Sodium-ion battery cathode additive

Abstract

The application discloses a sodium ion battery positive electrode additive, and the chemical formula of the additive is Na 1‑x M x N y Cr z O2; wherein N is a transition metal element, M is an alkali metal or alkaline earth metal element, the value range of x is 0-0.2, the value range of y is 0-0.2, and the value range of z is 0.8-1. The sodium ion battery positive electrode additive has the characteristics of high sodium supplement efficiency, excellent electrochemical performance and simple process.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a sodium ion battery positive electrode additive. BACKGROUND

[0002] Lithium ion battery-based power modules have been the main driving force behind the explosive growth of portable electronic devices and the resurgence of electric vehicles over the past decade. However, as the demand for lithium ion batteries increases, the lack of lithium resources and the rising price of lithium batteries have exposed problems, which also restrict the further large-scale application of energy storage devices. In contrast, sodium is the fifth most abundant element in the earth's crust, with abundant reserves and low price, so sodium ion batteries are more ideal large-scale energy storage battery systems.

[0003] However, in the sodium ion full battery system, the formation of the negative electrode SEI film will cause serious irreversible loss of sodium ions in the positive electrode material, thereby greatly reducing the specific capacity and energy density of the full battery. Although the N / P in the sodium ion full battery system can be adjusted to provide excess sodium ions in the positive electrode for the formation of the SEI film, this undoubtedly increases the cost and reduces the energy density of the full battery. In recent years, pre-sodium technology has gradually developed, which can either treat the negative electrode with a pre-sodium reagent to form the SEI film in advance, but this technology is difficult to industrialize; or introduce a positive electrode additive to enable the positive electrode system to provide additional sodium ions for the formation of the SEI film, which is simple to operate and has a very broad application prospect.

[0004] The commonly used positive electrode additives for sodium ion batteries include sodium oxalate, sodium square acid and sodium azide. These additives have a high decomposition voltage, with a complete decomposition voltage of 4.3 V or higher, and generate carbon dioxide and other gases during decomposition, which is not conducive to widespread application in sodium ion full battery systems.

[0005] At the same time, sodium nickelate and sodium chromate are also used as positive electrode additives in sodium ion full battery systems.

[0006] Sodium nickelate (Na2NiO2, theoretical specific capacity 392.13 mAh / g) has a high theoretical specific capacity, but when used as a sodium supplement, the charge specific capacity is about 350 mAh / g, and the reversible capacity is about 100 mAh / g. Although sodium nickelate has a high specific capacity, it is not an ideal sodium supplement due to its high reversible capacity.

[0007] Sodium chromate (NaCrO2, theoretical specific capacity 250.49 mAh / g) has a charge specific capacity of about 220 mAh / g when charged to 4.5 V, and the specific capacity does not change significantly when charged to a higher voltage. Sodium chromate can release about 88% of sodium ions, and about 10% of sodium ions remain in the crystal lattice and cannot be released.

[0008] The theoretical specific capacity of sodium chromate is lower than that of sodium nickelate, and the reversible capacity after desodiation is also lower, and in contrast, sodium chromate is a more suitable sodiation supplement. As a sodiation supplement, sodium chromate has a high specific charge capacity, but has two problems: the sodium ions in the sodium chromate cannot be completely removed; and even if the charging is to 4.5V, the sodium chromate still has a reversible specific capacity of about 30mAh / g. The residual sodium ions in the sodium chromate limit the upper limit of the sodium ions provided by the material, and the existence of the reversible capacity reduces the actual sodium ions provided by the material. SUMMARY

[0009] The purpose of the present application is to provide a sodium ion battery positive electrode additive with the characteristics of high sodiation efficiency, excellent electrochemical performance and simple process.

[0010] The present application can be realized by the following technical solutions:

[0011] The present application discloses a sodium ion battery positive electrode additive, the chemical formula of the additive is Na 1-x M x N y Cr z O2; wherein, N is a transition metal element, M is an alkali metal or alkaline earth metal element, x is in the range of 0~0.2, y is in the range of 0~0.2, and z is in the range of 0.8~1.

[0012] In the present application, the transition metal element can be but is not limited to Ti 4+ , Zr 4+ , and Ru 4+ , etc., the introduction of Ti 4+ , Zr 4+ , and Ru 4+ , etc. Ti 4+ , Zr 4+ , and Ru 4+ transition metal is conducive to enhancing the stability of the transition metal layer; the alkali metal or alkaline earth metal element can be but is not limited to Ca 2+ , Mg 2+ , K + , etc., the introduction of Ca 2+ , Mg 2+ , K + ions is conducive to widening the sodium ion transmission channel, and has a certain barrier effect when the sodium ion is embedded in the material.

[0013] Further, the lattice point group of the additive is hexagonal R3m, which is a typical layered structure, transition metal ions and sodium ions occupy different octahedral sites to form transition metal layers and sodium ion layers. In the present application, the values of x, y and z correspond to the above-mentioned proportion range. When the doping proportion of alkali metal or alkaline earth metal is too high, the sodium ion layer of the material will be damaged, and since the doped alkali metal and alkaline earth metal do not have activity, the sodium supplementing ability of the material will be reduced. If the doping proportion of transition metal elements is too high, the charge and discharge performance of the material will change greatly, and the most obvious is the increase of reversible capacity, which reduces the actual sodium supplementing ability, so x, y and z in the material are controlled within a certain range.

[0014] Further, the positive electrode additive is prepared by using a chromium source, a sodium source and a doping ion source as raw materials, ball milling, high-temperature solid-phase reaction, and then grinding and sieving in anhydrous environment.

[0015] Further, the chromium source is selected from one or more of two or more of chromium sesquioxide, chromium nitrate nonahydrate, chromium trichloride and / or chromium sulfate.

[0016] Further, the sodium source is selected from one or more of two or more of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium sulfate, sodium bisulfate and / or sodium hydroxide.

[0017] Further, the doping ion source is one or more of two or more of vanadium pentoxide, aluminum sesquioxide, titanium dioxide, potassium carbonate, lithium carbonate, sodium tungstate, carbon fluoride, calcium oxide, magnesium oxide, barium carbonate, ferrous oxalate, ferric sesquioxide and / or ferric nitrate.

[0018] Further, in the high-temperature solid-phase reaction, the temperature is controlled to be 700-1200 DEG C, and calcination is carried out in an air, argon, nitrogen or oxygen atmosphere for 6-24h.

[0019] Further, in the ball milling, the ball milling rate is 200-400r / min, and wet ball milling or dry ball milling is carried out for 8-24h.

[0020] Further, in the wet ball milling, the ball milling solvent is selected from one or more of two or more of ethanol, acetone, isopropanol and / or deionized water.

[0021] Further, the anhydrous environment is an argon or nitrogen filled glove box or a dry room with a dew point lower than-40 DEG C.

[0022] The principle of the present application is that the chromium source, the sodium source and the doping ion source are mixed by ball milling and calcined to obtain a new type of sodium ion battery positive electrode additive Na 1-x M x N y Cr zO2. This additive is a layered metal oxide material, which can be divided into sodium layers and transition metal layers in the structure, and larger ions are introduced into the sodium layer for doping. These ions have stronger repulsion with sodium ions due to charge and volume, so they can promote more sodium ions to be removed, and when sodium ions are to be re-embedded into the lattice, these ions introduced into the sodium layer will repel and prevent the embedding of sodium ions. Secondly, transition metal elements are introduced into the chromium layer for doping, especially smaller transition metal ions. When a large number of sodium ions are removed, chromium ions and doped transition metal ions will migrate to the sodium layer, which can effectively reduce the reversible capacity. The new sodium ion battery positive electrode additive Na 1- x M x N y Cr z O2. The reversible capacity is only 0.1 mAh / g (charged to 4.5V), and the utilization rate of sodium ions in the additive is significantly improved compared to the previous 30 mAh / g reversible capacity. The negligible reversible capacity will not consume sodium ions in the full battery during subsequent charge and discharge. Experiments show that the application of the additive to the sodium ion full battery system can effectively improve the battery efficiency and energy density, and the overall energy density of the full battery can be increased by 10%~20%; and the additive has a simple preparation method and low cost, and is very suitable for application in large-scale energy storage systems.

[0023] The sodium ion battery positive electrode additive has the following beneficial effects:

[0024] First, the sodium supplement efficiency is high. The application provides a preparation method and application of a new type of sodium ion battery positive electrode additive. The additive basically eliminates its own reversible capacity through ion doping, and the sodium supplement efficiency is almost 100%;

[0025] Second, the electrochemical performance is excellent. The new type of sodium ion battery positive electrode additive has a specific capacity of about 220 mAh / g when charged to 4.5V, which is much higher than the specific capacity of existing sodium ion battery positive electrode materials, and close to the specific capacity of 200~300 mAh / g of hard carbon negative electrode. A small amount of addition can meet the additional sodium ion demand of 10%~20% (compared to the specific capacity of hard carbon itself) of the negative electrode;

[0026] First, the process is simple. The new type of sodium ion battery positive electrode additive is prepared by one-step high-temperature solid phase method, which greatly simplifies the production process and is suitable for popularization and application.

[0027] Fourth, the cost is low. The application uses chromium source and sodium source as main raw materials, and introduces other ion sources to prepare a new type of sodium ion battery positive electrode additive, which has a very broad commercial prospect. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The first week charge-discharge curve of the new positive electrode additive prepared in Example 1 was directly used as a half battery of the positive electrode material;

[0029] Figure 2 The first week charge-discharge curve of the half battery of the positive electrode tab without additive in Comparative Example 1 and the positive electrode tab with additive in Application Examples 1, 4 and 5;

[0030] Figure 3 The cycle performance graph of the half battery of the positive electrode tab without additive in Comparative Example 1 and the positive electrode tab with additive in Application Example 5;

[0031] Figure 4 The XRD spectrum of the material obtained in Example 1 and sodium chromate. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solutions of the present application, the product of the present application is further described in detail below in combination with embodiments and drawings.

[0033] The present application discloses a sodium ion battery positive electrode additive, the chemical formula of the additive is Na 1-x M x N y Cr z O2; wherein N is one or more selected from transition metal elements, M is one or more selected from alkali metal or alkaline earth metal, the value range of x is 0~0.2, the value range of y is 0~0.2, and the value range of z is 0.8~1.

[0034] Further, the lattice point group of the additive is hexagonal R3m.

[0035] Further, the positive electrode additive is prepared by using a chromium source, a sodium source and a doping ion source as raw materials, ball milling, high-temperature solid-phase reaction, and then grinding and sieving in anhydrous environment.

[0036] Further, the chromium source is selected from one or more of chromium sesquioxide, chromium nitrate nine water, chromium trichloride and / or chromium sulfate.

[0037] Further, the sodium source is selected from one or more of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium sulfate, sodium bisulfate and / or sodium hydroxide.

[0038] Further, the doping ion source is one or more of vanadium pentoxide, aluminum sesquioxide, titanium dioxide, potassium carbonate, lithium carbonate, sodium tungstate, carbon fluoride, calcium oxide, magnesium oxide, barium carbonate, ferrous oxalate, iron sesquioxide and / or iron nitrate.

[0039] Further, in the high-temperature solid-phase reaction, the temperature is controlled at 700-1200℃, and calcination is performed in an air, argon, nitrogen or oxygen atmosphere for 6-24h.

[0040] Further, in the ball milling, the ball milling rate is 200-400r / min, and wet ball milling or dry ball milling is performed for 8-24h.

[0041] Further, in the wet ball milling, the ball milling solvent is selected from one or more of ethanol, acetone, isopropyl alcohol and / or deionized water.

[0042] Further, the anhydrous environment is an argon or nitrogen filled glove box or a dry room with a dew point of less than -40℃.

[0043] In the present application, the sodium ion battery cathode additive is used as a sodium ion battery cathode additive, and the specific application steps include: mixing the additive, the cathode material, the conductive carbon and the binder in proportion to prepare a uniform slurry, and then setting on the surface of a metal substrate to prepare a cathode sheet.

[0044] In the present application, the sodium supplement is suitable for all types of cathode materials, and the polyanion type cathode material is preferred as the implementation object, the cathode material is Na4Fe3(PO4)2(P2O7), and the binder can be selected from one or more of PVDF, PTFE and SBR; the solvent for dissolving the binder is selected from N-methyl-pyrrolidone or deionized water; the metal substrate can be selected from conductive metal materials such as aluminum foil, aluminum mesh or stainless steel foil; the conductive carbon can be selected from one or more of acetylene black, superconducting carbon black, graphite, Ketjen black, carbon fiber and carbon nanotube

[0045] In the present application, the mass ratio of the additive, the cathode active material, the conductive carbon and the binder is (1-2):(7-6):1:1. Example 1

[0046] A novel sodium ion battery cathode additive, the preparation method thereof comprises the following steps:

[0047] 1) 1.5199g of chromium sesquioxide, 1.0069g of sodium carbonate and 0.1282g of potassium carbonate (molar ratio of chromium source, sodium source and potassium source is 100:90:10) are weighed and mixed, then put into a ball milling tank, add acetone to immerse the solid powder, and ball mill at 300r / min for 12h;

[0048] 2) The ball milling tank is transferred into an 80℃ air oven together with the materials, and dried for 3h to completely remove the acetone;

[0049] 3) After the material is dried in step 2), it is transferred into a porcelain boat and placed in a tube furnace, and heated to 900 DEG C at a heating rate of 5 DEG C / min under the protection of argon gas with a flow rate of 20 mL / min, and kept at 900 DEG C for 10 h;

[0050] 4) After the calcined material in step 3) is cooled to 200 DEG C, it is taken out of the tube furnace and transferred into an argon-filled glove box, ground, and sieved through a 200 mesh sieve to obtain the novel sodium-ion battery cathode additive. Example 2

[0051] A novel sodium-ion battery cathode additive, a preparation method thereof comprises the following steps:

[0052] 1) 1.5199 g of chromium sesquioxide, 1.0599 g of sodium carbonate and 0.0691 g of potassium carbonate (molar ratio of chromium source, sodium source and potassium source is 100:95:5) are weighed and mixed, and then put into a ball mill jar, and acetone is added to immerse the solid powder, and ball milling is carried out at 300 r / min for 12 h;

[0053] 2) The ball mill jar is transferred into an 80 DEG C air oven together with the material, and dried for 3 h to completely remove the acetone;

[0054] 3) After the material is dried in step 2), it is transferred into a porcelain boat and placed in a tube furnace, and heated to 900 DEG C at a heating rate of 5 DEG C / min under the protection of argon gas with a flow rate of 20 mL / min, and kept at 900 DEG C for 10 h;

[0055] 4) After the calcined material in step 3) is cooled to 200 DEG C, it is taken out of the tube furnace and transferred into an argon-filled glove box, ground, and sieved through a 200 mesh sieve to obtain the novel sodium-ion battery cathode additive. Example 3

[0056] A novel sodium-ion battery cathode additive, a preparation method thereof comprises the following steps:

[0057] 1) 1.3679 g of chromium sesquioxide, 1.0599 g of sodium carbonate and 0.5397 g of ferrous oxalate dihydrate (molar ratio of chromium source, sodium source and iron source is 90:100:10) are weighed and mixed, and then put into a ball mill jar, and acetone is added to immerse the solid powder, and ball milling is carried out at 300 r / min for 12 h;

[0058] 2) The ball mill jar is transferred into an 80 DEG C air oven together with the material, and dried for 3 h to completely remove the acetone;

[0059] 3) After the material is dried in step 2), it is transferred into a porcelain boat and placed in a tube furnace, and heated to 900 DEG C at a heating rate of 5 DEG C / min under the protection of argon gas with a flow rate of 20 mL / min, and kept at 900 DEG C for 10 h;

[0060] 4) After the calcined material in step 3) is cooled to 200°C, it is taken out of the tube furnace, transferred into an argon-filled glove box, ground, and passed through a 200-mesh sieve to obtain the novel sodium-ion battery cathode additive. Example 4

[0061] A novel sodium-ion battery cathode additive, a preparation method thereof comprises the following steps:

[0062] 1) 1.4439 g of chromium sesquioxide, 1.0599 g of sodium carbonate, and 0.2699 g of ferrous oxalate dihydrate (the molar ratio of the chromium source, the sodium source, and the iron source is 95:100:5) are weighed, mixed, and then placed in a ball mill jar, and acetone is added to immerse the solid powder, and the ball milling is performed at 300 r / min for 12 h;

[0063] 2) The ball mill jar is transferred into an 80°C air oven together with the material, and the acetone is completely removed by drying for 3 h;

[0064] 3) The material dried in step 2) is transferred into a porcelain boat, placed in a tube furnace, and heated to 900°C at a heating rate of 5°C / min under the protection of argon gas with a flow rate of 20 mL / min, and then kept at 900°C for 10 h;

[0065] 4) After the calcined material in step 3) is cooled to 200°C, it is taken out of the tube furnace, transferred into an argon-filled glove box, ground, and passed through a 200-mesh sieve to obtain the novel sodium-ion battery cathode additive. Example 5

[0066] A novel sodium-ion battery cathode additive, a preparation method thereof comprises the following steps:

[0067] 1) 1.3679 g of chromium sesquioxide, 1.0599 g of sodium carbonate, and 0.1198 g of titanium dioxide (the molar ratio of the chromium source, the sodium source, and the titanium source is 90:100:10) are weighed, mixed, and then placed in a ball mill jar, and acetone is added to immerse the solid powder, and the ball milling is performed at 300 r / min for 12 h;

[0068] 2) The ball mill jar is transferred into an 80°C air oven together with the material, and the acetone is completely removed by drying for 3 h;

[0069] 3) The material dried in step 2) is transferred into a porcelain boat, placed in a tube furnace, and heated to 900°C at a heating rate of 5°C / min under the protection of argon gas with a flow rate of 20 mL / min, and then kept at 900°C for 10 h;

[0070] 4) After the calcined material in step 3) is cooled to 200℃, it is taken out of the tube furnace, transferred into an argon-filled glove box, ground, and sieved through a 200-mesh sieve to obtain the novel sodium-ion battery cathode additive. Example 6

[0071] A novel sodium-ion battery cathode additive, the preparation method thereof comprising the following steps:

[0072] 1) 1.4439 g of chromium sesquioxide, 1.0069 g of sodium carbonate, and 0.0599 g of titanium dioxide (molar ratio of chromium source, sodium source, and potassium source is 95:100:5) are weighed, mixed, and then placed in a ball mill jar, and acetone is added to submerge the solid powder, and ball milling is performed at 300 r / min for 12 h;

[0073] 2) The ball mill jar is transferred into an 80℃ air oven together with the material, and drying is performed for 3 h to completely remove the acetone;

[0074] 3) The material dried in step 2) is transferred into a porcelain boat, placed in a tube furnace, and heated to 900℃ at a heating rate of 5℃ / min under the protection of an argon atmosphere with a flow rate of 20 mL / min, and held at 900℃ for 10 h;

[0075] 4) After the calcined material in step 3) is cooled to 200℃, it is taken out of the tube furnace, transferred into an argon-filled glove box, ground, and sieved through a 200-mesh sieve to obtain the novel sodium-ion battery cathode additive. Example 7

[0076] A novel sodium-ion battery cathode additive, the preparation method thereof comprising the following steps:

[0077] 1) 1.3679 g of chromium sesquioxide, 1.0599 g of sodium carbonate, and 0.2039 g of aluminum sesquioxide (molar ratio of chromium source, sodium source, and aluminum source is 90:100:10) are weighed, mixed, and then placed in a ball mill jar, and acetone is added to submerge the solid powder, and ball milling is performed at 300 r / min for 12 h;

[0078] 2) The ball mill jar is transferred into an 80℃ air oven together with the material, and drying is performed for 3 h to completely remove the acetone;

[0079] 3) The material dried in step 2) is transferred into a porcelain boat, placed in a tube furnace, and heated to 900℃ at a heating rate of 5℃ / min under the protection of an argon atmosphere with a flow rate of 20 mL / min, and held at 900℃ for 10 h;

[0080] 4) After the calcined material in step 3) is cooled to 200℃, it is taken out of the tube furnace, transferred into an argon-filled glove box, ground, and sieved through a 200-mesh sieve to obtain the novel sodium-ion battery cathode additive. Example 8

[0081] A novel sodium-ion battery cathode additive, the preparation method thereof comprises the following steps:

[0082] 1) 1.4439 g of chromium sesquioxide, 1.0599 g of sodium carbonate and 0.1020 g of aluminum trioxide (molar ratio of chromium source, sodium source and potassium source is 95:100:5) are weighed and mixed, then put into a ball mill tank, add acetone to immerse the solid powder, and mill at 300 r / min for 12 h;

[0083] 2) the ball mill tank is transferred into an 80°C air oven together with the materials, dried for 3 h, and the acetone is completely removed;

[0084] 3) the dried material in step 2) is transferred into a porcelain boat and placed in a tube furnace, heated to 900°C at a heating rate of 5°C / min under the protection of argon gas with a flow rate of 20 mL / min, and kept at 900°C for 10 h;

[0085] 4) after the calcined material in step 3) is cooled to 200°C, it is taken out of the tube furnace and transferred into an argon-filled glove box, ground and sieved through a 200-mesh sieve to obtain the novel sodium-ion battery cathode additive. Example 9

[0086] A novel sodium-ion battery cathode additive, the preparation method thereof comprises the following steps:

[0087] 1) 1.3679 g of chromium sesquioxide, 1.0599 g of sodium carbonate and 0.3298 g of sodium tungstate dihydrate (molar ratio of chromium source, sodium source and tungsten source is 90:100:10) are weighed and mixed, then put into a ball mill tank, add acetone to immerse the solid powder, and mill at 300 r / min for 12 h;

[0088] 2) the ball mill tank is transferred into an 80°C air oven together with the materials, dried for 3 h, and the acetone is completely removed;

[0089] 3) the dried material in step 2) is transferred into a porcelain boat and placed in a tube furnace, heated to 900°C at a heating rate of 5°C / min under the protection of argon gas with a flow rate of 20 mL / min, and kept at 900°C for 10 h;

[0090] 4) after the calcined material in step 3) is cooled to 200°C, it is taken out of the tube furnace and transferred into an argon-filled glove box, ground and sieved through a 200-mesh sieve to obtain the novel sodium-ion battery cathode additive. Example 10

[0091] A novel sodium-ion battery cathode additive, the preparation method thereof comprises the following steps:

[0092] 1) Take 1.4439g of chromium trioxide, 1.0599g of sodium carbonate and 0.1649g of sodium tungstate dihydrate (molar ratio of chromium source, sodium source and potassium source is 95:100:5), mix them together and put them into a ball mill tank, add acetone to submerge the solid powder, and mill at 300r / min for 12h;

[0093] 2) Put the ball mill tank together with the material into an 80℃ air oven, dry for 3h to completely remove the acetone;

[0094] 3) Put the material dried in step 2) into a porcelain boat and place it in a tube furnace, heat it to 900℃ at a heating rate of 5℃ / min under the protection of argon gas with a flow rate of 20mL / min, and keep it at 900℃ for 10h;

[0095] 4) After the calcined material in step 3) is cooled to 200℃, take it out of the tube furnace and transfer it into an argon-filled glove box, grind it and pass it through a 200-mesh sieve to obtain the novel sodium-ion battery cathode additive.

[0096] Application Examples 1-10

[0097] The novel additives obtained in Examples 1-10 are respectively applied to the preparation of CR2032 button cells with cathode materials, and the specific steps include:

[0098] The additives (obtained in Examples 1-10), cathode materials, PVDF and superconducting carbon black are mixed in a mass ratio of 1:7:1:1 to prepare electrode sheets. First, the additives, cathode materials and superconducting carbon black are mixed uniformly in a mortar, and the PVDF is pre-dispersed in NMP to prepare a 4wt% PVDF solution. The mixed additives, cathode materials and superconducting carbon black are transferred into a coating tube added with 4% PVDF solution, and oscillated on a shaker for 18min to obtain a cathode slurry. Then, it is uniformly coated on a 16μm thick aluminum foil (coating thickness is 100μm), and placed in a 100℃ vacuum drying oven for 5h. The obtained cathode sheet and blank aluminum foil are weighed and recorded. The CR2032 button cell is assembled in an argon-filled glove box using a metal lithium sheet as the anode, polypropylene as the separator, and an electrolyte system of 1mol / L LiPF6 FEC:DMC=3:7.

[0099] Application Example 11

[0100] The novel cathode additive obtained in this example is applied to the preparation of CR2032 button full cells with cathode materials, and the specific steps include:

[0101] The additive (obtained in Example 1), the positive electrode material, PVDF, and superconducting carbon black were mixed in a mass ratio of 1:7:1:1 to prepare an electrode sheet. The additive, the positive electrode material, and the superconducting carbon black were mixed uniformly in a mortar, and PVDF was dispersed in NMP to prepare a 4 wt% PVDF solution. The mixed additive, the positive electrode material, and the superconducting carbon black were transferred into a coating tube containing the 4% PVDF solution, and oscillated on a shaker for 18 min to obtain a positive electrode slurry. Then, the positive electrode slurry was uniformly coated on a 16 μm thick aluminum foil (coating thickness was 100 μm), and placed in a 100°C vacuum drying oven for 5 h. The positive electrode sheet was punched into a diameter of 12 mm, and the mass of the obtained positive electrode sheet and the blank aluminum foil was measured and recorded. Hard carbon, acetylene black, and 1 wt% sodium carboxymethyl cellulose (dispersed in deionized water) were mixed in a mass ratio of 8:1:1 to prepare a uniform slurry, which was coated on a 16 μm thick aluminum foil (coating thickness was 100 μm), and placed in a 100°C vacuum drying oven for 5 h. The positive electrode sheet was punched into a diameter of 12 mm, and the mass of the obtained positive electrode sheet and the blank aluminum foil was measured and recorded. The positive electrode sheet with the additive, the hard carbon negative electrode, and polypropylene as a separator were used to assemble a CR2032 button cell in an argon-filled glove box, and the electrolyte system was 1 mol / L LiPF6 FEC:DMC=3:7.

[0102] Comparative Example 1

[0103] The positive electrode material, PVDF, and superconducting carbon black were mixed in a mass ratio of 8:1:1 to prepare an electrode sheet. The positive electrode material and the superconducting carbon black were mixed uniformly in a mortar, and PVDF was dispersed in NMP to prepare a 4 wt% PVDF solution. The mixed positive electrode material and the superconducting carbon black were transferred into a coating tube containing the 4% PVDF solution, and oscillated on a shaker for 18 min to obtain a positive electrode slurry. Then, the positive electrode slurry was uniformly coated on a 16 μm thick aluminum foil (coating thickness was 100 μm), and placed in a 100°C vacuum drying oven for 5 h. The positive electrode sheet was punched into a diameter of 12 mm, and the mass of the obtained positive electrode sheet and the blank aluminum foil was measured and recorded. Metal lithium was used as the negative electrode, polypropylene was used as the separator, and the electrolyte system was 1 mol / L LiPF6 FEC:DMC=3:7 to assemble a CR2032 button cell in an argon-filled glove box.

[0104] Comparative Example 2

[0105] The positive electrode material, PVDF, and superconducting carbon black were prepared into a positive electrode sheet in a mass ratio of 8:1:1. The additives, positive electrode material, and superconducting carbon black were mixed uniformly in a mortar, and the PVDF was dispersed in NMP to prepare a 4 wt% PVDF solution. The mixed additives, positive electrode material, and superconducting carbon black were transferred into a coating tube with 4% PVDF solution, and oscillated on a shaker for 18 min to obtain a positive electrode slurry. Then, the slurry was uniformly coated on a 16 μm thick aluminum foil (coating thickness was 100 μm), and placed in a 100°C vacuum drying oven for 5 h. The positive electrode sheet was punched into a diameter of 12 mm, and the mass of the positive electrode sheet and the blank aluminum foil was measured and recorded. The hard carbon, acetylene black, and 1 wt% sodium carboxymethyl cellulose (dispersed in deionized water) were mixed into a uniform slurry in a mass ratio of 8:1:1, and coated on a 16 μm thick aluminum foil (coating thickness was 100 μm). The slurry was placed in a 100°C vacuum drying oven for 5 h, and the positive electrode sheet was punched into a diameter of 12 mm. The mass of the positive electrode sheet and the blank aluminum foil was measured and recorded. The positive electrode sheet with additives, hard carbon negative electrode, and polypropylene as a separator were used to assemble a CR2032 button cell with an electrolyte system of 1 mol / L LiPF6 FEC:DMC=3:7 in an argon-filled glove box.

[0106] Figure 1 The positive electrode additive obtained in Example 1 was used as a positive electrode material to assemble a CR2032 button cell, and the first cycle charge-discharge curve was obtained at a current density of 125 mA / g. It can be clearly seen from Figure 1 that the discharge specific capacity of the positive electrode additive is 0.3831 mAh / g after charging to 4.5 V, and it can be considered that it cannot embed sodium ions any more. This indicates that the additive will not affect the subsequent charge-discharge behavior of the positive electrode material after completing the task of providing additional sodium ions. In addition, it can be seen from Figure 1 that the charge specific capacity of the positive electrode additive is 207.25 mAh / g, which is much higher than that of conventional positive electrode materials, and can effectively provide additional sodium ions, making it an ideal positive electrode additive.

[0107] Figure 2 The positive electrode sheet without additives in Comparative Example 1 and the positive electrode sheets with additives in Application Examples 1, 4, and 5 were used to assemble CR2032 button cells, and the first cycle charge-discharge curve was obtained at a current density of 20 mA / g. From Figure 2As can be seen from the above, the first-week charge specific capacity of the positive plate containing the additive in application examples 1, 4 and 5 is obviously higher than that of the positive plate without the additive in comparative example 1, and the first-week discharge specific capacity of the positive plate containing the additive is improved to a certain extent. The introduction of the positive additive effectively reduces the first-week coulomb efficiency of the positive plate. The coulomb efficiency of comparative example 1 is 95.81%, and the coulomb efficiencies of application examples 1, 4 and 5 are 87.81%, 84.64% and 88.67% respectively. The coulomb efficiency of the positive plate containing the additive is obviously reduced, which is more suitable for the hard carbon negative electrode and is beneficial to the assembly of the full battery.

[0108] Figure 3 The CR2032 button cell was assembled by using the positive plate without the additive in comparative example 1 and the positive plate containing the additive in application example 5, activated for 3 weeks at a current density of 20 mA / g, and then discharged at a current density of 200 mA / g to obtain a cycle performance graph. As can be seen from the above, Figure 3 As can be seen from the above, the first-week discharge specific capacity of the positive plate containing the additive in application example 5 is higher than that of the positive plate without the additive in comparative example 1. In the long cycle at a current density of 200 mA / g, the discharge specific capacities of the positive plate containing the additive in application example 5 and the positive plate without the additive in comparative example 1 are very close to each other, and the cycle capacity retention rates of the two are close to 100%. It is indicated that the introduction of the positive additive does not affect the cycle performance of the positive material, and has a broad application prospect.

[0109] Figure 4 The XRD spectrum of the material obtained in example 1 and sodium chromate is shown in the figure. As can be seen from the above, the XRD spectrum of the material obtained in example 1 is shifted to a high angle compared with that of sodium chromate. According to the Bragg diffraction equation, the peak position is shifted to a high angle, the lattice spacing is reduced, the introduction of potassium ions reduces the lattice spacing, and when a large amount of sodium ions are removed, the lattice is further collapsed, and the removed sodium ions are difficult to embed. The reversible capacity of the material obtained in example 1 is effectively reduced.

[0110] The above examples are only specific embodiments of the present application, which are described in detail, but should not be construed as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious alternative forms all belong to the protection scope of the present application.

Claims

1. A sodium-ion battery cathode additive, characterized in that: The chemical formula of the positive electrode additive is Na 1- x M x N y Cr z O2; where N is a transition metal element, M is an alkali metal element K, the value range of x is 0 < x ≤ 0.2, the value range of y is 0 < y ≤ 0.2, and the value range of z is 0.8 ≤ z < 1; the lattice point group of the positive electrode additive is R3M; The positive electrode additive is obtained by using chromium source, sodium source and doped ion source as raw materials, and grinding and sieving in an anhydrous environment after ball milling, high temperature solid-phase reaction; In the high-temperature solid-state reaction, the temperature is controlled at 700-1200℃, and calcination is carried out in an atmosphere of argon or nitrogen for 6-24 hours. The doped ion source is at least one of potassium carbonate, titanium dioxide, and ferrous oxalate dihydrate. The chromium source is chromium trioxide; The sodium source is one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

2. The sodium-ion battery cathode additive according to claim 1, characterized in that: In ball milling, the ball milling rate is 200-400 r / min, the ball milling method is wet ball milling or dry ball milling, and the ball milling time is 8-24 h.

3. The sodium-ion battery cathode additive according to claim 2, characterized in that: In wet ball milling, the milling solvent is selected from one or more of ethanol, acetone, isopropanol, and deionized water.

4. The sodium-ion battery cathode additive according to claim 1, characterized in that: The anhydrous environment is a glove box filled with argon or nitrogen gas and a dry room with a dew point below -40°C.

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