A bipolar material, a preparation method and a sodium ion battery with symmetrical electrodes

Abstract

The present invention relates to a bipolar material, a preparation method and a sodium ion battery with symmetrical electrodes, belonging to the technical field of sodium ion batteries. The general formula of the bipolar material is Na 0.8‑x Ni 0.4‑y Mg 0.8‑ z Ti 0.65‑m O2, and the space group is R‑3m, with O3 phase structure; 0

Description

Technical Field

[0001] The invention relates to a bipolar material, a preparation method and a sodium ion battery with symmetrical electrodes, belonging to the technical field of sodium ion batteries. Background Art

[0002] Sodium-ion batteries have broad application prospects in new large-scale energy storage systems and smart grids due to their abundant raw materials and low cost. The research and development of symmetric bipolar material systems plays a vital role in the application of sodium-ion batteries. Symmetrical batteries use the same material as both the positive and negative electrodes. Compared with asymmetric batteries, their advantages such as low material cost, small volume expansion, and high operational safety have attracted great interest. The structure of symmetrical electrodes makes it a more feasible option for new battery configurations, which is superior to traditional monopolar structures. In non-aqueous sodium-ion batteries, denser and cheaper aluminum brings cost benefits to battery manufacturing.

[0003] Among the electrodes of many symmetrical sodium-ion batteries, O3-phase layered nickel-titanium-based materials have been reported. The results show that the positive electrode of this type of material passes through Ni at around 3.5V. 2+ / 3+ and Ni 3+ / 4+ The redox couple provides capacity, while the negative electrode is at around 0.8V through Ti 4+ / 3+ The redox couple is provided.

[0004] However, this symmetrical battery has two disadvantages. First, the positive and negative electrodes of the symmetrical sodium-ion battery use the same electrode material, which may not be the best positive electrode or the best negative electrode, so the actual cycle capacity and energy density of the battery are limited. On the other hand, the symmetrical sodium-ion battery will undergo multiple redox reactions at high and low voltages, and it is easy to undergo adverse phase changes during the cycle, thereby hindering the stability of the symmetrical battery. Summary of the invention

[0005] The technical problem to be solved by the present invention is that when O3 phase layered nickel-titanium-based materials are used as both positive and negative electrode materials of bipolar sodium ion batteries, irreversible phase changes occur, which in turn leads to limited cycle capacity and flux density.

[0006] The present invention provides a new O3 phase layered nickel-titanium-based material. The prepared O3 phase layered nickel-titanium-based bipolar material is assembled into a full battery through a magnesium doping strategy to obtain better cycle capacity and rate performance.

[0007] A bipolar material with the general formula: Na 0.8-x Ni 0.4-y Mg0.8-z Ti 0.65-m O2, and the space group is R-3m, with O3 phase structure; 0 <x<0.1,0<y<0.2,0<z<0.1,0<m<0.5。

[0008] The general formula of the bipolar material is: Na 0.75 Ni 0.3 Mg 0.075 Ti 0.625 O2.

[0009] The above-mentioned bipolar material is prepared by a solid phase method.

[0010] The solid phase method comprises the following steps: taking Na2CO3, NiO, MgO and TiO2 according to the stoichiometric ratio, ball milling, tableting and calcining to obtain a bipolar material.

[0011] The rotation speed during the ball milling process is 200-400 rpm and the time is 1-30 hours.

[0012] The calcination process temperature is 800-1000°C and the time is 10-20h.

[0013] Application of the above-mentioned bipolar material in the positive electrode and / or negative electrode of a sodium ion symmetric battery.

[0014] Beneficial Effects

[0015] This patent adopts the strategy of magnesium doping on layered O3 phase nickel-titanium-based materials, and the bipolar materials prepared are assembled into full batteries to achieve better cycle capacity and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Na 0.75 Ni 0.3 Mg 0.075 Ti 0.625 X-ray powder diffraction spectrum of O2 material

[0017] Figure 2 Na 0.9 Ni 0.4 Mg 0.05 Ti 0.5 Mn 0.05 X-ray powder diffraction spectrum of O2 material

[0018] Figure 3 Na 0.9 Ni 0.4 Cu 0.05 Ti 0.5 Mn 0.05 X-ray powder diffraction spectrum of O2 material

[0019] Figure 4 Na 0.9 Ni 0.4 Mg 0.05 Ti 0.5 Mn 0.05 X-ray powder diffraction spectrum of O2 material

[0020] Figure 5 Na 0.9 Ni 0.4 5Ti 0.55 X-ray powder diffraction spectrum of O2 material

[0021] Figure 6 The charge and discharge curves of the NNMT material in the first three cycles at a current density of 20 mA / g in the voltage range of 2-4 V.

[0022] Figure 7 The charge and discharge curves of the NNMT material in the first three cycles at a current density of 20 mA / g in the voltage range of 0.05-2.5 V.

[0023] Figure 8 The charge and discharge curve of the first cycle of the NNMT material full battery at a current density of 20mA / g in the voltage range of 1-4V

[0024] Fig. 9 The charge and discharge curves of the first cycle of the NNMT material full battery at different current densities in the voltage range of 1-4V

[0025] Fig.10 First cycle cyclic voltammetry curve of NNMT material

[0026] Fig.11 The charge and discharge curves of the first cycle of the full battery assembled with NNMT positive electrode and NMT negative electrode at different current densities in the voltage range of 1-4V.

[0027] Fig.12 The charge and discharge curves of the first cycle of the NNMTM material full battery at different current densities in the voltage range of 1-4V

[0028] Fig.13 The charge and discharge curves of the first three cycles of the NNCT material full battery at a current density of 20mA / g in the voltage range of 1-4V.

[0029] Fig.14 The charge and discharge curves of the first cycle of the NNCTM material full battery at different current densities in the voltage range of 1-4V DETAILED DESCRIPTION

[0030] Example 1Na 0.75 Ni 0.3 Mg 0.075 Ti 0.625 Preparation of O2(NNMT)

[0031] The material was prepared by traditional high-temperature solid-phase sintering method. The raw materials were Na2CO3, NiO, MgO and TiO2. According to the corresponding molar ratio, the ball milling was carried out at 300rpm for 12h. The wet grinding aid was anhydrous ethanol. The precursor powder was dried at 80℃. The precursor powder was pressed into a 16mm mold and calcined in a muffle furnace. The process was 5℃ / min heating, calcined at 900℃ for 15h, and then naturally cooled to obtain the bipolar material Na 0.75 Ni 0.3 Mg 0.075 Ti 0.625 O2(NNMT).

[0032] Comparative Example 1Na 0.9 Ni 0.4 Mg 0.05 Ti 0.5 Mn 0.05 Preparation of O2(NNMTM)

[0033] The material was prepared by traditional high-temperature solid-phase sintering method. The raw materials were Na2CO3, NiO, MgO, TiO2 and MnO2. According to the corresponding molar ratio, the ball milling was carried out at 300rpm for 12h. The wet grinding aid was anhydrous ethanol. The precursor powder was dried at 80℃. The precursor powder was pressed into a 16mm mold and calcined in a muffle furnace. The process was 5℃ / min heating, calcined at 900℃ for 15h, and then naturally cooled to obtain the bipolar material Na 0.9 Ni 0.4 Mg 0.05 Ti 0.5 Mn 0.05 O2.

[0034] Comparative Example 2Na 0.75 Ni 0.3 Cu 0.075 Ti 0.625 Preparation of O2(NNCT)

[0035] The material was prepared by traditional high-temperature solid-phase sintering method. The raw materials were Na2CO3, NiO, CuO and TiO2. According to the corresponding molar ratio, the ball milling was carried out at 300rpm for 12h. The wet grinding aid was anhydrous ethanol. The precursor powder was dried at 80℃. The precursor powder was pressed into a 16mm mold and calcined in a muffle furnace. The process was 5℃ / min heating, calcined at 900℃ for 15h, and then naturally cooled to obtain the bipolar material Na 0.75 Ni 0.3 Cu 0.075 Ti 0.625 O2.

[0036] Comparative Example 3Na 0.9 Ni 0.4Cu 0.05 Ti 0.5 Mn 0.05 Preparation of O2(NNCTM) materials

[0037] The material was prepared by traditional high-temperature solid-phase sintering method. The raw materials were Na2CO3, NiO, CuO, TiO2 and MnO2. According to the corresponding molar ratio, the ball milling was carried out at 300rpm for 12h. The wet grinding aid was anhydrous ethanol. The precursor powder was dried at 80℃. The precursor powder was pressed into a 16mm mold and calcined in a muffle furnace. The process was 5℃ / min heating, calcined at 900℃ for 15h, and then naturally cooled to obtain the bipolar material Na 0.9 Ni 0.4 Cu 0.05 Ti 0.5 Mn 0.05 O2.

[0038] XRD characterization

[0039] The X-ray powder diffraction test results of the materials prepared in Example 1 and Comparative Examples 1-3 are as follows: Figure 1-4 As shown, the space group is R-3m, and the result shows a standard O3 phase structure.

[0040] The NNMT material was tested for its electrochemical properties. The NNMT powder material prepared in Example 1 was used as the positive and negative electrode active materials, and was fully ground with the conductive agent SuperP and the binder PVDF (dispersant NMP) in a mass ratio of 75:20:5 until uniformly mixed to prepare the positive and negative electrode sheets. The electrolyte used was 1.0 mol L -1 The sodium perchlorate electrolyte is PC, and 5% FEC additive is added. The positive electrode and the negative electrode are assembled into half-cells with the metal sodium electrode respectively to explore the performance of the material as the positive electrode and the negative electrode. When used as a full battery, the negative electrode plate is first pretreated, and the negative electrode plate and the metal sodium electrode are assembled into a half-cell. The half-cell is charged and discharged in the voltage range of 0.05-2.5V. After the test, the negative electrode plate is taken out and cleaned with DME more than three times. The pretreated negative electrode plate is assembled with the positive electrode plate to form a positive and negative bipolar sodium ion full battery, in which the mass ratio of the active materials of the positive and negative electrodes is about 1:1.2.

[0041] like Figure 6 , which is the charge and discharge curve of NNMT material as positive electrode at a current density of 20mA / g. The voltage window is 2-4V, and the first-cycle reversible specific capacity can reach 87.7mAh / g. Figure 7 This is the charge and discharge curve of NNMT material as the negative electrode at a current density of 20 mA / g. The voltage window is 0.05-2.5 V, and the reversible specific capacity can reach 97.9 mAh / g. Figure 8 This is the first cycle charge-discharge curve of NNMT material used as positive and negative dual electrodes at a current density of 20mA / g, where the negative electrode has been pre-embedded for 3 cycles and the positive electrode has not been pre-embedded. The voltage window is 1-4V, and the reversible discharge specific capacity can reach 112.5mAh / g. Fig. 9 The first cycle charge and discharge curves of NNMT materials used as positive and negative dual electrodes at current densities of 10mA / g, 50mA / g and 100mA / g, where the negative electrode has been pre-embedded for one cycle and the positive electrode has not been pre-embedded. The voltage window is 1-4V, and the reversible discharge specific capacities are 90.23mAh / g, 83.08mAh / g and 72.90mAh / g, respectively. Fig.10 This is the first cycle cyclic voltammetry curve of the NNMT material half-cell in the voltage range of 0.01-4.2V at a scan rate of 0.1mV / s, with metallic sodium as the negative electrode.

[0042] Fig.11 NNMT material is used as the positive electrode, while undoped Na 0.9 Ni 0.45 Ti 0.55 The first cycle charge and discharge curves of O2 material at current densities of 10mA / g, 50mA / g and 100mA / g, where the negative electrode has been pre-embedded for one cycle and the positive electrode has not been pre-embedded. The voltage window is 1-4V, and the reversible discharge specific capacities are 52.52mAh / g, 46.79mAh / g and 42.94mAh / g, respectively, which are lower than NNMT bipolar materials.

[0043] In addition, as the Na prepared in Comparative Example 1 0.9 Ni 0.4 Mg 0.05 Ti 0.5 Mn 0.05 O2, Na prepared in Comparative Example 2 0.75 Ni 0.3 Cu 0.075 Ti 0.625 O2 and the Na prepared in Comparative Example 3 0.9 Ni 0.4 Cu 0.05 Ti 0.5 Mn 0.05 The full battery performance of these three materials is as follows: Fig.12 , Fig.13 and Fig.14 As shown (test method is the same as above), it can be seen that other materials cannot effectively realize the battery cycle when used as a dual-electrode full battery.

Claims

1. Application of a bipolar material in the positive electrode and negative electrode of a sodium ion symmetric battery for the first cycle of charge and discharge, characterized in that: The general formula of bipolar materials is: Na 0.75 Ni 0.3 Mg 0.075 Ti 0.625 O2, and the space group is R-3m, with an O3 phase structure; the preparation method of the bipolar material uses a high-temperature solid-phase sintering method to prepare the material, and the raw materials are Na2CO3, NiO, MgO and TiO2. According to the corresponding molar ratio, the raw materials are ball-milled at 300rpm for 12h, and the wet grinding aid is anhydrous ethanol. Then, the precursor powder is dried at 80°C to obtain a precursor powder. The precursor powder is pressed into a tablet through a 16mm mold and calcined in a muffle furnace. The process is 5°C / min heating, calcined at 900°C for 15h, and then naturally cooled to obtain the bipolar material.

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