CN103594685A - Preparation method of lithium ion battery positive electrode material modified molybdenum trioxide - Google Patents

Abstract

The invention discloses a preparation method of modified molybdenum trioxide, which is a cathode material of a lithium ion battery. Molybdenum trioxide material, the molecular formula is (ZnO) _x (MoO ₃ ) _1-x (0< x ≤0.1); add the intermediate product to the mixed solvent of water and absolute ethanol, drop by drop into the mixed system under stirring Drop titanate and add a hydrolysis accelerator, so that the hydrated titanium dioxide produced by the hydrolysis of titanate is coated on the surface of the molybdenum trioxide material, and after calcination, a molybdenum trioxide electrode material co-modified by doping and coating is obtained. The molecular formula is (ZnO) _x (MoO ₃ ) _1-x /TiO ₂ . The invention adopts two methods of doping and coating to modify the molybdenum trioxide material at the same time, and enhances the structural stability of the molybdenum trioxide material in the process of intercalating and removing lithium. The process of the invention is simple, and the prepared material has high specific capacity and good cycle performance.

Description

A kind of preparation method of lithium-ion battery cathode material modified molybdenum trioxide

technical field

The invention belongs to the field of lithium-ion secondary battery cathode materials, and in particular relates to a preparation method of modified molybdenum trioxide as a lithium-ion battery cathode material.

Background technique

Lithium-ion secondary battery is a newly developed green power source in the 1990s. It has attracted the attention of researchers due to its excellent performance such as high reversible capacity, high voltage, high cycle performance and high energy density. It is called the leading battery in the 21st century power supply. The research on cathode materials for lithium-ion batteries mainly focuses on lithium cobalt oxide LiCoO ₂ , lithium nickel oxide LiNiO ₂ , olivine-structured LiFePO ₄ and spinel-structured LiMn ₂ O ₄ . Currently commercialized lithium-ion batteries mainly use LiCoO ₂ as the cathode material. Due to the increasing scarcity of cobalt resources, the relatively high price and certain toxicity limit its further application; the synthesis of LiNiO ₂ cathode materials is difficult and safe. Poor electrical conductivity; LiFePO ₄ has poor electronic conductivity, and is mostly modified by C coating, but it will reduce its volume energy density; LiMn ₂ O ₄ with spinel structure has low discharge capacity (about 110mAh/g), and the applicable temperature range is narrow (<55°C). Therefore, seeking new and high-performance cathode materials has become a matter of great concern to lithium-ion battery researchers.

MoO ₃ is an orthogonal layered structure composed of [MoO ₆ ] octahedrons sharing edges and corners. Since the two-dimensional layered structure of MoO ₃ provides an open channel for Li ion transport, it is suitable for Li ion deintercalation and is an ideal lithium ion intercalation material. About 1.5 units of lithium can be reversibly intercalated and deintercalated in α- _MoO3 . As a lithium battery electrode material, it has the advantages of large specific capacity, abundant resources, and good safety performance, but it also has the disadvantage of rapid capacity decay. According to literature reports, using ammonium molybdate as raw material, MoO ₃ ·nH ₂ O aqueous sol was prepared by ion exchange, and then blended with PEG for hydrothermal reaction to prepare MoO ₃ nanobelts. At a current density of 0.4 mA cm ^-2 and 1.5-3.45V voltage range, the discharge specific capacity is 313mAh/g, and the capacity retention rate after 20 cycles is 77%. The main reasons for the capacity decline include two aspects: one is that with the intercalation of lithium, the [MoO ₆ ] octahedron will be slightly distorted, so that the active sites of partial lithium intercalation and desorption in the crystal structure disappear; the other is that the electrode material and Long-term contact with the electrolyte will cause some molybdenum ions to dissolve into the electrolyte, which will also cause the loss of electrode active materials.

Contents of the invention

The purpose of the present invention is to overcome the shortcoming that the molybdenum trioxide positive electrode material decays rapidly during the charge-discharge cycle, and to modify the molybdenum trioxide material by means of doping and coating to increase the structure of the molybdenum trioxide material stability and improve its cycle performance. The process of the method is simple, and the prepared product has the characteristics of high specific capacity and good cycle performance.

The present invention is implemented by adopting the following technical solutions: a preparation method for modifying molybdenum trioxide as a positive electrode material of a lithium ion battery, the preparation method comprising the following steps:

(1) Mix molybdenum salt and zinc salt by ball milling, according to the mass ratio molybdenum salt: zinc salt = 1/7 m ₁ (1- x ): m ₂ x , where m ₁ is the molecular weight of molybdenum salt, m ₂ is the molecular weight of the zinc salt, x is the content of zinc doped in the molybdenum trioxide cathode material, 0 < x ≤ 0.1;

(2) Put the ball-milled mixture into a muffle furnace, heat it to 450°C and calcinate for 10 to 15 hours to obtain an intermediate product, that is, a molybdenum trioxide cathode material doped with zinc, with a molecular formula of (ZnO) _x (MoO ₃ ) _1-x ;

(3) After grinding the intermediate product obtained in step (2), pour it into the mixed solvent, and under the stirring of a magnetic stirrer, add titanate dropwise to the mixed system, and then add hydrolysis Accelerator, continue to stir for 0.5 to 2 h, centrifuge for sedimentation, wash with distilled water for 3 times, and then dry in an oven at 110°C. The components added are based on the mass ratio of intermediate product: mixed solvent: titanate: hydrolysis accelerator Agent=1:8:ym ₃ /m ₄ :0.2, where m ₃ is the molecular weight of titanate, m ₄ is the molecular weight of titanium dioxide, y is the mass fraction of titanium dioxide in the intermediate product, 0 < y ≤ 0.08;

(4) Put the dried product obtained in step (3) into a muffle furnace, heat to 450°C and calcinate for 4 to 6 hours to obtain a molybdenum trioxide cathode material co-modified by doping and coating, and the molecular formula is (ZnO) _x (MoO ₃ ) _1-x /TiO ₂ ;

The molybdenum salt in the step (1) is ammonium paramolybdate, and the zinc salt is zinc nitrate or zinc acetate;

The ball milling speed of the ball milling mixture in step (1) is 200-300 rpm, the time of ball milling and mixing is 0.5-2 h, and the mass ratio of the mixture to zirconium balls is 1:4;

The heating rate of the muffle furnace in step (2) and step (4) is 5-10°C/min;

The mixed solvent in step (3) is obtained by mixing water and absolute ethanol at a volume ratio of 1:10, and the titanate is tetrabutyl titanate or tetraethyl titanate;

The hydrolysis accelerator in the step (3) is 65%～68% nitric acid;

In step (3), the stirring speed of the magnetic stirrer is 300-500 rpm.

The present invention has the following advantages and effects: by calcining the mixture of zinc salt and molybdenum salt, the molybdenum trioxide material doped with zinc is obtained, and the doping of zinc plays a supporting role in the lattice framework of the molybdenum trioxide material , can effectively inhibit the structural distortion of molybdenum trioxide in the process of lithium intercalation and desorption, and stabilize the structure of the material; through the hydrolysis of titanate, the surface of the zinc-doped molybdenum trioxide material is coated with titanium dioxide, and the surface of titanium dioxide is coated The direct contact between the molybdenum trioxide electrode material and the organic electrolyte can be reduced, the dissolution of the molybdenum ion in the material can be suppressed, and the loss of the active material can be avoided; the process of the invention is simple, and the prepared material has high specific capacity and good cycle performance.

Description of drawings

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is an XRD pattern of the molybdenum trioxide cathode material (ZnO) _0.05 (MoO ₃ ) _0.95 /TiO ₂ co-modified by doping and coating prepared in Example 1 of the present invention.

Fig. 2 is a cycle performance curve of the doped and coated co-modified molybdenum trioxide positive electrode material (ZnO) _0.05 (MoO ₃ ) _0.95 /TiO ₂ prepared in Example 1 of the present invention.

In Figure 1, compared with the standard XRD pattern card JCPDS No. 76-1003, it can be seen that the molybdenum trioxide cathode material (ZnO) _0.05 (MoO ₃ ) _0.95 /TiO ₂ co-modified by doping and coating has an orthorhombic layered phase structure, the doping of a small amount of zinc and the surface coating of titanium dioxide did not change the crystal structure of the molybdenum trioxide material.

In Figure 2, the charge and discharge voltage range is 1.5V to 4.0V, and the discharge rate is 0.1C. The initial discharge capacity of (ZnO) _0.05 (MoO ₃ ) _0.95 /TiO ₂ cathode material is 279.9mAh/g, after 20 cycles, the discharge capacity is 245.2mAh/g, and the capacity retention rate is 87.6%.

Detailed ways

Example 1: Production of 4.9 g of molybdenum trioxide cathode material (ZnO) _0.05 (MoO ₃ ) _0.95 /TiO ₂ powder co-modified by doping and coating, with a yield of 98%. Specific steps are as follows:

(1) Mix 5.67g ammonium paramolybdate tetrahydrate and 0.5g zinc nitrate hexahydrate, and the mass ratio of molybdenum salt and zinc salt is 1:0.088. Add zirconium balls with a material-to-ball ratio of 1:4 into the ball mill jar, and ball mill the mixture for 1 hour at a speed of 250 rpm on a planetary ball mill.

(2) Put the ball-milled mixture into a muffle furnace, heat up to 450°C at a rate of 8°C/min, keep it warm for 12 hours, and cool down to room temperature with the furnace to obtain an intermediate product, that is, zinc-doped molybdenum trioxide Positive electrode material powder 4.7g, molecular formula is (ZnO) _0.05 (MoO ₃ ) _0.95 ;

(3) After the intermediate product is ground, pour it into a mixed solvent of 38g of water and absolute ethanol, which is obtained by mixing water and absolute ethanol at a volume ratio of 1:10. Stir the mixing system with a magnetic stirrer at a stirring speed of 400 rpm, add 0.99g of tetrabutyl titanate liquid dropwise to the mixing system under stirring, and then add 0.94g of 65%~ 68% nitric acid (hydrolysis accelerator), continue to stir for 1 h, centrifuge for sedimentation, wash with distilled water for 3 times, and then dry in an oven at 110°C. The components added are based on the mass ratio of intermediate product: mixed solvent: titanic acid Ester: hydrolysis accelerator=1:8:0.21:0.2, the quality of titanium dioxide obtained by tetrabutyl titanate hydrolysis accounts for 5% of intermediate product quality;

(4) Put the dried product obtained in step (3) into a muffle furnace, heat up to 450°C at a rate of 8°C/min, and then calcinate for 5 hours to obtain a doped and coated co-modified molybdenum trioxide cathode material , the molecular formula is (ZnO) _0.05 (MoO ₃ ) _0.95 /TiO ₂ . Its XRD spectrum is shown in Figure 1.

The electrochemical properties of the obtained samples were measured as follows: positive electrode active material powder, conductive agent acetylene black, and binder polyvinylidene fluoride were mixed in a mass ratio of 85:9:6. Weigh 2.5g of modified molybdenum trioxide cathode material powder, add 0.26g of acetylene black as a conductive agent, then add 0.18g of polyvinylidene fluoride PVDF as a binder, and use N-methylpyrrolidone NMP as a solvent. The ball mill was mixed at a speed of 280 rpm for 2 hours, and the obtained slurry was evenly coated on the aluminum current collector, and vacuum-dried at 80° C. for 10 hours to obtain a positive electrode sheet. With metal lithium sheet as the negative electrode, 1.0mol/L LiPF ₆ /EC+DMC (1:1) as the electrolyte, and Celgard2320 film as the separator, the battery was assembled in a glove box filled with argon, and the battery was assembled at a rate of 0.1C. Constant current charge and discharge test, the voltage range is 1.5V ~ 4.0V, to test the charge and discharge capacity and cycle performance of the positive electrode material. Its cycle performance curve is shown in Figure 2.

Example 2: Production of molybdenum trioxide cathode material (ZnO) _0.01 (MoO ₃ ) _0.99 /TiO ₂ powder 3.75g co-modified by doping and coating, with a yield of 98.7%. Specific steps are as follows:

(1) Mix 4.59g ammonium paramolybdate tetrahydrate and 0.058g zinc acetate dihydrate, wherein the mass ratio of molybdenum salt and zinc salt is 1:0.013. Add zirconium balls with a material-to-ball ratio of 1:4 into the ball mill pot, and ball mill the mixture on a planetary ball mill at a speed of 200 rpm for 0.5 hours.

(2) Put the ball-milled mixture into a muffle furnace, raise the temperature to 450°C at a rate of 5°C/min, keep it warm for 10 hours, and cool to room temperature with the furnace to obtain an intermediate product, that is, zinc-doped molybdenum trioxide Positive electrode material powder 3.71g, molecular formula is (ZnO) _0.01 (MoO ₃ ) _0.99 ;

(3) After the intermediate product is ground, it is poured into a mixed solvent of 30 g of water and absolute ethanol, and the mixed solvent is obtained by mixing water and absolute ethanol at a volume ratio of 1:10. Stir the mixing system with a magnetic stirrer at a stirring speed of 300 rpm, add 0.11g of tetraethyl titanate liquid dropwise to the mixing system under stirring, and then add 0.74g of 65%~ 68% nitric acid (hydrolysis accelerator), continue to stir for 0.5 h, centrifuge sedimentation, wash with distilled water for 3 times, and then dry in an oven at 110°C. The components added are based on the mass ratio of intermediate product: mixed solvent: titanic acid Ester: hydrolysis accelerator=1:8:0.03:0.2, the quality of titanium dioxide obtained by tetraethyl titanate hydrolysis accounts for 1% of intermediate product quality;

(4) Put the dried product obtained in step (3) into a muffle furnace, heat up to 450°C at a rate of 5°C/min, and then calcinate for 4 hours to obtain a doped and coated co-modified molybdenum trioxide cathode material , the molecular formula is (ZnO) _0.01 (MoO ₃ ) _0.99 /TiO ₂ .

The detection method is the same as in Example 1. The initial discharge capacity of the prepared material is 291mAh/g, after 20 cycles, the discharge capacity is 242.5mAh/g, and the capacity retention rate is 83.3%.

Example 3: Production of molybdenum trioxide cathode material (ZnO) _0.1 (MoO ₃ ) _0.9 /TiO ₂ powder 8.5g co-modified by doping and coating, yield 97.7%. Specific steps are as follows:

(1) Mix 9.3g ammonium paramolybdate tetrahydrate and 1.28g zinc acetate dihydrate, wherein the mass ratio of molybdenum salt and zinc salt is 1:0.14. Add zirconium balls with a material-to-ball ratio of 1:4 into the ball mill jar, and ball mill the mixture for 1.5 hours at a speed of 300 rpm on a planetary ball mill.

(2) Put the ball-milled mixture into a muffle furnace, heat up to 450°C at a rate of 10°C/min, keep it warm for 13 hours, and cool down to room temperature with the furnace to obtain an intermediate product, namely molybdenum trioxide doped with zinc Positive electrode material powder 8g, molecular formula is (ZnO) _0.1 (MoO ₃ ) _0.9 ;

(3) After the intermediate product is ground, it is poured into a mixed solvent of 64g of water and absolute ethanol, and the mixed solvent is obtained by mixing water and absolute ethanol at a volume ratio of 1:10. Stir the mixing system with a magnetic stirrer at a stirring speed of 500 rpm, add 2.72g of tetrabutyl titanate liquid dropwise to the mixing system under stirring, and then add 1.6g of 65%~ 68% nitric acid (hydrolysis accelerator), continue to stir for 1.5 h, centrifuge sedimentation, wash with distilled water for 3 times, and then dry in an oven at 110°C. The components added are based on the mass ratio of intermediate product: mixed solvent: titanic acid Ester: hydrolysis accelerator=1:8:0.34:0.2, the quality of titanium dioxide obtained by tetrabutyl titanate hydrolysis accounts for 8% of intermediate product quality;

(4) Put the dried product obtained in step (3) into a muffle furnace, heat up to 450°C at a rate of 10°C/min, and then calcinate for 6 hours to obtain a molybdenum trioxide cathode material co-modified by doping and coating , the molecular formula is (ZnO) _0.1 (MoO ₃ ) _0.9 /TiO ₂ .

The detection method is the same as in Example 1. The initial discharge capacity of the prepared material is 275.6mAh/g, after 20 cycles, the discharge capacity is 237mAh/g, and the capacity retention rate is 86%.

Example 4: Production of molybdenum trioxide cathode material (ZnO) _0.04 (MoO ₃ ) _0.96 /TiO ₂ powder 11.8g co-modified by doping and coating, yield 98.3%. Specific steps are as follows:

(1) Mix 13.56g ammonium paramolybdate tetrahydrate and 0.95g zinc nitrate hexahydrate, and the mass ratio of molybdenum salt and zinc salt is 1:0.07. Add zirconium balls with a material-to-ball ratio of 1:4 into the ball mill jar, and ball mill the mixture for 2 hours at a speed of 250 rpm on a planetary ball mill.

(2) Put the ball-milled mixture into a muffle furnace, raise the temperature to 450°C at a rate of 10°C/min, keep it warm for 15 hours, and cool to room temperature with the furnace to obtain an intermediate product, namely molybdenum trioxide doped with zinc Positive electrode material powder 11.2g, molecular formula is (ZnO) _0.04 (MoO ₃ ) _0.96 ;

(3) After the intermediate product is ground, it is poured into a mixed solvent of 90 g of water and absolute ethanol, and the mixed solvent is obtained by mixing water and absolute ethanol at a volume ratio of 1:10. Stir the mixing system with a magnetic stirrer at a stirring speed of 450 rpm, add 1.9g of tetraethyl titanate liquid dropwise to the mixing system under stirring, and then add 2.24g of 65%~ 68% nitric acid (hydrolysis accelerator), continue to stir for 2 h, centrifuge for precipitation, wash with distilled water for 3 times, and then dry in an oven at 110°C. Ester: hydrolysis accelerator=1:8:0.17:0.2, the quality of titanium dioxide obtained by tetraethyl titanate hydrolysis accounts for 6% of intermediate product quality;

(4) Put the dried product obtained in step (3) into a muffle furnace, heat up to 450°C at a rate of 10°C/min, and then calcinate for 5 hours to obtain a molybdenum trioxide cathode material co-modified by doping and coating , the molecular formula is (ZnO) _0.04 (MoO ₃ ) _0.96 /TiO ₂ .

The detection method is the same as in Example 1. The initial discharge capacity of the prepared material is 280.5mAh/g, after 20 cycles, the discharge capacity is 244mAh/g, and the capacity retention rate is 87%.

The reagents involved in the present invention are ammonium paramolybdate tetrahydrate, zinc nitrate hexahydrate, zinc acetate dihydrate, absolute ethanol, tetraethyl titanate, tetrabutyl titanate, 65% to 68% nitric acid, N-methyl All base pyrrolidones are chemically pure reagents, and acetylene black, polyvinylidene fluoride, and electrolyte LiPF ₆ /EC+DMC (1:1) are all battery grade.

Claims (7)

1. a preparation method for anode material for lithium-ion batteries modification molybdenum trioxide, is characterized in that: preparation method comprises the following steps:

(1) molybdenum salt and zinc salt are carried out to ball mill mixing, in mass ratio molybdenum salt: zinc salt=1/7 m ₁(1- x): m ₂ x, wherein m ₁for the molecular weight of molybdenum salt, m ₂for the molecular weight of zinc salt, xfor the zinc content adulterating in molybdenum trioxide positive electrode, 0 < x≤ 0.1;

(2) batch mixing after ball milling is put into Muffle furnace, be heated to 450 ℃ of calcining 10～15 h, obtain intermediate product, the molybdenum trioxide positive electrode of the zinc that adulterates, molecular formula is (ZnO) _x(MoO ₃) _1-x;

(3) by step (2) gained intermediate product after grinding, be poured in mixed solvent, under the stirring of magnetic stirring apparatus, in mixed system, dropwise drip titanate esters, after dropwising, add again hydrolytic accelerating agent, continue to stir 0.5～2 h, through centrifugal, distilled water, after washing 3 times, in 110 ℃ of baking ovens, dry, wherein add each component intermediate product in mass ratio: mixed solvent: titanate esters: hydrolytic accelerating agent=1:8:ym ₃/ m ₄: 0.2, wherein m ₃for the molecular weight of titanate esters, m ₄for the molecular weight of titanium dioxide, yfor titanium dioxide accounts for the mass fraction of intermediate product, 0 < y≤ 0.08;

(4) step (3) gained is dried to thing and put into Muffle furnace, be heated to 450 ℃ of calcining 4～6 h, obtain doping and the coated molybdenum trioxide positive electrode of modification altogether, molecular formula is (ZnO) _x(MoO ₃) _1-x/ TiO ₂.

2. the preparation method of a kind of anode material for lithium-ion batteries modification molybdenum trioxide according to claim 1, is characterized in that: the molybdenum salt in step (1) is ammonium paramolybdate, and zinc salt is zinc nitrate or zinc acetate.

3. the preparation method of a kind of anode material for lithium-ion batteries modification molybdenum trioxide according to claim 1, it is characterized in that: the ball milling speed of the ball mill mixing in step (1) is 200～300 revs/min, the time of ball mill mixing is 0.5～2 h, and the mass ratio of batch mixing and zirconium ball is 1:4.

4. the preparation method of a kind of anode material for lithium-ion batteries modification molybdenum trioxide according to claim 1, is characterized in that: in step (2) and step (4), the heating rate of Muffle furnace is 5～10 ℃/min.

5. the preparation method of a kind of anode material for lithium-ion batteries modification molybdenum trioxide according to claim 1, it is characterized in that: the mixed solvent in step (3) is that water mixes gained with absolute ethyl alcohol by the volume ratio of 1:10, and titanate esters is butyl titanate or tetraethyl titanate.

6. the preparation method of a kind of anode material for lithium-ion batteries modification molybdenum trioxide according to claim 1, is characterized in that: the hydrolytic accelerating agent in step (3) is 65%～68% nitric acid.

7. the preparation method of a kind of anode material for lithium-ion batteries modification molybdenum trioxide according to claim 1, is characterized in that: in step (3), the mixing speed of magnetic stirring apparatus is 300～500 revs/min.

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