CN108550845B - Application of lithium vanadium phosphate sodium material and low-temperature battery thereof - Google Patents
Application of lithium vanadium phosphate sodium material and low-temperature battery thereof Download PDFInfo
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- CN108550845B CN108550845B CN201810350305.3A CN201810350305A CN108550845B CN 108550845 B CN108550845 B CN 108550845B CN 201810350305 A CN201810350305 A CN 201810350305A CN 108550845 B CN108550845 B CN 108550845B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses an application of a vanadium-lithium-sodium phosphate material in a low-temperature lithium ion battery and the low-temperature lithium ion battery, belonging to the field of lithium ion batteries3‑ xNaxV2(PO4)3，0<x<3 as the anode active material applied to the anode of the low-temperature lithium ion battery, wherein the rhombohedral phase lithium vanadium phosphate sodium material is selected from a pure phase rhombohedral phase lithium vanadium phosphate sodium material, a mixed material of rhombohedral phase lithium vanadium phosphate and rhombohedral phase sodium vanadium phosphate, and a mixed material of rhombohedral phase lithium vanadium phosphate, rhombohedral phase sodium vanadium phosphate and a small amount of monoclinic phase lithium vanadium phosphate. In the invention, when rhombohedral phase lithium vanadium phosphate sodium is used as the anode active material of the low-temperature lithium ion battery, the external circuit can be effectively simplified and the electrochemical performance of the low-temperature lithium ion battery can be improved.
Description
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to an application of a rhombohedral phase lithium vanadium phosphate sodium material and a low-temperature battery thereof.
Background
Lithium ion batteries have dominated the consumer electronics market and have evolved into hybrid electric vehicles/motorsIn the field of automobiles, rapid popularization of new energy electric automobiles provides greater challenges for the existing lithium ion battery systems. Wherein the polyanionic compound LiFePO4The battery has the advantages of high structural stability, long cycle life and environmental friendliness, and is widely applied to the field of power batteries, but the low-temperature performance of the battery is poor, the energy and the power of the battery are seriously lost along with the reduction of the environmental temperature, and the cruising ability of the electric automobile is remarkably reduced.
It is reported that the root cause of energy and power loss of the battery at low temperature is slow kinetic process of electrode material, while olivine type LiFePO4Li in the middle one-dimensional direction+Diffusion channels make the reaction kinetics slower, resulting in poor low temperature performance. In contrast, possess three-dimensional Li+Li of diffusion channel3V2(PO4)3The material shows better low-temperature performance and is considered to be an ideal material for low-temperature lithium ion batteries.
Monoclinic phase Li3V2(PO4)3Is a thermodynamically stable phase and belongs to P21A/n space group, cell parameters of
α ═ γ ═ 90 °, β ═ 90.6 °; slightly distorted VO6Octahedron and PO4The tetrahedra being joined in such a way as to share oxygen vertices to form [ V ]2(PO4)3]The structural units are arranged and extended in a Z shape to form a three-dimensional network structure; the lithium has three crystallographic positions, Li (1) occupying tetrahedral positions, and Li (2) and Li (3) occupying quasi-tetrahedral positions consisting of longer Li-O bonds.
Currently, Li for low temperature lithium ion batteries3V2(PO4)3All based on monoclinic phase. Monoclinic phase Li3V2(PO4)3In the method, Li at different positions has different potential energy, so that the ion migration capacity is different, and the reaction corresponds to a plurality of phase transformation processes in the charge and discharge process in the aspect of electrochemical behavior. Li at 3.0-4.3V vs+Monoclinic phase Li during charge-discharge in Li voltage range3V2(PO4)3Three voltage plateaus are shown on the charging curve, which are respectively positioned at 3.6V, 3.7V and 4.1V and correspond to the extraction of lithium ions at the positions of Li (3), Li (3) and Li (1). Monoclinic phase Li3V2(PO4)3Typical multistep Li used as cathode material of low-temperature lithium ion battery+The insertion and extraction feature complicates an external circuit and a Battery Management System (BMS), causing inconvenience to practical use; in addition, the large voltage difference between the voltage platforms makes it difficult to actually utilize the capacity from the low potential in a full cell system.
Therefore, there is a need to develop a new Li alternative to the monoclinic phase3V2(PO4)3The material of (2) to improve the performance of the lithium ion battery under low temperature application.
Disclosure of Invention
In view of the defects of monoclinic phase lithium vanadium phosphate and the improvement requirement of a low-temperature lithium ion battery, the invention provides the application of rhombohedral phase sodium vanadium phosphate materials in the low-temperature battery and the low-temperature battery thereof, and aims to effectively simplify an external circuit by using a single voltage platform when rhombohedral phase sodium vanadium phosphate is used as a positive electrode active material of the low-temperature lithium ion battery, and simultaneously, the faster ion conductor structure of the rhombohedral phase sodium vanadium phosphate is favorable for Li+Thereby improving the electrochemical performance of the low-temperature lithium ion battery.
In order to achieve the above object, according to one aspect of the present invention, there is provided a use of a lithium vanadium phosphate material, which is a rhombohedral phase lithium vanadium phosphate material Li3-xNaxV2(PO4)3，0<x<3 as the anode active material to be applied to the anode of the low-temperature lithium ion battery. Compared with monoclinic phase, the rhombohedral phase has more open structural framework and larger gap positions, and the Li < + > has smaller radius and is not enough to support the gap positions in the rhombohedral phase, so that products directly synthesized by a solid phase method or a liquid phase method are thermodynamically stable monoclinic phase Li3V2(PO4)3. In contrast, Na+The radius of the diamond-shaped structure is larger, and the diamond-shaped structure can support larger clearance positions and be stabilizedThus by introducing Na+Partially substituted Li+The rhombohedral phase lithium vanadium phosphate sodium Li can be obtained by the method3-xNaxV2(PO4)3Wherein, 0<x<3。
Rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate sodium material Li selected from pure phase3- xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Sodium vanadium phosphate Na mixed with rhombohedral phase3V2(PO4)3Mixed material of (1), and rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Rhombohedral phase sodium vanadium phosphate Na3V2(PO4)3And a small amount of monoclinic phase lithium vanadium phosphate Li3V2(PO4)3Wherein the monoclinic phase lithium vanadium phosphate Li is contained in the mixed material3V2(PO4)3The content of (b) is not more than 20% by mass of the whole positive electrode active material. According to different preparation methods, different lithium vanadium phosphate sodium products can be obtained: for example, vanadium sodium phosphate Na in rhombohedral phase3V2(PO4)3The rhombohedral phase lithium vanadium phosphate sodium Li of pure phase can be obtained by a Na-Li ion exchange method as a precursor3-xNaxV2(PO4)3Wherein, 0<x<3. In the synthesis process, a lithium source and a sodium source are added into the raw materials simultaneously to obtain rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Sodium vanadium phosphate Na mixed with rhombohedral phase3V2(PO4)3The mixed material of (1); furthermore, depending on the ratio of the lithium source to the sodium source, it is also possible to incorporate monoclinic lithium vanadium phosphate Li into the product3V2(PO4)3。
Further, rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3In (1), 0 is preferred<x is less than or equal to 1, due to rhombohedral phase Li3V2(PO4)3Three of Li+Only two reversibly inserted and removed, x>1 hour, Na exists in the first charging process+Thus, the range of x is preferably 0<x is less than or equal to 1. When the lithium vanadium phosphate sodium material shows rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Rhombohedral phase sodium vanadium phosphate Na3V2(PO4)3In the mixture, the vanadium sodium phosphate in rhombohedral phase is 3.0-4.3V vs. Li+the/Li range also shows a single platform, and the potential platform (3.75V) is very close to the voltage platform (3.77V) of rhombohedral phase lithium vanadium phosphate, so that the existence of rhombohedral phase sodium vanadium phosphate has little influence on the electrochemical performance. When the lithium vanadium phosphate sodium material shows rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Rhombohedral phase sodium vanadium phosphate Na3V2(PO4)3And monoclinic phase lithium vanadium phosphate Li3V2(PO4)3In which the monoclinic phase Li is present3V2(PO4)3The content of (b) should preferably be 10% or less by mass of the entire positive electrode active material. Monoclinic phase Li3V2(PO4)3The voltage platforms and the large voltage difference between the voltage platforms are not beneficial to the practical application of the low-temperature lithium ion battery, so the content of the lithium ion battery is preferably less than or equal to 10% of the mass of the whole positive active material.
Further, the positive active material of the cathode is rhombohedral phase lithium vanadium phosphate sodium Li3-xNaxV2(PO4)3(0<x<3) The crystal structure of (A) belongs to the rhombohedral system, and the unit cell parameter is
α ═ β ═ 90 °, γ ═ 120 °. The specific values of the cell parameters are related to the value of x. When the rhombohedral phase lithium vanadium phosphate sodium is used as the anode active material, the voltage is 3.0-4.3V vs+In the voltage range of/Li, chargeA voltage plateau is mainly represented on the discharge curve. Wherein, the voltage platform of the pure-phase rhombohedral-phase lithium vanadium phosphate sodium is positioned at 3.77V; the voltage platforms of rhombohedral phase lithium vanadium phosphate and rhombohedral phase sodium vanadium phosphate are respectively positioned at 3.75V and 3.77V, and the voltage platforms of the rhombohedral phase lithium vanadium phosphate and the rhombohedral phase sodium vanadium phosphate are very close to each other, so that the rhombohedral phase lithium vanadium phosphate and the rhombohedral phase sodium vanadium phosphate can be regarded as a voltage platform on a charge-discharge curve. If monoclinic phase lithium vanadium phosphate is present, there are also two smaller voltage plateaus at 3.6V and 4.1V, respectively.
According to the second aspect of the invention, the invention also provides a low-temperature lithium ion battery, which comprises a positive electrode, a negative electrode, a diaphragm between the positive electrode and the negative electrode and an electrolyte, wherein the positive electrode adopts rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3As a positive electrode active material, wherein 0<x<3, preferably 0<x is less than or equal to 1, and the rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3Selected from pure phase lithium vanadium phosphate rhombic sodium material Li3-xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Sodium vanadium phosphate Na mixed with rhombohedral phase3V2(PO4)3Mixed material of (1), and rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Rhombohedral phase sodium vanadium phosphate Na3V2(PO4)3And a small amount of monoclinic phase lithium vanadium phosphate Li3V2(PO4)3Wherein the monoclinic phase lithium vanadium phosphate Li is contained in the mixed material3V2(PO4)3The content of (b) is not more than 20% by mass of the whole positive electrode active material.
Furthermore, the surface of the positive electrode active material in the low-temperature lithium ion battery is provided with a conductive coating layer, or the positive electrode active material and the conductive material are subjected to composite modification to improve the electrochemical performance of the positive electrode material, wherein the conductive coating layer or the conductive material is selected from amorphous carbon, graphitized carbon, carbon nanotubes, carbon fibers, redox graphene, metal Ni, metal Al and metal Ti. In the polyanionic lithium vanadium phosphate sodium, the electron conductivity of the material is poor due to the existence of the electrically insulated phosphate radical functional group, and the conductivity of the material of the polyanionic lithium vanadium phosphate sodium can be improved by coating the surface with the conductive layer or compounding the conductive layer with the conductive material, so that the electrochemical performance of the material of the polyanionic lithium vanadium phosphate sodium is effectively improved.
Further, the active material adopted by the negative electrode of the low-temperature lithium ion battery is selected from graphite, hard carbon, soft carbon and Li4Ti5O12、Li3VO4The material comprises a silicon simple substance and a conductive compound thereof, a germanium simple substance and a conductive compound thereof, a tin simple substance and a conductive compound thereof, a phosphorus simple substance and a conductive compound thereof, a silicon-phosphorus alloy, a germanium-phosphorus alloy, a tin-phosphorus alloy, a zinc-phosphorus alloy, a phosphorus-antimony alloy, a cobalt-tin alloy, a copper-tin alloy and a nickel-tin alloy. The simple substance tin and the conductive compound thereof comprise one or more compounds of the simple substance tin and carbon nanotubes, carbon black, graphene and metal, the simple substance phosphorus and the conductive compound thereof comprise one or more compounds of the simple substance phosphorus and carbon nanotubes, carbon black, graphene and metal, the simple substance silicon and the conductive compound thereof comprise one or more compounds of the simple substance silicon and carbon nanotubes, carbon black, graphene and metal, and the simple substance germanium and the conductive compound thereof comprise one or more compounds of the simple substance germanium and carbon nanotubes, carbon black, graphene and metal.
Further, the electrolyte of the low-temperature lithium ion battery comprises an organic solvent and a lithium salt, wherein the organic solvent is selected from ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, ethyl methyl carbonate, ethyl acetate and polycarbonate; the lithium salt is selected from lithium perchlorate (LiClO)4) Lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) Lithium bis (oxalato) borate (LiBOB), lithium difluoro (oxalato) borate (LiDFOB) and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), wherein the concentration of the lithium salt is 1-5 mol/L. The conductivity is an important parameter for measuring the performance of the electrolyte, and the higher conductivity is a necessary condition for ensuring the better low-temperature performance of the lithium ion battery. By optimizing the components of the organic solvent and increasing the solubility of the lithium salt in the organic solvent, the conductivity of the electrolyte can be improved, thereby improving the lithium ionLow temperature performance of the subcell.
Further, an additive accounting for 0.5-10% of the total mass of the electrolyte is added into the electrolyte, and the additive is selected from fluoroethylene carbonate, lithium bis (oxalato) borate, vinylene carbonate, vinyl ethylene carbonate, dimethyl sulfite, diethyl sulfite, methyl vinyl sulfone and ethyl vinyl sulfone to neutralize N, N-dimethyl trifluoroacetamide. The small amount of the additive can improve the stability of the electrode material, thereby improving the low-temperature performance of the battery.
Further, the diaphragm is a polyethylene microporous membrane, a polypropylene microporous membrane or a glass fiber microporous membrane, which forms physical insulation before the positive electrode and the negative electrode, and only allows ions to pass through but not electrons to pass through. Besides the active electrode material, the positive electrode is also added with a conductive agent and a binder, the positive electrode active material, the conductive agent and the binder are mixed and ground into slurry, and the slurry is uniformly coated on an electrode current collector to prepare a positive electrode film. Besides the active electrode material, a conductive agent and a binder are also added into the negative electrode. Mixing and grinding the negative active material, the conductive agent and the binder into slurry, and uniformly coating the slurry on an electrode current collector to prepare a negative electrode film.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
the cathode active material of the low-temperature lithium ion battery adopts rhombohedral phase lithium vanadium phosphate sodium Li3-xNaxV2(PO4)3Compared with monoclinic phase, rhombohedral phase has faster ion conduction structure and is more beneficial to Li+The diffusion and transmission of the high-temperature-resistant material are beneficial to obtaining better low-temperature performance; meanwhile, the single voltage platform can effectively simplify the control system of the circuit outside the battery. The lithium ion battery prepared by the anode active material has very good low-temperature performance: reversible capacity at-30 ℃ hold 80% at room temperature; after 5000 cycles of charge and discharge at-20 ℃, the capacity retention rate is as high as 85%, and the coulombic efficiency is close to 100%.
Drawings
FIG. 1 is an XRD spectrum of monoclinic phase lithium vanadium phosphate;
FIG. 2 is an XRD pattern of pure phase rhombohedral phase lithium vanadium phosphate sodium;
FIG. 3 is an XRD spectrum of a mixed material of rhombohedral phase lithium vanadium phosphate and rhombohedral phase sodium vanadium phosphate;
FIG. 4 is an XRD spectrum of a mixed material of rhombohedral phase lithium vanadium phosphate, rhombohedral phase sodium vanadium phosphate and monoclinic phase lithium vanadium phosphate;
FIG. 5 is a charge-discharge curve of monoclinic phase lithium vanadium phosphate;
FIG. 6 is a charge-discharge curve of pure phase rhombohedral phase lithium vanadium phosphate sodium;
FIG. 7 is a charge-discharge curve of a mixed material of rhombohedral phase lithium vanadium phosphate and rhombohedral phase sodium vanadium phosphate;
FIG. 8 is a charge-discharge curve of a mixed material of rhombohedral phase lithium vanadium phosphate, rhombohedral phase sodium vanadium phosphate and monoclinic phase lithium vanadium phosphate;
FIG. 9 is a charge-discharge curve of rhombohedral phase sodium vanadium phosphate at 25 deg.C and-30 deg.C;
FIG. 10 is a discharge curve of rhombohedral phase sodium vanadium phosphate lithium cycled at 0 deg.C;
FIG. 11 is a discharge curve of rhombohedral phase sodium vanadium phosphate lithium cycled at-10 deg.C;
FIG. 12 is a discharge curve of rhombohedral phase sodium vanadium phosphate lithium cycled at-20 deg.C;
FIG. 13 is a cycle curve of rhombohedral phase sodium vanadium phosphate at-10 deg.C.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below 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. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Studies show that Li3V2(PO4)3There are two crystal structures: the rhombohedral phase and thermodynamically stable monoclinic phase of fast ion conductor structures are distinguished by a "lantern" structureYuan [ V ]2(PO4)3]The connection modes of (a) and (b) are different. Monoclinic phase Li3V2(PO4)3Belonging to P21A/n space group, cell parameters of
α ═ γ ═ 90 °, β ═ 90.6 °; slightly distorted VO6Octahedron and PO4The tetrahedra being joined in such a way as to share oxygen vertices to form [ V ]2(PO4)3]The structural units are arranged and extended in a Z shape to form a three-dimensional network structure; the lithium has three crystallographic positions, Li (1) occupying tetrahedral positions, and Li (2) and Li (3) occupying quasi-tetrahedral positions consisting of longer Li-O bonds. Rhombus phase Li3V2(PO4)3Belong to
Space group, cell parameter of
α＝β＝120°，γ＝90°；PO4Tetrahedron and VO6Octahedra are connected in a common vertex mode to form [ V ]2(PO4)3]Structural unit, edge [001 ]]The direction is extended to form a three-dimensional network structure; wherein the lithium atom has only one crystallographic position.
Rhombohedral phase Li in comparison with monoclinic phase3V2(PO4)3The position of the middle Li is only one, and the middle Li has the same potential energy and ion migration capacity, so that the potential energy and the ion migration capacity are 3.0-4.3V vs+When the battery is charged and discharged in the voltage range of/Li, the charging and discharging curve only shows a simple voltage platform, which is positioned at 3.77V, thereby simplifying the control system of the circuit outside the battery and simultaneously fully utilizing the capacity of the material. In addition, rhombohedral phases have a more open structural framework and larger interstitial sites than monoclinic phases, which are more favorable for Li+The conduction of the battery improves the multiplying power performance of large-current charging and discharging of the battery. Is singleThe advantages of both a voltage plateau and a faster ion conducting structure make rhombohedral phase more suitable for use as an electrode material than monoclinic phase.
Based on the research results, the invention provides application of a lithium vanadium phosphate sodium material, namely rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3，0<x<3 as the anode active material to be applied to the anode of the low-temperature lithium ion battery.
In the invention, rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate sodium material Li selected from pure phase3-xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Sodium vanadium phosphate Na mixed with rhombohedral phase3V2(PO4)3Mixed material of (1), and rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Rhombohedral phase sodium vanadium phosphate Na3V2(PO4)3And a small amount of monoclinic phase lithium vanadium phosphate Li3V2(PO4)3Wherein the monoclinic phase lithium vanadium phosphate Li is contained in the mixed material3V2(PO4)3The content of (b) is not more than 20% by mass of the whole positive electrode active material.
In the preferred embodiment of the invention, rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3 Middle 0<x is less than or equal to 1, and when the lithium vanadium phosphate sodium material is expressed as the mixed material, the monoclinic phase Li3V2(PO4)3The content of (b) should preferably be 10% or less by mass of the entire positive electrode active material.
Specifically, the positive active material of the cathode is rhombohedral phase lithium vanadium phosphate sodium Li3-xNaxV2(PO4)3，0<x<3 belongs to rhombohedral system and has unit cell parameters of
α ═ β ═ 90 °, γ ═ 120 °, when used as a positive electrode active material, li ranges from 3.0 to 4.3V vs+In the voltage range of/Li, a voltage platform is mainly shown on a charge-discharge curve.
Based on the novel application of the materials, the invention provides a low-temperature lithium ion battery which comprises a positive electrode, a negative electrode, a diaphragm between the positive electrode and the negative electrode and electrolyte, and is characterized in that the positive electrode adopts rhombohedral phase lithium vanadium phosphate sodium material Li3- xNaxV2(PO4)3As a positive electrode active material, wherein 0<x<3, preferably 0<x is less than or equal to 1, and the rhombohedral phase lithium vanadium phosphate sodium material Li3- xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate sodium material Li selected from pure phase3-xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Sodium vanadium phosphate Na mixed with rhombohedral phase3V2(PO4)3Mixed material of (1), and rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Rhombohedral phase sodium vanadium phosphate Na3V2(PO4)3And a small amount of monoclinic phase lithium vanadium phosphate Li3V2(PO4)3Wherein the monoclinic phase lithium vanadium phosphate Li is contained in the mixed material3V2(PO4)3The content of (B) is not more than 20% of the total mass of the positive electrode active material
In an embodiment of the present invention, a conductive coating layer is disposed on a surface of the cathode active material, or the cathode active material and the conductive material are compositely modified to improve electrochemical performance of the cathode material, wherein the conductive coating layer or the conductive material is selected from amorphous carbon, graphitized carbon, carbon nanotubes, carbon fibers, redox graphene, metal Ni, metal Al, and metal Ti. The cathode active material adopted by the cathode is selected from graphite, hard carbon, soft carbon and Li4Ti5O12、Li3VO4Elemental silicon and conductive compound thereof, elemental germanium and conductive compound thereof, and tin sheetThe material and the conductive compound thereof comprise a phosphorus simple substance and a conductive compound thereof, a silicon-phosphorus alloy, a germanium-phosphorus alloy, a tin-phosphorus alloy, a zinc-phosphorus alloy, a phosphorus-antimony alloy, a cobalt-tin alloy, a copper-tin alloy and a nickel-tin alloy, wherein the tin simple substance and the conductive compound thereof comprise one or more compounds of the tin simple substance and a carbon nano tube, carbon black, graphene and metal, the phosphorus simple substance and the conductive compound thereof comprise one or more compounds of the phosphorus simple substance and the carbon nano tube, carbon black, graphene and metal, the silicon simple substance and the conductive compound thereof comprise one or more compounds of the silicon simple substance and the carbon nano tube, carbon black, graphene and metal, and the germanium simple substance and the conductive compound thereof comprise one or more compounds of the germanium simple substance and the carbon nano tube, carbon black, graphene and metal.
In yet another embodiment of the present invention, the electrolyte includes an organic solvent and a lithium salt, wherein the organic solvent is selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, ethyl methyl carbonate, ethyl acetate, and polycarbonate; the lithium salt is selected from lithium perchlorate (LiClO)4) Lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) Lithium bis (oxalato) borate (LiBOB), lithium difluoro (oxalato) borate (LiDFOB) and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), wherein the concentration of the lithium salt is 1-5 mol/L. And an additive accounting for 0.5-10% of the total mass of the electrolyte is also added into the electrolyte, and the additive is selected from fluoroethylene carbonate, lithium bis (oxalato) borate, vinylene carbonate, vinyl ethylene carbonate, dimethyl sulfite, diethyl sulfite, methyl vinyl sulfone and ethyl vinyl sulfone to neutralize N, N-dimethyl trifluoroacetamide. The diaphragm is a polyethylene microporous membrane, a polypropylene microporous membrane or a glass fiber microporous membrane, physical insulation is formed between the positive electrode and the negative electrode, the positive electrode is added with a conductive agent and a binder besides an active electrode material, and the negative electrode is also added with the conductive agent and the binder besides the active electrode material.
To illustrate the long-life low temperature lithium ion battery of the present invention in more detail, specific examples and components thereof are shown below in tabular form.
Among them, Li in example 12.99Na0.01V2(PO4)3The cell parameter of which is
α＝β＝90°，γ＝120°。
Li in example 91.3Na1.7V2(PO4)3The cell parameter of which is
α＝β＝90°，γ＝120°。
Li in example 150.1Na2.9V2(PO4)3The cell parameter of which is
α＝β＝90°，γ＝120°。
The positive electrode active materials in examples 2, 3, 5, and 6 had conductive coating layers of amorphous carbon, carbon fiber, carbon nanotube, and graphene on the surfaces thereof, respectively.
The positive electrode active materials in examples 10, 13, and 15 were compositely modified with metal Ni, metal Al, and metal Ti, respectively.
In practical engineering practice, the conductive coating layer on the surface of the positive electrode active material is not limited to have amorphous carbon, carbon fiber, carbon nanotube and graphene, but may also be graphitized carbon and redox graphene arranged according to actual needs.
In the above embodiments, the negative electrode active material adopted by the negative electrode of the low-temperature lithium ion battery is not specifically shown, in actual engineering practice, the negative electrode active material may be selected from various materials on the market, similarly, the electrolyte may also be a disclosed electrolyte suitable for the low-temperature lithium ion battery, an additive accounting for 0.5-10% of the total mass of the electrolyte is further added to the electrolyte, and the specifically added additive and the content of the additive can be adjusted according to actual needs. The additive accounting for 0.5-10% of the total mass of the electrolyte is most suitable. The low-temperature lithium ion battery diaphragm is a polyethylene microporous film, a polypropylene microporous film or a glass fiber microporous film and is used for forming physical insulation between a positive electrode and a negative electrode, a conductive agent and a binder are added in the positive electrode besides an active electrode material, and a conductive agent and a binder are also added in the negative electrode besides the active electrode material. In fact, the structure of the low-temperature lithium ion battery is similar to that of the existing report, and the technical scheme adopted and disclosed by the negative active material selection, the electrolyte component, the additive, the diaphragm, the conductive agent and the binder is also feasible. How to choose specifically needs to comprehensively consider the performance, cost and actual engineering requirements of the final battery.
In order to better illustrate the process of the invention, further details are given below with reference to specific experimental data.
FIG. 1 is an XRD pattern of monoclinic phase lithium vanadium phosphate, FIG. 2 is an XRD pattern of pure phase rhombohedral phase lithium vanadium phosphate sodium, FIG. 3 is an XRD pattern of a mixed material of rhombohedral phase lithium vanadium phosphate and rhombohedral phase sodium vanadium phosphate, FIG. 4 is an XRD pattern of a mixed material of rhombohedral phase lithium vanadium phosphate, rhombohedral phase sodium vanadium phosphate and monoclinic phase lithium vanadium phosphate, and comparing the above four patterns, the standard XRD patterns of rhombohedral phase lithium vanadium phosphate, rhombohedral phase sodium vanadium phosphate and monoclinic phase lithium vanadium phosphate are obviously different, so that the composition of the product can be judged by XRD.
FIG. 5 is a charge-discharge curve of monoclinic phase lithium vanadium phosphate; FIG. 6 is a charge-discharge curve of pure phase rhombohedral phase lithium vanadium phosphate sodium; FIG. 7 is rhombohedral phase lithium vanadium phosphate and rhombohedral phase vanadium phosphateCharge-discharge curves of the sodium hybrid material; FIG. 8 is a charge-discharge curve of a mixed material of rhombohedral phase lithium vanadium phosphate, rhombohedral phase sodium vanadium phosphate and monoclinic phase lithium vanadium phosphate. Comparing the above four figures, Li is in the range of 3.0-4.3V vs+In the voltage range of/Li, different from a plurality of charging and discharging platforms of monoclinic phase lithium vanadium phosphate, the pure phase rhombohedral phase sodium vanadium phosphate only has one voltage platform, and the voltage platforms of rhombohedral phase lithium vanadium phosphate and rhombohedral phase sodium vanadium phosphate are very close to each other in the mixed material, so that the mixed material can be approximately regarded as one voltage platform on a charging and discharging curve. If monoclinic phase lithium vanadium phosphate is also present in the mixed material, the concentration is respectively 3.6V and 4.1V vs. Li+at/Li, two smaller voltage plateaus are also observed.
FIG. 9 is a charge-discharge curve of rhombohedral phase sodium vanadium phosphate at 25 deg.C and-30 deg.C, which shows that at-30 deg.C, it still has a very flat voltage platform, and its reversible capacity is maintained at 80% at 25 deg.C, indicating that the material has very good low-temperature potential.
FIG. 10 is a discharge curve of rhombohedral phase lithium vanadium phosphate sodium circulating at 0 deg.C, FIG. 11 is a discharge curve of pure phase rhombohedral phase lithium vanadium phosphate sodium circulating at-10 deg.C, FIG. 12 is a discharge curve of pure phase rhombohedral phase lithium vanadium phosphate sodium circulating at-20 deg.C, it can be seen from the above three figures that after rhombohedral phase lithium vanadium phosphate sodium circulating for 1000 cycles at 0 deg.C, -10 deg.C, -20 deg.C, the capacity and voltage are almost not attenuated, indicating that the material has good circulation stability.
FIG. 13 is a circulation curve of rhombohedral phase lithium vanadium phosphate sodium at-10 ℃, and it can be known that after 5000 cycles of charge and discharge, the capacity retention rate is as high as 85%, and the coulombic efficiency is close to 100%, indicating that the material has good circulation stability and long circulation life.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. The application of the sodium vanadium phosphate material is characterized in thatIs prepared from rhombohedral phase lithium vanadium phosphate Li3-xNaxV2(PO4)3，0<x<3 as the anode active material applied to the anode of the low-temperature lithium ion battery,
rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate sodium material Li selected from pure phase3-xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Sodium vanadium phosphate Na mixed with rhombohedral phase3V2(PO4)3Mixed material of (1), and rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Rhombohedral phase sodium vanadium phosphate Na3V2(PO4)3And a small amount of monoclinic phase lithium vanadium phosphate Li3V2(PO4)3Wherein the monoclinic phase lithium vanadium phosphate Li is contained in the mixed material3V2(PO4)3The content of (b) is not more than 20% by mass of the whole positive electrode active material.
2. The use of the lithium vanadium phosphate sodium material as claimed in claim 1, characterized in that the rhombohedral phase lithium vanadium phosphate sodium material Li is3-xNaxV2(PO4)3Middle 0<x is less than or equal to 1, and when the rhombohedral phase lithium vanadium phosphate sodium material is represented as a mixed material, the monoclinic phase Li3V2(PO4)3The content of (b) is 10% or less of the total mass of the positive electrode active material.
3. The use of the lithium vanadium phosphate sodium material as claimed in claim 2 wherein the positive electrode active material is rhombohedral phase lithium vanadium phosphate sodium Li3-xNaxV2(PO4)3，0<x<3, the crystal structure of which belongs to rhombohedral system and has unit cell parameters of
α＝β＝90°，Gamma is 120 DEG, and when used as a positive electrode active material, the amount of gamma is 3.0 to 4.3V vs. Li+In the voltage range of/Li, a voltage platform is mainly shown on a charge-discharge curve.
4. The low-temperature lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm between the positive electrode and the negative electrode and electrolyte, and is characterized in that the positive electrode adopts rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3As a positive electrode active material, wherein 0<x<3，
The rhombohedral phase lithium vanadium phosphate sodium material Li3-xNaxV2(PO4)3Selected from pure phase lithium vanadium phosphate rhombic sodium material Li3- xNaxV2(PO4)3Rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Sodium vanadium phosphate Na mixed with rhombohedral phase3V2(PO4)3Mixed material of (1), and rhombohedral phase lithium vanadium phosphate Li3V2(PO4)3Rhombohedral phase sodium vanadium phosphate Na3V2(PO4)3And a small amount of monoclinic phase lithium vanadium phosphate Li3V2(PO4)3Wherein the monoclinic phase lithium vanadium phosphate Li is contained in the mixed material3V2(PO4)3The content of (a) is not more than 20% of the whole mass of the positive electrode active material;
the surface of the anode active material is provided with a conductive coating layer, or the anode active material and the conductive material are subjected to composite modification to improve the electrochemical performance of the anode material, wherein the conductive coating layer or the conductive material is selected from amorphous carbon, graphitized carbon, carbon nano tubes, carbon fibers, redox graphene, metal Ni, metal Al and metal Ti.
5. The low-temperature lithium ion battery of claim 4, wherein the negative active material of the negative electrode is selected from graphite, hard carbon, soft carbon and Li4Ti5O12、Li3VO4Elemental silicon and a conductive compound thereof, elemental germanium and a conductive compound thereof, elemental tin and a conductive compound thereof, elemental phosphorus and a conductive compound thereof, silicon-phosphorus alloy, germanium-phosphorus alloy, tin-phosphorus alloy, zinc-phosphorus alloy, phosphorus-antimony alloy, cobalt-tin alloy, copper-tin alloy and nickel-tin alloy,
the tin simple substance and the conductive compound thereof comprise a compound formed by the tin simple substance and one or more of carbon nano tubes, carbon black, graphene and metal,
the phosphorus simple substance and the conductive compound thereof comprise a compound formed by the phosphorus simple substance and one or more of carbon nano tubes, carbon black, graphene and metal,
the silicon simple substance and the conductive compound thereof comprise a compound formed by the silicon simple substance and one or more of carbon nano tubes, carbon black, graphene and metal,
the germanium simple substance and the conductive compound thereof comprise a compound formed by the germanium simple substance and one or more of carbon nano tubes, carbon black, graphene and metal.
6. The low-temperature lithium ion battery of claim 5, wherein the electrolyte comprises an organic solvent and a lithium salt, wherein the organic solvent is selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, ethyl methyl carbonate, ethyl acetate, and polycarbonate;
the lithium salt is selected from lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate and lithium bis (trifluoromethanesulfonyl) imide, wherein the concentration of the lithium salt is 1-5 mol/L.
7. The low-temperature lithium ion battery of claim 6, wherein an additive is further added to the electrolyte in an amount of 0.5-10% by mass based on the total mass of the electrolyte, and the additive is selected from fluoroethylene carbonate, lithium bis (oxalato) borate, vinylene carbonate, vinyl ethylene carbonate, dimethyl sulfite, diethyl sulfite, methyl vinyl sulfone, ethyl vinyl sulfone, and N, N-dimethyl trifluoroacetamide.
8. The low-temperature lithium ion battery according to claim 7, wherein the separator is a polyethylene microporous membrane, a polypropylene microporous membrane or a glass fiber microporous membrane for forming physical insulation between the positive electrode and the negative electrode,
besides active electrode materials, the positive electrode is also added with a conductive agent and a binder, and the negative electrode is also added with the conductive agent and the binder besides the active electrode materials.
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