Sodium electrode layered oxide positive electrode material and preparation method thereof

Abstract

The invention belongs to the field of sodium-ion battery positive electrode materials, and particularly relates to a sodium-ion battery layered oxide positive electrode material and a preparation method thereof. The invention discloses a sodium electric layered oxide positive electrode material, the chemical expression is Na < x > (M < 1y > M < 21-y-z > M < 3z >) O < 2 >, the element M < 1 > is an element with the basic valence being bivalent, the element M < 2 > is an element with the basic valence being trivalent, and the element M < 3 > is an element with the basic valence being tetravalent; wherein 0.87 < = x < = 0.95, 0.2 < = y < = 0.5, and 0.4 < = z < = 0.65; the sodium-electrode layered oxide positive electrode material has sodium vacancies, and the molar ratio of the sodium vacancies in the sodium-electrode layered oxide positive electrode material is greater than 0. According to the invention, sodium vacancies are introduced on the premise that the basic valence state of elements is balanced, so that sodium ions can be directly diffused through adjacent octahedral vacancies in the charging and discharging process, and the problem of poor cycling stability in the charging and discharging process of the sodium ion battery is avoided.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery cathode materials, specifically relating to a sodium-ion battery layered oxide cathode material and its preparation method. Background Technology

[0002] Sodium-ion batteries have gained widespread attention due to their outstanding advantages, including high operating voltage, high energy density, excellent rate performance, strong adaptability to high and low temperatures, and abundant and widely distributed sodium resources, making them one of the potential alternative technologies to lithium-ion batteries. Sodium-ion layered oxide cathode materials share the same crystal structure as lithium cobalt oxide and ternary lithium battery cathode materials. Thanks to their structural compatibility and suitability for fabrication processes, they have become a cathode material system with great application potential in the field of sodium-ion batteries. However, compared to lithium ions, sodium ions have a larger ionic radius. This characteristic leads to poor cycle stability of sodium-ion layered oxide cathode materials in high-voltage charge-discharge scenarios of 4.2V and above, despite exhibiting high specific capacity, becoming a core technological bottleneck restricting their industrial application.

[0003] The key to improving the cycle performance of battery materials lies in enhancing the structural stability of the material matrix. Currently, industry research on sodium-ion battery layered oxide cathode materials mainly focuses on O3-structured Na(Ni) cathodes. 0.33 Fe 0.33 Mn 0.33 O2 (abbreviated as NFM111) and Na(Ni) 20 Fe 22 Cu 13 Mn 45 The study focuses on two main material categories: NFM111 and NFM2 (NFCM), as well as products based on these two material categories with adjusted and modified compositions. While NFM111 exhibits high discharge capacity in 4.2V coin cell testing, its 1C cycle stability is poor. Even after modification, its full-cell operation is limited to 4.0V, failing to fully realize its high-capacity advantage. Although NFCM shows improved cycle stability compared to NFM111, the high copper content in the material results in an initial discharge capacity of only about 160mAh / g at 4.2V and 0.1C. Furthermore, the high iron content and tendency for copper to undergo microscopic segregation further hinder the ideal cycle stability of its full-cell operation at 4.15V. Summary of the Invention

[0004] To address the problem of poor cycle stability of sodium-ion layered oxide cathode materials during operation, this invention provides a sodium-ion layered oxide cathode material and its preparation method.

[0005] In the research and development of layered oxide cathodes for lithium-ion and sodium-ion batteries, the valence balance of materials has generally not been considered a core design factor due to the variable valence characteristics of most transition elements. For example, mainstream cathode materials in lithium-ion batteries such as NCM523, NCM622, and NCM811 have a fixed lithium site ratio of 1, and their transition elements are clearly not in common and stable valence states. Similarly, the transition elements in the two sodium-ion layered oxide cathode materials currently of great interest to the industry, NFM111 and NFCM, are also not in common and stable basic valence states. Because the initial valence state of the material is not the basic stable valence state of the transition elements, the material structure may not be in its most stable state. When the cathode material is under high-voltage charge and discharge, the extraction and insertion of sodium will further damage the structural stability of the material. This defect makes the structure of the material more prone to instability under high-voltage charge and discharge, making it difficult to guarantee the cycle stability of the battery and limiting the improvement of the overall performance of sodium-ion layered oxide cathode materials.

[0006] This invention first determines that the transition group elements in the sodium-ion layered oxide cathode material are in a basic and stable valence state. Through reasonable and scientific composition design, the amount of sodium is determined based on the balance of the basic valence states of each element, ensuring that the amount of sodium is less than 1. This introduces a certain amount of vacancies (without requiring order) into the sodium sites (sodium layer), thus significantly improving the cycle stability of the prepared sodium-ion layered oxide cathode material. The matrix material prepared by this invention has achieved a first-scale amplification of over 173 mAh / g at 0.1C with a coin charge of 4.3V, and a cycle retention rate of over 91% for 50 cycles at 1C.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows.

[0008] This invention provides a sodium-ion battery layered oxide cathode material, the chemical formula of which is Na. x (M1 y M2 1-y-z M3 z O2, wherein M1 is selected from at least one of Ni, Cu, Zn and Mg; M2 is selected from at least one of Fe, Co and Cr; M3 is selected from at least one of Mn, Ti and Zr; M1 is an element with a basic oxidation state of +2, M2 is an element with a basic oxidation state of +3, and M3 is an element with a basic oxidation state of +4; wherein 0.87≤x≤0.95, 0.2≤y≤0.5, 0.4≤z≤0.65; the sodium-electric layered oxide cathode material has sodium vacancies, and the molar percentage of sodium vacancies in the sodium-electric layered oxide cathode material is greater than 0.

[0009] Preferably, the magnitude of x is determined by the valence equilibrium of the basic valences of M1, M2, and M3.

[0010] Preferably, the molar percentage of sodium sites and vacancies in the sodium-electric layered oxide cathode material is the difference between z and y, where z > y.

[0011] Preferably, when the molar ratio of sodium vacancies in the sodium-electric layered oxide cathode material is 0.1, the cathode material exhibits the best overall performance.

[0012] This invention also provides a method for preparing a sodium-ion layered oxide cathode material, comprising the following steps: The expression Na according to claim 1 x (M1 y M2 1-y-z M3 z O2, determine the molar percentages of elements M1, M2, M3 and sodium.

[0013] Based on the molar ratio of sodium, M1, M2 and M3 elements, sodium-containing carbonates and hydroxides and / or oxides containing M1, M2 and M3 elements are used as raw materials, and the raw materials are mixed evenly to obtain a mixture.

[0014] The mixture was subjected to staged sintering to prepare a sodium-ionized layered oxide cathode material with sodium sites and vacancies.

[0015] Preferably, the staged sintering treatment method is as follows: sintering at 450℃~650℃ for 3h~8h, followed by sintering at 800℃~1000℃ for 10h~20h.

[0016] Preferably, the sintering atmosphere for the staged sintering process is an air atmosphere or an oxygen atmosphere.

[0017] Preferably, the flow rate of the sintering atmosphere is 60 L / min to 80 L / min.

[0018] The beneficial effects of this invention are: 1. This invention introduces sodium vacancies under the premise of basic valence equilibrium of elements, so that sodium ions can diffuse directly through the nearest octahedral vacancies during charging and discharging, avoiding lattice distortion and structural damage caused by passing through smaller tetrahedral gaps in the full sodium state, thus fundamentally solving the problem of poor cycle stability of sodium-ion layered oxide cathode materials.

[0019] 2. For the first time, the sodium site vacancy design logic of "prioritizing the balance of basic valence states of transition elements" is proposed, which is different from the existing technology of "blindly introducing vacancy without considering the balance of basic valence states". This makes the sodium site vacancy structurally compatible with the material composition system and avoids the performance loss caused by ineffective vacancy. Attached Figure Description

[0020] Figure 1 Na, the sodium-ion battery layered oxide cathode material in Example 1 0.9 (Ni 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05 X-ray diffraction results of O2.

[0021] Figure 2 Na, the sodium-ion battery layered oxide cathode material in Example 1 0.9 (Ni 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05 Results of the tethering test for O2.

[0022] Figure 3 Na, the sodium-ion battery layered oxide cathode material in Example 2 0.92 (Ni 0.35 Mn 0.46 Ti 0.08 Cu 0.08 Zn 0.03 X-ray diffraction pattern of O2.

[0023] Figure 4 Na, the sodium-ion battery layered oxide cathode material in Example 2 0.92 (Ni 0.35 Mn 0.46 Ti 0.08 Cu 0.08 Zn 0.03 Results of the tethering test for O2.

[0024] Figure 5 Na, the sodium-ion battery layered oxide cathode material in Example 3 0.94 (Ni 0.36 Mn 0.45 Ti 0.08 Cu 0.08 Zn 0.03 X-ray diffraction pattern of O2.

[0025] Figure 6 Na, the sodium-ion battery layered oxide cathode material in Example 3 0.94 (Ni 0.36 Mn 0.45 Ti 0.08 Cu 0.08 Zn 0.03 Results of the tethering test for O2.

[0026] Figure 7 Na1(N) is the sodium-ion battery layered oxide cathode material in Comparative Example 1. i0.4 Mn0.1 Ti 0.1 Cu 0.05 Zn 0.05 X-ray diffraction pattern of O2.

[0027] Figure 8 Na1(Ni) is the sodium-ion battery layered oxide cathode material in Comparative Example 1. 0.4 Mn 0.1 Ti 0.1 Cu 0.05 Zn 0.05 Results of the tethering test for O2.

[0028] Figure 9 Na1(Ni) is the sodium-ion battery layered oxide cathode material in Comparative Example 2. 0.33 Fe 0.33 Mn 0.33 X-ray diffraction pattern of O2 (NFM111).

[0029] Figure 10 Na1(Ni) is the sodium-ion battery layered oxide cathode material in Comparative Example 2. 0.33 Fe 0.33 Mn 0.33 The results of the tethering test of O2 (NFM111).

[0030] Figure 11 Na1(Ni) is the sodium-ion battery layered oxide cathode material in Comparative Example 3. 0.20 Fe 0.22 Cu 0.13 Mn 0.45 X-ray diffraction pattern of O2 (NFCM).

[0031] Figure 12 Na1(Ni) is the sodium-ion battery layered oxide cathode material in Comparative Example 3. 0.20 Fe 0.22 Cu 0.13 Mn 0.45 The results of the coin cell test for O2 (NFCM). Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] The technical solution of the present invention will be further described below through specific embodiments.

[0035] In the following embodiments, unless otherwise specified, the methods described are conventional methods; and unless otherwise specified, the reagents and materials described are commercially available.

[0036] Example 1 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. The chemical formula of the sodium electrode layer oxygen cathode material in this embodiment is determined to be Na. 0.9 (Ni 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05 O2 was used, and then the raw materials for each element were determined. Sodium was made from sodium carbonate, nickel and manganese from hydroxide precursors, titanium dioxide from titanium dioxide, copper oxide from copper oxide, and zinc oxide from zinc oxide. The weight ratio of the raw materials containing each element was determined according to the molar ratio of the chemical formulas, and after thorough mixing, the mixture was placed into a sintering furnace.

[0037] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 5 hours, then heat to 950℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material with a certain number of sodium vacancy sites (sodium layer). The chemical formula is Na. 0.9 (Ni 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05 )O2.

[0038] Figure 1 The sodium-ion battery layered oxide cathode material Na was prepared under the above process conditions. 0.9 (Ni 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05 The X-ray diffraction pattern of O2 shows that the space group of the prepared sodium-ion battery cathode material is R-3m, which belongs to a rhombohedral lattice crystal with lattice constants of a=b=0.297nm, c=1.61nm, α=β=90̊, γ=120̊. It is a typical O3 structure, and the diffraction pattern has no impurity peaks.

[0039] Figure 2 The sodium-ion battery cathode material Na produced under the above process conditions 0.9 (Ni 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05The coin cell test results for O2 under charge-discharge conditions of 2.0-4.3V showed that the 0.1C charging capacity reached 183.9 mAh / g, the discharge capacity reached 173.8 mAh / g, the initial efficiency at 0.1C reached 94.5%, the initial discharge capacity at 1C was 165.8 mAh / g, the discharge capacity at 1C for 50 cycles was 152.1 mAh / g, and the actual retention rate after 50 cycles reached 91.7%. The 1C / 0.1C discharge rate was 95.4%. These results indicate that when the sodium-ion electrode material has suitable valence states of transition metals, and the molar ratio of sodium is 0.9 when the valence states are balanced, a 10% vacancy appears in the sodium layer. Under a high voltage of 4.3V, the material exhibits excellent electrochemical performance.

[0040] Example 2 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. Determine the chemical formula of the sodium electrode layer oxygen cathode material as Na. 0.92 (Ni 0.35 Mn 0.46 Ti 0.08 Cu 0.08 Zn 0.03 O2 was used, and then the raw materials for each element were determined. Sodium was made from sodium carbonate, nickel and manganese from hydroxide precursors, titanium dioxide from titanium dioxide, copper oxide from copper oxide, and zinc oxide from zinc oxide. The weight ratio of the raw materials containing each element was determined according to the molar ratio of the chemical formulas, and after thorough mixing, the mixture was placed into a sintering furnace.

[0041] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 4 hours, then heat to 950℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material with a certain number of sodium vacancies in the sodium ion sites (sodium layer). The chemical formula is Na. 0.92 (Ni 0.35 Mn 0.46 Ti 0.08 Cu 0.08 Zn 0.03 )O2.

[0042] Figure 3 The sodium-ion battery layered oxide cathode material Na was prepared under the above process conditions. 0.92 (Ni 0.35 Mn 0.46 Ti 0.08 Cu 0.08 Zn 0.03The X-ray diffraction pattern of O2 shows that the space group of the prepared sodium-ion battery cathode material is R-3m, belonging to a rhombohedral lattice crystal with lattice constants: a=b=0.298nm, c=1.612nm, α=β=90̊, γ=120̊. It is a typical O3 structure, and the diffraction pattern shows no impurity peaks.

[0043] Figure 4 The sodium-ion battery cathode material Na produced under the above process conditions 0.92 (Ni 0.35 Mn 0.46 Ti 0.08 Cu 0.08 Zn 0.03 The coin cell test results for O2 under charge-discharge conditions of 2.0-4.3V show that the 0.1C charging capacity reaches 183.8mAh / g, the discharge capacity reaches 172.7mAh / g, the initial efficiency at 0.1C is 94.4%, the initial discharge capacity at 1C is 162.82mAh / g, the discharge capacity at 1C after 50 cycles is 149.53mAh / g, and the actual retention rate after 50 cycles reaches 91.28%. The 1C / 0.1C discharge rate is 94.25%. These results indicate that when the sodium molar ratio of oxygen in the sodium electrode layer is 0.92 at valence equilibrium, 8% vacancies appear in the sodium layer, and the material still exhibits excellent electrochemical performance under a high voltage of 4.3V during charge-discharge.

[0044] Example 3 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. The chemical formula of the sodium electrode layer oxygen cathode material in this embodiment is determined to be Na. 0.94 (Ni 0.36 Mn 0.45 Ti 0.08 Cu 0.08 Zn 0.03 O2 is used, and then the raw materials for each element are determined. Sodium is made from sodium carbonate, nickel and manganese from hydroxide precursors, titanium dioxide from titanium dioxide, copper from copper oxide, and zinc from zinc oxide. The weight ratio of the raw materials containing each element is determined according to the molar ratio of the chemical formula, and after thorough mixing, the mixture is placed in a sintering furnace.

[0045] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 4 hours, then heat to 950℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material with a certain number of sodium vacancies in the sodium ion sites (sodium layer). The chemical formula is Na. 0.94 (Ni 0.36 Mn 0.45 Ti 0.08 Cu 0.08 Zn 0.03 )O2.

[0046] Figure 5 The sodium-ion battery layered oxide cathode material Na was prepared under the above process conditions. 0.94 (Ni 0.36 Mn 0.45 Ti 0.08 Cu 0.08 Zn 0.03 The X-ray diffraction pattern of O2 shows that the space group of the prepared sodium-ion battery cathode material is R-3m, belonging to a rhombohedral lattice crystal with lattice constants: a=b=0.298nm, c=1.612nm, α=β=90̊, γ=120. It is a typical O3 structure. A small amount of NiO impurity peaks appear in the diffraction pattern, but the amount is very small.

[0047] Figure 6 The sodium-ion battery cathode material Na produced under the above process conditions 0.94 (Ni 0.36 Mn 0.45 Ti 0.08 Cu 0.08 Zn 0.03 The O2 electrode was tested under charge / discharge conditions of 2.0-4.3V. The 0.1C charging capacity reached 182.3 mAh / g, and the discharge capacity reached 174.8 mAh / g. The initial efficiency at 0.1C was 95.9%, the initial discharge capacity at 1C was 165.1 mAh / g, and the discharge capacity at 1C for 50 cycles was 149.5 mAh / g. The actual retention rate after 50 cycles reached 90.6%. The 1C / 0.1C discharge rate was 94.5%. These results indicate that when the sodium molar ratio in the sodium electrode layer reaches 0.94 at valence equilibrium, the sodium layer has only 6% vacancies. Although the charge / discharge capacities are very high at a high voltage of 4.3V, the 1C 50-cycle retention rate shows a significant decrease, exceeding one percentage point compared to when the sodium molar ratio is 0.9.

[0048] Example 4 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. The chemical formula of the sodium electrode layer oxygen cathode material in this embodiment is determined to be Na. 0.91 (Ni 0.38 Mn 0.42 Ti 0.1 Cu 0.05 Co 0.05 O2 was used, and then the raw materials for each element were determined. Sodium was made from sodium carbonate, nickel and manganese from hydroxide precursors, titanium dioxide from titanium dioxide, copper oxide from copper oxide, and cobalt tetroxide from cobalt. The weight ratio of the raw materials containing each element was determined according to the molar ratio of the chemical formulas, and after thorough mixing, the mixture was placed into the sintering furnace.

[0049] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 4 hours, then heat to 950℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material with a certain number of sodium vacancies in the sodium ion sites (sodium layer). The chemical formula is Na. 0.91 (Ni 0.38 Mn 0.42 Ti 0.1 Cu 0.05 Co 0.05 )O2.

[0050] The prepared sodium-ion battery layered oxide cathode material Na 0.91 (Ni 0.38 Mn 0.42 Ti 0.1 Cu 0.05 Co 0.05 X-ray diffraction results of O2 show that the space group of the prepared sodium-ion battery cathode material is R-3m, which belongs to rhombohedral lattice crystal. Its lattice constants are: a=b=0.298nm, c=1.612nm, α=β=90̊, γ=120̊, which is a typical O3 structure.

[0051] The prepared sodium-ion battery cathode material Na 0.91 (Ni 0.38 Mn 0.42 Ti 0.1 Cu 0.05 Co 0.05 The coin cell test results of O2 under charge-discharge conditions of 2.0-4.3V show that the 0.1C charging capacity reaches 183.4mAh / g, the discharge capacity reaches 172.7mAh / g, the initial discharge capacity at 1C is 163.2mAh / g, and the actual retention rate after 50 cycles reaches 91.5%. The 1C / 0.1C discharge rate is 94.7%. These results indicate that when the sodium molar ratio of the sodium element reaches 0.91 at valence equilibrium, the sodium layer has 9% vacancies. Under a high voltage of 4.3V, the charge-discharge capacity of the material is quite high, and the 1C 50-cycle retention rate is also at a very high level.

[0052] Example 5 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. Determine the chemical formula of the sodium electrode layer oxygen cathode material as Na. 0.93 (Ni 0.38 Mn 0.42 Ti 0.1 Cu 0.07 Co 0.03O2 was used, and then the raw materials for each element were determined. Sodium was made from sodium carbonate, nickel and manganese from hydroxide precursors, titanium dioxide from titanium dioxide, copper oxide from copper oxide, and cobalt tetroxide from cobalt. The weight ratio of the raw materials containing each element was determined according to the molar ratio of the chemical formulas, and after thorough mixing, the mixture was placed into the sintering furnace.

[0053] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 4 hours, then heat to 950℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material with a certain number of sodium vacancies in the sodium ion sites (sodium layer). The chemical formula is Na. 0.93 (Ni 0.38 Mn 0.42 Ti 0.1 Cu 0.07 Co 0.03 )O2.

[0054] The prepared sodium-ion battery layered oxide cathode material Na 0.93 (Ni 0.38 Mn 0.42 Ti 0.1 Cu 0.07 Co 0.03 X-ray diffraction results of O2 show that the space group of the prepared sodium-ion battery cathode material is R-3m, which belongs to rhombohedral lattice crystal. Its lattice constants are: a=b=0.298nm, c=1.612nm, α=β=90̊, γ=120̊, which is a typical O3 structure.

[0055] The prepared sodium-ion battery cathode material Na 0.93 (Ni 0.38 Mn 0.42 Ti 0.1 Cu 0.07 Co 0.03 The coin cell test results of O2 under charge-discharge conditions of 2.0-4.3V show that the 0.1C charging capacity reaches 185.6mAh / g, the discharge capacity reaches 174.5mAh / g, the initial discharge capacity at 1C is 163.7mAh / g, and the actual retention rate after 50 cycles reaches 91.2%. The 1C / 0.1C discharge rate is 93.8%. These results indicate that when the sodium molar ratio of the oxygen cathode material in the sodium electrode layer reaches 0.93 at valence equilibrium, there are 7% vacancies in the sodium layer. Under a high voltage of 4.3V, the charge-discharge capacity of the material is quite high, and the 1C 50-cycle retention rate is also at a very high level.

[0056] Comparative Example 1 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. First, determine the chemical formula of the sodium electrode layer oxygen cathode material as Na1(Ni). 0.4 Mn0.1 Ti 0.1 Cu 0.05 Zn 0.05 O2 was used, and then the raw materials for each element were determined. Sodium was made from sodium carbonate, nickel and manganese from hydroxide precursors, titanium dioxide from titanium dioxide, copper from copper oxide, and zinc from zinc oxide. The weight ratio of the raw materials containing each element was determined according to the molar ratio of the chemical formulas, and after thorough mixing, the mixture was placed into the sintering furnace.

[0057] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 4 hours, then heat to 950℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material without sodium vacancies (sodium ion sites). The chemical formula is Na1(Ni 0.4 Mn 0.1 Ti 0.1 Cu 0.05 Zn 0.05 )O2.

[0058] Figure 7 The sodium-ion battery layered oxide cathode material Na1(Ni) was prepared under the above process conditions. 0.4 Mn 0.1 Ti 0.1 Cu 0.05 Zn 0.05 The X-ray diffraction pattern of O2 shows that the space group of the prepared sodium-ion battery cathode material is R-3m, which belongs to a rhombohedral lattice crystal with lattice constants of a=b=0.298nm, c=1.612nm, α=β=90̊, γ=120̊, which is a typical O3 structure.

[0059] Figure 8 The sodium-ion battery cathode material Na1(Ni) prepared under the above process conditions 0.4 Mn 0.1 Ti 0.1 Cu 0.05 Zn 0.05The O2 electrode was tested under charge / discharge conditions of 2.0-4.3V. The 0.1C charge capacity reached 205.9 mAh / g, and the discharge capacity was 167.2 mAh / g, with an initial efficiency of 81.4% at 0.1C. The initial discharge capacity at 1C was 139.8 mAh / g, and the discharge capacity at 1C after 50 cycles was 118.3 mAh / g. The actual retention rate after 50 cycles was 84.6%. The 1C / 0.1C discharge rate was 83.6%. These results indicate that when the sodium molar ratio in the sodium electrode layer reaches 1 at valence equilibrium, and there are no vacancies in the sodium layer, although the initial charge capacity at 0.1C is very high under a high voltage of 4.3V, the discharge capacity is not high, resulting in a low initial efficiency. The 1C discharge capacity is also significantly lower than that of the sample in the example, and its cycle stability is considerably worse. The 1C / 0.1C rate is more than 10 percentage points lower than that of the example.

[0060] Comparative Example 2 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. First, determine the chemical formula of the sodium electrode layer oxygen cathode material as Na1(Ni). 0.33 Fe 0.33 Mn 0.33 O2, then determine the raw materials for each element, where sodium is produced using sodium carbonate, and nickel, iron, and manganese are produced using hydroxide precursors (Ni). 0.33 Fe 0.33 Mn 0.33) (OH)2. Determine the weight ratio of each element in the raw materials according to the chemical formula molar ratio, mix them thoroughly, and then put them into the sintering furnace.

[0061] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 4 hours, then heat to 950℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material without sodium vacancies (sodium ion sites). The chemical formula is Na1(Ni 0.33 Fe 0.33 Mn 0.33 )O2.

[0062] Figure 9 The sodium-ion battery layered oxide cathode material Na1(Ni) was prepared under the above process conditions. 0.33 Fe 0.33 Mn 0.33 The X-ray diffraction pattern of O2 (NFM111) shows that the space group of the prepared sodium-ion battery cathode material is R-3m, which belongs to a rhombohedral lattice crystal with lattice constants of a=b=0.298nm, c=1.599nm, α=β=90̊, γ=120̊, which is a typical O3 structure.

[0063] Figure 10The sodium-ion battery cathode material Na1(Ni) prepared under the above process conditions 0.33 Fe 0.33 Mn 0.33 O2 ( The NFM111 (NFM111) was tested under charge / discharge conditions of 2.0-4.3V. The 0.1C charge capacity reached 205.8 mAh / g, and the discharge capacity was 183.5 mAh / g. The initial efficiency at 0.1C was 89.1%, the initial discharge capacity at 1C was 153.2 mAh / g, and the discharge capacity at 1C after 50 cycles was 125.3 mAh / g. The actual retention rate after 50 cycles was 81.8%. The 1C / 0.1C discharge rate was 83.3%. NFM111 has a sodium molar ratio of 1 at valence equilibrium, and there are no vacancies in the sodium layer. While the initial charge / discharge capacity at 0.1C is very high at a high voltage of 4.3V, the initial efficiency and the 1C / 0.1C rate are relatively low, indicating poor cycle stability. In fact, NFM111 has even worse cycle performance under full-electric testing. Currently, even under full-electric testing, the cathode materials in this series can only cycle stably at a charge-discharge voltage below 4.0V, and the energy density at 4.0V charge-discharge is very low.

[0064] Comparative Example 3 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. First, determine the chemical formula of the sodium electrode layer oxygen cathode material as Na1(Ni). 0.20 Fe 0.22 Cu 0.13 Mn 0.45 O2, then determine the raw materials for each element, where sodium is produced using sodium carbonate, and nickel, iron, copper, and manganese are produced using hydroxide precursors (Ni). 0.20 Fe 0.22 Cu 0.13 Mn 0.45 (OH)2. Determine the weight ratio of each element in the raw materials according to the chemical formula molar ratio, mix them thoroughly, and then put them into the sintering furnace.

[0065] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 4 hours, then heat to 900℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material without sodium vacancies (sodium ion sites). The chemical formula is Na1(Ni 0.20 Fe 0.22 Cu 0.13 Mn 0.45 )O2.

[0066] Figure 11 The sodium-ion battery layered oxide cathode material Na1(Ni) was prepared under the above process conditions. 0.20 Fe 0.22Cu 0.13 Mn 0.45 The X-ray diffraction pattern of O2 (NFCM) shows that the space group of the prepared sodium-ion battery cathode material is R-3m, which belongs to a rhombohedral lattice crystal with lattice constants of a=b=0.296nm, c=1.616nm, α=β=90̊, γ=120̊, which is a typical O3 structure.

[0067] Figure 12 The sodium-ion battery cathode material Na1(Ni) prepared under the above process conditions 0.20 Fe 0.22 Cu 0.13 Mn 0.45 The NFCM (Non-Fluorescent Cell Molecular Weight) was tested under charge / discharge conditions ranging from 2.0 to 4.3V. The initial charge capacity at 0.1C was 179.5 mAh / g, and the discharge capacity was 171.1 mAh / g. The initial efficiency at 0.1C was 95.3%, the initial discharge capacity at 1C was 143.0 mAh / g, and the discharge capacity at 50 cycles at 1C was 127.2 mAh / g. The actual retention rate after 50 cycles was 88.9%. The 1C / 0.1C discharge rate was 83.6%. The molar ratio of sodium in NFCM at valence equilibrium should be 0.88, but currently, the sodium ratio in industrial preparation is 1, resulting in no vacancies in the sodium layer. While the initial charge / discharge capacity at 0.1C is relatively high under high voltage (4.3V), the 1C / 0.1C rate is low, indicating poor electrochemical performance under high current. Although the cycle retention rate reached 88.9% under 1C charge and discharge at 4.3V, the actual cycle stability of the material was not good under full charge at 4.25V. After modification and coating, NFCM could only barely cycle stably at 4.15V under full charge. Its electrochemical cycle stability was still significantly lower than that of the example with vacancy at sodium sites.

[0068] Comparative Example 4 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. First, determine the chemical formula of the sodium electrode layer oxygen cathode material as Na1(Ni). 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05 O2 was used, and then the raw materials for each element were determined. Sodium was made from sodium carbonate, nickel and manganese from hydroxide precursors, titanium dioxide from titanium dioxide, copper oxide from copper oxide, and cobalt tetroxide from cobalt. The weight ratio of the raw materials containing each element was determined according to the molar ratio of the chemical formulas, and after thorough mixing, the mixture was placed into the sintering furnace.

[0069] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 4 hours, then heat to 950℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material with no vacancies in the sodium ion sites (sodium layer). The chemical formula is Na1(Ni 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05 )O2.

[0070] The prepared sodium-ion battery layered oxide cathode material Na1(Ni) 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05 X-ray diffraction results of O2 show that the space group of the prepared sodium-ion battery cathode material is R-3m, which belongs to rhombohedral lattice crystal. Its lattice constants are: a=b=0.298nm, c=1.612nm, α=β=90̊, γ=120̊, which is a typical O3 structure.

[0071] The prepared sodium-ion battery cathode material Na1(Ni) 0.32 Mn 0.48 Ti 0.07 Cu 0.08 Zn 0.05 The results of the O2 coin cell test under charge-discharge conditions of 2.0-4.3V showed that the 0.1C charging capacity reached 204.7mAh / g, the discharge capacity was 168.3mAh / g, the initial discharge capacity at 1C was 138.7mAh / g, and the actual retention rate after 50 cycles reached 83.5%. The 1C / 0.1C discharge rate was 82.4%. These results indicate that when the sodium molar ratio of the sodium element in the sodium electrode layer reaches 1 at valence equilibrium, there are no vacancies in the sodium layer. Although the charging capacity of the material is very high under a high voltage of 4.3V, the discharge capacity is not significantly improved. Its 1C 50-cycle retention rate is significantly lower than that of Example 4 (the two samples only differ in sodium ratio), and its rate performance is also significantly worse.

[0072] Comparative Example 5 A method for preparing a sodium-ion battery layered oxide cathode material includes the following steps: S1. First, determine the chemical formula of the sodium electrode layer oxygen cathode material as Na1(Ni). 0.38 Mn 0.42 Ti 0.1 Cu 0.05 Co 0.05O2 was used, and then the raw materials for each element were determined. Sodium was made from sodium carbonate, nickel and manganese from hydroxide precursors, titanium dioxide from titanium dioxide, copper oxide from copper oxide, and cobalt tetroxide from cobalt. The weight ratio of the raw materials containing each element was determined according to the molar ratio of the chemical formulas, and after thorough mixing, the mixture was placed into the sintering furnace.

[0073] S2. Sintering in air atmosphere: First, heat to 550℃ and hold for 4 hours, then heat to 950℃ and hold for 12 hours to obtain a sodium-ion layered oxide cathode material with no vacancies in the sodium ion sites (sodium layer). The chemical formula is Na1(Ni 0.38 Mn 0.42 Ti 0.1 Cu 0.05 Co 0.05 )O2.

[0074] The prepared sodium-ion battery layered oxide cathode material Na1(Ni) 0.38 Mn 0.42 Ti 0.1 Cu 0.05 Co 0.05 X-ray diffraction results of O2 show that the space group of the prepared sodium-ion battery cathode material is R-3m, which belongs to rhombohedral lattice crystal. Its lattice constants are: a=b=0.298nm, c=1.612nm, α=β=90̊, γ=120̊, which is a typical O3 structure.

[0075] The prepared sodium-ion battery cathode material Na1(Ni) 0.38 Mn 0.42 Ti 0.1 Cu 0.05 Co 0.05 The coin cell test results of O2 under charge-discharge conditions of 2.0-4.3V showed that the 0.1C charging capacity reached 204.9 mAh / g, the discharge capacity was 170.6 mAh / g, the initial discharge capacity at 1C was 141.3 mAh / g, and the actual retention rate after 50 cycles reached 83.2%. The 1C / 0.1C discharge rate was 82.8%. These results indicate that when the sodium molar ratio of the sodium element in the sodium electrode layer reaches 1 at valence equilibrium, there are no vacancies in the sodium layer. Although the charging capacity of the material is very high under a high voltage of 4.3V, the discharge capacity is not significantly improved. Its 1C 50-cycle retention rate is significantly lower than that of Example 5 (the two samples only differ in sodium ratio), and its 0.1C initial efficiency and rate performance are significantly worse.

[0076] Table 1 Electrochemical Performance of Examples Table 2 Comparative Electrochemical Performance Table The above test results demonstrate that the sodium-ion battery cathode material provided in this invention improves the rate performance and cycle stability of sodium-ion battery cathode materials. Compared with the layered oxide cathode material with a sodium-vacancy molar ratio of 0 in Comparative Example 1, and the NFM111 and NFCM layered oxide cathode materials in Comparative Examples 2 and 3, the material exhibits significantly improved first-efficiency at 0.1C under high voltage charging and discharging at 4.3V. Its 1C discharge capacity is also significantly higher than that of the comparative examples, and its cycle stability is improved by more than 7%. This illustrates the excellent performance of the sodium-ion battery cathode material provided by this invention.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sodium-electric layered oxide cathode material, characterized in that, The chemical formula for the sodium-ion layered oxide cathode material is Na. x (M1 y M2 1-y-z M3 z O2, wherein M1 is selected from at least one of Ni, Cu, Zn and Mg; M2 is selected from at least one of Fe, Co and Cr; M3 is selected from at least one of Mn, Ti and Zr; M1 is an element with a basic oxidation state of +2, M2 is an element with a basic oxidation state of +3, and M3 is an element with a basic oxidation state of +4; wherein 0.87≤x≤0.95, 0.2≤y≤0.5, 0.4≤z≤0.65; the sodium-electric layered oxide cathode material has sodium vacancies, and the molar percentage of sodium vacancies in the sodium-electric layered oxide cathode material is greater than 0.

2. The sodium-ion layered oxide cathode material according to claim 1, characterized in that, The magnitude of x is determined by the valence equilibrium of the basic valences of M1, M2, and M3.

3. The sodium-ion battery layered oxide cathode material according to claim 1, characterized in that, The molar percentage of sodium vacancies in sodium-ion layered oxide cathode materials is the difference between z and y, where z > y.

4. The sodium-ion battery layered oxide cathode material according to claim 1, characterized in that, The molar percentage of sodium vacancies in sodium-ion layered oxide cathode material is 0.

1.

5. The sodium-ion layered oxide cathode material according to claim 1, characterized in that, The space group of the sodium-electric layered oxide cathode material is R-3m, which belongs to rhombohedral hexagonal crystal.

6. A method for preparing a sodium-ion battery layered oxide cathode material according to claim 1, characterized in that, Includes the following steps: The expression Na according to claim 1 x (M1 y M2 1-y-z M3 z O2, determine the molar percentages of sodium, M1, M2 and M3 elements; Based on the molar ratio of sodium, M1, M2 and M3, sodium-containing carbonates and hydroxides and / or oxides containing M1, M2 and M3 are used as raw materials. The raw materials are mixed evenly to obtain a mixture. The mixture was subjected to staged sintering to prepare a sodium-ionized layered oxide cathode material with sodium sites and vacancies.

7. The method for preparing the sodium-ion layered oxide cathode material according to claim 6, characterized in that, The staged sintering process is as follows: sinter at 450℃~650℃ for 3h~8h, followed by sintering at 800℃~1000℃ for 10h~20h.

8. The method for preparing the sodium-ion layered oxide cathode material according to claim 6, characterized in that, The sintering atmosphere for the staged sintering process is either an air atmosphere or an oxygen atmosphere.

9. The method for preparing the sodium-ion battery layered oxide cathode material according to claim 8, characterized in that, The flow rate of the sintering atmosphere is 60 L / min to 80 L / min.

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