Titanium-doped layered oxide cathode materials for sodium-ion batteries, their preparation methods and applications

Abstract

This invention discloses a titanium-doped layered oxide material for the cathode of a sodium-ion battery, its preparation method, and its application. The general chemical formula of the titanium-doped layered oxide material for the cathode of a sodium-ion battery is Na. x Ni (1‑y) / 2 Mn (1‑y) / 2 Ti y O2, 0.7≤x<1, 0.01≤y<0.3; In the titanium-doped sodium-ion battery cathode layered oxide material, titanium ions are tetravalent, manganese ions are trivalent and tetravalent, and nickel ions are divalent; The titanium-doped sodium-ion battery cathode layered oxide material is used as the positive electrode active material for sodium-ion secondary batteries. During the first week of charging, nickel ions change from divalent to tetravalent, and trivalent manganese ions change from trivalent to tetravalent; During the first week of discharging, nickel ions change from tetravalent back to divalent. In the charging and discharging process after the second week, only nickel ions change valence, while manganese and titanium ions do not change valence.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery materials technology, and in particular to a titanium-doped layered oxide cathode material for sodium-ion batteries, its preparation method, and its application. Background Technology

[0002] With continuous social development, non-renewable fossil fuels such as oil and natural gas have gradually become the main source of social energy supply. Large-scale extraction of fossil fuels causes a series of serious environmental pollution problems. Therefore, reducing dependence on fossil fuels and finding and developing new renewable energy sources is imperative. Current renewable energy sources include wind power, tidal power, solar power, and hydrogen energy. However, some of these new energy sources are dependent on changes in climate, time, and geographical location, and cannot meet social needs in a timely manner. Furthermore, achieving efficient conversion between various renewable energy sources presents significant problems and difficulties, hindering their efficient utilization. Among various energy storage devices, electrochemical energy storage dominates. Secondary batteries mainly include lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and lithium batteries. Lead-acid batteries were first used in 1890 and were widely adopted due to their low price, mature technology, and high safety. However, they suffer from a series of problems such as low energy density, short lifespan, and environmental unfriendliness. Nickel-cadmium batteries emerged in the 1950s and 60s. Although they had good high and low temperature performance, their low energy density hindered their large-scale production. The advent of nickel-metal hydride (NiMH) batteries effectively improved energy density, but their high price hindered their large-scale application. It wasn't until the 1990s, with the emergence of lithium-ion batteries, that their advantages—including higher operating voltage, lower price, fast charging, higher energy density, and longer cycle life—allowed them to rapidly dominate the market. They are now widely used in various electronic devices, aerospace, and transportation fields. However, the large-scale mining and use of lithium resources has led to a rapid increase in lithium prices. Lithium resources are limited in quantity and unevenly distributed in the Earth's crust. Global lithium consumption increased from 130,000 tons in 2011 to 300,000 tons in 2020. Limited resources and rising production costs have limited their large-scale application in energy storage devices, making their future development prospects challenging.

[0003] Sodium and lithium belong to the same group and share the same physical and chemical properties. Sodium-ion batteries operate on the same principle as lithium-ion batteries, allowing for the direct application of lithium-ion battery production technologies and methods in large-scale production, thus accelerating the industrialization of sodium-ion batteries. Due to the abundance and uniform distribution of sodium in the Earth's crust, as well as its low production cost, sodium can be applied to large-scale energy storage devices. Furthermore, developing new sodium-ion batteries can not only alleviate the severe shortage of lithium resources but also meet societal energy supply demands.

[0004] Sodium-ion battery cathode materials include transition metal layered oxides, polyanionic materials, Prussian blue materials, and organic materials. Currently, sodium-ion research is still in its early stages, with energy density only half that of lithium-ion batteries. However, the energy density of sodium-ion batteries is far higher than that of lead-acid batteries. One of the earliest researched types is layered oxide cathode materials, with the general structural formula Na₂O₃. x MO2 (M represents one or more transition metal elements).

[0005] These high-performance layered oxide cathode materials are crucial for the industrialization of sodium-ion batteries. However, a solid electrolyte interphase (SEI) film forms on the negative electrode side of a full cell, consuming active sodium ions and causing irreversible capacity loss, thus limiting the improvement of its energy density.

[0006] The main methods for modifying layered oxide cathode materials include: cathode pre-sodiumization and anode pre-sodiumization. Cathode pre-sodiumization involves selecting sacrificial sodium salts as additives to improve energy density, while anode pre-sodiumization involves forming a negative half-cell and cycling it to form an SEI on one side of the negative electrode, and then re-matching it with the positive electrode to form a full cell.

[0007] However, the types of sacrificial sodium salt additives used for cathode pre-sodiumization are limited, and due to the low capacity utilization of these sacrificial sodium salts and the release of by-products, sodium-ion batteries suffer from low first-cycle coulombic efficiency and poor cycle performance, which in particular limits the practical application of sodium-ion full batteries. Summary of the Invention

[0008] This invention provides a titanium-doped sodium-ion battery cathode layered oxide material, its preparation method, and its application. The secondary spherical titanium-doped sodium-ion battery cathode layered oxide material prepared by co-precipitation is actually formed in NaNi. 0.5 Mn 0.5 O2 is doped with tetravalent titanium, which increases Mn 3+ The content of Ti 4+ The increased spacing between sodium layers helps suppress irreversible phase transitions and improves the structural stability of the material. When this titanium-doped layered oxide cathode material is applied to a sodium-ion secondary battery, during the first charge cycle, trivalent manganese ions transform from trivalent to tetravalent, undergoing a redox reaction. This suppresses the consumption of sodium ions during the formation of the solid electrolyte interphase (SEI), thereby increasing the specific capacity. Meanwhile, Mn... 3+ / 4+ As a redox agent, it replaces part of Ni. 3+ / 2+ This can reduce the use of nickel, saving costs without reducing the overall battery capacity / energy density.

[0009] The titanium-doped layered oxide cathode material of this invention, when applied to sodium-ion full cells, can significantly improve their operating voltage and give them high capacity retention and high energy density.

[0010] The preparation method of titanium-doped sodium-ion battery cathode layered oxide material provided in this invention is a co-precipitation method. This method can obtain polycrystalline secondary particles with uniformly distributed synthetic elements. The secondary particles are dense and without gaps, which reduces the erosion of the electrolyte and thus reduces the occurrence of surface side reactions.

[0011] In a first aspect, embodiments of the present invention provide a titanium-doped layered oxide material for a sodium-ion battery cathode, wherein the general chemical formula of the titanium-doped layered oxide material for a sodium-ion battery cathode is Na. x Ni (1-y) / 2 Mn (1-y) / 2 Ti y O2, 0.7≤x<1, 0.01≤y<0.3;

[0012] The titanium ions in the titanium-doped sodium-ion battery cathode layered oxide material are tetravalent, the manganese ions are trivalent and tetravalent, and the nickel ions are divalent.

[0013] The titanium-doped sodium-ion battery cathode layered oxide material is used as the cathode active material of sodium-ion secondary batteries. During the first week of charging, nickel ions change from +2 to +4, and manganese ions change from +3 to +4. During the first week of discharging, nickel ions change from +4 back to +2. In the charging and discharging process after the second week, only nickel ions change their valence, while manganese and titanium ions do not change their valence.

[0014] The titanium-doped sodium-ion battery cathode layered oxide material is a secondary spherical particle prepared by a co-precipitation method; the secondary spherical particle is composed of closely packed atomic-level microparticles;

[0015] The titanium-doped sodium-ion battery cathode layered oxide material is an O3 phase with space group R-3m.

[0016] Preferably, during the charging and discharging process, the titanium-doped sodium-ion battery cathode layered oxide material undergoes a transformation from the O3 phase to the P3 phase when 0.2 mol of sodium is removed. It remains in the P3 phase until the voltage is increased to 4.0V, and then transforms from the P3 phase to the OP2 phase when the voltage is greater than 4.0V. Moreover, the phase transformation is reversible.

[0017] Secondly, embodiments of the present invention provide a method for preparing the titanium-doped sodium-ion battery cathode layered oxide material described in the first aspect above, wherein the preparation method is a co-precipitation method, comprising:

[0018] Weigh out the nickel source material, manganese source material and titanium source material according to the required stoichiometric ratio, dissolve them in deionized water, and stir evenly to form a mixed solution;

[0019] A mixed solution of complexing agent ammonia and sodium hydroxide is used as a precipitant and placed in a reaction vessel. Under a nitrogen atmosphere, the mixed solution is introduced into the reaction vessel by a peristaltic pump to react with the precipitant and generate a precipitate.

[0020] The precipitate was washed with deionized water at least three times, dried, and then mixed uniformly with the sodium source material according to the stoichiometric ratio to obtain the precursor.

[0021] The precursor was placed in a crucible and then placed in a muffle furnace for heat treatment in an air atmosphere. After discharge, the precursor powder was obtained.

[0022] The heat-treated precursor powder was ground and sieved to obtain a titanium-doped sodium-ion battery cathode layered oxide material.

[0023] Preferably, the nickel source material includes one or more of nickel nitrate, nickel sulfate, and nickel hydroxide;

[0024] The manganese source material includes one or more of manganese nitrate, manganese sulfate, and manganese hydroxide.

[0025] The titanium source material includes one or more of titanium nitrate, titanium sulfate, and titanium hydroxide.

[0026] The sodium source material includes sodium carbonate and / or sodium hydroxide.

[0027] Preferably, the temperature of the circulating water bath in the reactor is 50℃-80℃, and the rotation speed is 500rpm-800rpm;

[0028] The pH value inside the reactor is controlled between 9.0 and 11.5;

[0029] The feed rate of the peristaltic pump is 100ml / h-300ml / h.

[0030] Preferably, the molar ratio of ammonia to sodium hydroxide in the precipitant is [7:3]-[9:1].

[0031] Preferably, the heat treatment temperature is between 600℃ and 1000℃, and the heat treatment time is between 12 hours and 24 hours.

[0032] Thirdly, embodiments of the present invention provide a positive electrode sheet, the positive electrode sheet comprising the titanium-doped sodium-ion battery positive electrode layered oxide material described in the first aspect above.

[0033] Fourthly, embodiments of the present invention provide a sodium-ion battery, the sodium-ion battery comprising the positive electrode sheet described in the third aspect above.

[0034] This invention provides a titanium-doped sodium-ion battery cathode layered oxide material, its preparation method, and its application. The secondary spherical titanium-doped sodium-ion battery cathode layered oxide material prepared by co-precipitation is actually formed in NaNi. 0.5 Mn 0.5 O2 is doped with tetravalent titanium, which increases Mn 3+ The content of Ti 4+ The increased spacing between sodium layers helps suppress irreversible phase transitions and improves the structural stability of the material. When this titanium-doped layered oxide cathode material is applied to sodium-ion secondary batteries, during the first charge cycle, trivalent manganese ions transform from trivalent to tetravalent, undergoing a redox reaction. This suppresses the consumption of sodium ions during SEI formation, thereby increasing the specific capacity. Meanwhile, Mn... 3+ / 4+ As a redox agent, it replaces part of Ni. 3+ / 2+ This can reduce the use of nickel, saving costs without reducing the overall battery capacity / energy density.

[0035] The titanium-doped layered oxide cathode material of this invention, when applied to sodium-ion full cells, can significantly improve their operating voltage and give them high capacity retention and high energy density.

[0036] The preparation method of titanium-doped sodium-ion battery cathode layered oxide material provided in this invention is a co-precipitation method. This method can obtain polycrystalline secondary particles with uniformly distributed synthetic elements. The secondary particles are dense and without gaps, which reduces the erosion of the electrolyte and thus reduces the occurrence of surface side reactions. Attached Figure Description

[0037] The technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0038] Figure 1 This is a flowchart illustrating the preparation method of the titanium-doped sodium-ion battery cathode layered oxide material provided in this embodiment of the invention.

[0039] Figure 2 This is a comparison of the X-ray diffraction (XRD) patterns of NaNMT provided in Example 1 and NaNM prepared in Comparative Example 1.

[0040] Figure 3 These are scanning electron microscope (SEM) images of NaNMT provided in Example 1 and NaNM prepared in Comparative Example 1.

[0041] Figure 4This is a nanoscale X-ray computed tomography (Nano-CT) image of NaNMT provided in Example 1.

[0042] Figure 5 This is the energy dispersive spectrum (EDS) of NaNMT provided in Example 1.

[0043] Figure 6 This is a comparison of the charge-discharge curves of sodium-ion half-cells assembled from NaNMT provided in Example 1 and NaNM prepared in Comparative Example 1.

[0044] Figure 7 This is a cycle capacity curve of a sodium-ion full cell assembled using NaNMT to prepare the positive electrode sheet, as provided in Example 1. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any way, that is, not intended to limit the scope of protection of the present invention.

[0046] This invention provides a titanium-doped layered oxide material for the positive electrode of a sodium-ion battery. The general chemical formula of the titanium-doped layered oxide material for the positive electrode of a sodium-ion battery is Na. x Ni (1-y) / 2 Mn (1-y) / 2 Ti y O2, 0.7≤x<1, 0.01≤y<0.3; the titanium-doped sodium-ion battery cathode layered oxide material is a secondary spherical particle prepared by co-precipitation method; the secondary spherical particle is composed of atomic-level microparticles closely packed together.

[0047] In the titanium-doped sodium-ion battery cathode layered oxide material, titanium ions are tetravalent, manganese ions are trivalent and tetravalent, and nickel ions are divalent.

[0048] Titanium-doped layered oxide materials are used as positive electrode active materials for sodium-ion secondary batteries. During the first week of charging, nickel ions change from +2 to +4, and manganese ions change from +3 to +4. During the first week of discharging, nickel ions change back from +4 to +2. In the charging and discharging process after the second week, only nickel ions change their valence, while manganese and titanium ions do not change their valence.

[0049] The titanium-doped sodium-ion battery cathode layered oxide material is an O3 phase with space group R-3m.

[0050] During the charging and discharging process, the layered oxide material of the positive electrode of titanium-doped sodium-ion battery undergoes a transformation from the O3 phase to the P3 phase when 0.2 mol of sodium is removed. It remains in the P3 phase until the voltage is increased to 4.0V, and then transforms from the P3 phase to the OP2 phase when the voltage is greater than 4.0V. Moreover, the above phase transformation process is reversible.

[0051] This invention provides a method for preparing a titanium-doped sodium-ion battery cathode layered oxide material, which is a co-precipitation method, such as... Figure 1 As shown, the specific steps include:

[0052] Step 110: Weigh out the nickel source material, manganese source material and titanium source material according to the required stoichiometric ratio, dissolve them in deionized water, and stir until uniform to form a mixed solution;

[0053] The nickel source material includes one or more of nickel nitrate, nickel sulfate, and nickel hydroxide; the manganese source material includes one or more of manganese nitrate, manganese sulfate, and manganese hydroxide; and the titanium source material includes one or more of titanium nitrate, titanium sulfate, and titanium hydroxide.

[0054] The amount of deionized water used is also determined according to stoichiometry.

[0055] Step 120: The mixed solution of complexing agent ammonia and sodium hydroxide is placed in the reaction vessel as a precipitant. Under a nitrogen atmosphere, the mixed solution is introduced into the reaction vessel by a peristaltic pump to react with the precipitant and generate a precipitate.

[0056] The molar ratio of ammonia to sodium hydroxide in the precipitant is [7:3]-[9:1].

[0057] The temperature of the circulating water bath in the reactor is 50℃-80℃, and the rotation speed is 500rpm-800rpm;

[0058] The pH value inside the reactor is controlled between 9.0 and 11.5. In this invention, the pH value inside the reactor is controlled by controlling the rate at which the precipitant is introduced into the reactor.

[0059] The feed rate of the peristaltic pump is 100ml / h-300ml / h.

[0060] Step 130: Wash the precipitate with deionized water at least three times, dry it, and then mix it uniformly with the sodium source material according to the stoichiometric ratio to obtain the precursor.

[0061] The sodium source materials include sodium carbonate and / or sodium hydroxide.

[0062] Step 140: Place the precursor in a crucible, put it in a muffle furnace, and heat treat it in an air atmosphere. After discharge, the precursor powder is obtained.

[0063] The heat treatment temperature is between 600℃ and 1000℃, and the heat treatment time is between 12 hours and 24 hours.

[0064] Step 150: Grind and sieve the heat-treated precursor powder to obtain titanium-doped sodium-ion battery cathode layered oxide material.

[0065] The resulting titanium-doped sodium-ion battery cathode layered oxide material has the general chemical formula Na. x Ni (1-y) / 2Mn (1-y) / 2 Ti y O2, 0.7≤x<1, 0.01≤y<0.3

[0066] The titanium-doped sodium-ion battery cathode layered oxide materials prepared by the above two preparation methods provided in this embodiment of the invention can be used as a sodium supplementation additive for cathode active materials or other cathode active materials. They can be mixed with conductive agents and binders to prepare a slurry, which is then coated on a cathode current collector to prepare a cathode electrode sheet. The cathode current collector includes, but is not limited to, aluminum foil.

[0067] The above-mentioned positive electrode sheet containing titanium-doped sodium-ion battery positive electrode layered oxide material provided in the embodiments of the present invention is assembled together with a separator, electrolyte or solid electrolyte and negative electrode sheet to form a sodium-ion battery.

[0068] The separator includes, but is not limited to, any one of double-sided alumina separators and separators containing sodium ion solid electrolytes; the base membrane of the separator includes, but is not limited to, any one of polyolefin membranes, non-woven membranes, fiber membranes, and polyaramid membranes.

[0069] The negative electrode sheet includes any one of sodium sheet or negative electrode current collector containing negative electrode active material; specifically, the negative electrode current collector includes, but is not limited to, copper foil or titanium foil, and the active material layer on the surface of the negative electrode current collector also includes a conductive agent and a binder; the negative electrode active material includes, but is not limited to, any one of carbon materials, tin-based negative electrode materials, silicon-based negative electrode materials, silicon-carbon composite materials, nano-oxide materials, and titanate-based negative electrode materials; carbon materials include any one of graphite, hard carbon, carbon fiber, petroleum coke, and mesophase carbon microspheres.

[0070] The electrolyte comprises a solute and a solvent. The solute is a conductive salt, including but not limited to any one of the following: sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium hexafluoroarsenate (NaAsF6), and sodium trifluoroacetate (CF3COONa). Solvents include, but are not limited to, one of the following: ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), ethyl butyrate (EB), 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), ethyl methanesulfonate (EMS), or dimethyl sulfoxide (DMSO).

[0071] To better understand the technical solution provided by the present invention, the following uses several specific examples to illustrate the preparation process and characteristics of the titanium-doped sodium-ion battery cathode layered oxide material of the present invention.

[0072] Example 1

[0073] This embodiment provides a titanium-doped sodium-ion battery cathode layered oxide material, Na. 0.86 Ni 0.4 Mn 0.4 Ti 0.2 The preparation process and performance testing of O2 include the following steps:

[0074] (1) Weigh out NiSO4·6H2O (analytical grade), MnSO4·H2O (analytical grade) and Ti(SO4)2 (analytical grade) according to the required stoichiometric ratio, dissolve them in deionized water, stir evenly to form a 2mol / L mixed solution, and the volume of the mixed solution is 4L.

[0075] (2) 3L of a mixture of complexing agent ammonia (NH3·H2O) and NaOH was placed in a reaction vessel as a precipitant. Under a nitrogen atmosphere, the mixture was fed into the reaction vessel at a rate of 100ml / h by a peristaltic pump to react with the precipitant and generate a precipitate. The molar ratio of ammonia to sodium hydroxide was 8.5:1.5. The pH value in the reaction vessel was controlled at around 9.0. The temperature of the circulating water bath was 50℃ and the rotation speed was 600rpm.

[0076] (3) The precipitate was washed five times with deionized water, dried, and then mixed with Na2CO3 (analytical grade) in stoichiometric ratio to obtain the precursor.

[0077] (4) Place the precursor in a crucible, put it in a muffle furnace, and heat treat it at 900°C for 15 hours in an air atmosphere. After discharge, the precursor powder is obtained.

[0078] (5) The heat-treated precursor powder was ground and sieved to obtain a titanium-doped sodium-ion battery cathode layered oxide material with the chemical formula Na. 0.86 Ni 0.4 Mn 0.4 Ti 0.2 O2 (abbreviated as NaNMT).

[0079] To better illustrate the effects of the embodiments of the present invention, Comparative Examples 1-2 are compared with Example 1.

[0080] Comparative Example 1

[0081] This comparative example prepares NaNi 0.5 Mn 0.5 The O2 material differs from that in Example 1 in that it does not use Ti(SO4)2 (analytical grade) as a raw material, and the amounts of each material are calculated according to NaNi. 0.5 Mn 0.5 The stoichiometric weighing of O2 followed the same preparation process as in Example 1, ultimately yielding NaNi. 0.5 Mn 0.5 O2 material (abbreviated as NaNM).

[0082] The performance of NaNMT from Example 1 and NaNM from Comparative Example 1 is compared below.

[0083] The XRD comparison chart of NaNMT in Example 1 and NaNM in Comparative Example 1 is shown below. Figure 2 As shown, both materials have a pure-phase O3 structure, with high crystallinity and no impurity peaks.

[0084] SEM images of NaNMT in Example 1 and NaNM in Comparative Example 1 are shown below. Figure 3 As shown, both materials are secondary particles composed of closely packed primary particles, and the spherical particle shape is largely preserved. The average diameter of these spherical secondary particles is between 8μm and 10μm.

[0085] The nanoscale X-ray computed tomography (Nano-CT) image of NaNMT in Example 1 is shown below. Figure 4 As shown, this further demonstrates that NaNMT is composed of secondary particles formed by the close packing of primary particles.

[0086] The energy dispersive spectroscopy (EDS) spectrum of NaNMT in Example 1 is as follows: Figure 5 As shown, the fundamental mapping indicates that the transition elements Ni, Mn, and Ti are uniformly distributed in Na. 0.86 Ni 0.4 Mn 0.4 Ti 0.2 In O2 samples.

[0087] Positive electrode sheets were prepared using NaNMT from Example 1 and NaNM from Comparative Example 1, and sodium-ion half-cells and full cells were assembled. Charge-discharge tests were performed on the half-cells and the hard carbon-matched full cells, and cycle capacity tests were performed on the full cells. The specific battery preparation process is as follows:

[0088] Preparation of positive electrode sheets: NaNMT from Example 1 and NaNM from Comparative Example 1 were mixed with acetylene black and polyvinylidene fluoride (PVDF) binder at a mass ratio of 80:10:10, respectively. An appropriate amount of N-methylpyrrolidone (NMP) solution was added, and the mixture was ground in a dry environment at room temperature to form a slurry. The slurry was then uniformly coated onto a current collector aluminum foil to prepare two types of positive electrode sheets. After drying under an infrared lamp, the sheets were cut into (8×8) mm pieces. 2 The electrode sheets were dried at 110°C for 10 hours under vacuum and then transferred to a glove box for later use.

[0089] Assemble sodium-ion half-cells: The assembly of the simulated cells was carried out in a glove box under an Ar atmosphere. Using the two positive electrode plates mentioned above, metallic sodium was used as the counter electrode, and a 1M (molar mass) solution of NaClO4 / ethylene carbonate, dimethyl carbonate, propylene carbonate (EC:DMC:PC volume ratio of 1:1:1) + 2% fluoroethylene carbonate (FEC) was used as the electrolyte to assemble two CR2032 coin cells.

[0090] Half-cell charge / discharge test procedure: Use constant current charge / discharge mode, conduct charge / discharge tests at C / 10 current density, with discharge cut-off voltage of 2.0V and charge cut-off voltage of 4.0V.

[0091] A comparison of the charge-discharge curves of sodium-ion batteries assembled with NaNMT in Example 1 and NaNM in Comparative Example 1 is shown in the figure below. Figure 6 As shown in the curve comparison, the NaNMT in Example 1 has a first-week discharge specific capacity of 139.9 mAh / g and a first-week coulombic efficiency of approximately 97.33%. The initial capacity of the battery assembled with NaNMT in Example 1 is relatively low (NaNi...). 0.5 Mn 0.5 The capacity of O2 is 143.3 mAh / g, and Na... 0.86 Ni 0.4 Mn 0.4 Ti0.2 The capacity of O2 is 139.9 mAh / g, which is due to the inactive Ti. 4+ It replaced Ni with redox activity 2+ Therefore, the initial capacity is relatively low; NaNM materials contain multiple voltage plateaus and steps, reflecting complex phase transition processes; compared with NaNM, NaNMT materials, by replacing Ni and Mn with Ti, have smoother charge-discharge curves, mainly consisting of a long plateau around 2.8V and a sloping portion above 3.0V, which is due to the wider interlayer spacing, corresponding to the O3-P3 phase transition; the sloping portion of the charge-discharge curve below 2.5V corresponds to Mn 3+ / 4+ Redox reactions.

[0092] Assemble sodium-ion full cells: The assembly of full cells was carried out in an argon-filled glove box. Using the two types of positive electrode plates mentioned above, hard carbon was used as the counter electrode, and a 1M (molar mass) solution of NaClO4 / ethylene carbonate, dimethyl carbonate, propylene carbonate (EC:DMC:PC volume ratio of 1:1:1) + 2% fluoroethylene carbonate (FEC) was used as the electrolyte to assemble two types of CR2032 coin cells.

[0093] Full cell testing method: Constant current charge / discharge mode was used, with charge / discharge tests conducted at a current density of C / 2. The discharge cutoff voltage was 0.5V, and the charge cutoff voltage was 4.0V. The coulombic efficiency and cycle capacity curves were obtained, as shown in the figure. Figure 7 As shown, the cycle capacity retention rate after 300 cycles is 83%, indicating stable cycling. When the full battery is tested under charge-discharge cycle conditions of 0.5C current density, a discharge cutoff voltage of 0.5V, and a charge cutoff voltage of 4.0V, the first-cycle discharge specific capacity of the full battery in Example 1 reaches 111.4 mAh / g, and the first-cycle coulombic efficiency is approximately 82%.

[0094] The first-cycle discharge specific capacity and first-cycle coulombic efficiency of the sodium-ion half-cells assembled in Example 1 and Comparative Example 1, the first-cycle coulombic efficiency of the full cell at a current density of 0.5C, and the cycle capacity retention after 250 cycles and 300 cycles are detailed in Table 1.

[0095] Comparative Example 2

[0096] This comparative example uses a high-temperature solid-state method to prepare Na. 0.86 Ni 0.4 Mn 0.4 Ti 0.2 The specific preparation process of O2 material is as follows: Na2CO3, Mn2O3, NiO, and TiO2 are weighed according to the stoichiometric ratio and ball-milled for 8 hours. The mixture is then pressed into 14mm diameter discs under 10MPa pressure and calcined at 900℃ for 15 hours to obtain Na2CO3.0.86 Ni 0.4 Mn 0.4 Ti 0.2 O2 materials.

[0097] Na prepared using the high-temperature solid-state method of Comparative Example 2 0.86 Ni 0.4 Mn 0.4 Ti 0.2 The O2 material was used to prepare the positive electrode sheet using the same method as in Example 1, and sodium-ion half-cells and full cells were assembled. Charge-discharge and cycle capacity tests were conducted using the same methods as in Example 1. The first-cycle discharge specific capacity of the sodium-ion half-cell was 135.7 mAh / g, and the first-cycle coulombic efficiency was approximately 92.7%, both of which were inferior to the NaNMT material prepared by precipitation in Example 1. This is because the NaNMT material prepared by precipitation in Example 1 yielded polycrystalline secondary particles with uniformly distributed synthetic elements. The secondary particles were dense and without gaps, which reduced electrolyte erosion and decreased the occurrence of surface side reactions.

[0098] The first-cycle discharge specific capacity and first-cycle coulombic efficiency of the sodium-ion half-cell assembled in Comparative Example 2, the first-cycle coulombic efficiency of the full cell at a current density of 0.5C, and the cycle capacity retention after 250 and 300 cycles are detailed in Table 1.

[0099] Example 2

[0100] This embodiment provides a titanium-doped sodium-ion battery cathode layered oxide material, Na. 0.7 Ni 0.475 Mn 0.475 Ti 0.05 The preparation process and performance testing of O2 include the following steps:

[0101] (1) Weigh Ni(NO3)2 (analytical grade), Mn(OH)2 (analytical grade) and Ti(NO3)4 (analytical grade) according to the required stoichiometric ratio, dissolve them in deionized water, stir evenly to form a 2mol / L mixed solution, and the volume of the mixed solution is 6L.

[0102] (2) 5L of a mixture of complexing agent ammonia (NH3·H2O) and NaOH was placed in a reaction vessel as a precipitant. Under a nitrogen atmosphere, the mixture was fed into the reaction vessel at a rate of 300ml / h by a peristaltic pump to react with the precipitant and generate a precipitate. The molar ratio of ammonia to sodium hydroxide was 9:1. The pH value in the reaction vessel was controlled at around 11.0. The temperature of the circulating water bath was 60℃ and the rotation speed was 700rpm.

[0103] (3) The precipitate was washed five times with deionized water, dried, and then mixed with Na2CO3 (analytical grade) in stoichiometric ratio to obtain the precursor.

[0104] (4) Place the precursor in a crucible, put it in a muffle furnace, and heat treat it at 800°C for 24 hours in an air atmosphere. After discharge, the precursor powder is obtained.

[0105] (5) The heat-treated precursor powder was ground and sieved to obtain a titanium-doped sodium-ion battery cathode layered oxide material with the chemical formula Na. 0.7 Ni 0.475 Mn 0.475 Ti 0.05 O2.

[0106] Na prepared using Example 2 0.7 Ni 0.475 Mn 0.475 Ti 0.05 O2 was used to assemble and test sodium-ion half-cells and full-cells, and the assembly and testing process was the same as in Example 1.

[0107] The first-cycle discharge specific capacity and first-cycle coulombic efficiency of the sodium-ion half-cell assembled in Example 2, the first-cycle coulombic efficiency of the full cell at a current density of 0.5C, and the cycle capacity retention after 250 cycles and 300 cycles are detailed in Table 1.

[0108] Example 3

[0109] This embodiment provides a titanium-doped sodium-ion battery cathode layered oxide material, Na. 0.9 Ni 0.35 Mn 0.35 Ti 0.3 The preparation process and performance testing of O2 include the following steps:

[0110] (1) Weigh Ni(OH)2 (analytical grade), Mn(OH)2 (analytical grade) and Ti(OH)4 (analytical grade) according to the required stoichiometric ratio, dissolve them in deionized water, stir evenly to form a 2 mol / L mixed solution, and the volume of the mixed solution is 6 L.

[0111] The nickel source material includes one or more of nickel nitrate, nickel sulfate, and nickel hydroxide; the manganese source material includes one or more of manganese nitrate, manganese sulfate, and manganese hydroxide; and the titanium source material includes one or more of titanium nitrate, titanium sulfate, and titanium hydroxide.

[0112] The amount of deionized water used is also determined according to stoichiometry.

[0113] (2) 5L of a mixture of complexing agent ammonia (NH3·H2O) and NaOH was placed in a reaction vessel as a precipitant. Under a nitrogen atmosphere, the mixture was fed into the reaction vessel at a rate of 200ml / h by a peristaltic pump to react with the precipitant and generate a precipitate. The molar ratio of ammonia to sodium hydroxide was 7:3. The pH value in the reaction vessel was controlled at around 10.0. The temperature of the circulating water bath was 80℃ and the rotation speed was 800rpm.

[0114] (3) The precipitate was washed three times with deionized water, dried, and then mixed with NaOH (analytical grade) in a stoichiometric ratio to obtain the precursor.

[0115] (4) Place the precursor in a crucible, put it in a muffle furnace, and heat treat it at 1000°C for 20 hours in an air atmosphere. After discharge, the precursor powder is obtained.

[0116] (5) The heat-treated precursor powder was ground and sieved to obtain a titanium-doped sodium-ion battery cathode layered oxide material with the chemical formula Na. 0.9 Ni 0.35 Mn 0.35 Ti 0.3 O2.

[0117] Na prepared using Example 3 0.9 Ni 0.35 Mn 0.35 Ti 0.3 O2 was used to assemble and test sodium-ion half-cells and full-cells, and the assembly and testing process was the same as in Example 1.

[0118] The first-cycle discharge specific capacity and first-cycle coulombic efficiency of the sodium-ion half-cell assembled in Example 3, the first-cycle coulombic efficiency of the full cell at a current density of 0.5C, and the cycle capacity retention after 250 cycles and 300 cycles are detailed in Table 1.

[0119] Table 1 summarizes the first-cycle coulombic efficiency and discharge specific capacity of sodium-ion half-cells assembled in Examples 1-3 and Comparative Examples 1-2, as well as the first-cycle coulombic efficiency, cycle capacity retention after 250 cycles, and cycle capacity retention after 300 cycles of sodium-ion full cells.

[0120]

[0121]

[0122] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A titanium-doped layered oxide material for the cathode of a sodium-ion battery, characterized in that, The chemical general formula of the titanium-doped sodium-ion battery positive electrode layered oxide material is Na x Ni (1-y) / 2 Mn (1-y) / 2 Ti y O2, 0.7≤x<1, 0.01≤y<0.3; The titanium ions in the titanium-doped sodium-ion battery cathode layered oxide material are tetravalent, the manganese ions are trivalent and tetravalent, and the nickel ions are divalent. The titanium-doped sodium-ion battery cathode layered oxide material is used as the cathode active material of sodium-ion secondary batteries. During the first week of charging, nickel ions change from +2 to +4, and manganese ions change from +3 to +4. During the first week of discharging, nickel ions change from +4 back to +2. In the charging and discharging process after the second week, only nickel ions change their valence, while manganese and titanium ions do not change their valence. The titanium-doped sodium-ion battery cathode layered oxide material is a secondary spherical particle prepared by a co-precipitation method; the secondary spherical particle is composed of closely packed atomic-level microparticles; The titanium-doped sodium-ion battery cathode layered oxide material is an O3 phase with space group R-3m.

2. The titanium-doped sodium-ion battery cathode layered oxide material according to claim 1, characterized in that, During the charging and discharging process, the titanium-doped sodium-ion battery cathode layered oxide material undergoes a transformation from the O3 phase to the P3 phase when 0.2 mol of sodium is removed. It remains in the P3 phase until the voltage is increased to 4.0V, and then transforms from the P3 phase to the OP2 phase when the voltage is greater than 4.0V. The phase transformation is reversible.

3. A method for preparing the titanium-doped sodium-ion battery cathode layered oxide material according to any one of claims 1-2, characterized in that, The preparation method is a co-precipitation method, including: Weigh out the nickel source material, manganese source material and titanium source material according to the required stoichiometric ratio, dissolve them in deionized water, and stir evenly to form a mixed solution; A mixed solution of complexing agent ammonia and sodium hydroxide is used as a precipitant and placed in a reaction vessel. Under a nitrogen atmosphere, the mixed solution is introduced into the reaction vessel by a peristaltic pump to react with the precipitant and generate a precipitate. The precipitate was washed with deionized water at least three times, dried, and then mixed uniformly with the sodium source material according to the stoichiometric ratio to obtain the precursor. The precursor was placed in a crucible and then placed in a muffle furnace for heat treatment in an air atmosphere. After discharge, the precursor powder was obtained. The heat-treated precursor powder was ground and sieved to obtain a titanium-doped sodium-ion battery cathode layered oxide material.

4. The preparation method according to claim 3, characterized in that, The nickel source material includes one or more of nickel nitrate, nickel sulfate, and nickel hydroxide. The manganese source material includes one or more of manganese nitrate, manganese sulfate, and manganese hydroxide. The titanium source material includes one or more of titanium nitrate, titanium sulfate, and titanium hydroxide. The sodium source material includes sodium carbonate and / or sodium hydroxide.

5. The preparation method according to claim 3, characterized in that, The temperature of the circulating water bath in the reactor is 50℃-80℃, and the rotation speed is 500rpm-800rpm. The pH value inside the reactor is controlled between 9.0 and 11.5; The feed rate of the peristaltic pump is 100ml / h-300ml / h.

6. The preparation method according to claim 3, characterized in that, The molar ratio of ammonia to sodium hydroxide in the precipitant is [7:3]-[9:1].

7. The preparation method according to claim 3, characterized in that, The heat treatment temperature is between 600℃ and 1000℃, and the heat treatment time is between 12 hours and 24 hours.

8. A positive electrode sheet, characterized in that, The positive electrode sheet comprises the titanium-doped sodium-ion battery positive electrode layered oxide material as described in any one of claims 1-2.

9. A sodium-ion battery, characterized in that, The sodium-ion battery includes the positive electrode sheet as described in claim 8.

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