阅读说明：本技术 负极活性材料的制备方法 (Method for preparing negative active material ) 是由 唐子龙 张俊英 王诗童 赵黎江 张中太 于 2019-09-27 设计创作，主要内容包括：本发明提供一种负极活性材料的制备方法,包括：S1,提供提纯后的层状硅酸盐；以及S2,将所述提纯后的层状硅酸盐与锂源溶液或钠源溶液混合,所述锂源溶液或钠源溶液的pH值为8至14,进行水热反应或溶剂热反应,使所述层状硅酸盐锂化或钠化,得到所述负极活性材料。(The invention provides a preparation method of a negative electrode active material, which comprises the following steps: s1, providing a purified layered silicate; and S2, mixing the purified layered silicate with a lithium source solution or a sodium source solution, wherein the pH value of the lithium source solution or the sodium source solution is 8-14, and carrying out hydrothermal reaction or solvothermal reaction to lithiate or sodium the layered silicate to obtain the negative electrode active material.)

1. A method of preparing an anode active material, comprising:

s1, providing a purified layered silicate; and

s2, mixing the purified layered silicate with a lithium source solution or a sodium source solution, wherein the pH value of the lithium source solution or the sodium source solution is 8-14, and carrying out hydrothermal reaction or solvothermal reaction to lithiate or sodium the layered silicate to obtain the negative electrode active material.

2. The method for preparing an anode active material according to claim 1, wherein a concentration of lithium ions in the lithium source solution of step S2 is 0.1 to 10mol/L, and a concentration of sodium ions in the sodium source solution is 0.1 to 10 mol/L.

3. The method for producing the anode active material according to claim 1, wherein the hydrothermal reaction or the solvothermal reaction has a reaction temperature of 60 ℃ to 200 ℃ and a reaction pressure of 0.15MPa to 60 MPa.

4. The method for preparing an anode active material according to claim 1, wherein the lithium source in the lithium source solution of step S2 is at least one selected from the group consisting of lithium hydroxide, lithium nitrate, lithium sulfate, lithium carbonate, lithium phosphate, lithium chlorate, lithium fluoride, lithium chloride, lithium bromide, and lithium iodide.

5. The method for preparing the negative electrode active material according to claim 1, wherein the sodium source in the sodium source solution of step S2 is at least one selected from the group consisting of sodium hydroxide, sodium nitrate, sodium sulfate, sodium carbonate, sodium phosphate, sodium chlorate, sodium fluoride, sodium chloride, sodium bromide, and sodium iodide.

6. The method for producing an anode active material according to claim 1, characterized by further comprising:

s3, heating the lithiated or sodium-modified layered silicate obtained in the step S2, removing at least part of crystal water and/or structural water, and keeping the silicon-oxygen tetrahedral layer structure of the layered silicate.

7. The method for producing the negative electrode active material according to claim 6, wherein the layered silicate is montmorillonite, and the heating temperature in step S3 is 80 ℃ to 800 ℃.

8. The method for preparing an anode active material according to claim 7, wherein the layered silicate is palygorskite, and the temperature to be heated in step S3 is 150 ℃ to 600 ℃.

9. The method of preparing the negative active material of claim 1, wherein the mixture of the lithium source solution or the sodium source solution and the purified layered silicate is mechanically stirred or ultrasonically oscillated during the lithiation or sodium treatment of step S2.

10. The method of preparing an anode active material according to claim 1, further comprising a step of filtering, washing and drying after step S2 to separate a solid phase lithiation/sodium-treatment product from the lithium source solution or sodium source solution.

Technical Field

The invention relates to the technical field of batteries, in particular to a preparation method of a novel layered negative active material.

Background

Nowadays, people's demand for pure electric vehicles and consumer electronics is increasing day by day, and the new generation of electrochemical batteries represented by lithium ion batteries are more and more paid attention to their high energy density, high power density and long cycle life compared with the traditional nickel-cadmium batteries and nickel-hydrogen batteries. In a lithium ion battery, the negative active material is a substance that undergoes a reversible electrochemical reaction with lithium ions and provides reversible lithium deintercalation capacity.

The currently widely adopted negative electrode active material is a graphite material, the theoretical capacity of the graphite material is 372mAh/g, and the graphite material has the advantages of good cycle performance, small volume change in the lithium desorption and intercalation process and the like. However, carbon atoms on the surface of the carbon material have a large number of unsaturated bonds, and the Electrolyte can be decomposed on the surface of the carbon material during first charging to form an SEI (solid Electrolyte interface) film, so that the cycle efficiency of the battery during first discharging is low. The other applied negative active material is lithium titanate which has higher ionic conductivity, and an SEI film does not need to be formed in the first charge-discharge process of the lithium ion battery, so that the lithium ion battery has higher energy conversion efficiency. However, lithium titanate has poor electronic conductivity and a high discharge voltage plateau. Negative active materials still under investigation at present are also alloy negative materials such as silicon, copper, tin, etc., which provide reversible charge and discharge capacity by forming an alloy compound with lithium, wherein the theoretical specific capacity of silicon is as high as 4200mAh/g, but the alloy negative material has large volume expansion and contraction during repeated lithium deintercalation, and thus is separated from the conductive agent after many cycles and even peeled off from the surface of the current collector. In the prior art, porous silicon dioxide is prepared into porous silicon through magnesiothermic reduction, and the pore channel is used as buffer to inhibit volume change in the charging and discharging process, but the magnesiothermic reduction reaction is complex and the requirement of reducing the manufacturing cost of the battery is difficult to meet.

Disclosure of Invention

Accordingly, it is necessary to provide a method for preparing a novel anode active material.

A method of preparing an anode active material, comprising:

s1, providing a purified layered silicate; and

s2, mixing the purified layered silicate with a lithium source solution or a sodium source solution, wherein the pH value of the lithium source solution or the sodium source solution is 8-14, and carrying out hydrothermal reaction or solvothermal reaction to lithiate or sodium the layered silicate to obtain the negative electrode active material.

In one embodiment, the concentration of lithium ions in the lithium source solution of step S2 is 0.1mol/L to 10mol/L, and the concentration of sodium ions in the sodium source solution is 0.1mol/L to 10 mol/L.

In one embodiment, the hydrothermal reaction or the solvothermal reaction has a reaction temperature of 60 ℃ to 200 ℃ and a reaction pressure of 0.15MPa to 60 MPa.

In one embodiment, the lithium source in the lithium source solution of step S2 is at least one selected from the group consisting of lithium hydroxide, lithium nitrate, lithium sulfate, lithium carbonate, lithium phosphate, lithium chlorate, lithium fluoride, lithium chloride, lithium bromide, and lithium iodide.

In one embodiment, the sodium source in the sodium source solution of step S2 is at least one selected from the group consisting of sodium hydroxide, sodium nitrate, sodium sulfate, sodium carbonate, sodium phosphate, sodium chlorate, sodium fluoride, sodium chloride, sodium bromide, and sodium iodide.

In one embodiment, the method further comprises:

s3, heating the lithiated or sodium-modified layered silicate obtained in the step S2, removing at least part of crystal water and/or structural water, and keeping the silicon-oxygen tetrahedral layer structure of the layered silicate.

In one embodiment, the layered silicate is montmorillonite, and the heating temperature of step S3 is 80 ℃ to 800 ℃.

In one embodiment, the layered silicate is palygorskite and the heating temperature of step S3 is 150 ℃ to 600 ℃.

In one embodiment, the mixture of the lithium source solution or sodium source solution and the purified layered silicate is mechanically stirred or ultrasonically oscillated during the lithiation or sodium treatment of step S2.

In one embodiment, the lithium source solution or the sodium source solution is separated from the solid phase lithiation/sodium treatment product after step S2, and the lithium source solution or the sodium source solution is filtered, washed, and dried.

According to the preparation method provided by the invention, under the conditions of heating and pressurizing, lithium ions or sodium ions enter a layered structure of the layered silicate to replace metal ions of the original layered silicate, and a silica tetrahedral layer of the layered silicate is kept, so that a material with a layered silicate-like structure can be obtained, the material can be used as a negative electrode active material, is a silica system layered material with a novel lithium storage mechanism, and provides a large number of migration channels of lithium ions by utilizing gaps between the layered structures, so that the lithium ions can be reversibly inserted into and removed from the layered silicate-like structure, and the layered silicate-like structure has electrochemical capacity, and becomes a novel negative electrode active material. The lithium storage mechanism is also applicable to other electrochemical cells with alkali metal ions or alkaline earth metal ions. In addition, the raw materials used by the preparation method are phyllosilicate minerals, so that the cost is low, the preparation method is simple and cheap, the manufacturing cost of the negative active material can be reduced, and the preparation method has a large-scale industrial application prospect.

Drawings

FIG. 1 is a schematic representation of the crystal structure of a layered silicate;

FIG. 2 is a schematic structural view of a silicon oxygen tetrahedral layer of a layered silicate-like structure according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of an electrochemical cell according to an embodiment of the present invention;

FIG. 4 is an XRD pattern of a layered silicate like Li-H-Si-O-1 material of example 1 of the present invention;

FIG. 5 is a thermogravimetric plot of the Li-H-Si-O-1 precursor obtained in step S2 of example 1 from room temperature to 1300 ℃ in accordance with the present invention;

FIG. 6 is an XRD pattern of a layered silicate-like Na-H-Si-O-1 material of example 3 of the present invention;

FIG. 7 is a thermogravimetric plot of the Na-H-Si-O-1 precursor obtained in step S2 of example 3 of the present invention from room temperature to 1300 ℃;

FIG. 8 shows the 1.0mA cm half cell assembled by using the layered silicate-like material as the negative electrode active material in example 3 of the present invention^-2Current density of (2)A drawing;

FIG. 9 is an XRD spectrum of the Li-H-Si-O-2 material of comparative example 1 of the present invention;

FIG. 10 is an XRD spectrum of a Li-H-Si-O-3 material of comparative example 2 of the present invention;

FIG. 11 is an XRD pattern of a Na-H-Si-O-2 material of comparative example 3 of the present invention;

FIG. 12 shows a half cell assembled at 1.0mA · cm for a Na-H-Si-O-2 material of comparative example 3 of the present invention as a negative active material^-2A cyclic plot at current density of (a);

FIG. 13 shows the results of the present invention in comparative example 4, in which the half cell was assembled with the palygorskite mineral powder material as the negative electrode active material at 1.0mA cm^-2A cyclic plot at current density of (a);

FIG. 14 shows a half cell assembled at 1.0mA cm of the Na-H-Si-O-3 material of comparative example 5 of the present invention as a negative active material^-2A cyclic plot at current density of (a).

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The embodiment of the invention provides a preparation method of a negative electrode active material, which comprises the following steps:

s1, providing a purified layered silicate; and

s2, mixing the purified layered silicate with a lithium source solution or a sodium source solution, wherein the pH value of the lithium source solution or the sodium source solution is 8-14, and carrying out hydrothermal reaction or solvothermal reaction to lithiate or sodium the purified layered silicate to obtain the layered negative electrode active material.

The type of the layered silicate is not limited as long as it has a layered doped or undoped layered silicon-oxygen tetrahedral layer, and may be at least one of 1:1 type layered silicate, 2:1 type layered silicate, and other types of layered silicate, for example. The 1:1 type layered silicate may be selected from at least one of serpentine, kaolinite, and halloysite, for example. The 2:1 type layered silicate may be, for example, at least one selected from talc, pyrophyllite, muscovite, glauconite, phlogopite, biotite, lepidolite, vermiculite, montmorillonite and palygorskite. The silicate of the other structure may be selected from at least one of chrysoberyl, saponite and rectorite.

In step S1, the mineral raw material may be associated with other non-layered silicates, such as framework, chain or island silicates, and the layered silicate-containing mineral raw material is purified to obtain the layered silicate. The purification method is preferably a mechanical, physico-chemical, chemical or electrical method. Specifically, the purification method may be selected according to physical properties of different kinds of minerals in the raw material, such as particle size and shape, density, rolling and sliding friction angle, wettability, electromagnetic properties, solubility, and the like of the minerals. Before or after purification, the phyllosilicate can be crushed and ball-milled to form powder.

In step S2, the concentration of lithium ions in the lithium source solution is 0.1mol/L to 10 mol/L. The concentration of sodium ions in the sodium source solution is 0.1mol/L to 10 mol/L. More preferably, the concentration of lithium ions in the lithium source solution is 0.2mol/L to 2.0 mol/L. The concentration of sodium ions in the sodium source solution is 0.3mol/L to 4.0 mol/L. The lithium source solution or sodium source solution is obtained by dissolving a lithium source or a sodium source in a solvent, such as water. The lithium source may be selected from lithium hydroxide and/or a soluble lithium salt, such as at least one of lithium nitrate, lithium sulfate, lithium carbonate, lithium phosphate, lithium chlorate, lithium fluoride, lithium chloride, lithium bromide, and lithium iodide. The sodium source may be selected from sodium hydroxide and/or soluble sodium salts, such as at least one of sodium nitrate, sodium sulfate, sodium carbonate, sodium phosphate, sodium chlorate, sodium fluoride, sodium chloride, sodium bromide and sodium iodide. In one embodiment, when the lithium source or sodium source is a soluble lithium salt or a soluble sodium salt, the step of adding an alkaline substance to adjust the pH of the solution may be further included after dissolving the lithium source or sodium source in the solvent. The alkaline substance is preferably sodium hydroxide and/or potassium hydroxide. When the lithium source includes lithium hydroxide, or the sodium source includes sodium hydroxide, a lithium source solution or a sodium source solution having a suitable pH can be obtained without further addition of an alkaline substance.

Specifically, the solid-liquid mixture can be put into a sealed autoclave to react under the conditions that the temperature is 60 ℃ to 200 ℃ and the reaction pressure is 0.15MPa to 60 MPa. The reaction time is preferably from 0.5h to 72 h. In step S2, the main occurrence is the replacement reaction of the metal ions in the layered silicate, such as aluminum, magnesium, iron, etc., with the lithium ions in the lithium source solution or the sodium ions in the sodium source solution, so that the metal ions with weaker binding force in the layered silicate material, especially the metal ions in the interlayer domain of the layered silicate and the aluminum octahedron, can be replaced by the lithium ions or the sodium ions more thoroughly, thereby lithiating/sodifying the layered silicate, and a large amount of Li or Na prone to ionization exists in the lithiation/sodification product, thereby improving the lithium ion diffusion rate and conductivity of the negative electrode active material. The above reaction conditions may not be the same for different types of layered silicates in order to achieve the same degree of metal ion removal. For example, in one embodiment, the layered silicate is montmorillonite, the concentration of lithium ions in the lithium source solution or sodium ions in the sodium source solution of step S2 is 0.1mol/L to 8mol/L, the hydrothermal or solvothermal reaction temperature is 30 ℃ to 200 ℃, and the reaction pressure is 0.15 to 60 MPa. In another embodiment, the layered silicate is palygorskite, the concentration of lithium ions in the lithium source solution or sodium ions in the sodium source solution of step S2 is 0.1mol/L to 10mol/L, the hydrothermal or solvothermal reaction temperature is 30 to 180 ℃, and the reaction pressure is 0.15 to 50 MPa. In general, the higher the binding force of the metal ions and the silicate framework, the higher the concentration of the required lithium source solution/sodium source solution, the higher the reaction temperature and the higher the reaction pressure, but the concentration of the lithium source solution or sodium source solution should not be too high, the reaction time should not be too long, and the reaction temperature and the reaction pressure should not be too high, so as to avoid damaging the tetrahedral layer framework of the layered silicate. Because the silicon-oxygen tetrahedron has a more stable crystal structure relative to the octahedral layer, the first metal element M of the octahedral layer and the interlayer domain is enabled to pass through milder conditions₁Reduction of the first metal element M by ion exchange with Li or Na₁While maintaining the morphology of the doped or undoped silicon oxy tetrahedral layer substantially undamagedAnd (4) finishing.

Preferably, in step S2, the reaction is sufficiently performed by continuously mechanically stirring or ultrasonically vibrating the mixture of the lithium source solution or the sodium source solution and the purified layered silicate. The step S2 may be followed by further steps of filtering, washing and drying to separate the lithiation/sodium treatment product in the solid phase from the lithium source/sodium source solution in the liquid phase. The drying temperature may be relatively low, for example, may be less than 80 ℃, and is used to evaporate liquid water to effect a two-phase solid-liquid separation.

The layered silicate after lithiation/sodium treatment in step S2 contains a large amount of water in various forms, and if only the adsorbed water is removed, the method can be achieved by drying the electrode sheet at 80 to 120 ℃ during the preparation of the negative electrode. In a preferred embodiment, the method for preparing the negative active material may further include a step S3 of heating the lithiated/sodium-modified layered silicate obtained in the step S2 to remove at least part of the crystal water and/or the structural water and maintain the silicon-oxygen tetrahedral layer structure of the layered silicate. In step S3, it is still necessary to control the heating temperature not to be too high in order to maintain the silicon-oxygen tetrahedral layer structure of the layered silicate, and only to remove water having weak bonding with the layered skeleton, such as all adsorbed water, partially crystallized water and partially structured water, by heating the lithiation/sodium-treatment product. The heating may be carried out in air, vacuum or a protective gas, such as an inert gas or a reducing gas. The heating temperature is greater than or equal to 80 ℃ and less than 800 ℃, the heating rate is 2 ℃/min to 10 ℃/min, and the heating time is 0.5 hour to 12 hours. It is understood that 800 c is the temperature at which the silicon-oxygen tetrahedral lamellar structure is completely destroyed, and therefore 80 c to 800 c is a broader temperature range, but for different types of layered silicates, where there is a certain difference in the amount of binding force of the crystalline water and the structural water to the lamellar framework, and therefore to maintain the tetrahedral layer framework structure of the layered silicate, different heating temperature ranges can be used for different layered silicates, and can be specifically determined by the thermogravimetric curve of a specific type of layered silicate, i.e. for a specific layered silicate, the upper limit of the heating temperature is the temperature at which the tetrahedral lamellar structure is not destroyed. In one embodiment, the layered silicate is montmorillonite, and the heating temperature of step S4 is 80 ℃ to 800 ℃. In another embodiment, the layered silicate is palygorskite, and the temperature of the heating of step S4 is 150 ℃ to 600 ℃; preferably, all the adsorbed water and part of the crystal water are removed, and the heating temperature is 150-200 ℃; in another embodiment, all adsorbed water, part of the crystal water, and part of the structural water are removed, and the temperature of the heating is 200 to 600 ℃. It will be appreciated that after some phyllosilicate minerals have adsorbed water removed, the crystalline water and/or structural water in the material will not be removed into the electrolyte during the electrochemical reaction, and side reactions that reduce the electrochemistry will occur, and such materials can be dispensed with step S3.

According to the embodiment of the invention, the layered silicate is treated by the lithium source solution or the sodium source solution, so that the layered silicate is lithiated or sodium-modified, and the migration capability of lithium ions between tetrahedral layers is improved. Furthermore, the octahedral layer is at least partially dissolved in the hydrothermal reaction process, so that a large number of nano pore channel structures are formed, the specific surface area of the material is favorably improved, the control on the subsequent heating temperature is combined, the water with weak binding force is removed, and a part of the crystallized water and the structural water with strong binding force are reserved, so that the surface diversity of the material is improved, more binding sites are provided for lithium ions, and the lithium storage capacity of the material is improved.

The embodiment of the invention provides a negative electrode active material which has a layered silicate-like structure, comprises Li/Na, H, Si and O, and does not comprise other metal elements; or the layered silicate-like structure comprises Li/Na, H, Si, O and other metal elements, and the molar ratio of the other metal elements to Si is less than or equal to 0.4. The layered silicate-like structure comprises a plurality of doped or undoped silicon oxygen tetrahedral layers stacked on top of each other.

Referring to fig. 1, illite is taken as an example, and the layered silicate has a laminated tetrahedral layer and an octahedral layer as basic structural units. Four equivalent sp of Si³The hybrid orbitals are bonded with one O to form a silicon-oxygen tetrahedron, Si occupies the center of the tetrahedron, and O occupies the four corners of the tetrahedron. O with three vertex angles is shared among silicon-oxygen tetrahedrons, and the silicon-oxygen tetrahedrons extend in two-dimensional directions to form the silicon-oxygen tetrahedron layer. Part of Si in the silicon-oxygen tetrahedral layer can be replaced by metal elements such as Al, Mg or Fe and the like to form a doped silicon-oxygen tetrahedral layer. And O at the fourth vertex angle in the silicon-oxygen tetrahedral layer is connected with the metal element of the octahedral layer to form a metal-oxygen octahedral structure, the metal element is positioned in the center of the octahedron, and O or OH is positioned at the vertex angle of the octahedron. O sharing a vertex angle between the octahedrons, wherein when 2/3 of the octahedron gap is filled with a metal element, the O is shared by two metal elements to form a dioctahedral octahedron layer; when the octahedral voids are completely filled with the metal elements, O is shared by the three metal elements to form a trioctahedral octahedral layer. An octahedral layer is sandwiched between two tetrahedral layers, and interlayer connection is formed by O sharing the vertex angle of the tetrahedron, so that a TOT type (namely 2:1 type) laminated structure is formed. When a tetrahedral layer is laminated with an octahedral layer and interlayer connection is formed by O sharing corners of the tetrahedron, a TO type (i.e., 1:1 type) layered structure is formed. Metallic elements may also be present in ionic form between these layered structures (i.e., interlayer domains).

Referring to fig. 2, in the embodiment of the present invention, the silicon-oxygen tetrahedral layer of the layered silicate is used as a basic structural unit, the content of other metal elements in the original layered silicate is reduced through hydrothermal or solvothermal reaction, even metal ions in the interlayer domain or octahedral layer are completely removed, and lithium ions or sodium ions are introduced between the silicon-oxygen tetrahedral layers, so as to obtain a layered silicate-like structure. The layered silicate structure is used as a negative active material of an electrochemical battery, such as a negative active material of a lithium ion battery, and a brand new lithium storage mechanism is provided. Conventional silicon negative electrodes provide lithium storage capacity in such a manner as to form an alloy with lithium, or silicon oxide negative electrodes provide lithium storage capacity by forming various substances such as Si, LiO, and Si — Li alloy through reaction with lithium. The layered silicate-like structure of the present application accommodates lithium ions by utilizing a gap between the mutually laminated doped or undoped silicon-oxygen tetrahedral layers, which is larger than the gapCan be used for absorbing and releasing lithium ions in the reversible electrochemical reaction process to form reversible electrochemical capacity. Besides lithium ions, alkali metal or alkaline earth metal ions such as sodium ions and magnesium ions can also be used as active elements to reversibly deintercalate between layers of the layered silicate structure, so that reversible electrochemical capacity is obtained. The doped or undoped silicon oxygen tetrahedral layers stacked on each other can be connected by van der waals force. By introducing lithium ions or sodium ions between the silicon-oxygen tetrahedral layers, the diffusion rate of lithium ions of the negative electrode active material can be increased. In addition, compared with a material which is not lithiated or subjected to sodium treatment, lithium ions or sodium ions in the negative active material of the embodiment of the invention may also participate in an SEI film forming reaction in the charging and discharging processes, so that the coulombic efficiency of the electrode material is improved.

The content of Li/Na in the layered silicate-like structure is not limited, and can be the upper limit which can be reached by exchanging with hydrogen ions, and in a preferred embodiment, the molar ratio x of Li/Na to Si in the layered silicate-like structure is 1:4 ≦ x ≦ 3: 1; in one embodiment, the molar ratio x is 1: 1. ltoreq. x.ltoreq.3: 2.

For metal elements other than lithium, the metal elements located in octahedron and in interlaminar domains are both defined as the first metal element M₁The metal element substituting for Si in a tetrahedron is defined as a second metal element M₂。

Preferably, the first metal element M is greatly reduced₁I.e., the content of metal elements other than lithium or sodium in the interlayer domain and octahedral layer of the layered silicate is reduced. In one embodiment, M₁The mol ratio of the Si to the Si is less than or equal to 0.25. In a more preferred embodiment, M₁The mole ratio of the first metal element M to Si is less than or equal to 0.025₁Only in the form of impurities. In some embodiments, the first metal element M of the interlayer domain and octahedral layer₁Is completely removed. When being a negative electrode active material obtained by lithiation, the first metal element M₁May be selected from one or more of Al, Mg, Fe, Ca, Zn, K and Na. When it is sodium modifiedIn the case of the obtained negative electrode active material, the first metal element M₁May be selected from one or more of Al, Mg, Fe, Ca, Zn, K and Li.

Due to the great reduction or complete removal of the first metal element M₁In some embodiments, lithium ions or sodium ions can be combined with organic matters and then inserted into silicon-oxygen tetrahedral layers to form a composite structure in which lithium/sodium-containing organic layers and silicon-oxygen tetrahedral layers are alternately stacked, so that the negative active material has higher coulombic efficiency. It is understood that with the first metal element M₁The octahedral layers are also substantially partially or completely removed from the layer-like silicate structure, i.e. the layer-like silicate structure may contain no octahedral layers or only a small amount of octahedral layers locally, compared to the layer silicate. O at the apex angle originally used to form the octahedron may be either H or H₃O⁺Combining to form structural water or crystal water.

The tetrahedral layer of some phyllosilicates is a doped silicon-oxygen tetrahedral layer, in which a metal element partially substituting silicon is present, i.e. the second metal element M₂. The other metal element may include a second metal element M located in the silicon oxygen tetrahedral layer in place of a portion of Si located at the center of a tetrahedron₂A second metal element M₂The binding force with oxygen is strong in the tetrahedral structure and serves to maintain the morphology of the tetrahedral layered structure, so that the second metal element M is made to react by controlling the temperature and pressure of the hydrothermal or solvothermal reaction₂The content of (c) is not reduced by too much. When the second metal element M in the original layered silicate₂Y represents a second metal element M at a molar ratio of 1:3 to Si₂The molar ratio of the Si to the Si is more than or equal to 0.2:3 and less than or equal to 1:3 in one embodiment; in a more preferred embodiment, 0.4: 3. ltoreq. y.ltoreq.0.6: 3. The second metal element M₂May be selected from at least one of Fe, Mg and Al.

Not shown in FIG. 2 are water and lithium/sodium ions, H and part of O in the layered silicate-like structure being present in the form of structured water and/or crystal waterWith H⁺、OH^-And/or H₃O⁺In the form of H₂The O form exists. Water is detrimental in electrochemical cells, especially those using fluorine-containing electrolytes, such as LiPF₆The decomposition to generate HF when meeting water, the capacity of the positive active material is reduced under the acid environment and even the safety problem is generated, however, the inventor finds that by controlling the reaction temperature of the step S2 and the heating temperature of the step S3, a certain content of the crystal water and/or the structure water is reserved, so that the silicon-oxygen tetrahedral laminated structure is maintained not to collapse while removing the metal ions in the octahedral and interlayer regions, the diversity of the crystal structure of the material and the ion migration capability of the material are improved, and the part of the crystal water and the structure water does not have adverse effect on the cycle performance of the battery. Of course, the original phyllosilicate minerals contain a large amount of weakly bound water, such as adsorbed water and partially crystallized water, which is removed by heating to protect the long cycle life of the battery. It is understood that the temperature for removing the adsorbed water and part of the crystal water may be lower, for example, 80 ℃ to 120 ℃, and the part of the water may also be removed by drying when the electrode plate is prepared.

More preferably, it is represented by H₂The water present in the form of O is only crystal water, i.e. the adsorbed water originally present in the phyllosilicate is completely removed. Further, by controlling the heating temperature, the ratio of the crystal water and/or the structure water can be controlled to be small, and in one embodiment, the mole ratio of the crystal water to Si in the layered silicate-like structure is less than or equal to 0.5, and more preferably less than or equal to 0.1. It will be appreciated that the crystal water originally present in the layered silicate can also be completely removed as long as the tetrahedral layered structure is maintained without being destroyed.

H in the layered silicate-like structure is preferably present mainly as structural water, since structural water is a more strongly binding water, which contributes more to the maintenance of the silicon-oxygen tetrahedral layered structure than crystal water. Preferably, the molar ratio of said structural water to Si of the phyllosilicate-like structure is from 0.01 to 1, more preferably the molar ratio of said structural water to Si is from 0.5 to 1.

In addition, during the heating process, the local area of the material may lose metal ions and/or water to form defects and vacancies, and the vacancies can enable the layered silicate-like structure to have more sites capable of being combined with metal ions such as lithium ions, and further improve the ion storage capacity of the material.

The phyllosilicate-like material as the negative electrode active material is powder, and the average particle size is preferably 0.5 to 10 micrometers.

The embodiment of the invention also provides an electrochemical cell cathode material which comprises the cathode active material, a conductive agent and a binder.

Preferably, the negative electrode active material accounts for 50% or more of the total mass, and more preferably accounts for 80 to 95% of the total mass. The conductive agent may be at least one selected from activated carbon, graphene, carbon nanotubes, ketjen black, Super P, acetylene black, and graphite. The binder may be selected from at least one of polyvinylidene fluoride (PVDF), Styrene Butadiene Rubber (SBR), butadiene rubber, polyethylene oxide (PEO), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), lauric acid acrylate (LA), Polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), epoxy resin, polyacrylic acid (PAA), and sodium carboxymethyl cellulose (CMC). The conductive agent and the binder are uniformly mixed with the negative electrode active material. The mass ratio of the conductive agent to the binder is preferably 1: 9-9: 1.

In an embodiment, the negative electrode material may further include a thickener. The thickener is preferably at least one of sodium carboxymethylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, diutan, chitosan and a cross-linked polysaccharide structure polymer, polyvinyl alcohol and polyacrylic acid, and accounts for 0-5% of the total mass of the negative electrode material.

Referring to fig. 3, an electrochemical cell according to an embodiment of the present invention includes a positive electrode 10, a negative electrode 20, and an electrolyte 30, where the negative electrode 20 includes the negative electrode material of the electrochemical cell. In an embodiment, the negative electrode 20 may further include a negative electrode current collector, the negative electrode material and a volatile organic solvent are prepared into a slurry, the slurry is coated on the surface of the negative electrode current collector, and the negative electrode 20 is obtained after drying in vacuum, protective gas or inert gas.

The organic solvent is selected from solvents that are incapable of dissolving the negative electrode active material, do not react with the negative electrode active material, and can be completely removed at a relatively low temperature (e.g., 30 to 150 ℃), such as low-molecular-weight volatile organic solvents, and may be one or more selected from N-methylpyrrolidone (NMP), methanol, ethanol, ethylene glycol, propanol, isopropanol, acetonitrile, acetone, diethyl ether, N Dimethylformamide (DMF), N dimethylacetamide (DMAc), and Tetrahydrofuran (THF). The temperature of the drying step is lower than the heating temperature of step S2 in the anode active material preparation method.

The positive electrode 10 may include a positive electrode material and a positive electrode current collector, the positive electrode material and a volatile organic solvent are prepared into slurry, the slurry is coated on the surface of the positive electrode current collector, and the positive electrode 10 is obtained after drying in vacuum, protective gas or inert gas. Preferably, the electrochemical cell is a lithium ion cell, a sodium ion cell or a magnesium ion cell. The positive electrode material comprises a positive electrode active material, a conductive agent and a binder.

Preferably, the electrochemical cell is a lithium ion cell, and the positive electrode active material and the electrolyte both contain lithium ions. The positive electrode active material may be at least one of lithium transition metal oxides such as layered-structured lithium transition metal oxides, spinel-structured lithium transition metal oxides, and olivine-structured lithium transition metal oxides, for example, olivine-type lithium iron phosphate, layered-structured lithium cobaltate, layered-structured lithium manganate, spinel-type lithium manganate, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide.

In another preferred embodiment, the electrochemical cell is a sodium ion cell, and the positive active material and the electrolyte both contain sodium ions. The positive active material may be a layered transition metal oxide of sodium (e.g., Na)_xCoO₂) Tunnel structure oxides (e.g. Na)_0.44MnO₂) And polyanionic compound (Na)₃V₂(PO₄)₃) At least one of (1).

The conductive agent and the binder in the positive electrode material and the negative electrode material may be the same or different, respectively.

The positive electrode current collector and the negative electrode current collector are used for respectively loading the positive electrode material and the negative electrode material and conducting current, and can be foil or net-shaped. The material of the positive electrode current collector may be selected from aluminum, titanium, stainless steel, carbon cloth, or carbon paper. The material of the negative electrode current collector may be selected from copper, nickel, stainless steel, carbon cloth, or carbon paper.

In an embodiment, the electrochemical cell may further include a separator 40 disposed between the positive electrode 10 and the negative electrode 20, and the electrolyte 30 is an electrolyte solution, and infiltrates the separator 40, the positive electrode 10, and the negative electrode 20. In another embodiment, the electrolyte 30 of the electrochemical cell is a solid electrolyte membrane or a gel electrolyte membrane, instead of a separator, disposed between the cathode 10 and the anode 20.

The separator may be a conventional lithium battery separator capable of blocking electrons and passing metal ions, such as lithium ions. The separator may be any one of an organic polymer separator and an inorganic separator, and may be selected from, for example, but not limited to, any one of a polyethylene porous membrane, a polypropylene porous membrane, a polyethylene-polypropylene double-layer porous membrane, a polypropylene-polyethylene-polypropylene triple-layer porous membrane, a glass fiber porous membrane, a nonwoven fabric porous membrane, an electrospun porous membrane, a PVDF-HFP porous membrane, and a polyacrylonitrile porous membrane. Examples of the nonwoven fabric separator include polyimide nanofiber nonwoven fabrics, polyethylene terephthalate (PET) nanofiber nonwoven fabrics, cellulose nanofiber nonwoven fabrics, aramid nanofiber nonwoven fabrics, nylon nanofiber nonwoven fabrics, and polyvinylidene fluoride (PVDF) nanofiber nonwoven fabrics. Examples of the electrospun porous membrane include a polyimide electrospun membrane, a polyethylene terephthalate electrospun membrane, and a polyvinylidene fluoride electrospun membrane.

The electrolyte 30 is a non-aqueous electrolyte, and includes a solvent and an electrolyte dissolved in the solvent, and the solvent may be selected from one or more of cyclic carbonate, chain carbonate, cyclic ether, chain ether, nitrile and amide, such as ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, diethyl ether, acetonitrile, propionitrile, anisole, butyrate, glutaronitrile, adiponitrile, γ -butyrolactone, γ -valerolactone, tetrahydrofuran, 1, 2-dimethoxyethane and one or more of acetonitrile and dimethylformamide.

When the electrochemical cell is a lithium ion cell, the electrolyte is a lithium salt, which may be selected from, but not limited to, lithium chloride (LiCl), lithium hexafluorophosphate (LiPF)₆) Lithium tetrafluoroborate (LiBF)₄) Lithium methanesulfonate (LiCH)₃SO₃) Lithium trifluoromethanesulfonate (LiCF)₃SO₃) Lithium hexafluoroarsenate (LiAsF)₆) Lithium perchlorate (LiClO)₄) And lithium bis (oxalato) borate (LiBOB).

When the electrochemical cell is a sodium ion cell, the electrolyte is a sodium salt selected from sodium hexafluorophosphate (NaPF)₆) Sodium perchlorate (NaClO)₄) Sodium bistrifluoromethylsulfonimide (NaTFSI), preferably sodium perchlorate (NaClO)₄)。

The electrochemical cell further includes a sealed housing 50, and the positive electrode 10, the negative electrode 20, the separator 30, and the electrolyte 40 are disposed in the sealed housing 50.

Example 1

S1, the natural palygorskite mineral is purified by natural drying, crushing, air flow drying, grinding and air separation grading to obtain high-grade palygorskite mineral powder.

S2, stirring the palygorskite powder in lithium hydroxide aqueous solution with the concentration of 1.5mol/L, then transferring the palygorskite powder into a reaction kettle with a polytetrafluoroethylene inner container, placing the palygorskite powder into a blast drying box with the temperature of 120 ℃, wherein the internal pressure of the reaction kettle is 0.7MPa, the reaction time is 5 hours, filtering a solid phase, washing the solid phase with deionized water for 2 to 3 times, and drying the solid phase in vacuum at normal temperature to obtain a powder labeled as a Li-H-Si-O-1 precursor.

S3, carrying out heat treatment on the dried solid-phase product at 200 ℃ for 2 hours in vacuum (the heating rate is 5 ℃/min), and obtaining the negative active material powder (marked as Li-H-Si-O-1 material) with the layered silicate-like structure.

Referring to fig. 4, the obtained negative electrode active material powder was subjected to XRD measurement, and it was judged from the peak around 10 ° that the negative electrode active material had a layered crystal structure. The molar ratio of the metal elements other than Li, H, Si and O to Si in the material was 0.09 by ICP elemental analysis. Referring to fig. 5, the mass content of structural water in the material was 6.5% by thermogravimetric analysis.

Example 2

S1, the natural montmorillonite mineral is purified through natural drying, crushing, air flow drying, grinding, air separation and classification to obtain high-grade montmorillonite mineral powder.

S2, stirring the montmorillonite powder in a lithium hydroxide aqueous solution with the concentration of 1mol/L, then transferring the mixture into a reaction kettle with a polytetrafluoroethylene inner container, placing the reaction kettle in a forced air drying oven with the temperature of 180 ℃, wherein the internal pressure of the reaction kettle is 1.5MPa, the reaction time is 12 hours, filtering the solid phase, washing the solid phase with deionized water for 2 to 3 times, and drying the solid phase in vacuum at normal temperature.

S3, carrying out heat treatment on the dried solid-phase product at 600 ℃ for 10 hours in vacuum (the heating rate is 10 ℃/min), and obtaining the negative active material powder with the layered silicate-like structure.

Example 3

S1, the natural palygorskite mineral is purified by natural drying, crushing, air flow drying, grinding and air separation grading to obtain high-grade palygorskite mineral powder.

S2, stirring the palygorskite powder in a sodium hydroxide aqueous solution with the concentration of 0.8mol/L, then transferring the palygorskite powder into a reaction kettle with a polytetrafluoroethylene inner container, placing the palygorskite powder into a blast drying box with the temperature of 120 ℃, wherein the internal pressure of the reaction kettle is 0.3MPa, the reaction time is 2 hours, filtering a solid phase, washing the solid phase with deionized water for 2 to 3 times, and drying the solid phase in vacuum at normal temperature to obtain a powder labeled Na-H-Si-O-1 precursor.

S3, carrying out heat treatment on the dried solid-phase product at 300 ℃ for 3 hours in vacuum (the heating rate is 2 ℃/min), and obtaining the negative active material powder (marked as Na-H-Si-O-1 material) with the layered silicate-like structure.

The product was analyzed by the same method as in example 1 to determine that the material had a layered crystal structure (see fig. 6) and the molar ratio of the metal elements other than Na, H, Si, O to Si was 0.04, and the mass content of structural water in the material was 5.7% by thermogravimetric analysis (see fig. 7).

The Na-H-Si-O-1 material of example 3 as a negative electrode active material, conductive graphite and polyvinylidene fluoride as a binder were sequentially added into 10mL of N-methylpyrrolidone (NMP) solvent in a mass ratio of 8:1:1, stirred for 4 hours, coated on a copper foil, and vacuum-dried at 120 ℃ for 10 hours to obtain a negative electrode.

The prepared negative electrode is assembled into a lithium ion battery, a metal lithium sheet is taken as a counter electrode, a Celgard 2400 polypropylene microporous membrane is taken as a diaphragm, and 1mol/L LiPF₆The mixed solution of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) (wherein the volume ratio of EC to DMC is 1:1) is used as electrolyte, and 2032 type button lithium ion batteries are respectively assembled in glove boxes in high-purity argon atmosphere with water and oxygen content lower than 1 ppm.

And testing the electrochemical cycle characteristics of the button cell by adopting a LAND cell testing system within the voltage range of 0.01V-1.50V. Referring to FIG. 8, the cell was operated at 1.0mA cm^-2The charge and discharge cycles were carried out under a constant current at a current density of (1.0 mA · cm)^-2Before the current density of (2) was cycled, the cell was at 0.1mA cm^-2Constant current charge-discharge cycle of 5 times at current density). It can be seen that the battery exhibited excellent high rate cycling performance after the 10 th cycle, with coulombic efficiency of almost 100%. This shows that the layered structure and the pore channel structure in the Na-H-Si-O-1 structure can provide a large number of migration channels for metal ions, thereby improving the diversity of the crystal structure of the material and the ion migration capability of the material, and the part of the crystallized water and the structural water do not have adverse effects on the cycle performance of the battery.

Comparative example 1

The same natural palygorskite mineral as in example 1 was used, and the preparation method of the negative active material was the same as in example 1 except that the concentration of the lithium hydroxide solution in S2 was 12mol/L, to obtain a product designated as Li-H-Si-O-2 material.

Referring to fig. 9, the XRD analysis shows that the layered structure of the material disappears after the material is treated with the high-concentration lithium hydroxide solution, which indicates that the concentration of 12mol/L lithium hydroxide is too high for the palygorskite-like mineral to maintain its layered structure.

Comparative example 2

The same natural palygorskite mineral as in example 1 was used, and the preparation method of the negative active material was the same as in example 1 except that the heating temperature in S3 was 600 ℃, and the product was noted as Li-H-Si-O-3 material.

Referring to fig. 10, the XRD analysis shows that the layered structure of the material disappears after the high temperature treatment, which indicates that the temperature of the heat treatment at 600 ℃ is too high for the palygorskite-like mineral to maintain its layered structure.

Comparative example 3

The same natural palygorskite mineral as in example 3 was used, and the preparation method of the negative active material was the same as in example 1 except that the heating temperature in S3 was 800 ℃, to obtain a product designated as Na-H-Si-O-2 material.

Referring to fig. 11, the XRD analysis shows that the layered structure of the material disappears after the high temperature treatment, which indicates that the temperature of the heat treatment should not be too high to maintain the layered structure of the palygorskite-like mineral.

The method and conditions for preparing the negative electrode using the negative electrode active material powder and assembling the battery were the same as in example 3. Referring to fig. 12, the cycle performance graph of comparative example 3 is compared with that of example 3, and it can be seen that the reversible capacity of the material after high temperature treatment is reduced, which indicates that the electrochemical performance of the material is not good due to the damage of the layered structure of the material caused by high temperature treatment.

Comparative example 4

The high-grade palygorskite mineral powder obtained by purification in step S1 in example 3 is directly used as a negative electrode active material, and the obtained product is recorded as a palygorskite mineral powder material. The method and conditions for preparing the negative electrode using the negative electrode active material powder and assembling the battery were the same as in example 3.

Referring to fig. 13, the cycle performance diagram of comparative example 4 is compared with that of example 3, and it can be seen that the first discharge capacity of the electrode material is only about 50% of that of example 3, and the overall electrochemical performance is not satisfactory, which illustrates the importance of performing sodium treatment and dehydration treatment on palygorskite mineral powder.

Comparative example 5

The method and conditions for preparing the negative electrode and assembling the battery by using the high-grade palygorskite mineral powder obtained by purification in the step S1 in the example 1 as the negative electrode active material are basically the same as those in the example 1, except that the vacuum drying temperature is kept below 80 ℃ (60 ℃), and the product is recorded as Na-H-Si-O-3 material. The method and conditions for assembling the battery were the same as in example 3.

Referring to fig. 14, as can be seen from the comparison between the cycle performance diagram of the comparative example 5 and the example 3, the reversible capacity of the palygorskite material maintained at the vacuum drying temperature of 60 ℃ is reduced, which indicates that the adsorbed water of the material cannot be completely removed due to the too low vacuum drying temperature, and the part of the water component with weak binding force and the electrolyte undergo side reaction during the cycle process, which is unfavorable for the electrochemical performance of the material.

The battery cycle data of each of the above examples in which the assembled battery was subjected to charge and discharge cycles are shown in table 1.

TABLE 1

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.