A manganese-based composite cathode material with a high sodium content P2 phase, a preparation method thereof, and a battery

Abstract

The present invention relates to a manganese-based composite cathode material with a high sodium content in the P2 phase, a preparation method thereof, and a battery. The chemical general formula of the manganese-based composite cathode material is: Na x M y1 N y2 Fe y3 Mn z O2, where x, y1, y2, y3, and z are the molar percentages of the corresponding elements respectively, and the relationship between y1, y2, y3, and z satisfies y1 + y2 + y3 + z = 1, 0.75 ≤ x ≤ 0.9, 0 < y1 ≤ 0.2, 0 < y2 ≤ 0.2, 0.05 ≤ y3 ≤ 0.2, 0.6 ≤ z ≤ 0.9; M includes at least one of Zn, Li, Nb, Ca, B, Al, Zr, Sn, Ti, Ru, Nb, Sb, or Mo; N includes at least one of Ni, Mg, or Cu; the sodium-ion battery prepared from this manganese-based composite cathode material has a working voltage of 2V to 4.3V and has the characteristics of good electrochemical performance, high safety performance, and wide application.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery materials, and particularly to a manganese-based composite cathode material with a high sodium content in the P2 phase, a preparation method thereof, and a battery. Background Art

[0002] Sodium ion batteries have received extensive attention due to the abundant reserves and low cost of sodium resources. Preparing cathode materials with excellent performance is the key to the practical application of sodium ion batteries. Among various cathode materials, layered oxides have a higher specific capacity than other types of materials when used as battery cathode materials, so they have become a hot topic of extensive research. Layered oxides mainly have two structures: P2-phase layered oxides and O3-phase layered oxides. Among them, P2-type layered transition metal oxides (Na x TMO2, where TM represents transition metal) cathodes have attracted extensive attention from researchers due to their advantages such as large specific capacity, high ionic conductivity, and easy synthesis.

[0003] In the P2-type structure, the unique occupation mode of sodium ions and the strong Na-Na and Na-TM electrostatic interactions usually cause the sodium layer to exhibit obvious Na + / vacancy ordered arrangement. The rearrangement between different Na + / vacancies generates metastable phases, resulting in many voltage plateaus in the charge-discharge curves of P2-type cathode materials, thus affecting the diffusion of Na + in the interlayer and the cycling performance of the material. At the same time, Na + shields the electrostatic repulsion between the transition metal layers (TMO2). During the charging process, when Na + is removed, the shielding of the sodium layer weakens, causing the TMO2 layer to slide, resulting in lattice distortion and limiting its future commercial application. Especially for manganese-based materials, due to the more complex phase transformation of manganese-based cathode materials and the relatively low average voltage of manganese-based materials (<2.8V), although their specific capacity is relatively higher, there are still significant limitations in practical applications.

[0004] Therefore, during the charge-discharge process, if more Na can be retained in the P2 structure matrix, the Na + / vacancy ordered arrangement can be inhibited, the electrostatic repulsive force between the TM layers can be alleviated, and the structural stability can be better maintained. Most of the currently proposed P2-phase cathode materials with a high sodium content are P2-Na 0.67 Ni 0.33 Mn 0.67Based on O2, the Mn content of the material is low while the Ni content is high. However, the price of Ni element is high, which will have a greater impact on the cost of the material and is not conducive to industrial production. But as the Ni content decreases, the inherent properties of the material may decay; in addition, a relatively high content of Ni is somewhat toxic and not conducive to safe production. Then, how to retain more sodium in the P2 structure matrix, thereby maintaining or improving the performance of the P2-type layered transition metal oxide material, while reducing the content of Ni in the material is what we need to study. Summary of the Invention

[0005] The object of the present invention is to address the problems existing in the prior art, and propose a manganese-based composite cathode material with a high sodium content P2 phase, a preparation method, and a battery.

[0006] The preparation method of a manganese-based composite cathode material with a high sodium content P2 phase provided by an embodiment of the present invention obtains a series of manganese-based composite cathode materials with a high sodium content P2 phase for sodium ion batteries, which have excellent cycle life, rate capability, and high specific capacity. The material contains an extremely low amount of Ni or no Ni, reducing the cost of the material and improving safety. At the same time, by adjusting the doped elements and ratios, the large polarization and low capacity retention rate that may be brought by Fe elements are eliminated. Since the raw materials are cheap and easily available, it is suitable for commercial production and has extremely excellent practical application prospects, and can be widely applied in fields such as solar energy, wind energy power generation, and electric vehicles.

[0007] To achieve the above object, in the first aspect, an embodiment of the present invention provides a manganese-based composite cathode material with a high sodium content P2 phase. The chemical general formula of the manganese-based composite cathode material is: Na x M y1 N y2 Fe y3 Mn z O2, where x, y1, y2, y3, and z are the molar percentages of the corresponding elements respectively, and the relationship between y1, y2, y3, and z satisfies y1 + y2 + y3 + z = 1, 0.75 ≤ x ≤ 0.9, 0 < y1 ≤ 0.2, 0 < y2 ≤ 0.2, 0.05 ≤ y3 ≤ 0.2, 0.6 ≤ z ≤ 0.9; M is an element that dopes and replaces Mn at the transition metal site, including at least one of Zn, Li, Nb, Ca, B, Al, Zr, Sn, Ti, Ru, Nb, Sb, or Mo; N is an element that dopes and replaces Mn at the transition metal site, including at least one of Ni, Mg, and Cu.

[0008] When the manganese-based composite cathode material is used in a sodium ion battery, the working voltage is between 2V and 4.3V.

[0009] Preferably, the manganese-based composite cathode material is used in a sodium-ion battery. During the first-cycle charging, iron ions are oxidized from +3 to +4, while manganese ions are oxidized from +3 to +4, and oxygen ions are oxidized from -2 (O 2- ) to -1 (O - ). During the first-cycle discharging, iron ions are reduced from +4 to +3, while manganese ions are reduced from +4 to +3, and oxygen ions are reduced from -1 (O - ) to -2 (O 2- ).

[0010] When the manganese-based composite cathode material contains nickel element, during the first-cycle charging, nickel ions will first be oxidized from +2 to +3, and then from +3 to +4; during the first-cycle discharging, nickel ions will first be reduced from +4 to +3, and then from +3 to +2.

[0011] Other elements in the manganese-based composite cathode material do not change their valence states.

[0012] The valence change process of the manganese-based composite cathode material after the first-cycle charge and discharge is the same as that of the first-cycle charge and discharge.

[0013] Preferably, the space group of the manganese-based composite cathode material is any one of P63 / mmc, P6322 or P63 / mcm, and the crystal structure is P2 phase.

[0014] In a second aspect, an embodiment of the present invention provides a preparation method of the manganese-based composite cathode material with high sodium content and P2 phase described in the first aspect above. The preparation method is a sol-gel method, including.

[0015] Weigh sodium source material, manganese source material, iron source material, compound containing M element and compound containing N element as raw materials according to the stoichiometric ratio of the chemical general formula of the manganese-based composite cathode material. Dissolve the raw materials in deionized water, add a complexing agent after stirring and mixing, and continue to stir at a certain temperature to form a precursor gel.

[0016] Place the precursor gel in a muffle furnace and carry out carbonization treatment in an air atmosphere to obtain an intermediate product powder.

[0017] Press the intermediate product powder into a disc, carry out calcination treatment in an air atmosphere, and then naturally cool to room temperature to obtain the manganese-based composite cathode material with high sodium content and P2 phase.

[0018] The chemical general formula of the manganese-based composite cathode material is: Na x M y1 N y2 Fe y3 Mn zO2, where x, y1, y2, y3, and z are the molar percentages of the corresponding elements respectively, and the relationship among y1, y2, y3, and z satisfies y1 + y2 + y3 + z = 1, 0.75 ≤ x ≤ 0.9, 0 < y1 ≤ 0.2, 0 < y2 ≤ 0.2, 0.05 ≤ y3 ≤ 0.2, 0.6 ≤ z ≤ 0.9; M is an element that dopes and substitutes the transition metal site Mn, including at least one of Zn, Li, Nb, Ca, B, Al, Zr, Sn, Ti, Ru, Nb, Sb, or Mo; N is an element that dopes and substitutes the transition metal site Mn, including at least one of Ni, Mg, and Cu.

[0019] Preferably, the sodium source material includes one or more of sodium nitrate, sodium acetate, sodium carbonate, sodium bicarbonate, sodium oxalate, and sodium hydroxide.

[0020] The manganese source material includes manganese nitrate and / or manganese acetate.

[0021] The iron source material includes at least one of iron nitrate, ferrous acetate, ferrous oxalate, and ferrous lactate.

[0022] The compound containing element M includes: containing Zn 2+ , Li + , Nb 5+ , Ca 2+ , B 3+ , Al 3+ , Zr 4+ , Sn 4+ , Ti 4+ , Ru 4+ , Sb 5+ , or Mo 6+ compounds containing at least one of the ions.

[0023] The compound containing element N includes: containing Ni 2+ , Mg 2+ , Cu 2+ compounds containing at least one of the ions.

[0024] The complexing agent is citric acid monohydrate; the mass ratio of the complexing agent to the raw materials is 2:1.

[0025] The mass ratio of the deionized water to the raw materials is 20:1 to 30:1.

[0026] Preferably, the carbonization treatment includes: heating to 300°C to 500°C at a heating rate of 2°C / min to 8°C / min and holding for 1 hour to 4 hours in an air atmosphere.

[0027] Preferably, the calcination treatment includes: heating to 800°C - 1000°C at a heating rate of 2°C / min - 8°C / min and calcining for 10 hours - 20 hours in an air atmosphere.

[0028] In a third aspect, an embodiment of the present invention provides a positive electrode sheet, which includes the high-sodium-content P2-phase manganese-based composite positive electrode material described in the first aspect above.

[0029] In a fourth aspect, an embodiment of the present invention provides a sodium-ion battery, which includes the positive electrode sheet described in the third aspect above; the sodium-ion battery further includes a separator, an electrolyte or a solid electrolyte, and a negative electrode sheet.

[0030] The operating voltage range of the sodium-ion battery is between 2V and 4.3V.

[0031] In a fifth aspect, an embodiment of the present invention provides a use of the sodium-ion battery described in the fourth aspect above, and the sodium-ion battery is used in one or more of energy storage devices for solar energy, wind energy power generation, smart grid peak shaving, distributed power stations, backup power supplies, communication base stations, and electric vehicles.

[0032] A preparation method of a high-sodium-content P2-phase manganese-based composite positive electrode material provided by an embodiment of the present invention prepares a high-sodium-content P2-phase manganese-based composite positive electrode material by forming a precursor gel from raw materials through a sol-gel method and then through a carbonization and calcination process; this preparation method is simple in operation, the raw materials are cheap and easy to obtain, the cost is low, and it is suitable for large-scale production.

[0033] For the high-sodium-content P2-phase manganese-based composite positive electrode material obtained by the preparation method provided by an embodiment of the present invention, firstly, the relatively high sodium content can effectively improve the first-cycle Coulombic efficiency, the first-cycle charging capacity and the cycle stability of the material and can inhibit the transformation of the material from the P2 phase to the O2 phase in the high-voltage range; secondly, the inexpensive Fe element is doped and introduced into the material to replace the Ni element, and the Fe element and the Mn element act synergistically to reduce the content of the Ni element to an extremely low level or completely without the Ni element, which not only reduces the material cost but also improves the safety of the material and is beneficial to industrial production. At the same time, by adjusting the proportion of each element in the material, the problems of large polarization and poor cycle stability that may be brought by the Fe element are avoided.

[0034] The sodium-ion battery prepared by using the high-sodium-content P2-phase manganese-based composite positive electrode material provided by an embodiment of the present invention has the characteristics of high specific capacity, excellent cycle performance, good safety performance and high practical value; the sodium-ion battery containing the high-sodium-content P2-phase manganese-based composite positive electrode material has a wide range of applications and can be applied to large-scale energy storage devices for solar power generation, wind power generation, electric vehicles, smart grid peak shaving, distributed power stations, backup power supplies or communication base stations. Description of the Drawings

[0035] Figure 1 Flow chart of the preparation method of the manganese-based composite cathode material with a high sodium content in the P2 phase provided by the embodiment of the present invention.

[0036] Figure 2 Flow chart of the method for preparing a cathode electrode sheet using the manganese-based composite cathode material with a high sodium content in the P2 phase as the cathode active material provided by the embodiment of the present invention.

[0037] Figure 3 X-ray diffraction (XRD) pattern of the manganese-based composite cathode material with a high sodium content in the P2 phase prepared in Examples 1-10 of the present invention.

[0038] Figure 4 XRD pattern of the manganese-based composite cathode material with a high sodium content in the P2 phase prepared in Examples 11-14 of the present invention.

[0039] Figure 5 Charge-discharge curve graph of the first week of the batteries assembled in Example 1, Example 2, and Example 5.

[0040] Figure 6 For the manganese-based composite cathode material with a high sodium content in the P2 phase prepared in Example 2, Na 0.8 Li 0.1 Ni 0.1 Fe 0.1 Mn 0.7 Charge-discharge curve graphs of the first to fifth weeks of the battery assembled with O2.

[0041] Figure 7 100-week cycle capacity curve graph of the batteries assembled in Example 1, Example 2, and Example 5.

[0042] Figure 8 For the manganese-based composite cathode material with a high sodium content in the P2 phase prepared in Example 5, Na 0.8 Li 0.07 Ni 0.11 Fe 0.12 Mn 0.7 Charge-discharge curve graphs of the first to fifth weeks of the battery assembled with O2.

[0043] Figure 9 100-week cycle capacity curve graph of the batteries assembled in Example 3, Example 4, and Examples 6-10.

[0044] Figure 10 Rate performance test graph of the battery assembled in Example 5.

[0045] Figure 11 Charge-discharge curve graph of the first week of the batteries assembled in Examples 11-14.

[0046] Figure 12 Charge and discharge curves of the battery assembled with the high-sodium-content P2-phase manganese-based composite cathode material Na 0.8 Mg 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2 in the first to fifth weeks.

[0047] Figure 13 100-week cycle capacity curves of the batteries assembled in Examples 11-14.

[0048] Figure 14 Na prepared for Comparative Example 1 0.67 Li 0.1 Ni 0.1 Fe 0.1 Mn 0.7 O2 material in the first to fifth weeks.

[0049] Figure 15 Comparison chart of the charge and discharge curves of the batteries assembled in Example 2 and Comparative Example 1 in the first week.

[0050] Figure 16 Comparison chart of the 100-week cycle capacity curves of the batteries assembled in Example 2 and Comparative Example 1.

[0051] Figure 17 Na prepared for Comparative Example 2 0.67 Mg 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2 material in the first to fifth weeks.

[0052] Figure 18 Charge and discharge curves of the batteries assembled in Example 11 and Comparative Example 2 in the first week.

[0053] Figure 19 100-week cycle capacity curves of the batteries assembled in Example 11 and Comparative Example 2. Detailed implementation manners

[0054] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0055] For those not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not indicated by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0056] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0057] An embodiment of the present invention provides a manganese-based composite cathode material with a high sodium content in the P2 phase, and its chemical general formula is: Na x M y1 N y2 Fe y3 Mn z O2, where x, y1, y2, y3, and z are the molar percentages of the corresponding elements respectively, and the relationship between y1, y2, y3, and z satisfies y1 + y2 + y3 + z = 1, 0.75 ≤ x ≤ 0.9, 0 < y1 ≤ 0.2, 0 < y2 ≤ 0.2, 0.05 ≤ y3 ≤ 0.2, 0.6 ≤ z ≤ 0.9.

[0058] Among them, the value of x can be any value within the range of 0.6 to 0.9. For example, it can be 0.6, 0.7, 0.8, 0.9, etc., but it is not limited to the listed values. Other unlisted values within this value range are equally applicable.

[0059] In the manganese-based composite cathode material of the present invention, a relatively high sodium content can effectively improve the first-cycle Coulombic efficiency, first-cycle charge capacity, and cycle stability of the material, and can inhibit the transformation of the material from the P2 phase to the O2 phase in the high-voltage range, avoiding problems such as a decrease in the initial Coulombic efficiency and overall capacity, poor cycle stability, deterioration of rate performance, and obvious voltage hysteresis during the charge and discharge process due to the phase change of the material. The reason is that in the conventional manganese-based P2-type layered oxide cathode material for sodium-ion batteries, the unique occupancy mode of sodium ions and the strong Na-Na and Na-TM electrostatic interactions usually lead to an obvious Na + / vacancy ordered arrangement in the sodium layer. At the same time, Na + shields the electrostatic repulsion between the transition metal layers (TMO2). During the charging process, when Na + is removed, the shielding of the sodium layer weakens, causing the TMO2 layer to slide, resulting in lattice distortion. This lattice distortion means that during the charge and discharge process, especially in the high-voltage range, the structure of the material changes, and it may not only transform from the P2 phase to the O2 phase, but also transform into other structures such as the OP4 phase. Therefore, during the charge and discharge process, if more Na can be retained in the P2 structure matrix, enhancing the shielding of the sodium layer during charging, weakening the sliding of the TMO2 layer, and inhibiting Na + / When the vacancies are arranged in an orderly manner, the stability of the structure can be better maintained. Therefore, when the sodium content in the manganese-based composite cathode material with a high sodium content provided by the embodiment of the present invention is relatively high, during the charging process, not only can more Na + be removed, but also more Na can remain in the structure to play a supporting role and inhibit structural distortion.

[0060] The value of y1 can be any value within the range of 0 to 0.2. For example, it can be 0, 0.05, 0.1, 0.15, 0.2, etc., but is not limited to the listed values. Other unlisted values within this value range are equally applicable.

[0061] The value of y2 can be any value within the range of 0 to 0.2. For example, it can be 0, 0.05, 0.1, 0.15, 0.2, etc., but is not limited to the listed values. Other unlisted values within this value range are equally applicable.

[0062] The value of y3 can be any value within the range of 0.05 to 0.2. For example, it can be 0, 0.05, 0.1, 0.15, 0.2, etc., but is not limited to the listed values. Other unlisted values within this value range are equally applicable.

[0063] The value of z can be any value within the range of 0.6 to 0.9. For example, it can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, etc., but is not limited to the listed values. Other unlisted values within this value range are equally applicable.

[0064] M is an element that dopes and replaces the transition metal site Mn, including at least one of Zn, Li, Nb, Ca, B, Al, Zr, Sn, Ti, Ru, Nb, Sb, or Mo.

[0065] N is an element that dopes and replaces the transition metal site Mn, including at least one of Ni, Mg, and Cu.

[0066] The crystal structure of the manganese-based composite cathode material is P2, and the phase space group is any one of the space groups P63 / mmc, P6322, or P63 / mcm.

[0067] When the manganese-based composite cathode material is used in a sodium-ion battery, the working voltage of the sodium-ion battery is between 2V and 4.3V.

[0068] During the first charge-discharge process of the manganese-based composite cathode material in a sodium-ion battery, charge compensation is mainly achieved by the gain and loss of electrons of transition metal cations, and at the same time, a small amount of anion redox occurs. The specific process of ion valence change of the manganese-based composite cathode material is introduced as follows.

[0069] During the first-week charging, the iron ions in the manganese-based composite cathode material are oxidized from trivalent (Fe 3+ ) to tetravalent (Fe 4+ ). At the same time, the manganese ions are also oxidized from trivalent (Mn 3+ ) to tetravalent (Mn 4+ ), and the oxygen ions are oxidized from divalent (O 2- ) to monovalent (O - ); during the first-week discharging, the iron ions are reduced from tetravalent (Fe 4+ ) to trivalent (Fe 3+ ). Similarly, the manganese ions are also reduced from tetravalent (Mn 4+ ) to trivalent (Mn 3+ ), and the oxygen ions are reduced from monovalent (O - ) to divalent (O 2- ).

[0070] When the manganese-based composite cathode material provided by the present invention contains nickel elements, during the first-week charging, the nickel ions will first be oxidized from divalent to trivalent, and then from trivalent to tetravalent; during the first-week discharging, the nickel ions will first be reduced from tetravalent to trivalent, and then from trivalent to divalent.

[0071] During the charge-discharge cycling process of the sodium-ion battery, in addition to the above-mentioned iron ions, manganese ions and nickel ions in the manganese-based composite cathode material, other elements do not change their valence during the battery cycling process.

[0072] For the cycling of the manganese-based composite cathode material after the first-week charge and discharge of the sodium-ion battery, the ion valence change process is the same as that of the first-week charge and discharge.

[0073] During the element ion valence change process of the manganese-based composite cathode material with a high sodium content in the P2 phase provided by the embodiment of the present invention during the first-week charge and discharge of the sodium-ion battery, the charge compensation is mainly achieved by the gain and loss of electrons by transition metal cations, indicating that it does not completely rely on anion redox reactions to provide capacity for the battery, and most of the capacity is obtained through cation redox.

[0074] The embodiment of the present invention provides a preparation method of the above-mentioned manganese-based composite cathode material with a high sodium content in the P2 phase, which is the sol-gel method, and specifically includes the following steps.

[0075] Step 110, weigh the sodium source material, manganese source material, iron source material, compound containing M element and compound containing N element as raw materials according to the stoichiometric ratio of the chemical general formula of the manganese-based composite cathode material, dissolve the raw materials in deionized water, add a complexing agent after stirring and mixing, and continue to stir at a certain temperature to form a precursor gel.

[0076] Among them, the chemical general formula of the manganese-based composite cathode material is: Na xM y1 N y2 Fe y3 Mn z O2, wherein x, y1, y2, y3, z are the molar percentages of the corresponding elements respectively, and the relationship between y1, y2, y3 and z satisfies y1+y2+y3+z=1, 0.75≤x≤0.9, 0<y1≤0.2, 0<y2≤0.2, 0.05≤y3≤0.2, 0.6≤z≤0.9; M is an element doped to replace Mn in the transition metal position, including at least one of Zn, Li, Nb, Ca, B, Al, Zr, Sn, Ti, Ru, Nb, Sb or Mo; N is an element doped to replace Mn in the transition metal position, including at least one of Ni, Mg and Cu.

[0077] The sodium source material includes one or more of sodium nitrate, sodium acetate, sodium carbonate, sodium bicarbonate, sodium oxalate and sodium hydroxide.

[0078] The manganese source material includes: manganese nitrate and / or manganese acetate.

[0079] The iron source material includes at least one of ferric nitrate, ferrous acetate, ferrous oxalate and ferrous lactate.

[0080] Compounds containing M elements include: 2+ , Li + , Nb 5+ , Ca 2+ , B 3+ 、Al 3+ 、Zr 4+ Sn 4+ 、Ti 4+ 、Ru 4+ , Sb 5+ Or Mo 6+ A compound containing at least one ion.

[0081] Compounds containing N include: 2+ Mg 2+ , Cu 2+ A compound containing at least one ion.

[0082] The complexing agent is citric acid monohydrate; the mass ratio of the complexing agent to the raw material is 2:1.

[0083] The mass ratio of deionized water to raw materials is 20:1 to 30:1.

[0084] Step 120, placing the precursor gel in a muffle furnace and performing carbonization treatment under air atmosphere to obtain an intermediate product powder.

[0085] Among them, the carbonization treatment includes: heating to 300°C to 500°C at a heating rate of 2°C / min to 8°C / min and holding for 1 hour to 4 hours in an air atmosphere.

[0086] Step 130: Press the intermediate product powder into a round tablet, perform calcination treatment in an air atmosphere, and then naturally cool to room temperature to obtain a manganese-based composite cathode material with a high sodium content P2 phase.

[0087] Among them, the calcination treatment includes: heating to 800°C to 1000°C at a heating rate of 2°C / min to 8°C / min and calcining for 10 hours to 20 hours in an air atmosphere.

[0088] In the present invention, when the calcination temperature in the above step 130 is in the range of 800°C to 1000°C, it can be any temperature value within this range. For example, it can be 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, etc., but it is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. The crystal structure of the manganese-based composite cathode material with a high sodium content P2 phase prepared within this calcination temperature range is the P2 phase, and it has good specific capacity and cycle stability.

[0089] In the embodiment of the present invention, the preparation method provided is applicable to all manganese-based composite cathode materials with a high sodium content P2 phase included in the aforementioned chemical formula Na x M y1 N y2 Fe y3 Mn z O2, and has universality.

[0090] The manganese-based composite cathode material with a high sodium content P2 phase provided by the embodiment of the present invention can be used as a cathode active material to prepare a cathode electrode sheet. The preparation of the cathode electrode sheet adopts a conventional preparation method, which can specifically include the following steps.

[0091] Step 210: Grind and mix the manganese-based composite cathode material with a high sodium content P2 phase and a conductive additive until evenly mixed to obtain a mixed powder.

[0092] Among them, the conductive additive includes one or more of conductive carbon black super p, acetylene black, carbon nanotubes, Ketjen black, and conductive graphite, preferably conductive carbon black super p; the mass ratio of the conductive additive to the manganese-based composite cathode material is 0 to 30 wt%.

[0093] The method of grinding and mixing adopts the existing known conventional methods, and it is only necessary to mix the manganese-based composite cathode material and the conductive additive evenly.

[0094] Step 220: Add a binder to the mixed powder, add a solvent, and continue to grind evenly to obtain a mixed slurry.

[0095] Among them, the binder includes one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), and polyimide (PI), preferably PVDF; the mass ratio of the binder to the manganese-based composite cathode material is 0-30 wt%.

[0096] The solvent includes one or more of N-methylpyrrolidone (NMP), dimethyl carbonate, ethylene carbonate, or diethyl carbonate, and preferably N-methylpyrrolidone is used.

[0097] Step 230: Coat the mixed slurry on the current collector, dry it, then place it in an oven for drying treatment, and cut it to obtain a positive electrode sheet.

[0098] Among them, the current collector includes but is not limited to aluminum foil; the conditions for the drying treatment are: vacuum baking at a temperature of 90°C to 120°C for 5 hours to 10 hours, and the cutting size is a small square of 8×8 mm or a circular sheet with a diameter of 12 mm. Then quickly transfer the cut electrode sheet to a glove box filled with argon for subsequent use. 2 and then quickly transfer the cut electrode sheet to a glove box filled with argon for subsequent use.

[0099] The embodiment of the present invention also provides a sodium ion battery, which includes the positive electrode sheet of the manganese-based composite cathode material containing the P2 phase with a high sodium content as described above, as well as a separator, an electrolyte or a solid electrolyte, and a negative electrode sheet; the working voltage range of the sodium ion battery is between 2V and 4.3V.

[0100] The embodiment of the present invention provides a use of the above sodium ion battery. The sodium ion battery can be used in large-scale energy storage devices for solar and wind power generation, or in energy storage devices for smart grid peak shaving, distributed power stations, backup power supplies, communication base stations, and electric vehicles.

[0101] To better understand the technical solutions provided by the present invention, the following uses multiple specific examples to separately illustrate the preparation process and characteristics of the manganese-based composite cathode material with a high sodium content P2 phase of the present invention.

[0102] Example 1

[0103] This example provides a preparation process of a manganese-based composite cathode material with a high sodium content P2 phase. The chemical formula of the manganese-based composite cathode material is Na 0.8 Li 0.1 Fe0.1 Mn 0.8 O2 (wherein, corresponding to the general formula x = 0.8, y1 = 0.1, y2 = 0, y3 = 0.1, z = 0.8, and M is the Li element), and the specific preparation process is as follows.

[0104] (1) Weigh 1 g of sodium source material anhydrous sodium acetate (CH3COONa), manganese source material manganese acetate tetrahydrate ((CH3COO)2Mn·4H2O), iron source material iron(III) nitrate nonahydrate (Fe(NO3)3·9H2O), and Li-ion-containing compound lithium acetate dihydrate (CH3COOLi·2H2O) as raw materials according to the stoichiometric ratio of the chemical formula of the manganese-based composite cathode material. Dissolve the raw materials in 20 g of deionized water, stir and mix for 30 min, then add 2 g of complexing agent citric acid monohydrate, and continue to stir at 80 °C for 10 hours to form a precursor gel.

[0105] (2) Place the precursor gel in a muffle furnace, heat it to 400 °C at a heating rate of 5 °C / min in an air atmosphere, sinter for 2 hours, and carbonize the raw materials to obtain an intermediate product powder.

[0106] (3) Press the intermediate product powder into a compact disk and place it in a muffle furnace. In an air atmosphere, heat it to 850 °C at a heating rate of 5 °C / min for calcination. The calcination time is 15 hours. After the calcination is completed, it is naturally cooled to room temperature to obtain a manganese-based composite cathode material with a high sodium content in the P2 phase, and the chemical formula is Na 0.8 Li 0.1 Fe 0.1 Mn 0.8 O2.

[0107] The XRD pattern of the manganese-based composite cathode material with a high sodium content in the P2 phase, Na 0.8 Li 0.1 Fe 0.1 Mn 0.8 O2, prepared in this example is as shown in Figure 3 It can be seen that the crystal structure of the manganese-based composite cathode material prepared in this example is the P2 phase.

[0108] Use the manganese-based composite cathode material with a high sodium content in the P2 phase prepared in this example to prepare a positive electrode plate, and use this positive electrode plate to assemble and test a sodium-ion battery. The specific assembly and test processes are as follows.

[0109] (1) Grind and mix the above-mentioned manganese-based composite cathode material powder with carbon black to obtain a mixed powder, and then add the binder PVDF. Among them, the manganese-based composite cathode material powder, carbon black, and binder are mixed at a mass ratio of 70:20:10, with a total of 0.1 g.

[0110] (2) Add an appropriate amount of N-methylpyrrolidone (NMP) solution and continue to grind evenly in a dry environment at room temperature to form a mixed slurry.

[0111] (3) Coat the mixed slurry evenly on the current collector aluminum foil, and dry it at 120 °C for 10 hours under vacuum conditions, then cut it into square electrodes with a size of 8×8 mm 2 and then quickly transfer it to a glove box filled with argon for subsequent use.

[0112] (4) Assemble the positive electrode obtained in the above steps with a separator, electrolyte, and negative electrode in a glove box filled with argon to form a sodium-ion battery. Using metallic sodium as the counter electrode, the electrolyte of the sodium-ion battery is a NaClO4 solution with a molar mass of 1 mol / L (where the solvent is 100 Vol% of polycarbonate PC and 5 Vol% of fluoroethylene carbonate FEC), and a glass fiber membrane is used as the battery separator, and a sodium-ion battery (CR2032 button battery) is assembled according to the conventional process.

[0113] Test the assembled sodium-ion battery: Use the constant current charge-discharge mode to perform charge-discharge tests at a current density of 1C, with a discharge cut-off voltage of 2V and a charge cut-off voltage of 4.3V.

[0114] The first-week charge-discharge curve of the sodium-ion battery assembled in this example at a 1C rate is as Figure 5 shown, and the cycle capacity curve is as Figure 7 shown. The first-week discharge specific capacity at 1C is 85.9 mAh / g, and the 100-week capacity retention rate is 99.8%. The test data summary is shown in Table 1.

[0115] Example 2

[0116] This example provides a preparation process and performance test of a manganese-based composite positive electrode material with a high sodium content P2 phase. The chemical formula of the prepared positive electrode material is Na 0.8 Li 0.1 Ni 0.1 Fe 0.1 Mn 0.7 O2 (where, corresponding to the general formula x = 0.8, y1 = 0.1, y2 = 0.1, y3 = 0.1, z = 0.7, M is the Li element, and N is the Ni element).

[0117] The difference between the preparation process of the manganese-based composite cathode material with a high sodium content in this example and that in Example 1 lies in that in step (1) of the preparation process, nickel source material nickel acetate tetrahydrate ((CH3COO)2Ni·4H2O) needs to be added as a raw material, together with sodium source material anhydrous sodium acetate (CH3COONa), manganese source material manganese acetate tetrahydrate ((CH3COO)2Mn·4H2O), iron source material iron(III) nitrate nonahydrate (Fe(NO3)3·9H2O), and Li-ion-containing compound lithium acetate dihydrate (CH3COOLi·2H2O), with a total of 1 g as raw materials, which are dissolved in 20 g of deionized water and stirred and mixed. Other preparation processes are exactly the same as those in Example 1.

[0118] The XRD pattern of the manganese-based composite cathode material with a high sodium content prepared in this Example 2 is as Figure 3 shown. It can be judged from the XRD pattern that the crystal structure of the material prepared in Example 2 is the P2 phase.

[0119] The manganese-based composite cathode material with a high sodium content prepared in this example is used to prepare a positive electrode sheet, and a sodium-ion battery is assembled using this positive electrode sheet for testing. The preparation process of the positive electrode sheet, the battery assembly process, and the testing process are all the same as those in Example 1.

[0120] The first-week charge-discharge curve of the sodium-ion battery assembled in this Example 2 at a 1C rate is as Figure 5 shown, the charge-discharge curves from the first week to the fifth week at 1C are as Figure 6 shown, and the cycle capacity curve is as Figure 7 shown. The first-week discharge specific capacity at 1C is 96.7 mAh / g, and the 100-week capacity retention rate is 91.2%. The test data summary is shown in Table 1.

[0121] The preparation methods, CR2032 coin cell assembly, and testing methods of the manganese-based composite cathode materials with a high sodium content provided in Examples 3 to 10 are all the same as those in Example 2. The specific differences lie in the contents of Li element, Fe element, Ni element, and Mn element, which are as follows.

[0122] Example 3

[0123] The chemical formula of the manganese-based composite cathode material with a high sodium content prepared in this example is Na 0.8 Li 0.05 Ni 0.1 Fe 0.1 Mn 0.75 O2 (where, corresponding to the general formula x = 0.8, y1 = 0.05, y2 = 0.1, y3 = 0.1, z = 0.75, M is Li element, N is Ni element), and its XRD is as Figure 3As shown in Example 3, it can be seen that the crystal structure is the P2 phase; the cyclic capacity curve of the test battery is as Figure 9 shown. At 1C, the initial discharge specific capacity is 90.1 mAh / g, the capacity retention rate after 100 cycles is 81.6%, the operating voltage range is 2V to 4.3V, and the test data summary is shown in Table 1.

[0124] Example 4

[0125] The chemical formula of the high-sodium-content P2-phase manganese-based composite cathode material prepared in this example is Na 0.8 Li 0.1 Ni 0.05 Fe 0.1 Mn 0.75 O2 (where, corresponding to the general formula x = 0.8, y1 = 0.1, y2 = 0.05, y3 = 0.1, z = 0.75, M is the Li element, and N is the Ni element). Its XRD is as Figure 3 shown in Example 4, and it can be seen that the crystal structure is the P2 phase; the cyclic capacity curve of the test battery is as Figure 9 shown. At 1C, the initial discharge specific capacity is 100.2 mAh / g, the capacity retention rate after 100 cycles is 99.6%, the operating voltage range is 2V to 4.3V, and the test data summary is shown in Table 1.

[0126] Example 5

[0127] The chemical formula of the high-sodium-content P2-phase manganese-based composite cathode material prepared in this example is Na 0.8 Li 0.07 Ni 0.11 Fe 0.12 Mn 0.7 O2 (where, corresponding to the general formula x = 0.8, y1 = 0.07, y2 = 0.11, y3 = 0.12, z = 0.7, M is the Li element, and N is the Ni element). Its XRD is as Figure 3 shown in Example 5, and it can be seen that the crystal structure is the P2 phase.

[0128] The first-week charge-discharge curve of the sodium-ion battery assembled in this example at a 1C rate is as Figure 5 shown, the cyclic capacity curve of the test battery is as Figure 7 shown, the charge-discharge curves for the first five weeks at 1C are as Figure 8 shown. At 1C, the initial discharge specific capacity is 99.9 mAh / g, the capacity retention rate after 100 cycles is 97.4%, the operating voltage range is 2V to 4.3V, and the test data summary is shown in Table 1. The rate chart is as Figure 10As shown, at discharge rates of 0.5C, 1C, 2C, 3C, and 5C, the discharge capacities of Example 5 are 109.8 mAh / g, 103.8 mAh / g, 97.5 mAh / g, 93.9 mAh / g, and 89.9 mAh / g respectively. The specific capacity at 5C can reach 82.2% of that at 0.5C, indicating excellent rate performance.

[0129] Example 6

[0130] The chemical formula of the prepared high-sodium-content P2-phase manganese-based composite cathode material is Na 0.8 Li 0.04 Ni 0.15 Fe 0.13 Mn 0.68 O2 (where, corresponding to the general formula x = 0.8, y1 = 0.04, y2 = 0.15, y3 = 0.13, z = 0.68, M is the Li element, and N is the Ni element). Its XRD is as shown in Example 6 of Figure 3 It can be seen that the crystal structure is the P2 phase; the cyclic capacity curve of the test battery is as shown in Figure 9 At 1C, the first-cycle discharge specific capacity is 97.7 mAh / g, the 100-cycle capacity retention rate is 96.2%, and the working voltage range is 2V - 4.3V. The test data summary is shown in Table 1.

[0131] Example 7

[0132] The chemical formula of the prepared high-sodium-content P2-phase manganese-based composite cathode material in this example is Na 0.8 Li 0.09 Ni 0.06 Fe 0.15 Mn 0.7 O2 (where, corresponding to the general formula x = 0.8, y1 = 0.09, y2 = 0.06, y3 = 0.15, z = 0.7, M is the Li element, and N is the Ni element). Its XRD is as shown in Example 7 of Figure 3 It can be seen that the crystal structure is the P2 phase; the cyclic capacity curve of the test battery is as shown in Figure 9 At 1C, the first-cycle discharge specific capacity is 93.5 mAh / g, the 100-cycle capacity retention rate is 88.1%, and the working voltage range is 2V - 4.3V. The test data summary is shown in Table 1.

[0133] Example 8

[0134] The chemical formula of the prepared high-sodium-content P2-phase manganese-based composite cathode material in this example is Na 0.8 Li 0.06 Ni 0.08 Fe 0.16 Mn 0.7O2 (wherein, corresponding to the general formula x = 0.8, y1 = 0.06, y2 = 0.08, y3 = 0.16, z = 0.7, M is the Li element, and N is the Ni element), its XRD is as shown in Figure 3 Example 8 in, and it can be seen that the crystal structure is the P2 phase; the cyclic capacity curve graph of the test battery is as shown in Figure 9 shown, the initial discharge specific capacity at 1C is 93.8 mAh / g, the capacity retention rate after 100 cycles is 88.2%, the working voltage range is 2V to 4.3V, and the test data summary is shown in Table 1.

[0135] Example 9

[0136] The chemical formula of the high-sodium-content P2-phase manganese-based composite cathode material prepared in this example is Na 0.8 Li 0.08 Ni 0.04 Fe 0.17 Mn 0.71 O2 (wherein, corresponding to the general formula x = 0.8, y1 = 0.08, y2 = 0.04, y3 = 0.17, z = 0.71, M is the Li element, and N is the Ni element), its XRD is as shown in Figure 3 Example 9 in, and it can be seen that the crystal structure is the P2 phase; the cyclic capacity curve graph of the test battery is as shown in Figure 9 shown, the initial discharge specific capacity at 1C is 90.9 mAh / g, the capacity retention rate after 100 cycles is 87.1%, the working voltage range is 2V to 4.3V, and the test data summary is shown in Table 1.

[0137] Example 10

[0138] The chemical formula of the high-sodium-content P2-phase manganese-based composite cathode material prepared in this example is Na 0.8 Li 0.06 Ni 0.05 Fe 0.18 Mn 0.71 O2 (wherein, corresponding to the general formula x = 0.8, y1 = 0.06, y2 = 0.05, y3 = 0.18, z = 0.71, M is the Li element, and N is the Ni element), its XRD is as shown in Figure 3 Example 10 in, and it can be seen that the crystal structure is the P2 phase; the cyclic capacity curve graph of the test battery is as shown in Figure 9 shown, the initial discharge specific capacity at 1C is 95.2 mAh / g, the capacity retention rate after 100 cycles is 89.2%, the working voltage range is 2V to 4.3V, and the test data summary is shown in Table 1.

[0139] Example 11

[0140] This example provides a preparation process and performance test of a manganese-based composite cathode material with a high sodium content in the P2 phase. The chemical formula of the prepared cathode material is Na 0.8 Mg 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2 (where, in the corresponding general formula, x = 0.8, y1 = 0.05, y2 = 0.15, y3 = 0.1, z = 0.7, M is the Mg element, and N is the Cu element). The specific preparation and test processes are as follows.

[0141] (1) Weigh 1 g of raw materials including the sodium source material anhydrous sodium acetate (CH3COONa), the manganese source material manganese acetate tetrahydrate ((CH3COO)2Mn·4H2O), the iron source material iron(III) nitrate nonahydrate (Fe(NO3)3·9H2O), the copper source material anhydrous copper acetate ((CH3COO)2Cu), and the magnesium source material magnesium acetate tetrahydrate ((CH3COO)2Mg·4H2O) according to the stoichiometric ratio. Dissolve the raw materials in 20 g of deionized water, stir and mix for 30 min, then add 2 g of the complexing agent citric acid monohydrate. After that, continue stirring at 80 °C for 10 hours to form a precursor gel.

[0142] (2) Place the precursor gel in a muffle furnace. Under an air atmosphere, heat it to 400 °C at a heating rate of 5 °C / min, and sinter for 2 hours to carbonize the raw materials to obtain an intermediate product powder.

[0143] (3) Press the intermediate product powder into a compact disc and place it in a muffle furnace. Under an air atmosphere, heat it to 850 °C at a heating rate of 5 °C / min for calcination. The sintering time is 15 hours. After the calcination is completed, let it cool to room temperature naturally to obtain the manganese-based composite cathode material with a high sodium content in the P2 phase, and its chemical formula is Na 0.8 Mg 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2.

[0144] The XRD pattern of the manganese-based composite cathode material with a high sodium content in the P2 phase, Na 0.8 Mg 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2 prepared in this example is as shown in Figure 4 It can be seen that the crystal structure is the P2 phase.

[0145] Using the manganese-based composite cathode material with a high sodium content in the P2 phase, Na 0.8 Mg 0.05 Cu 0.15 Fe 0.1 Mn0.7 Prepare the positive electrode plate with O2 and assemble a sodium-ion battery using this positive electrode plate for testing. The specific testing process is as follows.

[0146] (1) Mix the above-mentioned manganese-based composite positive electrode material powder with a high sodium content in the P2 phase with carbon black and the binder PVDF in a mass ratio of 70:20:10.

[0147] (2) Add an appropriate amount of NMP solution and grind it into a slurry in a dry environment at room temperature.

[0148] (3) Coat the slurry evenly on the current collector aluminum foil and dry it at 120 °C for 10 hours under vacuum conditions, then cut it into square electrode plates with a size of 8×8 mm 2 and then quickly transfer it to a glove box filled with argon for subsequent use.

[0149] (4) Assemble the positive electrode plate obtained in the above steps with a separator, electrolyte, and negative electrode plate into a sodium-ion battery in a glove box filled with argon. Use metallic sodium as the counter electrode, and use a sodium-ion battery electrolyte with a molar mass of 1 mol / L of NaClO4 solution (where the solvent is 100 Vol% of polycarbonate PC and 5 Vol% of fluoroethylene carbonate FEC). Use a glass fiber membrane as the battery separator and assemble it into a sodium-ion battery (CR2032 button cell) according to the conventional process.

[0150] Test the assembled sodium-ion battery: Use the constant current charge-discharge mode and perform charge-discharge tests at a current density of 1C. The discharge cut-off voltage is 2V, and the charge cut-off voltage is 4.3V.

[0151] The first-week charge-discharge curve of the sodium-ion battery assembled in this example at a 1C rate is as shown in Figure 11 as shown, the charge-discharge curves of the first five weeks are as shown in Figure 12 as shown, the cycle capacity curve is as shown in Figure 13 as shown. The first-week discharge specific capacity at 1C is 82.7 mAh / g, and the 100-week capacity retention rate is 83.1%. The test data summary is shown in Table 2.

[0152] The preparation methods, CR2032 button cell assembly, and test methods of the manganese-based composite positive electrode materials with a high sodium content in the P2 phase provided in Examples 12 to 14 are the same as those in Example 10. The specific difference lies in the different doped M elements, which are as follows.

[0153] Example 12

[0154] The chemical formula of the manganese-based composite positive electrode material with a high sodium content in the P2 phase prepared in this example is Na 0.8 Ni 0.05 Cu 0.15 Fe 0.1Mn 0.7 O2 (wherein, corresponding to the general formula x = 0.8, y1 = 0.15, y2 = 0.05, y3 = 0.1, z = 0.7, M is the Cu element, and N is the Ni element), and its XRD is as shown in Figure 4 Example 12, and it can be seen that the crystal structure is the P2 phase; the first-cycle charge-discharge curve of the sodium-ion battery assembled in this example at 1 C is as shown in Figure 11 shown, and the cycle capacity curve is as shown in Figure 13 shown. The first-cycle specific capacity at 1 C is 94.9 mAh / g, the capacity retention rate after 100 cycles is 80.2%, the working voltage range is 2 V to 4.3 V, and the test data summary is shown in Table 2.

[0155] Example 13

[0156] The chemical formula of the high-sodium-content P2-phase manganese-based composite cathode material prepared in this example is Na 0.8 Zn 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2 (wherein, corresponding to the general formula x = 0.8, y1 = 0.05, y2 = 0.15, y3 = 0.1, z = 0.7, M is the Zn element, and N is the Cu element), and its XRD is as shown in Figure 4 Example 14, and it can be seen that the crystal structure is the P2 phase; the first-cycle charge-discharge curve of the sodium-ion battery assembled in this example at 1 C is as shown in Figure 11 shown, and the cycle capacity curve is as shown in Figure 13 shown. The first-cycle specific capacity at 1 C is 94.8 mAh / g, the capacity retention rate after 100 cycles is 76.9%, the working voltage range is 2 V to 4.3 V, and the test data summary is shown in Table 2.

[0157] Example 14

[0158] The chemical formula of the high-sodium-content P2-phase manganese-based composite cathode material prepared in this example is Na 0.8 Al 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2 (wherein, corresponding to the general formula x = 0.8, y1 = 0.05, y2 = 0.15, y3 = 0.1, z = 0.7, M is the Al element, and N is the Cu element), and its XRD is as shown in Figure 4 Example 15, and it can be seen that the crystal structure is the P2 phase; the first-cycle charge-discharge curve of the sodium-ion battery assembled in this example at 1 C is as shown in Figure 11 shown, and the cycle capacity curve is as shown in Figure 13As shown, the first - cycle specific capacity is 90.8 mAh / g at 1C, the capacity retention rate after 100 cycles is 73.1%, the working voltage range is 2V - 4.3V, and the test data summary is shown in Table 2.

[0159] To better illustrate the effects of the embodiments of the present invention, Comparative Examples 1 - 2 are compared with the above - mentioned embodiments.

[0160] Comparative Example 1

[0161] Using Na with low sodium content 0.67 Li 0.1 Ni 0.1 Fe 0.1 Mn 0.7 O2 as Comparative Example 1, the preparation method is basically the same as that of Example 2, except that only the mass of the sodium - source material is different. The subsequent preparation materials and test processes are the same as those of Example 2. The crystal structure of Na 0.67 Li 0.1 Ni 0.1 Fe 0.1 Mn 0.7 O2 is the P2 phase. The first - cycle charge - discharge curve at 1C is shown as Figure 15 shown, the charge - discharge curves for the first five weeks are shown as Figure 14 shown, and the cycle capacity curve is shown as Figure 16 shown. The first - cycle specific capacity at 1C is only 84.7 mAh / g, the capacity retention rate after 100 cycles is 89.6%, the working voltage range is 2V - 4.3V, and the test data summary is shown in Table 1.

[0162] Comparative Example 2

[0163] Using Na with low sodium content 0.67 Mg 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2 as Comparative Example 2, the preparation method is basically the same as that of Example 11, except that only the mass of the sodium - source material is different. The subsequent preparation materials and test processes are the same as those of Example 11. The crystal structure of Na 0.67 Mg 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2 is the P2 phase. The first - cycle charge - discharge curve at 1C is shown as Figure 18 shown, the charge - discharge curves for the first five weeks are shown as Figure 17 shown, and the cycle capacity curve is shown as Figure 19 shown. The first - cycle specific capacity at 1C is only 75.4 mAh / g, the capacity retention rate after 100 cycles is 86.2%, the working voltage range is 2V - 4.3V, and the test data summary is shown in Table 2.

[0164] Table 1 summarizes the test data of the material chemical formulas prepared in Examples 1-10 and Comparative Example 1 and the assembled batteries, as follows.

[0165]

[0166] Table 2 summarizes the test data of the material chemical formulas prepared in Examples 11-14 and Comparative Example 2 and the assembled batteries, as follows.

[0167]

[0168] Through the test data in Table 1 and Table 2, and the attached Figure 3-19 to illustrate the performance of the high-sodium-content P2-phase manganese-based composite cathode material of the present invention.

[0169] Through Figure 3 , Figure 4 XRD of the materials, it can be seen that the obtained high-sodium-content P2-phase manganese-based composite cathode materials are all of pure-phase structure, proving that M ions and N ions have successfully replaced manganese and doped into the structure.

[0170] Through Figure 5 and Figure 7 It can be seen that Example 2 is doped with Ni element compared with Example 1, and Example 5 changes the doping ratio of each element in the material compared with Example 2, which has different degrees of electrochemical effects on the material. Among them, the initial specific capacity of Example 1 is 85.9 mAh / g, and the initial specific capacity of Example 2 is 96.7 mAh / g, proving that the introduction of a small amount of Ni element has a positive effect on the improvement of the material specific capacity. The 100-week capacity retention rate of Example 2 is 91.2%, and the 100-week capacity retention rate of Example 5 is 97.4%, proving that changing the element doping ratio in the cathode material can affect the cycle stability of the cathode material.

[0171] Through Figure 9 It can be seen that the 100-week capacity retention rates of Examples 3-10 are: 81.6%, 99.6%, 97.4%, 96.2%, 88.1%, 88.2%, 87.1% and 89.2% respectively, proving that the element doping ratio has a greater impact on the cycle stability of the cathode material, and it is found that the Na 0.8 Li 0.07 Ni 0.11 Fe 0.12 Mn 0.7 O2 prepared in Example 5 has the best performance. The specific capacity reaches 123 mAh / g at a rate of 0.1C, and the capacity retention rate is 97.4% after 100 cycles at a rate of 1C.

[0172] Through Figure 15 and Figure 16It can be seen that, under the condition that the elemental composition and content of the transition metal layer remain unchanged, the first-cycle specific capacity of the low-sodium-content P2-phase layered oxide Na 0.67 Li 0.1 Ni 0.1 Fe 0.1 Mn 0.7 O2 prepared in Comparative Example 1 is only 84.7 mAh / g, and the capacity retention rate after 100 cycles is also lower than that of the Na 0.8 Li 0.1 Ni 0.1 Fe 0.1 Mn 0.7 O2 prepared in Example 2, which proves that increasing the sodium content plays a great positive role in improving the specific capacity and cycle stability of the material.

[0173] It can be seen through Figure 10 that for the preferably selected material Na 0.8 Li 0.07 Ni 0.11 Fe 0.12 Mn 0.7 O2 (prepared in Example 5), when the rates are 0.5C, 1C, 2C, 3C, and 5C, the discharge capacities of Example 5 are 109.8 mAh / g, 103.8 mAh / g, 97.5 mAh / g, 93.9 mAh / g, and 89.9 mAh / g respectively. Its specific capacity at the 5C rate can reach 82.2% of that at the 0.5C rate, and the rate performance is excellent.

[0174] In Examples 11-14 of the present invention, syntheses were carried out using materials with different Fe and Mn contents, different M elements, and N elements. Figure 4 XRD images of Examples 11-14 are shown. It can be seen that the crystal structures are all of the P2 phase. Figure 11-13 The electrochemical performances of Examples 11-14 prove that different M and N elements have a great influence on the specific capacity and cycle stability of the material. The preferably selected M element is Li, and the N element is Ni. It can be seen through Figure 18 and Figure 19 that, under the condition that the elemental composition and content of the transition metal layer remain unchanged, the first-cycle specific capacity of the low-sodium-content P2-phase layered oxide Na 0.67 Mg 0.05 Cu 0.15 Fe 0.1 Mn 0.7 O2 prepared in Comparative Example 2 is only 75.4 mAh / g, which further proves that increasing the sodium content plays a great positive role in improving the specific capacity and cycle stability of the cathode material.

[0175] The inventors found during the synthesis of composite materials that to synthesize materials with different crystal phase structures, it is necessary to obtain them by changing the sodium content in the materials. According to the chemical general formula of the manganese-based composite cathode material of the present invention (Na x M y1 N y2 Fe y3 Mn z O2, where x, y1, y2, y3, and z are the molar percentages of the corresponding elements respectively, and the relationship between y1, y2, y3, and z satisfies y1 + y2 + y3 + z = 1, 0.75 ≤ x ≤ 0.9, 0 < y1 ≤ 0.2, 0 < y2 ≤ 0.2, 0.05 ≤ y3 ≤ 0.2, 0.6 ≤ z ≤ 0.9), even if only the sodium content range in the general formula is changed and the contents of other elements remain unchanged, it is still very difficult to synthesize pure O3 and P3 phases, but the main structure of the P2 phase is still retained. Unless the ratio of the transition metal layer is changed, that is to say, it further shows that by the preparation method of the present invention and weighing the raw materials according to the molar ratio of each element in the chemical general formula of the present invention, the obtained manganese-based composite cathode material is a pure P2 phase crystal structure.

[0176] A preparation method of a manganese-based composite cathode material with a high sodium content P2 phase provided by an embodiment of the present invention prepares a manganese-based composite cathode material with a high sodium content P2 phase through a sol-gel method to form a precursor gel from raw materials and then through a carbonization and calcination process; this preparation method is simple in operation, the raw materials are cheap and easy to obtain, the cost is low, and it is applicable to large-scale production.

[0177] For the manganese-based composite cathode material with a high sodium content P2 phase obtained by the preparation method provided by an embodiment of the present invention, firstly, a relatively high sodium content can effectively improve the first-cycle Coulombic efficiency, the first-cycle charge capacity, and the cycle stability of the material and can inhibit the transformation of the material from the P2 phase to the O2 phase in the high-voltage range; secondly, the doping of the low-cost Fe element is introduced into the material to replace the Ni element, and the Fe element and the Mn element act synergistically to reduce the content of the Ni element to an extremely low level or completely without the Ni element, which not only reduces the material cost but also improves the safety of the material, facilitating industrial production. At the same time, by adjusting the ratio of each element in the material, the problems of large polarization and poor cycle stability that the Fe element may bring are avoided.

[0178] The sodium-ion battery prepared by applying the manganese-based composite cathode material with a high sodium content P2 phase provided by an embodiment of the present invention has the characteristics of high specific capacity, excellent cycle performance, good safety performance, and high practical value; the sodium-ion battery containing the manganese-based composite cathode material with a high sodium content P2 phase has a wide range of applications and can be applied to large-scale energy storage devices such as solar power generation, wind power generation, electric vehicles, smart grid peak shaving, distributed power stations, backup power supplies, or communication base stations.

[0179] The specific embodiments described above have further elaborated on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only for the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A manganese-based composite cathode material with a high sodium content P2 phase, characterized in that, The chemical general formula of the manganese-based composite cathode material is: Na x M y1 N y2 Fe y3 Mn z O2, where x, y1, y2, y3, and z are the molar percentages of the corresponding elements, respectively, and the relationship between y1, y2, y3, and z satisfies y1 + y2 + y3 + z = 1, 0.75 ≤ x ≤ 0.9, 0 < y1 ≤ 0.2, 0 < y2 ≤ 0.2, 0.05 ≤ y3 ≤ 0.2, 0.6 ≤ z ≤ 0.9; M is an element that dopes and substitutes for Mn in the transition metal site, including at least one of Zn, Li, Nb, Ca, B, Al, Zr, Sn, Ti, Ru, Nb, Sb, or Mo; N is an element that dopes and substitutes for Mn in the transition metal site, including at least one of Ni, Mg, or Cu; When the manganese-based composite cathode material is used in a sodium-ion battery, its working voltage is between 2V and 4.3V; The manganese-based composite cathode material has a pure P2-phase crystal structure; The manganese-based composite cathode material is prepared by forming a precursor gel from raw materials through the sol-gel method and then undergoing carbonization and calcination processes; When the manganese-based composite cathode material is used in a sodium-ion battery, during the first-cycle charging, iron ions are oxidized from +3 to +4, manganese ions are oxidized from +3 to +4, and oxygen ions are oxidized from -2 to -1; during the first-cycle discharging, iron ions are reduced from +4 to +3, manganese ions are reduced from +4 to +3, and oxygen ions are reduced from -1 to -2; When the manganese-based composite cathode material contains nickel element, during the first-cycle charging, nickel ions will first be oxidized from +2 to +3 and then from +3 to +4; during the first-cycle discharging, nickel ions will first be reduced from +4 to +3 and then from +3 to +2; Other elements in the manganese-based composite cathode material do not change their valences; The valence change process of the manganese-based composite cathode material after the first-cycle charge and discharge is the same as that of the first-cycle charge and discharge.

2. The manganese-based composite cathode material according to claim 1, wherein The space group of the manganese-based composite cathode material is any one of P63 / mmc, P6322, or P63 / mcm.

3. A method for preparing the manganese-based composite cathode material with a high sodium content P2 phase according to any one of the above claims 1-2, characterized in that, The preparation method is the sol-gel method, including: Weighing sodium source material, manganese source material, iron source material, compound containing M element, and compound containing N element as raw materials according to the stoichiometric ratio of the chemical general formula of the manganese-based composite cathode material, dissolving the raw materials in deionized water, adding a complexing agent after stirring and mixing, and continuously stirring at a certain temperature to form a precursor gel; Placing the precursor gel in a muffle furnace and performing carbonization treatment in an air atmosphere to obtain an intermediate product powder; Pressing the intermediate product powder into a disc, performing calcination treatment in an air atmosphere, and then naturally cooling to room temperature to obtain the manganese-based composite cathode material with high sodium content and P2 phase; The chemical general formula of the manganese-based composite cathode material is: Na x M y1 N y2 Fe y3 Mn z O2, where x, y1, y2, y3, and z are the molar percentages of the corresponding elements, respectively, and the relationship between y1, y2, y3, and z satisfies y1 + y2 + y3 + z = 1, 0.75 ≤ x ≤ 0.9, 0 < y1 ≤ 0.2, 0 < y2 ≤ 0.2, 0.05 ≤ y3 ≤ 0.2, 0.6 ≤ z ≤ 0.9; M is an element that dopes and replaces Mn at the transition metal site, including at least one of Zn, Li, Nb, Ca, B, Al, Zr, Sn, Ti, Ru, Nb, Sb, or Mo; N is an element that dopes and replaces Mn at the transition metal site, including at least one of Ni, Mg, or Cu.

4. The preparation method according to claim 3, characterized in that, The sodium source material includes one or more of sodium nitrate, sodium acetate, sodium carbonate, sodium bicarbonate, sodium oxalate, and sodium hydroxide; The manganese source material includes manganese nitrate and / or manganese acetate; The iron source material includes at least one of iron nitrate, ferrous acetate, ferrous oxalate, and ferrous lactate; The compound containing the M element includes: containing Zn 2+ , Li + , Nb 5+ , Ca 2+ , B 3+ , Al 3+ , Zr 4+ , Sn 4+ , Ti 4+ , Ru 4+ , Sb 5+ or Mo 6+ ; and a compound of at least one of the ions The N-element-containing compound includes: a compound containing at least one ion of Ni 2+ , Mg 2+ , Cu 2+ ; The complexing agent is citric acid monohydrate; the mass ratio of the complexing agent to the raw materials is 2:1; The mass ratio of deionized water to the raw materials is 20:1 to 30:

1.

5. The preparation method according to claim 3, characterized in that, The carbonization treatment includes: heating at a heating rate of 2°C / min to 8°C / min to 300°C to 500°C and keeping warm for 1 hour to 4 hours in an air atmosphere.

6. The preparation method according to claim 3, characterized in that, The calcination treatment includes: heating at a heating rate of 2°C / min to 8°C / min to 800°C to 1000°C and calcining for 10 hours to 20 hours in an air atmosphere.

7. A positive electrode sheet, characterized in that, The positive electrode plate includes the manganese-based composite cathode material with high sodium content and P2 phase according to any one of claims 1-2 above.

8. A sodium-ion battery, characterized in that, The sodium-ion battery includes the positive electrode plate according to claim 7 above; the sodium-ion battery further includes a separator, an electrolyte or a solid electrolyte, and a negative electrode plate; The operating voltage range of the sodium-ion battery is between 2V and 4.3V.

9. Use of the sodium ion battery according to claim 8 above, characterized in that, The sodium-ion battery is used in one or more of energy storage devices for solar energy, wind energy power generation, smart grid peak shaving, distributed power stations, backup power supplies, communication base stations, and electric vehicles.

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