Background
The lithium ion power battery is a core part of the new energy automobile, and the quality of the performance of the lithium ion power battery is directly related to the smooth popularization of the new energy automobile and the future of the new energy automobile industry. And the wide new energy automobile market can also drive the explosion development of the lithium ion battery industry.
The anode material is used as an important component of the lithium ion battery, and the performance of the anode material is important for the performance of the lithium ion battery. Among various cathode materials, the ternary cathode material has become the first choice cathode material for lithium ion power batteries for new energy vehicles (especially passenger vehicle types) due to its high energy density, and has also become the development focus in the industry at present.
In view of the service life of conventional fuel-powered vehicles and the cost of batteries, batteries for new energy vehicles are generally required to have a cycle life of at least 3000 times or more. In addition, the automobile may need to endure exposure to sunlight at high temperature in summer, and may need to be in a fully charged standby state for a long time so as to be used at any time. Therefore, the lithium ion battery for the new energy automobile has high requirements on the cycle life and the storage life of the anode material. Research shows that one main reason influencing the cycle performance and the storage performance of the ternary material is the degradation of the surface of the material, but not the damage of the bulk structure of the material. The degradation comprises phase transition of the material surface, dissolution of transition metal ions, oxidation of electrolyte by high-valence transition metal ions in a release state, and corrosion of the material surface by hydrogen fluoride which is a decomposition product of lithium salt.
To address this problem, the conventional approach is to coat oxide materials, such as: al (Al)2O3、ZrO2And TiO2And the contact between the anode material and the electrolyte is reduced, so that the surface stability of the material is improved, and the cycle performance of the material is improved. However, as a decomposition product of the electrolyte, hydrogen fluoride also corrodes the oxide coated on the surface of the ternary material to generate a loose and porous metal fluoride, so that the surface of the positive electrode material is unprotected, and the modification effect of the oxide coating is affected. Therefore, in order to improve the stability of the coating layer and further improve the cycle performance and the storage performance of the ternary material, the metal fluoride coating capable of resisting HF corrosion becomes an effective coating modification method.
At present, the metal fluoride coating modification method mainly comprises the following steps:
1. the combined liquid phase precipitation-heat treatment process is adopted. Such as CN201210038229.5, 201310414823.4, CN201410401724.7 and CN 201510262219.3.
2. By dry mixing-thermal treatment process of fluorine-containing precursor and the like. Such as CN201410208783.2, CN 201410208876.5.
3. The metal fluoride coating modification of the positive electrode material is carried out by heat treatment after grinding of the metal fluoride-positive electrode material. Such as CN201510050462.9, CN 201510843893.0.
However, these processes have drawbacks such as the possibility of generating highly corrosive HF gas, the use of fluorine-containing reagents which are easily decomposed to generate hydrogen fluoride, or the lack of uniformity of coating.
Therefore, it is necessary to develop a new metal fluoride coating process for coating the ternary positive electrode material of the lithium ion battery with metal fluoride, so as to further improve the cycle and storage performance of the ternary material.
Disclosure of Invention
The invention mainly aims to provide a metal fluoride coated ternary material and a preparation method thereof, which can improve the cycle performance and the storage performance of a positive electrode material.
The invention relates to a preparation method of a metal fluoride coated ternary material, which comprises the following steps:
adding the ternary material into ball milling equipment, wherein the ball milling equipment comprises ball milling beads, metal fluoride is attached to the inner wall of the ball milling equipment and/or the ball milling beads, and ball milling is carried out at a second rotating speed, and the ball milling time is a second time;
repeating the above operation for a plurality of times so that the ternary material contains 0.1 to 0.5 weight percent of metal fluoride.
Preferably, the ball milling apparatus attaches the metal fluoride by:
adding metal fluoride into ball milling equipment, and carrying out ball milling at a first rotation speed for a first time period, so that a layer of metal fluoride is attached to ball milling beads and the inner surface of the equipment, and metal fluoride powder which is not attached is separated.
Preferably, the step of separating the unattached metal fluoride powder comprises:
and separating the metal fluoride powder and the ball milling beads in a sieving mode, and pouring the ball milling beads back to the ball milling tank after separation.
Preferably, the metal fluoride is AlF3,ZrF4,MgF2One or more of (a).
Preferably, the first rotating speed is 500-.
Preferably, the mass ratio of the ball milling beads to the added metal fluoride is 5:1-20: 1.
Preferably, the ternary material comprises LiNi1-x-yCoxMnyO2Or a dopant thereof, x + y<1,x>0,y>0。
Preferably, the second rotating speed is 50-300 r/min, and the second time period is 20-35 min.
Preferably, the mass ratio of the ball milling beads to the ternary material is 10:1-20: 1.
Preferably, the number of the repeated operations is 20 to 30 times.
The invention also provides a metal fluoride coated ternary material prepared by any one of the preparation methods.
The invention provides a metal fluoride coated ternary material and a preparation method thereof. The invention avoids adopting a wet process to coat fluoride, does not need to use a fluoride precipitator, does not corrode the anode material, and has lower requirement on corrosion resistance of equipment. By adopting the preparation method of the ternary material coated by the metal fluoride, the ternary anode material can be coated by the nano-scale metal fluoride particles. The preparation method is simple and efficient, has operability, and is suitable for large-scale industrial production. The obtained metal fluoride-coated ternary material improves the cycle performance and the storage performance of the anode material.
Detailed Description
It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The embodiment of the invention provides a preparation method of a metal fluoride coated ternary material, which comprises the following steps:
adding the ternary material into ball milling equipment, wherein the ball milling equipment comprises ball milling beads, metal fluoride is attached to the inner wall of the ball milling equipment and/or the ball milling beads, and ball milling is carried out at a second rotating speed, and the ball milling time is a second time;
repeating the above operation for a plurality of times so that the ternary material contains 0.1 to 0.5 weight percent of metal fluoride.
In this embodiment, a ternary positive electrode material of a certain mass is placed in a ball milling device that has been ball milled with a metal fluoride, ball milling is started at a second rotation speed, and after a second duration of ball milling, a ternary material coated with a small amount of metal fluoride can be obtained. The general formula of the ternary cathode material is LiNi1-x-yCoxMnyO2,x+y<1,x>0,y>0. The ternary material may be doped and coated in other ways, or may be undoped and coated. In practical application, LiNi1-x-yCoxMnyO2May not meet the actual requirement, therefore, other elements such as molybdenum oxide and the like are doped on the basis of the LiNi to form LiNi1-x-yCoxMnyO2And (3) doping. The metal fluoride may be AlF3,ZrF4,MgF2One or more of (a). The second speed may be 50-300 rpm and the second duration may be 20-35 min. The mass ratio of the ball milling beads to the ternary material is 10:1-20: 1. The material of the ball milling beads can be alumina or zirconia. Ball milling can be carried out by using ball milling beads with different particle sizes. The ball milling bead particle size may be 1-10 mm. Taking the example of using two ball milling beads with different particle sizes, the mass ratio of the sizes of the ball milling beads to the particle sizes can be 1:1-4: 1.
The above steps are repeated for many times, and the metal fluoride coating amount of the ternary material can be increased each time until the ternary material contains 0.1-0.5 wt% of metal fluoride. In one embodiment, the number of the repeated operations is 20-30 times.
In one embodiment, the ball milling apparatus attaches the metal fluoride by:
adding metal fluoride into ball milling equipment, and carrying out ball milling at a first rotation speed for a first time period, so that a layer of metal fluoride is attached to ball milling beads and the inner surface of the equipment, and metal fluoride powder which is not attached is separated. The first rotation speed may be 500-700 rpm and the first time period may be 20-30 min. The mass ratio of the ball milling beads to the metal fluoride may be 5:1 to 20: 1. The amount of fluoride added may be 5 to 30 g.
In one embodiment, the step of separating the unattached metal fluoride powder comprises:
and separating the metal fluoride powder and the ball milling beads in a sieving mode, and pouring the ball milling beads back to the ball milling tank after separation. Thus, the metal fluoride powder is adhered to the inside of the ball milling apparatus and the ball milling beads used. However, the amount of the metal fluoride powder should not be too large, so that the metal fluoride powder cannot form a coating on the surface of the ternary material.
The method provided by the invention obtains the metal fluoride coated and modified ternary cathode material through a very simple and efficient method. First, the fluoride material may be coated on the surface of the positive electrode material as nano-sized particles, thereby improving the coating uniformity and effect of the dry coating.
Secondly, the ternary anode material coated by the metal fluoride prepared by the method avoids the direct contact of the anode material and the electrolyte, thereby reducing the dissolution of transition metal ions, slowing down the oxidation of the anode material to the electrolyte in a charging state, and relieving the corrosion of hydrofluoric acid and the like generated by the decomposition of lithium salt in the electrolyte to the anode, and further playing a role in protecting the anode material. And the fluoride coating layer can not be corroded by hydrofluoric acid, so that the stability and the durability of the coating layer are ensured, and the cycle performance, the storage performance and the like of the modified cathode material are further improved.
Meanwhile, in the ball milling process, the tip protrusions in the ternary positive electrode material particles can be milled off, or the metal fluoride can be coated on the parts more. These tip projections, which have higher activity, are less stable, and are more likely to strip lithium ions during charging, result in a deeper delithiation state relative to the bulk material, thereby affecting the overall properties of the material, such as stability, etc. Therefore, the ball milling process can remove the tip protruding parts in the ternary cathode material particles and coat more, so that the performance of the cathode material can be further improved.
The preparation method of the metal fluoride coated ternary material provided by the invention also has the following characteristics:
1. to minimize the particle size of the fluoride coating material and to maximize the uniformity of the coating
2. The control of the coating amount of the metal fluoride can be realized by controlling the ball milling time, the ball milling strength and the like, and the ternary cathode material with different coating amounts of the metal fluoride is prepared;
3. the preparation process is simple and feasible, the flow is short, the equipment processing capacity is strong, and the method is suitable for industrial production;
4. the whole preparation process belongs to a dry process, does not relate to wet treatment and has little pollution to the environment.
The invention also provides a metal fluoride coated ternary material prepared by any one of the preparation methods.
Example 1
Step 1, putting 18g of aluminum fluoride into ball milling equipment, for example, a QM3-SP4 planetary ball mill is adopted, the lining of the ball mill is subjected to metal isolation treatment by using a ceramic material, ball milling beads made of zirconia are used, the ball milling beads are selected to be 5mm and 1mm in particle size, the mass ratio of the large particle size ball milling beads to the small particle size ball milling beads is 1:1, the ball-material ratio is controlled to be 10:1, ball milling is carried out for 25min at the rotating speed of the ball mill of 600 revolutions per minute, a layer of metal fluoride is attached to the surfaces of the ball milling beads and the inner surface of the ball milling equipment, the rest metal fluoride powder and the ball milling beads are separated in a screening mode, and the ball milling beads are returned to a ball milling tank after separation and are used in the next working procedure.
Step 2, adding a certain mass of ternary cathode material (LiNi) according to a ball-to-material ratio of 15:10.84Co0.1Mn0.06O2) And (3) putting the metal fluoride-containing powder into ball milling equipment for ball milling of metal fluoride in the step (1), and carrying out ball milling for 25min at the rotating speed of the ball mill of 150 r/min. And separating the obtained ternary material coated with a small amount of metal fluoride and the ball milling beads in a sieving mode, and pouring the ball milling beads into a ball milling tank after separation for use in the next working procedure.
And (3) preparing another ball milling device (the same as the above) while carrying out ball milling treatment on the ternary material, and repeating the operation in the step (1) to carry out ball milling on the metal fluoride. The rotating speed of the ball mill can be the same as that of the step 1, and can also be 600 revolutions per minute for ball milling for 25 min. And after the ball milling is finished, separating the residual metal fluoride powder and the ball milling beads in a sieving mode, and pouring the ball milling beads into a ball milling tank after separation. And (3) repeating the process of the step (2) to process the ternary cathode material, and continuously increasing the metal fluoride coating amount of the ternary material.
And repeating the operation steps for 25 times to obtain the metal fluoride coated ternary material, and realizing the coating modification of the ternary cathode material. In the obtained metal fluoride-coated ternary material, the mass fraction of the metal fluoride is 0.3%. Referring to fig. 1, fig. 1 is an SEM image at 100nm of the metal fluoride-coated ternary positive electrode material of example 1.
The button half cell prepared by using the metal fluoride coated ternary cathode material of the embodiment 1 as the cathode has the capacity of 203mAh/g within the voltage range of 2.8-4.25V and the discharge rate of 0.1C (theoretical gram capacity calculated by 200 mAh/g).
The soft package battery prepared by the metal fluoride-coated ternary cathode material is subjected to electrical property test, and the direct current internal resistance of the soft package battery at 50% SOC is as follows: 15.3m omega. The product can be cycled for 2700 times (the capacity retention rate is 80%) at 25 ℃; at 45 ℃, the cycle can be 2100 times (the capacity retention rate is 80%). As shown in fig. 2, fig. 2 is a graph of cycle performance of example 1. The product can be cycled for 1100 times at 60 ℃ (capacity retention rate is 80%). The capacity retention rate is higher than 80 percent when the full storage is carried out for 14 months at the temperature of 60 ℃ and 4.2V. As shown in FIG. 3, FIG. 3 is a graph showing the change in the capacity retention ratio at 60 ℃ in example 1. At 60 ℃, the full storage at 4.2V for 120 days has the volume expansion of less than 20 percent. As shown in FIG. 4, FIG. 4 is a graph showing the change in volume expansion rate at 60 ℃ in example 1.
The procedure of examples 2-5 was as in example 1, with the specific process conditions set forth in the table below.
The invention provides a metal fluoride coated ternary material and a preparation method thereof. The invention avoids adopting a wet process to coat fluoride, does not need to use a fluoride precipitator, does not corrode the anode material, and has lower requirement on corrosion resistance of equipment. By adopting the preparation method of the ternary material coated by the metal fluoride, the ternary anode material can be coated by the nano-scale metal fluoride particles. The preparation method is simple and efficient, has operability, and is suitable for large-scale industrial production. The obtained metal fluoride-coated ternary material improves the cycle performance and the storage performance of the anode material.
The above description is only an example of the present invention, and is not intended to limit the present invention, and it is obvious to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.