A sodium-ion battery positive electrode material and a preparation method and application thereof

Abstract

The application belongs to the field of functional electronic materials, and particularly relates to a sodium ion battery positive electrode material and a preparation method and application thereof. x TM 1‑x O2, 0.7<=x<=0.97, the layered oxide positive electrode material provided by the application can effectively improve the valence state of the transition metal Cr and reduce the valence state of oxygen by substituting the Cr ion in the NaCrO2 with a low-valence transition metal ion, thereby enhancing the bond energy of the metal ion and oxygen bond, inhibiting the slip of the transition metal layer, stabilizing the structure, and enabling the material to have better cycle performance. Moreover, the introduction of the new transition metal expands the layer spacing of the sodium ion layer, widens the sodium ion transmission channel, optimizes the sodium ion transmission kinetics, and greatly improves the rate performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of functional electronic materials, and more specifically, relates to a sodium-ion battery cathode material, its preparation method, and its application. Background Technology

[0002] With the continuous progress and development of human society, fossil fuels such as oil, coal, and natural gas have become important energy sources for our daily production and life. However, these resources produce large amounts of greenhouse gases, which have a detrimental impact on the environment on which humanity depends for survival. Furthermore, the output of clean and renewable energy sources such as nuclear energy, wind energy, solar energy, tidal energy, and hydropower is intermittent and geographically limited, largely constrained by factors such as time, space, season, and climate change. Currently, large-scale energy storage systems are an effective means to solve this problem. Sodium resources are abundant and widely distributed, and the development of sodium-ion battery technology has a positive promoting effect on large-scale power storage systems. Sodium-ion batteries have high specific energy density, excellent energy conversion efficiency, and long charge-discharge cycle life. Therefore, sodium-ion batteries are expected to complement lithium-ion batteries and gradually replace lead-acid batteries.

[0003] Layered oxide cathode materials for sodium-ion batteries have been extensively studied due to their relative ease of synthesis, tunable voltage range, and high specific capacity. Among them, O3-type NaCrO2 is considered a promising material due to its stable electrochemical performance. However, several major challenges remain to be addressed. First, layered oxides often exhibit much more complex phase transitions during high-voltage charging, leading to irreversible and significant volumetric structural changes, resulting in decreased cycle life. Second, kinetic defects restrict kinetic transport, causing slow ion diffusion and rapid capacity decay at high rates.

[0004] To address the aforementioned issues, it is crucial to develop materials with high rate performance and long-term stability. Summary of the Invention

[0005] To address the shortcomings and improvement needs of existing technologies, this invention provides a sodium-ion battery cathode material, its preparation method, and its applications. The purpose of this invention is to...

[0006] To achieve the above objectives, according to one aspect of the present invention, a sodium-ion battery cathode material is provided, which is obtained by replacing Cr ions in NaCrO2 with low-valence transition metal ions that have an O3 structure, and has the general chemical formula NaCr. x TM 1-x O2, 0.7≤x≤0.97;

[0007] The low-valence transition metal ions are transition metal ions with a valence lower than +3.

[0008] Furthermore, low-valence transition metal ions are metal ions with radii in the range of 0.5-0.7 ppm.

[0009] Furthermore, the low-valence transition metal ion is Ni. 2+ Fe 2+ At least one of them.

[0010] Furthermore, the material particles have a hexagonal morphology and a particle size distribution of 50 nm to 100 nm.

[0011] The present invention also provides a method for preparing the sodium-ion battery cathode material as described above, comprising the following steps:

[0012] (1) A solid mixture containing a sodium source, a chromium source and a low-valence transition metal source is prepared to obtain a first precursor, wherein the stoichiometric ratio of Na:Cr:TM in the solid mixture is 1:(0.7~0.97):(0.03~0.3);

[0013] (2) The first precursor is pulverized to obtain the second precursor;

[0014] (3) After subjecting the second precursor to a solid-state sintering reaction, a third precursor is obtained, which serves as the positive electrode material of the sodium-ion battery, denoted as NaCr. x TM 1-x O2, 0.7≤x≤0.97, TM is a transition metal.

[0015] Furthermore, in step (1), the sodium source is at least one of Na2CO3, NaHCO3, NaOH, NaNO3, NaSO4, and Na2C2O4, and the low-valence transition metal source is at least one of NiO, Ni(OH)2, FeO, and Fe(OH)2.

[0016] Furthermore, in step (1), anhydrous ethanol is used as a dispersant, and sodium salt, chromium source and low-valence transition metal source are added to obtain the solid mixture;

[0017] In step (2), when wet ball milling is used for pulverization, the ball milling speed is 200-500 rpm and the pulverization time is 5-8 hours.

[0018] Furthermore, in step (3), the heat treatment temperature is 600-1000℃, the heat treatment time is 5-12h, and the heat treatment is carried out under the protection of a protective gas, which includes at least one of nitrogen, helium, argon and neon.

[0019] The present invention also provides a sodium-ion battery, wherein the positive electrode material is a sodium-ion battery positive electrode material as described above.

[0020] Furthermore, its negative electrode is at least one of graphite, hard carbon, mesophase carbon microspheres, carbon fiber, or graphene; in its sodium-containing electrolyte, the sodium salt is one or more of NaPF6, NaClO4, NaTFSI, NaBF4, NaBOB, NaODFB, NaFSI, C2F6NaNO4S2, and Na3PO4, and the solvent in the electrolyte is at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, 1,3-dioxocyclopentane, dimethyl sulfoxide, and propylene carbonate.

[0021] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0022] (1) The layered oxide cathode material provided by this invention can effectively increase the valence state of the transition metal Cr by substituting it with a low-valence transition metal element, and decrease the valence state of oxygen, thereby enhancing the bond energy between metal ions and oxygen bonds, suppressing the slippage of the transition metal layer, stabilizing the structure, and giving the material better cycle performance. Moreover, the introduction of the new transition metal expands the interlayer spacing of the sodium ion layer, widens the sodium ion transport channels, and optimizes the sodium ion transport kinetics, resulting in a significant improvement in the rate performance of the material.

[0023] (2) In this invention, a transition metal element with a radius similar to that of sodium ions in the same period is selected to replace NaCrO2. Due to the similar ionic radii, the transition metal element ions can enter the Cr layer uniformly without affecting its O3-type layered configuration.

[0024] (3) The present invention also adopts high-temperature solid-state sintering technology, which has a simple preparation process, low cost, and is similar to the process of lithium-ion battery cathode materials, and can be mass-produced; no industrial wastewater is generated during the production process, which is environmentally friendly. Attached Figure Description

[0025] Figure 1 A structural diagram of a sodium-ion battery cathode material provided in an embodiment of the present invention;

[0026] Figure 2 The X-ray diffraction pattern of the material corresponding to Example 1 provided in this embodiment of the invention;

[0027] Figure 3 SEM images of the materials corresponding to Example 1 provided in this embodiment of the invention;

[0028] Figure 4 The first charge-discharge curves of the cathode materials prepared using the materials corresponding to Example 1, Example 2 and Comparative Example 1 are provided for embodiments of the present invention.

[0029] Figure 5The rate performance diagrams of the materials corresponding to Example 1 and Comparative Example 1 are provided for embodiments of the present invention.

[0030] Figure 6 Cyclic performance diagrams of Example 1 and Comparative Example 1 provided for embodiments of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1

[0033] A sodium-ion battery cathode material is obtained by replacing Cr ions in NaCrO2 with low-valence transition metal ions that form an O3 structure. Its general chemical formula is NaCr. x TM 1-x O2, 0.7≤x≤0.97; where the above-mentioned low-valence transition metal ions are transition metal ions with a valence lower than +3, such as... Figure 1 As shown, sodium ions occupy octahedral sites between transition metal oxide layers, while Cr ions occupy octahedral 3b Wyckoff sites within the transition metal layer.

[0034] In this embodiment, the substitution of a low-valence transition metal allows the cathode material to possess both high cycle performance and high rate performance. Sodium chromite cathode materials undergo complex phase transitions during charging and discharging due to Cr layer slippage. These irreversible phase transitions cause drastic volume changes during cycling, severely impacting material stability. The introduction of a low-valence transition metal increases the valence of Cr ions while decreasing the valence of O ions, enhancing the bond energy between Cr and O, effectively suppressing phase transitions, and improving cycle stability. Furthermore, sodium chromite layered compounds exhibit poor rate performance when used as cathode materials in sodium-ion batteries, primarily due to their small interlayer spacing. This small interlayer spacing results in a high sodium ion diffusion barrier, hindering rapid ion diffusion and leading to rapid capacity decay during high-rate charging and discharging. Substitution with a low-valence transition metal helps increase interlayer repulsion, widening the sodium ion transport channels and improving the diffusion coefficient, thus resulting in better rate performance for the cathode material.

[0035] Sodium-ion battery cathodes need to maintain structural stability and good kinetic transport performance during sodium-ion insertion and extraction, while also exhibiting high reversible capacity, excellent rate performance, and good cycle stability and air stability. Currently, it has been reported that Ti... 4+ Ni 3+ Sb 3+ Mn 3+ etc., for Cr 3+ Improving the electrochemical performance of NaCrO2 through equivalent or higher-valence substitution is a common research approach. Researchers typically use ions with higher valence states to refine the grain size, stabilize the structure, and enhance the material's cycle performance. However, these high-valence ions are usually electrochemically inactive and do not participate in redox reactions during cycling to provide capacity, resulting in a loss of reversible capacity. Therefore, designing a high-performance sodium-ion battery cathode material through substitution with low-valence ions is particularly important.

[0036] In this embodiment, the design is 0.7≤x≤0.97. If the transition metal substitution is too small, the valence state of the transition metal cannot be effectively improved, and the improvement of material performance is limited. If the transition metal substitution is too large, the overall valence state of the transition metal layer will decrease, which will damage the structural stability of the material.

[0037] As a further preferred embodiment, the low-valence transition metal ions are metal ions with a radius in the range of 0.5-0.7 ppm.

[0038] As a further preferred embodiment, the low-valence transition metal ion is Ni. 2+ Fe 2+ At least one of the following. In this embodiment, a transition metal element from the same period with a radius similar to that of sodium ions was selected to substitute NaCrO2. Due to the similar ionic radii, the transition metal element ions can uniformly enter the Cr layer without affecting its O3-type layered configuration.

[0039] As a further preferred embodiment, the material particles have a hexagonal morphology and a particle size distribution of 50 nm to 100 nm. Smaller particle size facilitates the transport of sodium ions in the bulk phase and electrolyte, improving rate performance. However, excessively small particle size can cause severe agglomeration, affecting performance.

[0040] Example 2

[0041] A method for preparing a sodium-ion battery cathode material as described in Example 1 above includes the following steps:

[0042] (1) A solid mixture containing a sodium source, a chromium source and a low-valence transition metal source is prepared to obtain a first precursor, wherein the stoichiometric ratio of Na:Cr:TM in the solid mixture is 1:(0.7~0.97):(0.03~0.3);

[0043] (2) The first precursor is pulverized (by wet ball milling, dry ball milling, grinding, mixing machine, spray drying or sand milling) to obtain the second precursor;

[0044] (3) After subjecting the second precursor to a solid-state sintering reaction, a third precursor is obtained, which serves as the positive electrode material of the sodium-ion battery, denoted as NaCr. x TM 1-x O2, 0.7≤x≤0.97, TM is a transition metal.

[0045] After being ball-milled, the solid mixed powder is converted into a gaseous or liquid phase at the sintering temperature. It then diffuses from the outside of the particles to the non-contact surface of another solid phase to react. Once a product layer is formed between the reacting particles, further reactions will continue depending on the diffusion of one or more reactants through the product layer. This migration and diffusion occurs through the crystal lattice, surface, grain boundaries, or crystal cracks, generating the final product, namely the sodium-ion battery cathode material.

[0046] As a further preferred embodiment, in step (1), the sodium source is at least one of Na2CO3, NaHCO3, NaOH, NaNO3, NaSO4, and Na2C2O4, and the low-valence transition metal source is at least one of NiO, Ni(OH)2, FeO, and Fe(OH)2.

[0047] As a further preferred embodiment, in step (1), anhydrous ethanol is used as a dispersant, and sodium salt, chromium source and low-valence transition metal source are added to obtain the solid mixture;

[0048] In step (2), when using wet ball milling for pulverization, the ball milling speed is 200-500 rpm and the pulverization time is 5-8 hours.

[0049] As a further preferred embodiment, in step (3), the heat treatment temperature is 600-1000°C, the heat treatment time is 5-12 hours, and the heat treatment is carried out under the protection of a protective gas, which includes at least one of nitrogen, helium, argon and neon.

[0050] Example 3

[0051] A sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode material is a sodium-ion battery positive electrode material as described in Example 1.

[0052] Furthermore, its negative electrode is at least one of graphite, hard carbon, mesophase carbon microspheres, carbon fiber, or graphene; in its sodium-containing electrolyte, the sodium salt is one or more of NaPF6 (sodium hexafluorophosphate), NaClO4 (sodium perchlorate), NaTFSI (sodium trifluoromethanesulfonate), NaBF4 (sodium tetrafluoroborate), NaBOB (lithium bis(oxalato)borate), NaODFB (sodium difluorooxalato)borate, NaFSI (sodium bis(fluorosulfonyl)imide), C2F6NaNO4S2 (lithium bis(trifluoromethanesulfonyl)imide), and Na3PO4 (sodium phosphate). The solvent in the electrolyte is at least one of EC (ethylene carbonate), DEC (diethyl carbonate), DMC (dimethyl carbonate), EMC (methyl ethyl carbonate), FEC (fluoroethylene carbonate), DOL (1,3-dioxocyclopentane), DMSO (dimethyl sulfoxide), and PC (propylene carbonate).

[0053] The full cell prepared using a high-performance sodium-ion battery cathode in this embodiment has high power density, energy density, and safety performance, and is also low in cost, has good stability, and is practical.

[0054] To better illustrate the present invention, the following examples are provided for comparative explanation.

[0055] The relevant substitutions for Example 1 are shown in Table 1 below.

[0056] Table 1 Examples and Comparative Examples

[0057]

[0058]

[0059] The preparation methods of the examples and comparative examples are similar, both including the following steps:

[0060] (1) Precursor preparation by ball milling: Sodium carbonate, chromium oxide and transition metal oxide in the corresponding stoichiometric ratio are placed into a zirconia ball milling jar according to the value of x. An additional 5 wt.% sodium carbonate is added to prevent sodium ion loss. Anhydrous ethanol is used as a dispersant for ball milling. The obtained sample is vacuum dried at 60°C for 12 h.

[0061] (2) The precursor is sintered by solid-state method, that is, a certain amount of ground precursor powder is placed in a corundum crucible and placed in a tube furnace, and sintered in an argon atmosphere to obtain the product, which is the high-stability layered oxide cathode material.

[0062] (3) Battery fabrication: The sintered powder is ground and NMP is used as a solvent to mix 80g of active material, 10g of acetylene black (conductive agent) and 10g of PVDF (binder) evenly to obtain a slurry. The slurry is then evenly coated on an aluminum foil current collector, dried, sliced, and used as the positive electrode. A sodium sheet is used as the negative electrode. A button cell is fabricated in an argon-filled glove box and battery performance is tested.

[0063] The X-ray diffraction pattern of the cathode material in Example 1 is shown in the table below. Figure 2 As shown, the cathode material of Example 1 has a configuration of O3-type layered oxide with R-3m symmetry group; the SEM image of the cathode material of Example 1 is shown below. Figure 3 As shown, the particles are hexagonal in shape and approximately 0.4 μm in size. The small particle radius minimizes the transport pathway of Na, thus improving rate performance. The initial charge-discharge test results of the battery are as follows: Figure 4 As shown, the discharge capacities of Example 1, Example 2, and Comparative Example 1 are 135.8 mAh g, respectively. -1 120.0mAh g -1 and 111.3mAh g -1 The battery's rate performance test results are as follows: Figure 5 As shown, the discharge specific capacity was tested from 0.2C to 50C. At 50C, the discharge capacity of Example 1 was still 89.1 mAh g. -1 The battery's cycle performance test results are as follows: Figure 6 As shown, after 1000 cycles at 10C, the capacities of Example 1 and Comparative Example 1 were 74.4 and 39.1 mAh g, respectively. -1 .

[0064] Table 2 Discharge capacity and cycle performance test data

[0065]

[0066] The cycle performance test conditions were: voltage range of 2–3.6V, temperature of 25℃, and 50 cycles at 10C. Discharge capacity and cycle performance at 10C were tested at 0.2C and 50C respectively. The discharge capacity test conditions were: ambient temperature of 25℃ and voltage range of 2–3.6V.

[0067] The conclusions are as follows:

[0068] (1) By comparing the cathode materials obtained in Example 1, Example 2 and Comparative Example 1, it can be seen that the reversible capacity of Example 1 and Example 2 has been greatly improved. Among them, due to the reasonable ratio and selection of elements, the comprehensive performance of Example 1 is the highest. Compared with the prior art, the present invention proposes the substitution of low-valence elements, which can greatly improve the cycle performance and rate performance of the material.

[0069] (2) Comparing Example 1 with Comparative Examples 2 and 3, excessively low substitution concentrations result in insufficient transition metal atoms entering the transition metal layer, thus having a limited effect on optimizing the crystal structure; excessively high substitution concentrations reduce the valence state of the entire transition metal layer, leading to a decrease in performance. The range of 0.7≤x≤0.97 selected in this invention can achieve dual regulation of bond energy and crystal structure, and the reversible capacity is improved with increasing concentration.

[0070] (3) Comparing Example 1 and Comparative Example 4, the substitution of low-valence elements is more conducive to enhancing bond energy and maintaining higher stability. Although equivalent elements also enhance bond energy, their lack of chemical activity leads to a decrease in capacity.

[0071] (4) Comparing Example 1 and Comparative Example 5, during high-valence substitution, only substituted ions with properties (valence state and radius) closer to the substituted ion can undergo uniform substitution without destroying the original configuration, thus further improving the material performance. Ions with properties significantly different from the substituted ion will cause severe lattice distortion, leading to performance degradation.

[0072] (5) Comparing Example 1 and Comparative Example 5, during high-valence substitution, only substituted ions with properties (valence state and radius) closer to the substituted ion can undergo uniform substitution without destroying the original configuration, thus further improving the material performance. Ions with properties significantly different from the substituted ion will cause severe lattice distortion, leading to performance degradation.

[0073] (6) Comparing Example 1 and Comparative Example 6, during ball milling, appropriate ball milling speed and ball milling time can achieve sufficient stirring, which helps to control the particle size and thus improve performance.

[0074] (7) Comparing Example 1 and Comparative Example 7, during sintering, appropriate sintering temperature and sintering time can enable substitution ions to enter the transition metal layer and control the grain size.

[0075] In summary, this invention selects Ni, a low-valence transition metal ion with a similar periodic radius to chromium ions. 2+ Fe 2+ By replacing chromium, bond energy is enhanced and structure is optimized, resulting in a significant improvement in the cycle performance and rate performance of sodium-ion battery cathode materials.

[0076] In summary, this invention utilizes low-valence transition metal ions (such as Ni) 2+ Fe 2+ At least one low-valence ion in Cr 3+By substituting chromium ions to increase their valence and decrease the valence of oxygen ions, the Cr-O bond energy is enhanced, transition metal layer slip is suppressed, and phase transitions during charge and discharge are inhibited, thus improving the material's cycle performance. Optimizing the lattice constant widens the sodium ion transport channels, optimizes sodium ion kinetics, accelerates sodium ion diffusion, and improves the material's rate performance. Furthermore, this invention employs high-temperature solid-state sintering technology, resulting in a simple and low-cost preparation process, similar to that of lithium-ion battery cathode materials, allowing for mass production. The production process does not generate industrial wastewater, making it environmentally friendly.

[0077] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is 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 scope of protection of the present invention.

Claims

1. A sodium-ion battery cathode material, characterized in that, It is obtained by replacing the Cr ion in NaCrO2 with a low-valence transition metal ion, which has an O3 structure, and its general chemical formula is NaCr. x TM 1-x O2, 0.7≤x≤0.97; The low-valence transition metal ions are transition metal ions with a valence state lower than +3. The low-valence transition metal ion is Ni. 2+ Fe 2+ At least one of; Specifically, it is prepared through the following steps: (1) A solid mixture containing a sodium source, a chromium source and a low-valence transition metal source is prepared to obtain a first precursor, wherein the stoichiometric ratio of Na:Cr:TM in the solid mixture is 1:(0.7~0.97):(0.03~0.3). (2) The first precursor is pulverized to obtain the second precursor; (3) After subjecting the second precursor to a solid-state sintering reaction, a third precursor is obtained, which serves as the positive electrode material of the sodium-ion battery, denoted as NaCr. x TM 1-x O2, 0.7≤x≤0.97, TM is a transition metal; In step (1), anhydrous ethanol is used as a dispersant, and sodium salt, chromium source and low-valence transition metal source are added to obtain the solid mixture; In step (2), when wet ball milling is used for pulverization, the ball milling speed is 200~500 rpm and the pulverization time is 5~8 h; In step (3), the heat treatment temperature is 600~1000 ℃, the heat treatment time is 5~12 h, and the heat treatment is carried out under the protection of a protective gas, which includes at least one of nitrogen, helium, argon and neon.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The material particles have a hexagonal morphology and a particle size distribution of 50 nm to 100 nm.

3. A method for preparing the sodium-ion battery cathode material as described in claim 1, characterized in that, Includes the following steps: (1) A solid mixture containing a sodium source, a chromium source and a low-valence transition metal source is prepared to obtain a first precursor, wherein the stoichiometric ratio of Na:Cr:TM in the solid mixture is 1:(0.7~0.97):(0.03~0.3). (2) The first precursor is pulverized to obtain the second precursor; (3) After subjecting the second precursor to a solid-state sintering reaction, a third precursor is obtained, which serves as the positive electrode material of the sodium-ion battery, denoted as NaCr. x TM 1-x O2, 0.7≤x≤0.97, TM is a transition metal; In step (1), anhydrous ethanol is used as a dispersant, and sodium salt, chromium source and low-valence transition metal source are added to obtain the solid mixture; In step (2), when wet ball milling is used for pulverization, the ball milling speed is 200~500 rpm and the pulverization time is 5~8 h; In step (3), the heat treatment temperature is 600~1000 ℃, the heat treatment time is 5~12 h, and the heat treatment is carried out under the protection of a protective gas, which includes at least one of nitrogen, helium, argon and neon.

4. The preparation method according to claim 3, characterized in that, In step (1), the sodium source is at least one of Na2CO3, NaHCO3, NaOH, NaNO3, NaSO4, and Na2C2O4, and the low-valence transition metal source is at least one of NiO, Ni(OH)2, FeO, and Fe(OH)2.

5. A sodium-ion battery, characterized in that, Its positive electrode material is a sodium-ion battery positive electrode material as described in claim 1 or 2.

6. A sodium-ion battery according to claim 5, characterized in that, Its negative electrode is at least one of graphite, hard carbon, mesophase carbon microspheres, carbon fiber or graphene; in its sodium salt electrolyte, the sodium salt is one or more of NaPF6, NaClO4, NaTFSI, NaBF4, NaBOB, NaODFB, NaFSI, C2F6NaNO4S2, Na3PO4, and the solvent in the electrolyte is at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, 1,3-dioxocyclopentane, dimethyl sulfoxide, and propylene carbonate.

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