P2-type NaCrFeTi layered oxide, preparation method thereof and application of P2-type NaCrFeTi layered oxide as electrode material

Abstract

The invention discloses a P2 type NaCrFeTi layered oxide, which is prepared by the following steps: by taking sodium carbonate, ferric oxide, chromic oxide and titanium dioxide as raw materials, carrying out high-temperature solid-phase sintering to obtain a Na < 0.67 > Cr < 1 / 3 > Fe < 1 / 3 > Ti < 1 / 3 > O < 2 > layered oxide NCFT-33 / 33; a P2 phase structure belonging to a P63 / mmc space group; the microstructure is of a hexagonal prism-shaped structure, the particle size is 1-3 microns, and the material has a single-crystal structure; and the content of the main phase reaches more than 95. The preparation method is a one-step sintering method, and comprises the following steps: putting raw materials according to the chemical formula ratio, ball-milling, mixing, sintering and naturally cooling. When the material is used as a sodium ion battery negative electrode material, the reversible specific capacity is 60.00-80.00 mAh g <-1 >; when the number of cycles is 3000, the capacity retention rate is 91-93%, and the capacity loss rate of each cycle is only 0.0023-0.0030%.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for sodium-ion batteries, and particularly relates to a P2-type NaCrFeTi layered oxide, a preparation method thereof, and an application as an electrode material. Background Art

[0002] Sodium-ion batteries have the advantages of wide raw material sources and safety. Among the negative electrode materials for sodium-ion batteries, there are two most important types: hard carbon negative electrode materials and titanium-based oxide materials.

[0003] Regarding the technical problems existing in hard carbon negative electrode materials, as known from the existing literature 1 (Ultrafast Synthesis of HardCarbon Anodes for Sodium-ion Batteries: An Intense-Pulsed-Light-AssistedApproach to Photothermal Carbonization of Polymer / Carbon Nanotube CompositeFilms, Small Methods, 2025, 2401801. https: / / doi.org / 10.1002 / smtd.202401801), this technical solution uses agricultural waste olive shell as a raw material, and by regulating the carbonization temperature and pre-carbonization strategy, a hard carbon negative electrode material with excellent sodium storage performance is successfully prepared, obtaining a technical effect that the capacity retention rate is 87% after 1000 cycles under the condition of a current density of 1A g -1 However, such hard carbon negative electrode materials have the characteristic that more than half of the discharge capacity is distributed on an extremely low discharge plateau of 0 - 0.1V. According to the existing literature 2 (Electrochemical NaInsertion and Solid Electrolyte Interphase for Hard-Carbon Electrodes andApplication to Na-Ion Batteries, Adv. Funct. Mater., 2011. 21: 3859 - 3867. https: / / doi.org / 10.1002 / adfm.201100854), all organic electrolytes will undergo electrochemical decomposition near 0V, resulting in capacity attenuation. Moreover, the heat released by the decomposition reaction will also cause safety problems of thermal runaway, simply referred to as the voltage problem. From the existing literature 1 and the existing literature 2, due to the characteristics of hard carbon negative electrode materials, the above voltage problem cannot be completely solved.

[0004] Regarding titanium-based oxides, such as those prepared by the traditional solid-state sintering method in the existing literature 3 (An O3-type Oxide with Low Sodium Content as the Phase-Transition-Free Anode for Sodium-Ion Batteries, Angew. Chem. Int. Ed., 2018, 57, 7056. https: / / doi.org / 10.1002 / anie.201801923), to prepare an oxide material of Na 0.66 Mg 0.34 Ti 0.66 O2. The technical effect is to achieve a reversible specific capacity of 98 mAh g -1 in the voltage range of 0.4 - 2.0 V at a rate of 0.1 C, with an average voltage of 0.83 V. Comparing with the aforementioned existing literature, it can be seen that the redox potential of the titanium-based oxide Ti 3+ / Ti 4+ is 0.4 - 0.8 V, that is, there is no problem of electrolyte decomposition caused by the voltage problem mentioned above. However, this technical solution has the problem of poor cycle stability. There are two reasons for the poor cycle stability:

[0005] 1. The problem of failure caused by gas generation induced by trivalent titanium. The specific principle is that trivalent titanium itself has poor stability, and in this technical solution, there is a situation where the Ti element transforms between trivalent titanium and tetravalent titanium. Therefore, when the number of cycles is 128, the capacity retention rate drops to 94.2%. In the presence of trivalent titanium, it is easy to react with the electrolyte to generate gas, which will cause battery failure. This technical problem is simply referred to as the problem of failure caused by gas generation induced by trivalent titanium;

[0006] 2. Regarding the structural change problem caused by the O3-type phase transition, according to the existing literature 4 (Practical Cathodes for Sodium-Ion Batteries: Who Will Take The Crown?Adv. Energy Mater., 2023, 13, 2301975. https: / / doi.org / 10.1002 / aenm.202301975), it is known that P2-type layered structure materials have a lower Na diffusion activation energy than O3-type layered structure materials. The migration path of sodium ions in O3-type materials is from one octahedral position through a tetrahedral position and then to an octahedral position. The energy of the transition state tetrahedral position is relatively high, resulting in a large energy barrier. The migration path of sodium ions in P2-type materials is from one hexagonal prism to another hexagonal prism and then to another hexagonal prism, with a smaller migration energy barrier. On the other hand, during the insertion and extraction of Na ions in O3-type layered materials, there is often a "O3-P3-O3" phase transition, which leads to a decrease in rate performance and cycling performance. In contrast, P2 materials often maintain the P2 structure during cycling, which can avoid the above problems and ensure good performance at high rates. Summary of the Invention

[0007] The object of the present invention is to provide a P2-type NaCrFeTi layered oxide, its preparation method, and its application as an electrode material.

[0008] In view of the technical problems existing in the prior art, the following methods are adopted to solve the above problems:

[0009] 1. By adjusting the ratio of transition metal elements and the content of sodium element, a P2-phase structure NaCrFeTi layered oxide is prepared to improve the cycling performance and phase purity;

[0010] 2. By adjusting the voltage range, the oxidation and reduction of Ti element and Cr are inhibited during the charge and discharge process, and the high reversibility of Fe element, that is, the variable valence of Fe element, is used to achieve charge balance and improve the long-term cycling stability;

[0011] In order to achieve the above object of the invention, the technical solution adopted by the present invention is as follows:

[0012] A P2-type NaCrFeTi layered oxide, using sodium carbonate, iron oxide, chromium oxide, and titanium dioxide as raw materials, and obtaining Na 0.67 Cr 1 / 3 Fe 1 / 3 Ti 1 / 3O2-layered oxide NCFT-33 / 33; the NCFT-33 / 33 layered oxide belongs to the P2 phase structure of the P63 / mmc space group; the microscopic morphology of the NCFT-33 / 33 layered oxide is a hexagonal prism structure with a particle size of 1-3 microns and has a single crystal structure; the main phase of the NCFT-33 / 33 layered oxide is Na 0.67 Fe 1 / 3 Cr 1 / 3Ti 1 / 3 O2, with a content reaching more than 95-98%.

[0013] A preparation method of P2-type NaCrFeTi layered oxide, comprising the following steps: using a one-step sintering method. First, prepare sodium carbonate, iron oxide, chromium oxide and titanium dioxide as raw materials to meet a certain chemical formula, and an additional 5 wt.% burn loss of Na. Then, under certain conditions, ball-mill and mix the raw materials to obtain a mixed solution. After that, centrifuge, filter and dry the mixed solution to obtain a precursor and then press it into tablets. Finally, sinter the precursor under certain conditions, and cool it naturally after sintering to obtain the NaCrFeTi layered oxide, simply referred to as NCFT;

[0014] Among them, with the chemical formula of Na 0.67 Cr 1 / 3 Fe 1 / 3 Ti 1 / 3 O2, that is, the molar ratio of Na:Cr:Fe:Ti is 2:1:1:1, simply referred to as the Cr / Fe ratio of 0.33:0.33;

[0015] The chromium oxide is the Cr source;

[0016] The conditions for the ball milling are as follows: under air conditions, the ball milling speed is 300-500 r / min, the ball milling time is 3-6 h, and the ball milling medium is anhydrous ethanol;

[0017] The conditions for the sintering are as follows: under argon conditions, the sintering temperature is 800-1000 °C, and the sintering time is 10-15 h.

[0018] When the P2-type NaCrFeTi layered oxide is used as the anode material of a sodium-ion battery, in the voltage range of 0.8-2.7 V and the current density of 20 mAg -1 Under the conditions of, the reversible specific capacity is 60.00-80.00 mAh g -1 , reaching 67.1-89.53% of the theoretical specific capacity of 89.36 mAh g -1 ; in the voltage range of 0.8-2.7 V and the current density of 10C, when the number of cycles is 3000, the reversible specific capacity is 52.36-56.47 mAh g-1 , the capacity retention rate is 91 - 93%, and the capacity loss rate per cycle is only 0.0023 - 0.0030%.

[0019] The beneficial technical effects obtained by the present invention can be known through tests:

[0020] EDS test shows that the prepared NaCrFeTi layered oxide contains Na element, Cr element, Fe element and Ti element, and the distribution of each element is uniform.

[0021] Through XRD test and refinement, it can be known that there are Na 0.67 Fe 1 / 3 Cr 1 / 3 Ti 1 / 3 O2 and Cr 0.2 Fe 1.8 O3 characteristic peaks, and the content of Na 0.67 Fe 1 / 3 Cr 1 / 3 Ti 1 / 3 O2 reaches 95 - 98%, and the impurity phase is Cr 0.2 Fe 1.8 O3, with a content of 2 - 5%; in addition, Na 0.67 Fe 1 / 3 Cr 1 / 3 Ti 1 / 3 O2 belongs to the P2 phase structure in the P63 / mmc space group, thus determining that the material has a P2 phase structure. It is proved that by adjusting the element ratio and changing the precursor, two substantially different structures of P2 and O3 phases can be obtained, and changing the ratio can reduce the content of the impurity phase and improve the phase purity of the material.

[0022] SEM test and TEM test show that the NaCrFeTi layered oxide has a hexagonal columnar structure, and the surface is smooth, with a particle size of 1 - 3 microns. The layer spacing is It has a single crystal structure.

[0023] Charge-discharge performance test shows that the NaCrFeTi layered oxide electrode material has a voltage range of 0.8 - 2.7V and a current density of 20mAg -1 Under the condition of, 60.00 - 80.00mAh g -1 , reaching 67.1 - 89.53% of the theoretical specific capacity of 89.36mAh g -1 .

[0024] Long cycle tests show that for the NaCrFeTi layered oxide electrode material, at a voltage range of 0.8 - 2.7 V and a current density of 10 C, when the number of cycles is 3000, the reversible specific capacity is 52.36 - 56.47 mAh g -1 , and the capacity retention rate is 91 - 93%, with the capacity loss rate per cycle being only 0.0023 - 0.0030%.

[0025] Therefore, compared with the prior art, the present invention has the following advantages:

[0026] 1. Compared with the prior art, the prepared P2-type NaCrFeTi layered oxide has a higher redox potential, which can avoid the electrochemical decomposition of the organic electrolyte and improve the safety performance;

[0027] 2. Compared with the prior art, in the prepared P2-type NaCrFeTi layered oxide, Cr and Ti play a role in stabilizing the structure, and the redox of Fe has higher reversibility and stability during charge and discharge, which can improve the long cycle stability of the material; BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the EDS diagram of NCFT-33 / 33 in Example 1;

[0029] Figure 2 It is the XRD refinement diagram of NCFT-33 / 33 in Example 1;

[0030] Figure 3 It is the SEM diagram of NCFT-33 / 33 in Example 1;

[0031] Figure 4 It is the TEM diagram of NCFT-33 / 33 in Example 1;

[0032] Figure 5 It is the charge-discharge specific capacity diagram of the electrode material of NCFT-33 / 33 in Example 1;

[0033] Figure 6 It is the long cycle diagram of the electrode material of NCFT-33 / 33 in Comparative Example 1;

[0034] Figure 7 It is the XRD refinement diagram of the NCFT-30 / 36 material in Comparative Example 1;

[0035] Figure 8 It is the charge-discharge curve diagram of the NCFT-30 / 36 material in Comparative Example 2;

[0036] Figure 9 It is the XRD refinement diagram of the NCFT-Ac material with chromium acetate as the precursor in Comparative Example 2;

[0037] Figure 10 Charge-discharge curves of the NCFT-Ac material with chromium acetate as the precursor in Comparative Example 2. Detailed implementation manners

[0038] The present invention will be further described in detail with reference to the accompanying drawings of the specification through examples, but it is not a limitation to the present invention.

[0039] Example 1

[0040] A preparation method of a P2-type NaCrFeTi layered oxide, using a one-step sintering method. First, with the chemical formula of Na 0.67 Cr 1 / 3 Fe 1 / 3 Ti 1 / 3 O2, that is, the molar ratio of Na:Cr:Fe:Ti is 2:1:1:1, simply referred to as the Cr / Fe ratio of 0.33:0.33. Prepare sodium carbonate, iron oxide, chromium oxide and titanium dioxide as raw materials, and additionally, Na has a 5wt.% loss during sintering. Then, under air conditions, with a ball milling speed of 300 r / min and a ball milling time of 3 h, and using anhydrous ethanol as the ball milling medium, the raw materials are ball milled and mixed to obtain a mixed solution. After that, the mixed solution is centrifuged, filtered, dried to obtain a precursor and then tableted. Finally, under argon conditions, with a sintering temperature of 950 °C and a sintering time of 15 h, the precursor is sintered, and after sintering, it is naturally cooled to obtain the NaCrFeTi layered oxide, simply referred to as NCFT. The NCFT obtained in Specific Example 1 is Na 0.67 Cr 1 / 3 Fe 1 / 3 Ti 1 / 3 O2 layered oxide, simply referred to as NCFT. Since the Cr / Fe ratio of the NCFT obtained in Specific Example 1 is 0.33:0.33, it is simply referred to as NCFT-33 / 33.

[0041] In order to prove the composition of NCFT-33 / 33, an EDS test was carried out. The test results are as Figure 1 shown. NCFT-33 / 33 contains Na element, Cr element, Fe element and Ti element at the same time, and the distribution of each element is uniform.

[0042] In order to prove the crystal structure of NCFT-33 / 33, an XRD test was carried out and refined. The test results are as Figure 2 shown. NCFT-33 / 33 has Na 0.67 Fe 1 / 3 Cr 1 / 3 Ti 1 / 3 O2 and Cr 0.2 Fe 1.8Characteristic peak of O3, and,

[0043] The main phase is Na 0.67 Fe 1 / 3 Cr 1 / 3 Ti 1 / 3 O2, with a content of 97.3%, and the impurity phase is Cr 0.2 Fe 1.8 O3 is, with a content of 2.7%; in addition, Na 0.67 Fe 1 / 3 Cr 1 / 3 Ti 1 / 3 O2 belongs to the P2 phase structure in the P63 / mmc space group.

[0044] To further prove the microstructure of NCFT-33 / 33, SEM tests were carried out. The test results are as Figure 3 shown. The microstructure of NCFT-33 / 33 is a hexagonal columnar structure, and the surface is smooth, with a particle size of 2 microns.

[0045] To further prove the crystal structure and microstructure of NCFT-33 / 33, TEM tests were carried out. The test results are as Figure 4 shown. The microstructure of NCFT-33 / 33 is a regular hexagonal structure, and the interlayer spacing is In addition, according to Figure 4 the diffraction spots of c, it can be determined that the material has a single crystal structure. The test results show that NCFT-33 / 33 is of the P2 type, and the conclusion obtained from the TEM test is consistent with the XRD test.

[0046] To prove the electrochemical performance of NCFT-33 / 33, electrochemical performance tests were carried out. The specific method of the electrochemical performance test is to use the material to be tested as the working electrode, a Na sheet as the negative electrode, 1M NaFP6 sodium salt, and a DMC:EC = 1:1 Vol% as the electrolyte to form a button cell for the electrochemical performance test.

[0047] The charge-discharge performance test results of NCFT-33 / 33 are as Figure 5 shown. Under the conditions of a voltage range of 0.8 - 2.7V and a current density of 20 mA g -1 the reversible specific capacity is 80.00 mAh g -1 , reaching 89.5% of the theoretical specific capacity of 89.36 mAh g -1 .

[0048] The long cycle test results of NCFT-33 / 33 are as Figure 6As shown, at a voltage range of 0.8 - 2.7 V and a current density of 10 C, when the number of cycles is 3000, the reversible specific capacity is 52.36 mAh g -1 , and the capacity retention rate is 92.72%, and the capacity loss rate per cycle is only 0.0024%.

[0049] To prove the effect of the Cr / Fe ratio on the material, Comparative Example 1 is provided, which is a NaCrFeTi oxide with a Cr / Fe ratio of 0.30 / 0.36.

[0050] Comparative Example 1

[0051] A NaCrFeTi oxide with a Cr / Fe ratio of 0.30 / 0.36. The steps not specifically described are the same as those in Example 1, except that: the chemical formula is Na 0.67 Cr 0.30 Fe 0.36 Ti 0.33 O2, that is, keeping the addition amounts of Na and Ti unchanged, changing the Cr / Fe ratio from 0.33 / 0.33 to 0.30 / 0.36, the obtained NCFT is Na 0.67 Cr 0.30 Fe 0.36 Ti 0.33 O2 layered oxide. Specifically, the NCFT obtained in Example 2 of Comparative Example 1 has a Cr / Fe ratio of 0.30:0.36, so it is abbreviated as NCFT-30 / 36.

[0052] The results of XRD testing and refinement of NCFT-30 / 36 are as Figure 7 shown. NCFT-30 / 36 has characteristic peaks of Na 0.622 Fe 0.67 Mn 0.33 O2, NaTiFeO4, Na2CrO4, Cr2O3, and Fe2O3. And,

[0053] the main phase is Na 0.622 Fe 0.67 Mn 0.33 O2, with a content of only 68.2%. The impurity phases are NaTiFeO4, Na2CrO4, Cr2O3, and Fe2O3, with a total content of 31.8%. Specifically, the content of NaTiFeO4 is 17.9%, the content of Na2CrO4 is 8.6%, the content of Cr2O3 is 3.7%, and the content of Fe2O3 is 1.6%. In addition, Na 0.622 Fe 0.67 Mn 0.33 O2 belongs to the O3 phase structure of the R-3m space group.

[0054] Two conclusions can be drawn by comparing with Example 1:

[0055] 1. Changing the Cr / Fe ratio results in two substantial differences in the crystal structure of the obtained material, namely, the P2-phase structure and the O3-phase structure.

[0056] 2. Changing the Cr / Fe ratio significantly affects the purity of the main phase.

[0057] The charge-discharge performance test results of NCFT-30 / 36 are as Figure 8 shown. Under the conditions of a voltage range of 0.8 - 2.7 V and a current density of 20 mAg -1 , the reversible specific capacity is 53.00 mAh g -1 , only 59.3% of the theoretical specific capacity of 89.36 mAh g -1 . Comparing with Example 1, it can be seen that the reversible specific capacity of NCFT-30 / 36 is significantly lower than that of NCFT-33 / 33, only 66.25%.

[0058] From Example 1 and Comparative Example 1, it can be known that by regulating the Cr / Fe ratio of NCFT, the crystal structure of NCFT can be substantially changed. When the Cr / Fe ratio is 0.33:0.33, the crystal structure of NCFT changes from the O3-phase structure to the P2-phase structure, and moreover, the purity of the main phase is significantly improved, thereby significantly improving the charge-discharge performance of NCFT.

[0059] To prove the influence of the Cr source on the material, Comparative Example 2 is provided, which is a NaCrFeTi oxide with chromium acetate as the Cr source.

[0060] Comparative Example 2

[0061] A NaCrFeTi oxide with chromium acetate as the Cr source. The steps not specifically described are the same as those in Example 1, except that: chromium acetate is used instead of chromium oxide as the Cr source, and the obtained Na 0.67 Cr 1 / 3 Fe 1 / 3 Ti 1 / 3 O2 layered oxide is specifically abbreviated as NCFT-Ac because the Cr source of the NCFT obtained in Comparative Example 2 is chromium acetate.

[0062] The XRD test and refinement results of NCFT-Ac are as Figure 9 shown. NCFT-Ac contains Na 0.62 Fe 0.67 Mn 0.33 O2, Na 0.64 Mn 0.33 Fe 0.67 O2 and Ti 1.03 Fe 1.94Characteristic peaks of O4, and the phase content of NCFT-Ac does not exceed 50%, that is, there is no obvious main phase. Specifically, Na 0.64 Mn 0.33 Fe 0.67 The content of O2 is 46.8%, Na 0.62 Fe 0.67 Mn 0.33 The content of O2 is 38.1%, Ti 1.03 Fe 1.94 The content of O4 is 15.1%;

[0063] In addition, it should be particularly noted that

[0064] Na 0.64 Mn 0.33 Fe 0.67 O2 belongs to the P2 phase structure of P63 / mmc;

[0065] Na 0.62 Fe 0.67 Mn 0.33 O2 belongs to the O3 phase structure of the R-3m space group.

[0066] The test results show that although changing the Cr source can also obtain the P2 phase structure, there is still the O3 phase structure, that is, there are two phase structures of the P2 phase structure and the O3 phase structure at the same time; meanwhile, the content of the P2 phase structure does not exceed 50% and cannot become the main phase. Compared with Example 1, it can be seen that changing the Cr source can completely convert the O3 phase structure into the P2 phase structure, significantly increasing the content of the P2 phase structure, and the increase amplitude reaches 207.9%.

[0067] The charge-discharge performance test results of NCFT-Ac are as Figure 10 shown. Under the conditions of a voltage range of 0.8 - 2.7 V and a current density of 20 mAg -1 , the reversible specific capacity is 48.00 mAh g -1 , only 53.72% of the theoretical specific capacity of 89.36 mAh g -1 . Compared with Example 1, it can be seen that the reversible specific capacity of NCFT-Ac is significantly lower than that of NCFT-33 / 33, only 60.00%.

[0068] It can be seen from Example 1 and Comparative Example 12 that adjusting the Cr source can cause a substantial change in the crystal structure of NCFT. When the Cr source is chromium oxide, it causes a substantial change in the crystal structure of NCFT, changing from the O3 phase structure to the P2 phase structure, and significantly improving the purity of the main phase, thereby significantly improving the charge-discharge performance of NCFT.

Claims

1. A P2-type NaCrFeTi layered oxide, characterized in that: Using sodium carbonate, iron oxide, chromium oxide and titanium dioxide as raw materials, the Na 0.67 Cr 1 / 3 Fe 1 / 3 Ti 1 / 3 O2 layered oxide NCFT-33 / 33 is obtained by high-temperature solid-state sintering. The NCFT-33 / 33 layered oxide belongs to the P2 phase structure of the P63 / mmc space group.

2. The P2-type NaCrFeTi layered oxide according to claim 1, characterized in that: The microscopic morphology of the NCFT-33 / 33 layered oxide is a hexagonal columnar structure with a particle size of 1-3 microns and a single crystal structure.

3. The P2-type NaCrFeTi layered oxide according to claim 1, characterized in that: The main phase of the NCFT-33 / 33 layered oxide is Na 0.67 Fe 1 / 3 Cr 1 / 3 Ti 1 / 3 O2, with a content of over 95%.

4. A preparation method of P2-type NaCrFeTi layered oxide, characterized in that It includes the following steps: Using a one-step sintering method, first, to meet a certain chemical formula, sodium carbonate, iron oxide, chromium oxide, and titanium dioxide are used as raw materials, and 5 wt.% of Na source is added to compensate for high-temperature loss. The raw materials are ball-milled and mixed to obtain a mixed solution. After that, the mixed solution is centrifuged, filtered, dried to obtain a precursor, and then pressed. Finally, under certain conditions, the precursor is sintered and naturally cooled after sintering to obtain the NaCrFeTi layered oxide, abbreviated as NCFT. Among them, with the chemical formula Na 0.67 Cr 1 / 3 Fe 1 / 3 Ti 1 / 3 O2, that is, the molar ratio of Na:Cr:Fe:Ti is 2:1:1:1, simply referred to as the Cr / Fe ratio being 0.33:0.33; The chromium oxide is the Cr source.

5. The preparation method according to claim 4, characterized in that: The conditions for the ball milling are as follows: under air conditions, the ball milling speed is 300-500 r / min, the ball milling time is 3-6 h, and the ball milling medium is anhydrous ethanol; The conditions for the sintering are as follows: under argon conditions, the sintering temperature is 800-1000 °C, and the sintering time is 10-15 h.

6. The P2-type NaCrFeTi layered oxide according to claim 1, characterized in that: When used as the anode material of a sodium-ion battery, in the voltage range of 0.8 - 2.7 V and the current density of 20 mA g -1 under the conditions, the reversible specific capacity is 60.00 - 80.00 mAh g -1 , reaching 67.1 - 89.53% of the theoretical specific capacity of 89.36 mAh g -1 .

7. The P2-type NaCrFeTi layered oxide according to claim 1, characterized in that: When used as the anode material of a sodium-ion battery, under the conditions of a voltage range of 0.8 - 2.7 V and a current density of 10 C, when the number of cycles is 3000, the reversible specific capacity is 52.36 - 56.47 mAh g -1 , the capacity retention rate is 91 - 93%, and the capacity loss rate per cycle is only 0.0023 - 0.0030%.

Images