An amorphous cathode material, its preparation method and application

Abstract

The present invention provides an amorphous cathode material, a preparation method thereof and an application. The amorphous cathode material comprises active substance glass powder; the raw materials for preparing the active substance glass powder include a glass network former TeO2 and Li3PO4; a transition metal oxide V2O5 and an extra-network body Fe2P; the mass ratio of the glass network former, the transition metal oxide and the extra-network body is (15-50):(55-80):(1-20). The above raw materials are prepared into a glass bulk by the melt quenching method, and then put into a thermoelectric coupling field device for crystallization treatment to obtain a crystallized glass bulk, which is ground to obtain the active substance glass powder. The lithium ion battery assembled with this amorphous cathode material has the advantages of large specific capacity, high voltage and small first cycle loss rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials, and particularly relates to an amorphous cathode material, a preparation method thereof and an application thereof. Background Art

[0002] Currently, commercial lithium-ion cathode materials are mainly composite lithium-containing oxides (ternary) such as cobalt, manganese, nickel, etc. and lithium iron phosphate, etc. However, they are still limited by low energy density, and the specific capacity is significantly lower than the market expected requirements. The multi-electron reaction of transition metal (TM) elements is regarded as one of the effective methods to improve the capacity. The multi-electron reaction means that multiple Li + can be intercalated and deintercalated, so as to achieve a higher specific capacity, and then improve the energy density. Among many transition metal elements, vanadium has multiple stable oxidation states, and the common valence states are +5, +4, +3, +2, etc. Vanadium-based materials represented by V2O5 are a typical type of materials that can achieve multi-electron reactions due to the variable valence states of vanadium.

[0003] Whittingham proposed that today's commercialization can only reach 25% of its theoretical capacity. In the lithium field, one way to increase the energy density and at the same time reduce the cost is to perform multiple single-electron reactions at each redox center. For example, it can be achieved by intercalating two lithium / sodium ions or one magnesium / calcium into the host structure. Within the stability limit of today's electrolytes, few transition metals have two redox pairs. Fortunately, V is one of them, and its redox reaction can easily occur between the +5 and +2 states. Vanadium has rich reserves and is the fourth transition metal element, more than nickel and cobalt currently in use. During the multiple Li + intercalation-deintercalation process, the serious structural deterioration and rapid capacity decay of vanadium-based crystalline nanomaterials are common problems faced by these materials.

[0004] V2O5 is an amphoteric acid-base oxide, which has limitations such as fast dissolution rate, irreversible phase change, serious volume expansion, low electronic conductivity, etc. Therefore, many strategies have been explored to improve the performance of vanadium-based electrode materials, such as studying strategies of bulk structure transformation, mixing of conductive substances, element doping, valence bond transformation, disordered rock salt, crystal state transformation, etc. The crystalline V2O5 can be changed into an amorphous state by the melt quenching process, and no phase change occurs in the lithiated product amorphous Li x V2O5. As a typical amorphous material, glass has begun to be studied as an electrode material due to its special structural characteristics. The electronic conductivity of TeO2-V2O5 glass is about one order of magnitude higher than that of the corresponding crystal. The glass of V2O5 is a suitable electrode material for lithium batteries, such as vanadium phosphate glass electrodes (P2O5-V2O5, etc.) ), vanadium borate glass electrodes (such as V2O5-LiBO2), vanadium tellurium glass electrodes (such as TeO2-V2O5), vanadium silicon glass electrodes (such as SiO2-V2O5), etc.

[0005] Vanadium-based materials are attractive alternatives to traditional cathodes because the conversion of many oxidation states of vanadium brings a high theoretical specific capacity. It is well known that although vanadium-based crystalline materials are potential electrode materials for lithium-ion batteries, their cycling stability performance is poor, hindering the development of vanadium-based crystalline electrode materials. For crystalline V2O5, irreversible phase transitions and vanadium dissolution occur from the first charge-discharge cycle, resulting in significant capacity loss. SUMMARY OF THE INVENTION

[0006] In view of this, the object of the present invention is to provide an amorphous cathode material, its preparation method and application. The lithium-ion battery assembled with this amorphous cathode material has the advantages of large specific capacity, high voltage and small first-cycle loss rate.

[0007] The present invention provides an amorphous cathode material, including active substance glass powder;

[0008] The preparation raw materials of the active substance glass powder include the glass network former TeO2 and Li3PO4; the transition metal oxide V2O5 and the network modifier Fe2P;

[0009] The mass ratio of the glass network former, transition metal oxide and network modifier is (15-50):(55-80):(1-20).

[0010] The present invention introduces a transition metal oxide to improve the conductivity of vanadium tellurium glass and solve the problems of excessive first-cycle specific capacity loss and low capacity retention rate after cycling. The network modifier Fe2P, as a strong reducing agent, undergoes a redox reaction with V2O5 under high-temperature conditions to reduce the V valence state, thereby improving the electronic conductivity. During the preparation process of the active substance glass powder, selective crystallization is induced by a thermoelectric coupling field, reducing the charge transfer impedance and the coefficient of thermal expansion. The conductivity and specific capacity of the obtained electrode material are significantly improved, resulting in a new type of lithium-ion battery glass cathode with high capacity and long cycle life.

[0011] In the present invention, the mass ratio of TeO2 and Li3PO4 in the glass network former is (10-50):(50-90).

[0012] In specific embodiments, the mass ratio of TeO2, Li3PO4, V2O5 and Fe2P is 10:5:80:5; or 5:10:70:5; or 20:10:50:15; or 5:20:60:15; or 15:20:55:10.

[0013] In the present invention, the active material glass powder is prepared by the following method:

[0014] A glass block is prepared by melting and quenching a mixture obtained by mixing the glass network former TeO2, Li3PO4, the transition metal oxide V2O5, and the network modifier Fe2P in an inert atmosphere;

[0015] The glass block is transferred to a thermoelectric coupling field device for crystallization treatment to obtain a crystallized glass block;

[0016] The crystallized glass block is ground to obtain the active material glass powder.

[0017] In the present invention, the preparation of the glass block by the melting and quenching method specifically includes:

[0018] The mixture is heated to 500 - 800 °C in an inert atmosphere, held for 10 - 300 min, then further heated to 1000 - 2000 °C, held for 10 - 30 min, and cooled and formed to obtain the glass block.

[0019] In the present invention, it is heated to 500 - 800 °C at a rate of 4 - 7 °C / min; and heated to 1000 - 2000 °C at a rate of 13 - 17 °C / min. In a specific embodiment, it is heated to 700 °C at a rate of 5 °C / min and held for 100 min; then the temperature is raised to 1000 °C at a rate of 15 °C / min and held for 30 min.

[0020] In the present invention, the temperature of the crystallization treatment is 200 - 400 °C, the time of the crystallization treatment is 200 - 2000 min; the voltage intensity used for the crystallization treatment is 800 - 1400 V·cm -1 . The crystallization treatment increases the number of crystal nuclei in the glass block, resulting in the precipitation of crystal grains to obtain the crystallized glass block. In a specific embodiment, the temperature of the crystallization treatment is 200 °C; the time of the crystallization treatment is 200 min; the voltage intensity is 800 V·cm -1 .

[0021] In the present invention, the particle size of the active material glass powder is less than or equal to 10 microns. In the present invention, the active material glass powder is placed in a dry environment for subsequent testing and use.

[0022] In the present invention, it further includes a binder and a conductive filler;

[0023] The mass ratio of the active glass powder, the binder, and the conductive filler is (6 - 10):(2 - 3):(1 - 2), preferably (6 - 8):(2 - 3):(1 - 2). In a specific embodiment, the mass ratio of the active glass powder, the binder, and the conductive filler is 7:2:1;

[0024] In the present invention, the binder is selected from polyvinylidene fluoride;

[0025] The conductive filler is selected from conductive carbon black.

[0026] In the present invention, lithium ions are embedded in the glass matrix to form Li2Te nanocrystals; [PO4] 3- The groups are randomly distributed in the original glass structure, and under the action of an electric field, they aggregate with each other and combine with the embedded lithium ions to form Li3PO4 nanocrystals at room temperature; during the discharge-charge process, Li + interacts with the higher energy domain of the structural network, and some Li + are incorporated into the structural network, thereby reducing the potential energy through the formation of nanocrystals. The nanocrystals and the glass matrix synergistically enhance the glass anode capacity and cycle stability.

[0027] The present invention provides a preparation method for the amorphous cathode material described in the above technical solution, including the following steps:

[0028] Mix the active substance glass powder, binder, conductive filler and solvent, then ball mill and coat to obtain the amorphous cathode material.

[0029] The above preparation method is simple and easy to implement, which is conducive to popularization and application.

[0030] The present invention also provides a lithium-ion battery, including the amorphous cathode material described in the above technical solution.

[0031] The present invention provides an amorphous cathode material, including active substance glass powder; the preparation raw materials of the active substance glass powder include the glass network former TeO2 and Li3PO4; the transition metal oxide V2O5 and the network modifier Fe2P; the mass ratio of the glass network former, transition metal oxide and network modifier is (15-50):(55-80):(1-20). The above raw materials are prepared into a glass block by the melt quenching method, put into a thermoelectric coupling field device for crystallization treatment to obtain a crystallized glass block, and ground to obtain the active substance glass powder. The lithium-ion battery assembled with this amorphous cathode material has the advantages of large specific capacity, high voltage and small first-cycle loss rate. Experimental results show that: the average grain size of the active substance glass powder is 200-430 nm; when the active substance glass powder is applied in a lithium-ion battery, the conductivity is 9×10 -4 ~6×10 -4 S / m; the charge transfer impedance is 648-1032 Ω; the thermal expansion coefficient is 3×10 -6 ~6×10 -6 / K, the open circuit voltage is 3.6-4.1; the first discharge capacity is 290-360 mAh / g; the discharge capacity of the battery after 100 cycles is 278-347 mAh / g, and the cycle efficiency is 94%-97%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the hotspot coupling field device used in the present invention; wherein 1 is a ceramic mold, 2 is a resistance furnace, 3 is a glass block, 4 is a stainless steel plate, and 5 is a power supply;

[0033] Figure 2 This is a SEM electron scanning microscope image of the active material glass powder (before crystallization treatment) prepared in Example 5 of the present invention;

[0034] Figure 3 This is a SEM electron scanning microscope image of the active material glass powder (after crystallization treatment) prepared in Example 5 of the present invention. DETAILED DESCRIPTION

[0035] In order to further illustrate the present invention, an amorphous positive electrode material provided by the present invention, its preparation method and application are described in detail below in conjunction with embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0036] The reagents used in the following examples are all commercially available.

[0037] Example 1

[0038] By weight, 10 parts TeO2, 5 parts Li3PO4, 80 parts V2O5, and 5 parts Fe2P were mixed, stirred, and ground until uniform. The resulting mixture was then transferred to an alumina crucible. The mixture was then melted in a tubular furnace under argon atmosphere. The temperature was raised to 700°C at a rate of 5°C / min and held for 100 minutes. The temperature was then raised to 1000°C at a rate of 15°C / min and held for 30 minutes. The mixture was then quickly poured onto the surface of liquid tin to form the glass. The molten glass spread and flattened on the tin surface, forming smooth upper and lower surfaces. After hardening and cooling, it was drawn onto a transition roller table. The rollers of the table rotated, pulling the glass ribbon out of the tin bath and into an annealing furnace at 200°C. After annealing for 300 minutes, the glass block was obtained.

[0039] Place the glass block in Figure 1 The thermoelectric coupling field device shown is subjected to a crystallization process to increase the number of crystal nuclei in the glass block and cause the precipitation of crystal grains, thereby obtaining a crystallized glass block. The crystallization process temperature is 200°C; the crystallization process time is 200 minutes; the voltage intensity is 800V·cm -1 The crystallized glass block is ground, fully ground using a ball mill, and sieved to obtain a positive electrode active material glass powder.

[0040] The cathode active material glass powder, binder (polyvinylidene fluoride), and conductive carbon black (particle size distribution 1 - 10 μm) powder with a mass ratio of 7:2:1 were mixed, and then an appropriate amount of solvent N-methylpyrrolidone (20% of the powder) was added and ball-milled. The resulting slurry was coated on aluminum foil and dried. After vacuum drying at 60 °C for 12 hours, it was cut into circular discs with a diameter of 12 mm and used as the positive electrode. A lithium sheet was used as the reference electrode, and 1 M LiPF6 in a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (1:1:1 v / v / v) was used as the electrolyte. A CR2032 coin cell was prepared in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm). The cycle performance of the battery was tested using a LAND CT3001A battery test system. And an electrochemical impedance spectroscopy (EIS) test was performed using a CHI660E, and the recorded frequency range was 10 -2 ~10 5 Hz, with an amplitude of 5 mV.

[0041] Examples 2 - 5

[0042] According to the process flow of Example 1, the addition amounts of different TeO2, Li3PO4, V2O5, and Fe2P are shown in Table 1.

[0043] Table 1 Types and dosages of raw materials used to prepare the amorphous cathode material in Examples 1 - 5

[0044] :

[0045]

[0046] Figure 2 This is the SEM electron scanning microscope image of the active material glass powder (before crystallization treatment) prepared in Example 5 of the present invention.

[0047] Figure 3 This is the SEM electron scanning microscope image of the active material glass powder (after crystallization treatment) prepared in Example 5 of the present invention.

[0048] Comparative Example 1

[0049] The dry V2O5 powder and P2O5 powder were mixed in a stoichiometric ratio and melted in a hydrogen atmosphere to obtain an 80V2O5·20P2O5 glass sample. The mixture was placed in a quartz crucible after stirring and uniform mixing. Glass melting was carried out using a tube furnace. It was heated at 800 °C for 5 min to obtain a melt of the vanadium phosphorus glass sample. The molten glass was poured onto an iron plate and then annealed in a muffle furnace at 250 °C for 2 h, and then cooled with the furnace. The pre-prepared glass was ground into powder with a particle size < 20 μm using an agate mortar.

[0050] The electrode is made by mixing an active material (vanadium phosphorus glass powder), carbon black, and a polytetrafluoroethylene (PTFE) binder in a mass ratio of 8:1.5:0.5. The weighed vanadium phosphorus glass powder and carbon black are put into an agate mortar and ground for 30 minutes to obtain a uniform mixture. Then, polytetrafluoroethylene is added to the prepared mixture and vigorously mixed to obtain a uniform film (thickness 80 μm). After the prepared cathode film is punched into circular pieces with a circular cutter with a diameter of 8 mm, it is evenly pasted on an aluminum mesh. Then, a CR2032 coin cell (316L stainless steel, polypropylene gasket) is used as the cathode, 1 mol / L LiPF6 in ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte, Celgard 2025 as the separator, and a lithium sheet as the counter electrode to assemble a CR2032 coin cell in a glove box. The charge-discharge performance of this comparative sample lithium-ion battery is tested at different current densities within a voltage range of 2.0 - 4.2 V on an electrochemical workstation. The test data shows that it has an initial specific capacity of 270 mAh g -1 and a capacity retention rate of about 90% after 100 cycles. In addition, after 300 cycles, it can provide a specific capacity of 220 mAh g -1 at a high current density of 85 mA g -1 , which is equivalent to a capacity retention rate of 80%.

[0051] Comparative Example 2

[0052] Based on Example 1, the difference is that the raw materials used are 10 parts of TeO2, 10 parts of Li3PO4, and 80 parts of V2O5; Fe2P is not used. Other processes and parameters are exactly the same as those in Example 1.

[0053] The performance test results of the lithium-ion batteries assembled with the glass cathode materials prepared in Examples 1 - 5 and Comparative Example 1 are shown in Table 2.

[0054] Table 2 Performance test results of the batteries prepared in the examples and comparative examples of the present invention

[0055]

[0056] As can be seen from the above embodiments, the present invention provides an amorphous cathode material, which includes active substance glass powder; the preparation raw materials of the active substance glass powder include the glass network former TeO2 and Li3PO4; the transition metal oxide V2O5 and the network modifier Fe2P; the mass ratio of the glass network former, the transition metal oxide and the network modifier is (15-50):(55-80):(1-20). The above raw materials are prepared into a glass block by the melt quenching method, and then put into a thermoelectric coupling field device for crystallization treatment to obtain a crystallized glass block, which is ground to obtain the active substance glass powder. The experimental results show that: the average grain size of the active substance glass powder is 200-430 nm; when the active substance glass powder is applied in a lithium ion battery, the conductivity is 9×10 -4 ~6×10 -4 S / m; the charge transfer impedance is 648-1032 Ω; the thermal expansion coefficient is 3×10 -6 ~6×10 -6 / K, the open circuit voltage is 3.6-4.1 V; the initial capacitance is 290-360 mAh / g; the discharge capacitance of the battery after 100 cycles is 278-347 mAh / g, and the cycle efficiency is 94%-97%.

[0057] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An amorphous cathode material, comprising active substance glass powder; The preparation raw materials of the active substance glass powder include the glass network former TeO2 and Li3PO4; the transition metal oxide V2O5 and the network modifier Fe2P; The mass ratio of the glass network former, the transition metal oxide and the network modifier is (15~50) : (55~80):(1~20); The active substance glass powder is prepared by the following method: The mixture obtained by mixing the glass network former TeO2 and Li3PO4, the transition metal oxide V2O5 and the network modifier Fe2P is melted and quenched in an inert atmosphere to obtain a glass block; The glass block is subjected to crystallization treatment to obtain a crystallized glass block; The crystallized glass block is ground to obtain active substance glass powder; The temperature of the crystallization treatment is 200~400 °C, and the time of the crystallization treatment is 200~2000 min; The voltage intensity used for the crystallization treatment is 800~1400 V·cm -1 .

2. The amorphous cathode material according to claim 1, wherein The mass ratio of TeO2 and Li3PO4 in the glass network former is (10~50): (50~90).

3. The amorphous cathode material according to claim 1, wherein The method for obtaining the glass block by melting and quenching specifically includes: The mixture is heated to 500~800 °C in an inert atmosphere, held for 10~300 min, then further heated to 1000~2000 °C, held for 10~30 min, and cooled and formed to obtain a glass block.

4. The amorphous cathode material according to claim 3, wherein Heating to 500~800 °C at a rate of 4~7 °C / min; Heating to 1000~2000 °C at a rate of 13~17 °C / min.

5. The amorphous cathode material according to claim 1, wherein The particle size of the active substance glass powder is less than or equal to 10 microns.

6. The amorphous cathode material according to claim 1, characterized in that, It further includes a binder and a conductive filler; The mass ratio of the active substance glass powder, the binder and the conductive filler is (6~10) : (2~3) : (1~2).

7. A preparation method of the amorphous cathode material according to any one of claims 1~6, comprising the following steps: The active substance glass powder, the binder, the conductive filler and the solvent are mixed and then ball-milled and coated to obtain the amorphous cathode material.

8. A lithium-ion battery, comprising the amorphous cathode material according to any one of claims 1~6.

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