Composite for sodium ion battery positive electrode and manufacturing method thereof

Abstract

The invention relates to a composite for a sodium ion battery positive electrode and a manufacturing method thereof. Specifically, the invention provides a compound for a sodium-ion battery positive electrode, a manufacturing method of the compound for the sodium-ion battery positive electrode, a positive electrode material for a sodium-ion battery, a positive electrode for a sodium-ion battery and a sodium-ion battery. The compound for the positive electrode of the sodium ion battery comprises sodium super-ion conductive particles, the chemical formula of which is at least one of NaxMy (PO4) 2Rz and NaxVy (PO4) n; the chemical formula of the ferroelectric particles is WTO3, x is equal to 3, y is equal to 2, z is equal to 1.5 or 3, n is equal to 3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a metal element selected from niobium or titanium.

Description

Technical Field

[0001] The present application relates to a composite, and in particular to a composite for a positive electrode of a sodium ion battery. Background Art

[0002] Sodium-ion batteries (SIBs) are a promising new energy storage device. However, the poor cycling stability of SIB cathodes and the weak electrochemical performance of SIBs have limited their further development. Summary of the Invention

[0003] According to one aspect, the present application provides a composite for a sodium ion battery cathode, comprising: sodium superionic conductive particles having a chemical formula of Na x M y (PO4)2R z And Na x V y (PO4) n and a ferroelectric particle having a chemical formula of WTO3, wherein x=3, y=2, z=1.5 or 3, n=3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a metal element selected from niobium or titanium.

[0004] According to another aspect, the present application provides a method for manufacturing a composite material for a sodium ion battery cathode, the manufacturing method comprising: x M y (PO4)2R z And Na x V y (PO4) n At least one sodium superionic conductor particle of the present invention is mixed with ferroelectric particles of the chemical formula WTO3 to obtain a mixture, wherein x=3, y=2, z=1.5 or 3, n=3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a transition metal element selected from niobium or titanium; ball milling the mixture; drying the mixture to obtain a dry powder; and annealing the dry powder to obtain a composite for a positive electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The embodiments of the present application are described in detail below with reference to the accompanying drawings:

[0006] Figure 1 A block diagram showing a method for manufacturing a composite material for a positive electrode of a sodium ion battery according to an embodiment of the present application;

[0007] Figure 2The X-ray diffraction patterns of Na3V2(PO4)2F3@NaNbO3 (NVPF@NaNbO3) and NVPF@C after annealing in one example are shown, which show that the ferroelectric material does not affect the crystal structure of the positive electrode active material NVPF;

[0008] Figure 3 Show Figure 2 The rate capability of NVPF@NaNbO3 and NVPF@C, where the test current is between 0.1C and 5C, and 1C=128mA / g;

[0009] Figure 4 Show Figure 2 The charge and discharge stability of NVPF@NaNbO3 and NVPF@C at 10C and 500 cycles, respectively, of which the capacity retention rates of NVPF@NaNbO3 and NVPF@C are 92% and 79%, respectively;

[0010] Figure 5 Show Figure 2 The charge-discharge stability of NVPF@NaNbO3 at 2C, -20℃, and 1000 cycles increased by 38%;

[0011] Figure 6 Show Figure 2 The rate capability of NVPF@NaNbO3, where the test current is between 1C and 50C, the test temperature is 60℃, and 1C=128mA / g;

[0012] Figure 7 Show Figure 2 The charge and discharge stability of NVPF@NaNbO3 at 10C, 60℃, and 500 cycles, of which the capacity retention rate of NVPF@NaNbO3 is 95%;

[0013] Figure 8 The X-ray diffraction patterns of Na3V2(PO4)3@NaNbO3 (NVP@NaNbO3) and NVP@C after annealing in one example are shown, which show that the ferroelectric material does not affect the crystal structure of the positive electrode active material NVP; Figure 9A A scanning electron microscrope (SEM) image of NVP@NaNbO3 before annealing in one example is shown;

[0014] Figure 9B Show Figure 9ALayered image of NVP@NaNbO3 measured by Energy Dispersive X-Ray Spectroscopy (EDS);

[0015] Figure 9C Show Figure 9A Electronic image of NVP@NaNbO3;

[0016] Figure 9D Show Figure 9A C Kα1,2 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0017] Figure 9E Show Figure 9A O Kα1 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0018] Figure 9F Show Figure 9A Na Kα1,2 images of NVP@NaNbO3 measured by energy-dispersive X-ray spectroscopy;

[0019] Figure 9G Show Figure 9A P Kα1 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0020] Figure 9H Show Figure 9A V Kα1 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0021] Figure 9I Show Figure 9A Nb Lα1 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0022] Figure 9J Show Figure 9A The total number of distribution maps of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0023] Figure 10A Shows an SEM image of NVP@NaNbO3 after annealing in one example;

[0024] Figure 10B Show Figure 10A Layered image of NVP@NaNbO3 measured by Energy Dispersive X-Ray Spectroscopy;

[0025] Figure 10C Show Figure 10AElectronic image of NVP@NaNbO3;

[0026] Figure 10D Show Figure 10A C Kα1,2 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0027] Figure 10E Show Figure 10A P Kα1 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0028] Figure 10F Show Figure 10A Na Kα1,2 images of NVP@NaNbO3 measured by energy-dispersive X-ray spectroscopy;

[0029] Figure 10G Show Figure 10A Nb Kα1 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0030] Figure 10H Show Figure 10A V Kα1 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0031] Figure 10I Show Figure 10A O Kα1 image of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0032] Figure 10J Show Figure 10A The total number of distribution maps of NVP@NaNbO3 measured by energy dispersive X-ray spectroscopy;

[0033] Figure 11 Show Figure 8 The charge and discharge stability of the full battery composed of NVP@NaNbO3 and NVP at 1C and 2000 cycles, where NVP@NaNbO3 is used as the positive electrode active material and NVP is used as the negative electrode active material. The current density and specific capacity are calculated based on the positive electrode active material. The capacity retention rate of the full battery is 88%. DETAILED DESCRIPTION

[0034] The specific details and embodiments of the present application will be described in detail below with reference to the accompanying drawings, which illustrate possible implementation methods of the present application by way of illustration. These embodiments are described in detail to enable those skilled in the art to implement the present application. Other embodiments may be used, and structural, logical, and electrical changes may be made without departing from the scope of the present application. The various embodiments are not necessarily mutually exclusive, as some embodiments may be combined with one or more other embodiments to form new embodiments.

[0035] Features described in one embodiment may be applied accordingly to the same or similar features in other embodiments, even if not explicitly described in these other embodiments. In addition, additions, combinations and / or substitutions described for features may also be applied accordingly to the same or similar features in other embodiments.

[0036] The articles “a,” “an,” and “the” used with respect to a feature or element include reference to one or more features or elements.

[0037] In various embodiments, the term "about" or "approximately" when applied to a numerical value encompasses the stated value and a reasonable variance, for example, within + / - 10% of the stated value.

[0038] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0039] In this application, "positive electrode" refers to a positive electrode current collector coated with a positive electrode material for a sodium ion battery. "Positive electrode material" includes a positive electrode active material, conductive carbon or conductive agent, and a binder or adhesive. "Positive electrode active material" is a material that undergoes an electrochemical redox reaction during the operation of the positive electrode of a sodium ion battery to substantially provide electrochemical capacity. In this application, "positive electrode" and "cathode" are used interchangeably.

[0040] In this application, "negative electrode" refers to the negative electrode current collector coated with negative electrode material for sodium ion batteries. "Negative electrode material" includes negative electrode active material, conductive carbon or conductive agent, binder or adhesive. "Negative electrode active material" is the material that undergoes electrochemical redox reaction during the operation of the negative electrode of the sodium ion battery to substantially provide electrochemical capacity. In this application, "negative electrode" and "anode" are used interchangeably.

[0041] The embodiments described for one positive electrode, positive electrode material, or positive electrode active material are also applicable to another positive electrode, positive electrode material, or positive electrode active material. Similarly, the embodiments described for the method are also applicable to the positive electrode, positive electrode material, or positive electrode active material, and vice versa.

[0042] The embodiments described for one negative electrode, negative electrode material, or negative electrode active material are also applicable to another negative electrode, negative electrode material, or negative electrode active material. Similarly, the embodiments described for a method are also applicable to a negative electrode, negative electrode material, or negative electrode active material, and vice versa.

[0043] In this application, "composite" and "composite material" can be used interchangeably. In this application, "coating" refers to a material forming a uniform coating on the surface of another material that directly covers the surface, and the contact between the coating and the coated surface can be essentially considered as surface contact. In contrast, in this application, "surrounding" refers to a plurality of particles of a material being discretely distributed in a satellite shape around the surface of a particle of another material. Compared to the surface contact between the coating and the coated surface, the contact between the plurality of particles and the particle they surround can essentially be considered as point contact. In this application, "wrapping" and "coating" can be used interchangeably.

[0044] On the one hand, the present application provides a composite for a sodium ion battery cathode, comprising: sodium superionic conductive particles, the chemical formula of which is Na x M y (PO4)2R z And Na x V y (PO4) n and a ferroelectric particle having a chemical formula of WTO3, wherein x=3, y=2, z=1.5 or 3, n=3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a metal element selected from niobium or titanium.

[0045] Preferably, M is selected from the group consisting of vanadium, iron, titanium, manganese and chromium.

[0046] Preferably, R is selected from the group consisting of fluorine, chlorine and oxygen, wherein when R is selected from fluorine or chlorine, z=3, and when R is oxygen, z=1.5.

[0047] Preferably, the monovalent atom is selected from the group consisting of sodium and lithium, and the divalent atom is barium.

[0048] Preferably, when W is sodium or lithium, T is niobium.

[0049] Preferably, when W is barium, T is titanium.

[0050] Preferably, the sodium superion conductor particles are coated with carbon to form carbon-coated sodium superion conductor particles.

[0051] Preferably, the sodium superion conductor particles are nanoparticles having a particle size ranging from 100 nm to 2 μm.

[0052] Preferably, the ferroelectric particles are nanoparticles having a particle size ranging from 100 nm to 400 nm.

[0053] Preferably, the mass percentage of the ferroelectric particles in the composite is in the range of 0.01 wt % to 8 wt %.

[0054] Preferably, the sodium superion conductor particles are selected from Na3V2(PO4)2F3, Na3V2(PO4)2Cl3, Na3V2(PO4)2O 1.5 , Na3Fe2(PO4)2F3, Na3Fe2(PO4)2Cl3, Na3Fe2(PO4)2O 1.5 , Na3Ti2(PO4)2F3, Na3Ti2(PO4)2Cl3, Na3Ti2(PO4)2O 1.5 , Na3Mn2(PO4)2F3, Na3Mn2(PO4)2Cl3, Na3Mn2(PO4)2O 1.5 , Na3Cr2(PO4)2F3, Na3Cr2(PO4)2Cl3, Na3Cr2(PO4)2O 1.5 , Na3V2(PO4)3 or more materials.

[0055] Preferably, the ferroelectric particles are composed of one or more materials selected from NaNbO 3 , BaTiO 3 , and LiNbO 3 .

[0056] In one example, the composite includes sodium superionic conductive particles and ferroelectric particles, each sodium superionic conductive particle is contacted and surrounded by a plurality of ferroelectric particles, the ferroelectric particles do not coat the sodium superionic conductive particles, and no chemical bonds are formed between the sodium superionic conductive particles and the ferroelectric particles. The contact between each sodium superionic conductive particle and the plurality of ferroelectric particles is a point contact, as described above. Since each sodium superionic conductive particle is contacted and surrounded by a plurality of ferroelectric particles, the sodium salt in the electrolyte can be effectively dissociated, thereby increasing the sodium ion mobility. The increase in free sodium ions in the electrolyte can reduce the intrinsic impedance of the electrolyte. In addition, the ferroelectric particles do not coat the sodium superionic conductive particles, and no chemical bonds are formed between the sodium superionic conductive particles and the ferroelectric particles. Ultimately, a higher specific capacity, a higher specific energy, and a higher specific power are provided for sodium-ion batteries.

[0057] In this composite, the sodium superion-conducting particles are carbon-coated sodium superion-conducting particles. Each carbon-coated sodium superion-conducting particle is contacted and surrounded by a plurality of inorganic ferroelectric particles. The inorganic ferroelectric particles do not coat the carbon-coated sodium superion-conducting particles, and no chemical bonds are formed between the carbon-coated sodium superion-conducting particles and the inorganic ferroelectric particles. As described above, the contact between each carbon-coated sodium superion-conducting particle and the plurality of inorganic ferroelectric particles is point contact.

[0058] Ferroelectric materials improve the ionic conductivity of active cathode materials. Composites of inorganic ferroelectric materials with sodium superionic conductive materials offer higher specific capacity and energy density. Furthermore, composites of sodium superionic conductive materials with inorganic ferroelectric materials enhance the cycling stability of sodium superionic conductive materials at room temperature at high currents, as well as their overall electrochemical performance at both low and high temperatures.

[0059] According to another aspect, reference Figure 1 The present application provides a method 100 for manufacturing a composite material for a sodium ion battery cathode. The method 100 comprises: x M y (PO4)2R z And Na x V y (PO4) n At least one sodium superionic conductor particle of the present invention is mixed with ferroelectric particles of the chemical formula WTO3 to obtain a mixture, wherein x=3, y=2, z=1.5 or 3, n=3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a transition metal element selected from niobium or titanium (step 102), the mixture is ball-milled (step 104), the mixture is dried to obtain a dry powder (step 106), and the dry powder is annealed to obtain a composite for a positive electrode (step 108).

[0060] The contact between each sodium superion conductive particle and the plurality of ferroelectric particles is a point contact, as described above.

[0061] Preferably, the method 100 further includes forming a carbon layer on the surface of the sodium superionic conductor particles before mixing the sodium superionic conductor particles with the ferroelectric particles.

[0062] Preferably, method 100 further includes, before mixing the sodium superionic conductor particles with the ferroelectric particles, manufacturing the sodium superionic conductor particles, including calcining the sodium superionic conductor particles at least twice, wherein the temperature of the first calcination is lower than that of the second calcination. During the at least two calcinations, a carbon coating is formed in the first calcination, and the carbon coating is further graphitized in the second calcination, thereby further improving conductivity. In addition, in the first calcination, residual inorganic compounds from the previous synthesis process are volatilized and removed.

[0063] Preferably, in the method 100, the mixture is ball milled for 1 hour to 6 hours at a speed ranging from 100 rpm to 700 rpm.

[0064] Preferably, in the method 100 , the dry powder is annealed in an inert atmosphere at a temperature of 200° C. to 600° C. for 1 hour to 10 hours.

[0065] Preferably, in method 100, M is selected from the group consisting of vanadium, iron, titanium, manganese, and chromium.

[0066] Preferably, in method 100, R is selected from the group consisting of fluorine, chlorine, and oxygen. When R is selected from fluorine or chlorine, z=3. When R is oxygen, z=1.5.

[0067] Preferably, in method 100, the monovalent atom is selected from sodium and lithium, and the divalent atom is barium.

[0068] Preferably, in method 100, when W is sodium or lithium, T is niobium.

[0069] Preferably, in method 100, when W is barium, T is titanium.

[0070] Preferably, in method 100 , the sodium superion conductor particles are nanoparticles having a particle size ranging from 100 nm to 2 μm.

[0071] Preferably, in the method 100 , the ferroelectric particles are nanoparticles having a particle size ranging from 100 nm to 400 nm.

[0072] Preferably, in method 100, the sodium superionic conductor particles are selected from Na3V2(PO4)2F3, Na3V2(PO4)2Cl3, Na3V2(PO4)2O 1.5 , Na3Fe2(PO4)2F3, Na3Fe2(PO4)2Cl3, Na3Fe2(PO4)2O 1.5 , Na3Ti2(PO4)2F3,Na3Ti2(PO4)2Cl3, Na3Ti2(PO4)2O 1.5 , Na3Mn2(PO4)2F3, Na3Mn2(PO4)2Cl3, Na3Mn2(PO4)2O 1.5 ,Na3Cr2(PO4)2F3, Na3Cr2(PO4)2Cl3, Na3Cr2(PO4)2O 1.5 , Na3V2(PO4)3 and one or more materials selected from the group consisting of.

[0073] Preferably, in the method 100 , the ferroelectric particles are composed of one or more materials selected from the group consisting of NaNbO 3 , BaTiO 3 , and LiNbO 3 .

[0074] Preferably, in the method 100 , the mass percentage of the ferroelectric particles in the composite is 0.01 wt % to 8 wt %.

[0075] In one example, forming a composite comprising sodium superionic conductive particles and ferroelectric particles is forming a composite comprising carbon-coated sodium superionic conductive particles and ferroelectric particles. Forming a composite comprising carbon-coated sodium superionic conductive particles and ferroelectric particles includes: after the second calcination, compounding the mixture. Compounding includes ball milling, drying and annealing. During the compounding process, the total energy input to the mixture, that is, the sum of the energy inputs of the individual processes of ball milling, drying and annealing, is set so that each sodium superionic conductive particle is contacted and surrounded by a plurality of ferroelectric particles. In addition, the ferroelectric particles do not coat the sodium superionic conductive particles, and no chemical bonds are formed between the carbon-coated sodium superionic conductive particles and the ferroelectric particles.

[0076] In other words, during the composite process, the total energy input to the mixture is set to be sufficiently high so that each sodium superionic conductive particle is contacted and surrounded by multiple ferroelectric particles. At the same time, the total energy input to the mixture is also set to be sufficiently low so that the ferroelectric particles do not coat the sodium superionic conductive particles. In addition, no chemical bonds are formed between the carbon-coated sodium superionic conductive particles and the ferroelectric particles.

[0077] Ball milling allows the sodium superionic conductive particles and ferroelectric particles to be evenly distributed in the composite, and heating releases the stress generated in the composite during the ball milling process, thereby achieving atomic movement and structural rearrangement.

[0078] The method 100 for manufacturing a composite of a ferroelectric material and a sodium superionic conductive material avoids the use of hazardous chemicals, extreme temperature and pressure conditions, and can be scaled up for industrial applications due to its low cost and high efficiency.

[0079] In one example, the sodium superionic conductive particles are Na₃V₂(PO₄)₂F₃ (NVPF). For example, in step 102, NVPF can be produced via sol-gel method, with citric acid acting as a chelating agent and reducing agent. Specifically, citric acid, NH₄VO₃, NH₄H₂PO₄, and NaF are added in stoichiometric proportions to deionized water at 60°C to 90°C and stirred at this temperature for several hours until a gel forms. After complete drying in an oven for 12 hours, the calcination process begins. The calcination conditions, namely temperature, duration, and pressure, are set to avoid sublimation of fluorine, thereby ensuring the purity of the NVPF. The first calcination is performed in a tube furnace at 300°C to 500°C, continuously flowing with argon or nitrogen, for one to six hours. The second calcination is performed under the same conditions, but at a temperature of 600°C to 800°C, for one to eight hours. A relative excess of citric acid is used to carbonize the excess citric acid and form a coating on the surface of the NVPF particles. After calcination, in step 104, the NVPF powder is placed in a zirconia canister and inorganic ferroelectric materials (e.g., NaNbO3, LiNbO3, and BaTiO3) are added in varying weight ratios (typically between 0.01 wt% and 8 wt%). The mixture of the positive electrode material and the ferroelectric material is ball-milled in ethanol or acetone for several hours, e.g., not less than one hour, at a speed of not less than 100 rpm. Ethanol or acetone is used to disperse the particles to reduce the tendency of particles to agglomerate during the ball milling process, thereby ensuring uniformity in the ball milling process and the final product. Furthermore, the friction between the ball milling balls and the material is reduced by the ethanol or acetone, thereby reducing wear on the ball milling balls and the ball milling container, thereby improving the energy efficiency of the ball milling and reducing contamination of the product.

[0080] In step 106, the solvent is evaporated in an oven for 12 hours. In step 108, the ferroelectric powder particles are homogenized with the NVPF by heating in a tube furnace at 200° C. to 500° C. for 1 to 6 hours.

[0081] Because no chemical bonds form between the NVPF nanoparticles and the inorganic ferroelectric nanoparticles in steps 104, 106, and 108, the resulting composite contains no chemical bonds between the two materials—the NVPF and the inorganic ferroelectric. Therefore, the NVPF and the inorganic ferroelectric do not encapsulate each other; the inorganic ferroelectric does not encapsulate the NVPF, and the NVPF does not encapsulate the inorganic ferroelectric. In other words, in steps 104, 106, and 108, the total energy input to the NVPF nanoparticles and the inorganic ferroelectric nanoparticles is configured such that each NVPF particle is contacted and surrounded by ferroelectric particles, but no chemical bonds form between the NVPF and the inorganic ferroelectric. In contrast, other chemical methods (such as chemical vapor deposition) produce chemical bonds, allowing the ferroelectric material to encapsulate the surface of the NVPF. The ball milling process uniformly distributes the ferroelectric material and NVPF. This process introduces significant mechanical stresses into the composite material, which may include dislocations and grain boundary distortions. Subsequent heating helps relieve these stresses, thereby enabling atomic movement and structural rearrangement. NVPF and the inorganic ferroelectric material are arranged in close contact. Specifically, each NVPF particle is contacted and surrounded by some ferroelectric particles, but no coating is formed.

[0082] According to a third aspect, the present application provides a positive electrode material for a sodium ion battery. The positive electrode material comprises a composite comprising: sodium superionic conductive particles having a chemical formula of Na x M y (PO4)2R z And Na x V y (PO4) n and a ferroelectric particle having a chemical formula of WTO3, wherein x=3, y=2, z=1.5 or 3, n=3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a metal element selected from niobium or titanium.

[0083] According to a fourth aspect, the present application provides a positive electrode for a sodium ion battery. The positive electrode comprises a composite comprising: sodium superionic conductive particles, the chemical formula of which is Na x M y (PO4)2R z And Na x V y (PO4) n and a ferroelectric particle having a chemical formula of WTO3, wherein x=3, y=2, z=1.5 or 3, n=3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a metal element selected from niobium or titanium.

[0084] According to a fifth aspect, the present application provides a sodium ion battery. The sodium ion battery includes a positive electrode, a negative electrode including sodium or hard carbon, a separator including a porous material, and an electrolyte including a sodium salt. The positive electrode includes a composite, the composite including: sodium superionic conductive particles, the chemical formula of which is Na x M y (PO4)2R z And Na x V y (PO4) n and a ferroelectric particle having a chemical formula of WTO3, wherein x=3, y=2, z=1.5 or 3, n=3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a metal element selected from niobium or titanium.

[0085] The separator includes one selected from the group consisting of glass fiber / D, glass fiber / C, and a three-layer composite separator consisting of polypropylene / polyethylene / polypropylene. The three-layer composite separator may include Celgard 2320, Celgard 2400, or Celgard 2500. The sodium salt of the sodium-ion battery is selected from any one or more of sodium perchlorate, sodium tetrafluoroborate, or sodium hexafluorophosphate.

[0086] In one example, in the sodium ion battery, the negative electrode active material is sodium superion conductive particles. In other words, the negative electrode active material is not metallic sodium.

[0087] In one example, the sodium ion battery is an all-solid-state sodium ion battery. In other words, the electrolyte of the sodium ion battery is a solid electrolyte, not a liquid electrolyte.

[0088] Example 1

[0089] NVPF was fabricated using a sol-gel method using stoichiometric ratios of NH₄VO₃, NH₄H₂PO₄, and NaF, along with an excess of citric acid relative to the stoichiometric ratio. The reactants were stirred in deionized water at a temperature of 60°C to 90°C. The NVPF powder was calcined twice under argon at temperatures of 300°C to 500°C and 600°C to 800°C for one hour each. The resulting NVPF is referred to as NVPF@C. NVPF@C was then ball-milled with 0.05 wt% NaNbO₃ in pure ethanol at a speed ranging from 100 rpm to 700 rpm, for example, 600 rpm, for a time ranging from 1 hour to 6 hours, for example, 2 hours. Finally, the dry powder was heated under argon at a temperature ranging from 200°C to 500°C, for example, 350°C, for a time ranging from 1 hour to 6 hours, for example, 2 hours. The resulting product is referred to as NVPF@NaNbO₃. Among them, the NVPF in NVPF@NaNbO3 is carbon-coated, that is, the ball milling and subsequent heating processes do not destroy the carbon coating layer of NVPF.

[0090] Example 2

[0091] NVPF was fabricated using a sol-gel method using stoichiometric ratios of NH₄VO₃, NH₄H₂PO₄, and NaF, along with an excess of citric acid relative to the stoichiometric ratio. The reactants were stirred in deionized water at a temperature of 60°C to 90°C. The NVPF powder was calcined twice under argon at temperatures of 300°C to 500°C and 600°C to 800°C for 3 hours each. The resulting material was then ball-milled with 8 wt% BaTiO₃ in pure ethanol at a speed ranging from 100 rpm to 700 rpm, for example, 600 rpm, for a time ranging from 1 hour to 6 hours, for example, 2 hours. Finally, the dry powder was heated under argon at a temperature ranging from 200°C to 500°C, for example, 350°C, for a time ranging from 1 hour to 6 hours, for example, 2 hours. The resulting product is referred to as NVPF@BaTiO₃.

[0092] Example 3

[0093] NVPF was fabricated using a sol-gel method using stoichiometric ratios of NH₄VO₃, NH₄H₂PO₄, and NaF, along with an excess of citric acid relative to the stoichiometric ratio. The reactants were stirred in deionized water at a temperature of 60°C to 90°C. The NVPF powder was calcined twice under argon at 300°C to 500°C and 600°C to 800°C for 4 hours each. The resulting material was then ball-milled with 5 wt% LiNbO₃ in pure ethanol at a speed ranging from 100 rpm to 700 rpm, for example, 600 rpm, for a time ranging from 1 hour to 6 hours, for example, 2 hours. Finally, the dry powder was heated under argon at a temperature ranging from 200°C to 600°C, for example, 350°C, for a time ranging from 1 hour to 10 hours, for example, 2 hours. The resulting product is referred to as NVPF@LiNbO₃.

[0094] Example 4

[0095] Commercial NVP was co-milled with 2 wt% NaNbO3 in pure ethanol using a ball mill at 600 rpm for 2 hours. Finally, the dry powder was heated at 350°C for 2 hours under argon. The resulting product is called NVP@NaNbO3.

[0096] Materials characterization and electrochemical characterization

[0097] Structural characterization was performed using XRD with a 2𝜃 angle between 10° and 80°. Electrochemical impedance spectroscopy (EIS) was used to characterize the impedance spectrum, with an AC amplitude signal of 5 mV and a frequency range of 0.01 Hz to 100 kHz. Cyclic voltammetry (CV) was performed with a voltage window of 2.1 V to 4.3 V (vs Na / Na + ), the scan rate is 0.1mVs -1 The cycling performance of the half-cell is shown in the voltage window of 2.1V to 4.3V (vs Na / Na + ) and tested at multiple current densities from 0.1C to 50C, where 1C equals 128mAg -1 .

[0098] Battery Manufacturing

[0099] The positive electrode slurry is prepared by mixing NVPF or NVP, conductive carbon, and a binder in three different ratios: 70:20:10, 80:10:10, and 90:05:05. The conductive carbon can be carbon black, graphite, carbon nanotubes, or graphene. Binders include, but are not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol, polyacrylic acid, and carboxymethylcellulose (CMC). The solvent can be N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), acetone, or deionized (DI) water, depending on the binder used. The active material slurry is applied to a current collector using a doctor blade. The current collector is aluminum, but can also be other materials such as nickel or stainless steel foil. The coated slurry is dried in a conventional oven or a vacuum oven at a temperature of 60°C to 100°C. The electrolyte can be NaClO4, NaBF4, or NaPF6. Solvents include, but are not limited to, dimethyl carbonate, dimethyl acetate, ethyl acetate, and tetrahydrofuran. The separator is not particularly limited and can be D-grade glass fiber, C-grade glass fiber, or a polypropylene / polyethylene / polypropylene three-layer composite separator. The polypropylene / polyethylene / polypropylene three-layer composite separator can include Celgard 2320, Celgard 2400, or Celgard 2500. The battery also includes an electrolyte and a separator. The positive electrode (cathode) consists of a positive current collector and a positive electrode material coated on the current collector. The positive electrode material comprises a composite of NVPF and an inorganic ferroelectric material as the positive electrode active material. The negative electrode (anode) consists of a negative current collector and a negative electrode material coated on the negative current collector. The negative electrode material comprises pure sodium particles as the negative electrode active material. The assembly of the half-cells was performed in a glove box in an argon atmosphere with moisture and oxygen levels below 0.01 ppm.

[0100] Characterization results and battery performance

[0101] Figures 9A to 9J The SEM image and EDS analysis results of Na3V2(PO4)3(NVP)@NaNbO3 before annealing in Example 4 are shown respectively. 10A to 10JThe SEM image and EDS analysis results of the NVP@NaNbO3 composite after heating in Example 4 are shown. The molar percentage of the inorganic ferroelectric material NaNbO3 in the composite increases by approximately 17% after heating. Furthermore, the SEM image demonstrates that the relatively low heating temperature does not alter the shape or size of the composite particles.

[0102] Because the ball milling and annealing processes in Examples 1 to 4 do not produce any chemical bonds, the resulting composite contains no chemical bonds between the two materials—that is, between the NVPF or NVP and the inorganic ferroelectric material. Therefore, the NVPF or NVP and the inorganic ferroelectric material do not encapsulate each other; that is, the inorganic ferroelectric material does not encapsulate the NVPF or NVP, and the NVPF or NVP does not encapsulate the inorganic ferroelectric material. In contrast, other chemical methods (such as CVD) produce chemical bonds, allowing the ferroelectric material to encapsulate the surface of the active material. The ball milling process uniformly distributes the ferroelectric and active materials. This process introduces significant mechanical stresses into the composite material, which may include dislocations and grain boundary distortions. Subsequent heating helps to relieve the stress, thereby enabling atomic movement and structural rearrangement. The NVPF and the inorganic ferroelectric material are arranged in close contact; specifically, each active material particle is surrounded by a number of ferroelectric particles, but no encapsulation occurs.

[0103] Figure 2 The X-ray diffraction patterns of NVPF@NaNbO3 and NVPF@C after annealing in Example 1 are shown, which show that the ferroelectric material does not affect the crystal structure of the positive electrode active material NVPF.

[0104] The positive electrode material in Example 1 comprises a composite of NVPF as the positive electrode active material and an inorganic ferroelectric material. Since the ionic conductivity of NVPF after being composited with the inorganic ferroelectric material is greatly improved, the rate performance is greatly enhanced (e.g. Figure 3 As shown), thus ensuring the battery's high rate performance, capacity and energy density. Figure 4 After hundreds of charge / discharge cycles under the conditions shown in Figure 3, the capacity retention rate of the composite NVPF@NaNbO3 is as high as over 90%.

[0105] In addition, under low temperature and high temperature charging and discharging conditions (such as Figure 5 、 Figure 6 、 Figure 7 The 100 nm CMOS process (shown in Figure 2) also exhibited high capacity retention. This fabrication method avoids the use of toxic chemicals and extreme temperature and pressure conditions. Due to its low cost and high efficiency, this fabrication method can be scaled up for industrial applications. This can also be extended to other types of cathode materials and even ionic conductors.

[0106] Figure 5The charge-discharge stability of NVPF@NaNbO3 in Example 1 at 2C, -20°C, and 1000 cycles is shown. At 2C and -20°C, the cathode material exhibited a first-cycle discharge capacity of 40 mAh / g. After 140 cycles, this capacity increased by 38%. The discharge coulombic efficiency reached 98% after 1000 cycles, demonstrating that the inorganic ferroelectric material effectively dissociates sodium salts from the electrolyte, improving the stability of NVPF and promoting ion exchange at extremely low operating temperatures.

[0107] Figure 6 Show Figure 2 The rate capability of NVPF@NaNbO3 is shown in the figure, where the test current is between 1C and 50C, the test temperature is 60℃, and 1C=128mA / g, which proves that NVPF@NaNbO3 has good rate performance.

[0108] Figure 7 Show Figure 2 The charge and discharge stability of NVPF@NaNbO3 at 10C, 60℃, and 500 cycles was studied, among which the capacity retention rate of NVPF@NaNbO3 was as high as 95%.

[0109] Figure 8 The X-ray diffraction patterns of NVP@NaNbO3 and NVP@C after annealing in Example 4 are shown, which show that the ferroelectric material does not affect the crystal structure of the positive electrode active material NVP.

[0110] Figure 11 Example 4 shows the application of commercialized NVP. According to the principle of manufacturing NVPF@NaNbO3, NVP is mixed with NaNbO3 to form NVP@NaNbO3. The charge and discharge stability of a symmetrical full battery composed of NVP and NVP is tested under the conditions of 1C and 25°C after 2000 cycles. The capacity retention rate of the full battery is 88%.

[0111] Electrochemical characterization results indicate that ferroelectric materials enhance the ionic conductivity of the active cathode material. NVPF or NVP modified with inorganic ferroelectric materials offers high specific capacity and energy density. Composites with inorganic ferroelectric materials enhance the cycling stability of NVPF or NVP at room temperature and high current, as well as the overall electrochemical performance at low and high temperatures. NVPF or NVP modified with inorganic ferroelectric materials avoids the use of hazardous chemicals and extreme temperature and pressure conditions. Due to its low cost and high efficiency, this fabrication method can be scaled up for industrial applications.

[0112] The foregoing disclosure is for illustration and description purposes only and is not intended to be exhaustive or limiting. Many modifications and variations will be apparent to those skilled in the art. The exemplary embodiments are selected and described to explain the principles and practical applications and to enable others skilled in the art to understand the disclosures in the various embodiments, including possible modifications suitable for specific uses. Therefore, although illustrative exemplary embodiments have been described herein with reference to the accompanying drawings, it should be understood that the descriptions are not limiting and that various other changes and modifications may be made by those skilled in the art without departing from the scope of the disclosure.

Claims

1. A composite material for a sodium ion battery cathode, comprising: Sodium superionic conductive particles, whose chemical formula is Na x M y (PO4)2R z And Na x V y (PO4) n at least one of; and Ferroelectric particles, whose chemical formula is WTO3, wherein x=3, y=2, z=1.5 or 3, n=3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a metal element selected from niobium or titanium.

2. The composite of claim 1, wherein M is selected from the group consisting of vanadium, iron, titanium, manganese and chromium.

3. The complex according to claim 1, wherein R is selected from the group consisting of fluorine, chlorine, and oxygen, wherein when R is selected from fluorine or chlorine, z=3, and when R is oxygen, z=1.

5. The composite according to claim 1 , wherein the monovalent atom is selected from the group consisting of sodium and lithium, and the divalent atom is barium.

5. The composite of claim 4, wherein when W is sodium or lithium, T is niobium. The composite of claim 4 , wherein when W is barium, T is titanium.

7. The composite of claim 1, wherein the sodium superionic conductor particles are coated with carbon to form carbon-coated sodium superionic conductor particles.

8. The composite according to claim 1 or 7, wherein the sodium superion conductor particles are nanoparticles having a particle size ranging from 100 nm to 2 μm.

9. The composite of claim 1, wherein the ferroelectric particles are nanoparticles having a particle size ranging from 100 nm to 400 nm.

10. The composite according to claim 1, wherein a mass percentage of the ferroelectric particles in the composite ranges from 0.01 wt% to 8 wt%.

11. The composite according to claim 1 or 7, wherein the sodium superion conductor particles are selected from Na3V2(PO4)2F3, Na3V2(PO4)2Cl3, Na3V2(PO4)2O 1.5 , Na3Fe2(PO4)2F3, Na3Fe2(PO4)2Cl3, Na3Fe2(PO4)2O 1.5 , Na3Ti2(PO4)2F3, Na3Ti2(PO4)2Cl3, Na3Ti2(PO4)2O 1.5 , Na3Mn2(PO4)2F3, Na3Mn2(PO4)2Cl3, Na3Mn2(PO4)2O 1.5 , Na3Cr2(PO4)2F3, Na3Cr2(PO4)2Cl3, Na3Cr2(PO4)2O 1.5 , Na3V2(PO4)3 or more materials.

12. The composite according to claim 1 or 4, wherein the ferroelectric particles are composed of one or more materials selected from the group consisting of NaNbO3, BaTiO3, and LiNbO3.

13. A method for producing a composite material for a sodium ion battery cathode, the method comprising: The chemical formula is Na x M y (PO4)2R z And Na x V y (PO4) n At least one sodium superionic conductor particle of the formula WTO3 is mixed with ferroelectric particles to obtain a mixture, wherein x=3, y=2, z=1.5 or 3, n=3, M is one or more transition metal elements, R is one or more halogen elements, W is a monovalent atom or a divalent atom, and T is a transition metal element selected from niobium or titanium; ball milling the mixture; drying the mixture to obtain a dry powder; and The dry powder is annealed to obtain a composite for a positive electrode.

14. The method according to claim 13, further comprising: Before the sodium superionic conductor particles are mixed with the ferroelectric particles, a layer of carbon is formed on the surface of the sodium superionic conductor particles.

15. The method according to claim 13, further comprising: Before mixing the sodium superionic conductor particles with the ferroelectric particles, the sodium superionic conductor particles are manufactured, comprising: The sodium superion conductor particles are calcined at least twice, wherein the temperature of the first calcination is lower than that of the second calcination.

16. The method of claim 13, wherein the mixture is ball milled for 1 hour to 6 hours at a speed ranging from 100 rpm to 700 rpm. 17 . The method according to claim 13 , wherein the dry powder is annealed at a temperature of 200° C. to 600° C. for 1 to 10 hours under an inert atmosphere.

18. The method of claim 13, wherein M is selected from the group consisting of vanadium, iron, titanium, manganese, and chromium.

19. The method according to claim 13, wherein R is selected from the group consisting of fluorine, chlorine, and oxygen, and when R is selected from fluorine or chlorine, z=3, and when R is oxygen, z=1.

5.

20. The method of claim 13, wherein the monovalent atom is selected from sodium and lithium, and the divalent atom is barium.

21. The method of claim 20, wherein when W is sodium or lithium, T is niobium.

22. The method of claim 20, wherein when W is barium, T is titanium.

23. The method according to claim 13 or 14, wherein the sodium superion conductor particles are nanoparticles having a particle size ranging from 100 nm to 2 μm.

24. The method of claim 13, wherein the ferroelectric particles are nanoparticles having a particle size ranging from 100 nm to 400 nm.

25. The method according to claim 13 or 14, wherein the sodium superion conductor particles are selected from Na3V2(PO4)2F3, Na3V2(PO4)2Cl3, Na3V2(PO4)2O 1.5 , Na3Fe2(PO4)2F3, Na3Fe2(PO4)2Cl3, Na3Fe2(PO4)2O 1.5 , Na3Ti2(PO4)2F3, Na3Ti2(PO4)2Cl3, Na3Ti2(PO4)2O 1.5 , Na3Mn2(PO4)2F3, Na3Mn2(PO4)2Cl3, Na3Mn2(PO4)2O 1.5 , Na3Cr2(PO4)2F3, Na3Cr2(PO4)2Cl3, Na3Cr2(PO4)2O 1.5 , Na3V2(PO4)3 and one or more materials selected from the group consisting of.

26. The method according to claim 20, wherein the ferroelectric particles are composed of one or more materials selected from the group consisting of NaNbO3, BaTiO3, and LiNbO3.

27. The method of claim 13, wherein the mass percentage of the ferroelectric particles in the composite is 0.01 wt% to 8 wt%.

28. A cathode material for a sodium ion battery, comprising the composite according to any one of claims 1 to 12.

29. A positive electrode for a sodium ion battery, comprising the composite according to any one of claims 1 to 12.

30. A sodium ion battery comprising: A positive electrode comprising the composite according to any one of claims 1 to 12; A negative electrode comprising sodium or hard carbon; a diaphragm comprising a porous material; as well as Electrolytes including sodium salts.

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