CN114614018B - Lithium ion battery negative electrode material, preparation method thereof and lithium ion secondary battery - Google Patents

Lithium ion battery negative electrode material, preparation method thereof and lithium ion secondary battery Download PDF

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CN114614018B
CN114614018B CN202210306075.7A CN202210306075A CN114614018B CN 114614018 B CN114614018 B CN 114614018B CN 202210306075 A CN202210306075 A CN 202210306075A CN 114614018 B CN114614018 B CN 114614018B
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lithium
negative electrode
lithium ion
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郑卓群
许佳宁
申大卫
杜小红
王彪
费震宇
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Ningbo Meishan Free Trade Port Litai Enterprise Management Partnership LP
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Abstract

The invention relates to the field of lithium ion batteries, and discloses a lithium ion battery cathode material, a preparation method thereof and a lithium ion secondary battery. The negative electrode material is a lithium niobium titanium composite oxide, and the general formula of the negative electrode material is as follows: li 2δ Nb 2‑x Ta x TiO 7+δ Wherein, delta is more than or equal to 0.025 and less than or equal to 0.25,0 and less than or equal to 0.05. The preparation method comprises the following steps: mixing a lithium source compound, a niobium source compound, a tantalum source compound and a titanium source compound according to a stoichiometric ratio, and adding deionized water to prepare slurry; performing ball milling on the slurry, and then performing spray drying to obtain precursor powder; and roasting the precursor powder to obtain the cathode material. According to the invention, the lithium niobium titanium composite oxide with lower lithium content is used as the negative electrode material, so that the sintering temperature of the material can be reduced, and the side reaction of the material and the electrolyte can be effectively inhibited; meanwhile, the tantalum element is doped and modified, so that the specific capacity and the first charge-discharge efficiency of the material can be further improved, and the material has better rate performance.

Description

Lithium ion battery negative electrode material, preparation method thereof and lithium ion secondary battery
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a lithium ion battery cathode material, a preparation method thereof and a lithium ion secondary battery.
Background
At present, in the field of lithium ion secondary batteries, carbon materials are still the mainstream of negative electrode materials, wherein graphite is the most common, the theoretical specific capacity is about 370mAh/g, and the potential is about 0-0.2V (vs. Li/Li) + ). When graphite is charged with large multiplying power, the lithium intercalation potential of the graphite is very close to the lithium intercalation potential of metal, and the lithium metal is easy to precipitate on the surface of a pole piece due to concentration polarization, so that the safety performance and the cycle performance of the battery are influenced. Based on the alloy mechanism, the theoretical specific capacity of the cathode material such as simple substance silicon, simple substance tin and the like is 2-3 times or even close to 10 times of that of the graphite material, and the potential is about 0-0.45V (vs + ) The risk of lithium precipitation is reduced to a certain extent, but the structure of the material is damaged and pulverized along with huge volume change in the charging and discharging process, so that the material is separated from a conductive agent and the material is separated from a current collector, electron conduction is blocked, and finally the capacity of the material is sharply reduced, and the electrochemical performance of the battery is deteriorated. Li 4 Ti 5 O 12 Is another commercial material, like graphite, lithium storage is based on a deintercalation mechanism, with a potential of about 1.55V (vs. Li/Li) + ) And a lithium ion diffusion coefficient of 2X 10 -8 cm 2 and/S is higher than that of the common carbon-based material by one order of magnitude. Li 4 Ti 5 O 12 The charge and discharge platform is stable, under the condition of high-rate charge and discharge, lithium ions are not easy to precipitate on the surface of the material, the charge and discharge platform is a zero-strain material, crystals are very stable (although slight change occurs, the structure damage caused by the back-and-forth expansion and contraction of an electrode material in the charge and discharge process can be avoided unlike the graphite), and therefore the charge and discharge platform has excellent cycle performance. However, li 4 Ti 5 O 12 The theoretical specific capacity of the battery is only about 175mAh/g, the output voltage of the full battery is low, and the energy density cannot meet the requirements of various application scenes.
In order to improve the energy density of a lithium titanate battery and expand the application range while maintaining the advantages of the lithium titanate battery, a Chinese patent (CN 105990576B) discloses a niobium-titanium composite oxide negative electrode material. The niobium-titanium composite oxide has higher specific capacity and lower lithium intercalation potential. The theoretical specific capacity of the niobium-titanium composite oxide is up to 380mAh/g, and the lithium intercalation potential is reduced to about1.0V(vs.Li/Li + ) The material is a negative electrode material with a good application prospect. However, compared with lithium titanate having a spinel structure, niobium-titanium composite oxide has a high surface reactivity and is liable to cause a side reaction with an electrolyte, resulting in a large self-discharge capacity (self-discharge capacity per unit time) of the battery. Chinese patent (CN 112531143A) discloses a method for solving the above problems, i.e. by designing a double-layer electrode structure, the first layer of the electrode is niobium-titanium composite oxide, and the second layer is lithium titanate. Compared with monoclinic niobium-titanium composite oxides, the lithium titanate with the spinel structure has higher insulation resistance and lower surface activity, and can be used as an insulator to play a role when a battery is in a discharge state, so that the aim of reducing the self-discharge capacity can be fulfilled through the double-layer structure. However, the use of lithium titanate inevitably reduces the energy density of the battery, and is not an optimal solution. In addition, when the niobium titanium oxide composite oxide is synthesized by adopting a high-temperature solid phase method, the sintering temperature is higher, and the main sintering temperature range is generally 1000-1450 ℃ (Chinese patent CN 113745495A). The niobium-titanium-oxygen composite oxide material has poor electronic conductivity, and when the firing temperature is too high, crystal particles of the material grow excessively, so that the electronic conduction resistance is further increased, and the rate performance of the material is not favorably exerted. Therefore, it is also necessary to find a method for lowering the sintering temperature of the niobium-titanium-oxygen composite oxide.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a lithium ion battery cathode material, a preparation method thereof and a lithium ion secondary battery, wherein the lithium niobium titanium composite oxide with lower lithium content is adopted as the cathode material of the lithium ion secondary battery, so that the sintering temperature of the material can be reduced, and the side reaction of the material and electrolyte can be effectively inhibited, thereby reducing the self-discharge capacity of the battery; meanwhile, the lithium niobium titanium composite oxide is doped and modified by the tantalum element, so that the specific capacity and the first charge-discharge efficiency of the material can be further improved, and the material has better rate capability.
In order to achieve the purpose, the invention adopts the following technical scheme:
the negative electrode material of the lithium ion battery is a lithium-niobium-titanium compositeAn oxide having the general formula: li 2δ Nb 2-x Ta x TiO 7+δ Wherein, delta is more than or equal to 0.025 and less than or equal to 0.25,0 and less than or equal to 0.05.
Lithium is introduced into the niobium-titanium composite oxide to prepare the lithium-niobium-titanium composite oxide serving as a lithium ion battery cathode material. The value of delta in the general formula represents the percentage content of lithium element in the material, and the introduction of a lithium source compound can reduce the sintering temperature of the material, obtain nano-scale crystal grains under the condition of lower sintering temperature and improve the rate capability of the material; on the other hand, when the lithium ion secondary battery runs for a long time, lithium oxide can react with trace hydrofluoric acid in the electrolyte to generate lithium fluoride, the lithium fluoride generated in situ covers the surface of crystal grains to form an SEI (solid electrolyte interphase) film, the surface reactivity of the negative electrode material is reduced, the side reaction of the negative electrode material and the electrolyte is effectively inhibited, and the self-discharge capacity of the battery can be reduced. And, the content of lithium in the negative electrode material has a suitable interval: the lithium content is too high, and the alkalinity of the material is too strong, so that the electrolyte can be induced to generate a plurality of side reactions, such as the polymerization of a solvent, and the cycle performance of the lithium ion battery is influenced; in addition, in the manufacturing process of the battery, the alkalinity of the negative electrode material is too strong, and slurry with stable viscosity is not easy to prepare, so that the subsequent coating process is influenced. And if the lithium content is too low, the solid-phase reaction temperature of the material cannot be obviously reduced, and the electronic conductivity of the cathode material cannot be effectively improved due to overhigh firing temperature and overlarge material grains in the preparation process. The invention limits the lithium content in a proper range, can effectively reduce the sintering temperature of the material, improve the electronic conductivity of the cathode material, simultaneously effectively inhibit the side reaction of the material and the electrolyte and improve the cycling stability of the battery.
Meanwhile, the lithium niobium titanium composite oxide is doped with the tantalum element, the physical and chemical properties of tantalum and niobium are close to each other, the radius of tantalum atoms is larger, and the crystal structure of the lithium niobium titanium composite oxide can be improved through tantalum doping modification, so that the specific capacity and the first charge-discharge efficiency of the negative electrode material are further improved, and the lithium niobium titanium composite oxide has better rate capability.
Preferably, 0.075. Ltoreq. Delta. Ltoreq. 0.10,0. Ltoreq.X 0.05.
Preferably, 0.075. Ltoreq. Delta. Ltoreq. 0.10,0.0025. Ltoreq.X 0.025.
The invention also provides a preparation method of the lithium ion battery cathode material, which comprises the following steps:
(1) Mixing a lithium source compound, a niobium source compound, a tantalum source compound and a titanium source compound according to the stoichiometric ratio of Li, nb, ta and Ti, and adding deionized water to prepare slurry with the solid content of 30-70 wt%;
(2) Performing ball milling on the slurry, and then performing spray drying to obtain precursor powder;
(3) Roasting the precursor powder to obtain the negative electrode material; the roasting method comprises the following steps: presintering the precursor powder at 700-900 ℃ for 2-12 hours, and then firing at 900-1100 ℃ for 2-24 hours.
The introduction of the lithium source compound can reduce the solid phase reaction temperature from 1450 ℃ to below 1100 ℃, thereby not only reducing the energy consumption during roasting, but also inhibiting the growth of lithium niobium titanium composite oxide crystal grains and improving the electronic conductance of the cathode material.
Preferably, the lithium source compound in step (1) is at least one selected from the group consisting of lithium hydroxide, lithium oxyhydroxide, lithium oxide, lithium sulfide, lithium carbonate, lithium nitrate, lithium acetate and lithium halide;
the niobium source compound is selected from Nb 2 O 5 、NbO 2 At least one of;
the tantalum source compound is selected from Ta 2 O 5 、Ta 2 H、TaH、TaH 2 、TaH 3 At least one of;
the titanium source compound is selected from TiO 2 Titanium tetraisopropoxide, titanium tetrabutoxide and titanium tetrachloride.
Preferably, a chelating agent is further added into the slurry in the step (1), and the chelating agent is selected from at least one of cellulose, sucrose, glucose, citric acid, hexamethylenetetramine, glycine, salicylic acid, oxalic acid, malic acid, adipic acid, ethylenediamine tetraacetic acid, polyacrylic acid and polyethylene glycol; the mass of the chelating agent is 2-15% of the total mass of the slurry.
Preferably, the slurry is ball milled in step (2) until the particles have an average particle size of less than 0.5 microns. In the solid-phase reaction, the smaller the particle size of the raw material, the higher the reactivity, and the lower the calcination temperature.
More preferably, the slurry is ball milled in step (2) by means of a nano mill until the average particle size of the particles is less than 0.3 μm.
The invention also provides a lithium ion secondary battery, which comprises a negative electrode containing the lithium ion battery negative electrode material, a positive electrode containing a positive electrode active material, a diaphragm for separating the positive electrode and the negative electrode, and a non-aqueous electrolyte.
Preferably, the nonaqueous electrolytic solution comprises an organic solvent and an alkali metal salt, and the organic solvent comprises a carboxylic ester solvent with the following structure:
Figure GDA0003853553200000031
wherein R is selected from alkyl with 1-7 carbon atoms, R 'is hydrogen or alkyl with 1-7 carbon atoms, or R and R' are combined into a ring; the volume of the carboxylic ester solvent accounts for 70-90% of the total volume of the organic solvent.
Nb involves a change in valence state of a transition metal element accompanying repeated deintercalation of lithium ions 5+ And Nb 4+ And/or Nb 4+ And Nb 3+ And/or Ti 4+ With Ti 3+ Interconversion between them. The valence state change of the transition metal element can be selectively utilized by adjusting the voltage range. At present, people research niobium-titanium composite oxide materials, which are not related to compatibility/matching exploration with electrolyte, focuses on modification of the materials. In lithium ion batteries, a common non-aqueous electrolyte is LiPF 6 A system of mixed carbonate solvents; wherein the carbonate solvent is mainly a mixed solvent composed of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC). Commercialization of carbonate-based nonaqueous electrolytic solutions is based on research efforts for compatibility with carbon-based negative electrode materials. For example, carbonAcrylic ester (PC) is not suitable for a graphite cathode material, and PC molecules can be inserted into a graphite layer to ensure that a lithium storage mechanism (lithium ion extraction) fails; the EC can form an SEI film on the surface of the graphite electrode, so that the charge-discharge efficiency of the battery is improved, and the cycle life of the battery is prolonged. Unlike the carbon material, the lithium niobium titanium composite oxide contains a plurality of transition metal elements, and is accompanied by the change of multiple valence states of Nb and Ti in the process of repeated deintercalation of lithium ions. Carbon materials, which are composed mainly of carbon elements, have little oxidation or catalytic action on organic solvents and can be considered as chemically inert; the Nb and Ti elements have not only strong oxidizing property in a high valence state but also catalytic decomposition or catalytic polymerization to an organic solvent in a low valence state, and the situation is complicated. At present, lithium ion secondary batteries of niobium-titanium composite oxide systems have the problems of poor rate performance, large self-discharge capacity and the like, and have a long distance from commercialization. Besides the modification of the material itself, the search for the electrolyte matching with the material is also an important means for overcoming the bottleneck of the prior art.
Carbonates are chemically intrinsically highly active solvents, for example dimethyl carbonate (DMC) is a common methylating agent, which, under catalysis, gives a methyl substituent with the simultaneous release of the leaving methoxy and CO groups 2 . In contrast, carboxylic acid esters are much less capable of alkylation and are rarely used as alkylating agents, indicating that carboxylic acid esters have higher intrinsic chemical stability than carbonates. When the chemical activity of the cathode material is higher, the electrolyte system with weaker chemical activity is selected to be a reasonable and effective method. The research of the invention finds that the carboxylate solvent is particularly suitable for the nonaqueous electrolyte secondary battery taking the lithium niobium titanium composite oxide as the negative electrode material.
In the carboxylic ester solvent provided by the invention, R and R' are preferably selected from branched or unbranched alkyl with 1-7 carbon atoms; more preferably, the sum of the carbon atoms in the R and R' groups is greater than or equal to 3 and less than or equal to 10; it is further preferable that the total number of carbon atoms in the groups R and R' is not less than 4 and not more than 8.
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Preferably, the nonaqueous electrolytic solution further comprises an ionic liquid, and the cationic structure of the ionic liquid is selected from at least one of the following structures:
Figure GDA0003853553200000051
wherein, R, R' and R 1 、R 2 、R 3 、R 4 、R 5 、R 6 Are respectively selected from hydrogen or alkyl with 1 to 4 carbon atoms;
the anionic structure of the ionic liquid is selected from at least one of the following structures:
Figure GDA0003853553200000052
in order to improve the compatibility of the electrolyte and the lithium niobium titanium composite oxide material, the ionic liquid is added into the electrolyte. The ionic liquid has non-volatile property and almost no evaporationSteam pressure; the flame retardant still has good thermal stability at the temperature higher than 200 ℃ and has the characteristic of flame retardance; the ionic liquid has high conductivity up to 10 -2 S/cm, and therefore, the ionic liquid is preferable as a solvent for the high-temperature electrolyte. However, the ionic liquid electrolyte has not been industrially applied on a large scale. Except for the technical aspect of high difficulty in purifying the ionic liquid, the main reason is that the negative electrode material of the conventional lithium ion secondary battery mainly adopts a carbon material, the energy storage principle is based on a lithium ion de-intercalation mechanism with a layered structure, and cations of the ionic liquid can be embedded into a graphite layer under the action of an electric field to cause the failure of the energy storage mechanism. The energy storage mechanism of the lithium niobium titanium composite oxide material is based on the change of the chemical valence state of the transition metal element, does not depend on a layered structure, and can be compatible with the ionic liquid. By changing different combinations of cations and anions, different ionic liquids can be designed, and the ultrahigh-safety high-temperature power battery is expected to be obtained and can be applied to the field with harsh requirements on safety.
Preferably, the volume of the ionic liquid is 70% to 100%, preferably 85% to 100%, of the total volume of the organic solvent. Since the ionic liquid is nonflammable and the higher the content of the ionic liquid, the more flame retardancy of the electrolyte solution can be increased, the amount of the ionic liquid to be used is increased as much as possible in order to obtain a highly safe battery.
Preferably, the organic solvent in the nonaqueous electrolytic solution further includes at least one of a carbonate, a sulfite, a sulfonate, a sulfone, an ether, an organosilicon compound, an organoboron compound, a nitrile, an ionic liquid, and a phosphazene compound.
More preferably, the organic solvent in the nonaqueous electrolytic solution further includes at least one of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate, propylene methyl carbonate, propylene ethyl carbonate, phenol methyl carbonate, ethylene halogen carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, ethylene sulfite, propylene sulfite, butylene sulfite, dimethyl sulfite, diethyl sulfite, sulfolane, dimethyl sulfoxide, ethylmethylsulfoxide, 1,3-propanesulfonate, 1,4-butanesultone, dioxolane, dimethoxypropane, dimethyldimethoxysilane, pivalonitrile, valeronitrile, 2,2-dimethylvaleronitrile, ethoxypentafluorophosphononitrile, phenoxypentafluorophosphononitrile, N-methyl-N-butylpiperidine bis (trifluoromethylsulfonyl) imide salt and N-methyl-N-propylpyrrolidine bis (fluorosulfonyl) imide salt. Preferably, the carbonate includes cyclic carbonate and chain carbonate; the cyclic carbonate is at least one selected from ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate and alkenylene carbonate; the chain carbonate is at least one selected from dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.
Preferably, the alkali metal salt in the nonaqueous electrolytic solution is an alkali metal lithium salt and/or an alkali metal sodium salt; the alkali metal lithium salt is selected from LiPF 6 、LiBF 4 、LiN(SO 2 CF 3 ) 2 、LiN(SO 2 C 2 F 5 ) 2 、LiN(SO 2 F) 2 、LiPO 2 F 2 、LiCF 3 SO 3 、LiC(SO 2 CF 3 ) 3 、LiPF 3 (CF 3 ) 3 、LiPF 3 (C 2 F 5 ) 3 、LiPF 3 (iso-C 3 F 7 ) 3 、LiPF 5 (iso-C 3 F 7 )、LiB(C 2 O 4 ) 2 、LiBF 2 (C 2 O 4 ) And Li 2 B 12 F 12 At least one of; the alkali metal sodium salt is selected from NaPF 6 、NaBF 4 、NaN(SO 2 CF 3 ) 2 、NaN(SO 2 C 2 F 5 ) 2 、NaN(SO 2 F) 2 、NaPO 2 F 2 、NaCF 3 SO 3 、NaC(SO 2 CF 3 ) 3 、NaPF 3 (CF 3 ) 3 、NaPF 3 (C 2 F 5 ) 3 、NaPF 3 (iso-C 3 F 7 ) 3 、NaPF 5 (iso-C 3 F 7 )、NaBF 2 (C 2 O 4 ) And Na 2 B 12 F 12 At least one of (1).
Preferably, the total content of the alkali metal salt in the nonaqueous electrolytic solution is 0.5 to 3.0mol/L. More preferably, the total content of the alkali metal salt in the nonaqueous electrolytic solution is 0.8 to 2.5mol/L. More preferably, the total content of the alkali metal salt in the nonaqueous electrolytic solution is 0.9 to 1.5mol/L.
Preferably, the nonaqueous electrolytic solution further comprises an additive, and the additive comprises at least one of a film forming additive, an overcharge-preventing additive, a flame-retardant additive, a conductive additive and a wetting additive.
Preferably, the film forming additive comprises an organic film forming agent and an inorganic film forming agent; the organic film forming agent is selected from at least one of sulfate, sulfite, sulfone, sulfoxide, sulfonate, carbonate, halogenated carbonate, carboxylate, halogenated carboxylate, phosphate, halogenated phosphate, phosphite, halogenated phosphite, unsaturated carbonate containing double bonds, nitrile, crown ether and organic boride; the inorganic film-forming agent is selected from LiBOB, liODBF, naBOB, naODBF, li 2 CO 3 、Na 2 CO 3 、K 2 CO 3 And NH 4 At least one of I. Further preferably, the organic film forming agent is selected from at least one of Vinylene Carbonate (VC), vinyl Ethylene Carbonate (VEC), phenyl ethylene carbonate (PhEC), phenyl vinylene carbonate (PhVC), allyl Methyl Carbonate (AMC), allyl Ethyl Carbonate (AEC), ethylene Sulfite (ES), propylene Sulfite (PS), dimethyl sulfite (DMS), diethyl sulfite (DES), 1,3-propane sultone (1,3-PS), acrylonitrile (AAN), vinyl chlorocarbonate (ClEC), vinyl Fluorocarbonate (FEC), propylene Trifluorocarbonate (TFPC), bromo γ -butyrolactone (BrGBL), fluoro γ -butyrolactone (FGBL), glutaric Anhydride (GA), and Succinic Anhydride (SA).
Preferably, the wetting additive is at least one selected from the group consisting of quaternary ammonium surfactants, and carbonate compounds containing aromatic groups or long chain hydrocarbon groups. Preferably, the wetting additive is selected from methyl phenyl carbonate and/or bisoctyl carbonate.
Preferably, the total mass of the additives is 0 to 15.0% of the mass of the nonaqueous electrolytic solution. Preferably, the total mass of the additives is 0 to 5.0% of the mass of the nonaqueous electrolytic solution. More preferably, the total mass of the additives is 0 to 3.0% of the mass of the nonaqueous electrolytic solution. More preferably, the total mass of the additives is 1.0 to 10.0% of the mass of the nonaqueous electrolytic solution.
Preferably, the positive electrode active material is at least one selected from the group consisting of lithium nickel cobalt manganese composite oxide, sodium nickel cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, lithium manganese nickel composite oxide, olivine-type lithium phosphorus oxide, lithium cobalt oxide, sodium cobalt oxide, lithium manganese oxide, sodium manganese oxide, and sodium titanium nickel composite oxide.
Preferably, the positive electrode active material is lithium manganese iron phosphate (LiMn) 1-x Fe x PO 4 ，0<X<1). The material cost of the lithium manganese iron phosphate is lower than that of a ternary material, and the voltage platform is higher than that of the lithium iron phosphate, so that the lithium manganese iron phosphate is a material suitable for being paired with a lithium niobium titanium composite oxide.
Preferably, the positive electrode active material is a spinel-type lithium manganese nickel composite oxide. When the spinel type lithium manganese nickel composite oxide is used as a high-voltage positive electrode material and matched with the lithium niobium titanium composite oxide, the median voltage of the whole battery can reach more than 3V, and the energy density of the battery is greatly improved.
Therefore, the invention has the following beneficial effects:
(1) The lithium niobium titanium composite oxide is adopted as the lithium ion battery cathode material, and a lithium element with lower content is introduced into the composite oxide, so that on one hand, the sintering temperature of the material can be reduced, and the rate capability of the material is improved; on the other hand, the surface reactivity of the negative electrode material can be reduced, and the side reaction of the negative electrode material and the electrolyte can be effectively inhibited, so that the self-discharge capacity of the battery can be reduced;
(2) The lithium niobium titanium composite oxide is doped with the tantalum element, so that the crystal structure of the lithium niobium titanium composite oxide can be improved, the specific capacity and the first charge-discharge efficiency of the negative electrode material are further improved, and the negative electrode material has better rate capability;
(3) And the components of the non-aqueous electrolyte are screened and limited, so that the compatibility of the electrolyte and the lithium niobium titanium composite oxide material is improved.
Drawings
Fig. 1 is an SEM image of the lithium niobium titanium composite oxide negative electrode material produced in example 1.
Fig. 2 is an SEM image of the tantalum-doped lithium niobium titanium composite oxide negative electrode material prepared in example 4.
Fig. 3 is an SEM image of the niobium-titanium composite oxide anode material prepared in comparative example 1.
Fig. 4 is a graph comparing the rate performance of the batteries in example 1 and example 4.
Detailed Description
The invention is further described with reference to the following detailed description and accompanying drawings.
The structure of the lithium ion secondary battery is not limited, and the lithium ion secondary battery can be cylindrical, square or button type, flexible package or steel shell or aluminum shell. In the embodiment of the invention, a 2025 type button battery is used as a half battery to evaluate the physical and chemical properties of the cathode material; the full cell adopts a square aluminum shell structure, and the size model is 21115106.
LiNi is adopted as the positive electrode active material of the full cell 0.5 Co 0.2 Mn 0.3 O 2 (NCM 523) and lithium manganese iron phosphate (LiMn) 1- x Fe x PO 4 ，0<X<1) And nickel manganese binary LiMn 0.5 Ni 1.5 O 4 (ii) a The negative electrode materials prepared in the respective examples were used.
When the performance of the material and the electrolyte is evaluated by using a half-cell, mixing a negative electrode material, a conductive agent acetylene black and a binder polyvinylidene fluoride (PVDF) according to a mass ratio of 80. The slurry was coated on a copper foil having a thickness of 20 μm, and then vacuum-dried at 120 ℃ and punched into a circular piece having a diameter of about 14mm to prepare an electrode. A sheet of lithium metal was used as the counter electrode. The separator was a porous polyethylene film with a thickness of 20 μm, assembled into a 2025 type button cell in an Ar-protected glove box.
Example 1:
a lithium ion battery negative electrode material has a general formula: li 0.15 Nb 2 TiO 7.075 The preparation method comprises the following steps:
respectively weighing lithium source compounds LiOH & H according to the stoichiometric ratio of Li, nb and Ti 2 O, niobium source compound Nb 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the mixture into deionized water to prepare slurry with the solid content of 40 wt%; sampling the slurry after nano-grinding for 2 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; the precursor powder is roasted for 4 hours at 800 ℃, and then is roasted for 12 hours at 1000 ℃ to obtain the cathode material, wherein the roasting atmosphere is air. The SEM image of the obtained lithium niobium titanium composite oxide negative electrode material is shown in fig. 1.
Manufacturing a half cell: preparing an electrolyte: mixing ethyl n-propionate, propylene carbonate, ethylene carbonate and ethyl methyl carbonate according to a volume ratio of 70 6 Cooling to form a non-aqueous electrolyte with the concentration of 1.1 mol/L; (2) assembling the battery: active material using Li prepared as described above 0.15 Nb 2 TiO 7.075 The counter electrode was made of lithium metal and the nonaqueous electrolyte was composed as described above, and a 2025 type button cell was assembled.
The half cell test method comprises the following steps: and (3) at normal temperature, charging and discharging the button cell in a voltage range of 1.0-2.5V, wherein the constant current charging rate is 0.1C and the constant current discharging rate is 0.1C, inspecting the first charging and discharging curve and the first charging and discharging efficiency, and calculating the gram capacity of the material. And the rate performance and the cycling stability of the half cell were examined.
Example 2:
a lithium ion battery negative electrode material has a general formula: li 0.05 Nb 2 TiO 7.025 The preparation method comprises the following steps:
respectively weighing lithium source compounds LiOH & H according to the stoichiometric ratio of Li, nb and Ti 2 O, niobium source compound Nb 2 O 5 And a compound of titanium source TiO 2 Are added slowly toPreparing slurry with solid content of 50wt% in ionized water, and adding chelating agent citric acid accounting for 2% of the total mass of the slurry; sampling the slurry after nano-grinding for 1 hour for particle size analysis, wherein the average particle size of particles is less than 0.5 micron; spray drying to obtain precursor powder; the precursor powder is roasted for 4 hours at 800 ℃, and then is roasted for 12 hours at 1100 ℃ to obtain the cathode material, wherein the roasting atmosphere is air.
Manufacturing a half cell: preparing an electrolyte: mixing n-butyl acetate and propylene carbonate according to a volume ratio of 90 6 And LiPO 2 F 2 (the molar ratio of the two is 9.5; (2) assembling the battery: active material using Li prepared as above 0.05 Nb 2 TiO 7.025 The 2025 type button cell was assembled by using metallic lithium as the counter electrode and the nonaqueous electrolyte composition as described above.
The half-cell test method comprises the following steps: and (3) at normal temperature, charging and discharging the button cell in a voltage range of 1.0-2.5V, wherein the constant current charging rate is 0.1C and the constant current discharging rate is 0.1C, inspecting the first charging and discharging curve and the first charging and discharging efficiency, and calculating the gram capacity of the material. And the rate performance and the cycling stability of the half cell were examined.
Example 3:
a lithium ion battery negative electrode material has a general formula: li 0.50 Nb 2 TiO 7.25 The preparation method comprises the following steps:
respectively weighing lithium source compounds Li according to the stoichiometric ratio of Li, nb and Ti 2 CO 3 Niobium source compound Nb 2 O 5 And a compound of titanium origin TiO 2 Respectively and slowly adding the mixture into deionized water to prepare slurry with the solid content of 30wt%, and adding chelating agent glucose accounting for 5% of the total mass of the slurry; sampling the slurry after nano-grinding for 4 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; the precursor powder is roasted for 12 hours at 700 ℃, and then is roasted for 24 hours at 900 ℃ to obtain the cathode material, wherein the roasting atmosphere is air.
Manufacturing a half cell: preparing an electrolyte: mixing ethyl n-butyrate, methyl pivalate, ethyl methyl carbonate and propylene carbonate according to a volume ratio of 70 6 、LiBF 4 、LiN(SO 2 F) 2 (the molar ratio of the three is 9: 0.5), and cooling is carried out to form a nonaqueous electrolytic solution with the concentration of 1.2 mol/L; (2) assembling the battery: active material using Li prepared as above 0.50 Nb 2 TiO 7.25 The counter electrode was made of lithium metal and the nonaqueous electrolyte was composed as described above, and a 2025 type button cell was assembled.
The half-cell test method comprises the following steps: and (3) at normal temperature, charging and discharging the button cell in a voltage range of 1.0-2.5V, wherein the constant current charging rate is 0.1C and the constant current discharging rate is 0.1C, inspecting the first charging and discharging curve and the first charging and discharging efficiency, and calculating the gram capacity of the material. And the rate performance and the cycling stability of the half cell were examined.
Example 4:
a lithium ion battery negative electrode material has a general formula: li 0.15 Nb 1.95 Ta 0.05 TiO 7.075 The preparation method comprises the following steps:
respectively weighing lithium source compounds LiOH & H according to the stoichiometric ratio of Li, nb, ta and Ti 2 O, niobium source compound Nb 2 O 5 Tantalum source compound Ta 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the mixture into deionized water to prepare slurry with the solid content of 40 wt%; sampling the slurry after nano-grinding for 2 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; the precursor powder is roasted for 4 hours at 800 ℃, and then is roasted for 12 hours at 1000 ℃ to obtain the cathode material, wherein the roasting atmosphere is air. An SEM image of the obtained tantalum-doped lithium niobium titanium composite oxide negative electrode material is shown in fig. 2.
Manufacturing a half cell: preparing an electrolyte: the same as example 1; (2) assembling the battery: active material using Li prepared as above 0.15 Nb 1.95 Ta 0.05 TiO 7.075 The counter electrode is made of metallic lithium and the nonaqueous electrolyte is composed as described aboveAnd assembling the button cell 2025.
The half cell test method comprises the following steps: and (3) at normal temperature, charging and discharging the button cell in a voltage range of 1.0-2.5V, wherein the constant current charging rate is 0.1C and the constant current discharging rate is 0.1C, inspecting the first charging and discharging curve and the first charging and discharging efficiency, and calculating the gram capacity of the material. And the rate performance and the cycling stability of the half cell were examined.
Example 5:
a lithium ion battery negative electrode material has a general formula: li 0.10 Nb 1.9975 Ta 0.0025 TiO 7.05 The preparation method comprises the following steps:
respectively weighing lithium source compounds Li according to the stoichiometric ratio of Li, nb, ta and Ti 2 CO 3 Niobium source compound Nb 2 O 5 Tantalum source compound Ta 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the components into deionized water to prepare slurry with the solid content of 40 wt%; after the slurry is subjected to nano-grinding for 2 hours, sampling and carrying out particle size analysis, wherein the average particle size of particles is less than 0.3 micrometer; spray drying to obtain precursor powder; the precursor powder is roasted for 4 hours at 900 ℃, and then is roasted for 12 hours at 1050 ℃ to obtain the cathode material, wherein the roasting atmosphere is air.
Manufacturing a half cell: preparing an electrolyte: mixing ethyl n-propionate, propylene carbonate, ethylene carbonate and ethyl methyl carbonate according to a volume ratio of 70 6 Cooling to form a non-aqueous electrolyte with the concentration of 1.1 mol/L; (2) assembling the battery: active material using Li prepared as described above 0.10 Nb 1.9975 Ta 0.0025 TiO 7.05 The 2025 type button cell was assembled by using metallic lithium as the counter electrode and the nonaqueous electrolyte composition as described above.
The half cell test method comprises the following steps: and (3) at normal temperature, charging and discharging the button cell in a voltage range of 1.0-2.5V, wherein the constant current charging rate is 0.1C and the constant current discharging rate is 0.1C, inspecting the first charging and discharging curve and the first charging and discharging efficiency, and calculating the gram capacity of the material. And the rate performance and the cycling stability of the half cell were examined.
Example 6:
a lithium ion battery negative electrode material has a general formula: li 0.10 Nb 1.9975 Ta 0.0025 TiO 7.05 The preparation method comprises the following steps:
respectively weighing lithium source compounds LiOH & H according to the stoichiometric ratio of Li, nb, ta and Ti 2 O, niobium source compound Nb 2 O 5 Tantalum source compound Ta 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the mixture into deionized water to prepare slurry with the solid content of 40 wt%; sampling the slurry after nano-grinding for 2 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; the precursor powder is roasted for 4 hours at 900 ℃, and then is roasted for 12 hours at 1050 ℃ to obtain the cathode material, wherein the roasting atmosphere is air.
Manufacturing a half cell: preparing an electrolyte: mixing gamma-butyrolactone, ethyl propionate, ethylene carbonate and methyl ethyl carbonate according to a volume ratio of 30 6 Cooling to form a non-aqueous electrolyte with the concentration of 1.1 mol/L; then adding film forming additives of Vinylene Carbonate (VC) and Vinyl Ethylene Carbonate (VEC) which account for 2 percent of the total mass of the electrolyte; (2) assembling the battery: active material using Li prepared as described above 0.10 Nb 1.9975 Ta 0.0025 TiO 7.05 The counter electrode was made of lithium metal and the nonaqueous electrolyte was composed as described above, and a 2025 type button cell was assembled.
The half-cell test method comprises the following steps: and (3) at normal temperature, charging and discharging the button cell in a voltage range of 1.0-2.5V, wherein the constant current charging rate is 0.1C and the constant current discharging rate is 0.1C, inspecting the first charging and discharging curve and the first charging and discharging efficiency, and calculating the gram capacity of the material. And the rate capability and the cycling stability of the half-cell were examined.
Example 7:
a lithium ion battery negative electrode material has a general formula: li 0.20 Nb 1.995 Ta 0.005 TiO 7.10 The preparation method comprises the following steps:
respectively weighing according to the stoichiometric ratio of Li, nb, ta and TiTaking a lithium source compound LiOH & H 2 O, niobium source compound Nb 2 O 5 Tantalum source compound Ta 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the components into deionized water to prepare slurry with the solid content of 40 wt%; sampling the slurry after nano-grinding for 2 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; the precursor powder is roasted for 2 hours at 900 ℃, and then is roasted for 24 hours at 1000 ℃ to obtain the cathode material, wherein the roasting atmosphere is air.
Manufacturing a half cell: preparing an electrolyte: mixing Propylene Carbonate (PC) and N-methyl-N-propyl pyrrolidine bis (trifluorosulfonyl) imide (PP) 1,3 TFSI) was mixed in a volume ratio of 15 6 And lithium bistrifluoromethylsulfonyl imide (LiTFSI) and cooling, wherein the molar ratio of the lithium bistrifluoromethylsulfonyl imide to the lithium bistrifluoromethylsulfonyl imide (LiTFSI) is 5:5, and a nonaqueous electrolytic solution with the electrolyte salt concentration of 1.0mol/L is formed; then adding ethoxy pentafluorophosphazene, which accounts for 5 percent of the total mass of the electrolyte; (2) assembling the battery: active material using Li prepared as above 0.20 Nb 1.995 Ta 0.005 TiO 7.10 The 2025 type button cell was assembled by using metallic lithium as the counter electrode and the nonaqueous electrolyte composition as described above.
The half cell test method comprises the following steps: and (3) at normal temperature, charging and discharging the button cell in a voltage range of 1.0-2.5V, wherein the constant current charging rate is 0.1C and the constant current discharging rate is 0.1C, inspecting the first charging and discharging curve and the first charging and discharging efficiency, and calculating the gram capacity of the material. And the rate performance and the cycling stability of the half cell were examined.
Example 8:
a lithium ion battery negative electrode material has a general formula: li 0.25 Nb 1.99 Ta 0.01 TiO 7.125 The preparation method comprises the following steps:
respectively weighing lithium source compound lithium nitrate and niobium source compound NbO according to the stoichiometric ratio of Li, nb, ta and Ti 2 Tantalum source compound Ta 2 O 5 And titanium source compound titanium tetraisopropoxide, which are respectively and slowly added into deionized water to prepare slurry with the solid content of 40wt%, and the slurry is addedAdding glucose as a chelating agent accounting for 5 percent of the total mass of the slurry; sampling the slurry after nano-grinding for 2 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; the precursor powder is firstly roasted for 2 hours at 900 ℃, and then is roasted for 8 hours at 1000 ℃ to obtain the cathode material, wherein the roasting atmosphere is air.
Manufacturing a half cell: preparing an electrolyte: in N-methyl-N-propylpyrrolidine bis (trifluorosulfonyl) imide salt (PP) 1, 3 TFSI) (ionic liquid accounts for 100 percent of the solvent volume) and electrolyte salt LiPF is slowly added 6 And lithium bistrifluoromethylsulfonyl imide (LiTFSI) and cooling, wherein the molar ratio of the lithium bistrifluoromethylsulfonyl imide to the lithium bistrifluoromethylsulfonyl imide (LiTFSI) is 5:5, and a nonaqueous electrolytic solution with the electrolyte salt concentration of 1.0mol/L is formed; (2) assembling the battery: active material using Li prepared as above 0.25 Nb 1.99 Ta 0.01 TiO 7.125 The counter electrode was made of lithium metal and the nonaqueous electrolyte was composed as described above, and a 2025 type button cell was assembled.
The half cell test method comprises the following steps: and (3) at normal temperature, the button cell is charged and discharged within the voltage range of 1.0-3.0V, the constant current charging rate is 0.02C, the constant current discharging rate is 0.02C, the first charging and discharging curve and the first charging and discharging efficiency of the button cell are inspected, and the gram capacity of the material is calculated.
Example 9:
the general formula and preparation method of the lithium ion battery negative electrode material are the same as those of example 1.
The electrolyte preparation method in the half cell comprises the following steps: preparing a non-aqueous mixed solvent of dimethyl carbonate (DMC), ethyl Methyl Carbonate (EMC) and Propylene Carbonate (PC), wherein the volume ratio of the non-aqueous mixed solvent to the non-aqueous mixed solvent is 30 6 And cooled to form a nonaqueous electrolytic solution having a concentration of 1.1 mol/L. The rest is the same as in example 1.
Example 10:
a lithium ion battery negative electrode material has a general formula: li 0.15 Nb 1.975 Ta 0.025 TiO 7.075 The preparation method comprises the following steps:
respectively weighing lithium source compounds LiOH & H according to the stoichiometric ratio of Li, nb, ta and Ti 2 O, niobium source compound Nb 2 O 5 Tantalum source compound Ta 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the mixture into deionized water to prepare slurry with the solid content of 40 wt%; after the slurry is subjected to nano-grinding for 2 hours, sampling and carrying out particle size analysis, wherein the average particle size of particles is less than 0.3 micrometer; spray drying to obtain precursor powder; the precursor powder is roasted for 4 hours at 800 ℃, and then is roasted for 12 hours at 1000 ℃ to obtain the cathode material, wherein the roasting atmosphere is air.
Manufacturing a full battery: preparing an electrolyte: mixing ethyl n-butyrate, ethyl propionate, gamma-butyrolactone, ethyl methyl carbonate and propylene carbonate according to a volume ratio of 40 6 And LiN (SO) 2 F) 2 (the molar ratio of the two is 9:1) and cooling to form a nonaqueous electrolytic solution with the concentration of 1.2 mol/L; then adding film forming additives of Vinylene Carbonate (VC) and Vinyl Ethylene Carbonate (VEC) which account for 2 percent of the total mass of the electrolyte; (2) assembling the battery: the positive electrode material adopts LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM 523) as a negative electrode material, using the Li prepared above 0.15 Nb 1.975 Ta 0.025 TiO 7.075 The electrolyte composition is as described above, and the separator is a wet polyethylene separator and assembled into a square aluminum-shell battery (21115106).
The full battery test method comprises the following steps: under normal temperature conditions, the battery was charged and discharged at a voltage range of 1.5 to 3.2V, with a constant current charge rate of 1C, a constant voltage (3.2V) charge cutoff current of 0.1C, and a constant current discharge rate of 1C, and the development of capacity and charge-discharge cycle stability were examined. The fully charged battery was left in an oven environment at 60 ℃ for 7 days, the capacity of the battery was measured, and the self-discharge amount (capacity retention ratio) thereof was calculated.
Example 11:
the general formula and preparation method of the lithium ion battery negative electrode material are the same as those of example 10.
In the full cell, the positive active material adopts lithium iron manganese phosphate (LiMn) 0.6 Fe 0.4 PO 4 ) Otherwise, the same as in example 10 was repeated.
The full battery test method comprises the following steps: under normal temperature conditions, the battery was charged and discharged at a voltage range of 1.5 to 3.1V, with a constant current charge rate of 0.2C, a constant voltage (3.1V) charge cutoff current of 0.05C, and a constant current discharge rate of 0.2C, and the capacity and charge-discharge cycle stability were examined.
Example 12:
the general formula and preparation method of the lithium ion battery negative electrode material are the same as those of example 10.
In the full-cell, the positive active material adopts spinel nickel manganese composite oxide (LiNi) 0.5 Mn 1.5 O 4 ) Otherwise, the same as in example 10 was repeated.
The full battery test method comprises the following steps: the battery was charged and discharged at a voltage of 1.5 to 3.7V, with a constant current charge rate of 0.2C, a constant voltage (3.7V) charge cutoff current of 0.05C, and a constant current discharge rate of 0.2C, and the capacity and charge-discharge cycle stability were examined.
Comparative example 1:
a lithium ion battery negative electrode material has a general formula: nb 2 TiO 7 The preparation method comprises the following steps:
weighing niobium source compound Nb according to the stoichiometric ratio of Nb and Ti 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the mixture into deionized water to prepare slurry with the solid content of 40 wt%; sampling the slurry after nano-grinding for 2 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; the precursor powder is firstly roasted for 4 hours at 900 ℃, and then is roasted for 12 hours at 1200 ℃ to obtain the cathode material, wherein the roasting atmosphere is air. The SEM image of the obtained niobium-titanium composite oxide negative electrode material is shown in fig. 3.
The half-cell fabrication and performance testing methods were the same as in example 1.
Comparative example 2 (lithium content too high):
a lithium ion battery negative electrode material has a general formula: liNb 2 TiO 7.5 The preparation method comprises the following steps:
respectively weighing lithium source compounds LiOH & H according to the stoichiometric ratio of Li, nb and Ti 2 O, niobium source compound Nb 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the mixture into deionized water to prepare slurry with the solid content of 40 wt%; sampling the slurry after nano-grinding for 2 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; the precursor powder is roasted for 4 hours at 800 ℃, and then is roasted for 12 hours at 1000 ℃ to obtain the cathode material, wherein the roasting atmosphere is air.
The half-cell fabrication and performance testing methods were the same as in example 1.
Comparative example 3 (tantalum instead of niobium):
a lithium ion battery negative electrode material has a general formula: li 0.15 Ta 2 TiO 7.075 The preparation method comprises the following steps:
respectively weighing lithium source compounds LiOH & H according to the stoichiometric ratio of Li, ta and Ti 2 O, tantalum source compound Ta 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the mixture into deionized water to prepare slurry with the solid content of 40 wt%; sampling the slurry after nano-grinding for 2 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; the precursor powder is roasted for 4 hours at 800 ℃, and then is roasted for 12 hours at 1000 ℃ to obtain the cathode material, wherein the roasting atmosphere is air.
The half-cell fabrication and performance testing methods were the same as in example 1.
Comparative example 4 (too high tantalum doping):
a lithium ion battery negative electrode material has a general formula: li 0.15 Nb 1.90 Ta 0.10 TiO 7.075 The preparation method comprises the following steps:
respectively weighing lithium source compounds LiOH & H according to the stoichiometric ratio of Li, nb, ta and Ti 2 O, niobium source compound Nb 2 O 5 Tantalum source compound Ta 2 O 5 And a compound of titanium source TiO 2 Respectively and slowly adding the components into deionized water to prepare slurry with the solid content of 40 wt%; sampling the slurry after nano-grinding for 2 hours for particle size analysis, wherein the average particle size of particles is less than 0.3 micron; spray drying to obtain precursor powder; firstly, precursor powder is preparedAnd roasting the material at 800 ℃ for 4 hours, and then roasting the material at 1000 ℃ for 12 hours to obtain the cathode material, wherein the roasting atmosphere is air.
The half-cell fabrication and performance testing methods were the same as in example 4.
The results of the half cell performance test obtained in the above examples and comparative examples are shown in table 1, and the results of the full cell performance test are shown in table 2.
Table 1: and testing the performance of the half cell.
Negative electrode material Specific capacity (mAh/g) First efficiency (%)
Example 1 Li 0.15 Nb 2 TiO 7.075 270 92
Example 2 Li 0.05 Nb 2 TiO 7.025 260 89
Example 3 Li 0.50 Nb 2 TiO 7.25 272 92
Example 4 Li 0.15 Nb 1.95 Ta 0.05 TiO 7.075 278 93
Example 5 Li 0.10 Nb 1.9975 Ta 0.0025 TiO 7.05 265 91
Example 6 Li 0.10 Nb 1.9975 Ta 0.0025 TiO 7.05 268 90
Example 7 Li 0.20 Nb 1.995 Ta 0.005 TiO 7.10 238 85
Example 8 Li 0.25 Nb 1.99 Ta 0.01 TiO 7.125 222 83
Example 9 Li 0.15 Nb 2 TiO 7.075 260 88
Comparative example 1 Nb 2 TiO 7 254 89
Comparative example 2 LiNb 2 TiO 7.5 258 91
Comparative example 3 Li 0.15 Ta 2 TiO 7.075 170 85
Comparative example 4 Li 0.15 Nb 1.90 Ta 0.10 TiO 7.075 268 92
Table 2: and (5) testing the performance of the full cell.
Figure GDA0003853553200000151
As can be seen from fig. 1, 2 and 3, by introducing a proper amount of lithium source compound, nanoscale primary grains can be obtained at a lower sintering temperature, and the grain structure and morphology can be improved after tantalum doping.
As can be seen from the data in table 1, in example 1, compared with comparative example 1, the introduction of lithium element into the composite oxide can reduce the surface reactivity of the material, and effectively inhibit the side reaction between the material and the electrolyte, thereby reducing the self-discharge capacity of the battery, and significantly improving the specific capacity and the first charge-discharge efficiency of the battery. Compared with the embodiment 1, the embodiment 4 has the advantages that the lithium niobium titanium composite oxide is doped by the tantalum element, so that the specific capacity and the first charge and discharge efficiency of the material are further improved, and the material has better rate performance (see fig. 4).
On the other hand, when the content of lithium element in comparative example 2 is too high, on the one hand, the material sinters due to the too high content of lithium, and primary grains excessively grow at a lower sintering temperature, so that the performance of the material is deteriorated in contrast to that in example 1; on the other hand, the lithium source compound is expensive, and the material cost is increased, which is not favorable for practical use. In comparative example 3, tantalum is used to replace niobium in example 1 to prepare lithium tantalum titanium composite oxide as a negative electrode material, and the tantalum atom has too large mass, which results in very low specific capacity of the material, and tantalum is a rare element and is expensive and too high in material cost. Similarly, in the comparative example 4, too much tantalum element is doped in the lithium niobium titanium composite oxide, which also causes the specific capacity of the material to be reduced, and is not beneficial to the improvement of the battery performance.
As can be seen from a comparison of the data in table 1 between example 1 and example 9, the composition of the nonaqueous electrolytic solution also has a significant effect on the battery performance. In example 9, the conventional nonaqueous electrolytic solution mainly containing a carbonate solvent is used, and the secondary reaction with the negative electrode material is large, the lithium ion deintercalation reversibility is poor, and the first charge-discharge efficiency is significantly reduced as compared with example 1. The invention adopts non-carbonate solvent, especially non-aqueous electrolyte mainly comprising carboxylate solvent, which can obviously improve the first charge-discharge efficiency, thereby improving the charge-discharge cycle stability.
As can be seen from the data in table 2, the full battery made of the tantalum-doped lithium niobium titanium composite oxide negative electrode material prepared by the method has higher capacity and good cycle performance.

Claims (6)

1. The lithium ion battery negative electrode material is characterized in that the negative electrode material is a lithium niobium titanium composite oxide, and the general formula of the negative electrode material is as follows: li 2δ Nb 2-x Ta x TiO 7+δ Wherein，0.075≤δ≤0.10，0.0025≤X≤0.025；
The preparation method of the anode material comprises the following steps:
(1) Mixing a lithium source compound, a niobium source compound, a tantalum source compound and a titanium source compound according to the stoichiometric ratio of Li, nb, ta and Ti, and adding deionized water to prepare slurry;
(2) Performing ball milling on the slurry, and then performing spray drying to obtain precursor powder;
(3) Roasting the precursor powder to obtain the negative electrode material; the roasting method comprises the following steps: presintering the precursor powder at 700-900 ℃ for 2-12 hours, and then firing at 900-1100 ℃ for 2-24 hours.
2. The negative electrode material of a lithium ion battery according to claim 1, wherein the lithium source compound in step (1) is at least one selected from the group consisting of lithium hydroxide, lithium oxyhydroxide, lithium oxide, lithium sulfide, lithium carbonate, lithium nitrate, lithium acetate and lithium halide;
the niobium source compound is selected from Nb 2 O 5 、NbO 2 At least one of;
the tantalum source compound is selected from Ta 2 O 5 、Ta 2 H、TaH、TaH 2 、TaH 3 At least one of;
the titanium source compound is selected from TiO 2 Titanium tetraisopropoxide, titanium tetrabutoxide and titanium tetrachloride.
3. The negative electrode material of the lithium ion battery as claimed in claim 1 or 2, wherein a chelating agent is further added to the slurry in step (1), wherein the chelating agent is at least one selected from cellulose, sucrose, glucose, citric acid, hexamethylenetetramine, glycine, salicylic acid, oxalic acid, malic acid, adipic acid, ethylenediaminetetraacetic acid, polyacrylic acid, and polyethylene glycol; the mass of the chelating agent is 2-15% of the total mass of the slurry.
4. The negative electrode material of a lithium ion battery as claimed in claim 1, wherein the slurry is ball milled in step (2) until the average particle size of the particles is less than 0.5 μm.
5. A lithium ion secondary battery comprising a negative electrode containing the negative electrode material for lithium ion batteries according to any one of claims 1 to 4, a positive electrode containing a positive electrode active material, a separator for separating the positive electrode and the negative electrode, and a nonaqueous electrolytic solution; the non-aqueous electrolyte comprises an organic solvent and an alkali metal salt, wherein the organic solvent comprises a carboxylic ester solvent with the following structure:
Figure FDA0003853553190000011
wherein R is selected from alkyl with 1-7 carbon atoms, R 'is hydrogen or alkyl with 1-7 carbon atoms, or R and R' are combined into a ring;
the volume of the carboxylic ester solvent accounts for 70-90% of the total volume of the organic solvent.
6. The lithium ion secondary battery according to claim 5, wherein the positive electrode active material is at least one selected from the group consisting of lithium nickel cobalt manganese complex oxide, sodium nickel cobalt complex oxide, lithium nickel cobalt aluminum complex oxide, lithium manganese nickel complex oxide, olivine-type lithium phosphorus oxide, lithium cobalt oxide, sodium cobalt oxide, lithium manganese oxide, sodium manganese oxide, and sodium titanium nickel complex oxide.
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