CN109326781B - Preparation method of high-voltage lithium cobalt oxide positive electrode material - Google Patents
Preparation method of high-voltage lithium cobalt oxide positive electrode material Download PDFInfo
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Abstract
The invention discloses a preparation method of a high-voltage lithium cobaltate cathode material, which comprises the following steps: (1) mixing cobaltosic oxide containing a doping element M, a lithium source, an oxide containing a doping element M', a grain refiner and a fluxing agent to obtain a primary mixture; (2) sintering and crushing the primary mixture to obtain primary sintered powder; (3) mixing the primary sintering powder with the coating to obtain a secondary mixture; (4) and sintering and crushing the secondary mixture to obtain the lithium cobaltate cathode material. The doping of the invention is divided into two modes of pre-blending and dry mixing to solve the problem of segregation of the doping elements in the product on the microscopic scale; the problem of segregation of different substances during material mixing is solved by adopting a coulter type mixing technology; combining a grain refiner and a fluxing agent to synthesize a material with a mixed morphology; the double effects of doping element surface crystallization catalysis and cladding are adopted; so that the performance of the high-voltage lithium cobaltate is obviously improved.
Description
Technical Field
The invention belongs to a lithium ion battery anode material, and particularly relates to a preparation method of a high-voltage lithium cobalt oxide anode material.
Background
With the rapid development of electronic technology, the 3C products are updated more and more frequently, and the development of lithium ion battery cathode materials with higher energy density and better cycle performance becomes a goal of the lithium ion battery industry. Lithium cobaltate (LiCoO)2) The lithium ion battery positive electrode material has the advantages of high specific capacity, high compaction density, high volume energy density, simple production process and the like, is widely applied to consumer electronic products such as smart phones, tablet computers, notebooks and the like, and becomes one of the most common lithium ion battery positive electrode materials commercialized at present. The theoretical capacity of lithium cobaltate is 274mAh/g,in the conventional use process, only half of lithium is subjected to extraction and intercalation reactions, so that the actual capacity is only about 145 mAh/g. With the increasing demand for high capacity batteries and higher performance requirements, battery manufacturers have gradually used high voltage lithium cobaltate (4.4V, 4.45V or higher) instead of 4.2V conventional lithium cobaltate to make batteries. This is mainly because at higher voltages, more lithium in lithium cobaltate will participate in the deintercalation and intercalation reactions, thereby providing higher specific capacity. If the charge cut-off voltage of the lithium cobaltate is increased to 4.45V, the discharge specific capacity can be increased to about 180mAh/g, so that the increase of the charge voltage is an effective way for increasing the discharge specific capacity of the lithium cobaltate.
Although the specific capacity of lithium cobaltate can be obviously improved by increasing the charging voltage, the cycle performance of lithium cobaltate is reduced along with the increase of the charging voltage, and the main reasons are two aspects. On the one hand, LiCoO is used when the charge cut-off voltage is greater than 4.2V2Li in (1)+A large amount of Li ions can be deintercalated, so that + 3-valent Co ions in the structure are converted into + 4-valent Co ions, oxygen defects are formed, the binding force of cobalt and oxygen is weakened, the layered crystal structure of the material is finally collapsed and damaged, the Li ions can not be deintercalated normally during charging and discharging, and the capacity of the material is rapidly attenuated. On the other hand, in a high-voltage charge/discharge state, Co ions are easily dissolved in the electrolyte, and + 4-valent Co ions have strong oxidizing property, which causes oxidative decomposition of the electrolyte and shortens the service life of the battery.
In order to solve the problems of structural collapse and cobalt dissolution of the lithium cobaltate positive electrode material during high-voltage charge and discharge, modification means are adopted to solve the problems at present, and the lithium cobaltate positive electrode material is mainly doped and coated on the surface. A great deal of work is done by many researchers, compounds containing Al, Zr, Ti, Mg and the like are often doped in bulk phase doping, and a lithium cobaltate structure is stabilized by virtue of an M-O bond with higher bond energy; the surface coating is usually made of TiO2、MgO、ZrO2、Al2O3、SiO2The lithium cobaltate particles are coated by the oxides or the metal phosphates, so that the corrosion of the electrolyte on the surface of the lithium cobaltate under high voltage is inhibited, the dissolution of cobalt is reduced, and the stability of the structure is improved. But mixThere is still much work to improve the inclusion and coating. Such as: in the research work of the prior art, the phenomenon that doping substances of high-voltage lithium cobaltate are easily distributed unevenly inside lithium cobaltate particles is easily caused, and the phenomenon of doping substance segregation is more obvious as the charge cut-off voltage of the lithium cobaltate is continuously increased and the doping amount is gradually increased. In addition, the current coating work is mainly to coat a layer of oxide or metal phosphate on the surface of lithium cobaltate particles, inhibit the corrosion of electrolyte on the surface of the lithium cobaltate and reduce the cobalt dissolution. However, these coating works neglected a problem because of some surplus Li on the surface of lithium cobaltate+And Li+The chemical property is active, so that the material has overlarge activity under high voltage, self decomposition and other side reactions with electrolyte occur, and the stability of the material is influenced.
The uniformity of the high-voltage lithium cobaltate doping directly influences the structural stability of the anode material under high voltage, and further influences the electrochemical performance of the material. The traditional process method is carried out by adopting a solid-phase mixing method, namely, a lithium source, cobalt oxide and a dopant are mixed in a solid-phase form, and then sintering is carried out at high temperature to realize doping. Therefore, the uniformity of doping is affected by the morphology and the mixing state of the dopant, and also by the thermal diffusion of the metal ions during the high temperature reaction. The doped metal ions and the lithium ions are diffused and embedded into the cobalt oxide phase to form a competition process, the lithium ions as light metal ions have higher diffusion rate, a small amount of metal ion doped lithium cobalt oxide phase is formed in the reaction process, and then the remaining metal ions are diffused into the lithium cobalt oxide phase. Once the lithium cobaltate phase is formed, the diffusion of the metal dopant ions is hindered and the dopant metal ions tend to concentrate at the surface of the particle. Therefore, the traditional process method is difficult to realize uniform doping of the material, and particularly, as the charge cut-off voltage of the lithium cobaltate is increased continuously, more dopants are needed to stabilize the lithium cobaltate structure, so that the traditional process is more difficult to realize uniform doping.
In addition, the shape of the high-voltage lithium cobaltate is also one of the important factors influencing the performance of the high-voltage lithium cobaltate, and at present, the shape of the high-voltage lithium cobaltate has two trends, one trend is a single crystal shape, and the other trend is a single crystal-like shape. The high-voltage lithium cobaltate with the single crystal morphology is generally obtained by sintering at high temperature (higher than 1050 ℃) for a long time (higher than 12h)) in one-step sintering, and the single crystal material obtained by the method has smaller specific surface area, reduces side reaction with electrolyte and is beneficial to improvement of cycling performance; but the single particle diameter is larger, so that the material has poorer multiplying power and lower first coulombic efficiency, and the energy utilization rate of the material is reduced. The single crystal-like material is a secondary ball consisting of large primary particles, and has better multiplying power and higher first coulombic efficiency due to smaller granularity of the primary particles; however, the specific surface area is large, side reactions with the electrolyte solution increase, and secondary spherical particles are liable to be cracked at the time of rolling of the tablet, resulting in deterioration of cycle performance.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects and shortcomings in the background technology and provide a preparation method of a high-voltage lithium cobalt oxide positive electrode material.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a preparation method of a high-voltage lithium cobaltate positive electrode material comprises the following steps:
(1) primary mixing: mixing cobaltosic oxide containing a doping element M, a lithium source, a compound containing a doping element M', a grain refiner and a fluxing agent to obtain a primary mixture;
(2) primary sintering: sintering and crushing the primary mixture to obtain primary sintered powder;
(3) secondary material mixing: mixing the primary sintering powder with a coating to obtain a secondary mixture;
(4) and (3) secondary sintering: and sintering and crushing the secondary mixture to obtain the high-voltage lithium cobalt oxide positive electrode material.
In the invention, the primary sintering mainly has the function of forming the basic structure of lithium cobaltate to complete doping; the secondary sintering mainly has the function of forming a coating layer with a protective effect on the surface of the lithium cobaltate and repairing the surface. The technical effect that the high-voltage lithium cobalt oxide can not be doped and coated is realized only by directly sintering the coating and other raw materials once.
In the invention, the particle size D10 after the pulverization in the step (2) is 10.0-12.0 μm, D50 is 17.0-19.0 μm, and D90 is 26.0-28.0 μm. The primary sintering powder with the particle size distribution has slightly increased particle size (2.0-3.0 mu m larger than the primary sintering powder as a whole) after secondary sintering in the step (4), and can basically keep the same particle size distribution as the primary sintering powder after secondary crushing. The particle size distribution of the finished product is beneficial to improving the compaction density during battery manufacturing, and simultaneously, the quantity of micro powder and large particles is controlled, thereby being beneficial to improving the high-temperature performance and the rate capability.
In the above preparation method, preferably, the preparation method of the cobaltosic oxide containing the doping element M comprises the following steps:
(S1) adding a soluble raw material (cobalt source) containing cobalt into the aqueous solution to be mixed into slurry, then adding a soluble raw material (M source) containing a doping element M, and stirring to obtain mixed slurry;
(S2) adding a precipitator and a complexing agent into the mixed slurry obtained in the step (S1) in sequence, controlling the stirring speed in the reaction process to be 100-900 rmp, the temperature to be 20-90 ℃, the time to be 5-40 h, the pH value to be 6-11, and the solid-liquid mass ratio to be 1 (3-7), and reacting to obtain cobalt hydroxide slurry containing the doping element M;
(S3) adding an oxidant into the cobalt hydroxide slurry obtained in the step (S2), controlling the stirring speed in the reaction process to be 300-1300 rmp, the temperature to be 30-90 ℃, and the time to be 2-15 h, and reacting to obtain cobaltosic oxide slurry containing the doping element M;
(S4) filtering the cobaltosic oxide slurry obtained in the step (S3) until the filter cake contains 20-60% of water, and then drying the filter cake at the temperature of 80-400 ℃ for 1-30 h to obtain the cobaltosic oxide containing the doping element M.
The invention adopts cobaltosic oxide containing doping element M as an important raw material, and the raw material is prepared by a wet method; by adjusting proper process parameters, the coprecipitation reaction of the soluble raw material containing cobalt and the soluble raw material containing the doping element M can be simultaneously carried out in the aqueous solution, so that the cobalt element and the doping element M can be uniformly mixed at an atomic level in the product of the hydroxide, and the doping element M is completely and uniformly distributed on a microscale in the finally synthesized high-voltage lithium cobalt oxide product, thereby being beneficial to the improvement of the product performance.
In the above preparation method, preferably, the soluble material containing cobalt in the step (S1) is one or more of cobalt chloride, cobalt nitrate and cobalt sulfate; the soluble raw material containing the doping element M is one or more of sulfate, nitrate, acetate and chloride.
In the preparation method of the cobaltosic oxide containing the doping element M, the doping element M is an additive and mainly plays a role in stabilizing a structure, usually, the doping element M is a non-chemically active substance, the addition amount of the doping element M is required to be controlled within the range of the invention, if the addition amount exceeds the range of the invention, the capacity of the prepared high-voltage lithium cobaltate material can be reduced, and if the addition amount is lower than the range of the invention, the doping element M cannot play a role in stabilizing the structure.
In the above preparation method, preferably, the precipitant is sodium hydroxide in the step (S2); the molar ratio of the addition amount of the precipitator to the total amount of Co and M is n (precipitator), wherein n (Co + M) is (2-3) and 1; the complexing agent is ammonia water; the concentration of the complexing agent is 0.05-1 mol/L.
When ammonia water is not added in the system or the concentration of the ammonia water is lower than the range of the invention, the primary particle size of the precipitated product is very fine, and the particles are mutually agglomerated to form a loose spheroid with an irregular shape. Along with the increase of the concentration of ammonia water, the solubility of Co and M in the system is obviously increased, the supersaturation degree of the coprecipitation system is sharply reduced, the nucleation speed of crystals is greatly reduced, the growth speed of the crystals is continuously accelerated, and the grain size of the obtained precipitation product is gradually increased. On the other hand, along with the improvement of ammonia water concentration, the tiny precipitate granule that originally generates also is changeed in dissolving and deposit once more and separate out on the large granule surface for the large granule particle diameter constantly grows up, smooth. When the concentration of ammonia water in the system is higher than the range of the invention, new nuclei are less in the reaction process, small particles are basically absent, the formation of crystal nuclei only accounts for a small proportion, and the large total ammonia concentration enables the small particles to be dissolved in the solution and continue to grow on the surfaces of the large particles; however, excessively large precursor particles also cause excessively large particles of the battery material after sintering, and the electrochemical rate discharge characteristics of the material are degraded. Therefore, the concentration of the complexing agent ammonia water in the mixed slurry is controlled within the range of the invention, the spheroidal particles with proper particle size and smooth surface can be obtained, the sphericity and compactness of the spheroidal particles are larger, and the dispersibility among the particles is good.
In the above preparation method, preferably, the oxidant in the step (S3) is one or more of air, oxygen and hydrogen peroxide; more preferably, the oxidizing agent is compressed air, which is blown from the bottom of the reaction vessel through a conduit, and the gas flows in the reaction vessel from bottom to top, and can play a role in stirring the reaction slurry to accelerate the oxidation reaction; meanwhile, the stirring in the step (S3) may be realized by installing baffles and stirring paddles on the wall of the reaction vessel, and the turbulence generated during the stirring is favorable for uniformly mixing the oxidant and the hydroxide slurry, so as to accelerate the oxidation reaction.
Calculated by each kilogram of cobaltosic oxide containing the doping element M, the addition amount of the oxidant is 80-350 g/kg. When the amount of the oxidizing agent added is less than the range of the present invention, the hydroxide slurry cannot be completely oxidized; while above the range of the present invention, the production cost is increased; only when the amount of the oxidizing agent is controlled within the range of the present invention, the oxidation of the hydroxide slurry to the oxide can be sufficiently ensured while the cost is reduced.
In the above production method, the reaction temperature in the step (S2) is preferably 50 to 70 ℃. The reaction temperature is a key factor in determining the kinetics of chemical reactions, and the reaction rate increases with increasing reaction temperature. The reaction speed is slow and the efficiency is low due to the excessively low reaction temperature; and the reaction temperature is too high, the reaction energy consumption is correspondingly increased, and the discharge of products decomposed by ammonium salt is more concentrated, so that the working environment is poor.
In the above preparation method, preferably, the drying temperature in the step (S4) is 150 to 250 ℃.
The preparation method of the cobaltosic oxide containing the doping element M is theoretically carried out according to the following reaction process, wherein x is (0.995-0.9) and (0.005-0.1).
(1) Cobalt source + M source + H2O + precipitant + complexing agent → (Co)xMy)(OH)2；
(2)(CoxMy)(OH)2+O2→(CoxMy)3O4；
Firstly, the reaction process shown in the formula (1) occurs, cobaltosic oxide and metal ions in an M source react with hydroxide in a precipitator to generate hydroxide precipitates of cobalt and M, and a complexing agent can reduce the concentration of cobalt ions and M ions in a reaction system in a system and plays a role in controlling the nucleation rate and the crystal growth rate in the coprecipitation reaction process.
Next, a reaction process as shown in the formula (2) occurs. In (Co)xMy)(OH)2On oxidation, oxide (Co)xMy)3O4Is at (Co)xMy)(OH)2Surface nucleation and growth, volume shrinkage of product, reaction heat, and water escape to generate oxide (Co)xMy)3O4The surface is discontinuous and loose, so that unoxidized (Co) is continuously generated along with the progress of the oxidation reactionxMy)(OH)2The fresh surface is exposed so that the oxidation reaction can proceed rapidly and continuously until the oxidation reaction is complete.
In the above preparation method, preferably, in the step (3), the coating material is Co (OH)2And TiO2(ii) a The weight of the coating accounts for 0.005-5 wt% of the weight of the high-voltage lithium cobaltate cathode material. Lithium cobaltate particles synthesized by high temperature solid phase method, radial Li+There is a concentration gradient of Li from the region far from the surface to the surface region of the particle+The concentration gradually increases, so that the surface is Li-rich+State such that LiCoO2The positive electrode material has excessive activity and generatesSelf-decomposition and other side reactions with the electrolyte affect the performance of the material. Therefore, the invention adds the Li which can consume surplus into the doped lithium cobaltate in the coating process+Additive of Co (OH)2And TiO2By heat treatment, Li+And Co (OH)2The reaction forms active lithium cobaltate with a portion of Co (OH)2Forming a coating layer on the surface of the particles after heat treatment. By Co (OH)2Consuming Li+Process of (2), Li+Redistribute in the doped lithium cobaltate matrix particles and tend to a stable state, thereby realizing the precise regulation and control of n (Li)/n (Co) in the material; furthermore, Co (OH)2Absorbing Li+Not only can stabilize the internal structure of the particle, but also can form a coating layer of cobalt oxide on the surface of the particle to isolate Co at high potential4+The contact with the electrolyte can improve the surface stability of the particles. Furthermore, by heat treatment, the coating TiO2With surface-rich Li in doped lithium cobaltate+React to generate Li4Ti5O12Having a high chemical diffusion coefficient (2X 10)-8cm 2s-1) And the structure stability, the crystal structure hardly changes in the charging and discharging process, and the coating is an excellent coating, so that the material impedance is reduced, the capacity is improved, and the cycle performance is improved. Thus, Co (OH)2And TiO2The effect of the two coatings used in combination is significantly greater than the effect of one coating used alone: co (OH)2The coating of (2) has a surplus of Li+And a coating of oxide, and TiO2The coating also consumes Li in excess+And formation of Li4Ti5O12The coating layer has two functions, so that the coating layer plays a significant role in improving the capacity and the cycle performance of the high-voltage lithium cobaltate product.
In the above preparation method, preferably, the metal element M doped in the cobaltosic oxide is one or more of Ga, Mo, Al, Ni, Mn, Zn, and Zr.
In the preparation method, the weight of the doped metal element M is preferably 0.01 to 5wt% of the weight of the high-voltage lithium cobaltate cathode material.
In the above preparation method, preferably, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium nitrate and lithium acetate; the molar ratio of the lithium element in the lithium source to the cobalt element in the cobaltosic oxide is n (Li): n (Co): 1.1-0.9): 1. The element molar ratio determines the lattice constant, the number of oxygen defects, the particle size and the average valence state of the cobalt element of the sintered material, further influences the electrochemical discharge capacity, the coulombic efficiency and the cycle performance of the material, and the high-voltage lithium cobaltate anode material with the optimal comprehensive performance can be prepared by controlling the molar ratio of the lithium element to the cobalt element within the range of the invention.
In the preparation method, preferably, the doped metal element M 'is one or more of Al, La, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Nb, Tc, Ru, Rh, Pd, Ag and Cd, and the doping amount of M' is 0.005-5 wt% of the weight of the high-voltage lithium cobaltate positive electrode material.
The doping material is added in two times (added in one ingredient pre-blended in the cobaltosic oxide), which is mainly determined according to the difference of doping amount, the difficulty of doping ions entering lithium cobaltate crystal lattices and the feasibility of wet coprecipitation. The metal element M (Ga, Mo, Al, Ni, Mn, Zn and Zr) doped in the cobaltosic oxide is selected to be pre-doped in the cobaltosic oxide because the doping amount is large and the doped ions are difficult to enter the lithium cobaltate crystal lattice.
The compound containing the doped metal element M' also plays a role of a catalyst in the crystallization process of the high-voltage lithium cobaltate cathode powder material, and can perform surface crystallization catalysis to promote the conversion of divalent cobalt ions to trivalent cobalt ions, so that Co in the prepared cathode material basically exists in a trivalent state, and the higher the content of trivalent cobalt is, the better the cycle stability is and the higher the primary capacity is. Therefore, the surface crystallization catalysis is beneficial to improving the crystal integrity of the lithium cobaltate, improving the structural integrity of the material and effectively improving the discharge capacity of the material. In addition, after crystallization is finished, an inert protective layer at least containing catalytic element oxides or composite oxides is formed on the surface of the lithium cobaltate positive electrode powder material, so that cobalt dissolution in the charging and discharging process and side reactions between cobalt and electrolyte in the circulating process are prevented, and the circulating performance and safety performance of the positive electrode material under high voltage are effectively improved.
In the preparation method, preferably, in order to better obtain the mixed high-voltage lithium cobaltate with single crystal morphology and single crystal-like morphology, a grain refiner and a fluxing agent are added, wherein the grain refiner is one or more of oxides of Ti, Nb, V, Al and Zr; the addition amount of the grain refiner is 0.01-5 wt% of the weight of the high-voltage lithium cobalt oxide positive electrode material;
the fluxing agent is one or more of oxides of B, Ba, Bi, Pb, Mo, W, Li, K, Na, Ca and Mg; the adding amount of the fluxing agent is 0.01-5 wt% of the weight of the high-voltage lithium cobaltate positive electrode material.
In the above preparation method, preferably, in the step (2), the primary sintering is performed in an air or oxygen-rich atmosphere, and the primary sintering specifically comprises the following steps: and heating the primary mixed material from room temperature to 500-900 ℃, preserving heat for 2-10 hours, then heating to 900-1150 ℃, preserving heat for 5-20 hours, and naturally cooling along with the furnace.
In the above preparation method, preferably, in the step (4), the secondary sintering is performed in air or an oxygen-rich atmosphere, and the secondary sintering specifically comprises the following steps: and heating the secondary mixture from room temperature to 800-1100 ℃, preserving the heat for 5-20 hours, and then naturally cooling along with the furnace.
In the preparation method, the step heating sintering is carried out in one-time sintering, mainly because the one-time mixed material can carry out reactions such as dehydration, degasification and the like in the temperature range of 500-900 ℃, and the temperature is kept for 2-10 hours in the temperature range, so that the side reactions such as dehydration, degasification and the like can be fully completed; and the basic structure of lithium cobaltate is mainly formed at 900-1150 ℃ to finish doping. The secondary sintering mainly has the function of forming a coating layer with a protective effect on the surface of the lithium cobaltate and repairing the surface, and the amount of a coating material newly added during secondary burdening is less (generally less than 5 percent), so that the secondary sintering has fewer side reactions, and the secondary sintering can be directly sintered without stepped temperature rise sintering.
In the above preparation method, preferably, in the steps (2) and (4), the crushing means that the sintered material is coarsely crushed by a jaw crusher and a double-roll crusher and then crushed by a jet mill;
and (3) mixing materials by adopting a coulter type mixer in the steps (1) and (3). The coulter type mixer consists of a circular cylinder, a transmission mechanism, a coulter and a fly cutter; when the materials are mixed and stirred, the coulter moves circularly, the materials are divided into two directions by the knife surface of the coulter to form bidirectional material flows, the bidirectional material flows are intersected with the materials divided by the coulters on the two sides to form convection, and the material flows are cut and thrown by the blades of the high-speed fly cutter when passing through the high-speed fly cutter, so that uniform mixing is achieved in a short time. The coulter type mixer is applied to the industry of high-voltage lithium cobaltate cathode materials, and aims to solve the problems of material sticking on the inner wall and corrosion of materials to the coulter type mixer. The distance between the coulter and the inner wall of the coulter type mixer is accurately adjusted to overcome the problem of material sticking of the inner wall; the inner walls of the coulter, the fly cutter and the mixer are made of corrosion-resistant stainless steel, so that the problem of corrosion of materials to the coulter type mixer is solved.
Compared with the prior art, the invention has the advantages that:
(1) according to the characteristics of the difference of doping amount of doped metal ions, the difficulty of entering lithium cobaltate crystal lattices and the like, doping is divided into two modes of pre-doping during preparation of cobaltosic oxide and dry mixing during primary mixing. Because the doping amount of the pre-doped element is large, the pre-doped element is difficult to enter a lithium cobaltate crystal lattice, so that when the cobaltosic oxide is prepared by a wet method, the cobalt element and the pre-doped metal element can be uniformly mixed at an atomic level in a product by a coprecipitation method, and in a high-voltage lithium cobaltate product prepared by the method, the cobalt element and the pre-doped metal element are completely and uniformly distributed on a microscopic scale, so that the problem that the metal element is distributed and segregated on the microscopic scale in the product is solved, and the electrical property of the product is favorably improved. In addition, the doped metal elements mixed in by the dry method during the primary mixing are easy to enter lithium cobaltate crystal lattices due to small doping amount, and the difficulty of wet coprecipitation is high, so that the doping by the dry method is selected, and the complexity of preparing the material is simplified.
(2) The invention pre-dopes the raw materials, and the wet process ensures that the distribution of the cobalt element and the pre-doped metal element is completely uniform on the micro scale, thereby solving the problem of the segregation of different metal elements in the product on the micro scale; meanwhile, a coulter type mixer which is rarely applied in the lithium battery anode material industry is adopted for mixing, the mixing precision is high, different substances in the mixture are not separated, the problem of separation of a lithium source, cobaltosic oxide, a doping element added in a dry mixing mode, a grain refiner, a fluxing agent and the like is solved, the components of a sintered product are consistent due to the double effects, the micro-scale segregation is eliminated, and the electrochemical performance of the product is improved.
(3) The invention effectively combines the grain refiner and the fluxing agent for use, on one hand, ensures the full contact and reaction between the compounds in the solid phase synthesis process, and the crystal crystallization is more complete; on the other hand, the sintering temperature is reduced, the energy consumption is reduced, the high-voltage lithium cobalt oxide with the single crystal morphology and the single-crystal-like morphology mixed is obtained, the advantages of the high-voltage lithium cobalt oxide with the two morphologies are fully exerted, and the material which gives consideration to compaction, first coulombic efficiency, capacity, multiplying power and cycle performance is prepared.
(4) According to the invention, the catalytic action of surface crystallization of doped metal elements is utilized to promote the conversion of divalent cobalt ions to trivalent cobalt ions, and meanwhile, an inert protective layer is formed on the surface of the lithium cobaltate positive electrode material, so that the discharge capacity of the material can be effectively improved, and the cycle performance and safety performance of the positive electrode material under high voltage can be improved.
(5) The invention selects Co (OH)2And TiO2The coating is formed by heat treatment, on one hand, the surplus Li on the surface of the primary sintered product can be consumed+And meanwhile, an oxide coating layer is formed, so that the activity of the surface of the lithium cobaltate positive electrode material can be reduced, and the coating layer with excellent performance can be formed, and the safety performance of the material is improved.
(6) The preparation method has simple flow, is easy to control the reaction, and can obviously improve the consistency of the product, thereby ensuring the stable quality of products in different batches; and the product has uniform components, stable quality, excellent physical and chemical properties and excellent electrical properties.
Drawings
Fig. 1 is an SEM photograph of the high voltage lithium cobaltate positive electrode material prepared in example 1 of the present invention.
Fig. 2 is an SEM photograph of the high voltage lithium cobaltate cathode material prepared in comparative example 1 of the present invention.
Fig. 3 is an SEM photograph of the high voltage lithium cobaltate positive electrode material prepared in example 2 of the present invention.
Fig. 4 is an SEM photograph of the high voltage lithium cobaltate cathode material prepared in comparative example 2 of the present invention.
Detailed Description
In order to facilitate an understanding of the invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.
Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
Example 1:
the preparation method of the high-voltage lithium cobaltate positive electrode material comprises the following steps of:
(1) uniformly doping cobaltosic oxide containing Al ions, lithium carbonate, lanthanum oxide and a grain refiner TiO2And flux Mg (OH)2Burdening, and mixing by adopting a coulter type mixer to obtain a primary mixture; wherein the amount of Al metal element doped in the cobaltosic oxide is 0.50 wt% of the weight of the lithium cobaltite positive electrode material, the molar ratio of the lithium element in the lithium carbonate to the cobalt element in the cobaltosic oxide is n (Li): n (Co): 1.07:1, the doping amount of La is 0.1 wt% of the weight of the lithium cobaltite positive electrode material, and a grain refiner TiO2The addition amount of the cobalt acid0.1 wt% of lithium positive electrode material, flux Mg (OH)2The adding amount is 0.2 wt% of the weight of the lithium cobaltate cathode material; the evenly doped cobaltosic oxide containing Al ions is prepared by the following preparation method:
(S1) adding cobalt sulfate into the aqueous solution to be mixed into slurry, then adding aluminum chloride, and stirring to obtain mixed slurry;
(S2) adding sodium hydroxide and ammonia water into the mixed slurry obtained in the step (S1) in sequence, controlling the stirring speed in the reaction process to be 700rmp, the temperature to be 55 ℃, the time to be 20h, the pH value to be 10 and the solid-liquid mass ratio to be 1:5, and reacting to obtain cobalt hydroxide slurry containing Al element; wherein the concentration of ammonia water is 0.5mol/L, the molar ratio of the addition amount of sodium hydroxide as precipitant to the total amount of Co and Al is n (precipitant) n (Co2++Al3+)＝2.1:1；
(S3) adding oxidant air into the cobalt hydroxide slurry obtained in the step (S2), stirring at the stirring speed of 1000rmp and the reaction temperature of 60 ℃ for 10 hours to obtain aluminum-doped cobaltosic oxide slurry; wherein, the addition amount of air is 200g/kg calculated according to each kilogram of aluminum-doped cobaltosic oxide;
(S4) filtering the cobaltosic oxide slurry obtained in the step (S3) until the water content of a filter cake is 40%, and drying the filter cake for 15 hours at the temperature of 200 ℃ to obtain the evenly doped cobaltosic oxide containing Al ions.
(2) Placing the primary mixture obtained in the step (1) in air for sintering: firstly, heating the mixed material from room temperature to 700 ℃, preserving heat for 2 hours, then heating to 1030 ℃, preserving heat for 10 hours, and finally, naturally cooling along with the furnace; then the obtained blocky primary sintering material is coarsely crushed by a jaw crusher and a double-roller crusher and then crushed by a jet mill to obtain powdery primary sintering powder, wherein D50 is 17.45 mu m.
(3) Mixing the primary sintering powder obtained in the step (2) with Co (OH)2、TiO2Mixing, wherein a colter type mixer is adopted for mixing in the mixing process to obtain a secondary mixture; wherein, Co (OH)2TiO accounting for 3 weight percent of the weight of the lithium cobaltate cathode material2Is 0.05 wt% of the weight of the lithium cobaltate cathode material.
(4) Placing the secondary mixture obtained in the step (3) in air for sintering: heating the secondary mixture from room temperature to 920 ℃, preserving the heat for 10 hours, and then naturally cooling along with the furnace; and then coarsely crushing the obtained blocky secondary sintering material by a jaw crusher and a double-roll crusher, and crushing by a jet mill to obtain a high-voltage lithium cobaltate material product.
An SEM photograph of the high-voltage lithium cobaltate cathode material prepared in the example is shown in FIG. 1, and it can be seen from the SEM photograph that the material is a mixture of single crystal morphology and single crystal-like morphology, and the compaction density can reach 4.1g/cm when a battery is manufactured3The positive electrode material had D50 of 17.59 μm and a specific surface area of 0.21m2/g。
Comparative example 1:
the preparation method of the high-voltage lithium cobaltate cathode material comprises the following steps:
(1) cobaltosic oxide, lithium carbonate, aluminum oxide, lanthanum oxide and grain refiner TiO2And flux Mg (OH)2Burdening, and mixing by adopting a coulter type mixer to obtain a primary mixture; wherein the molar ratio of lithium element in lithium carbonate to cobalt element in cobaltosic oxide is n (Li): n (Co): 1.07:1, the doping amount of Al is 0.50 wt% of the weight of the secondary sintered product, the doping amount of La is 0.1 wt% of the weight of the lithium cobaltite positive electrode material, and a grain refiner TiO2The added amount of the lithium cobaltate positive electrode material is 0.1 weight percent of the weight of the lithium cobaltate positive electrode material, and the fluxing agent is Mg (OH)2The addition amount was 0.2 wt% based on the weight of the lithium cobaltate positive electrode material.
(2) Placing the primary mixture obtained in the step (1) in air for sintering: heating the mixed material from room temperature to 700 ℃, preserving heat for 2 hours, then heating to 990 ℃, preserving heat for 10 hours, naturally cooling along with the furnace, coarsely crushing the obtained blocky primary sintered material by a jaw crusher and a double-roll crusher, and crushing by a jet mill to obtain powdery primary sintered powder, wherein D50 is 17.31 mu m.
(3) Mixing the powdery primary sintering powder obtained in the step (2) with Co (OH)2、TiO2Putting the mixture into a coulter type mixer for mixing to obtain a secondary mixture; wherein, Co (OH)2TiO accounting for 3 weight percent of the weight of the lithium cobaltate cathode material2Is 0.05 wt% of the weight of the lithium cobaltate cathode material.
(4) Placing the secondary mixture obtained in the step (3) in air for sintering: and (3) heating the secondary mixture from room temperature to 920 ℃, preserving heat for 10 hours, naturally cooling along with the furnace, coarsely crushing the obtained blocky secondary sintered material by using a jaw crusher and a double-roll machine, and crushing by using a jet mill to obtain the high-voltage lithium cobaltate cathode material product.
The SEM photograph of the high voltage lithium cobaltate cathode material prepared in the comparative example is shown in FIG. 2, and it can be seen from the SEM photograph that the material is mainly in a single crystal-like shape, and the compaction density is only 3.9g/cm when a battery is manufactured3The positive electrode material had D50 of 17.21 μm and a specific surface area of 0.22m2/g。
Example 2:
the preparation method of the high-voltage lithium cobaltate positive electrode material comprises the following steps of:
(1) uniformly doping cobaltosic oxide containing Zr ions, lithium carbonate, aluminum oxide and grain refiner TiO2And flux Mg (OH)2Burdening, and mixing by adopting a coulter type mixer to obtain a primary mixture; wherein, the amount of Zr metal element doped in the cobaltosic oxide is 0.50 weight percent of the weight of the lithium cobaltite anode material, the molar ratio of the lithium element in the lithium carbonate to the cobalt element in the cobaltosic oxide is n (Li): n (Co): 1.06:1, the doping amount of Al is 0.1 weight percent of the weight of the lithium cobaltite anode material, and a grain refiner TiO2The added amount of the lithium cobaltate positive electrode material is 0.1 weight percent of the weight of the lithium cobaltate positive electrode material, and the fluxing agent is Mg (OH)2The adding amount is 0.1 wt% of the weight of the lithium cobaltate cathode material; the preparation method of the uniformly doped cobaltosic oxide containing Zr ions comprises the following steps:
(S1) adding cobalt chloride into the aqueous solution to be mixed into slurry, then adding zirconium nitrate, and stirring to obtain mixed slurry;
(S2) adding sodium hydroxide and ammonia water into the mixed slurry obtained in the step (S1) in sequence, controlling the stirring speed in the reaction process to be 600rmp, the temperature to be 45 ℃, the time to be 18h, and the pH value to be 9.5Reacting to obtain cobalt hydroxide slurry containing Zr element, wherein the solid-liquid mass ratio is 1: 4; wherein the concentration of ammonia water is 0.8mol/L, the molar ratio n of the addition amount of sodium hydroxide as precipitant to the total amount of Co and Zr (precipitant) n (Co2++Zr4+)＝2.3:1；
(S3) adding oxidant oxygen into the cobalt hydroxide slurry obtained in the step (S2), stirring, and reacting to obtain zirconium-doped cobaltosic oxide slurry; wherein, the addition amount of the oxidant is 300g/kg calculated by each kilogram of zirconium-doped cobaltosic oxide; the stirring speed is 1200rmp, the reaction temperature is 70 ℃, and the reaction time is 5 h;
(S4) filtering the cobaltosic oxide slurry obtained in the step (S3) until the water content of a filter cake is 55%, and drying the filter cake for 10 hours at the temperature of 300 ℃ to obtain the uniformly doped cobaltosic oxide containing Zr ions.
(2) Placing the primary mixture prepared in the step (1) in oxygen for sintering: heating the mixed material from room temperature to 750 ℃, preserving heat for 2 hours, heating to 1040 ℃, preserving heat for 8 hours, naturally cooling along with the furnace, coarsely crushing the obtained blocky primary sintered material by a jaw crusher and a pair roller machine, and crushing by a jet mill to obtain powdery primary sintered powder, wherein D50 is 18.34 mu m.
(3) Mixing the powdery primary sintering powder obtained in the step (2) with Co (OH)2、TiO2Adding the mixture into a coulter type mixer for mixing to obtain a secondary mixture; wherein, Co (OH)2TiO accounting for 2 weight percent of the weight of the lithium cobaltate cathode material2Is 0.08 wt% of the weight of the lithium cobaltate cathode material.
(4) And (4) placing the secondary mixture obtained in the step (3) in oxygen for sintering: and (3) heating the mixture from room temperature to 930 ℃, preserving heat for 8 hours, naturally cooling the mixture along with the furnace, coarsely crushing the obtained blocky secondary sintering material by using a jaw crusher and a double-roller crusher, and crushing the blocky secondary sintering material by using a jet mill to obtain the high-voltage lithium cobaltate positive electrode material product.
An SEM photograph of the high voltage lithium cobaltate cathode material prepared in this example is shown in fig. 3, which shows that the material is a mixture of single crystal morphology and single-crystal-like morphology, and when a battery is manufacturedThe compacted density can reach 4.15g/cm3The positive electrode material had D50 of 18.21 μm and a specific surface area of 0.20m2/g。
Comparative example 2:
the preparation method of the high-voltage lithium cobaltate cathode material of the comparative example comprises the following steps:
(1) mixing cobaltosic oxide and lithium carbonate which are uniformly doped with Zr ions by adopting a plough knife type mixer to obtain a primary mixture; wherein, the amount of Zr metal element doped in the cobaltosic oxide is 0.50 weight percent of the weight of the lithium cobaltite anode material, and the molar ratio of the lithium element in the lithium carbonate to the cobalt element in the cobaltosic oxide is n (Li) and n (Co) is 1.06: 1; the preparation method of the uniformly doped cobaltosic oxide containing Zr ions comprises the following steps:
(S1) adding cobalt chloride into the aqueous solution to be mixed into slurry, then adding zirconium nitrate, and stirring to obtain mixed slurry;
(S2) adding sodium hydroxide and ammonia water into the mixed slurry obtained in the step (S1) in sequence, controlling the stirring speed in the reaction process to be 600rmp, the temperature to be 45 ℃, the time to be 18 hours, the pH value to be 9.5, and the solid-liquid mass ratio to be 1:4, reacting to obtain cobalt hydroxide slurry containing Zr element; wherein the concentration of ammonia water is 0.8mol/L, the molar ratio n of the addition amount of sodium hydroxide as precipitant to the total amount of Co and Zr (precipitant) n (Co2++Zr4+)＝2.3:1；
(S3) adding oxidant oxygen into the cobalt hydroxide slurry obtained in the step (S2), stirring, and reacting to obtain zirconium-doped cobaltosic oxide slurry; wherein, the addition amount of the oxidant is 300g/kg calculated by each kilogram of zirconium-doped cobaltosic oxide; the stirring speed is 1200rmp, the reaction temperature is 70 ℃, and the reaction time is 5 h;
(S4) filtering the cobaltosic oxide slurry obtained in the step (S3) until the water content of a filter cake is 55%, and drying the filter cake for 10 hours at the temperature of 300 ℃ to obtain the uniformly doped cobaltosic oxide containing Zr ions.
(2) Placing the primary mixture prepared in the step (1) in oxygen for sintering: heating the mixed material from room temperature to 750 ℃, preserving heat for 2 hours, heating to 1040 ℃, preserving heat for 8 hours, naturally cooling along with the furnace, coarsely crushing the obtained blocky primary sintered material by a jaw crusher and a pair roller machine, and crushing by a jet mill to obtain powdery primary sintered powder, wherein D50 is 18.29 mu m.
(3) Mixing the powdery primary sintering powder obtained in the step (2) with Co (OH)2、TiO2Adding the mixture into a coulter type mixer for mixing to obtain a secondary mixture; wherein, Co (OH)2TiO accounting for 2 weight percent of the weight of the lithium cobaltate cathode material2Is 0.08 wt% of the weight of the lithium cobaltate cathode material.
(4) And (4) placing the secondary mixture obtained in the step (3) in oxygen for sintering: and (3) heating the mixture from room temperature to 930 ℃, preserving heat for 8 hours, naturally cooling the mixture along with the furnace, coarsely crushing the obtained blocky secondary sintering material by using a jaw crusher and a double-roller crusher, and crushing the blocky secondary sintering material by using a jet mill to obtain the high-voltage lithium cobaltate positive electrode material product.
The SEM photograph of the high voltage lithium cobaltate cathode material prepared in the comparative example is shown in FIG. 4, which shows that the material is a mixture of single crystal morphology and single crystal-like morphology, and the compaction density can reach 4.15g/cm when a battery is manufactured3The positive electrode material had D50 of 18.14 μm and a specific surface area of 0.20m2/g。
The high-voltage lithium cobaltate positive electrode materials prepared in the embodiments 1 and 2 and the comparative examples 1 and 2 are subjected to electrochemical performance tests (the voltage test range of the effective battery is 3.0-4.45V), the results of specific discharge capacity and rate performance are shown in table 1, and the results of cycle performance are shown in table 2.
Table 1 results of specific discharge capacity and rate capability of high voltage lithium cobalt oxide positive electrode material
Table 2 results of cycle performance of high voltage lithium cobaltate cathode material
Note: 1C-1 represents the first discharge capacity at 1C rate; 1C-200 represents the capacity retention rate after 200 cycles at 1C magnification.
From the above experimental results, it is understood that the results of examples 1 and 2 are superior to those of comparative example, and that examples 1 and 1 are structures for stabilizing lithium cobaltate at a high voltage, and equal Al element with a higher doping amount is used. The biggest difference between the two is that the cobaltosic oxide is prepared by a wet method in the embodiment 1, and the cobalt element and the pre-doped Al can be uniformly mixed at the atomic level in the product by a coprecipitation method, so that the problem of segregation of the metal elements distributed on the microscopic scale in the product is solved, and the electrical property of the product is improved; in comparative example 1, the Al element with a higher doping amount was mixed in by a dry method at the time of primary mixing, and it was difficult to uniformly enter the crystal lattice of lithium cobaltate due to the larger Al doping amount, thereby deteriorating the performance of the material.
In addition, example 2 and comparative example 2, in order to stabilize the structure of lithium cobaltate at a high voltage, the same Zr element was pre-doped in cobaltosic oxide. The biggest difference between the two is that in the preparation process of the comparative example 2, the oxide of the doping element M', the grain refiner and the fluxing agent are not added. The doping material is added in two times, and simultaneously, the grain refiner and the fluxing agent are also added, and the combination of multiple modes is the remarkable characteristic of the invention and simultaneously has better results. As can be seen from the results of tables 1 and 2, both the capacity and cycle performance of example 2 are significantly better than those of comparative example 2.
Claims (8)
1. A preparation method of a high-voltage lithium cobaltate positive electrode material is characterized by comprising the following steps:
(1) primary mixing: mixing cobaltosic oxide containing a doping element M, a lithium source, an oxide containing a doping element M', a grain refiner and a fluxing agent to obtain a primary mixture; the high-voltage lithium cobaltate positive electrode material is characterized in that a doping element M is one or more of Ga, Mo, Al, Ni, Mn, Zn and Zr, a doping element M 'is one or more of Al, La, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Nb, Tc, Ru, Rh, Pd, Ag and Cd, the weight of the doping element M is 0.5-5 wt% of the weight of the high-voltage lithium cobaltate positive electrode material, the doping amount of M' is 0.005-0.1 wt% of the weight of the high-voltage lithium cobaltate positive electrode material, and the cobaltosic oxide containing the doping element M is mainly prepared by the following preparation method:
(S1) adding a soluble raw material containing cobalt into the aqueous solution to be mixed into slurry, then adding a soluble raw material containing a doping element M, and stirring to obtain mixed slurry;
(S2) adding a precipitator and a complexing agent into the mixed slurry obtained in the step (S1) in sequence for reaction, controlling the stirring speed in the reaction process to be 100-900 rmp, the temperature to be 20-90 ℃, the time to be 5-40 h, the pH value to be 6-11, and the solid-liquid mass ratio to be 1 (3-7), and reacting to obtain cobalt hydroxide slurry containing the doping element M;
(S3) adding an oxidant into the cobalt hydroxide slurry obtained in the step (S2) to react, controlling the stirring speed in the reaction process to be 300-1300 rmp, the temperature to be 30-90 ℃, and the time to be 2-15 h, and reacting to obtain cobaltosic oxide slurry containing the doping element M;
(S4) filtering and drying the cobaltosic oxide slurry obtained in the step (S3), wherein the drying temperature is 80-400 ℃, and the drying time is 1-30 h, so that cobaltosic oxide containing the doping element M is obtained;
(2) primary sintering: sintering and crushing the primary mixture to obtain primary sintered powder;
(3) secondary material mixing: mixing the primary sintered powder with a coating to obtain a secondary mixture, wherein the coating is Co (OH)2And TiO2；
(4) And (3) secondary sintering: and sintering and crushing the secondary mixture to obtain the high-voltage lithium cobalt oxide positive electrode material.
2. The method according to claim 1, wherein in the step (3), the weight of the coating material is 0.005-5 wt% of the weight of the high-voltage lithium cobalt oxide positive electrode material.
3. The method according to claim 2, wherein in the step (S1), the soluble material containing cobalt is one or more of cobalt chloride, cobalt nitrate and cobalt sulfate; the soluble raw material containing the doping element M is one or more of sulfate, nitrate, acetate and chloride;
in the step (S2), the precipitant is sodium hydroxide; the molar ratio of the addition amount of the precipitator to the total amount of Co and M is n (precipitator) = (2-3): 1; the complexing agent is ammonia water, and the concentration of the complexing agent is 0.05-1 mol/L;
in the step (S3), the oxidant is one or more of air, oxygen and hydrogen peroxide; calculated by each kilogram of cobaltosic oxide containing doping elements, the addition amount of the oxidant is 80-350 g/kg.
4. The preparation method according to any one of claims 1 to 3, wherein the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium nitrate and lithium acetate; the molar ratio of the lithium element in the lithium source to the cobalt element in the cobaltosic oxide is n (Li): n (Co) = (1.1-0.9): 1.
5. The preparation method according to any one of claims 1 to 3, wherein the grain refiner is one or more of oxides of Ti, Nb, V, Al and Zr; the addition amount of the grain refiner is 0.01 to 5 weight percent of the weight of the high-voltage lithium cobalt oxide anode material; the fluxing agent is one or more of oxides of B, Ba, Bi, Pb, Mo, W, Li, K, Na, Ca and Mg; the adding amount of the fluxing agent is 0.01-5 wt% of the weight of the high-voltage lithium cobaltate positive electrode material.
6. The preparation method according to any one of claims 1 to 3, wherein in the step (2), the primary sintering is performed in air or oxygen-rich atmosphere, and the specific process of the primary sintering is as follows: and heating the primary mixed material from room temperature to 500-900 ℃, preserving heat for 2-10 hours, then heating to 900-1150 ℃, preserving heat for 5-20 hours, and naturally cooling along with the furnace.
7. The preparation method according to any one of claims 1 to 3, wherein in the step (4), the secondary sintering is performed in air or oxygen-rich atmosphere, and the secondary sintering comprises the following specific steps: and heating the secondary mixture from room temperature to 800-1100 ℃, preserving the heat for 5-20 hours, and then naturally cooling along with the furnace.
8. The preparation method according to any one of claims 1 to 3, wherein in the steps (2) and (4), crushing means that the sintered material is subjected to coarse crushing by a jaw crusher and a double roll crusher and then is crushed by a jet mill;
and (3) mixing materials by adopting a coulter type mixer in the steps (1) and (3).
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