Composite pyrophosphate magnesium battery cathode material and preparation method and application thereof

Abstract

The application discloses a composite pyrophosphate magnesium battery positive electrode material and a preparation method and application thereof. The positive electrode material comprises a magnesium ion positive electrode material pyrophosphate and a carbon layer coated on the magnesium ion positive electrode material pyrophosphate. The chemical formula of the positive electrode material is Mg a Na b M 2+x / 2 N y , wherein M is one or more of Fe, V, Ti, Cr, Ni, Cu, Mn, Co, Nb, N is one or more of P2O7 4‑ , PO4 3‑ , SO4 2‑ , BO3 3‑ , SiO4 4‑ , 0

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials technology, specifically relating to a composite magnesium pyrophosphate battery cathode material, its preparation method, and its application. Background Technology

[0002] Magnesium batteries are a promising new type of battery that has emerged in recent years. Compared to lithium, magnesium resources are extremely abundant. It is estimated that the world's magnesite resources amount to approximately 12 billion tons, and the magnesium content in seawater is estimated at 6 × 10⁻⁶ tons. 16 In addition to tons, there are also abundant dolomite and salt lake magnesium resources. The rich magnesium reserves give it a competitive advantage in terms of cost, and its high energy density (3833 mAh cm⁻¹) further contributes to its high value. -3 Compared to lithium metal 2046mAh cm -3 This also makes magnesium batteries an ideal alternative to lithium-ion batteries. Furthermore, magnesium ions are less prone to dendrite formation during negative electrode deposition, resulting in higher safety compared to lithium batteries. In-depth research into magnesium-ion battery technology will not only help advance the energy sector but also potentially make significant contributions to addressing global challenges such as environmental and energy security.

[0003] The cathode material in magnesium batteries largely determines the cost, safety, and energy density of the battery system, making the development of magnesium-ion battery cathode materials a top priority. Polyanionic cathode materials have the advantages of high operating voltage and structural stability, but their magnesium intercalation kinetics are poor. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the main objective of this invention is to provide a composite magnesium pyrophosphate battery cathode material, aiming to address the problem of poor magnesium intercalation kinetics in existing polyanion cathode materials.

[0005] Another objective of this invention is to provide a method for preparing and applying a composite magnesium pyrophosphate battery cathode material.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] In a first aspect, there is a composite magnesium pyrophosphate battery cathode material, the cathode material comprising pyrophosphate and a carbon layer coated on the surface of the pyrophosphate.

[0008] In some specific embodiments, the chemical formula of the pyrophosphate is Mg. a Na b M 2+x / 2 N y M is one or more of Fe, V, Ti, Cr, Ni, Cu, Mn, Co, and Nb, and N is P2O7. 4- PO43- SO4 2- BO3 3- SiO4 4- One or more of them, 0 <a<2,1.5<b<5,1<2+x / 2<3,0.7<y<2.1。

[0009] In some specific embodiments, the particle size of the pyrophosphate is 1 μm to 40 μm, and the thickness of the carbon layer is 1 nm to 10 nm.

[0010] In some specific embodiments, the morphology of the pyrophosphate is one of blocky, layered, or spherical.

[0011] Secondly, a method for preparing the aforementioned composite magnesium pyrophosphate battery cathode material includes the following steps:

[0012] 1) Add magnesium source, sodium source, transition metal M source, polyanion N source and carbon source to a volatile solvent, heat and stir until the solvent evaporates to dryness to obtain the precursor;

[0013] 2) The precursor is sintered in an inert atmosphere to obtain a composite magnesium pyrophosphate battery cathode material.

[0014] In some specific embodiments, the magnesium source in step 1) includes one or more of magnesium acetate, magnesium carbonate, magnesium hydroxide, magnesium bicarbonate, magnesium formate, and magnesium nitrate.

[0015] The sodium source includes one or more of sodium acetate, sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium formate, and sodium nitrate.

[0016] The transition metal M source includes an iron source, a vanadium source, a titanium source, a chromium source, a nickel source, a copper source, a manganese source, and a cobalt source. The iron source is one or more of the following: ferrous fluoride, ferrous chloride, ferrous bromide, ferrous nitrate, ferrous sulfate, ferrous carbonate, ferrous oxalate, ferrous acetate, ferrous hydroxide, ferrous oxide, ferrous sulfide, ferrous acetylacetonate, ferric trifluoride, ferric chloride, ferric tribromide, ferric nitrate, ferric sulfate, ferric carbonate, ferric oxalate, ferric acetate, ferric hydroxide, ferric oxide, ferric tetroxide, and ferric acetylacetonate. The vanadium source is... Vanadium, vanadium tribromide, vanadium trioxide, vanadium acetylacetonate, vanadium dichloride, vanadium oxysulfate, vanadium oxalate, vanadium dioxide, vanadium acetylacetonate, vanadium trichloride, sodium vanadate, sodium metavanadate, ammonium metavanadate, vanadium pentoxide, and metallurgical vanadium slag are selected from one or more of the following: vanadium chloride, titanium bromide, titanium sulfate, titanium nitrate, titanium oxalate, titanium formate, titanium acetate, titanium dioxide, titanium acetylacetonate, and tetrabutyl titanate; the chromium source includes chromium trichloride, chromium tribromide, chromium nitrate, chromium sulfate, chromium oxalate, chromium formate, chromium acetate, and chromic acid. The nickel source is one or more of the following: chromium, chromium lactate, basic chromium sulfate, chromium perchlorate, chromium trioxide, chromium hydroxide, chromium acetylacetone, sodium chromate, and sodium dichromate; the nickel source is one or more of the following: nickel fluoride, nickel chloride, nickel bromide, nickel nitrate, nickel sulfate, nickel carbonate, nickel oxalate, nickel acetate, nickel hydroxide, nickel oxide, nickel sulfide, and nickel acetylacetone; the copper source is copper fluoride, copper chloride, copper bromide, copper nitrate, copper sulfate, copper carbonate, copper oxalate, copper acetate, basic copper carbonate, copper hydroxide, copper oxide, and sulfide. The manganese source is one or more of copper and copper acetylacetonate; the manganese source is one or more of manganese fluoride, manganese chloride, manganese bromide, manganese nitrate, manganese sulfate, manganese carbonate, manganese oxalate, manganese acetate, manganese hydroxide, manganese oxide, manganese sulfide, manganese acetylacetonate, manganese trifluoride, manganese trichloride, manganese tribromide, manganese nitrate, manganese sulfate, manganese carbonate, manganese oxalate, manganese acetate, manganese hydroxide, manganese trioxide, manganese dioxide, and manganese acetylacetonate; the cobalt source is one or more of cobalt acetate, cobalt oxide, cobalt carbonate, cobalt nitrate, and cobalt chloride.

[0017] The polyanion N source is PO4. 3- P2O7 4- SO4 2- BO3 3- SiO4 4- The corresponding acids and / or salts;

[0018] The carbon source includes one or more of the following: citric acid, sodium citrate, sodium oleate, oleic acid, polyvinylpyrrolidone, glucose, sucrose, starch, dopamine hydrochloride, starch, graphene, Ketjen black, acetylene black, and carbon nanotubes.

[0019] The solvent is one or more of water, ethanol, isopropanol, acetone, and ethyl acetate.

[0020] In some specific embodiments, a reducing agent is added when the transition metal M source is in a high valence state; and the reducing agent includes one or more of ascorbic acid, oxalic acid, citric acid, charcoal, and hydroxylamine hydrochloride.

[0021] In some specific embodiments, in step 1), the molar ratio of the total amount of magnesium source to sodium source is 0-2:1.5-5, the molar ratio of the total amount of sodium source to transition metal source is 1.5-5:1-3, the molar ratio of the total amount of sodium source to polyanion source is 1-5:0.7-2.1, and the molar ratio of the total amount of carbon source to transition metal source is 1-6:1.

[0022] In some specific embodiments, in step 1), the heating and stirring temperature is 60℃~200℃, the stirring speed is 300rpm~1000rpm, and the time is 1h~24h; in step 2), the process parameters of the sintering treatment are: sintering temperature is 200℃~800℃, and sintering time is 4h~25h; the inert atmosphere is one of argon, nitrogen or helium.

[0023] A magnesium-ion battery, wherein the positive electrode material of the magnesium-ion battery adopts the aforementioned composite pyrophosphate magnesium battery positive electrode material.

[0024] Compared with the prior art, the present invention has at least the following advantages:

[0025] 1) The composite magnesium pyrophosphate battery cathode material provided by this invention exhibits excellent electrochemical performance, with a voltage range of 0.5-3.2V, which is higher than most reported magnesium battery cathode materials. Furthermore, its initial specific capacity exceeds 100 mAh g⁻¹. -1 It can stably cycle 50 times.

[0026] 2) The method for preparing the composite magnesium pyrophosphate battery cathode material provided by the present invention uses simple and readily available raw materials that are inexpensive, and the process steps are simple and easy to implement. It is highly portable and suitable for widespread application.

[0027] 3) The composite pyrophosphate magnesium battery cathode material provided by this invention, when used in magnesium-ion batteries, achieves a performance of 50 mAg. -1 Under conditions of high current density, charging cutoff voltage of 3.2V, and discharging cutoff voltage of 0.5V, after 30 cycles, the specific capacity can reach 75mAh g. -1 . Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0029] Figure 1 Examples 1, 2, 3, 4 and Comparative Examples 1 and 2 were tested at 50 mA g. -1 Cyclic performance under the conditions of current density, charging cutoff voltage of 3.2V, and discharging cutoff voltage of 0.5V. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0031] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0032] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0033] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0034] In the following examples, magnesium acetate tetrahydrate (analytical grade, 99%) and sodium acetate (analytical grade, 99%) were purchased from Maclean's; citric acid (analytical grade, ≥99.5%) was purchased from Maclean's; ferrous oxalate dihydrate (analytical grade, 99%) was purchased from Maclean's; and phosphoric acid (analytical grade, ≥85%) was purchased from Maclean's.

[0035] The test methods used in the following embodiments include:

[0036] The electrochemical performance of a material is determined by testing its cycle stability and specific capacity using constant current charge-discharge tests; the main performance parameters tested in this application include specific capacity and cycle performance.

[0037] Example 1

[0038] This embodiment provides a method for preparing a composite magnesium pyrophosphate battery cathode material, which specifically includes the following steps:

[0039] 1) Weigh 0.0005 mol of (CH3COO)2Mg·4H2O, 0.019 mol of NaCH3COO, and 0.01 mol of FeC2O4·2H2O and dissolve them in 40 mL of ethanol to obtain solution A; dissolve 0.02 mol of phosphoric acid and 0.015 mol of citric acid in 20 mL of ethanol to obtain solution B;

[0040] 2) Mix solution A and solution B, heat and stir at 90℃, evaporate to dryness, and then place in an 80℃ forced-air drying oven for 24 hours to obtain a mixture;

[0041] 3) Grind the mixture evenly in a mortar to obtain a mixed powder. Then, place the mixed powder in a crucible and transfer it to a tube furnace for high-temperature calcination in an argon atmosphere. The calcination conditions are 300℃-5h and 600℃-12h (heating rate of 5℃ / min). Then, cool it to room temperature at a cooling rate of 5℃ / min and grind it to obtain the black powder of Mo.1N3.8F2(Mg). 0.1 Na 3.8 Fe2(P2O7)2) Iron-based magnesium sodium pyrophosphate battery cathode material.

[0042] This application tests the electrochemical performance of the composite magnesium pyrophosphate battery cathode material prepared in this embodiment, specifically as follows:

[0043] 1) Preparation of positive electrode sheet

[0044] The prepared Mo.1N3.8F2 powder was mixed with Ketjen black and the binder polytetrafluoroethylene (PTFE) in a mass ratio of 8:1:1. The mixture was ground and rolled into thin sheets in a dry environment at room temperature. Then, it was cut into smaller thin sheets with a scalpel and immediately placed in a vacuum drying oven to dry at 120°C for 12 hours. After that, it was transferred to a glove box for later use.

[0045] 2) Preparation of magnesium-ion batteries

[0046] The magnesium-ion battery was assembled in an Ar atmosphere glove box, using magnesium metal as the negative electrode and bis(trifluoromethanesulfonyl)imide magnesium, aluminum chloride, magnesium chloride, and sodium bis(trifluoromethanesulfonyl)imide dissolved in dimethyl ethylene glycol (DME) as the electrolyte, to form a CR2032 coin cell.

[0047] At 50mA g -1 Electrochemical performance was tested under the conditions of high current density, charging cutoff voltage of 3.2V, and discharging cutoff voltage of 0.5V. The first discharge specific capacity was 101 mAh g. -1 The specific capacity after 30 cycles is 57mAh g. -1 For specific performance details, please refer to Table 1.

[0048] Example 2

[0049] This embodiment provides a method for preparing a composite magnesium pyrophosphate battery cathode material, which specifically includes the following steps:

[0050] 1) Weigh out 0.0025 mol of (CH3COO)2Mg·4H2O, 0.02 mol of NaCH3COO, and 0.0075 mol of FeC2O4·2H2O, and dissolve them in 40 mL of ethanol to obtain solution A; dissolve 0.02 mol of phosphoric acid and 0.01125 mol of citric acid in 20 mL of ethanol to obtain solution B;

[0051] 2) Mix solution A and solution B, heat and stir at 90℃, evaporate to dryness, and then place in an 80℃ forced-air drying oven for 24 hours to obtain a mixture;

[0052] 3) Grind the mixture evenly in a mortar to obtain a mixed powder. Then, place the mixed powder in a crucible and transfer it to a tube furnace for high-temperature calcination in an argon atmosphere. The calcination conditions are 300℃-5h and 600℃-12h (heating rate of 5℃ / min). Then, cool it to room temperature at a cooling rate of 5℃ / min and grind it to obtain the black powder of M0.5N4F1.5(Mg). 0.5 Na4Fe 1.5 (P2O7)2) Composite magnesium pyrophosphate battery cathode material.

[0053] This application tests the electrochemical performance of the composite magnesium pyrophosphate battery cathode material prepared in this embodiment, specifically as follows:

[0054] 1) Preparation of positive electrode sheet

[0055] The prepared M0.5N4F1.5 powder was mixed with Ketjen black and the binder polytetrafluoroethylene (PTFE) in a mass ratio of 8:1:1. The mixture was ground and rolled into thin sheets in a dry environment at room temperature. Then, it was cut into smaller thin sheets with a scalpel and immediately placed in a vacuum drying oven to dry at 120°C for 12 hours. After that, it was transferred to a glove box for later use.

[0056] 2) Preparation of magnesium-ion batteries

[0057] The magnesium-ion battery was assembled in an Ar atmosphere glove box, using magnesium metal as the negative electrode and bis(trifluoromethanesulfonyl)imide magnesium, aluminum chloride, magnesium chloride, and sodium bis(trifluoromethanesulfonyl)imide dissolved in dimethyl ethylene glycol (DME) as the electrolyte, to form a CR2032 coin cell.

[0058] At 50mA g -1 Electrochemical performance was tested under the conditions of high current density, charging cutoff voltage of 3.2V, and discharging cutoff voltage of 0.5V. The first discharge specific capacity was 110mAh g. -1 The specific capacity after 30 cycles is 81 mAh g. -1 For specific performance details, please refer to Table 1.

[0059] Example 3

[0060] This embodiment provides a method for preparing a composite magnesium pyrophosphate battery cathode material, which specifically includes the following steps:

[0061] 1) Weigh out 0.005 mol of (CH3COO)2Mg·4H2O, 0.015 mol of NaCH3COO, and 0.0075 mol of FeC2O4·2H2O and dissolve them in 40 mL of ethanol to obtain solution A; dissolve 0.02 mol of phosphoric acid and 0.01125 mol of citric acid in 20 mL of ethanol to obtain solution B;

[0062] 2) Mix solution A and solution B, heat and stir at 90℃, evaporate to dryness, and then place in an 80℃ forced-air drying oven for 24 hours to obtain a mixture;

[0063] 3) Grind the mixture evenly in a mortar to obtain a mixed powder. Then, place the mixed powder in a crucible and transfer it to a tube furnace for high-temperature calcination in an argon atmosphere. The calcination conditions are 300℃-5h and 600℃-12h (heating rate of 5℃ / min). Then, cool it to room temperature at a cooling rate of 5℃ / min and grind it to obtain the black powder M1N3F1.5(Mg). 1.0 Na3Fe 1.5 (P2O7)2) Composite magnesium pyrophosphate battery cathode material.

[0064] This application tests the electrochemical performance of the composite magnesium pyrophosphate battery cathode material prepared in this embodiment, specifically as follows:

[0065] 1) Preparation of positive electrode sheet

[0066] The prepared M1N3F1.5 powder was mixed with Ketjen black and the binder polytetrafluoroethylene (PTFE) in a mass ratio of 8:1:1. The mixture was ground and rolled into thin sheets in a dry environment at room temperature. Then, it was cut into smaller thin sheets with a scalpel and immediately placed in a vacuum drying oven to dry at 120°C for 12 hours. After that, it was transferred to a glove box for later use.

[0067] 2) Preparation of magnesium-ion batteries

[0068] The magnesium-ion battery was assembled in an Ar atmosphere glove box, using magnesium metal as the negative electrode and bis(trifluoromethanesulfonyl)imide magnesium, aluminum chloride, magnesium chloride, and sodium bis(trifluoromethanesulfonyl)imide dissolved in dimethyl glycol ether (DME) as the electrolyte, to form a CR2032 coin cell. At 50 mA g... -1Electrochemical performance was tested under the conditions of high current density, charging cutoff voltage of 3.2V, and discharging cutoff voltage of 0.5V. The first discharge specific capacity was 114 mAh g. -1 The specific capacity after 30 cycles is 75mAh g. -1 For specific performance details, please refer to Table 1.

[0069] Example 4

[0070] This embodiment provides a method for preparing a composite magnesium pyrophosphate battery cathode material, which specifically includes the following steps:

[0071] 1) Weigh 0.0075 mol of (CH3COO)2Mg·4H2O, 0.01 mol of NaCH3COO, and 0.0075 mol of FeC2O4·2H2O and dissolve them in 40 mL of ethanol to obtain solution A; dissolve 0.02 mol of phosphoric acid and 0.01125 mol of citric acid in 20 mL of ethanol to obtain solution B;

[0072] 2) Mix solution A and solution B, heat and stir at 90℃, evaporate to dryness, and then place in an 80℃ forced-air drying oven for 24 hours to obtain a mixture;

[0073] 3) Grind the mixture evenly in a mortar to obtain a mixed powder. Then, place the mixed powder in a crucible and transfer it to a tube furnace for high-temperature calcination in an argon atmosphere. The calcination conditions are 300℃-5h and 600℃-12h (heating rate of 5℃ / min). Then, cool it to room temperature at a cooling rate of 5℃ / min and grind it to obtain a black powder of M1.5N2F1.5(Mg). 1.5 Na2Fe 1.5 (P2O7)2) Composite magnesium pyrophosphate battery cathode material.

[0074] This application tests the electrochemical performance of the composite magnesium pyrophosphate battery cathode material prepared in this embodiment, specifically as follows:

[0075] 1) Preparation of positive electrode sheet

[0076] The prepared M1.5N2F1.5 powder was mixed with Ketjen black and polytetrafluoroethylene (PTFE) binder at a mass ratio of 8:1:1. The mixture was ground and rolled into thin sheets in a dry environment at room temperature. These sheets were then cut into smaller pieces with a scalpel and immediately placed in a vacuum drying oven at 120°C for 12 hours. Afterward, they were transferred to a glove box for later use. 2) Preparation of magnesium-ion batteries

[0077] The magnesium-ion battery was assembled in an Ar atmosphere glove box, using magnesium metal as the negative electrode and bis(trifluoromethanesulfonyl)imide magnesium, aluminum chloride, magnesium chloride, and sodium bis(trifluoromethanesulfonyl)imide dissolved in dimethyl ethylene glycol (DME) as the electrolyte, to form a CR2032 coin cell.

[0078] At 50mA g -1 Electrochemical performance was tested under the conditions of high current density, charging cutoff voltage of 3.2V, and discharging cutoff voltage of 0.5V. The first-cycle discharge specific capacity was 88mAh g. -1 The specific capacity after 30 cycles is 36mAh g. -1 For specific performance details, please refer to Table 1.

[0079] Comparative Example 1

[0080] This embodiment provides a method for preparing a composite magnesium pyrophosphate battery cathode material, which specifically includes the following steps:

[0081] 1) Weigh 0.01 mol of (CH3COO)2Mg·4H2O and 0.01 mol of FeC2O4·2H2O and dissolve them in 40 mL of ethanol to obtain solution A; dissolve 0.02 mol of phosphoric acid and 0.015 mol of citric acid in 20 mL of ethanol to obtain solution B;

[0082] 2) Mix solution A and solution B, heat and stir at 90℃, evaporate to dryness, and then place in an 80℃ forced-air drying oven for 24 hours to obtain a mixture;

[0083] 3) Grind the mixture in a mortar until uniform to obtain a mixed powder; then place the mixed powder in a crucible and transfer it to a tube furnace for high-temperature calcination in an argon atmosphere. The calcination conditions are 300℃-5h and 600℃-12h (heating rate of 5℃ / min). Then cool it to room temperature at a cooling rate of 5℃ / min and grind it to obtain the black powder M2F2(Mg2Fe2(P2O7)2) composite magnesium pyrophosphate battery cathode material.

[0084] This application tests the electrochemical performance of the composite magnesium pyrophosphate battery cathode material prepared in this embodiment, specifically as follows:

[0085] 1) Preparation of positive electrode sheet

[0086] The prepared M2F2 powder was mixed with Ketjen black and the binder polytetrafluoroethylene (PTFE) in a mass ratio of 8:1:1. The mixture was ground and rolled into thin sheets in a dry environment at room temperature. Then, it was cut into smaller thin sheets with a scalpel and immediately placed in a vacuum drying oven to dry at 120°C for 12 hours. After that, it was transferred to a glove box for later use.

[0087] 2) Preparation of magnesium-ion batteries

[0088] The magnesium-ion battery was assembled in an Ar atmosphere glove box, using magnesium metal as the negative electrode and bis(trifluoromethanesulfonyl)imide magnesium, aluminum chloride, magnesium chloride, and sodium bis(trifluoromethanesulfonyl)imide dissolved in dimethyl ethylene glycol (DME) as the electrolyte, to form a CR2032 coin cell.

[0089] At 50mA g -1 Electrochemical performance was tested under the conditions of high current density, charging cutoff voltage of 3.2V, and discharging cutoff voltage of 0.5V. The first discharge specific capacity was 101 mAh g. -1 After 30 cycles, the specific capacity is only 2mAh g. -1 For specific performance details, please refer to Table 1.

[0090] Comparative Example 2

[0091] This embodiment provides a method for preparing a composite magnesium pyrophosphate battery cathode material, which specifically includes the following steps:

[0092] 1) Weigh 0.03 mol of NaCH3COO and 0.005 mol of FeC2O4·2H2O and dissolve them in 40 mL of ethanol to obtain solution A; dissolve 0.02 mol of phosphoric acid and 0.01125 mol of citric acid in 20 mL of ethanol to obtain solution B;

[0093] 2) Mix solution A and solution B, heat and stir at 90℃, evaporate to dryness, and then place in an 80℃ forced-air drying oven for 24 hours to obtain a mixture;

[0094] 3) Grind the mixture in a mortar until homogeneous to obtain a mixed powder; then place the mixed powder in a crucible and transfer it to a tube furnace for high-temperature calcination in an argon atmosphere. The calcination conditions are 300℃-5h and 600℃-12h (heating rate of 5℃ / min). Then cool it to room temperature at a cooling rate of 5℃ / min and grind it to obtain the black powder N6F1(Na6Fe1(P2O7)2) composite magnesium pyrophosphate battery cathode material.

[0095] This application tests the electrochemical performance of the composite magnesium pyrophosphate battery cathode material prepared in this embodiment, specifically as follows:

[0096] 1) Preparation of positive electrode sheet

[0097] The prepared N6F1 powder was mixed with Ketjen black and the binder polytetrafluoroethylene (PTFE) in a mass ratio of 8:1:1. The mixture was ground and rolled into thin sheets in a dry environment at room temperature. Then, it was cut into smaller thin sheets with a scalpel and immediately placed in a vacuum drying oven to dry at 120°C for 12 hours. After that, it was transferred to a glove box for later use.

[0098] 2) Preparation of magnesium-ion batteries

[0099] The magnesium-ion battery was assembled in an Ar atmosphere glove box, using magnesium metal as the negative electrode and bis(trifluoromethanesulfonyl)imide magnesium, aluminum chloride, magnesium chloride, and sodium bis(trifluoromethanesulfonyl)imide dissolved in dimethyl ethylene glycol (DME) as the electrolyte, to form a CR2032 coin cell.

[0100] At 50mA g -1 Electrochemical performance was tested under the conditions of high current density, charging cutoff voltage of 3.2V, and discharging cutoff voltage of 0.5V. Figure 1 As shown, the first-cycle discharge specific capacity is 134 mAh g. -1 After 30 cycles, the specific capacity is only 2mAh g. -1 For specific performance details, please refer to Table 1.

[0101] Table 1 shows the results of each embodiment and comparative example at 50 mA g. -1 Performance comparison at current densities;

[0102]

[0103] As shown in Table 1, the composite pyrophosphate magnesium battery cathode material provided by this invention, when used in magnesium-ion batteries, exhibits performance at 50 mA g⁻¹. -1 Under conditions of high current density, charging cutoff voltage of 3.2V, and discharging cutoff voltage of 0.5V, after 30 cycles, the specific capacity can reach 75mAh g. -1 It exhibits excellent cycle stability.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A magnesium-ion battery, characterized in that, It includes a composite magnesium pyrophosphate cathode material for a battery, which consists of pyrophosphate and a carbon layer coated on the surface of the pyrophosphate. The chemical formula of the pyrophosphate is Mg a Na b M 2+x / 2 N y , where M is one or more of Fe, V, Ti, Cr, Ni, Cu, Mn, Co, Nb, and N is P2O7 4- , PO4 3- , SO4 2- , BO3 3- , SiO4 4- , where 1.0 ≤ a ≤ 1.5, 2 ≤ b ≤ 3, 1 < 2 + x / 2 < 3, 0.7 < y < 2.1; and the electrolyte of the magnesium ion battery is a mixture formed by dissolving magnesium bis(trifluoromethylsulfonyl)imide, aluminum chloride, magnesium chloride, and sodium bis(trifluoromethylsulfonyl)imide in ethylene glycol dimethyl ether (DME).

2. The magnesium-ion battery according to claim 1, characterized in that, The pyrophosphate has a particle size of 1 μm to 40 μm, and the carbon layer has a thickness of 1 nm to 10 nm.

3. The magnesium-ion battery according to claim 2, characterized in that, The morphology of the pyrophosphate is one of blocky, layered, or spherical.

4. The magnesium-ion battery according to claim 1, characterized in that, The composite magnesium pyrophosphate battery cathode material is prepared by the following method, including the following steps: 1) Add magnesium source, sodium source, transition metal M source, polyanion N source and carbon source to a volatile solvent, heat and stir until the solvent evaporates to dryness to obtain the precursor; 2) The precursor is sintered in an inert atmosphere to obtain a composite magnesium pyrophosphate battery cathode material.

5. The magnesium-ion battery according to claim 4, characterized in that, The magnesium source mentioned in step 1) includes one or more of magnesium acetate, magnesium carbonate, magnesium hydroxide, magnesium bicarbonate, magnesium formate, and magnesium nitrate. The sodium source includes one or more of sodium acetate, sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium formate, and sodium nitrate. The transition metal M source includes iron, vanadium, titanium, chromium, nickel, copper, manganese, and cobalt sources. The iron source is one of the following: ferrous fluoride, ferrous chloride, ferrous bromide, ferrous nitrate, ferrous sulfate, ferrous carbonate, ferrous oxalate, ferrous acetate, ferrous hydroxide, ferrous oxide, ferrous sulfide, ferrous acetylacetonate, ferric trifluoride, ferric chloride, ferric bromide, ferric nitrate, ferric sulfate, ferric carbonate, ferric oxalate, ferric acetate, ferric hydroxide, ferric oxide, magnetite, and ferric acetylacetonate. Or multiple sources; the vanadium source is one or more of vanadium trichloride, vanadium tribromide, vanadium trioxide, vanadium acetylacetonate, vanadium dichloride, vanadium oxysulfate, vanadium oxalate, vanadium dioxide, vanadium acetylacetonate, vanadium trichloride, sodium orthovanadate, sodium metavanadate, ammonium metavanadate, vanadium pentoxide, and metallurgical vanadium slag; the titanium source is one or more of titanium chloride, titanium bromide, titanium sulfate, titanium nitrate, titanium oxalate, titanium formate, titanium acetate, titanium dioxide, titanium acetylacetonate, and tetrabutyl titanate; the chromium source includes chromium trichloride, vanadium trichloride, and vanadium trichloride. The nickel source is one or more of the following: chromium bromide, chromium nitrate, chromium sulfate, chromium oxalate, chromium formate, chromium acetate, chromium chromate, chromium lactate, basic chromium sulfate, chromium perchlorate, chromium trioxide, chromium hydroxide, chromium acetylacetone, sodium chromate, and sodium dichromate; the nickel source is one or more of the following: nickel fluoride, nickel chloride, nickel bromide, nickel nitrate, nickel sulfate, nickel carbonate, nickel oxalate, nickel acetate, nickel hydroxide, nickel oxide, nickel sulfide, and nickel acetylacetone; the copper source is copper fluoride, copper chloride, copper bromide, etc. The source of manganese is one or more of the following: copper, copper nitrate, copper sulfate, copper carbonate, copper oxalate, copper acetate, basic copper carbonate, copper hydroxide, copper oxide, copper sulfide, and copper acetylacetonate; the source of manganese is one or more of the following: manganese fluoride, manganese chloride, manganese bromide, manganese trifluoride, manganese trichloride, manganese tribromide, manganese nitrate, manganese sulfate, manganese carbonate, manganese oxalate, manganese acetate, manganese hydroxide, manganese trioxide, manganese dioxide, and manganese acetylacetonate; the source of cobalt is one or more of the following: cobalt acetate, cobalt oxide, cobalt carbonate, cobalt nitrate, and cobalt chloride. The polyanion N source is PO4. 3- P2O7 4- SO4 2- BO3 3- SiO4 4- The corresponding acid and / or salt; The carbon source includes one or more of the following: citric acid, sodium citrate, sodium oleate, oleic acid, polyvinylpyrrolidone, glucose, sucrose, starch, dopamine hydrochloride, graphene, Ketjen black, acetylene black, and carbon nanotubes. The solvent is one or more of water, ethanol, isopropanol, acetone, and ethyl acetate.

6. The magnesium-ion battery according to claim 5, characterized in that, When the transition metal M source is in a high valence state, a reducing agent is added; and the reducing agent includes one or more of ascorbic acid, oxalic acid, citric acid, charcoal, and hydroxylamine hydrochloride.

7. The magnesium-ion battery according to claim 5, characterized in that, In step 1), the molar ratio of the total amount of magnesium source to sodium source is 0.1~2:1.5~5, the molar ratio of the total amount of sodium source to transition metal M source is 1.5~5:1~3, the molar ratio of the total amount of sodium source to polyanion N source is 1~5:0.7~2.1, and the molar ratio of the total amount of carbon source to transition metal M source is 1~6:

1.

8. The magnesium-ion battery according to claim 5, characterized in that, In step 1), the heating and stirring temperature is 60℃~200℃, the stirring speed is 300rpm~1000rpm, and the time is 1h~24h; in step 2), the sintering process parameters are: sintering temperature is 200℃~800℃, and sintering time is 4h~25h; the inert atmosphere is one of argon, nitrogen or helium.

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