Doped sodium oxyde cathode active materials having high crystallinity for batteries

Abstract

The present invention relates to an optimized chemical composition of a cathode active material having a P3 phase with improved crystallinity and cycle stability for sodium-ion batteries, to a method for preparing such cathode active material and to sodium-ion batteries comprising such cathode active material.

Description

DescriptionTitleDOPED SODIUM OXYDE CATHODE ACTIVE MATERIALS HAVING HIGH CRYSTALLINITY FOR BATTERIES TECHNICAL FIELD

[0001] The present invention relates to an optimized chemical composition of a cathode active material having a P3 phase with improved crystallinity and cycle stability for sodium-ion batteries, to a method for preparing such cathode active material and to sodium-ion batteries comprising such cathode active material.BACKGROUND

[0002] Sodium-ion batteries (SIBs) have recently gained significant attention as promising short-term alternatives to lithium-ion batteries (LIBs). They not only share a similar working mechanism with lithium-ion batteries but also benefit from sodium's abundance and wide distribution compared to lithium, potentially reducing concerns about resource availability and geopolitical issues. Additionally, sodium-ion batteries can offer cost advantages, particularly for large-scale energy storage applications where the lower cost of sodium compared to lithium becomes a significant factor. [Advanced Energy Materials 2016, 6 (19)] Among all components of SIBs, cathode materials play a pivotal role, as they typically constrain key metrics related to battery performance. Within the diverse types of cathode materials proposed for SIBs up to now, layered transition metal oxides, NaxMO2 (where M represents one or a mixture of transition metals), stand out as some of the most attractive.[Advanced Energy Materials 2018, 8 (16)]

[0003] While Na is the most abundant alkali metal, Fe and Mn are the most widespread transition metals. Thus, Na-Fe-Mn-containing structures could be ideal as low-cost cathode active materials for Na+ electrodes. In 2012, Yabuuchi et al. demonstrated excellent cycling performance for Na2 / 3Fe1 / 2Mn 1 / 202 [Nature Mater 11, 512-517 (2012)]. Nonetheless, this material encounters several challenges such as phase transitions (Z-phase) at high voltages, inadequate air stability, and transition metal dissolution. Fe and / or Mn dissolution from cathode active materials is related to instability in the cathode-electrolyte interphase and electrolyte corrosion, which translates into poor battery performance. These materials usually undergo obvious degradation of electrochemical performance due to the tendency of Mn dissolution and Fe migration during continuous sodium release and uptake.

[0004] Layered metal oxides have been widely studied as positive electrode materials for sodium-ion batteries. Among them, the P3-type layered oxide Na2 / 3Nii / 3Mn2 / 3O2 (NMO) hasattracted attention as a material with high diffusion performance of sodium ions. However, since P3-type materials can only be obtained under synthesis conditions below 700°C, the effect of crystallinity on electrode properties is unknown.

[0005] P2, 03 and P3 phases are well-known phases for SIBs cathode materials. P3 phase is known as low temperature phase below 700 °C. [M.Bianchini et al., NatureMaterials 19, 1088-1095 (2020)]. While P3 phase is expected to have a higher diffusion of Na ions, P3 phase has a limited cycle stability but it is unclear if it is inherent nature of P3 phase or due to low crystallinity. [ EJ.Kim et al., ACS Appl. Energy Mater. 7, 1015-1026 (2024)]

[0006] CN117117168A describes a sodium-deficient P3-type layered sodium transition metal oxide of general formula NaxNiAMnBMcO2, which is said to exhibit improved capacity and cycle stability compared to conventional P2 and O3 / P3 materials. The examples suggest that the materials obtained are of low crystallinity, and no evidence is presented to confirm the formation of a well-defined P3 phase.

[0007] CN110380024A discloses a sodium-containing transition metal oxide with a P3-type crystal structure, which is claimed to offer good structural stability and sodium ion deintercalation capacity. The disclosed Mg and Cu-doped samples appear to be of low crystallinity.

[0008] The aim of the present invention is to provide an optimized chemical composition of a cathode active material having a P3 phase with improved crystallinity and cycle stability for sodium-ion batteries, preferably without significant deterioration of initial discharge capacity.

[0009] It is a further object of the present invention to provide a method for manufacturing said cathode active material.SUMMARY

[0010] In a first aspect, the object of the present work is achieved by providing an optimized chemical composition of a cathode active material with improved structural and cycle stability.

[0011] The aim of the present work is achieved by providing a high crystallinity P3 phase by using highly crystalline roasted precursor. Thus inventors confirmed that the cycle stability is well improved. In addition, inventors found that doping can further increase the crystallinity and, thus further improve cycle stability.

[0012] In this first aspect, the object of the present work is achieved by providing a cathode active material for sodium-ion battery comprising a P3 phase layered structure having a composition according to a general formula (I):NaxNiaMribDcCh (I),wherein D is at least one element selected from the group of Li, Mg, Al, B, Si, K, Ca, Ti, Fe, Co, Cu, Zn, Sr, Zr, Nb, Mo, Sn, and Wandwherein 0.50=£x<1.00; 0.10=£a=£0.40; 0.40 '£b'S 0.90; 00.20; and a+b+c=1.0; characterized in that the ratio FWHM (003) I FWHM (110) < 0.60,wherein FWHM (110) is the full width at half maximum (FWHM) value of the diffraction peak assigned to the (110) signal, within the 2-theta range of 44 to 46 degrees with Cu-Ka X-ray source, andwherein FWHM (003) is the full width at half maximum (FWHM) value of the diffraction peak assigned to the (003) signal, within the 2-theta range of 14 to 18 degrees with Cu-Ka X-ray source.

[0013] The high crystallinity of the cathode active material is illustrated by the ratio FWHM (003) I FWHM (110). The inventors have found that such cathode active material have a P3 phase showing high crystallinity and good cycle stability for sodium-ion batteries.

[0014] In a second aspect, the present invention relates to a method for preparing the composition.

[0015] The second aspect of the present invention concerns a method for preparing a cathode active material, preferably according to the first aspect in any of its embodiments or combination of embodiments, comprising the following steps:1) Mixing a nickel source, a manganese source, an optional dopant source, and a complexing agent in a solvent;2) Drying the mixture from step 1);3) Roasting the dried mixture from step 2) comprising maintaining at a temperature T1 in the range of 900 to1000°C under air for a duration of 2 to 6 h;4) Adding and mixing a sodium source into the product from step 3) and then pelletizing the mixture;5) Heating treating the pelletized mixture from step 4) comprising maintaining at a temperature T2 in the range from 450 to 700 °C in an oxygen containing atmosphere for a duration of 12 to 24 h.

[0016] In a further aspect the present invention relates to a battery comprising the cathode active material and the use of the battery.BRIEF DESCRIPTION OF THE FIGURES

[0017] Fig 1. SEM image of EX1.

[0018] Fig 2. SEM image of EX2.

[0019] Fig 3. XRD plot of EX1 and CEX1.

[0020] Fig 4. XRD plot of EX2 and CEX2.

[0021] Fig. 5 shows the capacity retention vs initial discharge capacity of invention examples and comparative examples.DETAILED DESCRIPTION

[0022] In the following detailed description, preferred embodiments are described in detail to enable practice of the invention. Although the invention is described with reference to these specific preferred embodiments, it will be understood that the invention is not limited to these preferred embodiments. To the contrary, the invention includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description and accompanying drawings. Embodiments can be combined with one another.

[0023] The term “comprising”, as used herein and in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a composition comprising components A and B” should not be limited to compositions consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the composition are A and B.Accordingly, the terms “comprising” and “including” encompass the more restrictive terms “consisting essentially of” and “consisting of”.

[0024] The term “cathode active material” (also known as a positive electrode active material) as used herein and in the claims is defined as a material which is electrochemically active in a positive electrode or cathode. By active material, it must be understood to be a material capable to capture and release Li ions when subjected to a voltage change over a predetermined period of time. The term “anode active material” (also known as a negative electrode active material) as used herein and in the claims is defined as a material which is electrochemically active in a negative electrode or anode.

[0025] In the framework of the present invention, at% signifies atomic percentage. The at% or “atomic percent” of a given element expression of a concentration means how many percent of all atoms in the concerned compound are atoms of said element. The designation at% is equivalent to mol% or “molar percent”.

[0026] "About" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1 % or less of and from the specified value, in so far such variations are appropriate to perform in the present disclosure. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

[0027] In the sense of this application doping means that positive ions of D (where D is at least one of the following elements Li, Mg, Al, B, Si, K, Ca, Ti, Fe, Co, Cu, Zn, Sr, Zr, Nb, Mo, Sn, W) are added as inactive dopants into the transition metal oxide, substituting for transition metal cations in the transition metal layer, thereby helping to stabilize the structure.

[0028] The term "high crystallinity" in the sense of this application would still refer to the quality of the P3 crystal itself. The high crystallinity here means higher "crystallite size". It implies that fewer crystal defects are detected even within the 100% P3-phase, there could be imperfections, such as grain boundaries, dislocations, or vacancies but the high crystallinity suggests these are minimized.

[0029] In the framework of the present invention, the term “grain boundary” is defined as the interface between two primary particles, preferably wherein the atomic planes of the two primary particles are aligned to different orientations and meet as a crystalline discontinuity.

[0030] In X-ray diffraction (XRD), high crystallinity corresponds to sharp and narrow diffraction peaks, i.e. peaks having Full Width at Half Maximum (FWHM) <0.25°. A broader Full Width at Half Maximum (FWHM) , i.e. peak having FWHM>0.25°; indicates low or poorer crystallinity, as it suggests crystal having lattice strain, or structural disorder. High crystallinity means the FWHM is narrow, signaling a well-ordered structure or having a high crystallite size, for example of more than 40nm. Crystallinity is more reliably inferred from peak sharpness (narrowness) rather than height. A highly crystalline material produces sharp, narrow peaks (small FWHM), while a poorly crystalline or amorphous material shows broad, diffuse peaks. The (003) reflection is associated with the interlayer spacing between sodium layers in the layered oxide structure. It is a sensitive indicator of c-axis lattice parameter and reflects how much space is available for Na+ion diffusion. The (110) reflection is less important for Na+content.

[0031] In electrochemical applications, higher crystallinity can lead to better rate capability, enhanced capacity retention, and reduced degradation over cycling because the well- ordered structure facilitates more efficient sodium-ion diffusion and minimizes internal stresses.Cathode active material

[0032] In an embodiment of the present invention, the cathode active material for sodium-ion battery comprises a P3 phase layered structure having a composition according to a general formula (I):NaxNiaMnbDcO2 (I),wherein D is at least one element selected from the group of Li, Mg, Al, B, Si, K, Ca, Ti, Fe, <

[0033] In an embodiment of the cathode active material, x is 0.50x < 1.00, preferably 0.60, 0.70, most preferably x is about 0.67.

[0034] In an embodiment of the cathode active material, a is 0.100.40; preferably 0.20 0.35; more preferably a is about 0.33.

[0035] In an embodiment of the cathode active material, b is 0.400.90, preferably 0.50, 0.70, most preferably b is about 0.67.

[0036] In an embodiment of the cathode active material, c is 00.20, preferably c is about 0.08.

[0037] The inventors observed that the FWHM(003) or FWHM(110) values alone are insufficient to characterize cathode active materials that provide high capacity retention and initial discharge capacity. It appears that a certain balance of both values, as expressed by the FWHM(003) I FWHM(110) ratio best describes cathode active materials that provide high capacity retention and initial discharge capacity.

[0038] In an embodiment of the present invention in the XRD of the cathode active material has a FWHM (003) value of the diffraction peak assigned to the (003) signal, of FWHM (003)<0.23°, preferably FWHM (003)< 0.22°, more preferably FWHM(003) <0.21° .

[0039] In an embodiment of the present invention in the XRD of the cathode active material has a FWHM (003) value of the diffraction peak assigned to the (003) signal, of FWHM (003)>0.01°, alternately FWHM (003)>0.05°, alternately FWHM (003)>0.10°.

[0040] In an embodiment of the present invention in the XRD of the cathode active material according to this aspect has a FWHM(110) value of the diffraction peak assigned to the (110) signal, of FWHM(110) < 0.60°, alternately FWHM(110) < 0.50°. The (110) peak was found to be less affected by stacking faults or defects along the c-axis, in particular compared to the (003) peak is more sensitive to crystallinity change.

[0041] In an embodiment of the present invention in the XRD of the cathode active material according to this aspect has a FWHM(110) value of the diffraction peak assigned to the (110) signal, of FWHM(110) > 0.10°, alternately FWHM(110) > 0.20°, alternately FWHM(110) > 0.30°.

[0042] The cathode active material of the present invention may further be characterized by a FWHM (003) / FWHM (110) ratio where FWHM (003) I FWHM(110) < 0.60, preferably FWHM (003) I FWHM(110) < 0.55, more preferably FWHM (003) I FWHM(110) < 0.50. The more preferred ranges giving a better combined high capacity retention and high initial discharge capacity.

[0043] The cathode active material of the present invention may further be characterized by a FWHM (003) / FWHM (110) ratio where FWHM (003) I FWHM(110) >0.10, alternately FWHM (003) I FWHM(110) >0.20, alternately FWHM (003) I FWHM(110) >0.30.

[0044] FWHM (110), is the full width at half maximum (FWHM) value of the diffraction peak assigned to (110) signal, within the 2-theta range of 44 to 46 degrees with Cu-Ka X-ray source.

[0045] The main diffraction lines are assigned to the space group R3m of the rhombohedral crystal system, and both are P3-type layered oxides. The lattice constants are also similar.

[0046] In an embodiment of the present invention, the cathode active material for sodium-ion battery comprises at least 85 wt%, at least 90 wt% or even at least 95 wt% of material having a P3 phase layered structure. In an embodiment of the present invention, the cathode active material for sodium-ion battery essentially consists of or consists of material having a P3 phase layered structure. Here within ‘wt% stands for weight percent.

[0047] In a another aspect, the present invention provides a positive electrode or a positive electrode plate containing the cathode active material of the present invention in any of its embodiments or combination of embodiments, as described above.Method

[0048] In a further aspect, the present invention relates to a method for preparing the cathode active material as described above.

[0049] The solid-phase method is preferably performed in a dry room.

[0050] In an embodiment of the method of the present invention, the mixture obtained in step 1) comprises Ni in an amount ranging from 10 to 40mol%, Mn in an amount ranging from 40 to 90mol%, dopant D in an amount ranging from 0 to 20mol% and complexing agent in anamount ranging from 0 to 100%, the amounts being expressed relative to the total molar content of Ni, Mn and D.

[0051] In an embodiment of the method of the present invention, step 1) comprises Dissolving 0mol% to 55 mol% Ni from a Nickel source, 0mol% to 90 mol% Mn from a manganese source, 0mol% to 15 mol% dopant element, and 0mol% to 100 mol% complexing agent in solvent, the resulting solution being preferably stirred until a homogeneous mixture is obtained. Here the molar percentage amounts of the different elements or complexing agent are amounts relative to the total amount of Ni, Mn and D.

[0052] In an embodiment of the method of the present invention, step 2) is performed by spray drying. Thereby a particularly fine powder with highly uniform particle size may be obtained.

[0053] In an embodiment of the method of the present invention, step 3) comprises heating up the dried mixture from step 2) at a ramping rate of 3 to 10°C / min to temperature T 1.

[0054] In an embodiment of the method of the present invention, step 3) comprises cooling the heated product down to room temperature at a ramping rate of 3 to 10°C / min.

[0055] In an embodiment of the method of the present invention, step 3) comprises in sequence: heating up the dried mixture from step 2) at a ramping rate of about 5°C / min to a temperature T1 in the range of 900°C to 1000°C, maintaining the temperature T1 for a duration of 2 to 6 h and cooling the heated product down to room temperature at a cooling rate of about 5 °C / min.

[0056] In an embodiment of the method of the present invention, in step 4) sodium source is added in an amount so as to obtain a content of 60mol% to 100 mol% sodium, with respect to the total molar contents of nickel , manganese and D.

[0057] In an embodiment of the method of the present invention, step 5) comprises heating up the pelletized mixture from step 4) at a ramping rate of 3 to 10°C / min up to temperature T2.

[0058] In an embodiment of the method of the present invention, step 5) comprises cooling the heated product down to room temperature by quenching, in particular at a cooling rate of more than 10°C / min.

[0059] In an embodiment of the method of the present invention, step 5) comprises in sequence heating the pelletized mixture from step 4) up to a temperature T2 in the range from 450 to 700 °C in an oxygen containing atmosphere at a ramping rate of about 5 °C / min, maintaining the temperature at T2 for a duration in the range from 12 to 24 h, cooling the heated product to room temperature to obtain the cathode active material, preferably using a quenching method.

[0060] In the method of the present invention the oxygen containing atmosphere of step 5) may be selected from air and O2.

[0061] In an embodiment of the method of the present invention , the nickel source is selected from one or more of nickel acetate, nickel sulfate, nickel oxalate, nickel nitrate, and nickel chloride.

[0062] In an embodiment of the method of the present invention , the manganese source is selected from one or more of manganese acetate, manganese sulfate, manganese oxalate, manganese nitrate, and manganese chloride.

[0063] In an embodiment of the method of the present invention Dopant D is selected from at least one of the following elements Li, Mg, Al, B, Si, K, Ca, Ti, Fe, Co, Cu, Zn, Sr, Zr, Nb, Mo, Sn, W; and the dopant source can be in the form of acetate, sulfate, oxalate nitrate, or chloride of these elements.

[0064] In an embodiment of the method of the present invention, the dopant source is selected from lithium carbonate lithium hydroxide, magnesium acetate, iron acetate, iron sulfate, iron oxalate, iron nitrate and iron chloride.

[0065] In an embodiment of the method of the present invention, the complexing agent is selected from citric acid, sodium citrate, edetic acid (EDTA),.

[0066] In an embodiment of the method of the present invention, the solvent in step 1) is selected from water, acetone, ethanol, iso-propanol, and butanol.

[0067] In an embodiment of the method of the present invention, the sodium source is selected from sodium hydroxide and sodium carbonate.

[0068] Inventors have found that the crystallinity of P3-type layered oxides, can be improved by preparing first a highly crystalline precursor such as in steps 1) to 3) of the present method. The crystallinity of P3-type layered oxides may be illustrated by the ratio FWHM (003) I FWHM (110), in particular the ratio FWHM (003) I FWHM (110)< 0.60.Battery

[0069] In a third aspect, the present invention provides a battery. A battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode.

[0070] In an embodiment, the present invention provides a battery comprising the cathode active material as described above or a battery comprising the positive electrode plate as disclosed above in any embodiment or combination of embodiments.

[0071] In a preferred embodiment the battery is a sodium-ion battery, preferably a sodium-ion rechargeable battery. Preferably the battery comprises a positive electrode comprising the active material according to the first aspect of the invention, a negative electrode, an electrode, and a separator.

[0072] In a preferred embodiment the battery may comprise a liquid electrolyte, such as a lithium salt in an organic solvent. Preferably, the battery further comprises an anode comprising anode active material. Suitable electrochemically active anode materials are those known in the art. For example, the anode may comprise graphitic carbon, or a metal alloy comprising lithium.Use

[0073] The present disclosure further concerns the use of the battery according to the third aspect of the present invention, in an electrically powered device or system selected from the group consisting of: a portable computer, a tablet, a mobile phone, a telecommunication device, a power tool, mobile machinery, a robotic device, an energy storage system, an uninterruptible power supply system, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an extended-range electric vehicle, a fuel cell electric vehicle, a twowheeler transportation system, a rail vehicle, a marine vessel, an aircraft, an aerospace system.

[0074] The present invention concerns in particular the use of the battery according to the third aspect of the invention in either one of a portable computer, a tablet, a mobile phone, an energy storage system (ESS), an electric vehicle (EV) or in a hybrid electric vehicle (HEV), preferably in an electric vehicle or in a hybrid electric vehicle.

[0075] The use of the battery of the present disclosure comprising a cathode active material of the present invention in the above-listed electrically powered devices and systems enables efficient and reliable energy delivery across a wide range of operational environments. The integration of such batteries into consumer electronics (e.g., portable computers, tablets, mobile phones, telecommunication devices) provides compact and lightweight energy sources that support high energy density and long operational life, thereby enhancing user experience and device portability.

[0076] In industrial applications such as power tools, mobile machinery, and robotic devices, the battery enables high discharge rates and robust performance under variable load conditions, contributing to improved productivity and operational flexibility. The use in energy infrastructure systems, including energy storage systems and uninterruptible power supply(UPS) systems, ensures stable and scalable energy management, supporting grid resilience and backup power reliability.

[0077] In transportation systems, the battery supports electrification of mobility platforms, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), extended-range electric vehicles (EREVs), and fuel cell electric vehicles (FCEVs). These applications benefit from the battery’s ability to deliver consistent power output, fast charging capability, and thermal stability, which are critical for safety and performance in both passenger and freight transport. The inclusion of two-wheeler transportation systems, rail vehicles, marine vessels, aircraft, and aerospace systems demonstrates the versatility of the battery across diverse propulsion architectures and regulatory environments.EXAMPLES and EXPERIMENTAL TESTS

[0078] The invention is described below in greater details with reference to examples, but the invention is not limited in any way by these examples, as long as it does not exceed the scope and spirit of the present invention.Experimental tests used in the examples

[0079] The following analysis methods are used in the Examples:Scanning Electron Microscopy (SEM)

[0080] The morphology of positive electrode active materials is analyzed by a Scanning Electron Microscopy (SEM) technique. The measurement is performed using a JEOL JCM- 6000 at 25 °C. The particles in the image should be well distributed therefore avoiding overlap between particles. This can be achieved by pouring a small amount of powder sample to the adhesive attached on the SEM sample holder and blowing dry air to remove the excess powder.Powder X-ray Diffraction (XRD)

[0081] In the present invention X-ray diffraction (XRD) is used to analyze the crystallinity of cathode active material. The crystallinity is determined by observing the ratio FWHM (003) I FWHM (110), wherein FWHM (110) is the full width at half maximum (FWHM) value of the diffraction peak assigned to the (110) signal, within the 2-theta range of 44 to 46 degrees with Cu-Ka X-ray source, and wherein FWHM (003) is the full width at half maximum (FWHM) value of the diffraction peak assigned to the (003) signal, within the 2-theta range of 14 to 18 degrees with Cu-Ka X-ray source and also the full width at half maximum (FWHM) value of the (003) peak within the 2-theta range of 14 to 18 degrees in the XRD pattern.

[0082] XRD patterns are recorded on a Rigaku SmartLab X-ray diffractometer in the 0-752- theta range in a 0.010 degree scan step. Scan speed is set to 3.0 degrees per minute. The copper target X-ray tube is operated at 40KV and 40mA. The LynxEye XE-T detector is used to capture diffracted X-rays at 3.3 degree opening. The collected XRD patterns comprise Ka Cu radiations with typical wavelengths KAIphal =1.5418 A. The incident beam optic setup comprises a 1 -degree divergence slit (DS) and 2.5 degree vertical Soller slit. The diffracted beam optic setup includes an automatic anti-scatter slit (SS), and 2.5 degree vertical Soller slit. To prevent fluctuations the temperature is kept near room temperature all the time.Coin cell test

[0083] Coin cell preparation - The method comprises forming a slurry comprising a positive electrode active material powder, a conductive material (Super P, Timcal), and a binder (KF#9700, Kureha) in a weight ratio of 92:4.0:4.0, respectively, in a solvent (NMP, Mitsubishi). The slurry is homogenized using a high-speed homogenizer. The homogenized slurry is then uniformly applied to one side of an aluminum foil substrate using a doctor blade coater with a gap of 230 pm. The coated foil is subsequently dried in an oven at a temperature of 120 °C. Following the drying step, the coated foil is pressed using a calendaring tool and then subjected to a second drying process in a vacuum oven to ensure complete removal of the solvent from the electrode film.

[0084] The coin cell is assembled within an argon-filled glovebox to prevent contamination. A separator, a glass microfiber filter, is placed between the positive electrode and a piece of sodium foil, which serves as the negative electrode. An electrolyte solution comprising 0.6M NaPFe in a mixture of propylene carbonate (PC) and fluoroethylene carbonate (FEC) in a volume ratio of 3:7 is added between the separator and the electrodes. The coin cell is then sealed to prevent electrolyte leakage, completing the assembly process.

[0085] Testing method - The tests for discharge capacity (DQ) and irreversible capacity (Qirr) are performed using coin cells with electrodes consisting of 92 wt% of the cathode active material described in this invention. The electrode loading is approximately 9.5 mg / cm2. The discharge capacity for the first cycle (DQ1) is measured within the voltage range of 4.0-2.2 V at a rate of 1C (expressed in mAh / g) at a temperature of 25°C.EXAMPLES

[0086] The present invention is further illustrated by the following examples.Example 1

[0087] A highly crystalline positive electrode active material labelled as EX1 having a formula of P3-Nao.67Nio.33Mno.67O2 is prepared according to the following steps:1) Precursor preparation: 33 mol% Ni from nickel acetate tetrahydrate (Ni(C2H3O2)2'4H2O), 67 mol% Mn from manganese acetate tetrahydrate (Mn(C2H3O2)2'4H2O), and 60 mol% citric acid (C6H8O7), molar percentages being expressed with respect to the total molar contents of transition metal, is dissolved in water. The solution is stirred until a homogeneous mixture is obtained.2) Drying: The prepared mixture from step 1) is subjected to spray drying to obtain a fine powder.3) Precursor roasting: The dried mixture from step 2) is heated to 1000 °C under air at a ramping rate of 5 °C / min. It is kept at a temperature of 1000 °C for 3 h. Then, the heated product is cooled to room temperature at a cooling rate of 5 °C / min.4) Sodium addition: 67 mol% sodium from sodium carbonate (Na2CC>3), with respect to the total molar contents of nickel and manganese, is added to the product from step 3) and mixed thoroughly. Then, the mixture is pelletized.5) Heating: The pelletized mixture from step 4) is heated to 625 °C under air at a ramping rate of 5 °C / min. It is kept at a temperature of 625 °C for 15 h. Then, the heated product is cooled rapidly to room temperature using quenching method to obtain the final product EX1.Example 2

[0088] A highly crystalline positive electrode active material labelled as EX2 having a formula of P3-Nao.67Mgo.08Nio.25Mno.67O2 is prepared according to the following steps:1) Precursor preparation: 25 mol% Ni from nickel acetate tetrahydrate (Ni(C2H3O2)2'4H2O), 67 mol% Mn from manganese acetate tetrahydrate (Mn(C2H3O2)2'4H2O), 8 mol% Mg from magnesium acetate tetrahydrate (Mg(C2H3O2)2'4H2O), and 60 mol% citric acid (C6H8O7), molar percentages being expressed with respect to the total molar contents of transition metal, is dissolved in water. The solution is stirred until a homogeneous mixture is obtained.2) Drying: The prepared mixture from step 1) is subjected to spray drying to obtain a fine powder.3) Precursor roasting: The dried mixture from step 2) is heated to 1000 °C under air at a ramping rate of 5 °C / min. It is kept at a temperature of 1000 °C for 3 h. Then, the heated product is cooled to room temperature at a cooling rate of 5 °C / min.4) Sodium addition: 67 mol% sodium from sodium carbonate (Na2COs), with respect to the total molar contents of nickel and manganese, is added to the product from step 3) and mixed thoroughly. Then, the mixture is pelletized.5) Heating: The pelletized mixture from step 4) is heated to 625 °C under air at a ramping rate of 5 °C / min. It is kept at a temperature of 625 °C for 15 h. Then, the heated product is cooled rapidly to room temperature using quenching method to obtain the final product EX2.Comparative example 1

[0089] A highly crystalline positive electrode active material labelled as CEX1 having a formula of P3-Nao.67Nio.33Mno.67O2 is prepared according to the following steps:1) Precursor preparation: 67 mol% sodium from sodium carbonate (Na2COs), 33 mol% nickel from nickel hydroxide (Ni(OH)2), and 67 mol% manganese from manganese oxide (Mn2O3), molar percentages being expressed with respect to the total molar contents of transition metal, are ball-milled at 600 rpm for 12 h in acetone solution to obtain the first mixture.2) Drying: The prepared mixture from step 1) is dried at 60 °C overnight under air to obtain a dried powder. The dried powder is then pelletized.3) Heating: The dried mixture from step 2) is heated to 625 °C under air at a ramping rate of 5 °C / min. It is kept at a temperature of 625 °C for 15 h. Then, the heated product is cooled rapidly to room temperature using quenching method to obtain CEX1.Comparative example 2

[0090] A highly crystalline positive electrode active material labelled as CEX2 having a formula of P3- Nao.67Mgo o8Nio.25Mno.67O2 is prepared according to the following steps:1) Precursor preparation: 67 mol% Na from sodium carbonate (Na2COs), 25 mol% Ni from nickel hydroxide (Ni(OH)2), 67 mol% Mn from manganese oxide (Mn2C>3), and 8 mol% Mg from magnesium oxide (MgO), molar percentages being expressed with respect to the total molar contents of transition metal, are ball-milled at 600 rpm for 12 h in acetone solution to obtain the first mixture.2) Drying: The prepared mixture from step 1) is dried at 60 °C overnight under air to obtain a dried powder. The dried powder is then pelletized.3) Heating: The dried mixture from step 2) is heated to 625 °C under air at a ramping rate of 5 °C / min. It is kept at a temperature of 625 °C for 15 h. Then, the heated product is cooled rapidly to room temperature using quenching method to obtain CEX2.

[0091] The prepared EX1-EX2 and CE1-CEX2 are analyzed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and coin cell test to evaluate their characteristics, morphology, and electrochemical performance.

[0092] The summary of the preparation process for the examples and comparative examples can be found in Table 1.

[0093] Table 1. Summary of the coating process for the preparation of cathode active material

[0094] Table 2. Summary of the XRD result and the corresponding electrochemical properties of examples and comparative examples

[0095] Table 2 provides a summary of the X-ray diffraction (XRD) results alongside the corresponding electrochemical properties for the examples and comparative examples. The data indicate that the examples exhibit a lower full-width at half maximum (FWHM) at the (003) peak compared to the comparative examples, signifying higher crystallinity in the examples. This enhanced crystallinity is attributed to the precursor roasting step employed in the examples. Additionally, as illustrated in Figure 3, Example 1 (EX1) demonstrates a higher peak intensity at the (003) peak relative to Comparative Example 1 (CEX1), further corroborating the increased crystallinity. The examples with higher crystallinity (EX1 and EX2) exhibit superior capacity retention after 100 cycles in comparison to the comparative examples (CEX1 and CEX2).

[0096] Additional examples were prepared similarly to EX2 with other dopants in about the same amount as for Mg in EX2 and are summarized in the table 3 below.

[0097] Table 3. Summary of the XRD result and the corresponding electrochemical properties of additional examples

[0098] All these dopants show improved capacity retention when compared to CEX1 and CEX2.In the case of Ca dopant the highly increased capacity retention comes at the cost of significantly lower DQ1. For EX3 to EX8 large crystallite sizes are obtained ranging from 39.3nm to 44.2nm, though they remain lower than for EX2. EX3 and EX4 achieve higher DQ1 values than EX2, but with lower capacity retention. EX6 comes close to EX2 regarding capacity retention but with lower DQ1 performance.

[0099] Figure 5 shows the Capacity retention after 100 cycles (%) vs DQ1 obtained for invention examples and comparative examples. Each point is labelled with the corresponding FWHM(003) / FWHM(110) value, showing that too high FWHM(003) / FWHM(110) values in CEX1 and CEX2 lead to low capacity retention. Furthermore, while with Ca as a dopant in EX8 a higher capacity retention value is obtained the loss in DQ1 is clearly visible.

Claims

Claims

1. A cathode active material for sodium-ion battery comprising a P3 phase layered structure having a composition according to a general formula (I):NaxNiaMnbDcO2 (I),wherein D is at least one element selected from the group of Li, Mg, Al, B, Si, K, Ca, Ti, Fe, Co, Cu, Zn, Sr, Zr, Nb, Mo, Sn, and Wandwherein 0.50=£x<1.00; 0.10=£a=£0.40; 0.40 '£b'S 0.90; 00.20; and a+b+c=1.0; characterized in that the ratio FWHM (003) I FWHM (110) < 0.60,wherein FWHM (110) is the full width at half maximum (FWHM) value of the diffraction peak assigned to the (110) signal, within the 2-theta range of 44 to 46 degrees with Cu- Ka X-ray source, andwherein FWHM (003) is the full width at half maximum (FWHM) value of the diffraction peak assigned to the (003) signal, within the 2-theta range of 14 to 18 degrees with Cu- Ka X-ray source.

2. A cathode active material according to claim 1 wherein FWHM (003) is FWHM (003) <0.25°

3. A cathode active material according to claim 1 or claim 2, wherein the ratio FWHM (003) I FWHM(110) < 0.55, preferably FWHM (003) I FWHM(110) < 0.50 .

4. A cathode active material according to any one of claims 1 to 3, wherein 0.60 < x < 0.80, preferably 0.65 < x < 0.70, more preferably x is about 0.67.

5. A cathode active material according to any one of claims 1 to 4, wherein 0.10 < a < 0.40; preferably 0.20 < a < 0.35; more preferably a is about 0.33.

6. A cathode active material according to any one of claims 1 to 5, wherein 0.40 < b < 0.90, preferably 0.50 < b < 0.80, more preferably 0.65 < b < 0.70, most preferably b is about 0.67.

7. A cathode active material according to any one of claims 1 to 6, wherein 0 < c < 0.20, preferably c is about 0.08.

8. A cathode active material according to any one of claims 1 to 7, wherein FWHM (003)<0.23°, preferably FWHM (003)< 0.22°, more preferably FWHM(003) <0.21° .

9. A method for preparing a cathode active material according to any one of claims 1 to 8, wherein the method comprises the following steps:1) Mixing a nickel source, a manganese source, an optional dopant, and a complexing agent in a solvent;2) Drying the mixture from step 1);3) Roasting the dried mixture from step 2) at 900-1000 °C under air for 2-6 h;4) Adding and mixing a sodium source into the product from step 3) and then pelletizing the mixture;5) Heating the pelletized mixture from step 4) at 450-700 °C under air for 12-24 h.

10. A positive electrode plate containing the cathode active material according to any one of claims 1 to 8.

11. A sodium-ion battery comprising the positive electrode plate according to claim 10.

12. A sodium-ion battery comprising the cathode active material according to any one of claims 1 to 8.

13. Use of the battery according to claim 11 or 12 in an electrically powered device or system selected from the group consisting of: a portable computer, a tablet, a mobile phone, a telecommunication device, a power tool, mobile machinery, a robotic device, an energy storage system, an uninterruptible power supply system, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an extended-range electric vehicle, a fuel cell electric vehicle, a two-wheeler transportation system, a rail vehicle, a marine vessel, an aircraft, and an aerospace system..

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