Sodium-ion cathode active material for batteries

Abstract

The invention relates to a cathode active material for a rechargeable battery, comprising Na, M and O, wherein M consists of Fe in a molar ratio a, wherein 0.05 ≤ a ≤ 0.40 with respect to M; Mn in a molar ratio b, wherein 0.50 ≤ b ≤ 0.90 with respect to M; and X in a molar ratio c, wherein 0.01 ≤ c ≤ 0.10 with respect to M, and wherein X is at least one element selected from the group consisting of B, Si, K, Co, Ga, Rb, Rh, Cs, Re, Tl and Pb, wherein a+b+c is 1.00, the molar ratio of Na to M (Na / M) is between 0.40 and 1.10, and the content of Na, Fe, Mn and X is measured by ICP-OES; and to a method for manufacturing said cathode active material.

Description

Technical Field

[0001] The present invention relates to a cathode active material for sodium-ion batteries, a method for preparing such cathode active material, and a sodium-ion battery comprising such cathode active material. Background Technology

[0002] Growing global energy demand has driven the widespread adoption of lithium-ion batteries in electronic devices and transportation. However, concerns about over-reliance on lithium-ion batteries leading to increased demand and a raw material crisis have intensified. Therefore, sodium-ion batteries have emerged as a viable alternative to the energy storage technology revolution, particularly when considering the need for large-scale energy storage solutions. Among the components of sodium-ion batteries, layered oxide cathode active materials play a crucial role, showing promise especially due to their excellent electrochemical performance, synthetic feasibility, and versatility in element selection.

[0003] Although Na is the most abundant alkali metal, Fe and Mn are the most abundant transition metals. Therefore, the Na-Fe-Mn structure is ideally suited for use with Na. + Low-cost cathode active materials for electrodes. In 2012, Yabuuchi... et al. Confirmed Na 2 / 3 Fe 1 / 2Mn 1 / 2 O2 exhibits excellent cycling performance [Nature Materials 11, 512-517 (2012)]. Nevertheless, this material faces several challenges, such as phase transition at high voltages (Z-phase), insufficient air stability, and transition metal dissolution. Fe and / or Mn dissolution in the cathode active material is associated with instability at the cathode-electrolyte interface and electrolyte corrosion, leading to poor battery performance. These materials typically experience significant degradation in electrochemical performance due to the tendency for Mn dissolution and Fe migration during continuous sodium release and absorption.

[0004] The low stability of these cathode active materials in air poses a significant challenge to bringing them to market.

[0005] Na x Mn 1 / 2 Fe 1 / 2 O2 may be due to Mn 3+ / Mn 4+ and Fe 3+ / Fe 4+The excellent capacity of the two redox pairs and the low cost of Na, Fe, and Mn have attracted attention. Partial substitution of transition metals with other metallic elements can improve stability, thereby improving capacity loss and rate performance. Partial substitution of transition metals can improve structural stability and thus capacity retention. The presence of electrochemically inactive ions can stabilize the parent structure or promote desired phase transitions.

[0006] The purpose of this invention is to provide an optimized chemical composition for a cathode active material with improved structural stability and air stability.

[0007] Another objective of the present invention is to provide a method for manufacturing the cathode active material.

[0008] Another objective of the present invention is to provide a sodium-ion battery comprising the cathode active material. Summary of the Invention

[0009] In a first aspect, the object of the present invention is achieved by providing a sodium-ion cathode active material for a rechargeable battery, said sodium-ion cathode active material comprising Na, M and O, wherein M is composed of the following:

[0010] a. Fe in a molar ratio of a, where 0.05 ≤ a ≤ 0.40 relative to M; b. Mn with molar ratio b, where 0.50 ≤ b ≤ 0.90 relative to M; and c. X with molar ratio c, where relative to M, 0.01 ≤ c ≤ 0.10. And X is at least one element selected from B, Si, K, Co, Ga, Rb, Rh, Cs, Re, Tl and Pb; Where a+b+c is 1.00, the molar ratio of Na to M (Na / M) is between 0.40 and 1.10, and the contents of Na, Fe, Mn and X are measured by ICP-OES.

[0011] In one embodiment of the invention, the cathode active material has a composition according to general formula (I): Na x2 Fe a2 Mn b2 X c2 O2, Wherein 0.40 ≤ x² ≤ 1.10, 0.05 ≤ a² ≤ 0.40, 0.50 ≤ b² ≤ 0.90, 0.01 ≤ c² ≤ 0.10, and X is at least one element selected from B, Si, K, Co, Ga, Rb, Rh, Cs, Re, Tl, and Pb; wherein a² + b² + c² is 1.00, and the contents of Na, Fe, Mn, and X are measured by ICP-OES.

[0012] Surprisingly, this composition containing B, Si, K, Co, Ga, Rb, Rh, Cs, Re, Tl, or Pb exhibited improved air stability and / or reduced transition metal dissolution, indicating improved stability at the cathode-electrolyte interface and reduced electrolyte corrosion.

[0013] In another aspect, the present invention provides a battery comprising a cathode active material as described in the first aspect of the invention or any embodiment or combination thereof.

[0014] In another aspect, the present invention provides a method for manufacturing a cathode active material according to the first aspect of the invention or any embodiment or combination thereof. Detailed Implementation

[0015] In the following detailed description, preferred embodiments are described in detail to enable the practice of the invention. Although the invention has been described with reference to these specific preferred embodiments, it should be understood that the invention is not limited to these preferred embodiments. Rather, the invention includes numerous alternatives, modifications, and equivalents, as will become apparent from consideration of the following detailed description and drawings.

[0016] As used herein and in the claims, the term “comprising” should not be construed as limited to the manner listed thereafter; it does not exclude other elements or steps. It should be interpreted as specifying the presence of the stated features, integers, steps, or components as mentioned, but does not exclude the presence or addition of one or more other features, integers, steps, or components, or groups thereof. Therefore, the scope of the expression “composition comprising components A and B” should not be limited to compositions consisting solely of components A and B. This means that, for the purposes of this invention, the only relevant components of the composition are A and B. Therefore, the terms “comprising” and “including” encompass the more restrictive terms “consistently composed of” and “composed of”.

[0017] As used herein and in the claims, the term "cathode active material" (also known as "positive electrode active material") is defined as a material that is electrochemically active in a positive or negative electrode. An active material should be understood as a material capable of capturing and releasing Li ions when subjected to voltage variations over a predetermined time period.

[0018] Within the framework of this invention, at% represents atomic percentage. In the expression of concentration, at% or "atomic percentage" of a given element means what percentage of all atoms in the compound are atoms of that element. The designation at% is equivalent to mol% or "molar percentage".

[0019] As used herein, the term “about” when referring to measurable values ​​(such as parameters, quantities, time intervals, etc.) is intended to cover variations of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less and even more preferably + / -0.1% or less, provided such variations are suitable for implementation in this disclosure. However, it should be understood that the values ​​referred to by the modifier “about” are themselves specifically disclosed.

[0020] As used in this article, the range of values ​​for “X to Y” and “between X and Y” includes the endpoints X and Y.

[0021] Cathode active materials In a first aspect, the object of the present invention is achieved by providing a cathode active material for a rechargeable battery, the cathode active material comprising Na, M, and O, wherein M comprises: a. Fe in a molar ratio of a, where 0.05 ≤ a ≤ 0.40 relative to M; b. Mn with molar ratio b, where 0.50 ≤ b ≤ 0.90 relative to M; and c. X with molar ratio c, where relative to M, 0.01 ≤ c ≤ 0.10. And X is at least one element selected from B, Si, K, Co, Ga, Rb, Rh, Cs, Re, Tl and Pb; d. Where a+b+c is 1.00, the molar ratio of Na to M (Na / M) is between 0.40 and 1.10, and the contents of Na, Fe, Mn and X are measured by ICP-OES.

[0022] In another embodiment, the molar ratio of Na to M (Na / M) is between 0.50 and 0.75, preferably between 0.60 and 0.70, more preferably between 0.65 and 0.70, and even more preferably about 0.66; 0.05 ≤ a ≤ 0.30, preferably 0.08 ≤ a ≤ 0.13, more preferably a is about 0.08 or 0.13; 0.60 ≤ b ≤ 0.90, preferably 0.77 ≤ b ≤ 0.87, more preferably b is about 0.77, about 0.82 or about 0.87; and 0.05 ≤ c ≤ 0.10, preferably c is about 0.05 or about 0.10.

[0023] In another embodiment, the molar ratio of Na to M (Na / M) is between 0.50 and 0.75, preferably between 0.60 and 0.70, more preferably between 0.65 and 0.70, and even more preferably about 0.66; 0.05 ≤ a ≤ 0.30, preferably 0.08 ≤ a ≤ 0.13, more preferably a is about 0.08 or about 0.13; 0.60 ≤ b ≤ 0.90, preferably 0.77 ≤ b ≤ 0.87, more preferably b is 0.77, 0.82 or 0.87; and 0.05 ≤ c ≤ 0.10, preferably c is about 0.05 or about 0.10; wherein a+b+c is 1.00.

[0024] In one embodiment, the present invention provides a cathode active material having a composition according to general formula (I): Na x2 Fe a2 Mn b2 X c2 O2, (I) Wherein 0.40 ≤ x² ≤ 1.10, 0.05 ≤ a² ≤ 0.40, 0.50 ≤ b² ≤ 0.90, 0.01 ≤ c² ≤ 0.10, and X is at least one element selected from B, Si, K, Co, Ga, Rb, Rh, Cs, Re, Tl, and Pb; wherein a² + b² + c² is 1.00, and the contents of Na, Fe, Mn, and X are measured by ICP-OES.

[0025] In another embodiment, the cathode active material is according to formula (I), wherein a. x² is between 0.50 and 0.90; b. a² is between 0.08 and 0.13; c. b2 is between 0.77 and 0.87; d. c2 is between 0.05 and 0.10. Where a² + b² + c² = 1.00.

[0026] In one embodiment, the cathode active material is according to formula (I), where x2 = 0.66, a2 = 0.08 or 0.13, b2 = 0.77, 0.82 or 0.87 and c2 is 0.05 or 0.10, where a+b+c is 1.00.

[0027] In one embodiment of the invention, the cathode active material has a composition according to a formula selected from IIa, IIb and IIc: a. Formula IIa: Na 0.66 Fe 0.13 Mn 0.77X 0.1 O2 b. Formula IIb: Na 0.66 Fe 0.13 Mn 0.82 X 0.05 O2 c. Formula IIc: Na 0.66 Fe 0.08 Mn 0.87 X 0.05 O2 X is at least one element selected from B, Si, K, Co, Ga, Rb, Rh, Cs, Re, Tl, and Pb, and the contents of Na, Fe, Mn, and X are measured by ICP-OES.

[0028] In one embodiment of the cathode active material, X is at least one element selected from B, Si, Ga, Rb, Rh, Cs, Re, Tl and Pb, preferably X is selected from B, Si, Tl and Ga, and more preferably X is selected from B and Si.

[0029] In a specific embodiment of the present invention, the cathode active material is selected from: Na 0.66 Fe 0.13 Mn 0.77 B 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Si 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 K 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Ga 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Rb 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Rh 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Cs 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Re 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Tl 0.1 O2; Na0.66 Fe 0.13 Mn 0.77 Pb 0.1 O2;Na 0.66 Fe 0.13 Mn 0.77 Yes 0.1 O2;Na 0.66 Fe 0.13 Mn 0.82 B 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 From 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 K 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Go 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Rb 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Rh 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Cs 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Sell 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Tl 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Pb 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Yes 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 B 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 From 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 K 0.05O2;Na 0.66 Fe 0.08 Mn 0.87 Go 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Rb 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Rh 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Cs 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Sell 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Tl 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Pb 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Yes 0.05 O2;Na 0.50 Fe 0.13 Mn 0.82 From 0.05 O2;Na 0.58 Fe 0.13 Mn 0.82 From 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 From 0.05 O2;Na 0.75 Fe 0.13 Mn 0.82 From 0.05 O2;Na 0.50 Fe 0.13 Mn 0.82 B 0.05 O2;Na 0.58 Fe 0.13 Mn 0.82 B 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 B 0.05 O2;Na 0.75 Fe 0.13 Mn 0.82 B0.05 O2;Na 0.66 Fe 0.23 Mn 0.72 From 0.05 O2;Na 0.66 Fe 0.33 Mn 0.62 From 0.05 O2;Na 0.66 Fe 0.43 Mn 0.52 From 0.05 O2;Na 0.66 Fe 0.23 Mn 0.72 B 0.05 O2;Na 0.66 Fe 0.43 Mn 0.52 B 0.05 O2;Na 0.66 Fe 0.13 Mn 0.77 B 0.10 O2;Na 0.66 Fe 0.13 Mn 0.77 From 0.10 O2;Na 0.66 Fe 0.4 Mn 0.5 B 0.1 O2;Na 0.66 Fe 0.4 Mn 0.5 From 0.1 O2;Na 0.66 Fe 0.4 Mn 0.5 K 0.1 O2;Na 0.66 Fe 0.4 Mn 0.5 Yes 0.1 O2;Na 0.66 Fe 0.4 Mn 0.5 Go 0.1 O2;Na 0.66 Fe 0.4 Mn 0.5 Rb 0.1 O2;Na 0.66 Fe 0.4 Mn 0.5 Rh 0.1 O2;Na 0.66 Fe 0.4 Mn 0.5 Cs 0.1 O2;Na 0.66 Fe 0.4 Mn 0.5 Sell0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 Tl 0.1 O2; and Na 0.66 Fe 0.4 Mn 0.5 Pb 0.1 O2.

[0030] In one embodiment, the cathode active material according to the invention comprises a layered structure.

[0031] In one embodiment, the Fe solubility value of the cathode active material according to the present invention is less than 950 μm / g, preferably less than 900 μm / g, more preferably less than 800 μm / g, even more preferably less than 700 μm / g, and most preferably less than 600 μm / g.

[0032] In one embodiment, the Mn solubility value of the cathode active material according to the present invention is less than 150 μm / g, preferably less than 100 μm / g, more preferably less than 75 μm / g, and even more preferably less than 50 μm / g.

[0033] The Fe and Mn solubility values ​​were determined by transition metal solubility analysis as described herein.

[0034] In another embodiment, the structure retention rate of the cathode active material according to the invention is at least 5%, preferably at least 10%, more preferably at least 15%, even more preferably at least 20%, even more preferably at least 50%, and most preferably at least 80%, as determined by air stability analysis as described herein.

[0035] Method for manufacturing cathode active materials In another objective, the present invention provides a method for manufacturing a cathode active material according to the present invention or any embodiment or combination thereof, wherein the method comprises the following steps: Step 1) Dissolve one or more salts containing Na, Fe, Mn, and X in alcohol, water, or a mixture thereof in a stoichiometric molar ratio, and heat while stirring at a temperature ranging from 30°C to 100°C to obtain a mixture. Step 2) The mixture is dried at a temperature ranging from 300°C to 500°C to obtain a dried mixture. Step 3) The dried mixture is heated at a temperature in the range of 800°C to 1200°C to obtain a cathode active material.

[0036] Specifically, the mixture obtained through step 1) can be a sol-gel.

[0037] In one embodiment of the method of the present invention, in step 1), citric acid is added to the mixture in an amount equal to the total amount of Na, Fe, Mn and X.

[0038] In one embodiment of the method of the present invention, in step 1), the heating is performed at a temperature in the range of 50°C to 80°C, preferably at about 65°C.

[0039] In one embodiment of the method of the present invention, in step 2), the mixture is dried at a temperature in the range of 350°C to 450°C, preferably at about 400°C.

[0040] In one embodiment of the method of the present invention, in step 3), the dried mixture is heated at a temperature in the range of 800°C to 900°C, preferably at about 850°C.

[0041] In one embodiment, nitrates are selected for sol-gel synthesis. Therefore, in one embodiment of the method of the present invention, the salt containing Na, Fe, Mn, and X is a nitrate of Na, Fe, Mn, and X.

[0042] In one embodiment, the method of the present invention is a sol-gel auto-combustion method for preparing any of the different compositions according to the invention. Sol-gel auto-combustion can be achieved through an exothermic reaction between an oxidant (hereinafter a metal salt, particularly a metal nitrate) and a fuel (such as an organic amine, urea, or an acid, particularly citric acid). Auto-combustion can specifically occur during sol-gel heating, in the initial drying step, and / or in a subsequent heating step.

[0043] In one embodiment of the method of the present invention, the method comprises, in step 1), preparing a 2.4 M solution of sodium nitrate (NaNO3), manganese nitrate (Mn(NO3)2), and ferric nitrate (Fe(NO3)3), and dispensing it into 8×8 well plates according to the desired ratios listed below. In a preferred embodiment, nitrates are selected for sol-gel synthesis. The method further comprises adding an aqueous solution (1M) of the corresponding element X to the precursor solution at 5 mol% or 10 mol% relative to the total molar content of Na, Fe, and X, wherein X is at least one element selected from B, Si, Ga, Rb, Rh, Cs, Re, Tl, and Pb. The method further comprises adding citric acid (3M) as a chelating agent in a molar ratio equal to that of the metal cation to stabilize the metal ion. In a more preferred embodiment, the gelation process is carried out at 65°C for 2 days to form a homogeneous gel through strong carboxylic acid-metal bonding. The resulting gel is then pulverized and transferred to an alumina plate covered with an 8×8 aluminum chimney, separating the gel into different combustion chambers to prevent cross-contamination. Preferably, combustion is carried out at 400°C for 2 hours to remove citric acid and nitrates (heating rate: 2°C / min). In another step after chimney removal, the preheated sample is further heated at 850°C in ambient air for 12 hours (heating rate: 5°C / min), followed by a cooling rate of 5°C / min to room temperature.

[0044] Battery In another objective, the present invention provides a sodium-ion battery comprising the aforementioned cathode active material, particularly a cathode active material according to the first aspect of the invention or according to any embodiment or a combination thereof.

[0045] Example Method Description General schemes for synthesizing cathode active materials The sol-gel self-combustion method is used to achieve the exemplary composition according to the present invention.

[0046] Sodium nitrate (NaNO3), manganese nitrate (Mn(NO3)2), and ferric nitrate (Fe(NO3)3) were prepared as 2.4 M solutions from Sigma-Aldrich and partitioned into 8×8 wells according to the desired ratios listed below. Nitrates were chosen for sol-gel synthesis considering their potential impact on the final product. Aqueous solutions (1 M) of elements selected from B, Si, Ga, Rb, Rh, Cs, Re, Tl, or Pb were added to the precursor solutions at 5 mol% or 10 mol% relative to the total molar content of Fe, Mn, and X. Citric acid (3 M) was added as a chelating agent at a molar ratio equal to that of the metal cations to stabilize the metal ions. The gelation process was carried out at 65 °C for 2 days, forming a homogeneous gel through strong carboxylic acid-metal bonding. To prevent cross-contamination, the resulting gel was crushed and transferred to an alumina plate covered with an 8×8 aluminum chimney, separating the gel into different combustion chambers. Combustion was carried out at 400°C for 2 hours to remove citric acid and nitrates (heating rate: 2°C / min). After removing the chimney, the preheated sample was further heated at 850°C in ambient air for 12 hours (heating rate: 5°C / min), followed by a cooling rate of 5°C / min to room temperature.

[0047] Analytical methods The examples and comparative examples according to the present invention are analyzed using some analytical methods: Inductively Coupled Plasma-Optical Emission Analysis (ICP-OES) Inductively coupled plasma (ICP) quantification was performed using an Agilent ICP 5110. 1 g of powdered sample was dissolved in 50 mL of high-purity hydrochloric acid in an Erlenmeyer flask. The flask was covered with glass and heated on a hot plate until the material was completely dissolved. After cooling to room temperature, the solution was transferred to a 500 mL volumetric flask, which had been thoroughly cleaned and rinsed with distilled (DI) water. After filling the flask with the solution, the volumetric flask was filled with DI water up to the 500 mL mark and then homogenized completely. 5 mL of the solution was taken using a 5 mL pipette and transferred, along with an internal standard, to a 50 mL volumetric flask for a second dilution, in which the volumetric flask was filled with 10% hydrochloric acid up to the 50 mL mark and then homogenized. Finally, this 50 mL solution was used for IPC measurements.

[0048] X-ray diffraction (XRD) X-ray diffraction measurements were performed in high-throughput mode using a Panalytical Empyrean diffractometer equipped with a Mo target (60 kV, 40 mA) and a PIXcel 3D detector. Samples were mounted on a transparent mylar film with 96 3D-printed sample slots, ensuring no cross-contamination. The initial scattering angle range of 4–30° (for Mo Ka1, l = 0.70926 Å) was studied, followed by conversion to 10–70° for Cu radiation. Each sample reached a main peak intensity exceeding 3000 counts within 10 min, ensuring high-quality XRD for further Rietveld refinement. Phase identification and refinement of the XRD patterns were performed using Panalytical's HighScorePlus software in both manual and batch modes.

[0049] Transition metal dissolution analysis The samples were assembled into Swagelok-type batteries and cycled from 1.5 V to 4.6 V at a rate of 10 mAh / g under constant current conditions. After 10 complete cycles, the batteries were disassembled in an argon-filled glove box. The separator and Na anode were collected for further analysis using inductively coupled plasma-optical emission spectrometry (ICP-OES), performed by an Agilent Technologies 5100 ICP-OES system with an autosampler.

[0050] The surface elemental composition of the recycled cathode material was analyzed using X-ray photoelectron spectroscopy (XPS) on a Thermo Fisher Scientific Nexsa G2. Depth profiling was performed by Ar gun etching using a MAGCIS ion gun with 500 eV ion energy and moderate current intensity. The sputtering rate on the oxide material was estimated to be 0.09 nm / sec.

[0051] Electrochemical analysis To evaluate the battery performance of the cathode active material according to the present invention, the inventors applied electrochemical analysis to different samples in the half-cell.

[0052] Electrochemical analysis was evaluated using a laboratory-developed combined cell consisting of 64 parallel channels. A printed circuit board (PCB, Optima Tech) with 64 parallel gold pads was used as the cathode current collector and coated with aluminum foil. The cathode was prepared by combining 2 mg of active material with 20 wt% carbon black, followed by drop casting onto contact pads in N-methyl-2-pyrrolidone (NMP) using 20 wt% polyvinylidene fluoride (PVDF) as a binder. The NMP was then removed, and the cathode was dried at 80 °C for 12 h to obtain a cathode loading of 20 mg / cm². The combined cell was assembled in an argon-filled glove box using an electrolyte consisting of 1 M sodium perchlorate in propylene carbonate (PC) and 2 wt% fluoroethylene carbonate (FEC). Sodium metal foil was used as the anode, and a GF / D glass microfiber pre-filter was used as the separator. Cyclic voltammetry (CV) measurements were performed using a laboratory-constructed high-throughput electrochemical system equipped with a four-channel voltage source (Keithley 213) and a multimeter with a multiplexer (Keithley 2750). The voltage range was set between 1.5 and 4.3 V (relative to Na / Na+), with a scan rate of 0.1 V h⁻¹. The CV curves were further processed by integrating the current-time product (Idt) to obtain the capacitance versus voltage relationship. For the same cathode material, the high-throughput measurements exhibited excellent reproducibility, with a relative standard deviation (RSD) of 7% for the specific capacity. CV was performed at 0.1 V / h between 1.5 V and 4.3 V to analyze the electrochemical properties of samples used as cathode materials.

[0053] Air stability analysis To investigate air stability, samples were carefully stored under identical conditions. XRD measurements were performed at different time intervals and under varying humidity conditions. Initially, samples were stored in dry air (RH < 10%) for two months, followed by exposure to ambient air (RH = 45%) for one week, and finally placed in humid air (RH > 90%) for one week. A closed system was maintained to provide a stable, undisturbed relative humidity (RH) level, with the temperature maintained within 23 ± 1 °C. XRD scans obtained from these storage conditions were first analyzed by identifying the different phases present in the samples, followed by quantitative refinement using the methods described in the X-ray diffraction section.

[0054] Using Rietveld refinement, the inventors in this case correlated sample stability by quantifying the percentage of structure retention after exposure to humid conditions. Therefore, the higher the percentage of structure retention in a sample, the higher its air stability.

[0055] Exemplary components according to the present invention The invention will be described in more detail below with reference to examples, but the invention is not limited in any way by these examples without departing from the scope and spirit of the invention.

[0056] Some preferred examples of mixed metal compounds according to general formula (I) are selected from the following group: Na 0.66 Fe 0.13 Mn 0.77 B 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Si 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 K 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Ga 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Rb 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Rh 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Cs 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Re 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Tl 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Pb 0.1 O2; Na 0.66 Fe 0.13 Mn 0.77 Co 0.1 O2; Na 0.66 Fe 0.13 Mn 0.82 B 0.05 O2; Na 0.66 Fe 0.13 Mn 0.82 Si 0.05 O2; Na 0.66 Fe 0.13 Mn 0.82 K 0.05 O2; Na0.66 Fe 0.13 Mn 0.82 Go 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Rb 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Rh 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Cs 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Sell 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Tl 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Pb 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 Yes 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 B 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 From 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 K 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Go 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Rb 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Rh 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Cs 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Sell 0.05O2;Na 0.66 Fe 0.08 Mn 0.87 Tl 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Pb 0.05 O2;Na 0.66 Fe 0.08 Mn 0.87 Yes 0.05 O2;Na 0.50 Fe 0.13 Mn 0.82 From 0.05 O2;Na 0.58 Fe 0.13 Mn 0.82 From 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 From 0.05 O2;Na 0.75 Fe 0.13 Mn 0.82 From 0.05 O2;Na 0.50 Fe 0.13 Mn 0.82 B 0.05 O2;Na 0.58 Fe 0.13 Mn 0.82 B 0.05 O2;Na 0.66 Fe 0.13 Mn 0.82 B 0.05 O2;Na 0.75 Fe 0.13 Mn 0.82 B 0.05 O2;Na 0.66 Fe 0.23 Mn 0.72 From 0.05 O2;Na 0.66 Fe 0.33 Mn 0.62 From 0.05 O2;Na 0.66 Fe 0.43 Mn 0.52 From 0.05 O2;Na 0.66 Fe 0.23 Mn 0.72 B 0.05 O2;Na 0.66 Fe 0.43 Mn 0.52 B 0.05O2; Na 0.66 Fe 0.13 Mn 0.77 B 0.10 O2; Na 0.66 Fe 0.13 Mn 0.77 Si 0.10 O2; Na 0.66 Fe 0.4 Mn 0.5 B 0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 Si 0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 K 0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 Co 0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 Ga 0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 Rb 0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 Rh 0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 Cs 0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 Re 0.1 O2; Na 0.66 Fe 0.4 Mn 0.5 Tl 0.1 O2; and Na 0.66 Fe 0.4 Mn 0.5 Pb 0.1 O2.

[0057] Results of transition metal dissolution analysis The results for each example are presented in Table I as the dissolved mass (μg) of Fe or Mn deposited into the anode divided by the mass of the cathode active material (g). The comparative example (Com Ex 1) involves Na. 0.66 Fe 0.5 Mn 0.5 O2.

[0058] Table I

[0059] Compared with the exemplary compositions (Ex 1-8 and Ex 10-11) according to the present invention, the comparative example Na0.66Fe0.5Mn0.5O2 exhibits a higher level of Fe and / or Mn dissolution after 10 complete charge and discharge cycles in the battery, see Table I.

[0060] Compared with Comparative Example 1, the cathode active material according to the invention containing B, Si, K, Co, Ga, Rb, Rh, Re, Tl or Pb exhibits a positive effect in inhibiting the dissolution of either or both of Fe and Mn.

[0061] Therefore, the cathode active materials according to the present invention containing B, Si, K, Co, Ga, Rb, Rh, Re, Tl or Pb exhibit improved stability and / or reduced electrolyte corrosion at the cathode-electrolyte interface.

[0062] Results of air stability analysis Each component was tested under the conditions described above, and the results are shown in Table II. Comparative Example 2 (Com Ex 2) corresponds to Na. 0.66 Mn 0.13 Fe 0.87 O2.

[0063] Table II

[0064] According to the results shown in Table II, Comparative Examples 2 and 3 exhibit lower structural retention rates when compared with the exemplary compositions (Ex 12-22) according to the present invention, see Table II.

[0065] Therefore, compared to Comparative Example 2, the examples containing B, Si, K, Co, Ga, Rb, Cs, Tl, or Pb exhibit a higher percentage of structure retention. Thus, the cathode active materials according to the invention containing B, Si, K, Co, Ga, Rb, Cs, Tl, or Pb show improved air stability.

Claims

1. A cathode active material for a rechargeable battery, comprising Na, M, and O, wherein M is composed of the following: Fe with a molar ratio of a, where relative to M, 0.05 ≤ a ≤ 0.40; Mn with a molar ratio of b, where 0.50 ≤ b ≤ 0.90 relative to M; and X in molar ratio c, wherein relative to M, 0.01 ≤ c ≤ 0.10, and wherein X is at least one element selected from B, Si, K, Co, Ga, Rb, Rh, Cs, Re, Tl and Pb; Where a+b+c is 1.00, the molar ratio of Na to M (Na / M) is between 0.40 and 1.10, and the contents of Na, Fe, Mn and X are measured by ICP-OES.

2. The cathode active material according to claim 1, having a composition according to general formula (I): Na x2 Fe a2 Mn b2 X c2 O2, Where 0.40 ≤ x² ≤ 1.10, 0.05 ≤ a² ≤ 0.40, 0.50 ≤ b² ≤ 0.90, 0.01 ≤ c² ≤ 0.10, and X is at least one element selected from B, Si, K, Co, Ga, Rb, Rh, Cs, Re, Tl, and Pb; The a2+b2+c2 value was 1.00, and the contents of Na, Fe, Mn and X were measured by ICP-OES.

3. The cathode active material according to claim 1 or 2, comprising a layered structure.

4. The cathode active material according to any one of claims 1 to 3, wherein the molar ratio of Na to M (Na / M) is between 0.50 and 0.75, preferably between 0.60 and 0.70, more preferably between 0.65 and 0.70, and even more preferably about 0.

66.

5. The cathode active material according to any one of claims 1 to 4, wherein X is at least one element selected from B, Si, Ga, Rb, Rh, Cs, Re, Tl and Pb, preferably X is selected from B, Si, Tl and Ga, and more preferably X is selected from B and Si.

6. The cathode active material according to any one of claims 1 to 5, wherein a or a2 satisfies 0.05 ≤ a or a2 ≤ 0.30, preferably 0.08 ≤ a or a2 ≤ 0.13, and more preferably a or a2 is about 0.08 or about 0.

13.

7. The cathode active material according to any one of claims 1 to 6, wherein b or b2 satisfies 0.60 ≤ b or b2 ≤ 0.90, preferably 0.77 ≤ b or b2 ≤ 0.87, and more preferably b or b2 is about 0.77, about 0.82 or about 0.

87.

8. The cathode active material according to any one of claims 1 to 7, wherein c or c2 satisfies 0.05 ≤ c or c2 ≤ 0.10, preferably c or c2 is about 0.05 or about 0.

10.

9. The cathode active material according to any one of claims 1 to 8, comprising the following components according to general formula Na 0.66 Fe 0.13 Mn 0.77 X 0.1 O2, Na 0.66 Fe 0.13 Mn 0.82 X 0.05 O2 or Na 0.66 Fe 0.08 Mn 0.87 X 0.05 The composition of O2.

10. A method for manufacturing a cathode active material according to any one of claims 1 to 9, wherein the method comprises the following steps: • Step 1) Dissolve one or more salts containing Na, Fe, Mn, and X in alcohol, water, or a mixture thereof in a stoichiometric molar ratio, and heat while stirring at a temperature ranging from 30°C to 100°C to obtain a mixture. • Step 2) Dry the mixture at a temperature ranging from 300°C to 500°C to obtain a dried mixture, and • Step 3) The dried mixture is heated at a temperature in the range of 800°C to 1200°C to obtain the cathode active material.

11. The method of claim 10, wherein in step 1), citric acid is added to the mixture in an equimolar amount with the total amount of Na, Fe, Mn and X.

12. The method according to claim 10 or 11, wherein in step 1), the heating is performed at a temperature in the range of 50°C to 80°C, preferably at about 65°C.

13. The method according to any one of claims 10 to 12, wherein in step 2), the mixture is dried at a temperature in the range of 350°C to 450°C, preferably at about 400°C.

14. The method according to any one of claims 10 to 13, wherein in step 3), the dried mixture is heated at a temperature in the range of 800°C to 900°C, preferably at about 850°C.

15. A sodium-ion battery comprising a cathode active material according to any one of claims 1 to 9.

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