CN115172756A - Single crystal coated polycrystalline anode material with concentration gradient and preparation method thereof - Google Patents
Single crystal coated polycrystalline anode material with concentration gradient and preparation method thereof Download PDFInfo
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Abstract
The invention is applicable to the technical field of lithium ion battery materials for electric vehicles, and provides a single crystal coated polycrystalline anode material with concentration gradient x Co y Mn z O 2 Wherein, 0.3<x<0.7，0<y<0.4，0<z<0.4，x + y + z =1, the inner core layer is a polycrystalline material with a chemical formula LiNi a Co b Mn c O 2 Wherein, 0.7<a<1，0<b<0.3，0<c<0.3,a + b + c =1, so that the surface of the material is a low-nickel ternary material, the content of residual alkali is relatively low, the damage to the cathode material in the water washing process of the high-nickel cathode material is avoided, meanwhile, the irreversible phase change from H2 to H3 can be generated after the high-nickel material is excessively delithiated, cracks are formed on the surface and continuously generate side reaction with electrolyte, the structure is collapsed, the shell layer low-nickel single crystal layer is coated, the high-nickel material is prevented from being directly contacted with the electrolyte, the phenomenon is inhibited, the concentration gradient monocrystal-polycrystal ternary cathode material not only ensures higher discharge capacity, but also greatly improves the cycle stability and the safety.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries for electric vehicles, in particular to a single crystal coated polycrystalline anode material with a concentration gradient and a preparation method thereof.
Background
In recent years, lithium ion batteries have been increasingly used in the living of people, and with the development of electric vehicles, the demand for lithium ion energy density has been increasing. The nickel-cobalt-manganese ternary cathode material is used as one of important lithium ion battery cathode materials, has high discharge capacity and cycle stability, and is widely used in the field of new energy. Under the promotion of high energy density, the ternary cathode material gradually develops towards high nickel content, and the direction is shifted from NCM111 to NCM523 and NCM622, and then the generations are advanced to NCM811 and NCM 9055.
The high-nickel ternary material has some problems exposed in the using process, the pulverization phenomenon exists in the charging and discharging process, the anode material in contact with the electrolyte generates side reaction to generate a large amount of gas, cracks appear on the surface of the anode material, more new contact surfaces are exposed, and a new CEI passive film is formed, so that the active substance fails and does not release capacity any more, and even falls off from a current collector, and capacity water jump is caused. The reason that the high nickel ternary produces the pulverization is that self crystal structure causes, in the charging process, along with lithium ion's deviating from, the repulsion between the oxygen layer increases, the size in the c axle direction can increase, and along with lithium ion's further deviating from, after lacking the interlaminar supporting action of lithium ion, take place the layer and slide, the lithium layer shrink, the size in the c axle direction can sharply decline, can take place H2 to H3's irreversible phase transition in the material this moment, material itself becomes rock salt phase and loses the activity, the excessive shrink of material volume simultaneously, thereby make the material surface appear the crack, further contact with electrolyte, take place new side reaction, go round and go round, make high nickel positive pole material cycle performance relatively poor.
In order to solve the above problems of high nickel materials, in patent CN103236537A, a precursor with a polycrystalline ternary core and a polycrystalline binary and/or unitary shell are prepared by a coprecipitation method, and are uniformly mixed with a lithium source and then sintered at a high temperature, wherein the core is a ternary positive electrode material, the first layer of the shell is a nickel-manganese binary positive electrode material, and the second layer is a coating layer of a lithium cobaltate or lithium manganate positive electrode material, so that the cycle performance is improved, but the discharge capacity of the material is seriously reduced due to the excessively thick coating layer. The precursor prepared by the patent CN114349071A is of a core-shell structure, the core part is prepared by a solvothermal method, the ratio of nickel, cobalt and manganese is 0.82.
In view of the foregoing, it is apparent that the prior art has inconvenience and disadvantages in practical use, and thus, needs to be improved.
Disclosure of Invention
Aiming at the defects, the invention aims to provide a monocrystal-coated polycrystalline anode material with concentration gradient and a preparation method thereof, wherein the surface of the material is a low-nickel ternary material, the content of residual alkali is relatively low, the damage of the high-nickel anode material to the anode material in a water washing process is avoided, meanwhile, after the high-nickel material is excessively delithiated, the irreversible phase change from H2 to H3 can be generated, the material itself forms a rock salt phase, cracks are formed on the surface, and the cracks and the electrolyte continuously generate side reactions, so that the structure is collapsed, the low-nickel monocrystal layer coating of the shell layer can avoid the direct contact of the high-nickel material and the electrolyte, so that the phenomenon is inhibited, and the monocrystal-polycrystalline ternary anode material with concentration gradient not only ensures higher discharge capacity, but also greatly improves the cycle stability and the safety.
In order to achieve the above object, the present invention provides a single crystal coated polycrystalline positive electrode material having a concentration gradient, the positive electrode material including an outer shell layer and an inner core layer, the outer shell layer being a single crystal material, the single crystal material having a chemical formula of LiNi x Co y Mn z O 2 Wherein, 0.3<x<0.7，0<y<0.4，0<z<0.4, x + y + z =1; the inner nuclear layer is made of polycrystalline material, and the chemical formula of the polycrystalline material is LiNi a Co b Mn c O 2 Wherein, 0.7<a<1，0<b<0.3，0<c<0.3，a+b+c=1。
According to the monocrystalline coated polycrystalline positive electrode material with the concentration gradient, the thickness of a monocrystalline layer in the outer shell layer is 0-2 μm, and the granularity of a polycrystalline layer in the inner core layer is 4-10 μm.
According to the monocrystalline-coated polycrystalline anode material with the concentration gradient, the ternary precursor used by the anode material has the concentration gradient, and the chemical formula of the external shell layer of the ternary precursor is Ni x Co y Mn z (OH) 2 Wherein, 0.3<x<7，0<y<0.4，0<z<0.4, x + y + z =1; the internal nuclear layer of the ternary precursor has a chemical formula of Ni a Co b Mn c (OH) 2 Wherein, 0.7<a<1，0<b<0.2，0<c<0.2，a+b+c=1。
According to the monocrystalline coated polycrystalline positive electrode material with the concentration gradient, the thickness of an outer shell layer of the ternary precursor is 0-2 μm, and the granularity of an inner core layer of the ternary precursor is 4-10 μm.
The invention also provides a preparation method for preparing the monocrystalline coated polycrystalline cathode material with the concentration gradient, which comprises the following steps: s1: mixing materials, namely uniformly mixing a specially designed ternary precursor material, a proper amount of lithium source and an additive; s2: sintering, synthesizing a polycrystal-polycrystal core-shell structure with different Ni/Co/Mn ratios through a ternary precursor dehydration-lithium source dehydration-lithiation process, and doping high-valence ions such as one or more of W, ti, ta, nb and Sb at the grain boundary of primary particles to block Ni between a core phase and a shell phase 3+ The stability of the core-shell structure in the sintering process is maintained; s3: mixing, namely uniformly mixing the polycrystalline-polycrystalline core-shell structure intermediate with a cosolvent containing Sr or Mg; s4: and (4) secondary sintering, so that complete single crystallization of the intermediate shell is realized, and the single crystal coated polycrystalline ternary anode material with concentration gradient is prepared.
According to the preparation method, in the synthesis process S1 of the cathode material, a lithium source is one of lithium hydroxide or lithium carbonate, and the lithiation ratio Li/Me is 1.0-1.20; in the synthesis process S2 of the anode material, the additive is one or more of tungsten oxide, titanium oxide, tantalum oxide, niobium oxide and antimony oxide, and the addition amount is 1000-5000ppm; in the synthesis process S3 of the cathode material, the cosolvent is one or more of strontium carbonate, strontium oxide, strontium hydroxide, magnesium carbonate, magnesium oxide and magnesium hydroxide, and the addition amount is 1000-3000ppm.
According to the preparation method, in the synthesis process of the anode material, the sintering temperature in the first sintering stage is 650-850 ℃, and the heat preservation time is 10-50h; the sintering temperature of the secondary sintering stage is 850-1050 ℃, and the heat preservation time is 5-60h
The invention also provides a preparation method of the ternary precursor of the single crystal coated polycrystalline anode material with the concentration gradient, and the preparation method of the ternary precursor of the anode material comprises the following steps: c1: preparing two salt solutions, namely B1 and B2, from a metal salt solution according to the designed nickel-cobalt-manganese ratio of a nuclear layer and a shell layer, preparing a complexing agent and a precipitating agent into solutions according to required concentrations, and deoxidizing the three solutions; preparing reaction base liquid in a reaction kettle according to reaction conditions, and heating in a water bath to ensure that the temperature in the kettle is constant; c2: preparing a nuclear layer, maintaining proper pH and ammonia concentration and corresponding stirring speed, introducing a B1 salt solution, a complexing agent and a precipitator for coprecipitation reaction, continuously introducing nitrogen in the reaction, and finishing the preparation of the nuclear layer when the granularity grows to the required size; c3: preparing a shell, readjusting the pH value of the system, the ammonia concentration and the stirring speed, introducing a B2 salt solution, a complexing agent and a precipitator for coprecipitation reaction, continuously introducing air during the reaction, and finishing the preparation of the shell when the thickness meets the required requirement; c4: and after the reaction is finished, transferring the material to a centrifuge for washing, centrifuging at a high speed, drying, transferring to an oven, and finally, sieving and demagnetizing to obtain the required ternary precursor.
According to the preparation method of the ternary precursor, nickel, cobalt and manganese are selected as raw materials and are water-soluble salts such as sulfate, nitrate and the like; selecting water-soluble alkali such as NaOH, KOH and the like as a precipitator; the complexing agent is selected from ammonia water, soluble ammonium salt and the like.
According to the invention, the concentration of the salt solution is 0-2.5mol/L, the concentration of the alkali solution is 0-20mol/L, and the concentration of the complexing agent ammonia is 0-20mol/L; the pH value in the reaction kettle is 10-14 (at 25 ℃), the ammonia concentration is 0-1mol/L, and the nitrogen flow rate is 5-20L/min; the temperature in the reaction kettle is 40-80 ℃; the stirring speed is 400-1000rpm.
The invention has the technical effects that a precursor material with concentration gradient is prepared by a special structural design from a ternary precursor, and the cathode material with concentration gradient is prepared by sintering process control, wherein the core is a high-nickel polycrystalline ternary cathode material, and the shell is a low-nickel single crystal ternary cathode material. Ternary cathode material with Ni 3+ The content is increased, and the surface residual alkali content is relatively high. The surface of the designed material is a low-nickel ternary material, the content of residual alkali is relatively low, and the damage of a high-nickel anode material to the anode material in a water washing process is avoided. Meanwhile, after the lithium is excessively removed from the high-nickel material, irreversible phase change from H2 to H3 can occur, the material itself forms a rock salt phase, cracks are formed on the surface of the material, side reaction is continuously generated between the material and the electrolyte, the structure is collapsed, the cyclic attenuation is severe, the shell layer low-nickel single crystal layer is coated, the high-nickel material is prevented from being in direct contact with the electrolyte, and the phenomenon can be inhibited. The ternary anode material with concentration gradient monocrystal-polycrystal ensures high discharge capacity and greatly improves the cycle stability and safety performance.
Drawings
FIG. 1 is a schematic diagram of the structure of an intermediate of the present invention (a); FIG. 2 is a schematic structural view of the positive electrode material of the present invention (b); FIG. 3 is a line scan of the EDS of examples and comparative examples of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and embodiments, it being understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.
Example 1
With reference to fig. 1, 2 and 3, a single crystal coated polycrystalline positive electrode material having a concentration gradient, in which a core portion is a polycrystalline material, a particle size is 9 μm, and a molecular formula is Li (Ni) was prepared in example 1 0.9 Co 0.05 Mn 0.05 )O 2 The shell part is a single crystal material with a thickness of 0.5 μm and a molecular formula of Li (Ni) 0.33 Co 0.33 Mn 0.33 )O 2 . The preparation method of the ternary precursor with the concentration gradient and the monocrystalline-polycrystalline ternary precursor cathode material with the concentration gradient comprises the following steps:
1. synthesis of precursor
The method comprises the following steps of taking nickel sulfate, cobalt sulfate and manganese sulfate as raw materials, wherein the proportion of nickel, cobalt and manganese is 90 1 (ii) a Taking nickel sulfate, cobalt sulfate and manganese sulfate as raw materials, wherein the proportion of nickel, cobalt and manganese is 1 2 (ii) a The precipitant is 8mol/L NaOH solution, marked as B 3 (ii) a The complexing agent is NH 3 ·H 2 O is prepared to 5mol/L by deionized water and is marked as B 4 。
Controlling the feeding speed of the solution to mix the solution B 1 、B 3 、B 4 Dropwise adding into a reaction kettle, controlling the stirring speed in the reaction kettle to be 600rpm, the reaction temperature to be 50 ℃, the pH to be =13.00 (at 60 ℃), the ammonia concentration to be 0.1mol/L, and N 2 The flow rate was 10L/min.
When the particle diameter D50 is 9 μm, the solution B is mixed 2 、B 3 、B 4 Adjusting the stirring speed in the reaction kettle to 700rpm, the pH value to 10.50 (at 60 ℃), the ammonia concentration to 0.3mol/L and the air flow rate to 10L/min, stopping feeding when the particle size D50 reaches 10 micrometers, discharging all the slurry into an aging kettle, maintaining the reaction temperature in the kettle to be 50 ℃, the rotating speed to be 200rpm, aging for 10 hours, then washing the slurry by using deionized water, transferring the filtrate to an oven for 10 hours at 120 ℃, and controlling the water content to be less than 1%.
2. Synthesis of cathode Material
Adding a lithium source into LiOH serving as the lithium source according to the proportion that Li/Me is 1.01; and (3) uniformly mixing the intermediate product with 2000ppm of strontium oxide serving as a fluxing agent, and carrying out secondary sintering, wherein the sintering temperature in the secondary sintering process is 900 ℃, and the heat preservation time is 20 hours, so that the monocrystalline-polycrystalline ternary cathode material with the concentration gradient is finally prepared.
3. Preparation of lithium batteries
The positive electrode material, a conductive active material SuperP and a binder PVdF are mixed into slurry according to the proportion of 90.
And (3) carrying out charge and discharge tests by adopting a LAND-2001 type blue test system, wherein the charge and discharge interval is 3.0-4.3V, the temperature is 25 ℃, the discharge specific capacity and the first-loop coulombic efficiency are tested at 0.33 ℃, and the cycle efficiency of the battery is tested at 1 ℃. The test result shows that the specific discharge capacity of the battery assembled by the cathode material prepared in the embodiment 1 at 25 ℃ and 0.33C multiplying power is 211.43mAhg < -1 >, the coulombic efficiency of the first circle is 90.12%, and the capacity retention rate after 50 circles of circulation is 98.37%.
Example 2
With reference to fig. 1, 2 and 3, example 2 prepared a single crystal-polycrystalline ternary positive electrode material having a concentration gradient, in which the core portion was a polycrystalline material, the particle size was 9 μm, and the molecular formula was Li (Ni) 0.9 Co 0.05 Mn 0.05 )O 2 The shell part is a single crystal material with a thickness of 0.5 μm and a molecular formula of Li (Ni) 0.5 Co 0.2 Mn 0.3 ) And (3) O2. The preparation method of the ternary precursor with the concentration gradient and the monocrystalline-polycrystalline ternary precursor cathode material with the concentration gradient comprises the following steps:
1. synthesis of precursors
Taking nickel sulfate, cobalt sulfate and manganese sulfate as raw materials, wherein the proportion of nickel, cobalt and manganese is 90 1 (ii) a Taking nickel sulfate, cobalt sulfate and manganese sulfate as raw materials, wherein the proportion of nickel, cobalt and manganese is 5 2 (ii) a The precipitant is 10mol/L NaOH solution, and is marked as B 3 (ii) a The complexing agent is NH 3 ·H 2 O is mixed with deionized water to be 10mol/L and marked as B 4 。
Controlling the feeding speed of the solution, and adding the solution B 1 、B 3 、B 4 Dropwise adding into a reaction kettle, controlling the stirring speed in the reaction kettle to 700rpm, the reaction temperature to 60 ℃, the pH to be =13.20 (at 60 ℃), the ammonia concentration to be 0.15mol/L, and N 2 The flow rate was 15L/min.
When the particle diameter D50 is 9 μm, the solution B is prepared 2 、B 3 、B 4 Adjusting the stirring speed in the reaction kettle to 750rpm, the pH value to 11.00 (at 60 ℃), the ammonia concentration to 0.35mol/L and the air flow rate to 15L/min, stopping feeding when the particle size D50 reaches 10 mu m, discharging all the slurry into an aging kettle, maintaining the reaction temperature in the kettle to be 60 ℃, the rotating speed to be 200rpm, aging for 10h, then washing the slurry by using deionized water, transferring the filtrate to an oven for 10h at 120 ℃ after centrifugation, and controlling the water content to be less than 1%.
2. Synthesis of cathode Material
Adding a lithium source into LiOH serving as the lithium source according to the proportion that Li/Me is 1.03; and (3) uniformly mixing the intermediate product with 2500ppm magnesium carbonate serving as a fluxing agent, and carrying out secondary sintering, wherein the sintering temperature in the secondary sintering process is 950 ℃, and the heat preservation time is 15 hours, so that the monocrystalline-polycrystalline ternary cathode material with the concentration gradient is finally prepared.
3. Preparation of lithium batteries
The positive electrode material was prepared into a battery and tested in the same manner as in example 1. Adopting LAND-2001 type blue test system to perform charge and discharge test, wherein the charge and discharge interval is 3.0-4.3V, the temperature is 25 ℃, the discharge specific capacity and the first-loop coulombic efficiency are tested at 0.33 ℃, and the discharge specific capacity and the first-loop coulombic efficiency are tested atThe cycling efficiency of the cells was tested at 1C. The test result shows that the specific discharge capacity of the battery assembled by the cathode material prepared in the example 2 at the temperature of 25 ℃ and the multiplying power of 0.33C is 213.29mAhg -1 The coulombic efficiency of the first cycle is 90.54%, and the capacity retention rate after 50 cycles of circulation is 97.76%.
Example 3
With reference to fig. 1, 2 and 3, example 3 prepared a single crystal-polycrystalline ternary positive electrode material having a concentration gradient, in which the core portion was a polycrystalline material, the particle size was 9 μm, and the molecular formula was Li (Ni) 0.9 Co 0.05 Mn 0.05 )O 2 The shell part is a single crystal material with a thickness of 0.5 μm and a molecular formula of Li (Ni) 0.6 Co 0.2 Mn 0.2 )O 2 . The preparation method of the ternary precursor with the concentration gradient and the monocrystalline-polycrystalline ternary precursor cathode material with the concentration gradient comprises the following steps:
1. synthesis of precursor
The method comprises the following steps of taking nickel sulfate, cobalt sulfate and manganese sulfate as raw materials, wherein the proportion of nickel, cobalt and manganese is 90 1 (ii) a Taking nickel sulfate, cobalt sulfate and manganese sulfate as raw materials, wherein the proportion of nickel, cobalt and manganese is 5 2 (ii) a The precipitator is 12mol/L NaOH solution marked as B 3 (ii) a The complexing agent is NH 3 ·H 2 O is prepared with deionized water to 15mol/L and is marked as B 4 。
Controlling the feeding speed of the solution, and adding the solution B 1 、B 3 、B 4 Dropwise adding into a reaction kettle, controlling the stirring speed in the reaction kettle at 800rpm, the reaction temperature at 70 ℃, the pH =12.50 (at 60 ℃), the ammonia concentration at 0.2mol/L, and the N 2 The flow rate was 20L/min.
When the particle diameter D50 is 9 μm, the solution B is prepared 2 、B 3 、B 4 Adjusting the stirring speed in the reaction kettle to 800rpm, the pH value to 11.50 (at 60 ℃), the ammonia concentration to be 0.4mol/L and the air flow rate to be 20L/min, stopping feeding when the particle size D50 reaches 10 mu m, discharging all the slurry into an aging kettle, and discharging the slurry into the kettleKeeping the reaction temperature at 70 ℃ and the rotation speed at 200rpm, aging for 10h, washing the slurry with deionized water, centrifuging, transferring the filtrate to an oven at 120 ℃ for 10h, and keeping the water content less than 1%.
2. Synthesis of cathode Material
Adding a lithium source into LiOH serving as the lithium source according to the proportion that Li/Me is 1.05; and (3) uniformly mixing the intermediate product with 3000ppm strontium hydroxide serving as a fluxing agent, and carrying out secondary sintering at the sintering temperature of 1000 ℃ for 10 hours in the secondary sintering process to finally prepare the monocrystalline-polycrystalline ternary cathode material with the concentration gradient.
3. Preparation of lithium batteries
The positive electrode material was prepared into a battery and tested in the same manner as in example 1. And (3) carrying out charge and discharge tests by adopting a LAND-2001 type blue test system, wherein the charge and discharge interval is 3.0-4.3V, the temperature is 25 ℃, the discharge specific capacity and the first-loop coulombic efficiency are tested at 0.33 ℃, and the cycle efficiency of the battery is tested at 1 ℃. The test result shows that the specific discharge capacity of the battery assembled by the cathode material prepared in the example 2 at 25 ℃ and 0.33C rate is 214.58mAhg -1 The coulombic efficiency of the first cycle was 90.72%, and the capacity retention rate after 50 cycles was 95.59%.
Comparative example 1
Referring to fig. 1, 2 and 3, comparative example 1 prepared a polycrystalline-polycrystalline ternary cathode material having a concentration gradient in which the core portion was a polycrystalline material having a particle size of 9 μm and a molecular formula of Li (Ni) 0.9 Co 0.05 Mn 0.05 )O 2 The shell is made of polycrystalline material with thickness of 0.5 μm and molecular formula of Li (Ni) 0.5 Co 0.2 Mn 0.3 )O 2 . The preparation method of the ternary precursor with the concentration gradient and the polycrystalline-polycrystalline ternary precursor cathode material with the concentration gradient comprises the following steps:
1. synthesis of precursor
Nickel sulfate, cobalt sulfate and sulfurManganese acid is used as a raw material, the ratio of nickel, cobalt and manganese is 90 1 (ii) a Taking nickel sulfate, cobalt sulfate and manganese sulfate as raw materials, wherein the proportion of nickel, cobalt and manganese is 5 2 (ii) a The precipitant is 10mol/L NaOH solution, and is marked as B 3 (ii) a The complexing agent is NH 3 ·H 2 O is mixed with deionized water to prepare 10mol/L, and is marked as B 4 。
Controlling the feeding speed of the solution to mix the solution B 1 、B 3 、B 4 Dropwise adding into a reaction kettle, controlling the stirring speed in the reaction kettle to 700rpm, the reaction temperature to 60 ℃, the pH to be =13.20 (at 60 ℃), the ammonia concentration to be 0.15mol/L, and N 2 The flow rate was 15L/min.
When the particle diameter D50 is 9 μm, the solution B is prepared 2 、B 3 、B 4 Adjusting the stirring speed in the reaction kettle to 750rpm, the pH value to 11.00 (at 60 ℃), the ammonia concentration to 0.35mol/L and the air flow rate to 15L/min, stopping feeding when the particle size D50 reaches 10 mu m, discharging all the slurry into an aging kettle, maintaining the reaction temperature in the kettle to be 60 ℃, the rotating speed to be 200rpm, aging for 10h, then washing the slurry by using deionized water, transferring the filtrate to an oven for 10h at 120 ℃ after centrifugation, and controlling the water content to be less than 1%.
2. Synthesis of cathode Material
LiOH is used as a lithium source, the lithium source is added according to the proportion that Li/Me is 1.03.
3. Preparation of lithium batteries
The positive electrode material was prepared into a battery and tested in the same manner as in example 1. Performing charge and discharge test by adopting LAND-2001 type blue light test system at 25 deg.C with a charge and discharge interval of 3.0-4.3V, and testing specific discharge capacity and first-loop coulombic efficiency at 0.33 deg.C, and testing battery performance at 1CThe cycle efficiency. The test result shows that the specific discharge capacity of the battery assembled by the cathode material prepared in the example 2 at the temperature of 25 ℃ and the multiplying power of 0.33C is 212.86mAhg -1 The coulombic efficiency of the first cycle was 89.34%, and the capacity retention rate after 50 cycles was 94.61%.
Comparative example 2
Referring to fig. 1, 2 and 3, a conventional high-nickel ternary cathode material having a particle size D50 of 10 μm and a molecular formula of Li (Ni) was prepared in comparative example 2 0.9 Co 0.05 Mn 0.05 )O 2 . The preparation method of the high-nickel ternary precursor and the anode material thereof comprises the following steps:
1. synthesis of precursors
Taking nickel sulfate, cobalt sulfate and manganese sulfate as raw materials, wherein the proportion of nickel, cobalt and manganese is 90 1 (ii) a The precipitant is 10mol/L NaOH solution, marked as B 2 (ii) a The complexing agent is NH 3 ·H 2 O is mixed with deionized water to be 10mol/L and marked as B 3 。
Controlling the feeding speed of the solution to mix the solution B 1 、B 2 、B 3 Dropwise adding into a reaction kettle, controlling the stirring speed in the reaction kettle at 700rpm, the reaction temperature at 60 deg.C, pH =13.00 (at 60 deg.C), ammonia concentration at 0.15mol/L, and N 2 The flow rate was 15L/min.
Stopping feeding when the particle size D50 reaches 10 mu m, completely discharging the slurry into an aging kettle, maintaining the reaction temperature in the kettle at 60 ℃, rotating speed at 200rpm, aging for 10h, then washing the slurry by using deionized water, transferring the filtrate after centrifugation to an oven at 120 ℃ for 10h, wherein the conductivity of the filtrate is less than 10 mu s/cm, and the water content is less than 1%.
2. Synthesis of cathode Material
Adding a lithium source into LiOH serving as the lithium source according to the proportion that Li/Me is 1.03; washing the primary burned product with water at a water-material ratio of 1 for 5min, and then transferring the primary burned product to an oven for drying at 130 ℃ for 10 h; and (3) uniformly mixing the washing material with 1000ppm of boron oxide, carrying out secondary sintering at the sintering temperature of 300 ℃, and carrying out heat preservation for 10 hours to prepare the high-nickel ternary cathode material.
3. Preparation of lithium batteries
The positive electrode material was prepared into a battery and tested in the same manner as in example 1. And (3) carrying out charge and discharge tests by adopting a LAND-2001 type blue test system, wherein the charge and discharge interval is 3.0-4.3V, the temperature is 25 ℃, the discharge specific capacity and the first-loop coulombic efficiency are tested at 0.33 ℃, and the cycle efficiency of the battery is tested at 1 ℃. The test result shows that the specific discharge capacity of the battery assembled by the cathode material prepared in the example 2 at the temperature of 25 ℃ and the multiplying power of 0.33C is 215.63mAhg -1 The coulombic efficiency of the first cycle is 88.16%, and the capacity retention rate after 50 cycles is 92.18%.
Taking the NCM9055 ternary cathode material as an example, through comparison between example 1, example 2 and example 3 and comparative example 1 and comparative example 2: the cycle performance of the single crystal coated polycrystalline material with the concentration gradient is obviously improved; the discharge capacity is slightly lost, and particularly, the positive electrode material prepared in the example 3 is not greatly different from a pure-phase polycrystalline material. The results show that the single crystal coated polycrystalline type cathode material with the concentration gradient designed and invented by the patent has great advantages in improving the cycling stability of the material.
Table 1: test data for each example and comparative example CR2032 coin cell
| Sample numbering | Unit of | Example 1 | Example 2 | Example 3 | Comparative example 1 | Comparative example 2 |
| 0.33C specific discharge capacity | mAh g-1 | 211.43 | 213.29 | 214.58 | 212.86 | 215.63 |
| First turn coulombic efficiency | % | 90.12 | 90.54 | 90.72 | 89.34 | 88.16 |
| 0.5C specific discharge capacity | mAh g-1 | 208.64 | 210.77 | 211.05 | 210.36 | 211.39 |
| Specific discharge capacity of 1C | mAh g-1 | 202.35 | 204.03 | 204.96 | 203.72 | 205.22 |
| Specific capacity of 2C discharge | mAh g-1 | 195.51 | 197.62 | 198.47 | 197.01 | 198.84 |
| Specific discharge capacity of 3C | mAh g-1 | 191.38 | 193.33 | 194.11 | 192.88 | 194.57 |
| 1C (50 th) cycle Retention | % | 98.37 | 97.76 | 95.59 | 94.61 | 92.18 |
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.
Claims (10)
1. The single crystal coated polycrystalline positive electrode material with the concentration gradient is characterized by comprising an outer shell layer and an inner core layer, wherein the outer shell layer is made of single crystal materials, and the chemical formula of the single crystal materials is LiNi x Co y Mn z O 2 Wherein, 0.3<x<0.7，0<y<0.4，0<z<0.4, x + y + z=1; the inner nuclear layer is made of polycrystalline material, and the chemical formula of the polycrystalline material is LiNi a Co b Mn c O 2 Wherein, 0.7<a<1，0<b<0.3，0<c<0.3，a+b+c=1。
2. The monocrystalline coated polycrystalline positive electrode material with the concentration gradient according to claim 1, wherein the thickness of the monocrystalline layer in the outer shell layer is 0-2 μm, and the grain size of the polycrystalline layer in the inner core layer is 4-10 μm.
3. The single crystal coated polycrystalline cathode material with the concentration gradient as claimed in claim 1, wherein the ternary precursor used for the cathode material has the concentration gradient, and the chemical formula of the external shell layer of the ternary precursor is Ni x Co y Mn z (OH) 2 Wherein, 0.3<x<7，0<y<0.4，0<z<0.4, x + y + z =1; the internal nuclear layer of the ternary precursor has a chemical formula of Ni a Co b Mn c (OH) 2 Wherein, 0.7<a<1，0<b<0.2，0<c<0.2，a+b+c=1。
4. The monocrystalline coated polycrystalline positive electrode material with the concentration gradient according to claim 3, wherein the thickness of an outer shell layer of the ternary precursor is 0-2 μm, and the granularity of an inner core layer of the ternary precursor is 4-10 μm.
5. A production method for producing the single crystal-coated polycrystalline positive electrode material having a concentration gradient according to any one of claims 1 to 4, the production method comprising the steps of:
s1: mixing materials, namely uniformly mixing a specially designed ternary precursor material, a proper amount of lithium source and an additive;
s2: sintering, synthesizing a polycrystal-polycrystal core-shell structure with different Ni/Co/Mn ratios through a ternary precursor dehydration-lithium source dehydration-lithiation process, and doping high-valence ions such as one or more of W, ti, ta, nb and Sb at the grain boundary of primary particles to block Ni between a core phase and a shell phase 3+ The mutual diffusion of the components is realized, and the stability of the core-shell structure in the sintering process is maintained;
s3: mixing, namely uniformly mixing the polycrystalline-polycrystalline core-shell structure intermediate with a cosolvent containing Sr or Mg;
s4: and (4) secondary sintering to realize complete single crystallization of the intermediate shell layer, and prepare the single crystal coated polycrystalline ternary anode material with concentration gradient.
6. The preparation method according to claim 5, wherein in the synthesis process S1 of the positive electrode material, the lithium source is one of lithium hydroxide or lithium carbonate, and the lithiation ratio Li/Me is 1.0-1.20; in the synthesis process S2 of the anode material, the additive is one or more of tungsten oxide, titanium oxide, tantalum oxide, niobium oxide and antimony oxide, and the addition amount is 1000-5000ppm; in the synthesis process S3 of the cathode material, the cosolvent is one or more of strontium carbonate, strontium oxide, strontium hydroxide, magnesium carbonate, magnesium oxide and magnesium hydroxide, and the addition amount is 1000-3000ppm.
7. The preparation method of the positive electrode material, according to the claim 5, characterized in that in the synthesis process of the positive electrode material, the sintering temperature in the first sintering stage is 650-850 ℃, and the heat preservation time is 10-50h; the sintering temperature in the secondary sintering stage is 850-1050 ℃, and the heat preservation time is 5-60h.
8. A preparation method for preparing the ternary precursor of the single crystal coated polycrystalline cathode material with the concentration gradient, which is described in any one of claims 3 and 4, is characterized in that the preparation steps of the ternary precursor of the cathode material are as follows:
c1: preparing two salt solutions B1 and B2 by using a metal salt solution according to the designed nickel-cobalt-manganese ratio of a core layer and a shell layer, preparing a complexing agent and a precipitating agent into solutions according to required concentrations, and deoxidizing the three solutions; preparing reaction base liquid in a reaction kettle according to reaction conditions, and heating in a water bath to ensure that the temperature in the kettle is constant;
c2: preparing a nuclear layer, maintaining proper pH and ammonia concentration and corresponding stirring speed, introducing a B1 salt solution, a complexing agent and a precipitator for coprecipitation reaction, continuously introducing nitrogen in the reaction, and finishing the preparation of the nuclear layer when the granularity grows to the required size;
c3: preparing a shell, readjusting the pH value, the ammonia concentration and the stirring speed of the system, introducing a B2 salt solution, a complexing agent and a precipitator to perform coprecipitation reaction, continuously introducing air during the reaction, and completing the preparation of the shell when the thickness meets the required requirements;
c4: and after the reaction is finished, transferring the material to a centrifuge for washing, transferring the material to an oven for drying after high-speed centrifugation and spin-drying, and finally, sieving and demagnetizing to obtain the required ternary precursor.
9. The preparation method according to claim 8, characterized in that the raw materials of nickel, cobalt and manganese are selected as water-soluble salts such as sulfate and nitrate; selecting water-soluble alkali such as NaOH, KOH and the like as a precipitator; the complexing agent is selected from ammonia water, soluble ammonium salt and the like.
10. The preparation method according to claim 9, wherein the salt solution has a concentration of 0 to 2.5mol/L, the alkali solution has a concentration of 0 to 20mol/L, and the complexing agent has an ammonia concentration of 0 to 20mol/L; the pH value in the reaction kettle is 10-14 (at 25 ℃), the ammonia concentration is 0-1mol/L, and the nitrogen flow rate is 5-20L/min; the temperature in the reaction kettle is 40-80 ℃; the stirring speed is 400-1000rpm.
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