An alkali metal oxalate composite material and a preparation method thereof

Abstract

The present invention discloses an alkali metal squarate composite material and a preparation method thereof. The composite material includes an alkali metal squarate and a conductive carbon material, and the alkali metal squarate is attached to the surface of the conductive carbon material; the alkali metal squarate composite material is added to the positive electrode of an alkali metal ion battery as a material for supplementing alkali metal ions. The preparation method includes the following steps: (1) reacting an alkaline alkali metal compound with squaric acid to prepare an alkali metal squarate; (2) preparing a conductive carbon material dispersion; (3) mixing the alkali metal squarate obtained in step (1) with the conductive carbon material dispersion obtained in step (2) to obtain a mixed dispersion; (4) spray-drying the mixed dispersion obtained in step (3) to obtain an alkali metal squarate-conductive carbon composite material. The present invention realizes the green and energy-saving preparation of an alkali metal squarate, effectively reduces the oxidation overpotential of the alkali metal squarate, and the composite material can be directly added and used in the stirring process of the positive electrode material of an alkali metal ion battery without increasing the process cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of alkali metal compounds, and particularly relates to an alkali metal squarate composite material and a preparation method thereof. Background Art

[0002] Alkali metal ion batteries are secondary batteries that mainly rely on the movement of alkali metal ions between the positive and negative electrodes to work. During the charge and discharge process, alkali metal ions are intercalated and deintercalated back and forth between the two electrodes. During charging, alkali metal ions deintercalate from the positive electrode, pass through the electrolyte and intercalate into the negative electrode, and accumulate at the negative electrode, while the opposite occurs during discharge. Currently, the alkali metal ion batteries in use or under research are lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries. Among them, lithium-ion batteries and sodium-ion batteries have received much attention at present.

[0003] When the alkali metal ion battery is activated during the first cycle of charging, a part of the alkali metal ions in the battery will be consumed to form a solid electrolyte interface film (i.e., SEI film) on the surface of the negative electrode. Therefore, it is necessary to add supplementary materials to make up for this part of the consumed alkali metal ions.

[0004] Taking lithium-ion batteries as an example, in Chinese Patent CN201310413605.9, Lithium Ion Battery Cathode Sheet, Lithium Ion Battery and Preparation Method Thereof, it is mentioned that lithium squarate can be used as a lithium supplement additive. The specific capacity of lithium squarate is as high as 440 mAh / g, and its specific capacity is twice that of traditional cathode materials, making it suitable as a sacrificial lithium salt to supplement the irreversible capacity loss of lithium ions. Similarly, other alkali metal squarates are also suitable as supplementary materials for the corresponding alkali metal ion batteries.

[0005] However, alkali metal squarates have the problem of low electro-chemical reaction activity, which cannot fully exert the effect of supplementing alkali metal ions. Moreover, the poor conductivity of alkali metal squarates leads to an increase in the internal resistance of the positive electrode sheet, affecting the performance of the electrode material. However, adding more conductive agents will reduce the energy density of the battery. Taking lithium / sodium squarate as an example, currently, solutions such as material nanocrystallization, introducing catalysts, and special electrode sheet structures have been successively proposed to solve the problems of lithium / sodium squarate as a lithium supplement material. It is disclosed in Chinese Patent CN202011616037.9, "A Lithium Squarate and Its Preparation Method and Application", that lithium squarate is made into nanosheets with a size of 50-100 nm to reduce the oxidation overpotential of lithium squarate. It is disclosed in Chinese Patent CN202010713446.4, "A Multilayer Positive Electrode Sheet, Battery and Preparation Method with Lithium / Sodium Supplementing Function", that a double-layer electrode sheet structure of a positive electrode material layer and a lithium / sodium supplementing layer is adopted, and a metal oxide catalyst is added to reduce the influence of the lithium / sodium supplementing additive on the conductivity of the electrode sheet. It is disclosed in Chinese Patent CN202011136734.4, "Composite Positive Electrode Material and Its Preparation Method and Lithium Ion Battery", that a double-layer electrode sheet structure design is adopted. The composite positive electrode material includes a positive electrode material layer and a lithium supplementing layer. The supplementing layer contains lithium squarate and a metal fluoride catalyst. The metal fluoride catalyst and lithium squarate are mixed by ball milling to reduce the decomposition potential of lithium squarate.

[0006] The mixing uniformity of the catalyst and the prelithiation reagent, the conductivity of the catalyst, the particle size of lithium squarate, etc. all have crucial effects on the prelithiation effect. The function of the double-layer electrode structure design is undoubted, but the number of process steps increases, or rather, the risk of cost increase is significantly increased, which is not conducive to industrialization promotion. The ball milling mixing uniformity is not high and impurities are easily introduced. The conductivity of the metal fluoride or oxide catalyst itself is not high, resulting in poor catalytic effect. The freeze-drying equipment is expensive, the process energy consumption is high, and the time is long, making it difficult to be applicable to the large-scale production of bulk chemicals. Summary of the Invention

[0007] To solve the above technical problems, the purpose of the present invention is to provide an alkali metal squarate composite material and a preparation method, which realize the green and energy-saving preparation of alkali metal squarates, effectively reduce the oxidation overpotential of alkali metal squarates, and the composite material can be directly added and used in the stirring process of the positive electrode material of the alkali metal ion battery without increasing the process cost.

[0008] To achieve the above invention purpose, the technical solutions adopted by the present invention are as follows:

[0009] In the first aspect of the present invention, a method for preparing an alkali metal squarate composite material is provided, and the specific steps are as follows: (1) React an alkaline alkali metal compound with squaric acid to prepare an alkali metal squarate; (2) Prepare a conductive carbon material dispersion; (3) Mix the alkali metal squarate obtained in step (1) with the conductive carbon material dispersion obtained in step (2) to obtain a mixed dispersion; (4) Spray-dry the mixed dispersion obtained in step (3) to obtain an alkali metal squarate-conductive carbon composite material.

[0010] In the present invention, the alkali metal refers to the six metal elements in Group IA of the periodic table except hydrogen, namely lithium, sodium, potassium, rubidium, cesium, and francium; preferably, the alkali metal in the present invention refers to lithium, sodium, and potassium, and the alkali metal compound in the present invention refers to an alkaline lithium compound or sodium compound or potassium compound, and the alkali metal squarate refers to lithium squarate or sodium squarate or potassium squarate; more preferably, the alkali metal in the present invention is lithium.

[0011] In the present invention, after the alkali metal squarate is mixed with the conductive carbon material dispersion and spray-dried, the nano-sized alkali metal squarate adheres to the surface of the conductive carbon material to form a composite material. The composite material uses conductive carbon as a catalyst, effectively reducing the oxidation overpotential of the alkali metal squarate. Using the composite material as an additive for supplementing ions can solve the problem of low electrochemically reactive activity of the alkali metal squarate, and can also avoid introducing transition metal ions by using a transition metal compound catalyst.

[0012] The alkali metal squarate obtained in step (1) can be a solid or a solution, and the method for preparing the alkali metal squarate can be various. For example, an alkali metal squarate solution can be prepared by a liquid-phase mixing method, that is, the alkali metal compound is configured as an alkaline solution and then mixed and reacted with an aqueous squaric acid solution; or, an alkali metal squarate solid can be prepared by a solid-phase mixing and grinding method, that is, the alkali metal compound powder is mixed and ground with squaric acid powder to make them react; or, an alkali metal squarate solution can be prepared by a solid-liquid mixing method, that is, the alkali metal compound solution (or powder) is mixed and reacted with squaric acid powder (or solution) to prepare the alkali metal squarate.

[0013] In the practice of the present invention, due to the low solubility of squaric acid, a high-concentration aqueous squaric acid solution cannot be configured. Preferably, an alkali metal compound solution is mixed and reacted with squaric acid solid powder to prepare a squarate, and the specific steps are as follows: (1.1) Prepare an alkaline alkali metal compound solution; (1.2) Add squaric acid and react with the alkali metal compound solution to generate an alkali metal squarate solution. It is easy to understand that in step (1.2), the molar ratio of the alkali metal to squaric acid is 2:1, and the added squaric acid can completely react with the alkali metal compound, and there are no other impurities in the solution.

[0014] The reaction between the alkali metal compound solution and squaric acid is an acid-base neutralization reaction. Therefore, the alkali metal compound solution needs to be alkaline. The preparation methods of the alkali metal compound solution include dissolution and reaction. Dissolution means that the solid alkali metal compound is dissolved in water to form an alkaline solution, such as alkali metal carbonates, alkali metal bicarbonates, alkali metal hydroxides, alkali metal acetates, etc.; reaction means that the solid alkali metal compound reacts with water to form an alkaline solution, such as alkali metal oxides, alkali metal peroxides, alkali metal sulfides, etc. Among them, for the solution prepared by reaction, the solute is different from the solid alkali metal compound. For the convenience of description, in the present invention, unless otherwise specified, the reaction between the alkali metal compound solution and squaric acid refers to the reaction between the solute - alkali metal compound in the solution and squaric acid.

[0015] Preferably, the alkali metal in the present invention is lithium, and the lithium compound can be an alkaline lithium source such as lithium hydroxide, lithium carbonate, lithium bicarbonate, lithium acetate, lithium sulfide, lithium oxide, lithium peroxide, etc.

[0016] To save energy consumption and reduce processes, in step (3), the present invention directly mixes the alkali metal squarate solution with the conductive carbon material dispersion. To improve production efficiency, the concentration of the alkali metal squarate solution should be as high as possible. In step (1.1), a saturated alkali metal compound solution is prepared. In the practice of the present invention, under the same temperature conditions, the solubility of sodium compounds and potassium compounds is relatively large, but the solubility of lithium compounds is relatively small compared to sodium / potassium compounds, and the concentration of the prepared lithium squarate solution is relatively low.

[0017] In the practice of the present invention, the concentration of the alkali metal squarate solution can be increased by the method of alternating feeding. Among them, the effect on increasing the concentration of the lithium squarate solution is the best. The specific steps are: (1.3) Alternately add squaric acid and alkali metal compounds. Taking adding squaric acid first and then adding alkali metal compounds as one feeding operation, the number of feeding operations is greater than or equal to 0. It is easy to understand that when the number of feeding times is 0, it means that step (1.3) does not need to be carried out. For example, when preparing potassium squarate or sodium squarate, since the solubility of potassium compounds and sodium compounds is relatively large, step (1.3) can be omitted. When preparing lithium squarate, step (1.3) needs to be carried out to further increase the concentration of the lithium squarate solution. That is, when preparing the lithium squarate solution, the number of feeding operations is greater than or equal to 1.

[0018] The principle of step (1.3) is that squaric acid is a dibasic acid and can form acid salts. The added squaric acid reacts with the alkali metal squarate to form an alkali metal bisquarate, and then reacts with the alkali metal compound to generate an alkali metal squarate. It can be seen that after step (1.3), the concentration of the alkali metal squarate solution increases, and the solute is still the alkali metal squarate. For the preparation of lithium squarate, step (1.3) breaks through the limitation that the low concentration of the lithium compound solution leads to the low concentration of the lithium squarate solution prepared in step (1.2). It is easy to understand that by multiple feeding operations, the concentration of the lithium squarate solution can be increased to near the saturation concentration.

[0019] In the practice of the present invention, in step (1.3), the added squaric acid reacts with the alkali metal squarate in the solution, so the squaric acid cannot be in excess. That is, in each feeding operation, the molar ratio of the added squaric acid to the alkali metal squarate in the solution is (0-1):1, and the added amount of squaric acid is greater than 0; in each feeding operation, the molar ratio of the added squaric acid to the alkali metal of the added alkali metal compound is 1:2, ensuring that after one feeding operation, the solute in the solution is still the alkali metal squarate, without other impurities such as squaric acid or alkali metal compounds.

[0020] Furthermore, as the number of feeding operations increases, the concentration of the alkali metal squarate increases, and the amount of added squaric acid can be increased accordingly. For the convenience of metering and accelerating the reaction between squaric acid and alkali metal squarate, the molar ratio of the added squaric acid to the alkali metal squarate in the solution of step (1.2) is (0-1):1, and the added amount of squaric acid is greater than 0.

[0021] In the practice of the present invention, the alkali metal compound added in step (1.3) can be the same as or different from the alkali metal compound in step (1.1). Preferably, the alkali metal compound added in step (1.3) is an alkali metal compound that can react with water, such as alkali metal oxides, alkali metal peroxides, alkali metal sulfides, etc., to accelerate the reaction between the alkali metal compound and the alkali metal bisquarate solution.

[0022] In addition, when the number of feeding operations in step (1.3) is greater than or equal to two, the alkali metal compounds added in each feeding operation can be the same or different. For the later feeding operations, the reaction efficiency of the added squaric acid and alkali metal compounds is low. Selecting raw materials such as alkali metal oxides, alkali metal peroxides, alkali metal sulfides, etc. can improve the efficiency.

[0023] It should be noted that the present invention places no restrictions on the reaction temperature and reaction pressure. The present invention needs to prepare an alkali metal squarate solution close to saturation. When increasing the temperature and pressure is beneficial to increasing the concentration of the alkali metal compound aqueous solution and the alkali metal squarate solution, higher temperature and pressure can be selected. That is, the changes in temperature and pressure are based on increasing the solution concentration.

[0024] In step (2) of the present invention, the conductive material dispersion is formed by dispersing a conductive carbon material in a surfactant solution. The specific preparation steps are as follows: (2.1) Prepare a surfactant solution; (2.2) Add the conductive carbon material to the surfactant solution and disperse it evenly. The role of the surfactant is to enable the conductive carbon material to be dispersed in the solution, and to prevent the conductive carbon material from aggregating into clusters during the mixing process of the conductive carbon material dispersion and the alkali metal squarate solution.

[0025] Preferably, the present invention uses a non-ionic surfactant. In step (4), the non-ionic surfactant volatilizes and does not remain in the composite material. More preferably, the non-ionic surfactant is one or more of polyvinylpyrrolidone, Tween-80, and alkyl glycoside.

[0026] Considering that the mixing of the conductive carbon material dispersion and the alkali metal squarate solution will cause a decrease in the surfactant concentration, in the practice of the present invention, the surfactant concentration in step (2.1) is greater than the critical micelle concentration.

[0027] In the present invention, the conductive carbon material is one or more conductive carbon elemental materials such as multi-layer graphite, graphite oxide, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, and C60. From the perspective of the preparation method and preparation cost, the conductive carbon material of the present invention is preferably graphene. The preparation method is to add expanded graphite to a non-ionic surfactant solution and treat it by a mechanical exfoliation method to obtain a graphene material dispersion.

[0028] In the present invention, the mass ratio of the alkali metal squarate to the conductive carbon material is (4-49):1.

[0029] In the second aspect of the present invention, the present invention provides an alkali metal squarate composite material, which includes an alkali metal squarate and a conductive carbon material, and the alkali metal squarate is attached to the surface of the conductive carbon material.

[0030] Preferably, the mass ratio of the alkali metal squarate to the conductive carbon material is (4-49):1.

[0031] Preferably, the alkali metal squarate is lithium squarate, sodium squarate, or potassium squarate.

[0032] Preferably, the conductive carbon material is one or more conductive carbon elemental materials such as multi-layer graphite, graphite oxide, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, and C60. More preferably, the conductive carbon material is graphene.

[0033] In the third aspect of the present invention, the present invention provides an application of an alkali metal squarate composite material. The prepared alkali metal composite material is added to the positive electrode of an alkali metal ion battery as a material for supplementing alkali metal ions.

[0034] Beneficial effects:

[0035] The present invention proposes a preparation method of alkali metal squarate. By using a reaction instead of dissolution, it avoids the problem that squaric acid has low solubility in water and is difficult to prepare a high-concentration aqueous solution of squaric acid for metathesis synthesis reaction, which is beneficial to increasing the concentration of the entire reaction system. Especially for the preparation of lithium squarate, starting from the lithium squarate solution formed by the reaction of a lithium compound solution and squaric acid, using a unique alternating feeding method, squaric acid and lithium compound are repeatedly added alternately on the basis of the lithium squarate solution, effectively increasing the concentration of the reaction product lithium squarate solution significantly.

[0036] The present invention also proposes a method for reducing the oxidation overpotential of alkali metal squarate. Mix the alkali metal squarate solution with a conductive carbon material dispersion and perform spray drying, so that the alkali metal squarate of nanometer size adheres to the surface of the conductive carbon material. The conductive network formed by the conductive carbon material can effectively conduct electrons to the active reaction center of the alkali metal squarate quickly, which is beneficial to the exertion of the capacity of the alkali metal squarate, and can avoid introducing transition metal ions by transition metal compound catalysts and reduce the risk of deterioration of the cycle life.

[0037] The composite material prepared by the present invention can be directly added by stirring and mixing with the positive electrode material, which does not require changing the production process for the existing positive electrode sheet production process and will not increase additional costs, which is beneficial to reducing the application cost of alkali metal squarate in alkali metal ion batteries. Specific embodiments

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific embodiments of the present invention will be described below. Obviously, the following description is only some embodiments of the present invention. For those of ordinary skill in the art, other embodiments can be obtained based on these embodiments without creative efforts.

[0039] In the industry, alkali metal squarates are currently rarely sold on the market. Generally, enterprises prepare alkali metal squarates by themselves for use. Taking lithium squarate as an example, the conventional preparation method of lithium squarate has high cost, low yield or the product quality is difficult to meet the requirements, so the use of lithium squarate as a lithium supplement material is restricted. In addition, after obtaining the alkali metal squarate, how to use it as a supplement for alkali metal ions at low cost is still a problem that troubles the industry.

[0040] The present invention provides an alkali metal squarate composite material and a preparation method thereof, which propose a new preparation idea for alkali metal squarates and also propose a preparation method for the composite material as a supplement, in order to solve the defects of existing alkali metal squarates as supplements for ion batteries, adapt to large-scale industrial production, and make the entire production process more green and energy-saving.

[0041] The preparation method of the present invention includes: (1) reacting an alkaline alkali metal compound with squaric acid to prepare an alkali metal squarate; (2) preparing a conductive carbon material dispersion; (3) mixing the alkali metal squarate obtained in step (1) with the conductive carbon material dispersion obtained in step (2) to obtain a mixed dispersion; (4) spray-drying the mixed dispersion obtained in step (3) to obtain an alkali metal squarate-conductive carbon composite material. The following is an explanation of each preparation step.

[0042] Step (1) of the present invention is the step of preparing an alkali metal squarate. In this step, squaric acid and an alkaline alkali metal compound are used as raw materials to react to prepare an alkali metal squarate. The preparation methods include liquid-liquid mixing reaction preparation, solid-solid mixing reaction preparation, and liquid-solid reaction preparation. The present invention preferably adopts the liquid-solid reaction preparation method, that is, an alkali metal compound solution reacts with squaric acid powder to prepare an alkali metal squarate. The specific steps are as follows: (1.1) Prepare an alkali metal compound solution; (1.2) Add squaric acid to react with the alkali metal compound solution to prepare an alkali metal squarate solution.

[0043] The reaction between squaric acid and the alkali metal compound solution is essentially an acid-base neutralization reaction. Therefore, the alkali metal compound solution should be alkaline. The raw materials for preparing the alkali metal compound solution can be one or more of alkali metal carbonates, alkali metal bicarbonates, alkali metal hydroxides, alkali metal acetates, alkali metal oxides, alkali metal peroxides, and alkali metal sulfides.

[0044] It is easy to understand that, in order to complete the reaction, the molar ratio of the squaric acid added in step (1.2) to the alkali metal of the alkali metal compound in step (1.1) is 1:2. The present invention uses the reaction instead of the dissolution method to avoid the trouble that squaric acid has low solubility in water and it is difficult to prepare a high-concentration squaric acid aqueous solution, and solves the limitation of squaric acid on the concentration of the alkali metal squarate solution.

[0045] In the practice of the present invention, maintaining a relatively high temperature in steps (1.1) and (1.2) can increase the solubility of the alkali metal squarate, which is beneficial to increasing the concentration of the alkali metal squarate solution and is beneficial to the subsequent preparation of the composite material. Considering green and energy-saving production, preferably, the temperature in step (1.1) is controlled to be less than or equal to 85°C, and more preferably, the temperature in step (1.1) is controlled at 30-85°C.

[0046] In the practice of the present invention, the concentration of the lithium squarate solution prepared from the lithium compound solution is relatively low, and the concentration of the lithium compound solution limits the increase in the concentration of the lithium squarate solution.

[0047] Based on steps (1.1) and (1.2), the present invention proposes step (1.3) to increase the concentration of the alkali metal squarate solution by means of alternating feeding. Specifically, squaric acid and an alkali metal compound are alternately added. One feeding operation is defined as first adding squaric acid and then adding the alkali metal compound, and the number of feeding operations is greater than or equal to 0.

[0048] Squaric acid is a dibasic acid and can form acid salts. In step (1.3), the squaric acid added first reacts with the alkali metal squarate in the solution to form an alkali metal hydrogen squarate. Squaric acid also enters the solution by reaction instead of dissolution. Taking lithium squarate as an example, the reaction equation is Li2C4O4 + H2C4O4 = 2LiHC4O4. It is easy to understand that the molar ratio of squaric acid to the alkali metal squarate in the solution is (0-1):1, and the addition amount of squaric acid is greater than 0. If squaric acid is in excess, the excess squaric acid cannot dissolve in the solution and agglomeration occurs.

[0049] In step (1.3), the alkali metal compound added later reacts with the alkali metal hydrogen squarate in the solution to form an alkali metal squarate. After step (1.3), the added squaric acid and alkali metal compound are also converted into an alkali metal squarate, and the solution concentration is increased, solving the limitation of the concentration of the alkali metal compound solution in step (1.1) on the concentration of the alkali metal squarate solution. It is easy to understand that the molar ratio of the alkali metal element of the alkali metal compound added later to the squaric acid added first is 2:1. Taking lithium hydroxide as an example, the reaction equation is LiHC4O4 + LiOH = Li2C4O4.

[0050] In the practice of the present invention, when adding squaric acid in step (1.3), the temperature can be appropriately increased, for example, the temperature is controlled above 85 °C to accelerate the reaction between squaric acid and the alkali metal squarate. Considering green and energy-saving production, preferably, the temperature is controlled at 85-100 °C in step (1.1), and more preferably, the temperature is controlled at 90-95 °C in step (1.1).

[0051] Step (1.3) can effectively increase the concentration of the lithium squarate solution and relieve the limitations of the solubility of squaric acid and the lithium compound and the concentration of the lithium squarate solution.

[0052] In step (1.3), in a single feeding operation, squaric acid can be added in multiple portions until the reaction is completed and it enters the solution, and then the alkali metal compound is added. The alkali metal compound can also be added in multiple portions until the complete reaction enters the solution, and then the next feeding operation is carried out.

[0053] In the practice of the present invention, adding the alkali metal compound first and then the squaric acid or adding the alkali metal compound and squaric acid after mixing them has poor effects, especially it is disadvantageous for the preparation of lithium squarate. Taking the feeding method of adding alkali first and then acid as an example, if the lithium compound is added first in step (1.3), the lithium compound can only enter the lithium squarate solution by dissolution. The solubility of the lithium compound in the solution is lower than the solubility of the alkali metal compound in pure water, and the viscosity of the solution is also higher than that of pure water. Step (1.3) is difficult to implement, and the added lithium compound is difficult to completely dissolve, and insoluble lumps appear in the solution. After adding squaric acid subsequently, the caking phenomenon deteriorates further and cannot be solved by stirring or heating up. Even if the complete dissolution of the lithium source in step (1.3) is achieved by reducing the amount of lithium compound added, as the number of feeding operations increases and the solution concentration increases, the amount of lithium compound added each time needs to be continuously reduced. Besides increasing the operation steps and consuming energy, it is not beneficial to increase the solution concentration.

[0054] It should be noted that stirring is maintained throughout steps (1.1) to (1.3). Specifically, the stirring in step (1.1) accelerates the dissolution of the alkali metal compound in water, and the stirring speed is controlled at 100 - 400 r / min. Preferably, the stirring speed is controlled at 200 - 300 r / min. The stirring speeds in steps (1.2) and (1.3) are controlled at 100 - 600 r / min. Preferably, the stirring speed is controlled at 300 - 500 r / min.

[0055] In the practice of the present invention, it is better to maintain the alkali metal squarate solution at a relatively high temperature, and the solubility of the alkali metal squarate is increased. Taking lithium squarate as an example, it is measured in the present invention that the solubility of lithium squarate is 22.0 g at 30 °C, 32.2 g at 50 °C, and 45.2 g at 70 °C. It can be seen that the solubility of lithium squarate increases with the increase of temperature.

[0056] If the high-concentration alkali metal squarate solution prepared in step (1) of the present invention is not subjected to subsequent production, the pure product of the alkali metal squarate can be prepared by cooling crystallization or evaporation crystallization of the alkali metal squarate solution. Preferably, in the practice of the present invention, the method of cooling crystallization is more environmentally friendly and energy-saving, reducing the generation of waste gas and waste water, and the pure product of the alkali metal squarate can be obtained through simple separation and drying. It is easy to understand that if subsequent steps are carried out, the high-concentration alkali metal squarate solution prepared in step (1) can be mixed with the subsequent conductive carbon material dispersion without crystallization and purification.

[0057] Step (2) of the present invention is to prepare a dispersion of conductive carbon material. The conductive carbon material is insoluble in water. In the present invention, a surfactant solution is prepared, and the conductive carbon material is added to the surfactant solution and dispersed evenly. The function of step (2) is to evenly disperse the conductive carbon material in water, facilitating the mixing in the subsequent step (3).

[0058] In step (2.1), a surfactant solution is prepared. Based on the spray drying method adopted in the subsequent step (4), in order not to introduce impurity ions, the surfactant of the present invention is preferably a non-ionic surfactant, which volatilizes in the form of gas during spray drying and does not remain in the composite material. More preferably, the surfactant is one or more of polyvinylpyrrolidone, Tween-80, and alkyl glycoside.

[0059] In step (2.2), the conductive carbon material is added to the surfactant solution and dispersed evenly for later use.

[0060] Since the dispersion of conductive carbon material needs to be mixed with the alkali metal oxalate solution, the concentration of the surfactant will be diluted. Therefore, in step (2.1), the concentration of the surfactant solution is increased in advance. Preferably, the concentration of the surfactant solution is greater than its critical micelle concentration.

[0061] Step (3) of the present invention is to evenly distribute the conductive carbon material in the alkali metal oxalate solution. After spray drying in step (4), a composite material with the conductive carbon material as the core is obtained, and the nano-sized alkali metal oxalate adheres to the surface of the conductive carbon material. The conductive network formed by the conductive carbon material can effectively conduct electrons quickly to the active reaction center of the alkali metal oxalate, which is beneficial to reducing the overpotential of the alkali metal oxalate.

[0062] In the present invention, the mass ratio of the alkali metal oxalate to the conductive carbon material is (4 - 49):1.

[0063] In the present invention, the conductive carbon material is one or more conductive carbon elemental materials such as multi-layer graphite, graphite oxide, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, and C60. From the perspective of the preparation method and preparation cost, the conductive carbon material of the present invention is preferably graphene. In step (2.2), expanded graphite is added to the surfactant solvent solution, and mechanical exfoliation methods such as ultrasonic, sand grinding, or high-pressure homogenization are used to exfoliate the expanded graphite to obtain a graphene dispersion solution.

[0064] It should be noted that step (2) can also be replaced by adding a nonionic surfactant to the alkali metal squarate solution prepared in step (1), and step (3) is then replaced by adding a conductive carbon material to the mixed solution of step (2) for dispersion. The purpose of steps (2) and (3) before and after the replacement is essentially the same, both of which are to subsequently uniformly disperse the conductive carbon material in the alkali metal squarate solution. However, mixing the surfactant with the alkali metal squarate solution first will have an adverse effect on the surfactant, and further affect the subsequent dispersion of the conductive carbon material. In the practice of the present invention, the dispersion of the conductive carbon material and the preparation of the alkali metal squarate are carried out separately, which can improve production efficiency and reduce the effect of the alkali metal squarate solution on the dissolution of the surfactant.

[0065] The composite material prepared by the present invention can be directly added to the positive electrode material to mix and prepare the positive electrode sheet, thereby assembling the alkali metal ion battery.

[0066] The technical solution of the present invention is described in detail below using a specific embodiment of the lithium squarate-conductive carbon composite material.

[0067] Example 1

[0068] (1) Using lithium hydroxide and squaric acid as raw materials, a lithium squarate solution is prepared in the following steps:

[0069] (1.1) Add 100 ml of deionized water to a reactor, raise the temperature to 60°C, stir at 200 r / min, and dissolve 20.000 g of lithium hydroxide monohydrate (approximately 0.476 mol) in 100 ml of deionized water in four portions to prepare a lithium hydroxide solution.

[0070] (1.2) Add 27.183 g of squaric acid (approximately 0.238 mol) into the reactor in four portions. Stir continuously to allow the squaric acid to react completely with lithium hydroxide. Keep the temperature below 85°C for each addition.

[0071] (1.3) Add 6.7958 g of squaric acid to the reactor, control the addition temperature to be above 90°C, increase the stirring speed to 400 r / min to allow it to react and dissolve quickly, add 5.000 g of lithium hydroxide monohydrate to the reactor, keep stirring, allow it to react and dissolve, and control the addition temperature to be below 85°C each time; repeat this step three times to obtain a lithium squarate solution;

[0072] (2) Prepare graphene dispersion, the specific steps are as follows:

[0073] (2.1) Prepare a 0.2 g / L aqueous solution of the nonionic surfactant polyvinylpyrrolidone;

[0074] (2.2) Add expanded graphite with 100 mesh (mass concentration is 5 g / L, that is, the mass ratio of expanded graphite to the volume of water), and disperse it for 20 min using a 3000 W 20 kHz ultrasonic device to obtain a graphene dispersion liquid.

[0075] (3) Mix the squarylium lithium solution in step (1) with the graphene dispersion liquid in step (2) to obtain a mixed dispersion liquid, where the mass ratio of squarylium lithium to graphene is 9:1.

[0076] (4) Spray-dry the mixed dispersion liquid in step (3) to obtain a squarylium lithium-graphene composite material.

[0077] (5) Disperse the composite material, lithium iron phosphate, conductive carbon black, and binder PVDF in N-methylpyrrolidone according to the ratio of 10%:75%:5%:10%, stir to obtain a uniform slurry, then coat it on the positive current collector aluminum foil, and obtain a positive electrode sheet containing squarylium lithium after cold pressing and slicing. Assemble a button battery with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0078] Example 2

[0079] Compared with Example 1, in this example, the ratio of graphene to squarylium lithium is adjusted, and step (1) is the same as that in Example 1.

[0080] (2) Prepare a graphene dispersion liquid, and the specific steps are as follows:

[0081] (2.1) Prepare an aqueous solution of non-ionic surfactant polyvinylpyrrolidone with a concentration of 0.2 g / L.

[0082] (2.2) Add expanded graphite with 100 mesh (mass concentration is 5 g / L), and disperse it for 20 min using a 3000 W 20 kHz ultrasonic device to obtain a graphene dispersion liquid. [[ID=@]]

[0083] (3) Mix the squarylium lithium solution in step (1) with the graphene dispersion liquid in step (2) to obtain a mixed dispersion liquid, where the mass ratio of squarylium lithium to graphene is 19:1.

[0084] (4) Spray-dry the mixed dispersion liquid in step (3) to obtain a squarylium lithium-graphene composite material.

[0085] (5) The composite material, lithium iron phosphate, conductive carbon black, and binder PVDF are dispersed in N-methylpyrrolidone in a ratio of 10%:75%:5%:10%. After stirring, a uniform slurry is obtained, which is then coated on the positive current collector aluminum foil. After cold pressing and cutting, a positive electrode sheet containing squarylium lithium is obtained. A button battery is assembled with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0086] Example 3

[0087] Compared with Example 1, in this example, the concentration of the graphene dispersion is adjusted, and step (1) is the same as that in Example 1.

[0088] (2) Prepare a graphene dispersion, and the specific steps are as follows:

[0089] (2.1) Prepare an aqueous solution of non-ionic surfactant polyvinylpyrrolidone at 0.5 g / L.

[0090] (2.2) Add expanded graphite with a mesh size of 100 (mass concentration of 10 g / L), and disperse it for 20 min using a 3000 W 20 kHz ultrasonic device to obtain a graphene dispersion.

[0091] (3) Mix the squarylium lithium solution in step (1) with the graphene dispersion in step (2) to obtain a mixed dispersion, where the mass ratio of squarylium lithium to graphene is 9:1.

[0092] (4) Spray-dry the mixed dispersion in step (3) to obtain a squarylium lithium-graphene composite material.

[0093] (5) The composite material, lithium iron phosphate, conductive carbon black, and binder PVDF are dispersed in N-methylpyrrolidone in a ratio of 10%:75%:5%:10%. After stirring, a uniform slurry is obtained, which is then coated on the positive current collector aluminum foil. After cold pressing and cutting, a positive electrode sheet containing squarylium lithium is obtained. A button battery is assembled with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0094] Example 4

[0095] Compared with Example 1, in this example, the type of surfactant is changed, and step (1) is the same as that in Example 1.

[0096] (2) Prepare a graphene dispersion, and the specific steps are as follows:

[0097] (2.1) Prepare an aqueous solution of 1 g / L non-ionic surfactant Tween 80;

[0098] (2.2) Add expanded graphite with a mesh size of 100 (mass concentration of 5 g / L), and disperse it for 20 min using a 3000 W 20 kHz ultrasonic device to obtain a graphene dispersion;

[0099] (3) Mix the squaric acid lithium solution in step (1) with the graphene dispersion in step (2) to obtain a mixed dispersion, where the mass ratio of squaric acid lithium to graphene is 9:1;

[0100] (4) Spray-dry the mixed dispersion in step (3) to obtain a squaric acid lithium-graphene composite material.

[0101] (5) Disperse the composite material, lithium iron phosphate, conductive carbon black, and binder PVDF in N-methylpyrrolidone in a ratio of 10%:75%:5%:10%, stir to obtain a uniform slurry, then coat it on the positive current collector aluminum foil, and obtain a positive electrode sheet containing squaric acid lithium through cold pressing and slicing. Assemble a button battery with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0102] Example 5

[0103] Compared with Example 4, in this example, lithium bicarbonate, lithium hydroxide, and squaric acid are used to prepare squaric acid lithium.

[0104] (1.1) Add 113 ml of deionized water to a pressure reactor, stir at a speed of 200 r / min, add 17.608 g of lithium carbonate, and introduce CO2 (gas pressure of 2 Mpa). The lithium carbonate dissolves to obtain a lithium bicarbonate solution, where the lithium bicarbonate is approximately 0.476 mol;

[0105] (1.2) Divide 27.183 g of squaric acid (approximately 0.238 mol) into 4 portions and add them to the reactor successively, and keep stirring until the reaction between squaric acid and lithium bicarbonate is complete;

[0106] (1.3) Add 6.7958 g of squaric acid to the reactor, control the feeding temperature to be higher than 90 °C, increase the stirring speed to 400 r / min, and make it react and dissolve quickly; add 5.000 g of lithium hydroxide to the reactor, keep stirring, and make it react and dissolve, controlling the feeding temperature each time to be lower than 85 °C; repeat the above steps 3 times;

[0107] (2) Prepare a graphene dispersion, and the specific steps are as follows:

[0108] (2.1) Prepare an aqueous solution of 1 g / L non-ionic surfactant Tween 80;

[0109] (2.2) Add expanded graphite with a mesh size of 100 (mass concentration of 5 g / L), and disperse it for 20 min using a 3000 W 20 kHz ultrasonic device to obtain a graphene dispersion;

[0110] (3) Mix the squarylium lithium solution in step (1) with the graphene dispersion in step (2) to obtain a mixed dispersion, where the mass ratio of squarylium lithium to graphene is 9:1;

[0111] (4) Spray-dry the mixed dispersion in step (3) to obtain a squarylium lithium-graphene composite material.

[0112] (5) Disperse the composite material, lithium iron phosphate, conductive carbon black, and binder PVDF in N-methylpyrrolidone in a ratio of 10%:75%:5%:10%, stir to obtain a uniform slurry, then coat it on the positive current collector aluminum foil, and obtain a positive electrode sheet containing squarylium lithium through cold pressing and slicing. Assemble a button battery with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0113] Example 6

[0114] Compared with Example 4, in this example, lithium oxide, lithium hydroxide, and squaric acid are used as raw materials to prepare squarylium lithium.

[0115] (1.1) Add 113 ml of deionized water to a reactor, heat it to 60 °C, stir at a speed of 200 r / min, and dissolve 7.121 g of lithium oxide in 113 ml of deionized water to obtain a lithium hydroxide solution, where lithium hydroxide is approximately 0.474 mol;

[0116] (1.2) Divide 27.183 g of squaric acid (approximately 0.238 mol) into 4 portions and add them to the reactor successively. Keep stirring until the reaction between squaric acid and lithium oxide is complete, and control the temperature of each feeding to be lower than 85 °C;

[0117] (1.3) Add 6.7958 g of squaric acid to the reactor, control the feeding temperature to be higher than 90 °C, increase the stirring speed to 400 r / min, and make it react and dissolve quickly; add 5.000 g of lithium hydroxide monohydrate to the reactor, keep stirring, and make it react and dissolve, controlling the temperature of each feeding to be lower than 85 °C; repeat the above steps 3 times;

[0118] (2) Prepare a graphene dispersion, and the specific steps are as follows:

[0119] (2.1) Prepare an aqueous solution of 1 g / L non-ionic surfactant Tween 80;

[0120] (2.2) Add expanded graphite with a mesh size of 100 (mass concentration of 5 g / L), and disperse it for 20 min using a 3000 W 20 kHz ultrasonic device to obtain a graphene dispersion;

[0121] (3) Mix the squaric acid lithium solution in step (1) with the graphene dispersion in step (2) to obtain a mixed dispersion, where the mass ratio of squaric acid lithium to graphene is 9:1;

[0122] (4) Spray-dry the mixed dispersion in step (3) to obtain a squaric acid lithium-graphene composite material.

[0123] (5) Disperse the composite material, lithium iron phosphate, conductive carbon black, and binder PVDF in N-methylpyrrolidone in a ratio of 10%:75%:5%:10%, stir to obtain a uniform slurry, then coat it on the positive current collector aluminum foil, and obtain a positive electrode sheet containing squaric acid lithium through cold pressing and cutting. Assemble a button battery with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0124] Example 7

[0125] Compared with Example 4, in this example, lithium carbonate and squaric acid are used as raw materials to prepare squaric acid lithium.

[0126] (1.1) Add 100 ml of deionized water to a reactor, heat it to 60 °C, stir at a speed of 200 r / min, and dissolve 20.000 g of lithium hydroxide monohydrate (about 0.476 mol) in 100 ml of deionized water in 4 portions successively to obtain a lithium hydroxide solution;

[0127] (1.2) Add 27.183 g of squaric acid (about 0.238 mol) to the reactor in 4 portions successively, keep stirring until the reaction between squaric acid and lithium hydroxide is complete, and control the temperature of each feeding below 85 °C;

[0128] (1.3) Add 10.8727 g of squaric acid (about 0.095 mol) to the reactor, control the feeding temperature above 90 °C, increase the stirring speed to 400 r / min, and make it react and dissolve quickly;

[0129] Add 8.000 g of lithium hydroxide monohydrate (about 0.190 mol) to the reactor, keep stirring, make it react and dissolve, and control the temperature of each feeding below 85 °C;

[0130] Add 8.1545 g of squaric acid (about 0.072 mol) to the reactor, control the feeding temperature above 90 °C, increase the stirring speed to 400 r / min, and make it react and dissolve quickly;

[0131] Add 6.000 g of lithium hydroxide monohydrate (about 0.142 mol) to the reactor, keep stirring, make it react and dissolve, and control the temperature of each feeding below 85 °C;

[0132] Add 5.4363 g of squaric acid (about 0.048 mol) to the reactor, control the feeding temperature above 90 °C, increase the stirring speed to 400 r / min, and make it react and dissolve quickly;

[0133] Add 4.000 g of lithium hydroxide monohydrate (about 0.095 mol) to the reactor, keep stirring, make it react and dissolve, and control the temperature of each feeding below 85 °C;

[0134] Add 2.7181 g of squaric acid (about 0.023 mol) to the reactor, control the feeding temperature above 90 °C, increase the stirring speed to 400 r / min, and make it react and dissolve quickly;

[0135] Add 2.000 g of lithium hydroxide monohydrate (about 0.047 mol) to the reactor, keep stirring, make it react and dissolve, and control the temperature of each feeding below 85 °C;

[0136] (2) Prepare the graphene dispersion liquid, and the specific steps are as follows:

[0137] (2.1) Prepare an aqueous solution of non-ionic surfactant Tween 80 with a concentration of 1 g / L.

[0138] (2.2) Add expanded graphite with a mesh size of 100 (mass concentration of 5 g / L), and disperse it for 20 min using a 3000 W 20 kHz ultrasonic device to obtain the graphene dispersion liquid.

[0139] (3) Mix the lithium squarate solution in step (1) with the graphene dispersion liquid in step (2) to obtain a mixed dispersion liquid, where the mass ratio of lithium squarate to graphene is 9:1.

[0140] (4) Spray-dry the mixed dispersion liquid in step (3) to obtain the lithium squarate-graphene composite material.

[0141] (5) The composite material, lithium iron phosphate, conductive carbon black, and binder PVDF are dispersed in N-methylpyrrolidone in a ratio of 10%:75%:5%:10%. After stirring, a uniform slurry is obtained, which is then coated on the positive current collector aluminum foil. After cold pressing and cutting, a positive electrode sheet containing lithium squarate is obtained. A button battery is assembled with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0142] Example 8

[0143] Compared with Example 1, in this example, the particle size of expanded graphite is adjusted, and step (1) is the same as that in Example 1.

[0144] (2) Prepare a graphene dispersion liquid, and the specific steps are as follows:

[0145] (2.1) Prepare an aqueous solution of non-ionic surfactant polyvinylpyrrolidone with a concentration of 0.2 g / L.

[0146] (2.2) Add expanded graphite with a mesh size of 50 (mass concentration of 5 g / L), and disperse it for 20 min using a 3000W 20kHz ultrasonic device to obtain a graphene dispersion liquid.

[0147] (3) Mix the lithium squarate solution in step (1) with the graphene dispersion liquid in step (2) to obtain a mixed dispersion liquid, where the mass ratio of lithium squarate to graphene is 9:1.

[0148] (4) Spray-dry the mixed dispersion liquid in step (3) to obtain a lithium squarate-graphene composite material.

[0149] (5) The composite material, lithium iron phosphate, conductive carbon black, and binder PVDF are dispersed in N-methylpyrrolidone in a ratio of 10%:75%:5%:10%. After stirring, a uniform slurry is obtained, which is then coated on the positive current collector aluminum foil. After cold pressing and cutting, a positive electrode sheet containing lithium squarate is obtained. A button battery is assembled with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0150] Example 9

[0151] Compared with Example 1, in this example, the type of carbon material is adjusted, and step (1) is the same as that in Example 1.

[0152] (2) Prepare a graphene dispersion liquid, and the specific steps are as follows:

[0153] (2.1) Prepare an aqueous solution of non-ionic surfactant polyvinylpyrrolidone at a concentration of 0.2 g / L;

[0154] (2.2) Add expanded graphite with a mesh size of 100 (mass concentration of 4 g / L) and carbon nanotubes (1 g / L), and disperse them using a 3000W 20kHz ultrasonic device for 20 min to obtain a "graphene + carbon nanotube" dispersion;

[0155] (3) Mix the squaric acid lithium solution in step (1) with the "graphene + carbon nanotube" dispersion in step (2) to obtain a mixed dispersion, where the mass ratio of squaric acid lithium to "graphene + carbon nanotube" is 9:1;

[0156] (4) Spray-dry the mixed dispersion in step (3) to obtain a squaric acid lithium - "graphene + carbon nanotube" composite material.

[0157] (5) Disperse the composite material, lithium iron phosphate, conductive carbon black, and binder PVDF in N-methylpyrrolidone in a ratio of 10%:75%:5%:10%, stir to obtain a homogeneous slurry, then coat it on the positive current collector aluminum foil, and obtain a positive electrode sheet containing squaric acid lithium through cold pressing and slicing. Assemble a button battery with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0158] Comparative Example 1

[0159] A button battery without squaric acid lithium in the prior art.

[0160] (1) Disperse lithium iron phosphate, conductive carbon black, and binder PVDF in N-methylpyrrolidone in a ratio of 85%:5%:10%, stir to obtain a homogeneous slurry, then coat it on the positive current collector aluminum foil, and obtain a positive electrode sheet without squaric acid lithium through cold pressing and slicing.

[0161] (2) Assemble a button battery with metallic lithium, a separator, and the positive electrode sheet. The button battery model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0162] Comparative Example 2

[0163] Preparation of a button battery with squaric acid lithium added in the prior art.

[0164] (1) Lithium squarate, lithium iron phosphate, conductive carbon black and binder PVDF are dispersed in N-methylpyrrolidone in a ratio of 9%:75%:6%:10%. After stirring, a uniform slurry is obtained, and then it is coated on the positive current collector aluminum foil. After cold pressing and slicing, a positive electrode sheet containing lithium squarate is obtained.

[0165] (2) Assemble a coin cell with metallic lithium, a separator and the positive electrode sheet. The coin cell model is CR2032, and the electrolyte is an electrolyte containing 1 mol / L lithium hexafluorophosphate with ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate = 1:1:1.

[0166] Comparative Example 3

[0167] In this comparative example, lithium hydroxide and squaric acid are used as raw materials to prepare lithium squarate. Among them, in the step of alternate feeding, the feeding order is to add lithium hydroxide first and then squaric acid.

[0168] (1.1) Add 100 ml of deionized water to the reactor, heat it to 60 °C, stir at a speed of 200 r / min, divide 20.000 g of lithium hydroxide monohydrate into 4 portions, and dissolve them in 100 ml of deionized water successively to obtain a lithium hydroxide solution.

[0169] (1.2) Divide 27.183 g of squaric acid into 4 portions and add them to the reactor successively. Keep stirring until the reaction between squaric acid and lithium hydroxide is complete, and control the temperature of each feeding to be lower than 85 °C.

[0170] (1.3) Add 5.000 g of lithium hydroxide monohydrate to the reactor, control the feeding temperature to be higher than 90 °C, increase the stirring speed to 400 r / min, and dissolve it.

[0171] Add 6.7958 g of squaric acid to the reactor, and control the temperature of each feeding to be lower than 85 °C.

[0172] Add 5.000 g of lithium hydroxide monohydrate to the reactor, control the feeding temperature to be higher than 90 °C, increase the stirring speed to 600 r / min, and it cannot be completely dissolved.

[0173] Continue to add 6.7958 g of squaric acid to the reactor, and the solution agglomerates in large amounts, and the preparation fails, and thus the composite material cannot be prepared.

[0174] Comparative Example 4

[0175] In this comparative example, lithium hydroxide and squaric acid are used as raw materials to prepare lithium squarate. Among them, in the step of alternate feeding, the feeding order is to add lithium hydroxide first and then squaric acid, and lithium hydroxide is in excess.

[0176] (1.1) Add 100 ml of deionized water to the reactor, heat it up to 60 °C, stir at a speed of 200 r / min, divide 20.000 g of lithium hydroxide monohydrate into 4 portions, and dissolve them successively in 100 ml of deionized water to prepare a lithium hydroxide solution;

[0177] (1.2) Divide 27.183 g of squaric acid into 4 portions and add them to the reactor successively. Keep stirring until the reaction between squaric acid and lithium hydroxide is complete, and control the temperature of each feeding to be lower than 85 °C;

[0178] (1.3) Add 6.7958 g of squaric acid to the reactor, control the feeding temperature at 90 °C, and dissolve it completely;

[0179] Add 10.0000 g of lithium hydroxide monohydrate (about 0.238 mol) to the reactor, control the feeding temperature to be lower than 85 °C, increase the stirring speed to 600 r / min, and it cannot be completely dissolved, with a large amount of caking.

[0180] (3.3) Add 6.7954 g of squaric acid (about 0.060 mol) to the reactor, control the feeding temperature at 90 °C, and it cannot be completely dissolved, the reaction fails, and thus the composite material cannot be prepared.

[0181] Comparative Example 5

[0182] In this comparative example, lithium hydroxide and squaric acid are used as raw materials to prepare lithium squarate. Among them, in the step of alternating feeding, the feeding order is to add squaric acid first and then lithium hydroxide, and the amount of lithium hydroxide is insufficient.

[0183] (1.1) Add 100 ml of deionized water to the reactor, heat it up to 60 °C, stir at a speed of 200 r / min, divide 20.000 g of lithium hydroxide monohydrate into 4 portions, and dissolve them successively in 100 ml of deionized water to prepare a lithium hydroxide solution;

[0184] (1.2) Divide 27.183 g of squaric acid into 4 portions and add them to the reactor successively. Keep stirring until the reaction between squaric acid and lithium hydroxide is complete, and control the temperature of each feeding to be lower than 85 °C;

[0185] (1.3) Divide 13.5908 g of squaric acid into 4 portions and add them to the reactor successively, control the feeding temperature at 90 °C, and dissolve it completely;

[0186] Add 5.0000 g of lithium hydroxide monohydrate to the reactor, control the feeding temperature to be lower than 85 °C, keep stirring, and dissolve it completely.

[0187] Add 6.7954 g of squaric acid to the reactor, control the feeding temperature at 90 °C, and it cannot be completely dissolved, and the reaction fails.

[0188] 5.0000 g of lithium hydroxide monohydrate was added to the reactor. The feeding temperature was controlled below 85 °C, and the stirring speed was increased to 600 r / min. It could not be completely dissolved, and a large amount of agglomeration occurred, resulting in the failure of the reaction and thus the inability to prepare the composite material.

[0189] The button cells assembled from the above Examples 1-10 and Comparative Examples 1-3 were tested, and the test process was as follows:

[0190] (1) The battery was left standing at room temperature for 10 h;

[0191] (2) Constant current charging at 0.1C to 4.4 V, and constant voltage charging at 4.4 V to 0.05C (Cycle 1 charging);

[0192] (3) Leave it standing for 10 min;

[0193] (4) Constant current discharging at 0.1C to 2.0 V (Cycle 1 discharging);

[0194] (5) Leave it standing for 10 min;

[0195] (6) Terminate.

[0196] The key performance parameters of the button cells prepared in each comparative example and example were counted as shown in Table 1:

[0197] Table 1 Key performance parameters of button cells

[0198]

[0199]

[0200] From the comparison of the test results of Examples 1-9 and Comparative Examples 1-2 of the present invention, it can be seen that the composite material significantly improves the lithium supplementation rate, indicating that the conductive carbon material has a significant catalytic effect on reducing the overpotential of alkali metal squarates. It should be noted that potassium ion batteries in the current industry are still under research and development. From the lithium supplementation data of the present invention, it can be inferred that the sodium / potassium squarate-conductive carbon composite material also has similar advantages.

[0201] From the comparison of Examples 1-9 and Comparative Examples 3-5, it can be seen that the preparation of alkali metal squarates is very crucial for the composite material. For the alternating feeding step of preparing lithium squarate, only by adding squaric acid first and then lithium compound can the concentration of the lithium squarate solution be increased, otherwise agglomeration will occur and the preparation will fail.

[0202] Within the data range of the invention content, Examples 1-9 of the present invention prepared graphene composite lithium squarate materials with different technical parameters, and the lithium supplementation rates were slightly different, but all had relatively ideal lithium supplementation rates.

[0203] The above has elaborated in detail on the embodiments provided by the present invention. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an alkali metal squarate composite material, characterized in that, It includes the following steps: (1) Prepare an alkali metal squarate by reacting an alkaline alkali metal compound with squaric acid; (2) Prepare a conductive carbon material dispersion; (3) Mix the alkali metal squarate obtained in step (1) with the conductive carbon material dispersion obtained in step (2) to obtain a mixed dispersion; (4) Spray-dry the mixed dispersion obtained in step (3) to obtain an alkali metal squarate-conductive carbon composite material; Among them, the alkali metal squarate solution obtained in step (1) has the following preparation steps: (1.1) Prepare an alkaline alkali metal compound solution; (1.2) Add squaric acid and react with the alkali metal compound solution to generate an alkali metal squarate solution. The molar ratio of the added squaric acid to the alkali metal is 1:2; (1.3) Alternately add squaric acid and the alkali metal compound. Taking adding squaric acid first and then adding the alkali metal compound as one feeding operation, the number of feeding operations is greater than 0. The molar ratio of the added squaric acid to the alkali metal squarate in the solution is (0-1):1, and the addition amount of squaric acid is greater than 0. The molar ratio of the added alkali metal element to the added squaric acid is 2:

1.

2. The preparation method according to claim 1, wherein The conductive carbon material dispersion in step (2) is formed by dispersing the conductive carbon material in a surfactant solution.

3. The preparation method according to claim 2, characterized in that, The surfactant solution is a non-ionic surfactant solution.

4. The preparation method according to claim 2, wherein The concentration of the surfactant solution exceeds the critical micelle concentration.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the alkali metal compound in step (1) to the conductive carbon material in step (2) is (4-49):

1.

6. The preparation method according to claim 1, characterized in that, The alkali metal compound is one or more of alkali metal carbonates, alkali metal bicarbonates, alkali metal hydroxides, alkali metal acetates, alkali metal oxides, alkali metal peroxides, and alkali metal sulfides.

7. The preparation method according to claim 1, characterized in that, The conductive carbon material is one or more conductive carbon elemental materials such as multi-layer graphite, graphite oxide, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, and C60.

8. An alkali metal oxalate composite material, characterized in that Prepared by the preparation method according to any one of claims 1-7, including an alkali metal squarate and a conductive carbon material, and the alkali metal squarate is attached to the surface of the conductive carbon material; The alkali metal squarate composite material is added to the positive electrode of an alkali metal ion battery as a material for supplementing alkali metal ions.

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