CN108417833B - Positive electrode material lithium manganese fluosilicate and preparation method thereof - Google Patents

Abstract

The invention discloses a novel anode material lithium manganese fluosilicate and a hydrothermal preparation method thereof, wherein the chemical formula of the lithium manganese fluosilicate is L i₃MnSiO₄F, hydrothermal preparation methodWeighing a certain amount of lithium source, manganese source and silicon source compounds, adding the lithium source, manganese source and silicon source compounds into deionized water, mixing and dispersing, adding a certain amount of fluorine source compounds into the solution, continuously stirring for a period of time, transferring to a high-pressure reaction kettle, sealing for hydrothermal reaction for a period of time at a certain temperature, naturally cooling, taking out, drying and grinding to obtain a precursor, (2) placing the precursor into a heating device, heating to a certain temperature under a protective gas atmosphere, and carrying out constant-temperature heat treatment to obtain a target product L i₃MnSiO₄Material F L i obtained according to the invention₃MnSiO₄Material comparison of F L i₂MnSiO₄The material has higher charge-discharge platform and discharge capacity, and meanwhile, the method disclosed by the invention has the advantages of simple process operation, high product purity, good reproducibility of process control and product performance by adding the material at one time, and is beneficial to large-scale production, popularization and application of the material.

Description

A kind of cathode material lithium manganese fluorosilicate and preparation method thereof

technical field

The invention relates to the technical field of preparation of electrode materials for lithium batteries, in particular to a novel cathode material lithium manganese fluorosilicate and a preparation method thereof.

Background technique

As an efficient energy storage device, lithium battery has the advantages of high energy density, high voltage platform, long charge and discharge life, low self-discharge rate, and low environmental pollution. It is widely used in tools and aerospace fields. Therefore, the research and development of lithium batteries is very meaningful. Lithium batteries are mainly composed of positive and negative electrode materials, electrolyte solutions and separator materials. Among them, the positive electrode material is one of its most important components. Therefore, the research and development of high-performance positive electrode materials is very important for the development and application of lithium batteries. of.

Fluorinated polyanion-type cathode material is a hot research topic in recent years, which is characterized by the combination of the strong inductive effect of polyanions and the strong electronegativity of fluoride ions, so that the redox potential and structural stability of the material itself can be obtained. improve. In addition, since fluorination introduces a negative charge, considering the charge balance, it is expected to achieve more than one reversible exchange of lithium through the utilization of M ²⁺ /M ^{4 +} redox pair in fluorinated polyanions, so its electrochemical performance is comparable. Compared with that before the introduction of fluorine element, there is a significant improvement, and a higher specific discharge capacity can be obtained. For example, Li ₂ CoPO ₄ F is an emerging fluoropolyanionic cathode material in recent years. In 2005, Okada et al. (Fluoride phosphate Li ₂ CoPO ₄ F as a high-voltage cathode in Li-ion batteries, Journal of Power Sources, 146 (2005) 565-569) first reported the synthesis of LiCoPO ₄ materials based on The structure and electrochemical properties of Li ₂ CoPO ₄ F, a fluorophosphate cathode material with a high voltage of 5V, due to the presence of two Li ⁺ , its theoretical capacity can reach 287mAh/g, and its energy density can reach 1435Wh/kg. However, the current research in the field of fluorinated polyanion cathode material Li _a MYO _b F (M=Mn, Fe, Co, V, etc.; Y=Si, P, B, etc.) is very limited, and there is still a lot of room for development. The Li ₃ MnSiO ₄ F material proposed in the present invention is a potential positive electrode material for lithium batteries with high energy density, and is also very meaningful for its development and research.

The polyanionic cathode material Li ₂ MnSiO ₄ has the advantages of high theoretical capacity, low production cost and low environmental pollution. However, due to the low electrical conductivity and poor structural stability of the Li ₂ MnSiO ₄ material itself, it is difficult to insert and remove lithium ions, resulting in its The actual capacity is much lower than the theoretical capacity, and these factors seriously restrict its production and application. Therefore, on the basis of Li ₂ MnSiO ₄ material, the present invention synthesized a new type of fluorinated polyanionic positive electrode material Li ₃ MnSiO ₄ F by introducing fluorinated groups by hydrothermal method. Combined with the strong electronegativity of fluoride ions, it has higher redox potential and better structural stability than Li ₂ MnSiO ₄ materials. In addition, due to the introduction of fluorinated groups, the Li ₃ MnSiO ₄ F material contains one more lithium than the Li ₂ MnSiO ₄ material, so that more Li ⁺ reversible exchange can be achieved, and the actual discharge specific capacity of the material can be improved. All these favorable factors make Li ₃ MnSiO ₄ F material itself have more superior electrochemical performance, and it is a kind of potential new cathode material for lithium battery.

SUMMARY OF THE INVENTION

The present invention proposes a new type of fluorinated polyanionic positive electrode material, Li ₃ MnSiO ₄ F, which aims to combine the inductive effect of silicate with the strong electronegativity of fluoride ions to obtain high specific capacity, high energy density and Superior comprehensive electrochemical performance for better cycling performance. A new type of lithium manganese fluorosilicate lithium manganese silicate Li ₃ MnSiO ₄ F with high voltage was synthesized by hydrothermal method by one-time feeding method. It can be seen from the X-ray diffraction diagram of accompanying drawing 1 that the present invention has synthesized a new type of positive electrode material that is completely different from Li ₂ MnSiO ₄ ; in order to confirm the introduction of fluorinated groups in the material, the present invention is based on scanning electron microscopy. EDS energy spectrum analysis was carried out, and it can be seen from accompanying drawing 2 that there is fluorine in the material and it is evenly distributed, which further shows that the present invention has indeed obtained a brand-new material lithium manganese fluorosilicate; accompanying drawing 3 and accompanying drawing 4 It is shown that the material has higher charge-discharge potential and larger actual discharge specific capacity than Li ₂ MnSiO ₄ due to the introduction of fluorinated groups. It is a promising new cathode material for development and application. .

In order to achieve the above purpose, the present invention provides a novel cathode material lithium manganese fluorosilicate and a preparation method thereof. The chemical formula of the material is Li ₃ MnSiO ₄ F, and the preparation method includes the following steps:

(1) Weigh a certain amount of lithium source, manganese source and silicon source compound into deionized water, mix and disperse, add a certain amount of fluorine source compound into the above solution, continue stirring for a period of time, transfer it to a high pressure reactor, and at a certain The hydrothermal reaction is sealed for a period of time at the temperature, and then taken out after natural cooling, and the precursor is obtained after drying and grinding;

(2) The above precursor is placed in a heating device, heated to a certain temperature under a protective gas atmosphere for a period of time, and then a target product Li ₃ MnSiO ₄ F material is obtained.

The molar ratio of the lithium source, manganese source, silicon source and fluorine source compound described in the present invention is Li : Mn : Si : F=(1.95~2.15) : 1 : 1 : 1.

The lithium source compound described in the present invention is one or several mixtures of lithium hydroxide, lithium carbonate, lithium acetate, lithium chloride, lithium nitrate, lithium phosphate and lithium oxalate; the manganese source compound is manganese oxalate , one or more mixtures of manganese acetate, manganese chloride, manganese phosphate, manganese nitrate, manganese dioxide, manganese tetroxide; the silicon source compound is ethyl orthosilicate or methyl orthosilicate One or more mixtures of fluorine source compounds; the fluorine source compound is one or more mixtures of lithium fluoride and ammonium fluoride.

In the present invention, after adding the fluorine source compound, the stirring time is continued for 30-120 min.

The temperature of the hydrothermal reaction described in the present invention is 120-200° C., and the reaction time is 12-72 h.

The heating device described in the present invention can be a closed box furnace, a tube-and-tube furnace or a microwave tube furnace.

The protective gas described in the present invention is one or more mixed gases among nitrogen, argon, helium and hydrogen.

The constant temperature temperature range of the constant temperature heat treatment described in the present invention is 400~750°C, and the constant temperature time range is 2~12h.

Description of drawings

1 is an X-ray diffraction diagram of the Li ₃ MnSiO ₄ F cathode material prepared in Example 1 of the present invention and the Li ₂ MnSiO ₄ cathode material prepared in Comparative Example 1 and Comparative Example 2.

2 is a scanning electron microscope photograph and a corresponding surface scan energy spectrum of the Li ₃ MnSiO ₄ F cathode material prepared in Example 1 of the present invention.

3 is a graph comparing the first discharge curves of the Li ₃ MnSiO ₄ F cathode material prepared in Example 1 of the present invention and the Li ₂ MnSiO ₄ cathode material prepared in Comparative Example 2.

4 is a graph comparing the cycle performance curves of the Li ₃ MnSiO ₄ F cathode material prepared in Example 2 of the present invention and the Li ₂ MnSiO ₄ cathode material prepared in Comparative Example 2.

Detailed ways

In order to facilitate understanding of the present invention, the present invention is further described in detail below with reference to the accompanying drawings, specific embodiments and comparative examples. Obviously, the described embodiments are only some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Comparative Example 1

Referring to the experimental protocol of the literature (S. Devaraj, M. Kuezma, CT Ng, P. Balaya, Sol–gel derivednanostructured Li ₂ MnSiO ₄ /C cathode with high storage capacity, ElectrochimicaActa 102 (2013) 290-298), using sol-gel Preparation of Li ₂ MnSiO ₄ material by glue method: Weigh 0.04mol lithium acetate, 0.02mol manganese acetate and 0.02mol ethyl orthosilicate and add it to an appropriate amount of dispersant (40ml distilled water, 10ml ethanol), mix and disperse, then add 6ml mass dropwise Ammonia water with a fraction of 20% was used as a catalyst, heated and stirred at 80 °C for 6 hours, and then the solvent was evaporated and ground in a water bath to obtain the precursor; the precursor was placed in a tubular furnace, in a mixed atmosphere of 5% hydrogen/95% argon. Under the protection, after heating to 750℃ for 8h, the target product Li ₂ MnSiO ₄ material was obtained. After X-ray powder diffraction test and comparison with the XRD pattern in the literature, it was proved that the product was indeed a pure phase Li ₂ MnSiO ₄ material.

Comparative Example 2

Preparation of Li ₂ MnSiO ₄ material by hydrothermal method: Weigh 0.04mol lithium hydroxide, 0.02mol manganese acetate and 0.02mol ethyl orthosilicate into deionized water (30ml), mix and disperse, and then transfer it to a high pressure reactor ( 50ml) in a hydrothermal reaction at 200°C for 72h, take out after natural cooling, dry and grind to obtain the precursor; place the above precursor in a microwave tube furnace and heat it to 650°C under 8% hydrogen/92% argon atmosphere After constant temperature heat treatment for 2.5h, the target product Li ₂ MnSiO ₄ cathode material was obtained. The positive electrode material and the lithium sheet counter electrode were assembled into a battery, and the constant current charge and discharge test was carried out, and the voltage range was between 1.5V and 4.8V. Fig. 1 X-ray powder diffraction pattern shows that the product has the same diffraction peak position as the Li ₂ MnSiO ₄ material prepared by the sol-gel method in Comparative Example 1, so it is confirmed that the product is also pure phase Li ₂ MnSiO ₄ .

Example 1

Weigh 0.04mol lithium hydroxide, 0.02mol manganese acetate, 0.02mol ethyl orthosilicate, add them to deionized water (30ml), mix and disperse, then weigh 0.02mol lithium fluoride, add it to the above solution system, continue Stir for 90 min, then transfer it to an autoclave (50 ml) for hydrothermal reaction at 200 °C for 72 h, take out after natural cooling, dry and grind to obtain the precursor; place the above precursor in a microwave tube furnace at 8% After heating to 650°C for 2.5 hours under a hydrogen/92% argon atmosphere, the target product lithium manganese fluorosilicate Li ₃ MnSiO ₄ F cathode material was obtained. The positive electrode material and the counter electrode lithium sheet were assembled into a battery, and the constant current charge and discharge test was carried out, and the voltage range was between 1.5V and 4.8V. Fig. 1 X-ray powder diffraction pattern shows that the product and the lithium manganese silicate Li ₂ MnSiO ₄ material prepared by the hydrothermal method in Comparative Example 2 are completely different materials, indicating that the present invention has obtained a new type of material; Fig. 2 Scanning electron microscope image and energy spectrogram show that fluorine does exist in the product and is evenly distributed in the product, which further confirms that the material obtained by the present invention is indeed a brand-new cathode material lithium manganese fluorosilicate Li ₃ MnSiO ₄ F; It can be seen from the comparison chart of the first discharge curve in Fig. 3 that at 0.1C, the first discharge specific capacity of the Li ₃ MnSiO ₄ F material is 71mAhg ^-1 , while the Li ₂ MnSiO ₄ material prepared by the hydrothermal method in Comparative Example 2 has the first discharge capacity for the first time. The discharge specific capacity is only 25mAhg ^-1 , which proves that the charge-discharge platform and discharge specific capacity of the Li ₃ MnSiO ₄ F cathode material obtained by the present invention are obviously improved compared with Li ₂ MnSiO ₄ , and the completely different discharge behavior is also from the side It is further proved that the material obtained by the present invention is indeed a brand-new lithium manganese fluorosilicate cathode material, and has good electrochemical performance.

Example 2

Weigh 0.04mol lithium hydroxide, 0.02mol manganese acetate, 0.02mol ethyl orthosilicate, add them to deionized water (30ml), mix and disperse, then weigh 0.02mol lithium fluoride, add it to the above solution system, continue Stir for 120 min, then transfer it to an autoclave (50 ml) for hydrothermal reaction at 160 °C for 48 h, take out after natural cooling, dry and grind to obtain the precursor; place the above precursor in a microwave tube furnace and place it in an argon gas After heating to 700 ℃ under the atmosphere for 2h constant temperature heat treatment, the target product lithium manganese fluorosilicate Li ₃ MnSiO ₄ F cathode material was obtained. The positive electrode material and the counter electrode lithium sheet were assembled into a battery, and the constant current charge and discharge test was carried out, and the voltage range was between 1.5V and 4.8V. It can be seen from Figure 4 that the discharge specific capacity of Li ₃ MnSiO ₄ F material is always higher than that of the Li ₂ MnSiO ₄ material prepared by the hydrothermal method in Comparative Example 2 at 0.1 C, and the discharge specific capacity of the material remains after 20 cycles. It can be maintained at about 40mAhg ^-1 . For silicate-based cathode materials with poor self-conductivity, this is a very good electrochemical performance without any additional carbon modification. In Comparative Example 2 The capacity of the hydrothermally prepared Li ₂ MnSiO ₄ material is only 17mAhg ^-1 after 20 cycles.

Example 3

Weigh 0.04mol lithium carbonate, 0.02mol manganese nitrate, and 0.02mol methyl orthosilicate, add them to deionized water (30ml), mix and disperse, then weigh 0.02mol lithium fluoride, add it to the above solution system, and continue to stir 30min, then transferred to a high-pressure reactor (50ml) for hydrothermal reaction at 140°C for 24h, taken out after natural cooling, dried and ground to obtain the precursor; the above precursor was placed in a closed box furnace and heated in 6% hydrogen After heating to 700 ℃ for 10 hours under a 94% argon atmosphere, the target product lithium manganese fluorosilicate Li ₃ MnSiO ₄ F cathode material was obtained.

Example 4

Weigh 0.06mol lithium acetate, 0.02mol manganese acetate, 0.02mol methyl orthosilicate, add them to deionized water (30ml), mix and disperse, then weigh 0.02mol ammonium fluoride, add it to the above solution system, continue stirring 60min, then transferred to a high-pressure reactor (50ml) for hydrothermal reaction at 120°C for 36h, taken out after natural cooling, dried and ground to obtain the precursor; the above precursor was placed in a tube-and-tube furnace and heated at 2% After heating to 650°C for 12 hours under a hydrogen/98% argon atmosphere, the target product lithium manganese fluorosilicate Li ₃ MnSiO ₄ F cathode material was obtained.

Claims (7)

1. A positive electrode material lithium manganese fluorosilicate, characterized in that the chemical formula of the material is Li ₃ MnSiO ₄ F. 2. a preparation method of positive electrode material lithium manganese fluorosilicate, is characterized in that, comprises the following steps: (1) Weigh a certain amount of lithium source, manganese source and silicon source compound into deionized water, mix and disperse to obtain a dispersion liquid, add a certain amount of fluorine source compound into the above dispersion liquid, continue stirring for a period of time, and transfer it to high pressure reaction The kettle is closed for hydrothermal reaction at 120-200℃ for 12-72h, taken out after natural cooling, dried and ground to obtain the precursor; (2) The above-mentioned precursor is placed in a heating device, heated to 400-750° C. under a protective gas atmosphere for 2-12 hours, and then the target product Li ₃ MnSiO ₄ F material is obtained. 3. the preparation method of a kind of cathode material lithium manganese fluorosilicate as claimed in claim 2, it is characterized in that the lithium source, manganese source, silicon source and fluorine source compound mol ratio described in step (1) are Li: Mn : Si : F = (1.95~2.15) : 1 : 1:1. 4 . The method for preparing a positive electrode material lithium manganese fluorosilicate according to claim 2 , wherein the lithium source compound described in step (1) is lithium hydroxide, lithium carbonate, lithium acetate, and lithium chloride. 5 . , one or more mixtures in lithium nitrate, lithium phosphate, lithium oxalate; the manganese source compound is manganese oxalate, manganese acetate, manganese chloride, manganese phosphate, manganese nitrate, manganese dioxide, manganese tetroxide one or more mixtures; the silicon source compound is one or more mixtures in ethyl orthosilicate or methyl orthosilicate; the fluorine source compound is lithium fluoride, ammonium fluoride of one or several mixtures. 5 . The method for preparing a cathode material lithium manganese fluorosilicate according to claim 2 , wherein the stirring time is continued for 30-120 min after adding the fluorine source compound in step (1). 6 . 6 . The method for preparing a positive electrode material lithium manganese fluorosilicate according to claim 2 , wherein the heating device described in step (2) is a closed box furnace, a tubular furnace or a microwave tube furnace. 7 . furnace. 7 . The method for preparing a positive electrode material lithium manganese fluorosilicate according to claim 2 , wherein the protective gas described in step (2) is one of nitrogen, argon, helium, and hydrogen or Several mixed gases.

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