CN113725428B - A kind of Na and Cl co-doped lithium ion negative electrode material and preparation method thereof - Google Patents

Abstract

The invention disclosesA Na and Cl codoped lithium ion negative electrode material and its preparing process are disclosed, which is prepared through CH ₃ COOLi、NaCl、CH ₃ And preparing a precursor from COOH and tetrabutyl titanate, and calcining to obtain the co-doped lithium titanate material. The cation doping can enlarge the lithium layer spacing of the lithium titanate, increase the lithium ion diffusion rate and is beneficial to improving the material capacity. Anion doping improves electron conductivity significantly. Na (Na) ⁺ Element and Cl ^‑ The co-doping of the components not only improves the capacity of the battery material, but also improves the rate capability of the material.

Description

A kind of Na and Cl co-doped lithium ion negative electrode material and preparation method thereof

technical field

The invention belongs to the technical field of lithium ion negative electrode materials, and in particular relates to a Na and Cl co-doped lithium ion negative electrode material and a preparation method thereof.

Background technique

To better cope with the increasingly serious energy crisis, lithium-ion batteries (LIBs) have begun to play an increasingly important role in energy storage and conversion. However, lithium-ion batteries currently on the market generally use graphite as the negative electrode; however, graphite has poor performance, short cycle life, and the formation of solid electrolyte interfacial film (SEI), which poses serious safety hazards. The spinel framework structure of lithium titanate (Li ₄ Ti ₅ O ₁₂ , LTO) has the characteristics of "zero strain", that is, there is almost no volume expansion and contraction during the process of lithium intercalation and deintercalation. In addition, the stable voltage plateau (1.55 V vs Li ⁺ /Li) is less likely to generate Li dendrites and forms with good cycle stability and high thermal stability. Therefore, LTO is considered as a potential anode material. However, although LTO has many advantages, it also has disadvantages such as low theoretical specific capacity (175mAh·g ^-1 ) and poor rate performance, which greatly limit its commercial development.

In order to solve the problems of low capacity and poor rate performance of lithium titanate anode materials. At this stage, it is mainly realized by ion doping. By entering anions and cations of different valence states on the Li, Ti or O positions, the valence state of the main skeleton is unbalanced, and the ion transport channel is purposely changed to increase the migration concentration of lithium ions to reduce the concentration of lithium ions. The electrochemical impedance and electrode polarization of the material are used to increase the capacity and improve the ionic conductivity of the material. For example, the patent of Publication No. CN 111916742A records a tin-carbon co-doped lithium titanate material and its preparation method and application. This technology has a specific charge and discharge capacity of 160mAh·g ^-1 for the first time at 1C, and does not improve titanate The problem of low specific capacity and rate performance of lithium. Patent 201910777416.7 describes a co-doped lithium titanate negative electrode material and its preparation method, which achieves an initial capacity of 178mAh·g ^-1 , reaching the theoretical specific capacity of LTO. At present, there has been no breakthrough in improving both the low specific capacity and poor rate performance of lithium titanate, and usually only one of the defects can be improved by ion doping.

Contents of the invention

In view of the defects existing in the prior art, the object of the present invention is to provide anion and cation co-doped Li ₄ Ti ₅ O ₁₂ negative electrode materials, and adopt the method of anion and cation co-doping to improve the capacity of Li ₄ Ti ₅ O ₁₂ while improving the rate performance.

In order to achieve the above-mentioned technical purpose, the present invention specifically adopts the following technical solutions:

An anion and cation co-doped lithium ion negative electrode material, the anion and cation are sodium ions, the anion is chloride ion, and the lithium ion negative electrode material is Li ₄ Ti ₅ O ₁₂ .

Cation doping can expand the lithium layer spacing of lithium titanate, increase the diffusion rate of lithium ions, and form impurity phases, which is beneficial to improve the capacity of the material. Anion doping can significantly improve the electronic conductivity. The co-doping of Na ⁺ elements and Cl ^- not only increases the capacity of the battery material, but also improves the rate performance of the material.

In the present invention, metal ions with similar ionic radius and chemical properties to Na ⁺ may be used to substitute an anion with similar properties to Cl ^- to achieve similar effects.

In another aspect of the present invention, the preparation method of above-mentioned co-doped lithium ion negative electrode material is provided, comprising the following steps:

1) Dissolve CH ₃ COOLi and NaCl in deionized water, stir well, add CH ₃ COOH to obtain L liquid;

2) Take tetrabutyl titanate and place it in absolute ethanol to configure T liquid;

3) Slowly add T liquid into L liquid, after strong magnetic stirring, place in a constant temperature water bath magnetic stirrer to stir;

5) Stand still to form a gel, then dry to obtain a precursor, grind the precursor, calcinate and cool to obtain a co-doped lithium titanate material.

Further, the L liquid components are: CH ₃ COOLi 3.395g, CH ₃ COOH 0.29ml, NaCl 0.5g, H ₂ O 50ml.

Further, the T liquid components are: 13ml of tetrabutyl titanate, 50ml of absolute ethanol.

Further, the condition of the constant temperature water bath is 80°C.

Further, the calcination condition is 800° C. for 8 hours.

This preparation method realizes the modification of Na ⁺ , Cl ^- co-doping in one step by adding an appropriate proportion of NaCl in the process of synthesizing the precursor. The preparation method is simple and effective, and the crystal structure and surface interface of LTO are comprehensively optimized, which greatly improves the Discharge specific capacity and rate performance. Na ⁺ doped on the Li site expands the lithium interlayer spacing, which is beneficial to promote the migration of lithium ions and improve the specific discharge capacity of the material; Cl ^- replaces the O site to increase the lattice constant, and at the same time forms a more stable Ti with Ti The -Cl bond maintains the stability of the material, and the coexistence of Ti ⁴⁺ /Ti ³⁺ in the material increases the electronic conductivity and improves the rate performance.

The beneficial effects of the present invention are:

In the present invention, Na and Cl are successfully doped into the crystal of the material, and the lattice parameters are changed without destroying the Li ₄ Ti ₅ O ₁₂ spinel crystal structure. On the one hand, the ionic radius of Na ⁺ is larger than that of Li The ionic radius of Na, the successful doping of Na, expands the lithium interlayer spacing, which is beneficial to promote the migration of lithium ions. On the other hand, the ionic radius of Cl is larger than that of O, and Cl ^- substitution will lead to the reduction of part of Ti ⁴⁺ ions to Larger Ti ³⁺ , resulting in charge compensation, leading to an increase in the lattice parameter of the sample. With the increase of the lattice parameter, the insertion/extraction path of Li ⁺ becomes wider, which is beneficial to increase the migration concentration of lithium ions. Improve the diffusion coefficient of Li ⁺ . It can effectively improve the capacity and rate performance of the Li ₄ Ti ₅ O ₁₂ negative electrode material.

Description of drawings

Figure 1 is an electron microscope image of LTO and the co-doped Li ₄ Ti ₅ O ₁₂ negative electrode material of the present invention; a is LTO, b is co-doped Li ₄ Ti ₅ O ₁₂ ;

Fig. 2 is the cycle performance figure of LTO and the co-doped Li ₄ Ti ₅ O ₁₂ negative electrode material of the present invention;

Fig. 3 is a rate performance graph of LTO and the co-doped Li ₄ Ti ₅ O ₁₂ negative electrode material of the present invention.

detailed description

The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Apparently, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example 1

This example provides a method for preparing anion and cation co-doped Li ₄ Ti ₅ O ₁₂ negative electrode materials.

1) Use an electronic balance to weigh 3.395g of CH ₃ COOLi and 0.5g of NaCl, dissolve the weighed CH ₃ COOLi and NaCl in 50ml of deionized water, stir at room temperature for ten minutes, and then add 0.29 ml of CH ₃ COOH, prepared as L liquid.

2) Take 13ml of tetrabutyl titanate with a pipette gun and add it to 50ml of absolute ethanol to prepare T liquid.

3) Slowly add liquid T into liquid L to obtain a mixed liquid, and stir the mixed liquid with strong magnetic force for 20 minutes to avoid precipitation.

4) Transfer the uniformly stirred mixed solution to a magnetic stirrer in a constant temperature water bath, stir at a constant temperature of 80° C. for 40 minutes, take it out and let it stand to form a gel.

5) Transfer the gel to an 80°C constant temperature blast drying oven to dry to obtain a precursor, grind the obtained precursor into powder, calcinate in a muffle furnace at 800°C for 8 hours, and take it out after cooling to room temperature with the furnace to obtain a co-doped Heterolithium titanate material.

Example 2

The LTO negative electrode material and the co-doped lithium titanate material prepared in Example 1 were scanned by an electron microscope, and the results are shown in Figure 1. The left picture is LTO, and the right picture is Na and Cl co-doped LTO. It can be seen that The LTO primary particles aggregate together to form larger agglomerates, while the particle size of the material after co-doping is significantly reduced and the distribution is uniform.

Example 1 Na and Cl were successfully doped into the crystal of the material, and the lattice parameters were changed without destroying the Li ₄ Ti ₅ O ₁₂ spinel crystal structure, the successful doping of Na ⁺ expanded the The distance between lithium layers is conducive to promoting the migration of lithium ions. The NaLiTi ₃ O ₇ impurity phase appears in Na and Cl co-doped LTO, and the existence of NaLiTi ₃ O ₇ phase is conducive to improving the capacity of the material. The ionic radius of Cl ^- is larger than that of O, and the substitution of Cl ^- will lead to the reduction of some Ti ⁴⁺ ions to larger Ti ³⁺ , which will result in charge compensation and increase the lattice parameter of the sample. With the increase of the lattice parameter As , the intercalation/extraction path of Li ⁺ becomes wider, which is beneficial to increase the migration concentration of lithium ions and improve the diffusion coefficient of Li ⁺ . It can effectively improve the capacity and rate performance of the Li ₄ Ti ₅ O ₁₂ negative electrode material.

Example 3

Weigh 0.08g of the co-doped lithium titanate material of Example 1, mix and grind 0.01g of acetylene black and 0.01g of polyvinylidene fluoride (dissolved in N-methylpyrrolidone) to form a slurry, and evenly coat it on the copper foil. Dry it in a vacuum oven at 110°C to obtain pole pieces, and use metal lithium as a counter electrode to assemble into a button battery in a glove box. Carry out charge and discharge and cycle tests on the blue electric test system.

As shown in Figure 2, in the 1.0-2.5V, 0.2C long cycle, the first-cycle discharge capacity of LTO is 158.5mAh·g ^-1 , and the first-cycle discharge capacity of NC-LTO in Example 1 is 295.9mAh·g ^-1 , Much higher than the theoretical specific capacity of 175mAh·g ^-1 of Li ₄ Ti ₅ O ₁₂ .

As shown in Figure 3, the rate performance diagrams at different rates of 0.2, 0.5, 1, 2, 5, and 10C. At 0.2C, the specific discharge capacity of the LTO sample is 147.8mAh·g ^-1 and 58.1mAh at 10C. • g ⁻¹ . The specific discharge capacity of NC-LTO sample is 268.4mAh·g ^-1 at 0.2C and 149.4mAh·g ^-1 at 10C. It shows that the co-doping of Na ⁺ element and Cl ^- in the present invention can not only increase the capacity of the battery material, but also improve the rate performance of the material.

Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variants, the scope of the invention is defined by the appended claims and their equivalents.

Claims (3)

1. The preparation method of the negative electrode material of the anion-cation co-doped lithium ion battery is characterized in that the cation is selected from sodium ions, the anion is selected from chloride ions, and the negative electrode material of the lithium ion battery is Li ₄ Ti ₅ O ₁₂ ；

The preparation method comprises the following steps:

(1) Weighing CH ₃ Dissolving COOLi and NaCl in deionized water, stirring, and adding CH ₃ COOH to obtain L liquid;

(2) Placing tetrabutyl titanate in absolute ethyl alcohol to prepare a T liquid;

(3) Slowly adding the liquid T into the liquid L, stirring by strong magnetic force, and then placing the mixture into a constant-temperature water bath magnetic stirrer for stirring;

the L liquid component is: CH (CH) ₃ COOLi3.395g，CH ₃ COOH0.29ml, naCl0.5g and deionized water 50ml;

the T liquid comprises the following components: 13ml of tetrabutyl titanate and 50ml of absolute ethyl alcohol;

(4) And (4) standing the product obtained in the step (3) to form gel, drying to obtain a precursor, grinding the precursor, calcining and cooling to obtain the anion and cation co-doped lithium ion battery cathode material.

2. The method for preparing according to claim 1, wherein the constant temperature water bath condition is 80 ℃.

3. The method according to claim 1, wherein the calcination conditions are 800 ℃ for 8h.

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