CN115663128A - Method for reducing residual alkali on surface of high-nickel ternary electrode material through gas-liquid two-phase washing - Google Patents
Method for reducing residual alkali on surface of high-nickel ternary electrode material through gas-liquid two-phase washing Download PDFInfo
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Abstract
The invention discloses a method for reducing residual alkali on the surface of a high-nickel ternary electrode material by gas-liquid two-phase washing, which comprises the steps of introducing carbon dioxide into a mixed system of the high-nickel ternary electrode material and an alkaline detergent, stirring and washing, and carrying out solid-liquid separation to obtain a solid product; and drying the solid product, and sintering in an oxygen-containing atmosphere. The method adopts a mode of combining alkaline detergent liquid phase washing and carbon dioxide gas phase washing, greatly improves the washing and removing effect of residual alkali on the surface of the high-nickel ternary electrode material, can effectively remove a residual alkali resistance layer on the surface of the high-nickel material, improves the electronic conductivity and the ion diffusion rate, can inhibit the interface side reaction in the subsequent charge-discharge cycle process, and obviously enhances the structural thermal stability, the rate capability, the cycle stability and the safety performance of the high-nickel ternary electrode material.
Description
Technical Field
The invention relates to a method for reducing residual alkali on the surface of a high-nickel ternary cathode material, in particular to a method for reducing residual alkali on the surface of a high-nickel ternary electrode material by gas-liquid two-phase washing, and belongs to the technical field of battery materials.
Background
Lithium ion batteries are widely used in the fields of portable electronic devices, new energy vehicles, stationary energy storage, and the like because of the advantages of high energy conversion efficiency, long cycle life, environmental friendliness, and the like. As a main unit of an energy storage system of a lithium ion battery, a positive electrode material is a key factor influencing the safety performance and energy density of the battery. With the increasing demand of people, the requirements on the energy density and the production cost of the lithium ion battery are increased day by day, and the research of the lithium ion battery anode material with higher specific capacity, better cycle stability and excellent rate capability becomes a direction which is constantly pursued by researchers.
The high-nickel NCM ternary layered positive electrode material (the nickel content is more than or equal to 60 percent) is separated from the ternary positive electrode material by virtue of the advantages of high specific discharge capacity, high energy density, low toxicity, low cost and the like, and gradually becomes the development trend of the positive electrode material of the lithium ion battery. Research finds that the key for improving the discharge capacity of the NCM ternary cathode material is to improve the nickel content, and the discharge specific capacity and the energy density of the NCM ternary cathode material are improved along with the increase of the nickel content, but the inherent defects are also exposed along with the increase of the nickel content: (1) The average valence state of nickel is gradually increased from +2 to +3 3+ Unstable and very easily reduced to Ni during storage and electrochemical cycling 2+ Simultaneously with the precipitation of lithium, liOH and Li are formed on the surface layer of the particles 2 CO 3 Isobasic substances, and in addition, during the preparation process, the high-nickel NCM ternary layered cathode material needs to be added with excessive lithium source to balance the problem that part of the lithium source is deposited on the high-temperature treatment process due to the evaporation of lithiumLithium residues are formed on the surface of the material. On one hand, the excessive residual alkali content on the surface of the material can aggravate the micro-crack expansion and Li + /Ni 2+ Mixed arrangement, interface side reaction and lattice phase change of a layered R-3m structure gradually to a spinel Fd-3m structure and even a rock salt Fm-3m structure, so that the lattice structure is unstable, and lithium ions and transition metal ions (nickel, cobalt and manganese) on the surface of the deposited residual alkali layer are solidified to form a high-resistance layer to inhibit Li + The embedding and the releasing of the electrode material reduce the electronic conductivity and the ion diffusion rate of the material, and seriously restrict the improvement of the discharge specific capacity and the rate capability of the electrode material; on the other hand, in the subsequent processing, production and utilization processes, along with the increase of surface residual alkali, the excessively strong alkalinity causes viscosity increase and gel formation in the electrode material size mixing preparation process, so that uneven coating and insufficient adhesion are caused, the electrode material preparation and coating process is seriously affected, and the production cost is increased. Therefore, the method has important significance for removing the residual alkali on the surface of the high-nickel ternary electrode material by adopting an effective strategy.
At present, the effective modification strategy for removing the residual alkali on the surface of the high-nickel NCM ternary layered positive electrode material is mainly deionized water washing. In the washing process of the deionized water, the residual alkali can be quickly dissolved in the deionized water, so that the high-alkali resistance layer can be obviously removed, the discharge specific capacity and the ion diffusion rate are obviously improved, and the washing removal effect is excellent; but due to the high nickel NCM ternary material to CO in the air 2 /H 2 Micro-crack expansion, cation mixed discharge aggravation, structural instability and interface side reaction erosion in the charging and discharging process are easily caused in the sensitive effect washing process of O; in addition, the surface of the material is close to an ideal state after being washed by deionized water, the harmful phase transition from a layered structure (R3 m) to a disordered spinel-type structure (Fd 3 m) and a rock-salt phase structure (Fm 3 m) can be obviously intensified, the instability of the material structure is intensified, and a small amount of lithium oxide remained on the surface can continue to react with CO in the air 2 /H 2 O reacts continuously to generate LiOH and Li 2 CO 3 Causing a drastic deterioration in the electrochemical properties of the electrode material. Therefore, a modification method for reducing the residual alkali on the surface of the high-nickel ternary cathode material is needed to be found inOn the premise of effectively washing and removing surface residual alkali and ensuring high discharge specific capacity of the high-nickel ternary electrode material, the dissolution of lithium ions/transition metal ions in a bulk phase, lattice structure phase change and the like are inhibited, and meanwhile, an ideal state on the surface is avoided, so that the alkaline material balance is achieved, and the multiplying power and the cycling stability performance of the high-nickel ternary electrode material are improved.
Disclosure of Invention
Aiming at the defects of easy micro-crack expansion, aggravation of cation mixed discharge, structural instability, lattice phase change, interface side reaction corrosion in the charge-discharge process and the like of the existing high-nickel NCM ternary layered material residual alkali washing technology, the first purpose of the invention is to provide a method for reducing the residual alkali on the surface of a high-nickel ternary electrode material by gas-liquid two-phase washing, the method is simple to operate, the surface of the material can reach the balance of soluble alkaline substances in the washing process, and the crystal lattice Li can be greatly inhibited + And the transition metal ions are dissolved out, so that the trends of micro-crack expansion, material structure instability and lattice phase change can be further reduced, and the capacity and the cycling stability of the electrode material are obviously improved.
In order to realize the technical purpose, the invention provides a method for reducing residual alkali on the surface of a high-nickel ternary electrode material by gas-liquid two-phase washing, which comprises the steps of introducing carbon dioxide into a mixed system of the high-nickel ternary electrode material and an alkaline detergent, stirring and washing, and carrying out solid-liquid separation to obtain a solid product; and drying the solid product and then sintering in an oxygen-containing atmosphere.
The invention firstly adopts alkaline detergent to wash the high-nickel ternary electrode material to make up the defect of deionized water washing, avoids the ideal state of the surface due to excessive washing, so as to ensure that the surface of the material reaches the balance of soluble alkaline substances and greatly inhibit crystal lattice Li + And the transition metal ions are dissolved out, so that the trends of micro-crack expansion, material structure instability and lattice phase change can be further reduced, and the capacity and the cycling stability of the electrode material are remarkably improved; secondly, when the alkaline detergent liquid phase is stirred and washed, high-purity carbon dioxide gas is introduced to further strengthen the washing process, and high-purity CO 2 LiOH/Li with low solubility on material surface 2 CO 3 Transformation ofInto LiHCO with higher solubility 3 The alkaline washing and removing agent has a synergistic effect with alkaline washing, and the residual alkaline washing and removing effect on the surface of the high-nickel ternary electrode material is improved together; thirdly, the washed high-nickel ternary electrode material is sintered for the second time to form a layer of even LiHCO on the surface of the high-nickel NCM ternary layered positive electrode material 3 The coating layer can avoid the surface from generating an ideal state, and can isolate the high-nickel ternary anode material from continuing to be connected with H in the air 2 O and CO 2 Reaction to LiOH and Li 2 CO 3 Thereby avoiding or reducing the increase of the quantity of residual lithium, in addition, the secondary sintering can realize the reconstruction of the surface of the material, and the coating layer LiHCO 3 Li in (1) + The material is melted and embedded back to the bulk phase structure, so that the loss of lattice lithium is compensated, and the structural stability of the material is enhanced, thereby obtaining the high-nickel NCM ternary layered electrode material with excellent electrochemical properties such as large multiplying power, long cycle and the like.
As a preferred embodiment, the alkaline detergent comprises LiOH and/or Li 2 CO 3 The solution of (1). The alkaline detergent can effectively remove a surface residual alkali resistance layer, improve the electronic conductivity and the discharge specific capacity, greatly reduce the material instability phenomena of microcrack expansion, cation mixed discharge, interface side reaction, crystal lattice lithium dissolution and the like in the washing process, and remarkably improve the interface structure stability of the electrode material.
In a preferred embodiment, the concentration of LiOH in the alkaline detergent is 0.5 to 5.0mol/L.
As a preferred embodiment, li in the alkaline detergent 2 CO 3 The concentration of (A) is 0.01-0.15 mol/L.
Because the aqueous solution of the high-nickel NCM ternary electrode material is alkaline, and the pH value is concentrated in the range of 10-11, the selection of an alkaline detergent with a proper concentration range for washing and removing the residual alkali on the surface of the high-nickel NCM ternary electrode material is important. LiOH/Li 2 CO 3 Too low or too high concentration can lead the washing liquid to present relative over-acidity or over-alkalinity, and a large amount of transition metal ions in the material bulk phase can be dissolved out in the washing process of the high-alkali nickel-rich NCM ternary electrode material, so that the material structure is damaged, and the material lattice phase change is accelerated. In addition, the surface of the high-nickel NCM ternary electrode materialIn the process of washing and removing residual lithium on the surface, liOH/Li 2 CO 3 Li in detergents + If the concentration is too low, the precipitation of lattice lithium in a high-nickel ternary electrode material body can not be inhibited, the structural stability of the material is obviously reduced, if the concentration is too high, the effect of removing residual lithium on the surface can not be achieved, and the dissolution of the residual lithium on the surface in a washing liquid is inhibited, so that the instability of materials such as micro-crack expansion, cation mixed discharge, interface side reaction, lattice phase change and the like is aggravated, and if the concentration is too high, a large amount of LiOH/Li can be subjected to 2 CO 3 Remain on the surface of the material to increase the thickness of the high-resistance residual alkali layer, thereby inhibiting Li + Decrease the electronic conductivity and the ion diffusion rate of the material.
As a preferred scheme, the solid-to-liquid ratio of the high-nickel ternary electrode material to the alkaline detergent is 1g:5 to 15mL.
The solid-liquid ratio of the electrode material to the detergent is controlled in a proper range, so that the residual alkali removal effect is improved. When the solid-liquid ratio is too large, namely the high-nickel NCM ternary electrode material is relatively excessive in the washing process, the contact time of the electrode material and the washing liquid is shorter, and the contact area is smaller, so that the residual alkali washing and removing reaction on the surface is incomplete and insufficient; when the solid-liquid ratio is too small, namely the washing liquid is relatively excessive in the washing process, the excessive washing condition can occur, further a large amount of lattice lithium in the material body is induced to be lost, the crystal structure of the high-nickel NCM ternary electrode material is damaged, the lattice phase change is aggravated, meanwhile, more washing liquid needs to be prepared when the solid-liquid ratio is too small, the washing cost is increased, and therefore more washing waste liquid is generated.
Preferably, the aeration rate of the carbon dioxide is 20 to 50ml/min. The carbon dioxide is introduced in a jet cyclone mode, and the ventilation pressure is 0.3-0.5 MPa. The purity of the carbon dioxide is more than 99.9 percent. The carbon dioxide ventilation time is 2-15 min. The carbon dioxide gas enters a mixed system of the high-nickel ternary electrode material and the alkaline detergent along the wall of the washing device in a tangential direction, and is introduced tangentially by airflow to generate rotary motion, wherein the direction of the rotary motion is opposite to the stirring direction of the mixed system.
In the washing process, the gas-liquid mass transfer speed and the reaction rate can be enhanced by injecting the carbon dioxide gas by adopting a jet cyclone technology, the gas-liquid contact area is favorably increased, and the dissolution of the carbon dioxide gas in an alkaline detergent is promoted, so that the carbon dioxide gas and the residual alkali LiOH/Li on the surface of the high-nickel ternary electrode material are enabled to be 2 CO 3 The reaction is more complete.
Controlling the carbon dioxide aeration rate in the process to be in a suitable range is advantageous for improving the washing efficiency. When the aeration rate is too low, the gas-liquid mass transfer speed, the contact area and the dissolution of carbon dioxide gas in an alkaline detergent are reduced, which are not beneficial to the low-solubility residual alkali LiOH/Li on the surface of the high-nickel NCM ternary electrode material 2 CO 3 Towards high solubility LiHCO 3 The dissolution conversion reaction of the catalyst can not achieve the synergistic enhancement effect of reducing the surface residual alkali by gas-liquid two-phase washing; and when the aeration rate is too high, the reaction process is not easy to control, the requirement on a reaction device is high, and the washing and removing cost is obviously increased.
As a preferable scheme, in the stirring and washing process, the temperature is 25-35 ℃, the time is 5-15 min, and the stirring speed is 200-500 r/min.
Stirring and washing temperature, time and stirring speed have certain influence on the washing and removal of residual alkali on the surface of the high-nickel NCM ternary electrode material, and if the stirring temperature and speed are too low or the stirring time is too short, the dissolution rate of residual lithium on the surface in a washing solution can be reduced, and LiHCO with high solubility can be obtained 3 The conversion reaction rate of (2) causes incomplete and insufficient removal of surface residual alkali by gas-liquid two-phase cooperative washing and poor effect. On the contrary, the reaction uncertainty is aggravated by the overhigh stirring temperature, so that the alkali-reducing reaction of washing and removing is difficult to control, and the washing cost is increased; because the high nickel type ternary electrode material is used for H in the air 2 O and CO 2 The sensitive effect of (2) is that too long stirring time, i.e. too long dispersion time of the high-nickel NCM ternary electrode material in the solution, will aggravate the high-nickel NCM ternary electrode material and H in the air 2 O and CO 2 Leading to surface residuesContinued production of lithium; and too high stirring speed, that is, too high stirring strength, may aggravate structural pulverization of the electrode material, micro-crack expansion and serious interfacial side reaction in the subsequent electrochemical cycle process, and significantly worsen thermal stability of the lattice structure. Therefore, in the process of stirring, washing and alkali reduction, the stirring temperature, time and stirring speed need to be controlled within a reasonable range, so that the phenomena of excessive strength or weak aggravation of microcrack expansion, aggravation of cation mixed discharge, interface side reaction and lattice phase change in the charging and discharging processes are avoided, and the thermal stability and the electrochemical performance of a lattice structure are obviously worsened.
As a preferred embodiment, the oxygen-containing atmosphere is oxygen.
As a preferable scheme, the sintering conditions are: heating to 400-800 ℃ at the speed of 2-5 ℃/min, and preserving the heat for 5-15 h.
The control of the secondary sintering temperature, time and heating rate is beneficial to improving the thermal stability and electrochemical performance of the material lattice structure. The sintering temperature is too low, so that LiHCO remained after gas-liquid two-phase washing can be generated 3 Can not be uniformly coated on the surface of the high-nickel NCM ternary layered positive electrode material in a molten state, and can not inhibit H in the electrode material and air 2 O/CO 2 And the residual lithium is increased, and at the same time, the sintering temperature is too low to make Li + Re-melting and embedding the material phase structure, thereby compensating the loss of the crystal lattice lithium and enhancing the structural stability; the agglomeration of the high-nickel NCM ternary layered positive electrode material in a high-temperature molten state can be aggravated and the layered structure appearance can be damaged due to the fact that the sintering temperature is too high; and the sintering temperature is too high, so that the requirement on a sintering device is higher, and the production cost is increased. Too short a sintering soak time can result in residual LiHCO 3 The material surface can not be effectively coated, and the reaction of the surface coating and the melting and embedding of lattice lithium make up the incomplete reaction; the excessive heat preservation time can increase the content of residual alkali of the material, increase the production cost of the material, and deteriorate the structural stability and electrochemical performance of the electrode material, because the surface coating and the lattice lithium fusion-intercalation reaction are basically complete, and the surface of the high-nickel NCM ternary layered positive electrode material can possibly react with the increase of the timeRegeneration of Li 2 CO 3 Resulting in an increase in residual alkali and a thickening of the resistive layer. For the secondary sintering temperature rise rate, the too low rate can slow down the melting of the surface coating and the melting and embedding of crystal lattice lithium, so that a large amount of Li is generated on the surface of the material 2 CO 3 A residual alkali layer; too fast a temperature rise rate will result in LiHCO 3 The melting is too fast, so that the high-nickel NCM ternary layered positive electrode material is not favorably uniformly coated on the surface of the high-nickel NCM ternary layered positive electrode material, and the crystal lattice lithium is effectively embedded into a crystal lattice material bulk structure.
As a preferred embodiment, the drying conditions are: vacuum drying at 100-120 deg.c for 8-12 hr.
The low residual alkali high nickel ternary electrode material obtained by washing has good structural thermal stability, capacity rate performance, cycling stability and safety performance.
Compared with the prior art, the invention has the following beneficial effects:
(1) The method combines alkaline detergent liquid-phase washing with carbon dioxide gas-phase washing, greatly improves the effect of washing and removing residual alkali on the surface of the high-nickel ternary electrode material, greatly reduces the phenomena of material instability such as micro-crack expansion, cation mixed discharge, interface side reaction, crystal lattice lithium dissolution and the like in the washing process while effectively removing a surface residual alkali resistance layer and improving the electronic conductivity and the specific discharge capacity, and improves the stability of the interface structure of the anode material; in addition, the alkaline detergent can make up for the defect of single deionized water washing, avoid the surface washing ideal state, ensure the alkaline substance balance and further improve the cycle stability of the nickel NCM ternary layered positive electrode material.
(2) The secondary sintering is carried out on the washed high-nickel ternary electrode material to realize the small amount of LiHCO remained after gas-liquid two-phase washing 3 The surface of the high-nickel NCM ternary layered positive electrode material is uniformly coated, so that the appearance of an ideal surface state is avoided, and the high-nickel ternary positive electrode material is inhibited from continuing to react with H in the air 2 O and CO 2 Reaction to LiOH and Li 2 CO 3 Is obviously improvedThe surface structure of the material is that part of Li in the coating layer + And the lithium ions are re-embedded into the crystal lattice, so that the lithium loss in the gas-liquid two-phase washing process is compensated, and the thermal stability and the electrochemical performance of the crystal lattice structure of the material are enhanced.
(3) The method is simple, convenient to operate and low in cost, and has the potential of being commercially applied to subsequent treatment of the high-nickel ternary electrode material.
Drawings
FIG. 1 is a schematic diagram of a method for reducing alkali residue on the surface of a high-nickel ternary electrode material by gas-liquid two-phase washing.
Fig. 2 is a graph showing initial charge and discharge curves of the low-basicity high-nickel NCM ternary cathode materials prepared in examples 1 to 4 and comparative examples 1 to 6.
FIG. 3 is a graph of the cycle performance of the low-basicity high-nickel NCM ternary cathode materials prepared in examples 1-4 and comparative examples 1-6.
FIG. 4 is a graph of capacity retention of the low-basicity high-nickel NCM ternary positive electrode materials prepared in examples 1 to 4 and comparative examples 1 to 6.
Detailed Description
The following examples are intended to further illustrate the present disclosure, but not to limit the scope of the claims.
Example 1
The first method for reducing the residual alkali on the surface of the high-nickel ternary electrode material by gas-liquid two-phase washing comprises the following steps:
(1) Weighing 6.5g of anhydrous lithium hydroxide, dissolving in 100g of deionized water, placing in a 35 ℃ water bath, stirring and dissolving to prepare 2.7mol L -1 A lithium hydroxide solution of (a);
(2) Chemical composition of choice LiNi 0.8 Co 0.1 Mn 0.1 O 2 The commercial high-nickel LNCM ternary layered positive electrode material is used as a material to be washed, and 5g of the high-nickel LNCM ternary material is dissolved in 50mL of 2.7mol L of the solution according to the solid-to-liquid ratio of 1 -1 Quickly placing the lithium hydroxide solution into a water bath kettle for stirring and washing, wherein the set rotating speed is 200rmp/min, the stirring time is 5min, and the washing temperature is 35 ℃; simultaneously injecting carbon dioxide gas with purity of more than 99.9% into the slurry solution by adopting a jet flow cyclone technology, wherein the aeration time is5min, wherein the aeration rate is 50ml/min, and the aeration pressure is 0.3-0.5 MPa, wherein carbon dioxide gas enters a mixed system of the high-nickel ternary electrode material and the alkaline detergent along the wall of the washing device in the tangential direction, is introduced tangentially by airflow to generate rotary motion, and the direction of the rotary motion is opposite to the stirring direction of the mixed system;
(3) Rapidly transferring the slurry which is stirred and washed in a gas-liquid dual-phase manner for 5min to a circulating water type multipurpose vacuum pump for suction filtration, transferring the material obtained by suction filtration to a vacuum drying box, and drying for 12h at 100 ℃; and then, carrying out secondary sintering on the dried material in an oxygen atmosphere furnace, raising the temperature to 750 ℃ at the heating rate of 2 ℃/min, and preserving the temperature for 12 hours to obtain the high-nickel ternary layered anode material with low residual alkali.
The obtained high-nickel ternary layered positive electrode material ternary material with low residual alkali, conductive carbon black and PVDF are proportioned according to the mass ratio of 8/1/1, placed in NMP and stirred to be uniform slurry, uniformly coated on a current collector aluminum foil by using a coating machine, then placed in a vacuum drying oven for drying for 12 hours at the temperature of 100 ℃, and then the aluminum foil loaded with the electrode active material is uniformly cut into pole pieces with the diameter of 12 mm. And assembling a CR2016 type button cell in a glove box filled with high-purity argon by using the cut electrode aluminum foil as a working electrode, using metal lithium as a counter electrode and using Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (a), at 0.04 ag -1 At a current density of (2), the initial specific discharge capacity is 197.5mAh g -1 Coulombic efficiency 88.9%; further, 0.2 ag is set -1 The current density test shows that the cycle stability performance is shown in figure 3, and the reversible specific capacity is 178.4mAh g after 100 cycles of circulation -1 The capacity retention rate was 93.9% (fig. 4).
Example 2
The second method for reducing the residual alkali on the surface of the high-nickel ternary electrode material by gas-liquid two-phase washing comprises the following steps:
(1) Weighing 3.25g of anhydrous lithium hydroxide, dissolving in 100g of deionized water, placing in a 35 ℃ water bath kettle, stirring and dissolving to prepare 1.35mol L -1 A lithium hydroxide solution of (a);
(2) The chemical composition of choice is LiNi 0.8 Co 0.1 Mn 0.1 O 2 The commercial high-nickel LNCM ternary layered positive electrode material is used as a material to be washed, and 5g of the high-nickel LNCM ternary material is dissolved in 50mL of the 1.35mol L of the material according to the solid-to-liquid ratio of 1 -1 Quickly placing the lithium hydroxide solution into a water bath kettle for stirring and washing, wherein the set rotating speed is 200rmp/min, the stirring time is 5min, and the washing temperature is 35 ℃; simultaneously, injecting carbon dioxide gas with the purity of more than 99.9 percent into the slurry solution by adopting a jet flow cyclone technology, wherein the ventilation time is 5min, the ventilation rate is 50ml/min, and the ventilation pressure is 0.3-0.5 MPa, wherein the carbon dioxide gas enters a mixed system of the high-nickel ternary electrode material and the alkaline detergent along the wall of the washing device in a tangential direction, and is introduced tangentially by airflow to generate rotary motion, and the direction of the rotary motion is opposite to the stirring direction of the mixed system;
(3) Rapidly transferring the slurry which is stirred and washed in a gas-liquid dual-phase manner for 5min to a circulating water type multipurpose vacuum pump for suction filtration, transferring the material obtained by suction filtration to a vacuum drying box, and drying for 12h at 100 ℃; and then, carrying out secondary sintering on the dried material in an oxygen atmosphere furnace, raising the temperature to 750 ℃ at the heating rate of 2 ℃/min, and preserving the temperature for 12 hours to obtain the high-nickel ternary layered anode material with low residual alkali.
The obtained high-nickel ternary layered positive electrode material ternary material with low residual alkali, conductive carbon black and PVDF are proportioned according to the mass ratio of 8/1/1, placed in NMP and stirred to be uniform slurry, uniformly coated on a current collector aluminum foil by using a coating machine, then placed in a vacuum drying oven for drying for 12 hours at the temperature of 100 ℃, and then the aluminum foil loaded with the electrode active material is uniformly cut into pole pieces with the diameter of 12 mm. And assembling a CR2016 type button cell in a glove box filled with high-purity argon by using the cut electrode aluminum foil as a working electrode, using metal lithium as a counter electrode and using Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (b), at 0.04 ag -1 At a current density of (2), the initial specific discharge capacity is 201.1mAh g -1 Coulombic efficiency of 86.9%; further, 0.2 ag is set -1 Current density test for its cycling stabilityThe reversible specific capacity after 100 cycles of cycling was 176.8mAh g with constant performance, as shown in FIG. 3 -1 The capacity retention rate was 92.2% (fig. 4).
Example 3
The following is a third method for reducing the residual alkali on the surface of the high-nickel ternary electrode material by gas-liquid two-phase washing, and the method comprises the following steps:
(1) 0.6g of lithium carbonate is weighed and dissolved in 100g of deionized water, and the solution is placed in a 35 ℃ water bath kettle to be stirred and dissolved to prepare the solution with the concentration of 0.08mol L -1 Lithium carbonate solution of (4);
(2) The chemical composition of choice is LiNi 0.8 Co 0.1 Mn 0.1 O 2 The commercial high-nickel LNCM ternary layered positive electrode material is used as a material to be washed, and 5g of the high-nickel LNCM ternary material is dissolved in 50mL of the above 0.08mol L according to the solid-to-liquid ratio of 1 -1 The lithium carbonate solution is quickly placed in a water bath kettle for stirring and washing, the set rotating speed is 200rmp/min, the stirring time is 5min, and the washing temperature is 35 ℃; simultaneously, injecting carbon dioxide gas with the purity of more than 99.9 percent into the slurry solution by adopting a jet flow cyclone technology, wherein the ventilation time is 5min, the ventilation rate is 50ml/min, and the ventilation pressure is 0.3-0.5 MPa, wherein the carbon dioxide gas enters a mixed system of the high-nickel ternary electrode material and the alkaline detergent along the wall of the washing device in a tangential direction, and is introduced tangentially by airflow to generate rotary motion, and the direction of the rotary motion is opposite to the stirring direction of the mixed system;
(3) Quickly transferring the slurry which is stirred and washed in gas-liquid two-phase mode for 5min to a circulating water type multipurpose vacuum pump for suction filtration, transferring the material obtained by suction filtration to a vacuum drying box, and drying for 12h at 100 ℃; and then, carrying out secondary sintering on the dried material in an oxygen atmosphere furnace, raising the temperature to 750 ℃ at the temperature rise rate of 2 ℃/min, and preserving the temperature for 12h to obtain the high-nickel ternary layered positive electrode material with low residual alkali.
The obtained high-nickel ternary layered positive electrode material with low residual alkali, the conductive carbon black and the PVDF are proportioned according to the mass ratio of 8/1/1, placed in NMP and stirred to be uniform slurry, uniformly coated on a current collector aluminum foil by utilizing a coating machine, then placed in a vacuum drying oven for drying for 12 hours at the temperature of 100 ℃, and then an electrode is loadedThe aluminum foil of the active material was cut uniformly into pole pieces 12mm in diameter. And assembling a CR2016 type button cell in a glove box filled with high-purity argon by using the cut electrode aluminum foil as a working electrode, using metal lithium as a counter electrode and using Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (c), at 0.04 ag -1 At a current density of (2), the initial specific discharge capacity is 195.4mAh g -1 Coulombic efficiency was 87.0%; further, 0.2 ag is set -1 The current density test shows that the cycle stability performance is shown in figure 3, and the reversible specific capacity is 175.8mAh g after 100 cycles of circulation -1 The capacity retention rate was 92.8% (fig. 4).
Example 4
The following is a fourth method for reducing the residual alkali on the surface of the high-nickel ternary electrode material by gas-liquid two-phase washing, and the method comprises the following steps:
(1) 0.3g of lithium carbonate is weighed and dissolved in 100g of deionized water, and the solution is placed in a 35 ℃ water bath kettle to be stirred and dissolved to prepare the solution with the concentration of 0.04mol L -1 Lithium carbonate solution of (4);
(2) Chemical composition of choice LiNi 0.8 Co 0.1 Mn 0.1 O 2 The commercial high-nickel LNCM ternary layered cathode material is used as a material to be washed, and 5g of the high-nickel LNCM ternary material is dissolved in 50mL of the above 0.04mol L according to the solid-to-liquid ratio of 1 -1 The lithium carbonate solution is quickly placed in a water bath kettle for stirring and washing, the set rotating speed is 200rmp/min, the stirring time is 5min, and the washing temperature is 35 ℃; simultaneously, injecting carbon dioxide gas with the purity of more than 99.9 percent into the slurry solution by adopting a jet flow cyclone technology, wherein the ventilation time is 5min, the ventilation rate is 50ml/min, and the ventilation pressure is 0.3-0.5 MPa, wherein the carbon dioxide gas enters a mixed system of the high-nickel ternary electrode material and the alkaline detergent along the wall of the washing device in a tangential direction, and is introduced tangentially by airflow to generate rotary motion, and the direction of the rotary motion is opposite to the stirring direction of the mixed system;
(3) Quickly transferring the slurry which is stirred and washed in gas-liquid two-phase mode for 5min to a circulating water type multipurpose vacuum pump for suction filtration, transferring the material obtained by suction filtration to a vacuum drying box, and drying for 12h at 100 ℃; and then, carrying out secondary sintering on the dried material in an oxygen atmosphere furnace, raising the temperature to 750 ℃ at the temperature rise rate of 2 ℃/min, and preserving the temperature for 12h to obtain the high-nickel ternary layered positive electrode material with low residual alkali.
The obtained high-nickel ternary layered positive electrode material ternary material with low residual alkali, conductive carbon black and PVDF are proportioned according to the mass ratio of 8/1/1, placed in NMP and stirred to be uniform slurry, uniformly coated on a current collector aluminum foil by using a coating machine, then placed in a vacuum drying oven for drying for 12 hours at the temperature of 100 ℃, and then the aluminum foil loaded with the electrode active material is uniformly cut into pole pieces with the diameter of 12 mm. And (3) assembling a CR2016 type button cell in a glove box filled with high-purity argon by taking the cut electrode aluminum foil as a working electrode, taking metal lithium as a counter electrode and taking Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (d), at 0.04 Ag -1 At a current density of 197.1mAh g as a specific initial discharge capacity -1 Coulombic efficiency was 87.3%; further, 0.2 ag is set -1 The current density test shows that the cycle stability performance is as shown in figure 3, and the reversible specific capacity is 172.2mAh g after 100 cycles of circulation -1 The capacity retention rate was 90.1% (fig. 4).
Comparative example 1
The chemical composition of choice is LiNi 0.8 Co 0.1 Mn 0.1 O 2 The commercial high-nickel LNCM ternary layered cathode material is used as a material to be washed, 5g of the high-nickel LNCM ternary material is dissolved in 50mL of deionized water according to the solid-liquid ratio of 1; quickly transferring the slurry stirred and washed for 5min to a circulating water type multipurpose vacuum pump for suction filtration, transferring the material obtained by suction filtration to a vacuum drying box, and drying at 100 ℃ for 12h; and then, carrying out secondary sintering on the dried material in an oxygen atmosphere furnace, raising the temperature to 750 ℃ at the temperature rise rate of 2 ℃/min, and preserving the temperature for 12h to obtain the high-nickel ternary layered positive electrode material with low residual alkali.
The high-nickel ternary layered positive electrode material with low residual alkali obtained under the condition of the comparative exampleThe ternary material, the conductive carbon black and the PVDF are proportioned according to the mass ratio of 8/1/1, placed in NMP and stirred to be uniform slurry, uniformly coated on a current collector aluminum foil by using a coating machine, then placed in a vacuum drying oven for drying for 12 hours at 100 ℃, and then the aluminum foil loaded with the electrode active material is uniformly cut into pole pieces with the diameter of 12 mm. And (3) assembling a CR2016 type button cell in a glove box filled with high-purity argon by taking the cut electrode aluminum foil as a working electrode, taking metal lithium as a counter electrode and taking Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (e), at 0.04 Ag -1 The initial specific discharge capacity is 189.8mAh g at the current density of (2) -1 Coulombic efficiency 85.2%; further, 0.2 ag is set -1 The current density test shows that the cycle stability performance is shown in figure 3, and the reversible specific capacity after 100 cycles of circulation is 144.7mAh g -1 The capacity retention rate was 76.8% (fig. 4).
Comparative example 2
The method of example 1 is used to prepare a ternary material of a high-nickel ternary layered cathode material, and the difference is that: carbon dioxide gas is not injected in the stirring and washing process.
The high-nickel ternary layered positive electrode material ternary material with low residual alkali, the conductive carbon black and the PVDF which are obtained under the condition of the comparative example are proportioned according to the mass ratio of 8/1/1, placed in NMP and stirred to be uniform slurry, uniformly coated on a current collector aluminum foil by using a coating machine, then placed in a vacuum drying oven for drying for 12 hours at 100 ℃, and then the aluminum foil loaded with the electrode active material is uniformly cut into pole pieces with the diameter of 12 mm. And (3) assembling a CR2016 type button cell in a glove box filled with high-purity argon by taking the cut electrode aluminum foil as a working electrode, taking metal lithium as a counter electrode and taking Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (f), at 0.04 ag -1 The initial specific discharge capacity is 193.1mAh g at the current density of (2) -1 Coulombic efficiency 85.0%; further, 0.2 ag is set -1 The current density was measured for its cycling stability performance, as shown in FIG. 3, after 100 cyclesThe inverse specific capacity is 162.6mAh g -1 The capacity retention rate was 87.8% (fig. 4).
Comparative example 3
The method of example 3 is used to prepare the ternary material of the high-nickel ternary layered cathode material, and the difference is that: carbon dioxide gas is not injected in the stirring and washing process.
The high-nickel ternary layered positive electrode material ternary material with low residual alkali, the conductive carbon black and the PVDF which are obtained under the condition of the comparative example are proportioned according to the mass ratio of 8/1/1, placed in NMP and stirred to be uniform slurry, uniformly coated on a current collector aluminum foil by using a coating machine, then placed in a vacuum drying oven for drying for 12 hours at 100 ℃, and then the aluminum foil loaded with the electrode active material is uniformly cut into pole pieces with the diameter of 12 mm. And assembling a CR2016 type button cell in a glove box filled with high-purity argon by using the cut electrode aluminum foil as a working electrode, using metal lithium as a counter electrode and using Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (g), at 0.04 Ag -1 At a current density of 196.0mAh g as the initial specific discharge capacity -1 Coulombic efficiency 85.6%; further, 0.2 ag is set -1 The current density test shows that the cycle stability performance is shown in figure 3, and the reversible specific capacity is 159.8mAh g after 100 cycles -1 The capacity retention rate was 86.0% (fig. 4).
Comparative example 4
The chemical composition of choice is LiNi 0.8 Co 0.1 Mn 0.1 O 2 The commercial high-nickel LNCM ternary layered cathode material is used as a material to be washed, 5g of the high-nickel LNCM ternary material is dissolved in 50mL of deionized water according to the solid-liquid ratio of 1; simultaneously, injecting carbon dioxide gas with the purity of more than 99.9 percent into the slurry solution by adopting a jet flow cyclone technology, wherein the ventilation time is 5min, the ventilation rate is 50ml/min, and the ventilation pressure is 0.3-0.5 MPa, wherein the carbon dioxide gas enters a mixed system of the high-nickel ternary electrode material and the alkaline detergent along the wall of the washing device in a tangential direction, and the carbon dioxide gas passes through the gasThe tangential introduction of the flow generates rotary motion, and the direction of the rotary motion is opposite to the stirring direction of the mixing system; rapidly transferring the slurry which is stirred and washed in a gas-liquid dual-phase manner for 5min to a circulating water type multipurpose vacuum pump for suction filtration, transferring the material obtained by suction filtration to a vacuum drying box, and drying for 12h at 100 ℃; and then, carrying out secondary sintering on the dried material in an oxygen atmosphere furnace, raising the temperature to 750 ℃ at the temperature rise rate of 2 ℃/min, and preserving the temperature for 12h to obtain the high-nickel ternary layered positive electrode material with low residual alkali.
The high-nickel ternary layered positive electrode material ternary material with low residual alkali, the conductive carbon black and the PVDF which are obtained under the condition of the comparative example are proportioned according to the mass ratio of 8/1/1, placed in NMP and stirred to be uniform slurry, uniformly coated on a current collector aluminum foil by using a coating machine, then placed in a vacuum drying oven for drying for 12 hours at 100 ℃, and then the aluminum foil loaded with the electrode active material is uniformly cut into pole pieces with the diameter of 12 mm. And assembling a CR2016 type button cell in a glove box filled with high-purity argon by using the cut electrode aluminum foil as a working electrode, using metal lithium as a counter electrode and using Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (h), at 0.04 ag -1 The initial specific discharge capacity is 190.2mAh g at the current density of -1 Coulombic efficiency 84.1%; further, 0.2 ag is set -1 The current density test shows that the cycle stability performance is as shown in figure 3, and the reversible specific capacity after 100 cycles of circulation is 149.6mAh g -1 The capacity retention rate was 79.7% (fig. 4).
Comparative example 5
The method of example 1 is used to prepare a ternary material of a high-nickel ternary layered cathode material, and the difference is that: the product after vacuum drying is not subjected to secondary sintering treatment.
The high-nickel ternary layered positive electrode material ternary material with low residual alkali, the conductive carbon black and the PVDF which are obtained under the condition of the comparative example are proportioned according to the mass ratio of 8/1/1, are placed in NMP and stirred to be uniform slurry, are uniformly coated on a current collector aluminum foil by utilizing a coating machine, are then placed in a vacuum drying oven for drying for 12 hours at the temperature of 100 ℃, and then the aluminum foil loaded with the electrode active material is uniformly cutForming a pole piece with the diameter of 12 mm. And assembling a CR2016 type button cell in a glove box filled with high-purity argon by using the cut electrode aluminum foil as a working electrode, using metal lithium as a counter electrode and using Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (i), at 0.04A g -1 At a current density of (2), the initial specific discharge capacity is 195.5mAh g -1 Coulombic efficiency 85.6%; further, 0.2 ag is set -1 The current density test shows that the cycle stability performance is as shown in figure 3, and the reversible specific capacity is 155.0mAh g after 100 cycles of circulation -1 The capacity retention rate was 83.5% (fig. 4).
Comparative example 6
The method of example 3 is used to prepare the ternary material of the high-nickel ternary layered cathode material, and the difference is that: the product after vacuum drying is not subjected to secondary sintering treatment.
The high-nickel ternary layered positive electrode material ternary material with low residual alkali, the conductive carbon black and the PVDF which are obtained under the condition of the comparative example are proportioned according to the mass ratio of 8/1/1, placed in NMP and stirred to be uniform slurry, uniformly coated on a current collector aluminum foil by using a coating machine, then placed in a vacuum drying oven for drying for 12 hours at 100 ℃, and then the aluminum foil loaded with the electrode active material is uniformly cut into pole pieces with the diameter of 12 mm. And (3) assembling a CR2016 type button cell in a glove box filled with high-purity argon by taking the cut electrode aluminum foil as a working electrode, taking metal lithium as a counter electrode and taking Celgard 2500 as a diaphragm. And then carrying out electrochemical performance test on the assembled lithium ion battery on a blue light tester. As shown in FIG. 2 (j), at 0.04 ag -1 The initial specific discharge capacity is 193.4mAh g at the current density of (2) -1 Coulombic efficiency of 86.0%; further, 0.2 ag is set -1 The current density test shows that the cycle stability performance is shown in figure 3, and the reversible specific capacity after 100 cycles is 151.7mAh g -1 The capacity retention rate was 80.4% (fig. 4).
From examples 1 to 4, it is clear that LiOH and Li were selected 2 CO 3 Ternary high nickel NCM detergent used as alkaline detergent and injected with carbon dioxide gas by jet cyclone technologyThe electrode material is subjected to gas-liquid two-phase cooperative washing to strengthen the washing and removing process of the residual alkali on the surface; and then the low residual alkali ternary electrode material with excellent electrochemical performance is prepared by secondary sintering in oxygen atmosphere. The specific discharge capacity of the first ring is centralized at 195-200mAh g -1 The first library is concentrated in 86-90%, which shows that alkaline washing and secondary sintering can effectively remove the residual alkali resistance layer on the surface of the high-nickel NCM, and obviously improve the electronic conductivity and the ion diffusion rate, thereby causing the discharge specific capacity to be obviously improved. The electrochemical cycle stability of the electrode material is tested to be 0.2A g -1 After the current density is circulated for 100 circles, the capacity retention rate is more than 90 percent, which indicates that the alkaline detergents LiOH and Li 2 CO 3 And the carbon dioxide gas-liquid two-phase synergic washing effectively removes the surface residual alkali, does not damage the high-nickel NCM ternary electrode material structure and cause lattice phase change, can effectively inhibit the material structure instability phenomena such as microcrack expansion, cation mixed discharge, interface side reaction, lattice lithium dissolution and the like, and improves the material structure thermal stability and electrochemical cycle stability.
As can be seen from the comparative example 1, the electrode material prepared by alkaline detergent and high-purity carbon dioxide gas-liquid two-phase synergic washing is obviously superior to deionized water washing, although the initial discharge specific capacity and the coulombic efficiency of the electrode material are higher after deionized water washing; but the circulation stability and subsequent capacity multiplying power performance of the material are obviously degraded, which shows that the gas-liquid two-phase synergic washing of the alkaline detergent and the carbon dioxide gas can avoid the expansion of microcracks on the surface of the material, the mixed arrangement of cations, the dissolution of lattice lithium and the phase change of lattices caused by the washing of deionized water, protect the integrity of the lattice structure and obviously improve the electrochemical performance of the ternary electrode material.
As shown in comparative examples 2 and 3, the gas phase washing is carried out by injecting carbon dioxide gas by the jet flow cyclone technology, so as to strengthen the washing and removing process of the surface residual alkali and lead the LiOH/Li with low solubility on the surface of the material 2 CO 3 Conversion to LiHCO of greater solubility 3 The effect of removing the residual alkali on the surface can be further improved.
From comparative example 4, it can be seen that the alkaline detergent LiOH/Li 2 CO 3 The liquid phase washing can be effectiveRemoving residual alkali on the surface of the high-nickel NCM ternary electrode material and improving the capacity multiplying power and the cycling stability of the electrode material; the alkaline detergent can obviously inhibit the dissolution of transition metal ions of a high-nickel NCM ternary alkaline system and crystal lattice Li in a bulk phase + With H in aqueous solution + The exchange is carried out, the stability and the integrity of the lattice structure are obviously enhanced, and in addition, the material instability phenomena such as micro-crack expansion, cation mixed discharge, interface side reaction, lattice lithium dissolution and the like caused by deionized water washing can be avoided.
As can be seen from comparative examples 5 and 6, a small amount of LiHCO remained after the subsequent secondary sintering in the oxygen atmosphere and the gas-liquid two-phase washing 3 Forming a layer of uniform LiHCO on the surface of the high-nickel NCM ternary layered positive electrode material 3 Layer capable of isolating the high-nickel ternary positive electrode material from H in air 2 O and CO 2 Reaction to LiOH and Li 2 CO 3 Thereby avoiding or reducing an increase in the amount of residual lithium; in addition, the secondary sintering is also helpful for reconstructing the surface structure of the material, so that partial Li in the coating layer + Re-melting and embedding the crystal lattice to make up for lithium loss in the gas-liquid two-phase washing process, supplement the content of bulk lithium, enhance the thermal stability and integrity of the material crystal lattice structure, and obviously improve the capacity, multiplying power and electrochemical cycle stability.
The above description is only exemplary of the invention and should not be taken as limiting the scope of the invention, so that the invention is intended to cover all modifications and equivalents of the embodiments described herein. In addition, the technical features and the technical inventions of the present invention, the technical features and the technical inventions, and the technical inventions can be freely combined and used.
Claims (8)
1. A method for reducing residual alkali on the surface of a high-nickel ternary electrode material by gas-liquid two-phase washing is characterized by comprising the following steps: introducing carbon dioxide into a mixed system of a high-nickel ternary electrode material and an alkaline detergent, stirring and washing, and performing solid-liquid separation to obtain a solid product; and drying the solid product and then sintering in an oxygen-containing atmosphere.
2. The method for reducing the residual alkali on the surface of the high-nickel ternary electrode material by gas-liquid two-phase washing according to claim 1, characterized by comprising the following steps: the alkaline detergent contains LiOH and/or Li 2 CO 3 The solution of (1).
3. The method for reducing the residual alkali on the surface of the high-nickel ternary electrode material by gas-liquid two-phase washing according to claim 1 or 2, which is characterized in that:
the concentration of LiOH in the alkaline detergent is 0.5-5.0 mol/L;
li in the alkaline detergent 2 CO 3 The concentration of (A) is 0.01-0.15 mol/L.
4. The method for reducing the residual alkali on the surface of the high-nickel ternary electrode material through gas-liquid two-phase washing according to claim 1, which is characterized by comprising the following steps of: the solid-to-liquid ratio of the high-nickel ternary electrode material to the alkaline detergent is 1g:5 to 15mL.
5. The method for reducing the residual alkali on the surface of the high-nickel ternary electrode material by gas-liquid two-phase washing according to claim 1 or 4, which is characterized by comprising the following steps of: the aeration rate of the carbon dioxide is 20-50 ml/min; the carbon dioxide is introduced in a jet flow cyclone mode, and the ventilation pressure is 0.3-0.5 MPa; the purity of the carbon dioxide is more than 99.9%.
6. The method for reducing the residual alkali on the surface of the high-nickel ternary electrode material by gas-liquid two-phase washing according to claim 1 or 4, which is characterized by comprising the following steps of: in the stirring and washing process, the temperature is 25-35 ℃, the time is 5-15 min, and the stirring speed is 200-500 r/min.
7. The method for reducing the residual alkali on the surface of the high-nickel ternary electrode material through gas-liquid two-phase washing according to claim 1, which is characterized by comprising the following steps of: the oxygen-containing atmosphere is a pure oxygen atmosphere; the sintering conditions are as follows: heating to 400-800 deg.c at the rate of 2-5 deg.c/min and maintaining for 5-15 hr.
8. The method for reducing the residual alkali on the surface of the high-nickel ternary electrode material by gas-liquid two-phase washing according to claim 1 or 7, characterized by comprising the following steps: the drying conditions are as follows: vacuum drying at 100-120 deg.c for 8-12 hr.
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| CN116177625A (en) * | 2023-04-19 | 2023-05-30 | 新乡天力锂能股份有限公司 | Method for reducing residual alkali on surface of nickel-based positive electrode material and application thereof |
| CN117352706A (en) * | 2023-12-04 | 2024-01-05 | 宁波容百新能源科技股份有限公司 | Positive electrode material, preparation method thereof and lithium ion battery |
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| CN116177625A (en) * | 2023-04-19 | 2023-05-30 | 新乡天力锂能股份有限公司 | Method for reducing residual alkali on surface of nickel-based positive electrode material and application thereof |
| CN117352706A (en) * | 2023-12-04 | 2024-01-05 | 宁波容百新能源科技股份有限公司 | Positive electrode material, preparation method thereof and lithium ion battery |
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