CN113321244B - Preparation method and application of surface-modified layered oxide positive electrode material - Google Patents

Preparation method and application of surface-modified layered oxide positive electrode material Download PDF

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CN113321244B
CN113321244B CN202110547748.3A CN202110547748A CN113321244B CN 113321244 B CN113321244 B CN 113321244B CN 202110547748 A CN202110547748 A CN 202110547748A CN 113321244 B CN113321244 B CN 113321244B
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layered oxide
electrode material
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CN113321244A (en
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程芹
郭炳焜
陈日明
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University of Shanghai for Science and Technology
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    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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Abstract

The invention relates to a preparation method and application of a surface modified layered oxide anode material, belonging to the field of lithium ion battery anode materials. The invention can obviously improve the electrochemical performance of the layered oxide anode material under high cut-off voltage, and the 100-cycle capacity retention rate of the layered oxide anode material is improved from 14% to 78%. The modification method provided by the invention has a simple preparation process, and the surface of the layered oxide particles spontaneously generates an inert protective layer in situ in the heat treatment process, and the protective layer has good structural stability, can protect the electrode material from being corroded by HF in the electrolyte, effectively inhibits side reaction between the electrode material and the electrolyte, and remarkably improves the electrochemical cycle performance and the structural stability of the electrode material. In addition, the preparation method has low cost and can be applied to industrial large-scale modification.

Description

Preparation method and application of surface-modified layered oxide positive electrode material
Technical Field
The invention relates to the technical field of lithium ion battery anode materials, in particular to a preparation method and application of a surface-modified layered oxide anode material.
Background
The lithium ion battery is widely applied to various portable electronic devices due to the outstanding characteristics of high working voltage platform, high power density, good cycle stability, no memory effect and the like. The anode material is used as an important component of the lithium ion battery, and determines the energy density of the lithium ion battery to a great extent. Current commercial positive electrode materials can be classified into three categories according to structural differences: layered oxide materials, spinel structures, and olivine structures, wherein layered oxide positive electrode materials are sought after by numerous researchers due to high theoretical capacity and high voltage plateau. With the trend of light weight, thinness and durability of current consumer electronics, the energy density of lithium ion batteries is required to be higher and higher. A great deal of research work shows that higher specific discharge capacity can be obtained by increasing the cut-off voltage, however, the severe side reaction can be generated on the surface of the layered oxide particles in the charge-discharge cycle process under the high cut-off voltage, and the irreversible phase change can be generated on the phase structure, so that the capacity of the battery is rapidly attenuated. To this end, researchers have proposed many modification methods including surface modification, bulk doping, electrolyte optimization, and the use of functional separators, among others. Under high cut-off voltage, the surface interface side reaction of the layered oxide directly influences lithium ion transportation and the cycling stability of the lithium ion, so that the preferential surface modification of the layered oxide is crucial to the improvement of the electrochemical performance and the structural stability of the layered oxide.
The surface modification is to introduce other elements into the surface of the electrode material to optimize the surface interface structure, namely to form an external protective layer to prevent the electrode material from directly contacting with the electrolyte and inhibit the surface interface side reaction, thereby achieving the purpose of stabilizing the interface structure. Common surface modification techniques currently include deposition, wet chemical, chemical polymerization, and the like. The deposition method can accurately control the thickness and content of the coating layer, but the experiment cost is too high, so that the deposition method is difficult to be applied to large-scale modification production. The wet chemical method and the chemical polymerization method have simple operation and low cost, are modification methods suitable for large-scale production, but are difficult to ensure the uniform integrity of surface modification due to more controllable factors. Prior art (Lu, Y. -C., et al. (2009). "combining the organic of Enhanced Stability of" AlPO 4 ”Nanoparticle Coated LiCoO 2 during Cycling to High volts, chemical of Materials 21(19) 4408- 3 PO 4 The electrochemical performance is improved by the coating layer and the Al-containing solid solution modified layer, but the externally introduced modified layer is not uniform and compact enough, so that the corrosion of HF in electrolyte to the anode material cannot be completely inhibited, and the surface modified layer is easy to fall off from the particle surface after long-time circulation under high cut-off voltage.
Aiming at the problem that an external modified layer is easy to fall off in a long circulation process, researchers propose a modification method for growing the modified layer on the surface of particles in situ, the modified layer obtained by the method has high integrity and good lattice adaptability with a matrix, the corrosion of electrolyte to a positive electrode material can be effectively inhibited, and the electrochemical performance of the positive electrode material is improved. Prior work (Jeong, S., et al. (2011). "High-Performance, layred, 3D-LiCoO2 Cathodes with a Nanoscale Co 3 O 4 Coating via Chemical Etching, "Advanced Energy Materials 1(3):368- 3 O 4 The modified layer obviously improves the cycling stability of the modified sample under high cut-off voltage. In this work, in the presence of Ag + Surface O of lithium cobaltate under the chemical etching condition 2- Is oxidized into O - ，Co 3+ Charge compensated reduction to Co occurs 2+ Spontaneous generation of Co on the particle surface 3 O 4 A surface modification layer, the presence of which inhibits Co of lithium cobaltate at high cut-off voltage 4+ Dissolving out and effectively improving the electrochemical performance. However, although the method has obvious effect of improving the electrochemical performance of lithium cobaltate, the method has the defects of complicated experimental operation, limitation to laboratory research, high cost and unsuitability for large-scale production and application.
Therefore, it is important to develop a method that is simple to operate and can generate a complete modified layer on the surface of the cathode material in situ.
Disclosure of Invention
The invention aims to solve the technical problem of the prior art and provides a preparation method and application of a stable surface-modified layered oxide positive electrode material under high cut-off voltage.
The technical scheme for solving the technical problems is as follows: a preparation method of a surface modified layered oxide cathode material is characterized by comprising the following steps:
and (3) placing a proper amount of layered oxide particles in an atmosphere furnace, and carrying out heat treatment under a certain atmosphere condition to obtain the surface modified layered oxide cathode material.
Under certain atmosphere heat treatment, the interior of the anode material still has a layered structure, and an inert protective layer is spontaneously generated in the surface area, the integrity and the structural stability of the protective layer are higher, namely the surface interface area of the prepared layered oxide anode material comprises a layered oxide matrix and an inert oxygen loss layer spontaneously generated in situ.
Furthermore, the average particle size of the lamellar oxide particles is 1-20 μm.
Furthermore, the structural general formula of the layered oxide cathode material is LiNixCoyMzO 2 Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, x + y + z is 1, and M is one or more of K, Mg, Al, Ti, V, Cr, Mn, Fe, Zn and Zr.
Further, the heat treatment atmosphere is one or more of hydrogen, argon, nitrogen, ammonia, carbon monoxide and carbon dioxide. The heat treatment atmosphere does not react with the layered oxide at normal temperature.
Furthermore, the treatment temperature of the heat treatment atmosphere is 100-600 ℃, and the treatment time is 0.5-20 h.
The mechanism of the invention is as follows:
o in the interface region of the particles when the layered oxide particles are heat-treated in a predetermined atmosphere 2- Is reduced into O 2 The transition metal valence is changed in the surface interface region after escaping from the surface interface region according to the charge compensation principle, so that the particle surface region is converted into an inert protective layer containing an Fd-3m spinel structure and/or an Fm-3m rock salt structure due to oxygen loss, and the inert modified layer has good stability in the electrolyte, thereby effectively improving the electrochemical stability and the structural stability of the layered oxide cathode material under high cut-off voltage.
And the application of the surface modified layered oxide cathode material is characterized in that the surface modified layered oxide cathode material is used as a cathode material of a lithium ion battery.
The invention has the beneficial effects that:
1. according to the invention, the layered oxide particles are subjected to heat treatment in a certain atmosphere, an inert protective layer is automatically generated on the surfaces of the particles, which is different from an externally introduced coating layer, and the protective layer containing Fd-3m spinel structure and/or Fm-3m rock salt structure is generated through a certain heat treatment in-situ spontaneous reaction under a special atmosphere condition, so that the protective layer has higher uniformity and integrity. Because the structural stability of the modified layer is high, the side reaction between the electrolyte and the electrode material can be effectively inhibited, the structural stability of the surface interface of the layered oxide is improved, and the electrochemical performance under high cut-off voltage is improved;
2. the content of the in-situ generated inert protective layer is low, the thickness is about 1-20nm, and the influence on the lithium ion transportation rate in the circulation process is small;
3. the in-situ generated inert protective layer obtained by the method is uniform and compact, has good electrochemical stability, is not corroded by HF in an electrolyte under high cut-off voltage, and can obviously improve the structural stability of a lithium cobaltate positive electrode material;
4. when the modified layered oxide lithium cobaltate prepared according to the steps is subjected to long-cycle electrochemical test, the cut-off voltage interval is 3.0-4.6V, the capacity retention rate reaches 78% after 100-week cycle, and the coulombic efficiency is stable in the cycle process;
in a word, the layered oxide cathode material provided by the invention is simple in preparation process, has obviously improved cycle stability and structural stability under high cut-off voltage, and is suitable for large-scale industrial production due to low cost and simple operation.
Drawings
FIG. 1 is a TEM image of a modified cathode material prepared according to example one of the present invention;
FIG. 2 is an SEM image of a modified cathode material prepared according to a first embodiment of the invention;
FIG. 3 is an SEM image of a modified cathode material prepared according to comparative example one of the present invention;
FIG. 4 is XRD spectra of modified cathode materials prepared according to example one and comparative example one of the present invention;
fig. 5 shows long cycle stability of the modified positive electrode materials prepared in the first example and the first comparative example at a cut-off voltage of 4.6V.
Detailed Description
The principles and features of this invention are described below in conjunction with examples which are set forth to illustrate, but are not to be construed to limit the scope of the invention.
Example one
The preparation method of the surface-modified layered oxide cathode material of the embodiment includes the following steps:
taking 2g of layersLithium cobaltate (LiCoO) as a solid oxide 2 ) Placing the particles in a porcelain boat, placing the porcelain boat in a tubular furnace, introducing nitrogen to remove the original air in the tubular furnace, performing heat treatment at 300 ℃ for 0.5h in the nitrogen atmosphere, wherein the purity of the nitrogen atmosphere is more than 99%, and naturally cooling to obtain the modified layered oxide.
Specifically, the ceramic boat containing the layered oxide particles is placed in an atmosphere furnace, and the layered oxide particles are uniformly spread at the bottom of the ceramic boat, so that the particles can be effectively ensured to be completely reacted.
Example two
The present embodiment is different from the first embodiment in that the heat treatment temperature in the argon atmosphere is 200 ℃, and the other specific steps are the same as those in the first embodiment.
EXAMPLE III
The present embodiment is different from the first embodiment in that the heat treatment temperature in the hydrogen atmosphere is 400 ℃, and the remaining specific steps are the same as those in the first embodiment.
Example four
The present example is different from the first example in that the heat treatment temperature in the ammonia atmosphere is 500 ℃, and the other specific steps are the same as those of the first example.
EXAMPLE five
This example is different from the first example in that the heat treatment temperature in the carbon monoxide atmosphere is 600 ℃, and the remaining steps are the same as those in the first example.
EXAMPLE six
The present embodiment is different from the first embodiment in that the heat treatment time is 2 hours, and the remaining steps are the same as those of the first embodiment.
EXAMPLE seven
The present embodiment is different from the first embodiment in that the heat treatment time is 4 hours, and the remaining steps are the same as those of the first embodiment.
Example eight
The present embodiment is different from the first embodiment in that the heat treatment time is 8 hours, and the remaining steps are the same as those of the first embodiment
Example nine
The present embodiment is different from the sixth embodiment in that the heat treatment time is 20 hours, and the remaining steps are the same as those of the first embodiment.
Comparative example 1
2g of lithium cobaltate is put into a porcelain boat, the porcelain boat is put into a tube furnace, and the heat treatment is carried out for 0.5h at 300 ℃ under the condition of not introducing protective gas.
In the preparation process, the average particle size of the selected lamellar oxide particles is 1-20 mu m.
Test results
In order to prove that an inert oxygen loss layer is generated on the surface of the lithium cobaltate particles after heat treatment under a certain atmosphere, a TEM characterization test is performed on the first example. As can be seen from fig. 1, the interface of the surface of the lithium cobaltate particle includes a lithium cobaltate phase structure and an amorphous modification layer having a thickness of about 10 nm.
In order to observe the influence of the heat treatment under a certain atmosphere on the surface morphology of the lithium cobaltate particles, SEM tests were performed on the example one and the comparative example one. Fig. 2 shows the surface state of the modified lithium cobaltate particles in the example, and in combination with fig. 3, the comparative example shows that the particle surface has no obvious change, which indicates that the inert oxygen-loss layer obtained by surface modification has low content, less damage to the surface area and no change in the average particle size of the particles.
In order to observe the influence of the formation of the inert oxygen-deprived layer on the structure of the lithium cobaltate, fig. 4 shows XRD spectra of the modified particles of the lithium cobaltate prepared in the first example and the first comparative example, and comparing the XRD spectra with the standard PDF card shows that no other impurity phase is formed and the structure and crystallinity of the lithium cobaltate material are not changed.
In order to observe the effect of surface modification on the improvement of the electrochemical performance of lithium cobaltate, battery equipment and electrochemical cycle performance tests were performed on examples and comparative examples. The method comprises the following steps:
the positive pole piece is prepared by an active substance (the modified lithium cobaltate positive pole material prepared in the preferred embodiment of the invention), a conductive agent (acetylene black) and a binder (polyvinylidene fluoride) respectively in a ratio of 8:1: 1. Weighing all the experimental reagents, fully mixing in a defoaming machine for 30min, uniformly casting the prepared slurry on an aluminum foil, and drying in a constant-temperature oven at 70 ℃ for 6 h. Taking out and slicing after drying, and weighingDrying the pole piece in a vacuum transition bin at 100 ℃ for 10 hours after the pole piece is weighed. Corresponding battery equipment is finished in an Ar atmosphere glove box, wherein the prepared pole piece is used as a positive electrode material, the prepared lithium piece is used as a negative electrode material, the battery equipment is finished after a spring piece, a gasket and a diaphragm are assembled, 60 mu L of electrolyte is dripped in, and LiCoO for carrying out electrochemical test subsequently 2 The model number of the/Li half battery is CR 2032.
Fig. 5 is a cycle stability test at a cut-off voltage of 4.6V at room temperature of the example one and the comparative example one, and it can be seen that the capacity retention rate of the surface-modified lithium cobaltate positive electrode material after 200 cycles is 65%, and compared with the lithium cobaltate positive electrode material obtained without a certain atmosphere treatment, the electrochemical cycle stability is significantly improved. This is because the inert oxygen-loss layer has high electrochemical stability and can effectively suppress side reactions at the lithium cobaltate surface interface at a high cut-off voltage.
The first table shows the discharge specific capacity at 4.6V cutoff voltage for the first cycle and the discharge specific capacity at the fourth 1C cycle of examples one to nine and comparative example one. Under the first-cycle rate of 0.2C, the first-cycle specific discharge capacity of the lithium cobaltate positive electrode material prepared in the first embodiment is not much different from that of the first comparative example, but under the fourth-cycle rate of 1C, the specific discharge capacity is obviously improved, and compared with the lithium cobaltate positive electrode material obtained without heat treatment in a certain atmosphere, the specific discharge capacity is improved by 18%, which indicates that the in-situ generated inert oxygen-loss layer does not influence the transportation of interface lithium ions, and the structural stability of the surface interface is improved. In the ninth embodiment, the first discharge specific capacity and the fourth discharge specific capacity of the ninth embodiment are compared, when the temperature of the atmosphere heat treatment is too high, the surface structure of the lithium cobaltate particles is damaged, and when the temperature is too low, the inert oxygen-losing layer on the surface is not generated, so that the electrochemical performance cannot be effectively improved.
Table 1 shows the first cycle and fourth cycle specific discharge capacities (first three cycles of 0.2C activation and last 1C cycle) of the modified cathode materials prepared in examples one to nine and comparative example one at a 4.6V cut-off voltage.
TABLE 1
Sample name 0.2C discharge capacity (mAh g) -1 ) 1C discharge capacity (mAh g) -1 )
Example one 224 207
Example two 216.5 170.7
EXAMPLE III 225.1 185.8
Example four 211.5 167.6
EXAMPLE five 205.8 158
EXAMPLE six 224.8 187.5
EXAMPLE seven 225 173
ExamplesEight-part 218.1 174.3
Example nine 209.3 162.6
Comparative example 1 225.1 177
According to the invention, through heat treatment under a certain condition, the surface of the anode material spontaneously reacts to generate an inert protective layer, so that the electrochemical performance of the layered oxide anode material under high cut-off voltage can be remarkably improved, and the 100-circumference cycle capacity retention rate is improved from 14% to 78%. The modification method provided by the invention has a simple preparation process, and the surface of the layered oxide particles spontaneously generates an inert protective layer in situ in the heat treatment process, and the protective layer has good structural stability, can protect the electrode material from being corroded by HF in the electrolyte, effectively inhibits side reaction between the electrode material and the electrolyte, and remarkably improves the electrochemical cycle performance and the structural stability of the electrode material. In addition, the preparation method has low cost and can be applied to industrial large-scale modification.
The technical scheme and effect of the method are represented by taking lithium cobaltate as an example, but the method is not limited by the invention, and the method is also suitable for the method with the general formula of LiNixCoyMzO 2 Wherein x is 0. ltoreq. x.ltoreq.1, y is 0. ltoreq. y.ltoreq.1, z is 0. ltoreq. z.ltoreq.1, x + y + z is 1, and M is one or more of K, Mg, Al, Ti, V, Cr, Mn, Fe, Zn, and Zr.

Claims (3)

1. The preparation method of the surface modified layered oxide cathode material is characterized by comprising the following steps of:
placing a proper amount of layered oxide particles in an atmosphere furnace, and carrying out heat treatment under a certain atmosphere condition to obtain a surface modified layered oxide positive electrode material; the heat treatment atmosphere is one or more of hydrogen, argon, nitrogen, ammonia, carbon monoxide and carbon dioxide, the treatment temperature of the heat treatment atmosphere is 300 ℃ or 400 ℃, the treatment time is 0.5h, or the treatment temperature of the heat treatment atmosphere is 300 ℃ and the treatment time is 2 h;
the structural general formula of the layered oxide cathode material is LiNixCoyMzO 2 Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, x + y + z is 1, and M is one or more of K, Mg, Al, Ti, V, Cr, Mn, Fe, Zn and Zr.
2. The method for preparing a surface-modified layered oxide positive electrode material according to claim 1, wherein the average particle size of the layered oxide particles is in the range of 1 to 20 μm.
3. Use of the surface-modified, layered oxide positive electrode material according to any of claims 1 to 2 as a positive electrode material for lithium ion batteries.
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