CN111137902A

CN111137902A - H-Si-O system material, negative electrode active material and preparation method thereof, electrochemical battery negative electrode material and electrochemical battery

Info

Publication number: CN111137902A
Application number: CN201811308484.0A
Authority: CN
Inventors: 唐子龙; 张俊英; 王诗童; 赵黎江; 张中太
Original assignee: Tsinghua University; Beihang University
Current assignee: Tsinghua University; Beihang University
Priority date: 2018-11-05
Filing date: 2018-11-05
Publication date: 2020-05-12
Anticipated expiration: 2038-11-05
Also published as: CN111137902B

Abstract

The present invention provides a negative electrode active material, which is a layered silicate-like structure, includes H, Si, O, and includes or does not include other metal elements. When other metal elements are included, the molar ratio of the other metal elements to Si is ratio≤0.40. The invention also provides a preparation method of a negative electrode active material, an electrochemical battery negative electrode material, an electrochemical battery and a H-Si-O system material.

Description

H-Si-O system material, negative electrode active material and preparation method thereof, electrochemical cell negative electrode material and electrochemical cell

Technical Field

The invention relates to the technical field of batteries, in particular to a novel layered H-Si-O system material, a negative electrode active material, a preparation method of the negative electrode active material, an electrochemical battery negative electrode material and an electrochemical battery.

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 negative active material widely used at present is a graphite material, and the theoretical capacity of the material is 372mAh g^-1The lithium ion battery has the advantages of good cycle performance, small volume change in the lithium desorption 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 and the like, 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^-1However, the alloy negative electrode material has large volume expansion and contraction in the process of repeatedly releasing and inserting lithium, so that the alloy negative electrode material is separated from a conductive agent after multiple cycles and even peels off from the surface of a 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

Based on the above, it is necessary to provide a novel negative electrode active material, a preparation method thereof, a negative electrode material for an electrochemical cell, an electrochemical cell and an H-Si-O system material.

A negative electrode active material having a layered silicate-like structure including H, Si, O, and not including other metal elements; or H, Si, O and other metal elements, and the molar ratio of the other metal elements to Si is less than or equal to 0.40.

In one embodiment, the phyllosilicate-like structure includes a plurality of silicon-oxygen tetrahedral layers stacked on top of each other.

In one embodiment, the other metal elements include a first metal element M between the silicon-oxygen tetrahedral layers₁，M₁The mol ratio of the Si to the Si is less than or equal to 0.25.

In one embodiment, M₁The mol ratio of the Si to the Si is less than or equal to 0.03.

In one embodiment, the silicon-oxygen tetrahedral layer is a doped silicon-oxygen tetrahedral layer, and the other metal elements include a second metal element M located in the silicon-oxygen tetrahedral layer and replacing part of Si to be located at the center of tetrahedron₂，M₂The mol ratio of the Si to the Si is less than or equal to 0.33.

In one embodiment, the other metal element is selected from one or more of Al, Mg, Fe, Ca, Zn, Li, K, and Na.

In one embodiment, the H and the part O exist in the form of structural water and/or crystal water, and the structural water is H⁺、OH^-And/or H₃O⁺In the form of H₂The O form exists.

In one embodiment, the negative electrode active material is obtained by ion-exchanging layered silicate to exchange at least part of metal elements with hydrogen ions, and then performing heat treatment to maintain the silicon-oxygen tetrahedral layer structure of the layered silicate.

An H-Si-O system material has a layered silicate-like structure, comprises H, Si and O, and does not comprise other metal elements; or H, Si, O and other metal elements are included, and the molar ratio of the other metal elements to the Si is less than or equal to 0.40.

An H-Si-O system material is prepared from laminated silicate through ion exchange to exchange part of metal elements with hydrogen ions, heat treatment and maintaining the laminated structure of silicon-oxygen tetrahedron.

The negative electrode material for the electrochemical cell comprises the negative electrode active material, a conductive agent and a binder.

In one embodiment, the mass of the negative electrode active material accounts for 50% or more of the total mass.

An electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte, the negative electrode comprising the electrochemical cell negative electrode material.

In one embodiment, the electrochemical cell is a lithium ion cell, a sodium ion cell, or a magnesium ion cell.

A method of preparing an anode active material, comprising:

s1, providing a purified layered silicate;

and S2, mixing the layered silicate with an acid solution, and at least partially removing the metal elements in the layered silicate to obtain the negative electrode active material.

In one embodiment, the negative active material has a layered silicate-like structure.

In one embodiment, the concentration of hydrogen ions in the acid solution of step S2 is 0.01mol · L^-1To 4.00 mol. L^-1。

In one embodiment, the acid solution of step S2 is at least one selected from the group consisting of aqueous nitric acid, aqueous hydrochloric acid, aqueous sulfuric acid, aqueous acetic acid, aqueous phosphoric acid and aqueous oxalic acid.

In one embodiment, the method further comprises S3, heating the solid product obtained in the step S2, removing at least part of the crystal water and/or the structure water, and maintaining the silicon-oxygen tetrahedral layer structure of the layered silicate.

In one embodiment, the heating temperature of step S3 is 80 ℃ to 600 ℃.

The invention provides a material with a layered silicate-like structure as a negative active material and a hydrogen silicate material with a novel lithium storage mechanism, wherein gaps among layered structures are utilized to provide transfer channels of a large number of lithium ions, so that the lithium ions can be electrochemically and 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 active material. The lithium storage mechanism is also applicable to other electrochemical cells of alkali metal ions or alkaline earth metal ions, for example, the lithium storage mechanism can be used as a negative electrode active material in a sodium ion battery for electrochemically reversible sodium ion storage. In addition, the layered silicate-like structure can be obtained by purifying the layered silicate mineral, treating the layered silicate mineral by acid solution and heating the layered silicate mineral at low temperature, is simple and cheap, can reduce the manufacturing cost of the battery, and has 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 view of a layered silicon oxygen tetrahedral sheet 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 shows the XRD pattern and the crystal structure analysis result of the layered silicate-like material of example 1;

FIG. 5 is a thermogravimetric plot of the material from room temperature to 1300 ℃ obtained in step S2 of example 1 of the present invention;

FIG. 6 shows the layered silicate-like material of example 1 of the present invention as a negative active material in a half cell assembled at 1.0mA cm^-2A cyclic plot at current density of (a);

FIG. 7 shows the XRD pattern and the crystal structure analysis of the layered silicate-like material of example 3 according to the present invention;

FIG. 8 is a thermogravimetric plot of the material obtained in step S2 of example 3 of the present invention, from room temperature to 600 ℃;

FIG. 9 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^-2A cyclic plot at current density of (a);

FIG. 10 shows the XRD pattern and the result of crystal structure analysis of the comparative example 1 material according to the present invention;

FIG. 11 shows the case where the material of comparative example 1 of the present invention was used as a negative electrode active material to assemble a half cell at 1.0mA cm^-2A cyclic plot at current density of (a);

FIG. 12 shows the case where the material of comparative example 2 of the present invention was used as a negative electrode active material to assemble a half cell at 1.0mA cm^-2A cyclic plot at current density of (a);

FIG. 13 shows the case where the material of comparative example 3 of the present invention was used as a negative electrode active material to assemble a half cell at 1.0mA cm^-2A cyclic plot at current density of (a);

FIG. 14 shows the case where the material of comparative example 4 of the present invention was used as a negative electrode active material to assemble a half cell at 1.0mA cm^-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.

By "phyllosilicate-like structure" is meant herein a material having the layered crystal structure of the phyllosilicate, but with a lower content of H, O and/or water than the phyllosilicate, and a lower content of metallic elements than the phyllosilicate.

The embodiment of the invention provides an H-Si-O system material, which has a layered silicate-like structure obtained by ion replacement of layered silicate, so that at least part of metal elements are exchanged with hydrogen ions, and then heat treatment is carried out to keep the silicon-oxygen tetrahedral layer structure of the layered silicate, wherein the layered silicate-like structure comprises H, Si and O, and does not comprise other metal elements; or comprises H, Si, O and other metal elements, and the molar ratio of the other metal elements to Si is less than or equal to 0.40.

The embodiment of the invention provides a negative electrode active material which has a layered silicate-like structure, comprises H, Si and O, and optionally comprises other metal elements, wherein when the other metal elements are included, the molar ratio of the other metal elements to the Si is less than or equal to 0.40. 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, taking montmorillonite as an example, 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 or Mg 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 the basic structural unit, and the content of other metal elements is reduced, even the metal ions in the interlayer domain or octahedral layer are completely removed, so as to obtain the 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 utilizesThe gap between the mutually laminated doped or undoped silicon oxygen tetrahedral layers contains lithium ions, and the gap is more than 1.52 angstroms

Can 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.

The metal elements in the octahedron and in the interlayer region are 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 the metal element in the interlayer domain and the 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 0.03₁Only in the form of impurities. In some embodiments, the first metal element M of the interlayer domain and octahedral layer₁Is completely removed. The first metal element M₁May be selected from one or more of Al, Mg, Fe, Ca, Zn, Li, K and Na.

Due to the great reduction or complete removal of the first metal element M₁In some embodiments, lithium ions can be combined with organic matters and then inserted into silicon-oxygen tetrahedral layers to form a composite structure in which lithium-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 layer is also substantially partially or completely removed from the layer-like silicate structure, i.e. the layer-like silicate structure may be compared with the layer silicateDoes not contain an octahedral layer or only locally contains a small amount of octahedral layer. 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 layered silicate structure can be obtained by exchanging at least partial metal elements with hydrogen ions through ion replacement of layered silicate, and then performing heat treatment, or artificially synthesizing. While some of the tetrahedral layers of the layered silicate are doped silicon-oxygen tetrahedral layers, there being a metal element partially substituting for silicon, 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 sheet structure, so the magnitude of the decrease in the content thereof is not excessively large. When the second metal element M in the original layered silicate₂When the molar ratio of the second metal element to Si is 0.33, A represents a second metal element M₂The mole ratio of the Si to the A is more than or equal to 0.07 and less than or equal to 0.33 in one embodiment; in a more preferred embodiment, 0.13 ≦ A ≦ 0.20. The second metal element N may be at least one selected from Fe, Mg, and Al.

Water is not shown in FIG. 2, and H and part of O in the layered silicate-like structure exist in the form of structural water and/or crystal water, and the structural water is 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 water can be decomposed to generate HF when meeting water, the capacity of the positive active substance is reduced under an acid environment, and even safety problems are caused, however, the inventor finds that a certain content of crystal water and/or structural water is reserved, so that the metal ions in octahedron and interlayer regions are removed, the silicon-oxygen tetrahedral laminated structure is maintained not to collapse, the diversity of the material crystal structure and the ion migration capacity of the material are improved, and the part of the crystal water and the structural water do not generate the circulation performance of the batteryAdversely affecting. 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 low, for example, 80 ℃ to 120 ℃, and the part of the water may be removed by drying when the electrode sheet is manufactured.

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 structural water can be controlled to be small, and in one embodiment, the molar ratio of the crystal water to Si in the layered silicate-like structure is less than or equal to 2, and more preferably less than or equal to 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 1.00, more preferably the molar ratio of said structural water to Si is from 0.50 to 1.00.

In addition, because a lower heating temperature is adopted in the heating process, defects can be formed after metal ions and/or water are lost in a local area of the material, and the defects can enable the layered silicate-like structure to have more sites capable of being combined with metal ions such as lithium ions, and the ion storage capacity of the material is further improved.

The phyllosilicate-like material as the negative electrode active material is powder, and the average particle size is preferably 0.5 to 5.0 micrometers.

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

s1, providing a purified layered silicate;

and S2, mixing the layered silicate with an acid solution, and at least partially removing metal elements in the 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 silicates of other structure may be selected from 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 acid solution is preferably an acidic aqueous solution, such as at least one of an aqueous nitric acid solution, an aqueous hydrochloric acid solution, an aqueous sulfuric acid solution, an aqueous acetic acid solution, an aqueous phosphoric acid solution, and an aqueous oxalic acid solution. The acid solution may have a concentration of 0.10 mol.L^-1To 8.00 mol. L^-1The reaction time is preferably 0.5 to 48 hours, and the reaction temperature is preferably 25 to 80 ℃. Preferably, the reaction is carried out sufficiently by continuously mechanically stirring or ultrasonically shaking the mixture of the layered silicate and the acid solution. It is understood that the above condition ranges are wide ranges, and the substitution reaction of the metal ions with the hydrogen ions in the acid solution mainly occurs in step S2, so that the metal ions with weaker binding force in the material are replaced by the hydrogen ions, and for different types of materials, the above condition ranges are wide rangesThe reaction conditions of the layered silicate of type (I) may be adjusted according to the type of the layered silicate so as to achieve the same degree of removal of metal ions. For example, in one embodiment, the layered silicate is montmorillonite, and the concentration of hydrogen ions in the acid solution of step S2 is 0.01mol · L^-1To 4.00 mol. L^-1. In another embodiment, the layered silicate is palygorskite, and the concentration of hydrogen ions in the acid solution of the step S2 is 0.01 mol.L^-1To 7.00 mol. L^-1. In another embodiment, the layered silicate is illite, and the concentration of hydrogen ions in the acid solution of the step S2 is 0.01mol · L^-1To 8.00 mol. L^-1. In general, the stronger the binding force between the metal ions and the silicate framework, the higher the concentration of the acid solution that can be used, but the concentration of the acid solution should not be too high, the reaction time should not be too long, and the reaction temperature 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 conditions₁The first metal element M is reduced by ion replacement with H₁While maintaining the morphology of the doped or undoped silicon oxy tetrahedral layer substantially intact. In a preferred embodiment, a relatively lower concentration of the acid solution is suitably used for each phyllosilicate, the concentration of hydrogen ions in the acid solution preferably being 0.01mol · L^-1To 4.00 mol. L^-1。

The step S2 may be followed by further steps of filtering, washing and drying to separate the solid product from the acid solution.

The solid product passing through step S2 contains a large amount of water in various forms, and if only the adsorbed water is removed, it can be achieved by drying the pole piece at 80 to 120 ℃ during the preparation of the negative electrode. In a preferred embodiment, the method for preparing the anode active material may further include a step S3 of heating the solid product 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, heating still needs to be controlledThe temperature is not so high as to maintain the silicon-oxygen tetrahedral layer structure of the phyllosilicate, and only water which is weakly bonded to the layer skeleton, such as all adsorbed water, partially crystallized water and partially structured water, is removed by heating the solid product. The heating may be carried out in air, vacuum or a protective gas, such as an inert gas or a reducing gas. In order to maintain the structure of the layered silicate in the silicon-oxygen tetrahedral layer after the heating step, thermogravimetric analysis can be performed on the product of step S2 to determine different temperature stages of adsorbed water, crystal water and structural water extraction, and the temperature higher than the temperature at which the adsorbed water is completely extracted and lower than the temperature at which the structural water is completely extracted is selected as the heating temperature of step S3. The heating temperature is preferably greater than or equal to 80 ℃ and less than 600 ℃, and the heating rate is 2 ℃ min^-1To 10 ℃ min^-1And the heating time is 0.5 to 12 hours. For different types of phyllosilicates, there is a certain difference in the amount of binding force between the crystalline water and the structural water and the lamellar framework, so that different heating temperature ranges can be used for different phyllosilicates in order to maintain the tetrahedral layer framework structure of the phyllosilicate. In one embodiment, the layered silicate is montmorillonite, and the heating temperature of step S3 is 80 ℃ to 600 ℃. In another embodiment, the layered silicate is palygorskite, the heating temperature of step S3 is 150 ℃ to 500 ℃, preferably all adsorbed water and part of crystal water are removed, and the heating temperature is 150 ℃ to 300 ℃. In another embodiment, the layered silicate is illite and the temperature of the heating of step S3 is 80 ℃ to 600 ℃.

It can be seen that the upper limit of the temperature in step S3 of each type of phyllosilicate is substantially about 500 to 600 ℃, and thermogravimetric analysis of the product of different types of phyllosilicates treated with the acid solution in step S2 shows that the structural water of the product in step S2 is substantially the same in temperature since the framework structures of phyllosilicates are substantially the same and the metal ions are substantially removed in step S2.

Further, the inventors have found through extensive studies and experiments that the layered silicate is subjected to the acid solution of step S2After the treatment, although the layered structure can be maintained, the thermal stability of the product is somewhat reduced, depending on the concentration of the acid solution used, the higher the concentration of the acid solution, the worse the thermal stability of the product. Accordingly, in order to maintain the layered structure of the heated product of step S3, the temperature of the heating process of step S3 may be adjusted according to the concentration of the acid solution used in step S2. The heating temperature of 500 ℃ to 600 ℃ in the step S3 corresponds to a relatively low concentration of the acid solution in the step S2, for example, 0.01 mol. L^-1To 4.00 mol. L^-1. When the acid solution is used in a higher concentration, the temperature of the heating step may be controlled to a lower range, preferably below 300 ℃.

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.

In the embodiment of the invention, the metal ions in the interlayer domain and the octahedral layer are greatly reduced or completely removed by treating the phyllosilicate with the acid solution, so that the interlayer gap of the layered structure can be enlarged, and the migration capability of lithium ions among tetrahedral interlayers is improved. Furthermore, the octahedral layer is at least partially dissolved by the acid solution, 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 crystal 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 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, SuperP, 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 to 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 to be a solvent that is insoluble in the negative active material, does not chemically react with the negative active material, and can be completely removed at a relatively low temperature (e.g., 30 to 150 ℃), such as a low-molecular-weight volatile organic solvent, 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 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 sodium ionIn the case of a subcell, 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.

Preparation of negative electrode and assembly of battery

Example 1

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, adding montmorillonite powder at a concentration of 0.50 mol.L^-1Stirring in hydrochloric acid water solution for 2 hours at 70 ℃, filtering the reacted solid, washing with deionized water for 2-3 times, and vacuum drying at normal temperature.

S3, heat-treating the dried solid powder under vacuum at 200 deg.C for 2 hr (temperature rising rate of 5 deg.C. min)^-1) And obtaining the cathode active material powder with a 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 H, Si and O to Si in the material was 0.09 by elemental analysis. Referring to fig. 5, thermogravimetric analysis of the product obtained in S2 yields the contents of crystal water and structural water in the material, and if other metal elements are taken as impurity components, the chemical formula of the negative active material is calculated to be H_0.46SiO_2.23。

H is to be_0.46SiO_2.23Adding the conductive graphite and a binder polyvinylidene fluoride into 10mL of N-methylpyrrolidone (NMP) solvent according to the mass ratio of 8:1:1 in sequence, stirring for 4 hours, coating on a copper foil, and drying in vacuum at the temperature of 120 ℃ for 10 hours to obtain the negative electrode.

Assembling the prepared negative electrode into a lithium ion battery, and taking a metal lithium sheet as a counter currentVery high quality Celgard 2400 polypropylene microporous membrane as separator, 1.00 mol. L^-1LiPF of₆The 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.

The electrochemical cycle characteristics of the button cell are tested by adopting a LAND cell test system in a voltage range of 0.01V to 1.50V, wherein 1.50V is a charge cut-off voltage, and 0.01V is a discharge cut-off voltage. FIG. 6 shows the cell of example 1 at 1.0mA cm^-2Current density of (1.0 mA · cm) of a constant current charge-discharge cycle performance^-2Before the current density of (2) was cycled, the cell was at 0.1mA cm^-2Constant current charge-discharge cycle of (1) is activated for 5 times at current density, and the following cycle performance of the present application all adopt the same activation mode). It can be seen that the battery material exhibits excellent high rate cycling performance with coulombic efficiency of almost 100%. This illustrates H_0.46SiO_2.23The layered structure and the pore structure in the structure can provide a large number of migration channels of metal ions, so that the diversity of the crystal structure of the material and the ion migration capability of the material are improved, and the part of the crystallized water and the structural water do not have adverse effects on the cycle performance of the battery.

Example 2

S1, the natural illite mineral is purified through natural drying, crushing, airflow drying, grinding and air separation grading to obtain high-grade illite mineral powder.

S2, adding illite powder at a concentration of 3.00 mol.L^-1Stirring in hydrochloric acid water solution at 25 deg.C for 10 hr, filtering the reacted solid, washing with deionized water for 2-3 times, and vacuum drying at room temperature.

S3, heat-treating the dried solid powder at 600 deg.C for 10 hours under vacuum (heating rate of 10 deg.C. min)^-1) And obtaining the cathode active material powder with a 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, mixing the palygorskite powder at the concentration of 1.00 mol.L^-1Stirring in hydrochloric acid water solution for 3 hours at 50 ℃, filtering the reacted solid, washing with deionized water for 2-3 times, and vacuum drying at normal temperature.

S3, heat-treating the dried solid powder at 200 deg.C for 3 hr under vacuum (heating rate of 2 deg.C. min)^-1) And obtaining the cathode active material powder with a layered silicate-like structure.

The product was analyzed by the same method as in example 1, referring to fig. 7, XRD test was performed on the negative active material powder, and it was determined from the peak around 10 ° that the material had a layered crystal structure, and the molar ratio of the metal elements other than H, Si, and O to Si was 0.03, referring to fig. 8, the content of crystal water and structural water in the material was obtained by thermogravimetric analysis of the product obtained in S2, and if the other metal elements were regarded as impurity components, the chemical formula of the negative active material was calculated to be H_0.28SiO_2.14。

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 1. FIG. 9 shows the cell of example 3 at 1.0mA cm^-2Constant current charge-discharge cycle performance diagram under current density. It can be seen that the battery material exhibits excellent high rate cycling performance with coulombic efficiency of almost 100%. Similar to example 1, this illustrates H_0.28SiO_2.14The layered structure and the pore structure in the structure can provide a large number of migration channels of metal ions, so that the diversity of the crystal structure of the material and the ion migration capability of the material are improved, 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

Using the same natural palygorskite mineral as in example 3, a negative active material was prepared in the same manner as in example 1 except that the concentration of the acid solution in S2 was 5.00 mol. multidot.L^-1。

Referring to FIG. 10, it can be seen from the comparative XRD analysisAfter the high-concentration acid treatment, the diffraction peak of the material at about 10 degrees is shifted and broadened, which indicates that the layered structure of the material is damaged and collapsed. The above results show that 5.00 mol.L for palygorskite-like minerals to maintain their layered structure^-1Too high acid concentration.

The method and conditions for preparing the negative electrode using the negative electrode active material powder, and the charge-discharge cycle test conditions of the battery were the same as in example 3. As can be seen from the comparison of the cycle performance graph of fig. 11 and example 3, the reversible capacity of the material after the treatment with the high-concentration acid solution is reduced, indicating that the electrochemical performance of the material is not affected by the destruction of the layered structure of the material caused by the high-concentration acid treatment.

Comparative example 2

Using the same natural palygorskite mineral as in example 3, the negative active material was prepared in the same manner as in example 1 except that the heating temperature was 650 ℃ in S3.

The method and conditions for preparing the negative electrode using the negative electrode active material powder, and the charge-discharge cycle test conditions of the battery were the same as in example 3. As can be seen from the comparison of the cycle performance graph of fig. 12 with example 3, the reversible capacity of the material after high temperature treatment is reduced, indicating that high temperature treatment is detrimental to the electrochemical performance of the material.

Comparative example 3

Using the same natural palygorskite mineral as in example 3, the negative active material was prepared in the same manner as in example 1, except that step S2 was omitted, and the palygorskite mineral powder obtained in step S1 was directly heat-treated in vacuum at 200 ℃ for 3 hours (at a temperature increase rate of 2 ℃ C. min.)^-1) And taking the obtained product as negative active material powder. Methods and conditions for preparing a negative electrode using the negative electrode active material powder and assembling a battery, and charge and discharge cycle test conditions of the battery were the same as in example 3. As can be seen from the comparison between the cycle performance diagram in FIG. 13 and example 3, the reversible capacity of the powder material without acid treatment is reduced, which indicates that the acid washing process can reduce unnecessary impurity elements in the material, thereby improving the specific capacity of the material.

Comparative example 4

The same natural palygorskite mineral as in example 3 was used, the preparation method of the negative active material was the same as that of example 1, except that step S3 was not included, the palygorskite-like material obtained by purification through steps S1 and S2 in example 3 was directly used as the negative active material, and the method and conditions for preparing the negative electrode and the assembled battery using the negative active material powder were substantially the same as in example 3, except that the vacuum drying temperature was maintained at 70 ℃. The method and conditions for assembling the battery, and the charge-discharge cycle test conditions of the battery were the same as in example 3. As can be seen from the comparison between the cycle performance diagram of FIG. 14 and example 3, the reversible capacity of the palygorskite material maintained at 70 ℃ under vacuum drying temperature is reduced, which indicates that the adsorbed water in the material cannot be completely removed due to too low vacuum drying temperature, and the part of the water component with weak binding force has side reaction with the electrolyte during the cycle process, thus being unfavorable for the electrochemical performance of the material.

Second, electrochemical performance test

Electrochemical cycling performance parameters of button cells tested using the LAND cell test system over a voltage range of 0.01V to 1.50V are compared as follows.

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.

Claims

1. A negative electrode active material, characterized in that it has a layered silicate-like structure, includes H, Si, O, and does not include other metal elements; or includes H, Si, O, and other metal elements, and said The molar ratio of other metal elements to Si is less than or equal to 0.40.

2 . The negative electrode active material according to claim 1 , wherein the layered silicate-like structure comprises a plurality of mutually stacked silicon-oxygen tetrahedral layers. 3 .

3 . The negative electrode active material according to claim 2 , wherein the other metal elements comprise a first metal element M ₁ located between the silicon-oxygen tetrahedral layers, and the molar ratio of M ₁ to Si is ≤0.25. 4 . .

4 . The negative electrode active material according to claim 3 , wherein the molar ratio of M ₁ to Si is less than or equal to 0.03. 5 .

5 . The negative electrode active material according to claim 2 , wherein the silicon-oxygen tetrahedron layer is a doped silicon-oxygen tetrahedron layer, and the other metal element comprises a substituted silicon-oxygen tetrahedron layer located in the silicon-oxygen tetrahedron layer. 6 . Part of the Si is located in the second metal element M ₂ in the center of the tetrahedron, and the molar ratio of M ₂ to Si is ≤ 0.33.

6 . The negative electrode active material according to claim 1 , wherein the other metal elements are selected from one or more of Al, Mg, Fe, Ca, Zn, Li, K, and Na. 7 .

7. The negative electrode active material according to claim 1, wherein the H and part O exist in the form of structural water and/or crystal water, and the structural water is H ⁺ , ^OH- , and/or H exists in the form of ₃ O ⁺ , and the crystal water exists in the form of H ₂ O.

8. A H-Si-O system material, characterized in that it has a layered silicate-like structure, including H, Si, O, and does not include other metal elements; or includes H, Si, O, and other metal elements , and the molar ratio of the other metal elements to Si is less than or equal to 0.40.

9. An H-Si-O system material, characterized in that, through ion replacement by layered silicate, at least part of the metal element is exchanged with hydrogen ions, and then heat treated to maintain the silicon-oxygen four sides of layered silicate. The body layer structure is obtained.

10 . A negative electrode material for an electrochemical cell, characterized by comprising the negative electrode active material according to any one of claims 1 to 7 , a conductive agent and a binder. 11 .

11. An electrochemical cell, comprising a positive electrode, a negative electrode and an electrolyte, the negative electrode comprising the negative electrode active material according to any one of claims 1 to 7.

12. The electrochemical cell according to claim 11, characterized in that it is a lithium ion battery, a sodium ion battery or a magnesium ion battery.

13. A preparation method of a negative electrode active material, comprising:

S1, providing purified layered silicate;

S2, mixing the layered silicate with an acid solution to at least partially remove the metal element in the layered silicate to obtain the negative electrode active material having a layered silicate-like structure.

14 . The method for preparing a negative electrode active material according to claim 13 , wherein the concentration of hydrogen ions in the acid solution in the step S2 is 0.01 mol·L ⁻¹ to 4.00 mol·L ⁻¹ . 15 .

15. The preparation method of negative active material according to claim 13, wherein the acid solution in the step S2 is selected from the group consisting of aqueous nitric acid, aqueous hydrochloric acid, aqueous sulfuric acid, aqueous acetic acid, aqueous phosphoric acid and aqueous oxalic acid. at least one.

16. The preparation method of negative active material according to claim 13, characterized in that, further comprising S3, heating the solid product obtained in step S2, removing at least part of crystal water and/or structural water, and maintaining the layer Silica-like tetrahedral layer structure of silicate.

17 . The method for preparing a negative electrode active material according to claim 16 , wherein the heating temperature of the step S3 is 80° C. to 600° C. 18 .