A heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide cathode material and its preparation method and application

Abstract

The present invention relates to a heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide positive electrode material and its preparation method and application. The positive electrode material has a P2 and O3 dual-phase eutectic lattice structure. The P2 / O3 dual-phase eutectic lattice structure in the positive electrode material is induced by doping heteroatoms M and / or N in an alkali metal layer and / or a transition metal layer. The molecular formula of the positive electrode material is: Na x‑ny M y n+ Ni a Fe b‑ z Mn c N z O2; wherein: 0.7≤x≤0.85, 0≤y≤0.1, 0≤z≤0.1, a+b+c=1, n=1 or 2; in this material, M atoms mainly replace Na sites in the bulk structure, and N atoms mainly replace Fe sites in the bulk structure. Under the dual effects of bulk doping and P2 / O3 eutectic lattice, the positive electrode material effectively stabilizes lattice oxygen, relieves stress accumulation, improves structural stability, and has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode materials, and more specifically to a heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide positive electrode material, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have become a power source for portable electronics and power tools. With evolving market demands, the share of electric vehicles (EVs) and stationary storage devices has grown year by year, driving new momentum in the supply chain for the materials needed to manufacture LIBs. However, the scarcity and uneven distribution of lithium resources have prompted the exploration of alternative energy systems. In the ongoing exploration of electrochemical energy storage, sodium-ion batteries (SIBs) have become a focus of attention due to their abundant resources and similar principles to LIBs.

[0003] In order to achieve the high energy density, long cycle life and low cost requirements of sodium-ion batteries, layered oxides are considered to be one of the best candidates for cathode materials for sodium-ion batteries due to their high theoretical specific capacity, simple structure and easy synthesis. According to the coordination environment of sodium ions and the way oxygen is accumulated, layered oxides can be divided into O3, P3, P2 and O2, among which O3-type layered oxides have a higher initial capacity, but their structural stability and air stability are poor; in comparison, P2-type layered oxides have a faster sodium ion transfer rate, but in the highly desodiumated state, due to the strong structural distortion in the transition metal layer and the electrostatic repulsion between layers, interlayer slip or irreversible migration of transition metal ions will occur, resulting in complex structural changes (P2-O2). Among them, Na 0.7 Ni 0.2 Fe 0.3 Mn 0.5 O2 layered oxide is a typical P2-type positive electrode material. However, its capacity retention and rate performance are severely degraded in a higher voltage range. After narrowing the voltage range, although its cycle stability is improved, the capacity it can provide is limited and cannot meet the needs of actual applications. Summary of the Invention

[0004] Based on the above technical problems existing in the prior art, this application is based on P2 type Na 0.7 Ni 0.2 Fe 0.3 Mn 0.5 O2 layered oxide proposes a heterogeneous cation doped modified P2 / O3 dual-phase layered oxide cathode material, which is composed of heterogeneous heteroatoms doped in alkali metal layers and / or transition metal layers to induce the formation of a eutectic lattice of P2 and O3 dual-phase layered oxides. The molecular formula of the cathode material is: Na x-ny My n+ Ni a Fe b-z Mn c N z O2, wherein: 0.7≤x≤0.85, 0≤y≤0.1, 0≤z≤0.1, a+b+c=1, n=1 or 2; M is an element such as K, Ca, Sr, and N is at least one element such as Li, Cu, Mg, Zn, Ti, Zr, Sb, etc.

[0005] In some embodiments, the heterogeneous dopant atoms M and N are uniformly dispersed in the layered oxide.

[0006] In some embodiments, the P2 and O3 dual-phase layered oxide is a eutectic phase.

[0007] The present invention also provides a method for preparing the positive electrode material of any of the above embodiments, the method comprising the following steps:

[0008] Na2CO3, NiO, Fe2O3, Mn2O3 and a compound containing M and / or N elements are mixed in a stoichiometric ratio, an organic solvent is added, and ball milling is performed; after drying, sintering is performed under oxygen conditions at a temperature of 800-1000°C, and cooling is performed to obtain the positive electrode material.

[0009] In the above scheme, the role of the organic solvent is to make the precursors more evenly mixed during the ball milling process and prevent the precursors from agglomerating and depositing; the molar mass excess of the added sodium source is about 5-10%.

[0010] In some embodiments, during wet ball milling, the mass ratio of material, balls, and organic solvent is 1:(8-10):(0.8-1.2); and the rotation speed is 300-500 rpm / min.

[0011] In some embodiments, the ball milling time is 8-24 hours.

[0012] In some embodiments, after ball milling, the organic solvent is dried in an oven at 50-100° C., and the resulting mixed powder is then pressed into pellets at a pressure of 8-15 MPa.

[0013] In some embodiments, the sample is placed in a corundum crucible, the heating rate is 2-10° C. / min, and the sintering time is 10-24 h.

[0014] In some embodiments, after the sample is kept warm and sintered, it is first cooled to 100-200° C. in the furnace, taken out, and then placed in a glove box to cool to room temperature and stored.

[0015] In some embodiments, the compound containing the element M comprises at least one of an oxide, chloride, nitrate, sulfate, acetate, acetate, phosphate, carbonate, or hydroxide of M; and the compound containing the element N comprises at least one of an oxide, chloride, nitrate, sulfate, acetate, acetate, phosphate, carbonate, or hydroxide of N. Preferably, the compound containing the element M comprises at least one of K2CO3, KOH, K2O, CaCO3, CaO, Ca(OH)2, SrCO3, SrO, or Sr(OH)2; and the compound containing the element N comprises at least one of Li2CO3, LiOH, Li2O, CuO, Cu2O, MgO, ZnO, TiO2, ZrO2, or Sb2O3.

[0016] In some embodiments, the organic solvent is ethanol, acetone, or isopropanol.

[0017] The present invention also provides a positive electrode, which includes the positive electrode material of any of the above embodiments and / or the positive electrode material obtained by the preparation method of any of the above embodiments.

[0018] The present invention also provides an electrochemical energy storage device, which includes the above-mentioned positive electrode.

[0019] Specifically, the electrochemical energy storage device includes a sodium ion battery, a sodium ion capacitor, etc.

[0020] The present invention also provides a method for regulating the P2 / O3 phase ratio in a layered oxide, wherein the layered oxide has the structural formula of Na x Ni a Fe b Mn c O2, the method is: introducing M ions to replace Na sites in the alkali metal layer and / or introducing N ions to replace Fe sites in the transition metal layer; wherein, 0.7≤x≤0.85, a+b+c=1, the M ion doping molar amount y is 0≤y≤0.1, and the N ion doping molar amount z is 0≤z≤0.1; the M ion is +1 valence or +2 valence, M is at least one of K, Ca, and Sr, and N is at least one of Li, Cu, Mg, Zn, Ti, Zr, and Sb.

[0021] In some embodiments, the layered oxide is a pure P2 phase.

[0022] In some embodiments, the method specifically comprises: mixing Na2CO3, NiO, Fe2O3, Mn2O3 and a compound containing M and / or N elements in a stoichiometric ratio, adding an organic solvent, and ball milling; after drying, sintering under aerobic conditions at a temperature of 800-1000°C, and cooling to obtain the positive electrode material.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The positive electrode material provided by the present invention is based on Na 0.7 Ni 0.2 Fe 0.3 Mn 0.5 O2 layered oxide system, the phase composition of the controllable P2 / O3 two-phase layered oxide is induced by heterogeneous cations, and its molecular formula is: Na x-ny M y n+ Ni a Fe b-z Mn c N z O2; In layered oxides, the elements M and / or N are bulk-doped, with M replacing some Na sites and N replacing some Fe sites. This can effectively stabilize the crystal structure, inhibit high-voltage P2-Z phase transition, relieve stress accumulation, and improve structural stability. A properly proportioned P2 / O3 dual-phase eutectic lattice can increase capacity to a certain extent and further improve sodium ion diffusion kinetics. The P2 / O3 dual-phase material with controllable heterogeneous cation-induced phase components disclosed in this application is used as a positive electrode material and exhibits excellent electrochemical performance.

[0025] The preparation method of the composite electrode material provided by the present invention adopts wet ball milling and direct calcination after mixing, and realizes bulk doping and phase component regulation of layered oxides in a one-step process, thereby improving the structural stability of the layered oxide positive electrode material.

[0026] The preparation method of the present invention has a simple process and is suitable for promotion. It is a method for effectively improving the structural stability of sodium ion layered positive electrode materials and inhibiting the dissolution of transition metals and the generation of microcracks during the cycle process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The P2 / O3-Na prepared in Example 1 of the present invention 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Li 0.1 XRD pattern of O2 sample;

[0028] Figure 2 The P2 / O3-Na prepared in Example 1 of the present invention 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Li 0.1 Electrochemical cycling performance diagram of O2 sample under 5C condition in the voltage range of 2.4-4.5V;

[0029] Figure 3 P2 / O3-Na prepared in Example 2 of the present invention 0.7 Ni 0.2 Fe 0.25 Mn 0.5 Zn 0.05 SEM image of O2 sample;

[0030] Figure 4 P2 / O3-Na prepared in Example 2 of the present invention 0.7 Ni 0.2 Fe 0.25 Mn 0.5 Zn 0.05 XRD pattern of O2 sample;

[0031] Figure 5 P2 / O3-Na prepared in Example 2 of the present invention 0.7 Ni 0.2 Fe 0.25 Mn 0.5 Zn 0.05 Electrochemical cycling performance diagram of O2 sample under 5C condition in the voltage range of 2.4-4.5V;

[0032] Figure 6 The P2 / O3-Na prepared in Example 3 of the present invention 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 SEM image of O2 sample;

[0033] Figure 7 The P2 / O3-Na prepared in Example 3 of the present invention 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 XRD pattern of O2 sample;

[0034] Figure 8 The P2 / O3-Na prepared in Example 3 of the present invention 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 Electrochemical cycling performance diagram of O2 sample under 5C condition in the voltage range of 2.4-4.5V;

[0035] Figure 9 The P2 / O3-Na prepared in Example 4 of the present invention 0.66 Ca 0.02 Ni 0.2 Fe 0.2 Mn 0.5Zn 0.1 XRD pattern of O2 sample;

[0036] Figure 10 The P2 / O3-Na prepared in Example 4 of the present invention 0.66 Ca 0.02 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 Electrochemical cycling performance diagram of O2 sample under 5C condition in the voltage range of 2.4-4.5V;

[0037] Figure 11 The P2 / O3-Na prepared in Example 5 of the present invention 0.62 Ca 0.04 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 XRD pattern of O2 sample;

[0038] Figure 12 The P2 / O3-Na prepared in Example 5 of the present invention 0.62 Ca 0.04 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 Electrochemical cycling performance diagram of O2 sample under 5C condition in the voltage range of 2.4-4.5V;

[0039] Figure 13 P2 / O3-Na prepared in Comparative Example 1 of the present invention 0.7 Ni 0.2 Fe 0.3 Mn 0.5 SEM image of O2 sample;

[0040] Figure 14 P2 / O3-Na prepared in Comparative Example 1 of the present invention 0.7 Ni 0.2 Fe 0.3 Mn 0.5 XRD pattern of O2 sample;

[0041] Figure 15 P2 / O3-Na prepared in Comparative Example 1 of the present invention 0.7 Ni 0.2 Fe 0.3 Mn 0.5 Electrochemical cycling performance diagram of O2 sample under 5C condition in the voltage range of 2.4-4.5V; DETAILED DESCRIPTION

[0042] The following description sets forth numerous specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific implementations disclosed below.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0044] In the examples, unless otherwise specified, all means used are conventional means in the art.

[0045] As used herein, the terms "comprise," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a listed element is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0046] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0047] In the examples of the present invention, all experimental raw materials used are conventional commercially available products.

[0048] In the embodiments of the present invention, the equipment and instruments used can be purchased on the market or prepared using existing technologies.

[0049] Example 1

[0050] The present invention provides a method for preparing a P2 / O3 phase layered cathode material, comprising the following steps:

[0051] S1. Weigh Na2CO3, NiO, Fe2O3, Mn2O3, and Li2CO3 in stoichiometric proportions and place them in a ball mill, with a 5% excess of Na2CO3 to prevent volatilization loss during high-temperature calcination. Then, add 20 mL of isopropanol.

[0052] S2, placing the ball mill jar on a planetary ball mill at 400 rpm for 12 h; taking out the ball mill jar and placing it in a 60°C forced air drying oven for 6 h to evaporate the isopropyl alcohol;

[0053] S3, weigh 2g of the obtained precursor powder, press it into a disc under a pressure of 10MPa, place it in a crucible, heat it to 900℃ at a rate of 3℃ / min in a muffle furnace, keep it warm for 15h, cool it to 150℃ with the furnace, move it to a glove box for cooling, and obtain P2 / O3 type layered metal oxide Na 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Li 0.1 O2, its XRD test results are as follows Figure 1 shown.

[0054] Example 2

[0055] The present invention provides a method for preparing a P2 / O3 phase layered cathode material, comprising the following steps:

[0056] S1. Weigh Na2CO3, NiO, Fe2O3, Mn2O3, and ZnO in stoichiometric proportions and place them in a ball mill, with a 5% excess of Na2CO3 to prevent volatilization loss during high-temperature calcination. Then, add 20 mL of isopropanol.

[0057] S2, placing the ball mill jar on a planetary ball mill at 400 rpm for 12 h; taking out the ball mill jar and placing it in a 60°C forced air drying oven for 6 h to evaporate the isopropyl alcohol;

[0058] S3, weigh 2g of the obtained precursor powder, press it into a disc under a pressure of 10MPa, place it in a crucible, heat it to 900℃ at a rate of 3℃ / min in a muffle furnace, keep it warm for 15h, cool it to 150℃ with the furnace, move it to a glove box for cooling, and obtain P2 / O3 type layered metal oxide Na 0.7 Ni 0.2 Fe 0.25 Mn 0.5 Zn 0.05 O2, its SEM and XRD test results are as follows Figure 3 、 Figure 4 shown.

[0059] Example 3

[0060] The present invention provides a method for preparing a P2 / O3 phase layered cathode material, comprising the following steps:

[0061] S1. Weigh Na2CO3, NiO, Fe2O3, Mn2O3, and ZnO in stoichiometric proportions and place them in a ball mill, with a 5% excess of Na2CO3 to prevent volatilization loss during high-temperature calcination. Then, add 20 mL of isopropanol.

[0062] S2, placing the ball mill jar on a planetary ball mill at 400 rpm for 12 h; taking out the ball mill jar and placing it in a 60°C forced air drying oven for 6 h to evaporate the isopropyl alcohol;

[0063] S3, weigh 2g of the obtained precursor powder, press it into a disc under a pressure of 10MPa, place it in a crucible, heat it to 900℃ at a rate of 3℃ / min in a muffle furnace, keep it warm for 15h, cool it to 150℃ with the furnace, move it to a glove box for cooling, and obtain P2 / O3 type layered metal oxide Na 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 O2, its SEM and XRD test results are as follows Figure 6 、 Figure 7 shown.

[0064] Example 4

[0065] The present invention provides a method for preparing a P2 / O3 phase layered cathode material, comprising the following steps:

[0066] S1. Weigh Na2CO3, NiO, Fe2O3, Mn2O3, CaO, and ZnO in stoichiometric proportions and place them in a ball mill, with a 5% excess of Na2CO3 to prevent volatilization loss during high-temperature calcination. Then, add 20 mL of isopropanol.

[0067] S2, placing the ball mill jar on a planetary ball mill at 400 rpm for 12 h; taking out the ball mill jar and placing it in a 60°C forced air drying oven for 6 h to evaporate the isopropyl alcohol;

[0068] S3, weigh 2g of the obtained precursor powder, press it into a disc under a pressure of 10MPa, place it in a crucible, heat it to 900℃ at a rate of 3℃ / min in a muffle furnace, keep it warm for 15h, cool it to 150℃ with the furnace, move it to a glove box for cooling, and obtain P2 / O3 type layered metal oxide Na 0.66 Ca 0.02 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 O2, its XRD test results are as follows Figure 9 shown.

[0069] Example 5

[0070] The present invention provides a method for preparing a P2 / O3 phase layered cathode material, comprising the following steps:

[0071] S1. Weigh Na2CO3, NiO, Fe2O3, Mn2O3, CaO, and ZnO in stoichiometric proportions and place them in a ball mill, with a 5% excess of Na2CO3 to prevent volatilization loss during high-temperature calcination. Then, add 20 mL of isopropanol.

[0072] S2, placing the ball mill jar on a planetary ball mill at 400 rpm for 12 h; taking out the ball mill jar and placing it in a 60°C forced air drying oven for 6 h to evaporate the isopropyl alcohol;

[0073] S3, weigh 2g of the obtained precursor powder, press it into a disc under a pressure of 10MPa, place it in a crucible, heat it to 900℃ at a rate of 3℃ / min in a muffle furnace, keep it warm for 15h, cool it to 150℃ with the furnace, move it to a glove box for cooling, and obtain P2 / O3 type layered metal oxide Na 0.62 Ca 0.04 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 O2, its XRD test results are as follows Figure 11 shown.

[0074] Example 6

[0075] The present invention provides a method for preparing a P2 / O3 phase layered cathode material, comprising the following steps:

[0076] S1. Weigh Na2CO3, NiO, Fe2O3, Mn2O3, and ZnO in stoichiometric proportions and place them in a ball mill, with a 5% excess of Na2CO3 to prevent volatilization loss during high-temperature calcination. Then, add 20 mL of isopropanol.

[0077] S2, placing the ball mill jar on a planetary ball mill at 400 rpm for 12 h; taking out the ball mill jar and placing it in a 60°C forced air drying oven for 6 h to evaporate the isopropyl alcohol;

[0078] S3, weigh 2g of the obtained precursor powder, press it into a disc under a pressure of 10MPa, place it in a crucible, heat it to 800℃ at a rate of 3℃ / min in a muffle furnace, keep it warm for 15h, cool it to 150℃ with the furnace, move it to a glove box for cooling, and obtain P2 / O3 type layered metal oxide Na 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 O2-800℃.

[0079] Example 7

[0080] The present invention provides a method for preparing a P2 / O3 phase layered cathode material, comprising the following steps:

[0081] S1. Weigh Na2CO3, NiO, Fe2O3, Mn2O3, and ZnO in stoichiometric proportions and place them in a ball mill, with a 5% excess of Na2CO3 to prevent volatilization loss during high-temperature calcination. Then, add 20 mL of isopropanol.

[0082] S2, placing the ball mill jar on a planetary ball mill at 400 rpm for 12 h; taking out the ball mill jar and placing it in a 60°C forced air drying oven for 6 h to evaporate the isopropyl alcohol;

[0083] S3, weigh 2g of the obtained precursor powder, press it into a disc under a pressure of 10MPa, place it in a crucible, heat it to 950℃ at a rate of 3℃ / min in a muffle furnace, keep it warm for 15h, cool it to 150℃ with the furnace, move it to a glove box for cooling, and obtain P2 / O3 type layered metal oxide Na 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 O2-950℃.

[0084] Example 8

[0085] The present invention provides a method for preparing a P2 / O3 phase layered cathode material, comprising the following steps:

[0086] S1. Weigh Na2CO3, NiO, Fe2O3, Mn2O3, and ZnO in stoichiometric proportions and place them in a ball mill, with a 5% excess of Na2CO3 to prevent volatilization loss during high-temperature calcination. Then, add 20 mL of isopropanol.

[0087] S2, placing the ball mill jar on a planetary ball mill at 400 rpm for 12 h; taking out the ball mill jar and placing it in a 60°C forced air drying oven for 6 h to evaporate the isopropyl alcohol;

[0088] S3, weigh 2g of the obtained precursor powder, press it into a disc under a pressure of 10MPa, place it in a crucible, heat it to 1000℃ at a rate of 3℃ / min in a muffle furnace, keep it warm for 15h, cool it to 150℃ with the furnace, move it to a glove box for cooling, and obtain P2 / O3 type layered metal oxide Na 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 O2-1000℃.

[0089] Comparative Example 1

[0090] An embodiment of the present invention provides a method for preparing a P2 phase layered cathode material, comprising the following steps:

[0091] S1. Weigh Na2CO3, NiO, Fe2O3, and Mn2O3 in stoichiometric proportions and place them in a ball mill, with a 5% excess of Na2CO3 to prevent volatilization loss during high-temperature calcination. Then, add 20 mL of isopropanol.

[0092] S2, placing the ball mill jar on a planetary ball mill at 400 rpm for 12 h; taking out the ball mill jar and placing it in a 60°C forced air drying oven for 6 h to evaporate the isopropyl alcohol;

[0093] S3, weigh 2g of the obtained precursor powder, press it into a disc under a pressure of 10MPa, place it in a crucible, heat it to 900℃ at a rate of 3℃ / min in a muffle furnace, keep it warm for 15h, cool it to 150℃ with the furnace, move it to a glove box for cooling, and obtain P2-type layered metal oxide Na 0.7 Ni 0.2 Fe 0.3 Mn 0.5 O2, its SEM and XRD test results are as follows Figure 13 、 Figure 14 shown.

[0094] The samples prepared in Example 2, Example 3 and Comparative Example 1 were characterized, and the characterization results are as follows: Figure 3 、 Figure 6 and Figure 13 ;in, Figure 3 、 Figure 6 and Figure 13 The SEM images of the samples prepared in Example 2, Example 3 and Comparative Example 1 of the present invention are respectively shown at a magnification of 5000 times.

[0095] from Figure 3 、 Figure 6 and Figure 13 It can be seen that the prepared P2 / O3-Na 0.7 Ni 0.2 Fe 0.25 Mn 0.5 Zn 0.05 O2, P2 / O3-Na 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Zn 0.1 O2 and P2-Na 0.7 Ni 0.2 Fe 0.3 Mn 0.5 The O2 sample is a plate-like single crystal particle with an average size of about 5μm; the addition of heterogeneous cations has no obvious effect on its morphology.

[0096] Figure 1 、 Figure 4 、 Figure 7 、 Figure 9 、 Figure 11 These are the X-ray diffraction patterns of the P2 / O3 dual-phase layered oxide samples prepared in Examples 1, 2, 3, 4, and 5 of the present invention and the P2 phase layered oxide sample prepared in Comparative Example 14.

[0097] from Figure 1 、 Figure 4 、 Figure 7 、 Figure 9 、 Figure 11 It can be seen that the main bodies of the prepared samples are P2 and O3 layered structures, and the corresponding space groups are P63mmc and R-3m, respectively, with P2 phase being the main phase; in addition, the introduction of heterogeneous cations and sintering temperature significantly affect the phase composition.

[0098] Table 1 The composition ratio of P2 and O3 phases in the obtained P2 / O3 dual-phase layered oxide

[0099]

[0100] Combining the XRD patterns and the results in Table 1, it can be seen that the doping of heterogeneous cations and the calcination temperature can regulate the ratio of P2 and O3 phases.

[0101] The samples prepared in Examples 1-8 and Comparative Example 1 were respectively used as positive electrode materials for sodium ion batteries to prepare positive electrode sheets. The specific process is as follows:

[0102] (1) The prepared powdered cathode material was mixed with acetylene black (conductive agent) and polyvinylidene fluoride (PVDF, binder) at a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added as a dispersant. The mixture was ground into a slurry. Subsequently, the slurry was evenly coated on aluminum foil, vacuum-dried at 120°C for 12 h, and transferred to an argon atmosphere glove box for later use.

[0103] (2) A half-cell was assembled in an argon atmosphere glove box, using metallic sodium as the counter electrode and 1 M NaClO4 / propylene carbonate (100% PC + 5% FEC by volume) as the electrolyte. A button cell of the assembled specification was CR2016, and constant current charge and discharge mode was used for charge and discharge.

[0104] Figure 2 、 Figure 5 、 Figure 8 、 Figure 10 、 Figure 12The heterogeneous cation-induced P2 / O3 two-phase layered oxide samples prepared in Example 1, Example 2, Example 3, Example 4, and Example 5 of the present invention are respectively; Figure 15 This is a graph showing the electrochemical cycle performance of a button cell in the voltage range of 2.4-4.5 V, in which the P2 phase layered oxide sample prepared in Comparative Example 1 of the present invention is used as a positive electrode material for a sodium ion battery to prepare a positive electrode sheet.

[0105] Table 2 below shows the results of the first cycle discharge capacity and coulombic efficiency of button cells used as positive electrode materials for sodium ion batteries using the samples prepared in the embodiments and comparative examples of the present invention.

[0106] Table 2 The first cycle discharge capacity and coulombic efficiency of each sample after preparing the positive electrode

[0107]

[0108] Combined with the results in Table 2, it can be seen that the first coulombic efficiency of button cells for preparing positive electrode sheets of sodium ion battery positive electrode materials prepared by heterogeneous element doping and dual-phase eutectic lattice synergistic modification is significantly improved, and the irreversible capacity loss during charging is significantly suppressed.

[0109] Figure 2 This is a cycling performance graph of a button cell in which the heterogeneous cation-induced P2 / O3 dual-phase layered oxide sample prepared in Example 1 of the present invention is used as a positive electrode material for a sodium ion battery to prepare a positive electrode sheet after 100 cycles at a current density of 2C in the voltage range of 2.4-4.5V; Figure 15 The performance graph of the button cell of the positive electrode sheet of the sodium ion battery prepared by the P2 phase layered oxide sample in Comparative Example 1 of the present invention after 100 cycles in the voltage range of 2.4-4.5V. Figure 2 It can be seen that the retention rate after 100 cycles at a current density of 2C is 92.3% (P2 / O3-Na 0.7 Ni 0.2 Fe 0.2 Mn 0.5 Li 0.1 O2); from Figure 15 It can be seen that the retention rate after 100 cycles at 5C current density is 83.6% (P2-Na 0.7 Ni 0.2 Fe 0.3 Mn 0.5 O2).

[0110] Table 3 below shows the retention rates of button cells used as positive electrode materials for sodium ion batteries and positive electrode sheets after 100 cycles of the samples prepared in the embodiments and comparative examples of the present invention.

[0111] Table 3 Retention rate of each sample after 100 cycles of positive electrode sheets

[0112]

[0113] Combine Figure 2 、 Figure 15 From the results in Table 3, it can be seen that the P2 / O3 dual-phase cathode material after synergistic modification by heterogeneous element doping and dual-phase eutectic lattice can be used as the cathode material of sodium ion battery to effectively inhibit the capacity decay of button battery during the cycle process.

[0114] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0115] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide cathode material, characterized in that: The positive electrode material has a P2 and O3 dual-phase eutectic structure, with the P2 phase being the main phase; the P2 / O3 dual-phase eutectic structure in the positive electrode material is induced by doping heteroatoms M and N in the alkali metal layer and the transition metal layer; the molecular formula of the positive electrode material is: Na x-ny M y n + Ni a Fe b-z Mn c N z O2; wherein: 0.7≤x≤0.85, 0<y≤0.1, 0<z≤0.1, a+b+c=1, n = 1 or 2; M is at least one of K, Ca, and Sr, and N is at least one of Li, Cu, Mg, Zn, Ti, Zr, and Sb.

2. The heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide cathode material according to claim 1, characterized in that: The heteroatoms M and N are uniformly dispersed in the positive electrode material.

3. The method for preparing the heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide positive electrode material according to claim 1 or 2, characterized in that: The following steps are involved: Na2CO3, NiO, Fe2O3, Mn2O3 and a compound containing M and N elements are mixed in a stoichiometric ratio, an organic solvent is added, and ball milling is performed; after drying, sintering is performed under oxygen conditions at a temperature of 800-1000°C, and cooling is performed to obtain the positive electrode material.

4. The method for preparing the heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide positive electrode material according to claim 3, characterized in that: During wet ball milling, the mass ratio of material, balls, and organic solvent is 1: (8-10): (0.8-1.2); the rotation speed is 300-500 rpm / min; and / or the ball milling time is 8-24 hours.

5. The method for preparing the heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide positive electrode material according to claim 4, characterized in that: After ball milling, the organic solvent is dried in an oven at 50-100° C., and the resulting mixed powder is then pressed into pellets at a pressure of 8-15 MPa.

6. The method for preparing the heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide positive electrode material according to claim 3, characterized in that: The heating rate is 2-10°C / min; and / or the sintering time is 10-24h.

7. The method for preparing the heterogeneous cation-doped modified P2 / O3 dual-phase layered oxide positive electrode material according to claim 3, characterized in that: The compound containing the M element includes at least one of M's oxides, chlorides, nitrates, sulfates, acetates, acetates, phosphates, carbonates, and hydroxides; the compound containing the N element includes at least one of N's oxides, chlorides, nitrates, sulfates, acetates, acetates, phosphates, carbonates, and hydroxides.

8. A positive electrode, characterized in that The positive electrode material according to any one of claims 1 to 2 or the positive electrode material obtained by the preparation method according to any one of claims 3 to 7.

9. An electrochemical energy storage device, characterized in that Comprising the positive electrode according to claim 8.

10. A method for regulating the P2 / O3 phase ratio in the layered oxide positive electrode material according to claim 1, wherein the layered oxide has the structural formula of Na x Ni a Fe b Mn c O2, characterized in that M ions are introduced into the alkali metal layer to replace Na sites, and N ions are introduced into the transition metal layer to replace Fe sites; wherein, 0.7≤x≤0.85, 0<y≤0.1, 0<z≤0.1, a+b+c=1; the M ions are +1 valence or +2 valence, M is at least one of K, Ca, and Sr, and N is at least one of Li, Cu, Mg, Zn, Ti, Zr, and Sb.

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