stainless steel mesh as a positive electrode sheet at a pressure of 15 MPa. In an argon glove box, a metal lithium sheet was used as a negative electrode, a 1.0 M lithium bisfluorosulfonylimide salt was used as a solute, a volume ratio of 1:1 of ethylene carbonate and diethyl carbonate was used as a solvent, and a Celgard 2325 was used as a separator to separate the electrolyte, thereby assembling a button lithium battery for electrochemical performance testing.

[0041] Figure 7 The lithium ion battery assembled using the lithium-rich organic polymer prepared in Example 2 as a positive electrode material was subjected to constant current charge and discharge at 0.33 C for the first three cycles, and the cycle curve was plotted. As can be seen from the figure, the discharge capacity of the synthesized lithium-rich organic polymer reached 225 mAh g -1 , and had good electrochemical reversibility.

[0042] Figure 8 The specific capacity and coulombic efficiency of the lithium ion battery assembled using the lithium-rich organic polymer prepared in Example 2 as a positive electrode material were plotted for long cycles at 0.33 C. As can be seen from the figure, the synthesized lithium-rich organic polymer had good cycle stability, and the capacity did not decrease significantly after 70 cycles.

[0043] Example 3:

[0044] The organic lithium-rich polymer described in Example 1 was ground with conductive carbon material (ketjen black) at a mass ratio of 5:5, and 1 mg of the mixture was added to a demoldable infrared tablet press mold, and a 10 mm current collector stainless steel mesh current collector was used to press the active material and conductive carbon on the stainless steel mesh as a positive electrode sheet at a pressure of 15 MPa. In an argon glove box, a graphite negative electrode, 1.0 M lithium bisfluorosulfonylimide salt as a solute, and a volume ratio of 1:1 ethylene carbonate and diethyl carbonate as a solvent were used to assemble a coin lithium battery, which was used for electrochemical performance testing Figure 9 The organic lithium-rich polymer prepared in Example 1 was used as a positive electrode material, Figure 9 The first constant current charge-discharge curve of a lithium ion battery using graphite as a negative electrode at 0.33 C is shown in the figure. As can be seen from the figure, the discharge capacity of the full battery composed of the synthesized organic lithium-rich polymer and the graphite negative electrode can reach 110 mAh g -1 .

[0045] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A method for preparing a lithium ion battery cathode material, characterized in that, The strategy of one-step polymerization is used to bridge monomer molecules through sulfur atoms, expand molecular chains, and introduce lithium ions in the structure in advance through chemical reaction to form lithium-rich polymer positive electrode materials containing sulfur atoms, which have the characteristics of high voltage and high capacity, match graphite negative electrode, and the structural formula of the lithium-rich polymer positive electrode material containing sulfur atoms is as follows, wherein -X is -OLi or =N-OLi, n=(2)~(5), ; The specific preparation method is: under an inert atmosphere, a conjugated benzene ring derivative and lithium sulfide are mixed uniformly in a solvent at a molar ratio of 1:1-3, stirred and reacted at 140-180 DEG C for 12-24 h, a precipitate is generated, and the lithium-rich polymer positive electrode material containing sulfur atoms is obtained by vacuum filtration, washing and drying; the conjugated benzene ring derivative is 2,5,-dichloro-1,4-benzene phenol or 2,5-dichloro-1,4-benzene dihydrazine.

2. The production method according to claim 1, characterized by, The inert atmosphere is nitrogen or argon.

3. The production method according to claim 1, characterized by, The solvent is N-methyl pyrrolidone or N,N-dimethylformamide.

4. A method for preparing a lithium ion battery comprising the lithium ion battery cathode material of claim 1, characterized in that, The lithium-rich polymer positive electrode material containing sulfur atoms is mixed with a conductive carbon material, pressed on a current collector as a positive electrode sheet, a lithium sheet is used as a negative electrode, an electrolyte uses 1.0 M lithium bisfluorosulfonylimide salt as a solute, and volume ratio 1:1 of ethylene carbonate and diethyl carbonate as a solvent to assemble a lithium ion battery.

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