Application of sulfur atom-containing lithium-rich polymer as positive electrode material of lithium ion battery

Abstract

The invention belongs to the field of lithium ion batteries, and particularly relates to application of a sulfur atom-containing lithium-rich polymer as a lithium ion battery positive electrode material. According to the organic lithium-rich polymer, a conjugated benzene ring derivative is taken as a monomer, bridging is carried out through sulfur atoms, and the sulfur-atom-containing organic lithium-rich polymer positive electrode material is synthesized in one step. The positive electrode material has certain air stability and is beneficial to large-scale production; molecular chains are expanded through polymerization, so that the solubility of the polymer in organic electrolyte is reduced, and the cycle performance of the battery is improved; lithium ions are embedded in the structure in advance through chemical reaction and can be matched with a graphite negative electrode, so that the safety is higher; and the material has relatively high discharge voltage (about 3.0 V), and is beneficial to development of a secondary battery with high energy density.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion batteries, and in particular relates to the application of a lithium-rich polymer containing sulfur atoms as a positive electrode material for lithium ion batteries. Background Art

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

[0003] Different from the embedding and unembedding principle of inorganic electrode materials, organic electrode materials adopt the redox mechanism, which gives them unique advantages: (1) They use lightweight elements such as C, N, and H, which can participate in multi-electron redox reactions and achieve high specific capacity of batteries; (2) The structure of organic compounds is highly designable and the voltage is adjustable; (3) Organic compounds are low-cost and have abundant sources of synthetic raw materials, which is conducive to large-scale production. Therefore, organic positive electrode materials have great development prospects.

[0004] However, most organic materials, especially small molecule compounds, are easily soluble in electrolytes, resulting in poor cycle stability, which is an obstacle to achieving 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, which is not compatible with the existing lithium-ion battery production process. In addition, the discharge voltage of organic positive electrode materials is low, which is not conducive to the construction of high-energy lithium-ion batteries.

[0005] In view of the current situation where higher requirements are put forward for the energy density, cycle life and resource reserves of rechargeable secondary batteries, and the inorganic positive electrode has reached the upper limit of energy density, the present invention aims to obtain a high-voltage, high-capacity, and high-cycle stability sulfur-containing organic polymer lithium-rich polymer positive electrode material through function-oriented molecular structure design, and graphite can be used as the negative electrode to assemble a high-energy-density lithium-ion secondary battery. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an application of a lithium-rich polymer containing sulfur atoms as a positive electrode material for lithium-ion batteries. From the perspective of molecular design, a one-step polymerization strategy is used to bridge monomer molecules through sulfur atoms, expand the molecular chain, and reduce the solubility of the compound to solve the problem of dissolution. At the same time, lithium ions are introduced into the structure in advance through chemical reactions to form an organic polymer lithium-rich polymer positive electrode material, which has the characteristics of high voltage and high capacity, and can be matched with a graphite negative electrode to assemble a safer lithium-ion battery. Therefore, in view of the problems that organic compounds are easy to dissolve, do not contain lithium, and have low voltage, a sulfur-containing organic polymer lithium-rich polymer positive electrode material obtained by function-oriented molecular structure design is used as a positive electrode to assemble a high-energy-density lithium-ion secondary battery, which has broad application prospects.

[0007] The technical solution of the present invention to solve the technical problem is as follows:

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

[0009]

[0010] Furthermore, the preparation method of the lithium-rich polymer containing sulfur atoms is: 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, and the mixture is stirred and reacted at 140°C-180°C for 12-24 hours to produce a precipitate, and the precipitate is filtered under reduced pressure, washed, and dried to obtain a lithium-rich polymer containing sulfur atoms, wherein the conjugated benzene ring derivative is 2,5-dichloro-1,4-phenol or 2,5-dichloro-1,4-phenyldioxime.

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

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

[0013] Furthermore, a lithium-rich polymer containing sulfur atoms was mixed with a conductive carbon material and pressed onto a current collector as a positive electrode sheet, a lithium sheet was used as a negative electrode, and 1.0M LiTFSIDOL / DME (1.0M lithium bis(fluorosulfonyl)imide salt as a solute and ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 as a solvent) was used as an electrolyte to assemble a lithium-ion battery.

[0014] The advantages and beneficial effects of the present invention are:

[0015] (1) The organic lithium-rich polymer positive electrode material of the present invention uses conjugated benzene ring derivatives as monomers and is bridged by sulfur atoms. The molecular chain is enlarged by polymerization to reduce its solubility in the organic electrolyte and improve the cycle performance of the battery.

[0016] (2) The organic lithium-rich polymer positive electrode material provided by the present invention introduces lithium ions into the structure in advance through chemical reaction, and can be matched with graphite as the negative electrode to assemble an organic lithium-ion secondary battery, which is safer.

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

[0018] (4) The organic lithium-rich polymer cathode material provided by the present invention has mild conditions, low toxicity, and can be synthesized in one step. It has the potential for mass production and has broad application prospects in the fields of power batteries, intermittent renewable energy utilization, and large-scale energy storage. BRIEF DESCRIPTION OF THE 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 first three cycles of constant current charge and discharge curves of a lithium-ion battery assembled with the organic lithium-rich polymer prepared in Example 1 as the positive electrode material at 0.33C; it can be seen from the figure that the discharge voltage of the synthesized organic lithium-rich polymer is 2.75V;

[0024] Figure 6 The cycle curve of the organic lithium-rich polymer prepared in Example 1 as the positive electrode material assembled into a lithium-ion battery at 0.33C; it can be seen from the figure that the capacity of the synthesized organic lithium-rich polymer has no obvious attenuation after 350 cycles, and the cycle stability is good;

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

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

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

[0028] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0029] Embodiment 1:

[0030] In an argon atmosphere, 2,5-dichloro-1,4-phenol (0.19 g, 1 mmol) and lithium sulfide (0.092) were added to 20 ml of N-methylpyrrolidone and stirred at 160°C for 12 h. The mixture was filtered, washed with dimethyl sulfoxide and ethyl acetate, and dried at 80°C for 12 h to obtain an organic lithium-rich polymer.

[0031] Figure 1 This is the infrared spectrum of the organic lithium-rich polymer of Example 1. It can be seen from the figure that 3000cm -1 The above -OH peak disappears, thus transforming into -OLi structure.

[0032] Figure 3 This is the mass spectrum of the organic lithium-rich polymer of Example 1. It can be seen from the figure that the degree of polymerization of the synthesized organic lithium-rich material is 3.

[0033] After the organic lithium-rich polymer and the conductive carbon material (Ketjen black) described in Example 1 were ground uniformly 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, and the active material and conductive carbon were pressed on the stainless steel mesh at a pressure of 15 MPa as a positive electrode. In an argon glove box, a metal lithium sheet was used as the negative electrode, 1.0 M lithium bis(fluorosulfonyl)imide salt was used as the solute, and the electrolyte of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the solvent, and Celgard 2325 was used as a separator to separate them, and button lithium batteries were assembled for electrochemical performance testing.

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

[0035] Figure 6The organic lithium-rich polymer prepared in Example 1 is used as the positive electrode material to assemble a lithium-ion battery and the cycle curve is shown at 0.33C. It can be seen from the figure that the capacity of the synthesized organic lithium-rich polymer has no obvious attenuation after 350 cycles, and the cycle stability is good.

[0036] Embodiment 2:

[0037] In an argon atmosphere, 2,5-dichloro-1,4-benzenedioxime (0.21 g, 1 mmol) and lithium sulfide (0.092 g, 2 mmol) were added to 20 ml of N,N-dimethylformamide and stirred at 140°C for 12 h. The mixture was filtered, washed with methanol and ethyl acetate, and dried at 80°C for 12 h to obtain an organic lithium-rich polymer.

[0038] Figure 2 This is the infrared spectrum of the organic lithium-rich polymer positive electrode material of Example 2. It can be seen from the figure that 3000cm -1 The above -NOH peak disappears, thus transforming into -NOLi structure.

[0039] Figure 4 This is the mass spectrum of the organic lithium-rich polymer of Example 2. It can be seen from the figure that the degree of polymerization of the synthesized organic lithium-rich material is 3.

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

[0041] Figure 7 The first three cycles of constant current charge and discharge curves of a lithium-ion battery assembled with the organic lithium-rich polymer prepared in Example 2 as the positive electrode material at 0.33C; it can be seen from the figure that the discharge capacity of the synthesized organic lithium-rich polymer can reach 225mAh g -1 , and has good electrochemical reversibility.

[0042] Figure 8 The specific capacity and coulombic efficiency of a lithium-ion battery assembled with the organic lithium-rich polymer prepared in Example 2 as the positive electrode material at 0.33C for a long cycle. It can be seen from the figure that the synthesized organic lithium-rich polymer has good cycle stability, and there is no obvious capacity decay within 70 cycles.

[0043] Embodiment 3:

[0044] After the organic lithium-rich polymer and the conductive carbon material (Ketjen black) described in Example 1 were ground evenly at a mass ratio of 5:5, 1 mg of the above mixture was added to a demoldable infrared tabletting mold, and a 10 mm current collector stainless steel mesh was used as the current collector. The active material and the conductive carbon were pressed on the stainless steel mesh at a pressure of 15 MPa as the positive electrode. In an argon glove box, graphite was used as the negative electrode, 1.0 M lithium bis(fluorosulfonyl)imide salt was used as the solute, and the electrolyte of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 was used as the solvent. Celgard 2325 was used as a separator to separate them, and button lithium batteries were assembled for electrochemical performance testing. Fig. 9 The organic lithium-rich polymer prepared in Example 1 is used as the positive electrode material, Fig. 9 The first constant current charge and discharge curve of a lithium-ion battery assembled with graphite as the negative electrode at 0.33C. It can be seen from the figure that the discharge capacity of the full battery composed of the synthesized organic lithium-rich polymer and the graphite negative electrode can reach 110mAh g -1 .

[0045] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, which all belong to the protection scope of the present invention.

Claims

1. Application of a lithium-rich polymer containing sulfur atoms as a positive electrode material for a lithium-ion battery, characterized in that: The lithium-rich polymer containing sulfur atoms has the following structural formula, wherein -X is -OLi or =N-OLi, n=(2) to (5), 2. The use according to claim 1, characterized in that: 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, and stirred at 140°C-180°C for 12-24h to generate a precipitate, and the precipitate is filtered under reduced pressure, washed, and dried to obtain a lithium-rich polymer containing sulfur atoms, wherein the conjugated benzene ring derivative is 2,5-dichloro-1,4-phenol or 2,5-dichloro-1,4-phenyldioxime.

3. The use according to claim 2, characterized in that: The inert atmosphere is nitrogen or argon.

4. The use according to claim 2, characterized in that: The solvent is N-methylpyrrolidone or N,N-dimethylformamide.

5. The use according to claim 1, characterized in that: A lithium-rich polymer containing sulfur atoms is mixed with a conductive carbon material and pressed onto a current collector as a positive electrode sheet. A lithium sheet is used as a negative electrode. The electrolyte uses 1.0M lithium bis(fluorosulfonyl)imide salt as a solute and ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 as a solvent to assemble a lithium-ion battery.

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