Sodium electric layered oxide and preparation method and application thereof

Abstract

The application relates to a sodium battery layered oxide and a preparation method and application thereof. The sodium battery layered oxide comprises a positive electrode material and a coating layer on the surface of the positive electrode material particle; the coating layer comprises a perovskite and sodium metaaluminate. The sodium battery layered oxide has a uniform composite coating layer comprising the perovskite and the sodium metaaluminate, and can significantly improve the cycle stability of the positive electrode material at a high voltage in combination with an interface gradient doping.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a sodium battery layered oxide and a preparation method and application thereof, in particular to a sodium battery layered oxide coated with a perovskite assisted by aluminum hydroxide. BACKGROUND

[0002] Sodium ion batteries have similar electrochemical mechanisms to lithium ion batteries, and are regarded as an important supplement to lithium ion battery technology due to the advantages of low cost, environmental friendliness and high safety. Among a large number of positive electrode materials, O3-type positive electrode materials (Na x TMO2, 2 / 3 < x < 1) have become one of the positive electrode materials with commercial prospects due to their simple synthesis process and high theoretical capacity. In order to further improve the energy density of sodium ion batteries, increasing the charge cut-off voltage (> 4.0V) is an effective method. However, the cycle stability of O3-type positive electrode materials at high voltage (> 4.0V) still faces great challenges. The main reasons include: 1. At high voltage, deep desodium state will cause interlayer slip and exacerbate the generation of irreversible phase transition; 2. Anion redox reaction will cause the release of lattice oxygen, increasing the insecurity; 3. Volume change causes uneven stress distribution in the material, which in turn causes microcracks, increases the occurrence of side reactions, and ultimately causes rapid capacity decay of the battery.

[0003] Traditional modification strategies mainly include: anion / cation doping (enhancing the stability of the layered structure by inhibiting phase transition), surface coating (improving the stability of the interface and preventing electrolyte corrosion), and constructing a multi-phase structure (reducing irreversible phase transition). Therefore, how to improve the cycle stability of O3-type positive electrode materials at high voltage is still a great challenge.

[0004] The application proposes a new type of sodium battery layered oxide, which comprises a positive electrode material and a coating layer on the surface of the positive electrode material particles; the coating layer comprises a perovskite and sodium metaaluminate. The composite coating method of the application, aluminum hydroxide assisted perovskite type coated sodium battery layered oxide, combines interface gradient doping and surface coating, and takes into account the composite positive electrode material with high energy density and long cycle life, which can enhance the cycle stability of sodium ion batteries at high voltage. SUMMARY

[0005] The application aims to solve the problems in the prior art and provides a sodium battery layered oxide and a preparation method and application thereof.

[0006] The perovskite compound has high ion conductivity and is an ideal coating material. Traditional solid-phase dry mixing coating has simple process, low cost and is easy to mass produce, but coating is often uneven, resulting in poor coating effect, and the cycle performance at high voltage is not significantly improved. Therefore, the application introduces aluminum hydroxide assisted coating, under the joint action of aluminum hydroxide and the perovskite compound, a uniform composite coating layer is formed, and the interface gradient doping can significantly improve the cycle stability of the positive electrode material at high voltage of 4.1-4.2V.

[0007] The object of the application can be achieved by the following scheme:

[0008] The application provides a sodium battery layered oxide, including a positive electrode material and a coating layer on the surface of the positive electrode material particles; the coating layer includes a perovskite and sodium metaaluminate.

[0009] The perovskite and sodium metaaluminate in the coating layer are obtained by sintering a perovskite compound and aluminum hydroxide coated on the surface of the positive electrode material particles.

[0010] As an embodiment of the application, the positive electrode material is an O3-type sodium battery layered oxide. The positive electrode material is Na x TMO2; wherein 2 / 3 < x < 1, and TM is a transition metal element including one or more of Ni, Fe, Mn, Cu, Ti, Co, Nb, Zn, Y, Zr and Mo.

[0011] The positive electrode material Na x TMO2 is obtained by mixing a layered oxide precursor and Na2CO3 and then calcining. The amount of the layered oxide precursor and Na2CO3 is 1:1.5-2.5, preferably 1:2. x The composition ratio in Na2CO3 is set to 2.5-3.5%, preferably 3%.

[0012] The O3-type sodium battery layered oxide is preferably NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is synthesized by a solid-phase method (one-time sintering), specifically, Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 and Na2CO3 (mass excess 3%) are calcined at 900 DEG C for 12h in an air atmosphere, and finally the positive electrode material is obtained.

[0013] As an embodiment of the application, the perovskite compound is CaABO x; wherein AB comprises one or more of Ti, Mg, Co, Fe, Ni, Cu, Zn. The perovskite compound is preferably one or more of CaTiO3, CaMgTiO4, CaCu3Ti4O 12 , CaZnTiO4, CaCoTiO4, CaFe2TiO6, CaNiTiO4.

[0014] As an embodiment of the present application, the particle size of the cathode material is 5-20 μm, preferably 10-15 μm. The thickness of the coating layer on the surface of the cathode material particle is 2-10 nm, preferably 2-6 nm.

[0015] As an embodiment of the present application, the mass ratio of the total substances in the cathode material and the coating layer is 1:(0.01-0.11), preferably 1:(0.01-0.1), more preferably 1:(0.03-0.04).

[0016] The mass ratio of the perovskite and sodium aluminate in the coating layer is 1:(0.1-2.2), preferably 1:(0.1-2), more preferably 1:(0.4-0.75).

[0017] The present application provides a preparation method of the sodium electric layered oxide, comprising the following steps:

[0018] The cathode material, the perovskite compound and the aluminum hydroxide are mixed, sintered and cooled to obtain the sodium electric layered oxide.

[0019] As an embodiment of the present application, the aluminum hydroxide is one or more of nano-aluminum hydroxide powder (particle size not more than 100 nm) and aluminum hydroxide sol. Since the solid-solid (cathode material, perovskite compound) mixture is calcined, an inhomogeneous coating material is usually obtained. The main role of the aluminum hydroxide in the present application is to drive the perovskite compound to uniformly reach the surface of the cathode material in the molten state due to its low melting point and amphoteric property, and part of it reacts with the residual alkali on the surface to form sodium aluminate and form a coating layer with the perovskite compound. Therefore, the introduction of aluminum hydroxide utilizes its good fluidity in the molten state to drive the perovskite coating material to uniformly reach the surface of the cathode material.

[0020] As an embodiment of the present application, the mass ratio of the cathode material, the perovskite compound and the aluminum hydroxide is 100:(0.5-5):(0.5-5), preferably 100:(1.5-3):(1-2), more preferably 100:(2-2.5):(1-1.5).

[0021] As an embodiment of the present application, the positive electrode material, perovskite compound and aluminum hydroxide are mixed in a solid-solid or solid-sol mixed manner without using a solvent. The present application is uniformly mixed in a solid-solid or solid-sol manner in a certain mass ratio, and then calcined, so that the process operation is simple. Moreover, with the aid of solvent mixing (such as water and the like), Na in the positive electrode material is easily removed, resulting in structure damage and capacity attenuation, and finally the obtained coating layer can be blocky and uneven on the surface.

[0022] As an embodiment of the present application, the mixing method is ball milling mixing, which is divided into two stages of ball milling. The first stage parameters are: revolution 800-1100 rpm, rotation ratio 50-100%, time 60-120 s; the second stage parameters are: revolution 1100-1500 rpm, rotation ratio 50-100%, time 60-120 s.

[0023] As an embodiment of the present application, the sintering temperature is 600-800℃, preferably 600-750℃, more preferably 650-750℃, and the time is 6-10h.

[0024] Under the action of kinetics and thermodynamics, Ca and Na ions with close radii easily enter the Na layer under 600-800℃ two-sintering of the present application, so that the Na + / Ca 2+ ion exchange occurs, forming a gradient Ca 2+ doped layer. Ca doping is more obvious for the stability improvement of high voltage. Compared with traditional bulk doping, interface gradient doping significantly improves the stability and structural integrity of the material without loss of capacity and rate performance. Moreover, Ca 2+ can act as a pillar to reduce the phase structure change caused by high voltage, and also expands the sodium layer spacing, reduces the Na + migration energy barrier, and significantly improves the diffusion dynamics of Na + , and improves the rate performance.

[0025] The transition metal ions (TM) in the perovskite compound are also gradient-doped into the surface layer, forming TMO6 octahedra, which further fix the transition metal layer in the base material, slow down the slip of the transition metal layer under high voltage and high sodium removal. Moreover, the strong TM-O enhances the redox reversibility of the transition metal, effectively inhibits the escape of irreversible oxygen, and finally improves the stability of the layered positive electrode material under high voltage.

[0026] As an embodiment of the present application, the sintering is performed in the presence of a protective gas. The protective gas includes one or more of oxygen, nitrogen, and preferably oxygen. The protective gas is flowed during the sintering. The flowing of the protective gas can keep the purity of the gas in the furnace at a high level, and can also take away part of the impurities, avoiding the use of air containing moisture and the like, which can increase the residual alkali.

[0027] As an embodiment of the present application, the gas flow rate is 20-50 L / min, and preferably 20-40 L / min.

[0028] As an embodiment of the present application, the obtained sodium electric layered oxide has a coating layer composed of a composite coating layer including perovskite and sodium metaaluminate. Direct coating with sodium metaaluminate can also reduce side reactions and improve stability, but this is only effective at a low voltage of 4.0 V. If the voltage is increased, the internal volume change of the material structure is serious, and coating with sodium metaaluminate alone cannot improve the stability of the material.

[0029] The present application mainly realizes both coating and doping of perovskite compound composite positive electrode materials. Compared with direct bulk doping and interface gradient doping, the capacity loss is avoided, and the stability of the positive electrode material at high voltage (greater than 4.1 V) is improved. However, the melting point of perovskite compounds is relatively high, usually higher than 1000℃, and the particle size is relatively large. When mixed with the positive electrode material in a solid-solid manner and calcined at 600-700℃, the positive electrode material cannot be uniformly covered on the surface, which hinders the performance of the material. If the sintering temperature is higher than 700℃, the particles of the positive electrode material (Na x TMO2, primary sintered particles) will re-melt, the particles will become large and harden, and finally the capacity will also decrease. At the same time, the secondary sintering temperature is too high, and the sintering cost of the material will increase. Therefore, aluminum hydroxide powder (melting point 300℃) with a low melting point is introduced, which can uniformly reach the surface of the positive electrode material in a molten state, and react with the residual alkali on the surface to form a fast ion conductor of sodium metaaluminate, and further form a composite coating layer with the perovskite compound.

[0030] The present application also provides a positive electrode tab, characterized in that it comprises the sodium electric layered oxide.

[0031] The present application also provides a battery, characterized in that it comprises the positive electrode tab.

[0032] The present application also provides a sodium electric layered oxide for preparing a sodium ion battery.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] (1) Aluminum hydroxide is amphoteric, has a low melting point (300°C), and is in a molten state during sintering, and part of the aluminum hydroxide decomposes into aluminum oxide, which can react with surface residual alkali (Na2CO3, NaOH) to reduce the surface residual alkali, and the specific reaction formula is as follows:

[0035] Al(OH)3 + NaOH → NaAlO2 + 2H2O;

[0036] 2Al(OH)3 → Al2O3 + 3H2O; Al2O3 + Na2CO3 → 2NaAlO2 + CO2;

[0037] (2) Low melting point, good fluidity in a molten state, and the perovskite coating material can be uniformly brought to the surface of the positive electrode material by the aluminum hydroxide, forming a uniform coating layer;

[0038] (3) After sintering at a high temperature of 600-800°C, a sodium metaaluminate and perovskite composite coating layer is formed, and Ca 2+ Interface gradient doping effectively reduces the interface side reaction of the positive electrode material surface and the electrolyte and alleviates the volume change, improving the cycle stability and safety performance at high voltage. BRIEF DESCRIPTION OF DRAWINGS

[0039] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the following drawings:

[0040] Figure 1 SEM image of the positive electrode material obtained in Example 1 of the present application;

[0041] Figure 2 TEM image of the positive electrode material obtained in Example 1 of the present application;

[0042] Figure 3 TEM image of the positive electrode material obtained in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0043] The present application will be described in detail below with reference to specific embodiments. The following examples are implemented under the premise of the technical solutions of the present application, and provide detailed implementation methods and specific operation processes, which will help those skilled in the art to further understand the present application. It should be pointed out that the protection scope of the present application is not limited to the following examples, and several adjustments and improvements made under the premise of the concept of the present application also belong to the protection scope of the present application.

[0044] Example 1

[0045] The present embodiment provides a sodium electric layered oxide, and the preparation method comprises the following steps:

[0046] (1) Synthesizing NaNi1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material:

[0047] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, Na2CO3 (mass excess 3%) were ball-milled uniformly, calcined at 900°C for 12h under air atmosphere, and naturally cooled to room temperature. Finally, the positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0048] (2) Preparation of coated positive electrode material:

[0049] According to the mass ratio of 100:2:1, 100 g of positive electrode material, 2 g of perovskite compound (CaCu3Ti4O 12 ) 1 g of nano-aluminum hydroxide powder (the particle size of the nano-aluminum hydroxide powder used in the example is 20 nm), after ball-milling uniformly, sintering at 650°C for 6h in oxygen (maintain the gas flow rate at 30 L / min), and naturally cooling, the coated positive electrode material (average particle size 11.6μm, thickness of the coating layer about 3.0 nm, mass ratio of the positive electrode material, coating layer total substance 1:0.0302, mass ratio of perovskite, sodium metaaluminate in the coating layer 1:0.526) was obtained.

[0050] The ball-milling parameters are as follows: the first section 1000 rpm, the rotation ratio 70%, the time 120s; the second section 1200 rpm, the rotation ratio 70%, the time 120s.

[0051] Example 2

[0052] The present embodiment provides a sodium electric layered oxide, and the preparation method comprises the following steps:

[0053] (1) Synthesis of NaNi 0.5 Mn 0.5 O2 material:

[0054] Ni 0.5 Mn 0.5 (OH)2, Na2CO3 (mass excess 3%) were ball-milled uniformly, calcined at 900°C for 12h under air atmosphere, and naturally cooled to room temperature. Finally, the positive electrode material NaNi 0.5 Mn 0.5 O2.

[0055] (2) Preparation of coated positive electrode material:

[0056] 100 g of the positive electrode material, 2 g of the perovskite compound (CaCu3Ti4O 12 ) and 1 g of the nano-aluminum hydroxide powder were mixed uniformly by ball milling, and then sintered at 650 ℃ for 6 h in oxygen (the gas flow was kept at 30 L / min), and naturally cooled to obtain the coated positive electrode material (the average particle size was 11.3 μm, the thickness of the coating layer was about 3.1 nm, the mass ratio of the positive electrode material to the total substance in the coating layer was 1:0.0301, and the mass ratio of the perovskite to sodium meta-aluminate in the coating layer was 1:0.527).

[0057] The ball milling parameters were as follows: 1000 rpm of revolution and 70% of rotation ratio for 120 s in the first section, and 1200 rpm of revolution and 70% of rotation ratio for 120 s in the second section.

[0058] Example 3

[0059] The present embodiment provides a sodium battery layered oxide, and the preparation method comprises the following steps:

[0060] (1) The NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material was synthesized by a solid phase method:

[0061] The Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 and Na2CO3 (3% mass excess) were mixed uniformly by ball milling, calcined at 900 ℃ for 12 h in an air atmosphere, and naturally cooled to room temperature, and finally the positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was obtained.

[0062] (2) Preparation of the coated positive electrode material:

[0063] 100 g of the positive electrode material, 1 g of the perovskite compound (CaCu3Ti4O 12 ) and 2 g of the nano-aluminum hydroxide powder were mixed uniformly by ball milling, and then sintered at 650 ℃ for 6 h in oxygen (the gas flow was kept at 30 L / min), and naturally cooled to obtain the coated positive electrode material (the average particle size was 11.0 μm, the thickness of the coating layer was about 2.9 nm, the mass ratio of the positive electrode material to the total substance in the coating layer was 1:0.0219, and the mass ratio of the perovskite to sodium meta-aluminate in the coating layer was 1:2.181).

[0064] The ball milling parameters were as follows: 1000 rpm of revolution and 70% of rotation ratio for 120 s in the first section, and 1200 rpm of revolution and 70% of rotation ratio for 120 s in the second section.

[0065] Example 4

[0066] The present example provides a kind of perovskite type coated sodium electric layered oxide assisted by aluminum hydroxide, and the preparation method includes the following steps:

[0067] (1) by solid phase method synthesis NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material:

[0068] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, Na2CO3 (mass excess 3%) ball milling is uniformly mixed, calcination is carried out at 900 DEG C under air atmosphere for 12h, and natural cooling is carried out to room temperature, and finally positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0069] (2) coated positive electrode material preparation:

[0070] According to the mass ratio of 100:2.5:1.5, 100g of positive electrode material, 2.5g of perovskite compound (CaCu3Ti4O 12 ) 1.5g of nano aluminum hydroxide powder, after ball milling is uniformly mixed, sintering is carried out at 650 DEG C in oxygen (keep gas flow rate 30 L / min), and natural cooling is carried out to obtain coated positive electrode material (average particle size 11.2 μm, the thickness of coating layer is about 4.1 nm, the mass ratio of positive electrode material, coating layer and total material is 1:0.0398, and the mass ratio of perovskite, sodium metaaluminate in coating layer is 1:0.636).

[0071] Among them, the ball milling parameters are: the first section revolution 1000 rpm, rotation ratio 70%, time 120s;The second section revolution 1200 rpm, rotation ratio 70%, time 120s.

[0072] Example 5

[0073] The present example provides a kind of sodium electric layered oxide, and the preparation method includes the following steps:

[0074] (1) by solid phase method synthesis NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material:

[0075] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3Na2CO3 (mass excess 3%) were ball-milled uniformly, and calcined at 900℃ for 12h under air atmosphere, and naturally cooled to room temperature. Finally, the positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0076] (2) Preparation of coated positive electrode material:

[0077] According to the mass ratio of 100:5:5, the positive electrode material 100g, perovskite compound (CaCu3Ti4O 12 ) 5g, nano-aluminum hydroxide powder 5g, ball-milling uniformly, and sintering at 650℃ for 6h in oxygen (keeping the gas flow rate at 30L / min), and naturally cooling to obtain the coated positive electrode material (average particle size 11.5μm, thickness of coating layer about 4.9nm, mass ratio of positive electrode material, coating layer total substance 1:0.1025, mass ratio of perovskite, sodium metaaluminate in coating layer 1:1.060).

[0078] The ball-milling parameters are as follows: the first section 1000rpm, rotation ratio 70%, time 120s; the second section 1200rpm, rotation ratio 70%, time 120s.

[0079] Example 6

[0080] The present embodiment provides a sodium electric layered oxide, and the preparation method comprises the following steps:

[0081] (1) Synthesis of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material by solid phase method:

[0082] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, Na2CO3 (mass excess 3%) were ball-milled uniformly, and calcined at 900℃ for 12h under air atmosphere, and naturally cooled to room temperature. Finally, the positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0083] (2) Preparation of coated positive electrode material:

[0084] 100 g of the positive electrode material, 2 g of perovskite compound (CaTiO3), and 1 g of nano-aluminum hydroxide powder were mixed uniformly by ball milling, and then sintered at 650 ℃ for 6 h in oxygen (the gas flow was kept at 30 L / min), and naturally cooled to obtain the coated positive electrode material (the average particle size was 11.5 μm, the thickness of the coating layer was about 3.1 nm, the mass ratio of the positive electrode material to the total substance in the coating layer was 1:0.303, and the mass ratio of the perovskite to sodium meta-aluminate in the coating layer was 1:0.524).

[0085] The ball milling parameters were as follows: 1000 rpm of revolution and 70% of rotation ratio for 120 s in the first stage, and 1200 rpm of revolution and 70% of rotation ratio for 120 s in the second stage.

[0086] Example 7

[0087] The embodiment provides a sodium electric layered oxide, and a preparation method thereof.

[0088] (1) NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material was synthesized by a solid phase method.

[0089] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 and Na2CO3 (3% mass excess) were uniformly mixed by ball milling, calcined at 900 ℃ for 12 h in an air atmosphere, and naturally cooled to room temperature, to finally obtain the positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0090] (2) Preparation of the coated positive electrode material:

[0091] 100 g of the positive electrode material, 2 g of perovskite compound (CaMgTiO4), and 1 g of nano-aluminum hydroxide powder were mixed uniformly by ball milling, and then sintered at 650 ℃ for 6 h in oxygen (the gas flow was kept at 30 L / min), and naturally cooled to obtain the coated positive electrode material (the average particle size was 11.1 μm, the thickness of the coating layer was about 3.0 nm, the mass ratio of the positive electrode material to the total substance in the coating layer was 1:0.0302, and the mass ratio of the perovskite to sodium meta-aluminate in the coating layer was 1:0.527).

[0092] The ball milling parameters were as follows: 1000 rpm of revolution and 70% of rotation ratio for 120 s in the first stage, and 1200 rpm of revolution and 70% of rotation ratio for 120 s in the second stage.

[0093] Example 8

[0094] The embodiment provides a sodium battery layered oxide coated by perovskite type with the aid of aluminum hydroxide, and a preparation method thereof includes the following steps:

[0095] (1) Synthesizing NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material by a solid phase method:

[0096] Mixing Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 and Na2CO3 (3% mass excess) uniformly by ball milling, calcining at 900 DEG C for 12 h in an air atmosphere, and naturally cooling to room temperature, finally obtaining a positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0097] (2) Preparation of the coated positive electrode material:

[0098] According to a mass ratio of 100:2:1, 100 g of the positive electrode material, 2 g of perovskite compound (CaCu3Ti4O 12 ) and 1 g of nano-aluminum hydroxide powder are uniformly mixed by ball milling, and then sintered at 750 DEG C for 6 h in oxygen (keeping the gas flow at 30 L / min), and naturally cooled to obtain the coated positive electrode material (the average particle size is 11.5 μm, the thickness of the coating layer is about 3.3 nm, the mass ratio of the positive electrode material and the total substance in the coating layer is 1:0.0300, and the mass ratio of perovskite and sodium metaaluminate in the coating layer is 1:0.528).

[0099] The ball milling parameters are as follows: 1000 rpm of revolution, 70% of rotation ratio, 120 s of time in the first section, and 1200 rpm of revolution, 70% of rotation ratio, 120 s of time in the second section.

[0100] Example 9

[0101] The embodiment provides a sodium battery layered oxide, and a preparation method thereof includes the following steps:

[0102] (1) Synthesizing NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material by a solid phase method:

[0103] Mixing Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 and Na2CO3 (3% mass excess) uniformly by ball milling, calcining at 900 DEG C for 12 h in an air atmosphere, and naturally cooling to room temperature, finally obtaining a positive electrode material NaNi1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0104] (2) Preparation of coated positive electrode materials:

[0105] According to the mass ratio of 100:2:1, 100g of positive electrode material and perovskite compound (CaCu3Ti4O 12 ) 2 g and 1 g of nano-aluminum hydroxide powder were ball-milled and mixed evenly, then sintered at 800 °C for 6 h in oxygen (maintaining the gas flow rate at 30 L / min), and naturally cooled to obtain a coated positive electrode material (average particle size 11.3 μm, thickness of the coating layer about 3.2 nm, mass ratio of the total substance in the positive electrode material and the coating layer was 1:0.0301, and the mass ratio of perovskite to sodium aluminate in the coating layer was 1:0.524).

[0106] The ball milling parameters were as follows: the first stage revolution was 1000 rpm, the rotation ratio was 70%, and the time was 120 s; the second stage revolution was 1200 rpm, the rotation ratio was 70%, and the time was 120 s.

[0107] Example 10

[0108] This embodiment provides a sodium layered oxide coated with aluminum hydroxide sol-assisted perovskite, the preparation method of which includes the following steps:

[0109] (1) Synthesis of NaNi by solid phase method 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 Materials:

[0110] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 and Na2CO3 (3% excess by mass) were mixed evenly by ball milling, calcined at 900℃ for 12h in air atmosphere, and cooled naturally to room temperature to obtain the cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0111] (2) Preparation of coated positive electrode materials:

[0112] According to the mass ratio of 100:2:1, 100g of positive electrode material and perovskite compound (CaCu3Ti4O 122g, aluminum hydroxide sol 2 g (solid content 50%), together into the ball mill jar, high-speed mixing ball milling. Sintering at 650 ℃ for 6 h in oxygen (maintain the gas flow rate of 30 L / min), natural cooling to obtain the coated positive electrode material (average particle size 11.4 μm, the thickness of the coating layer is about 2.9 nm, the mass ratio of the positive electrode material, the coating layer is 1:0.0300, the mass ratio of perovskite, sodium aluminate in the coating layer is 1:0.515).

[0113] Wherein the ball milling parameters are: the first section of revolution 1500 rpm, rotation ratio 70%, time 120 s; the second section of revolution 2000 rpm, rotation ratio 70%, time 120 s.

[0114] Comparative Example 1

[0115] This comparative example provides a sodium battery layered oxide, the preparation method is basically the same as that of example 1, the difference is that: in step (2), no nano aluminum hydroxide powder and perovskite compound are added for coating.

[0116] Comparative Example 2

[0117] This comparative example provides a sodium battery layered oxide, the preparation method is basically the same as that of example 1, the difference is that: in step (2), no nano aluminum hydroxide powder is added for coating.

[0118] Comparative Example 3

[0119] This comparative example provides a sodium battery layered oxide, the preparation method is basically the same as that of example 1, the difference is that: in step (2), the nano aluminum hydroxide powder is replaced by equal mass of aluminum oxide powder.

[0120] Aluminum oxide powder has a high melting point (more than 2000 ℃), and cannot be melted at 600-700 ℃, so it cannot achieve uniform coating effect.

[0121] Comparative Example 4

[0122] This comparative example provides a sodium battery layered oxide, the preparation method is basically the same as that of example 1, the difference is that: in step (2), the nano aluminum hydroxide powder is replaced by equal mass of sodium aluminate.

[0123] Performance test:

[0124] 1. Residual alkali content test: acid-base titration method

[0125] 1) The sample residual alkali (sodium carbonate) content test method is:

[0126] Take the sample in a beaker, record the sample mass y1 grams, use a pipette to add V1 milliliters of ethylene glycol, cover the cup opening with plastic wrap and stir for more than 10 min, after stirring, use a funnel to filter, take V2 milliliters of the obtained filtrate and mix with 4 times V2 milliliters of pure water to obtain a mixed solution. Add 2-4 drops of methyl red-bromocresol green indicator to the mixed solution. Then titrate with a standard solution of hydrochloric acid with a concentration of c mol / L, titrate to the solution changes from green to pink, record the consumption of hydrochloric acid at this time V3. Calculate the residual base (sodium carbonate) content of the sample according to the following formula:

[0127]

[0128] 2) The sample residual base (sodium hydroxide) content test method is:

[0129] Take the sample in a beaker, record the sample mass y2 grams, use a pipette to add V4 milliliters of ethanol, cover the cup opening with plastic wrap and stir for more than 10 min, after stirring, use a funnel to filter, take V2 milliliters of the obtained filtrate and mix with 4 times V2 milliliters of pure water to obtain a mixed solution. Add 2-4 drops of methyl red-bromocresol green to the mixed solution. Then titrate with a standard solution of hydrochloric acid with a concentration of c mol / L, titrate to the solution changes from green to pink, record the consumption of hydrochloric acid at this time V5. Calculate the residual base (sodium hydroxide) content of the sample according to the following formula:

[0130]

[0131] 3) Calculate the total residual base content of the sample according to the test results of the above method steps 1) and 2), the formula is as follows:

[0132]

[0133] 2. Electrochemical performance test:

[0134] The button cell (referring to the 2032 type button cell for assembly) is tested for charge and discharge at 25±2℃, the voltage range is 2.0~4.2V, and the first discharge capacity at 0.1C rate, the first discharge capacity at 1C rate and the capacity retention rate after 50 cycles at 1C rate are tested respectively. The rate performance calculation formula is: 1C first discharge capacity / 0.1C first discharge capacity.

[0135] The composition of the button cell is: positive shell, spring sheet, gasket, positive electrode sheet, separator, negative electrode sheet, and negative shell. The positive electrode sheet is prepared from the prepared positive electrode material, the separator is a glass fiber separator, and the negative electrode is a metal sodium sheet.

[0136] The positive electrode material pole piece was prepared as follows: the positive electrode slurry was prepared by mixing the positive electrode powder, PVDF, and conductive carbon black in N-methylpyrrolidone in a mass ratio of (92:4:4), coating, drying, and cutting to obtain a disc with a diameter of 15 mm.

[0137] The coin cell assembly procedure is to place the positive electrode casing flat on an insulating surface, clamp the positive electrode sheet and place it in the center of the casing. Add an appropriate amount of electrolyte (1.0M NaPF6 in EC:DMC = 1:1 vol%), then add the separator, negative electrode sheet, gasket, spring sheet, and negative electrode casing in that order. The battery is then sealed in a sealing machine to produce a button cell. The entire process is performed in an argon glove box. Performance test results are shown in Table 1.

[0138] Table 1 Performance test of batteries assembled from sodium layered oxides obtained in Examples and Comparative Examples

[0139]

[0140] The particle size and coating thickness of the sodium layered oxides of each example were measured using scanning electron microscopy and transmission electron microscopy. The specific contents of Ca and Al in the coating layer were determined by ICP analysis, and the masses of the perovskite and sodium metaaluminate were then derived, as shown in Table 2 below.

[0141] Table 2 Particle size, coating thickness and composition of sodium layered oxide obtained in Example

[0142]

[0143] Table 2 shows that the average particle size of the coated examples is 11-12 μm, the coating layer thickness is 3-5 nm, and the amount of material in the coating layer is close to the amount added.

[0144] like Figure 1 The following is a scanning electron microscope image of Example 1. It can be seen from the figure that the average particle size of the synthesized layered oxide positive electrode material is 11.6 μm. As can be seen from Table 1, when Example 1 is compared with Comparative Example 1, it is found that 2% CaCu3Ti4O 12 After coating with 1% Al(OH)3, the 0.1C initial discharge capacity did not significantly decrease, and the residual alkali content after secondary calcination was reduced to 3261 ppm. At a high voltage of 4.2V, its rate capability and 50-cycle retention rate were 90.6% and 91.2%, respectively, higher than the 86.4% and 67.5% of the uncoated comparative example 1, demonstrating excellent stability at high voltages. Figure 2 and Figure 3 They are transmission electron microscope scanning images of Example 1 and Comparative Example 2 respectively. Figure 2 As shown in FIG, a uniform composite coating layer with a thickness of 3 nm can be seen on the surface of the positive electrode material.Figure 3 As shown in FIG. 1, only CaCu3Ti4O 12 The coating is obviously uneven, indicating that the addition of 1% Al(OH)3 can improve the CaCu3Ti4O 12 The coating is obviously uneven, indicating that the addition of 1% Al(OH)3 can improve the CaCu3Ti4O

[0145] Example 2 is NaNi 0.5 Mn 0.5 O2 cathode material coated with 2% CaCu3Ti4O 12 +1% Al(OH)3, 4.2V voltage, 1C rate, 50 cycles, the retention rate is 90.6%. It is indicated that this coating condition is also applicable to other cathode materials, and can have good stability at high voltage.

[0146] Example 3 is compared with Example 1, the mixing ratio of CaCu3Ti4O 12 and Al(OH)3 is 1:2, and the initial discharge capacity at 0.1C is not obviously decreased, and the cycle retention rate at 1C is only 83.4%, which is lower than 91.2% of Example 1, mainly because the CaCu3Ti4O 12 content is less, the interface gradient doping of Ca on the material surface is less, and the role of stabilizing the structure is limited.

[0147] Example 4 and Example 5 respectively increase the coating amount to 2.5% CaCu3Ti4O 12 +1.5% Al(OH)3 and 5% CaCu3Ti4O 12 +5% Al(OH)3, both of which have the effect of reducing residual alkali compared with Example 1. However, the initial discharge capacity at 0.1C of Example 4 and Example 5 is 182.4 mAh / g and 176.1 mAh / g, which is obviously decreased compared with Example 1. Moreover, the rate performance is also poor, only 87.4% and 80.3%. Mainly because the coating layer is thick, which hinders the embedding and extraction of Na + , resulting in a significant decrease in electrochemical performance. Therefore, the coating amount also needs to be within a suitable range.

[0148] Example 6 and Example 7 respectively select CaTiO3, CaMgTiO4 and Al(OH)3 as the composite coating, which also shows excellent cycle stability. At 4.2V, the capacity retention rate at 1C for 50 cycles is 91% and 90.8% respectively, which is close to Example 1. It is indicated that nano-aluminum hydroxide powder is also suitable for auxiliary uniform coating of other perovskite compounds.

[0149] Example 8 and Example 9 show that if the second sintering temperature is too high, exceeding 750°C, the particles will re-melt, and the particles will be agglomerated, which will result in the decrease of the initial 0.1C discharge capacity and the decrease of the cycle performance. Therefore, the second sintering should be performed at a suitable temperature.

[0150] Example 10 uses aluminum hydroxide sol to assist perovskite coating, and also shows excellent cycle stability. At 4.2V, the initial 0.1C discharge capacity is 186.8 mAh / g, and the 1C 50-cycle retention rate is 90.9%, close to that of Example 1. This shows that using aluminum hydroxide sol coating can achieve the same effect as using nano-aluminum hydroxide powder coating.

[0151] Comparative Example 2, compared with Example 1, only coated 2% CaCu3Ti4O 12 Although it can improve the rate capability and cycle stability, the coating is uneven, resulting in an increase in side reactions with the electrolyte. At 4.2V, the 50-cycle retention rate is 80.4%, lower than the 91.2% of Example 1.

[0152] Comparative Example 3, compared with Example 1, has an initial 0.1C discharge capacity of 184.8 mAh / g, lower than the 187.1 mAh / g of Example 1, and the rate capability is also decreased to 87.1%, lower than the 90.6% of Example 1. Since aluminum oxide is an inert compound, the initial capacity and rate capability will decrease after coating. Moreover, Al2O3 has a high melting point of 2050°C, and does not assist in perovskite coating, and cannot melt to drive the perovskite to uniformly reach the surface of the material during the second sintering. Therefore, the 1C 50-cycle retention rate is only 82.8%, lower than the 91.2% of Example 1.

[0153] Comparative Example 4 is 2% CaCu3Ti4O 12 After adding 1% NaAlO2 as a composite coating layer, compared with Comparative Example 1, the residual alkali can also be reduced after coating, the initial 0.1C discharge capacity is 185.1 mAh / g, slightly lower than Example 1, and the 1C rate 50-cycle retention rate is only 84.3%, lower than the 91.2% of Example 1. This shows that directly adding NaAlO2 does not play an auxiliary coating role.

[0154] Therefore, under the best conditions, 1% Al(OH)3 assists 2% CaCu3Ti4O 12 coating, forming a uniform composite coating layer on the surface of the sodium layered cathode material, and combining with the interface gradient doping, can significantly improve the cycle stability at high voltage 4.2V.

[0155] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which do not affect the essence of the present application.

Claims

1. A sodium electro-layered oxide characterized by, It includes a positive electrode material and a coating layer on the surface of the positive electrode material particles; the coating layer includes perovskite and sodium metaaluminate; The mass ratio of perovskite to sodium aluminate in the coating layer is 1:(0.1-2.2); The perovskite and sodium aluminate in the coating layer are obtained by sintering perovskite compounds and aluminum hydroxide mixed with positive electrode material particles.

2. The sodium electroactive layered oxide of claim 1, wherein, The positive electrode material is an O3-type sodium battery layered oxide; the O3-type sodium battery layered oxide is Na x TMO2; wherein, 2 / 3 < x ≤ 1, TM is a transition metal element including one or more of Ni, Fe, Mn, Cu, Ti, Co, Nb, Zn, Y, Zr, Mo.

3. The sodium electroactive layered oxide of claim 1, wherein, The perovskite compound is CaABO x ; wherein AB comprises one or more of Ti, Mg, Co, Fe, Ni, Cu, Zn.

4. The sodium electroactive layered oxide of claim 1, wherein, The average particle size of the positive electrode material is 5-20 μm; and / or, the coating layer on the surface of the positive electrode material particles has a thickness of 2-10 nm; And / or, the mass ratio of the positive electrode material to the total substance in the coating layer is 1:(0.01-0.11).

5. A method for producing a sodium electrocrystalline oxide as claimed in any one of claims 1 to 4, characterized by, The steps include: The positive electrode material, the perovskite compound and the aluminum hydroxide are mixed, sintered and then cooled to obtain the sodium electrode layered oxide.

6. The method of preparing a sodium electrocrystaline oxide according to claim 5, wherein Aluminum hydroxide is one or more of nano aluminum hydroxide powder and aluminum hydroxide sol; and / or, the mass ratio of the positive electrode material, the perovskite compound, and the aluminum hydroxide is 100:(0.5-5):(0.5-5); And / or, the sintering temperature is 600-800° C. and the sintering time is 6-10 hours.

7. The method of producing a sodium electroactive layered oxide according to claim 5, characterized in that, Sintering is carried out under the condition of protective gas; the protective gas includes one or more of oxygen and nitrogen.

8. A positive electrode sheet characterized by comprising: The invention comprises the sodium layered oxide according to any one of claims 1 to 4.

9. A battery, characterized by Comprising the positive electrode sheet as claimed in claim 8.

10. Use of the sodium layered oxide according to claim 1 in preparing sodium ion batteries.

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