An ultrahigh-magnification sodium-based dual-ion battery composite cathode material and a preparation method thereof

Abstract

The application relates to the technical field of energy storage and conversion materials, and particularly relates to a preparation method of a sodium-based double-ion battery composite positive electrode material with super-high rate capability, which comprises the following steps: S1: taking tetrabutyl titanate as a Ti source, uniformly mixing the tetrabutyl titanate with graphite powder, and placing the mixture in anhydrous ethanol to obtain a solid-liquid mixture; S2: continuously stirring the solid-liquid mixture in a water bath pot magnetic stirrer until the anhydrous ethanol is completely evaporated to obtain a sample; S3: uniformly mixing the sample with a certain proportion of a lithium source (one of lithium hydroxide monohydrate, lithium acetate, lithium carbonate or lithium oxalate) to obtain a mixed sample; and S4: heating and keeping warm of the sample under an inert protective atmosphere to obtain a sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3. The sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3 provided by the application has excellent rate capability, can realize stable cycle of 100C super-high rate charging and discharging, and specifically can realize 86% of fast charging and discharging capacity in 36s.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of energy storage and conversion materials, in particular to a super-high-rate sodium-based dual-ion battery composite positive electrode material and a preparation method thereof. BACKGROUND

[0002] With the development of the new energy automobile field and intelligent electronic devices, lithium metal faces great cost challenges. However, in sharp contrast, sodium metal is rich in reserves and has great cost advantages, and as a different period element in the same main group as lithium metal, has extremely similar electrochemical properties, and is an extremely market-application-prospective energy storage system. In addition, the fast-charging demand of intelligent devices also puts forward higher requirements on the rapid transmission capacity of the battery system under high current density.

[0003] Graphite is the most market-prospective positive electrode material in the dual-ion battery system at present, and the theoretical specific capacity is about 120 mAhg-1. -1 However, on the one hand, the sodium ion radius is large (about 0.102 nm) itself, which leads to slow ion transmission; on the other hand, the solvated anion is much larger than the lithium ion radius, which leads to a generally higher electrochemical reaction energy barrier of the sodium-based dual-ion battery; in addition, the high working voltage of about 5V will cause serious oxidative decomposition of the conventional ester electrolyte, resulting in the generation of a high-impedance value CEI film. Influenced by these factors, the kinetics of the anion intercalation and deintercalation of the graphite positive electrode of the sodium-based dual-ion battery is slow.

[0004] In the related art, in order to solve the above problems, high-pressure resistant additives or film-forming additives are generally added in the electrolyte to improve the rate performance of the dual-ion battery system. However, the above method cannot effectively solve the problem of graphite structure damage caused by the intercalation behavior of the large-size solvated anion; in addition, the addition of the electrolyte additive will inevitably lead to an increase in the viscosity of the electrolyte, which will also affect the electrochemical performance of the dual-ion battery system.

[0005] Therefore, it is necessary to provide a sodium-based graphite dual-ion battery composite positive electrode material coated with Li2TiO3 and a preparation method thereof, which are simple and efficient and have super-high rate, to solve the above problems. SUMMARY

[0006] The purpose of the present application is to overcome the above technical problems, and to provide a sodium-based graphite dual-ion battery composite positive electrode material with super-high rate performance and a preparation method thereof.

[0007] In order to achieve the above purpose, the present application provides a preparation method of a sodium-based graphite dual-ion battery composite positive electrode material coated with Li2TiO3, comprising the following steps:

[0008] S1: taking tetrabutyl titanate as a titanium source, mixing the tetrabutyl titanate with graphite powder uniformly, and placing the mixture into anhydrous ethanol to obtain a solid-liquid mixture;

[0009] S2: continuously stirring the solid-liquid mixture in a water bath pot magnetic stirrer until the anhydrous ethanol is completely evaporated to obtain sample 1;

[0010] S3: taking the sample 1 and mixing corresponding lithium salt (lithium hydroxide monohydrate or lithium acetate or lithium carbonate or lithium oxalate) according to a stoichiometric ratio to obtain sample 2;

[0011] S4: heating and incubating the sample 2 under an inert protective atmosphere to obtain a sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3.

[0012] Preferably, the mass ratio of the tetrabutyl titanate to the graphite powder is (0.01-0.15):1.

[0013] Preferably, the temperature of the water bath pot in the step S2 is 40-100℃.

[0014] Preferably, the excess of the lithium salt in the step S3 is 5-12%.

[0015] Preferably, the heating temperature in the step S4 is 800℃-900℃, and the incubation time is 8-20 hours.

[0016] The application further provides a sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3, which is prepared by the above preparation method.

[0017] Compared with the related art, the technical solution provided by the application utilizes the liquid phase method to coat the nano Li2TiO3 particles on the surface of the graphite particles, optimizes and improves the interface structure of the graphite / electrolyte, and thus has the following beneficial effects:

[0018] (1) Li2TiO3 is a chemically stable inorganic compound, and the coating of the Li2TiO3 on the surface of the graphite can effectively relieve the mechanical stress generated when the anions are inserted into the graphite, help maintain the stability of the positive electrode CEI film, and help the rapid transmission of ions in the long cycle process;

[0019] (2) The electronic conductivity of Li2TiO3 is very low, and the uniform coating of the nano particles of Li2TiO3 on the surface of the graphite positive electrode can avoid the direct contact of the electrolyte with the active material to some extent, thereby effectively slowing down the oxidative decomposition of the electrolyte at a high potential, improving the generation of a stable dense CEI film of the sodium-based double-ion battery, and further helping the high-rate capability of the sodium-based double-ion battery;

[0020] (3) The Li2TiO3 nanoparticles on the surface of graphite particles will suppress the solvent co-intercalation phenomenon caused by the insertion of anions into graphite during the charging process, effectively reducing the damage to the graphite particle structure and effectively improving the structural stability of sodium-based dual-ion batteries.

[0021] (4) The Li2TiO3 nanoparticles on the surface of graphite particles guide the growth of a low-impedance, high-stability CEI film, optimize the electrolyte-electrode interface, and enable rapid ion transport. Therefore, this composite cathode material with Li2TiO3 coating on the surface of graphite sheets achieves an ultra-high rate performance of up to 100C in sodium-based dual-ion batteries, which is far superior to the electrochemical performance of graphite cathodes without Li2TiO3 coating. [Attached Image Description]

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0023] Figure 1 A flowchart illustrating the steps of the method for preparing a sodium-based graphite dual-ion battery composite cathode material with ultra-high rate capability provided by the present invention.

[0024] Figure 2(a) is a comparison of the X-ray diffraction (XRD) spectra of the sodium-based graphite dual-ion battery composite cathode material coated with Li2TiO3 and the sodium-based graphite dual-ion battery cathode material not coated with Li2TiO3 in Example 1.

[0025] Figure 2(b) is an enlarged view of the diffraction peaks in Figure 2(a) with diffraction angle 2θ between 15° and 20°;

[0026] Figures 2(c) and 2(d) are low-magnification and high-magnification scanning electron microscope (SEM) images of the sodium-based graphite dual-ion battery composite cathode material coated with Li2TiO3 in Example 1, respectively.

[0027] Figure 2(e) shows the transmission electron microscope (TEM) morphology of the sodium-based graphite dual-ion battery composite cathode material coated with Li2TiO3 in Example 1;

[0028] Figure 2(f) shows the rate performance of the sodium-based graphite dual-ion battery composite cathode material coated with Li2TiO3 and the sodium-based graphite dual-ion battery cathode material without Li2TiO3 under different current densities of 5C-10C-20C-50C-100C (1C=100mA / g) in Example 1.

[0029] Figure 2(g) shows the rate performance of the sodium-based graphite dual-ion battery composite cathode material coated with Li2TiO3 under different current densities of 5C-10C-20C-50C-100C (1C=100mA / g) in Example 2.

[0030] Figure 2(h) shows the rate performance of the sodium-based graphite dual-ion battery composite cathode material coated with Li2TiO3 under different current densities of 5C-10C-20C-50C-100C (1C=100mA / g) in Example 3.

Detailed Implementation Methods

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Please see Figure 1 This invention provides a method for preparing a sodium-based dual-ion battery composite cathode material with ultra-high rate capability, comprising the following steps:

[0033] S1: Using tetrabutyl titanate as the titanium source, the tetrabutyl titanate is mixed evenly with graphite powder and placed in anhydrous ethanol to obtain a solid-liquid mixture.

[0034] S2: The solid-liquid mixture is continuously stirred in a water bath with a magnetic stirrer until the anhydrous ethanol is completely evaporated to obtain sample 1;

[0035] S3: Weigh the corresponding lithium salts of the sample 1 according to the stoichiometric ratio and mix them evenly to obtain sample 2;

[0036] S4: The sample 2 is heated and kept at a constant temperature under an inert protective atmosphere to obtain a sodium-based graphite dual-ion battery composite cathode material coated with Li2TiO3.

[0037] Preferably, the mass ratio of tetrabutyl titanate to graphite powder is (0.01-0.15):1.

[0038] Preferably, the water bath temperature in step S2 is 40-100℃.

[0039] Preferably, in step S3, the lithium salt is in excess by 5-12%.

[0040] Preferably, the heating temperature in step S4 is 800℃-900℃, and the holding time is 5-20 hours.

[0041] The application further provides a sodium-based double-ion battery composite positive electrode material with super-high magnification, which is prepared by the preparation method.

[0042] Example 1

[0043] Tetrabutyl titanate and graphite powder are mixed according to a mass ratio of 0.025:1 and placed in a proper volume of anhydrous ethanol, and then continuously magnetically stirred in a 65℃ water bath until all the anhydrous ethanol is evaporated; the collected sample is uniformly mixed with excess 8% lithium hydroxide monohydrate, carbonized at 800℃ for 20 hours under an argon atmosphere, to obtain a sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3.

[0044] Figure 2(a) is a comparison chart of X-ray diffraction spectra (XRD) of the sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3 and the sodium-based graphite double-ion battery positive electrode material without coating of Li2TiO3, and Figure 2(b) is an enlarged view of the diffraction peak between diffraction angles 2θ of 15° and 20° in Figure 2(a). In which, curve I is the X-ray diffraction spectrum (XRD) of the sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3; and curve II is the X-ray diffraction spectrum (XRD) of the graphite double-ion battery positive electrode material without coating of Li2TiO3. The graphite double-ion battery positive electrode material without coating of Li2TiO3 only has graphite diffraction peaks (PDF #41-1487), while the sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3 has diffraction peaks of monoclinic Li2TiO3 (PDF #33-0831) and graphite, and no diffraction peaks of other phases, indicating that Li2TiO3 is successfully coated on the surface of graphite by using the preparation method provided by the application.

[0045] Figure 2(c) and Figure 2(d) are low-magnification and high-magnification scanning electron microscope (SEM) morphology charts of the sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3, from which it can be clearly seen that the surface of the graphite is uniformly coated with nano-sized Li2TiO3 particles with a particle size of about 10-40nm.

[0046] Figure 2(e) is a transmission electron microscope (TEM) morphology chart of the sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3, which further confirms the uniform coating of Li2TiO3 nanoparticles on the surface of the graphite.

[0047] Figure 2(f) is a galvanostatic charge-discharge curve of the sodium-based graphite double-ion battery composite positive electrode material coated with Li2TiO3 at a current density of 0.5-10 Ag -1Figure 5 (I-II) are the rate capability plots of the Li2Ti03-coated sodium-based graphite dual-ion battery composite cathode material and the Li2Ti03-uncoated sodium-based graphite dual-ion battery cathode material under the condition of 5C-100C. Among them, curve I is the rate capability curve of the Li2Ti03-coated sodium-based graphite dual-ion battery cathode material; curve II is the rate capability curve of the Li2Ti03-uncoated sodium-based graphite dual-ion battery composite cathode material; the rate capability of the Li2Ti03-uncoated sodium-based graphite dual-ion battery cathode material is very poor, especially under a larger current density. As can be seen from the figure, its discharge specific capacity is about 50% of the initial 5C at a current density of 50C, and at a current density of 100C, there is almost no capacity due to the excessive thickness of the CEI film and the extremely large impedance. On the contrary, the Li2Ti03-coated sodium-based graphite dual-ion battery composite cathode material can still achieve 86% of the initial cycle capacity even at a current density of 100C, showing extremely strong rate capability, and the cycle stability is greatly improved compared with the Li2Ti03-uncoated sodium-based graphite dual-ion battery cathode material. This fully embodies the positive effect of Li2Ti03 on the sodium-based graphite dual-ion battery.

[0048] Example Two

[0049] Tetrabutyl titanate and graphite powder were mixed according to a mass ratio of 0.04:1 and placed in an appropriate volume of anhydrous ethanol, which was placed in a 80°C water bath and continuously magnetically stirred until all the anhydrous ethanol was evaporated; the collected sample was uniformly mixed with excess 5% lithium acetate, carbonized at 850°C for 15 hours under an argon atmosphere, to obtain the Li2Ti03-coated sodium-based graphite dual-ion battery composite cathode material.

[0050] Figure 2 (g) is a plot of the discharge capacity of the Li2Ti03-coated sodium-based graphite dual-ion battery composite cathode material under the condition of 5C-100C. As can be seen from the figure, even at a current density of 50C, or even at a current density of 100C, the Li2Ti03-coated sodium-based graphite dual-ion battery composite cathode material can still achieve a discharge specific capacity of >70 mAh / g, showing excellent rate capability. -1 Figure 5 (I-II) are the rate capability plots of the Li2Ti03-coated sodium-based graphite dual-ion battery composite cathode material and the Li2Ti03-uncoated sodium-based graphite dual-ion battery cathode material under the condition of 5C-100C. Among them, curve I is the rate capability curve of the Li2Ti03-coated sodium-based graphite dual-ion battery cathode material; curve II is the rate capability curve of the Li2Ti03-uncoated sodium-based graphite dual-ion battery composite cathode material; the rate capability of the Li2Ti03-uncoated sodium-based graphite dual-ion battery cathode material is very poor, especially under a larger current density. As can be seen from the figure, its discharge specific capacity is about 50% of the initial 5C at a current density of 50C, and at a current density of 100C, there is almost no capacity due to the excessive thickness of the CEI film and the extremely large impedance. On the contrary, the Li2Ti03-coated sodium-based graphite dual-ion battery composite cathode material can still achieve 86% of the initial cycle capacity even at a current density of 100C, showing extremely strong rate capability, and the cycle stability is greatly improved compared with the Li2Ti03-uncoated sodium-based graphite dual-ion battery cathode material. This fully embodies the positive effect of Li2Ti03 on the sodium-based graphite dual-ion battery.

[0051] Example Three

[0052] Tetrabutyl titanate and graphite powder were mixed in a mass ratio of 0.1:1 and placed in an appropriate volume of anhydrous ethanol, which was placed in a 50℃ water bath and continuously magnetically stirred until all the ethanol evaporated; the collected sample was uniformly mixed with excess 12% lithium hydroxide monohydrate, carbonized at 900℃ for 10 hours under an argon atmosphere, to obtain a Li2TiO3-coated sodium-based graphite dual-ion battery composite positive electrode material.

[0053] Figure 2(h) is a rate performance graph of the Li2TiO3-coated sodium-based graphite dual-ion battery composite positive electrode material under a current density of 0.5-10 Ag -1 (5C-100C) condition. In the graph, curve I is a charging capacity curve under different current densities; curve II is a discharging capacity curve under different current densities; and curve III is a charging and discharging efficiency curve. As can be seen from the graph, in the case of a higher coating amount in this example, although the specific discharge capacity has decreased, the rate performance is still excellent.

[0054] Compared with the related art, the technical solution provided by the present application uses a liquid phase method to coat nano Li2TiO3 particles on the surface of graphite particles, optimizes and improves the interface structure of graphite / electrolyte, and thus has the following beneficial effects:

[0055] (1) Li2TiO3 is a chemically stable inorganic compound, and its coating on the surface of graphite can effectively alleviate the mechanical stress generated when anions are inserted into the graphite, helping to maintain the stability of the positive electrode CEI film and helping to the rapid transmission of ions;

[0056] (2) Li2TiO3 has very low electronic conductivity, and uniform coating of its nanoparticles on the surface of the graphite positive electrode will to some extent avoid direct contact between the electrolyte and the active material, thereby effectively slowing down the oxidative decomposition of the electrolyte at high potential, improving the generation of a stable dense CEI film of the sodium-based dual-ion battery, which further helps to improve the high-rate capability of the sodium-based dual-ion battery;

[0057] (3) The Li2TiO3 nanoparticles on the surface of the graphite particles will inhibit the solvent co-insertion phenomenon caused by the insertion of anions into the graphite during the charging process, effectively reducing the destruction of the structure of the graphite particles and effectively improving the structural stability of the sodium-based dual-ion battery;

[0058] (4) The Li2TiO3 nanoparticles on the surface of the graphite particles will guide the growth of a low-impedance high-stability CEI film, optimize the electrolyte-electrode interface, and achieve rapid ion transmission. Therefore, this graphite sheet surface coated with Li2TiO3 composite positive electrode material achieves an ultra-high rate performance of up to 100C in the sodium-based dual-ion battery, which is much higher than the electrochemical performance of the graphite positive electrode without Li2TiO3 coating.

[0059] The above merely describes the embodiments of the present application, and it should be pointed out that, for those skilled in the art, improvements can be made without departing from the inventive concept, and these all belong to the protection scope of the present application.

Claims

1. A method for preparing a composite cathode material for ultra-high rate sodium-based dual-ion batteries, characterized in that, Includes the following steps: S1: Using tetrabutyl titanate as the titanium source, the tetrabutyl titanate is mixed evenly with graphite powder and placed in anhydrous ethanol to obtain a solid-liquid mixture. S2: The solid-liquid mixture is continuously stirred in a water bath with a magnetic stirrer until the anhydrous ethanol is completely evaporated to obtain sample 1; S3: Weigh the corresponding lithium salt according to the stoichiometric ratio of the sample 1, mix them evenly to obtain sample 2; wherein the lithium salt is lithium hydroxide monohydrate, lithium acetate, lithium carbonate, or lithium oxalate. S4: The sample 2 is heated and kept at a constant temperature under an inert protective atmosphere to obtain a sodium-based graphite dual-ion battery composite cathode material coated with Li2TiO3.

2. The preparation method according to claim 1, characterized in that, The mass ratio of tetrabutyl titanate to graphite powder is (0.01-0.15):

1.

3. The preparation method according to claim 1, characterized in that, In step S2, the water bath temperature is 40-100℃.

4. The preparation method according to claim 1, characterized in that, In step S3, lithium salt is used in excess by 5-12%.

5. The preparation method according to claim 1, characterized in that, In step S4, the heating temperature is 800℃-900℃, and the holding time is 8-20 hours.

6. A composite cathode material for ultra-high rate sodium-based dual-ion batteries, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

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