CN105742607A - Method for improving initial coulomb efficiency of lithium-rich cathode material - Google Patents

Abstract

The invention provides a method for improving the first coulombic efficiency of a lithium-rich positive electrode material, which is characterized by comprising the following steps: step 1: preparing a solution containing metal ions; step 2: coating the surface of the lithium-rich positive electrode material with a layer of A lithium-containing or low-lithium compound; step 3: heat-treating the lithium-rich cathode material coated with a lithium-free or low-lithium compound to obtain a pre-delithiated modified cathode material. The invention has the advantages of simple preparation process, low cost and wide application prospect, and the first coulombic efficiency of the prepared modified lithium-rich positive electrode material is greatly improved, and simultaneously has good rate performance and good cycle performance.

Description

A method to improve the first coulombic efficiency of lithium-rich cathode materials

technical field

The invention relates to the technical field of lithium-ion battery materials, in particular to a modification method for improving the first coulombic efficiency of a lithium-rich positive electrode material.

Background technique

Since the industrial revolution, human material civilization has developed rapidly, and the demand for energy is increasing day by day. Based on the limitation of fossil fuel resources and the environmental costs brought about by their use (greenhouse effect, PM2.5, etc.), people are forced to look for other clean and renewable energy sources, such as hydropower, solar power and wind power. However, the above-mentioned clean and renewable energy is greatly affected by external factors (for example, solar power generation is greatly affected by weather conditions such as seasons, day and night, and cloudy or sunny), and cannot continuously and stably generate power, such as with energy storage devices (energy storage and peak shaving, etc.) Combined use can realize stable and continuous external power supply. In addition, at the end of energy use (3C products and electric vehicles, etc.), energy storage devices are required to be used together. Lithium-ion batteries, as an important energy storage device, have received worldwide attention and research. Compared with other traditional chemical power sources (such as lead-acid batteries, nickel-metal hydride batteries, etc.), lithium-ion batteries have remarkable characteristics such as high energy density, high power density, long cycle life and environmental friendliness, thus becoming the most promising environment-friendly secondary battery .

At present, the capacity of commercial anode materials is about 300-400mAhg ^-1 , and the capacity of alternative materials in the research stage is as high as about 1000-2000mAhg ^-1 . However, the actual discharge specific capacity of commercial cathode materials is below 200mAhg ^-1 , so it is urgent to find a cathode material with higher capacity. In 1999, Johnson et al. used a weak acid leaching method to extract part of Li ₂ O from the Li ₂ MnO ₃ phase, and for the first time obtained LiMnO ₂ (Li _{2 -x} MnO _{3 -x/2} , where 0<x<2). The lithium-rich manganese-based material xLi ₂ MnO ₃ ·(1-x)LiMO ₂ (M=Mn, Co, Ni, Al, etc.) has a capacity of up to 250-300mAhg ^-1 , which is much higher than the capacity of existing commercial battery cathode materials At the same time, the proportion of manganese in lithium-rich manganese-based materials is relatively large, which further reduces the cost of materials, thus becoming a research hotspot of high-capacity lithium-ion cathode materials. However, lithium-rich manganese-based materials have problems such as poor electron/lithium ion transport ability, poor cycle performance, voltage attenuation, and manganese dissolution, especially the low Coulombic efficiency for the first time, which hinders the commercial application of lithium-rich cathode materials. Therefore, it is necessary to study the modification of lithium-rich manganese-based materials.

Different acidic salt solutions or weak acids are used to treat lithium-rich manganese-based materials to remove part of the lithium in the material in order to reduce its first irreversible capacity, but this method is easy to destroy the surface structure of the material, and the Li ⁺ in the material It will also undergo a substitution reaction with H ⁺ in the solution, resulting in the collapse of the layered structure of the material, which in turn makes its cycle performance significantly worse.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art, and to provide a modification method for improving the first Coulombic efficiency of lithium-rich cathode materials with simple preparation process, low cost and wide application prospects. The positive electrode material has both high reversible capacity and good rate performance.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A method for improving the first coulombic efficiency of a lithium-rich positive electrode material, characterized in that it comprises the following steps:

Step 1: preparing a solution containing metal ions;

Step 2: Dispersing the lithium-rich cathode material into the solution containing metal ions, removing the solvent therein to coat the surface of the lithium-rich cathode material with a compound that does not contain lithium or has a low lithium content;

Step 3: heat-treating the lithium-rich cathode material coated with a lithium-free or low-lithium compound to obtain a pre-delithiated modified cathode material.

Preferably, the lithium-rich cathode material is specifically Li _1+x Ni _a Co _b Mn _(1-abx) O ₂ , where 0<x<1, 0≤a≤1, 0≤b≤1, 0≤ a+b≤1.

Preferably, the lithium content of the low-lithium content compound is lower than that of the lithium-rich cathode material.

Preferably, there are more than one type of metal ions in the solution containing metal ions.

Preferably, the metal ion is at least one of aluminum ion, magnesium ion, zinc ion and zirconium ion.

Preferably, the solvent of the solution containing metal ions is water, ethanol or a mixture of water and ethanol in a certain proportion.

Preferably, the total metal ion concentration of the metal ion-containing solution is controlled below the saturation concentration.

Preferably, the method of "removing the solvent therein to coat a layer of lithium-free or low-lithium content compound on the surface of the lithium-rich positive electrode material" is a solvent evaporation method, a sol-gel method, a spray drying method or a spray drying method. Pyrolysis.

More preferably, the solvent evaporation method includes: dispersing the lithium-rich positive electrode material into the above-mentioned solution containing metal ions, controlling an appropriate amount of solid content, maintaining the temperature of the system at 40-100°C under stirring conditions, passing the solvent Evaporation coats a layer of lithium-free or low-lithium compound on the surface of the lithium-rich cathode material.

More preferably, the solid content is controlled at 2-80%.

Preferably, the heat treatment is calcination at 400-1200° C. for 1-40 hours.

Preferably, the lithium-rich positive electrode material coated with a lithium-free or low-lithium content compound has a mass ratio of 1:1 to 1:100 between the lithium-free or low-lithium content compound and the lithium-rich positive electrode material .

The present invention also provides a pre-delithiated modified cathode material prepared by the method for improving the first coulombic efficiency of the lithium-rich cathode material.

Compared with the prior art, the beneficial effect of the present invention is that by uniformly coating a layer of lithium-free or a small amount of lithium-containing compound on the surface of the lithium-rich positive electrode material, after proper heat treatment, the material structure can be The pre-delithiation of the matrix material is realized, so that the cycle performance of the lithium-rich cathode material can be improved while improving the first Coulombic efficiency of the lithium-rich cathode material. In summary, the electrochemical performance of the cathode material has been greatly improved, making up for the inability of conventional lithium-rich cathode materials to take into account both the first Coulombic efficiency and cycle performance, which is conducive to promoting the commercialization of high-capacity cathode materials for lithium-ion batteries. The invention has the advantages of simple preparation process, low cost and wide application prospect, and the first coulombic efficiency of the prepared modified lithium-rich positive electrode material is greatly improved, and simultaneously has good rate performance and good cycle performance.

Description of drawings

FIG. 1 is an XRD pattern of the modified lithium-rich cathode material prepared in Example 1 of the present invention.

Fig. 2 is a comparison chart of the initial charge and discharge performance of the modified lithium-rich cathode material prepared in Example 1 of the present invention and the pure-phase lithium-rich cathode material.

Fig. 3 is a comparison chart of cycle performance of the modified lithium-rich positive electrode material prepared in Example 1 of the present invention and the pure phase lithium-rich positive electrode material at a current of 250 mAg ^-1 .

detailed description

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

All percent concentrations in the present invention are weight percent concentrations unless otherwise specified.

Example 1:

A method for improving the first coulombic efficiency of lithium-rich positive electrode materials, the specific steps are:

(1) preparation contains the solution of metal ion: the zirconium nitrate solution of 2mol/L is prepared as raw material with the nitrate of zirconium and deionized water;

(2) Coating a lithium-free compound on the surface of the lithium-rich cathode material by solvent evaporation: weigh an appropriate amount of pure-phase lithium-rich cathode material Li _1.2 Mn _0.54 Ni _0.13 Co _0.13 O ₂ , and use mechanical stirring and ultrasonic dispersion to Method Disperse it evenly in the zirconium nitrate solution, control the solid content to 20%, maintain the system temperature at 90°C under appropriate stirring intensity, and remove the solvent by solvent evaporation to uniformly coat a layer on the surface of the lithium-rich cathode material Zirconium nitrate, the mass ratio of surface-coated zirconium nitrate to lithium-rich cathode material is 1:5;

(3) Heat treatment: calcining at 700° C. for 5 hours to obtain a lithium-rich cathode material after pre-delithiation modification.

The electrochemical properties of the cathode materials before and after modification were tested by button cells. The smear was weighed according to active substance: PVDF: acetylene black = 8:1:1 (mass ratio), and the test electrode was a disc with a diameter of about 14 mm. After the assembled battery was left to stand for 12 hours, various electrochemical performance tests were performed, and the charge and discharge voltage was between 2.5-4.6V.

The XRD pattern of the prepared modified lithium-rich cathode material is shown in Figure 1. In the XRD pattern of the modified lithium-rich cathode material, the diffraction peak of Li ₂ ZrO ₃ appears, which also proves that the lithium-rich cathode material in the matrix Part of the lithium ions pre-extracted into the cladding layer. The initial charge-discharge curves of the prepared modified lithium-rich cathode material and the pure-phase lithium-rich cathode material are shown in Figure 2. When the initial charge-discharge current is 12.5mAg ^-1 , the first Coulombic efficiency of the pure-phase cathode material is 71.3%, while the first coulombic efficiency of the lithium-rich cathode material after pre-delithiation modification was increased to 91.2%. The comparison chart of the cycle performance of the prepared modified lithium-rich cathode material and the pure-phase lithium-rich cathode material at a current charge and discharge of 250mAg ^-1 , as shown in Figure 3, shows that the capacity retention of the pure-phase lithium-rich cathode material after 100 cycles is 49%, while the cycle stability of the lithium-rich cathode material after pre-delithiation modification has been significantly improved, and the capacity retention rate after 100 cycles is as high as 92%.

Example 2:

A method for improving the first coulombic efficiency of lithium-rich positive electrode materials, the specific steps are:

(1) preparation contains the solution of metal ion: with magnesium nitrate, aluminum nitrate, deionized water and ethanol as raw material, the mol ratio of magnesium element and aluminum element is controlled at 1: 1, and the volume ratio of deionized water and ethanol is 5: 1. Prepare a solution with a total metal ion concentration of 0.5mol/L;

(2) Coating a lithium-free compound on the surface of the lithium-rich cathode material by spray drying: Weigh an appropriate amount of pure-phase lithium-rich cathode material Li _1.2 Mn _0.4 Ni _0.4 O ₂ , and mix it with mechanical stirring and ultrasonic dispersion. It is uniformly dispersed in the solution, using polyacrylamide (molecular weight about 10 million, anionic) as a dispersant, the amount of dispersant is 3% of Li _1.2 Mn _0.4 Ni _0.4 O ₂ ), and the solid content is controlled to be 5 %, and then the mixture was spray-dried at 150° C. to remove the solvent to coat a layer of magnesium-aluminum compound on the surface of the lithium-rich positive electrode material, and the mass ratio of the surface coating material to the lithium-rich positive electrode material was 1:7.

(3) Heat treatment: calcining at 900° C. for 3.5 hours to obtain a lithium-rich positive electrode material modified by pre-delithiation.

The electrochemical performance of the cathode material after pre-delithiation modification was tested by a button cell. The smear was weighed according to active substance: PVDF: acetylene black = 8:1:1 (mass ratio), and the test electrode was a disc with a diameter of about 14 mm. After the assembled battery was left to stand for 12 hours, various electrochemical performance tests were performed, and the charge and discharge voltage was between 2.5-4.6V. At the initial charge-discharge current of 12.5mAg ^-1 , the initial Coulombic efficiency is 95%. At 250mAg ^-1 , the discharge capacity is 180mAhg ^-1 , and the capacity retention rate after 100 cycles is 96%.

Example 3:

A method for improving the first coulombic efficiency of lithium-rich positive electrode materials, the specific steps are:

(1) Prepare a solution containing metal ions: use zinc chloride, aluminum nitrate, zirconium nitrate and ethanol as raw materials, the molar ratio of zinc, aluminum, and zirconium elements is controlled at 2:1:1, and the total metal ion concentration of the preparation is 0.6 mol/L solution;

(2) Coating a lithium-free compound on the surface of the lithium-rich cathode material by solvent evaporation: Weigh an appropriate amount of pure-phase lithium-rich cathode material Li _1.2 Mn _0.5 Ni _0.2 Co _0.1 O ₂ , and use mechanical stirring and ultrasonic dispersion to The method is to uniformly disperse it into the solution, using polyacrylamide (molecular weight of about 7 million, cationic) as a dispersant, and the amount of dispersant is 10% of Li _1.2 Mn _0.5 Ni _0.2 Co _0.1 O ₂ ), Control the solid content to 55%, maintain the system temperature at 50°C under appropriate stirring intensity, and obtain a lithium-rich positive electrode material coated with a zinc-aluminum-zirconium compound on the surface through solvent evaporation. The mass ratio of the surface coating material to the lithium-rich positive electrode material is 2:3, and then calcined at 800°C for 4 hours to obtain a lithium-rich positive electrode material modified by pre-delithiation.

The electrochemical performance of the cathode material after pre-delithiation modification was tested by a button cell. The smear was weighed according to active substance: PVDF: acetylene black = 8:1:1 (mass ratio), and the test electrode was a disc with a diameter of about 14 mm. After the assembled battery was left to stand for 12 hours, various electrochemical performance tests were performed, and the charge and discharge voltage was between 2.5-4.6V. At the initial charge-discharge current of 12.5mAg ^-1 , the first Coulombic efficiency is 93%. At 250mAg ^-1 , the discharge capacity is 185mAhg ^-1 , and the capacity retention rate after 100 cycles is 98%.

The above descriptions are only preferred implementations of the present invention, and the scope of protection of the present invention is not limited to the above examples. For those skilled in the art, improvements and transformations obtained without departing from the technical concept of the present invention should also be regarded as the protection scope of the present invention.

Claims (10)

1. A method for improving the first coulombic efficiency of a lithium-rich cathode material, comprising the following steps: Step 1: preparing a solution containing metal ions; Step 2: Dispersing the lithium-rich cathode material into the solution containing metal ions, removing the solvent therein to coat the surface of the lithium-rich cathode material with a compound that does not contain lithium or has a low lithium content; Step 3: heat-treating the lithium-rich cathode material coated with a lithium-free or low-lithium compound to obtain a pre-delithiated modified cathode material. 2. The method for improving the first coulombic efficiency of lithium-rich positive electrode materials according to claim 1, wherein the lithium-rich positive electrode material is specifically Li _1+x Ni _a Co _b Mn _(1-abx) O ₂ , wherein , 0<x<1, 0≤a≤1, 0≤b≤1, 0≤a+b≤1. 3. The method for improving the first Coulombic efficiency of lithium-rich positive electrode materials according to claim 1, wherein the metal ion is at least one of aluminum ions, magnesium ions, zinc ions and zirconium ions. 4. The method for improving the first coulombic efficiency of lithium-rich cathode materials as claimed in claim 1, wherein the solvent of the solution containing metal ions is water, ethanol or a mixture of water and ethanol in a certain proportion. 5. The method for improving the first coulombic efficiency of lithium-rich positive electrode materials as claimed in claim 1, wherein said "removing the solvent therein to coat a layer of lithium-free or low-lithium lithium-rich positive electrode materials on the surface of the lithium-rich positive electrode material The method of "compound of content" is solvent evaporation method, sol-gel method, spray drying method or spray pyrolysis method. 6. The method for improving the first coulombic efficiency of lithium-rich cathode materials as claimed in claim 1, wherein the solvent evaporation method comprises: dispersing lithium-rich cathode materials into the above-mentioned solution containing metal ions, controlling an appropriate amount of Under stirring conditions, maintain the system temperature at 40-100°C, and coat a layer of lithium-free or low-lithium-content compounds on the surface of the lithium-rich positive electrode material through solvent evaporation. 7. The method for improving the first coulombic efficiency of lithium-rich positive electrode materials according to claim 6, wherein the solid content is controlled at 2-80%. 8 . The method for improving the first Coulombic efficiency of lithium-rich cathode materials according to claim 1 , wherein the heat treatment is calcination at 400-1200° C. for 1-40 hours. 9. The method for improving the first coulombic efficiency of lithium-rich cathode materials according to claim 1, wherein the lithium-rich cathode materials coated with lithium-free or low-lithium content compounds do not contain lithium or have low lithium content. The mass ratio of the lithium content compound to the lithium-rich cathode material is between 1:1 and 1:100. 10. The pre-delithiated modified cathode material prepared by the method for improving the first coulombic efficiency of the lithium-rich cathode material according to any one of claims 1-9.