RU2755526C1 - Method for obtaining powder of lithium cobalt oxide with alloyed structure and modified surface - Google Patents

Abstract

FIELD: inorganic chemistry.

SUBSTANCE: invention relates to inorganic chemistry, in particular to the field of obtaining a powder of lithium cobalt oxide (LiCoO₂) used as a cathode material for lithium-ion batteries. In the method for producing lithium cobalt oxide, which includes mixing the initial components of lithium salts, cobalt oxide and additives, annealing in the furnace in two stages, after the first stage, the resulting charge is mixed and annealed again with subsequent cooling. According to the invention, one or more alloying additives of nanostructured thermally decomposable compounds based on salts or hydroxides of metals Mg, Al, Ti with a decomposition temperature below 660°C in the atomic ratio of metal to Co up to 0.07 are introduced into the mixture of the initial components of lithium salts, cobalt oxide, the mixture is subjected to dispersion using a mechanochemical activator at a specific power of 5-30 W/g, for 2.0-10 minutes, the initial components of lithium salts and cobalt oxide are taken in molar ratio Li:Co = (1.0-1.02):1.0.

EFFECT: reduction in the degree of degradation of the specific discharge capacity.

2 cl, 3 dwg, 12 ex, 4 tbl

Description

The invention relates to inorganic chemistry, in particular to the field of obtaining powder of lithiated cobalt oxide (LiCoO ₂ ) used as a cathode material for lithium-ion batteries.

One of the most significant achievements of modern electrochemistry over the past 25 years is the development and commercialization of portable rechargeable lithium-ion batteries (LIB). They have become the main power sources for portable electronic devices (laptops, video and cameras, mobile phones, smartphones, special equipment, etc.). According to various sources, about (70 - 90)% of LIB in the world are equipped with lithium-cobalt-oxide cathode materials. This fact explains the existence of a significant number of patents and publications on lithium-cobalt oxide material and especially on methods for its preparation.

Compounds capable of reversibly intercalating lithium ions are used as electrode materials in lithium-ion batteries. The electrolyte, as a rule, is a lithium salt in an organic aprotic solvent, and as an anode, as a rule, carbon-graphite or other materials. Lithium batteries generate electrical energy as a result of changes in the chemical potentials of electrode materials in the process of insertion - transfer - extraction of lithium ions. For use in portable electronic devices, batteries with an average discharge voltage of 3.7 V.

The most widespread cathode is lithiated cobalt oxide (lithium cobaltite) LiCoO ₂ , the advantages of which are: relative ease of synthesis, high discharge potential, ability to cycle at high current densities, etc. The disadvantages of lithiated cobalt oxide are its toxicity, high cost, and low practical capacity (about half of the theoretical (274 mAh / g)). The latter is connected, on the one hand, with structural instability at a charge above 4.3 V due to the transition from a hexagonal structure to a monoclinic one, as well as with side reactions of the cathode material with the electrolyte.

The technology and structure of LiCoO ₂ have been the subject of numerous studies, several directions for obtaining lithiated cobalt oxide have been worked out, namely: self-propagating high-temperature synthesis (SHS) in combustion mode (RF patent No. 2183587 dated 09.03.2000), low-temperature methods are known - "sol-gel" a method in which the key is the use of aqueous solutions of Li and Co precursors or (in some cases) suspensions of cobalt hydroxides (oxides) (US No. 5211933, app. 30.04.1992, US 5914094, Jun. 22, 1999), extraction (RF No. 2199798, 16.02.2001) and other methods. The disadvantages of these low-temperature methods are the need to remove large volumes of liquid reagents-solvents, the use of expensive metal salts.

The most widespread in industry is the method of solid-phase synthesis using dry powders of cobalt and lithium compounds. One of the first published a method of obtaining solid-phase synthesis of oxide compounds of the type LiCoO ₂ (A. Lundblad and B. Bergman. Synthesis of LiCoO ₂ - an alternative Material for MCFC Cathodes. - Proceedings of the 1st International Symposium on NEW MATERIALS FOR FUEL CELL SYSTEMS, Montreal, Canada, July 9-13, 1995, p. 449-457), which consists in carrying out a high-temperature treatment of a mixture of powders according to the scheme: Li ₂ CO ₃ + 2CoCO ₃ + 1 / 2O ₂ -> 2LiCoO ₂ + 3CO ₂ ...

The synthesis process is based on high-temperature sintering of powders at a temperature of 800-1000 ° C.

A known method of synthesizing lithiated cobalt oxide by high-temperature treatment of lithium carbonate or hydroxide and cobalt oxide. The starting materials are mixed in a molar ratio of lithium: cobalt = 1: 1, fired in an oven at a temperature of 600-900 ° C for 20 hours. After cooling, the product is ground in a mill in ethanol (Research of electrodes based on lithium cobaltites for lithium batteries / L.S.Kanevsky, T.S.Kulova, E.A. . Novocherkassk. 2000. p. 94-95).

The disadvantages of this method are the significant energy consumption of the process, which consists in carrying out the processes of drying the resulting suspension, as well as the use of fire-and-explosive ethanol.

A known method of obtaining (EP 0838096, 08.22.2001) lithium-cobalt-oxide cathode material, characterized by an atomic ratio of Co / Li = 0.94-1.06 (i.e., it is an oxide compound of non-stoichiometric composition) and consists of powder particles with sizes from 5 up to 25 microns, in which the specified lithium cobalt oxide is obtained by the reaction of Li ₂ CO ₃ and Co ₃ O ₄ . Cobalt lithium oxide has a degree of crystallinity such that the FWHM of the 003 diffraction peak in X-ray diffraction using CuKα rays is in the range from 0.15 ° to 0.18 °.

The advantage of the method lies in the possibility of obtaining a powder of lithium-cobalt-oxide cathode material of the desired fractional composition of high particle size up to 25 microns, and the disadvantage is low values of the specific capacity.

There is a known method of producing lithium-cobalt oxide (US patent 6103213, 25.03.1997), including mixing a powder of cobalt oxide having a BET specific surface area of 30 to 200 m ² / g or an average particle size of not more than 0.1 μm, with a lithium compound ; adding water to the resulting mixture of cobalt oxide powder and lithium compound in an amount of 1 to 30% by weight based on the weight of the mixture; compression molding the mixture to form a molded product having a molding density of 1.5 g / cm ³ ; and also calcining the resulting mixture at a temperature from 500 to 850 ° C. This method of producing lithium cobalt oxide particles is especially valuable as a cathode active substance for lithium ion batteries because the particles can be obtained uniform in composition by calcining within a short time, and have a narrow particle size distribution and a uniform small particle size. ...

The patent does not disclose compression molding technology and the material obtained by this method has low specific energy values (less than 135 mAh / g).

In the method (RF Patent 2311703 dated 20.01.2006, published 27.11.2007), a mixture of the initial components of powders (Li ₂ CO ₃ + Co ₃ O ₄ ) with an atomic ratio Li / Co = 1: 1 is preliminarily subjected to mechanical activation for 0.5- 3.0 minutes at a specific power per unit mass of the starting components of 7-9 W / g, the ratio of the weight of the starting components to the mass of the activating bodies is 1: 3-1: 8, the heating of the starting components is carried out at a rate of 150-350 degrees. /hour. Annealing is carried out at a temperature of 600-900 ° C, for 8-12 hours, and cooling is carried out at a rate of 130-200 degrees / hour, followed by grinding lithiated cobalt oxide in an inert gas or dry air. The technical result of the invention is to reduce the degree of degradation of the specific discharge capacity.

The use of the mechanical activation method makes it possible to intensify solid-phase reactions during the formation of LiCoO ₂ . The disadvantages of this method include the complexity of controlling the process of forming the surface morphology, high particle size (more than 10 microns) of the powder, which makes it difficult to reproduce the production of powder material with specified characteristics. Due to the developed rough surface, LiCoO ₂ powder is obtained with low fluidity, which creates problems in the industrial (on automated lines) cathode production, and also there is a need to use an inert gas or dry air.

In all the above examples on solid-phase synthesis, there are general disadvantages (according to the data given in the examples), such as: a low value of the specific discharge capacity of the first cycle is not higher than 137 mAh / g and significant degradation values after 8-10 cycles constituting more than 5-8% ... The latter circumstance is associated, on the one hand, with structural instability at a charge above 4.3V as a result of the transition from a hexagonal structure to a monoclinic one, and, on the other hand, with side reactions of the cathode material with an electrolyte.

To reduce the values of the specific capacity drop (to increase the Coulomb efficiency), it was proposed to introduce dopants (dopants) _{into the LiCoO 2 composition.} The introduction of additives leads to the stabilization of the structure of LiCoO ₂ at elevated synthesis temperatures (900-1000 ° C).

The process of electrochemical intercalation-deintercalation (insertion-exit) of lithium ions into the structure of LiCoO _{2 is} accompanied by deformation of its crystal structure, causing its partial destruction. The consequence of this is a decrease in the specific capacity of the material during cycling, i.e., the battery will operate in a smaller number of charge-discharge cycles. Alloying additives, being in the composition of LiCoO ₂ , increase the stability of its electrochemical properties during cycling due to the stabilization of the crystal structure. This effect is especially noticeable at high temperatures.

Lithium-cobalt composite oxides can be stably produced, which can increase the Coulomb efficiency, reduce irreversible capacity, and improve cycle performance, and inexpensive raw materials can also be used.

A known method of synthesis (RF patent No. 2344515 dated 08/15/2007, published 01/20/2009) lithiated cobalt oxide, including mixing the initial components of lithium salts and cobalt oxide in a molar ratio of Li: Co = 1: 1, annealing in an oven and further cooling, differing the fact that at least one doping additive in the form of MgO, TiO ₂ and Al ₂ O ₃ is introduced into the mixture of the starting components in the total amount from 0.5 to 5.0% with respect to the mass of the initial mixture, and the annealing process is carried out in two stages: first, the initial mixture is annealed at a temperature of 600-800 ° C, after which the resulting mixture is stirred and annealed at a temperature of 800-1000 ° C.

The values of the initial specific capacity obtained by the proposed method are higher than those of the prototype.

At the same time, the obtained values of the degradation of the initial specific capacity after 10 and 20 cycles remain high at the level of 5-8% for 10 cycles, the change in the specific capacity with a larger number of cycles (more than 100) is not shown.

In the patent (EP 1281673A1 Published 05.02.2003 Bulletin 2003/06) several aspects and they relate to particles of cobalt oxide, a method of obtaining particles of cobalt oxide using solutions with doping reagents, which are subsequently used to obtain a cathode material for a secondary cell with a non-aqueous electrolyte ... The aim of the invention is to obtain particles of cobalt oxide using a "wet method", that is, using solutions, to obtain particles of a cathode active material having not only a stable crystal structure, but also thermal stability and increased initial discharge capacity.

The invention provides a method for obtaining particles of cobalt oxide, doped composition, including:

- neutralization of a solution containing cobalt salt and magnesium salt with an aqueous alkali solution;

- carrying out an oxidation reaction with the resulting mixture to obtain magnesium-containing particles of cobalt oxide.

- further provides for the neutralization of the solution containing the cobalt salt, with an aqueous solution of alkali;

- subjecting the resulting mixture to an oxidation reaction to obtain an aqueous suspension containing cobalt oxide particles;

- adding a magnesium salt to an aqueous suspension containing particles of cobalt oxide;

- adjusting the pH value of the aqueous suspension to cover the surface of each particle of cobalt oxide with magnesium hydroxide.

The following particles of cobalt oxide are obtained

(Co (1-x) Mgx) ₃ O _4; where x is 0.001-0.15,

(1-x) Co ₃ O ₄ 3xMg (OH) ₂ , where x is 0.001-0.15,

Particles of cobalt oxide with aluminum can be obtained by adding an aluminum salt to a slurry containing particles of cobalt oxide; adjusting the pH of the resulting solution by adding an aqueous alkali solution to it, thereby coating the surface of the cobalt oxide particle with aluminum hydroxide; and, if necessary, heat treatment of the resulting material. Examples of the aluminum salt may include aluminum sulfate, aluminum nitrate, sodium aluminum, or the like. The amount of aluminum added is usually 0.1-5 mol%, preferably 0.1-3 mol%, based on cobalt.

(Co (1-x) Mgx) ₃ O ₄ 3yAl (OH) ₃ where x is 0.001-0.15 and y is 0.001-0.05.

The invention provides a method for producing a cathode active material for a non-aqueous electrode secondary cell comprising: mixing the obtained particles of a complex composition of cobalt oxide with a lithium compound and heat treatment of the resulting mixture to obtain particles of Li (Co (1-xy), Mgx, Aly) O ₂ , where x from 0.001 to 0.15 and y from 0.001 to 0.05.

The resulting lithium cobaltite composite particles show a uniform distribution of magnesium and aluminum inside the particle, and their crystal structure is stable. A secondary cell made using the cathode active material of the invention under consideration has an initial discharge capacity of 130 to 165 mAh / g, a thermal stability of at least 215 ° C, and a retention rate of at least 95% after 50 cycles at 60 ° C.

A significant disadvantage of this technology is the use of a "wet method" alloying particles of cobalt oxide, that is, using solutions. This entails the need to organize a complete technological redistribution for the production of doped cobalt oxide, processing and disposal of a large amount of waste in the form of solutions, which significantly increases the cost of the process of obtaining particles of the cathode material.

The closest to the invention in technical essence is a method for producing a surface-modified lithiated cobalt oxide (see RF patent No. 2583049, declared 02.12.2014, publ. 10.05.2016) - a prototype, including: obtaining a surface-modified lithiated cobalt oxide LiCoO ₂ by mixing the starting lithium salts and cobalt oxide, annealing, cooling and surface modification by introducing dopants in the form of Mg, Ti and Al oxides in a total amount of 1.0 to 5.5% with respect to the mass of the mixture of starting components ... The synthesis is carried out in two stages: the initial mixture is annealed at a temperature of 500-750 ° C, after which the resulting mixture is stirred and annealed at a temperature of 900-1100 ° C, and surface modification is carried out using an alcoholic solution of aluminum isopropoxide so that the content of the coating alumina Al ₂ O ₃ in terms of the weight of LiCoO ₂ was 4-5%, and with carrying out heat treatment of the coated and dried LiCoO ₂ for 0.8-1.2 hours.

The disadvantage of the method according to the examples of the prototype patent are the low results of the indicators of the specific discharge capacity of the first cycle not exceeding 147 mA / h and significant degradation after 10 cycles of 5-8%. Lack of data on the state of the lattice parameters of LiCoO ₂ upon the introduction of dopants. The introduction of oxide materials into the particles of the cathode material reduces the specific capacity index per unit mass of the cathode material. In addition, in the examples of the patent, there is no data on degradation during a long (more than 100 cycles) test. The size of the introduced particles of dopant powders is not indicated; the above synthesis modes cannot provide a uniform atomic distribution of oxides of other elements in the bulk of a particle of lithiated cobalt oxide (especially oxides).

Another disadvantage of the prototype under consideration is the use of fire-hazardous alcohol solutions, which requires additional safety measures to exclude fires and explosions; the heat treatment temperature is not indicated in the formula.

For patents with surface modification with metal oxides, the mechanism remains incompletely disclosed, due to which there is an improvement in conductivity and an increase in the value of the specific initial energy, because the specified oxide coating (aluminum oxide) is a poor conductor - an insulator.

The technical objective of the invention is to increase the stability of the properties of LiCoO ₂ powder during long-term operation: to reduce the degradation of the specific charge-discharge capacity at the initial stage and during long-term cycling, to increase the initial specific capacity and to reduce the risk of ignition risks during the production process.

The problem is solved by the fact that in the method for producing lithiated cobalt oxide, which includes mixing the initial components of lithium salts, cobalt oxide and additives, annealing in an oven in two stages, after the first stage, the resulting mixture is mixed and annealed again, followed by cooling. According to the invention, one or more alloying additions of nanostructured thermally decomposable compounds based on metal salts or hydroxides (Me): Mg, Al, Ti with a decomposition temperature below 660 ° C in the atomic ratio of metal to Co up to 0.07, the mixture is subjected to dispersion using a mechanochemical activator at a specific power of 5-30 W / g, for 2.0-10 minutes, the initial components of lithium salts and cobalt oxide are taken in the molar ratio Li: Co = (1.0- 1.02): 1.0. The resulting cake after the first annealing is ground to the required fractional composition, up to 3% by weight of lithium-containing solution is added to the total molar ratio of Li: (Co _(1-x-yz) Me _x Me _y Me _z ) = (1.0-1.04) : 1, where the sum x + y + z is less than 0.07, and Me _x is Mg, x varies from 0 to 0.07, Me _y is Al, Me _z is Ti, and y, z are varied from 0 to 0, 05, the crushed powder is mixed and re-annealed.

Annealing in the first stage is carried out preferably at a temperature of 660-800 ° C for 3-5 hours, and re-annealing in the second stage is carried out preferably at a temperature of 800-960 ° C for 6-10 hours.

These features are essential and are interconnected with the formation of a stable set of essential features sufficient to obtain the required technical result.

So the use as alloying additives of nanostructured thermally decomposable compounds shown in Table 1, based on salts or hydroxides of metals (Me) - Mg, Al, Ti, with a particle size of less than 1 μm, allows high-quality mixing and distribution of them in the charge as alloying additives. without significant changes in the basic values of the crystal lattice parameters of the particles of the finished lithiated cobalt oxide. The results of the examples are shown in Table 3.

The molar ratio of Li: Co = (1.0 - 1.02): 1.0 already at the first stage of annealing provides a compound with the structure LiCoO ₂ , the atomic ratio of the metal or the sum of metals to Co up to 0.07 does not violate the structure of LiCoO ₂ , allows alloying metals will be evenly distributed in the structure of LiCoO ₂ without the formation of other phases.

The total molar ratio of Li: (Co _(1-x-yz) Me _x Me _y Me _z ) = (1.0-1.04): 1, where the sum of x + y + z is less than 0.07, Me _x is Mg , and x, varies from 0 to 0.07, Me _y is Al and Me _z is Ti, while y, z vary from 0 to 0.05, which, in terms of the oxides of these metals in any combination, does not exceed 5% from the total mass of the initial mixture.

An increase in the content of alloying additions above the indicated values leads to a change in the parameters of the crystal lattice, namely to an increase in the values of "a" and "c". It should also be noted that while maintaining all properties, it is possible to reduce the specific capacity index per unit mass of the cathode material according to the data from the examples in Table 2.

If the content of aluminum or titanium with a coefficient of more than 0.05, a non-single-phase product is obtained.

In the process of mechanochemical action under the shock action of activating bodies in the working volume of the mechanoactivator chamber at a specific power of 5 - 30 W / g, for 2 - 10 minutes, already at room temperature due to high energy loading, partial formation of intermediate reaction products occurs. Mechanocomposites are formed that include all the starting reagents. Partially, the process of decomposition and mutual diffusion of components begins in the process of mechanical activation. In the theory of mechanochemical synthesis, it is preferable to use substances with hydroxyl groups as reagents than oxides with a more stable crystal lattice. In this case, nanostructured particles become even finer in the process of decomposition, which facilitates their uniform distribution and mutual diffusion into other particles, and the release of gaseous components that do not form explosive mixtures does not allow the formation of large agglomerates with high strength, while maintaining partially strong but porous particles.

In the case of using mechanochemical activators, the degree of grinding and mixing of the components is higher than with simple mixing. The indicated limits of mechanochemical action are determined by the fact that at lower values of power and time, the processes of grinding and mixing are insufficient, this leads to the formation of a heterogeneous final product. At higher parameters, the process of agglomeration of primary particles into large mechanocomposites occurs and the degree of contamination of the final product by the material of the grinding bodies and the walls of the reactor increases. This process is preferably carried out in a dry nitrogen atmosphere to eliminate contamination of the particle surface by products of interaction with components that make up the air: dust, CO ₂ , etc.

The energetic effect of a mechanochemical activator with a specific power of 5 - 30 W / g, for 2 - 10 minutes on the mixture with the addition of salts or hydroxides of metals (Me) Mg, Al, Ti in the atomic ratio of metal or the sum of metals to Co up to 0.07 provides qualitative distribution of additives in the particles of composites, without a significant change in the parameters of the crystal lattice of LiCoO ₂ after the second stage of annealing.

Carrying out the first annealing of the activated mixture at a temperature of 600-800 ° C, for 3-5 hours, already at the stage of raising the temperature to 660 ° C ensures the complete decomposition of the added additions of salts or metal hydroxides (Me) Mg, Al, Ti since the maximum decomposition temperature their less than 650 ° C. Due to the mechanochemical effect on lithium carbonate, in the temperature range from 660 ° C to 750 ° C, it melts and decomposes into lithium oxide. Upon melting, a uniform distribution in the particles occurs due to the filling of the pores of the particles of mechanocomposites and the mixture as a whole, which subsequently, when held for 3-5 hours, ensures their sufficiently strong adhesion and mutual penetration - diffusion. At temperatures above 800 ° C, the process of decomposition of lithium carbonate is accelerated, reducing the time of spreading of the melt over particles. With a holding time of less than 3 hours, the reaction between cobalt oxide and lithium carbonate does not sufficiently complete the sinter has low strength; with a holding time of 5 hours, the strength of the sinter is sufficient to obtain particles of the necessary and sufficient strength. It should also be borne in mind that metal oxides (Mg, Al, Ti) cited as dopants in the prototype, as a rule, in most cases are obtained by thermal decomposition of salts or metal hydroxides (Me) - Mg, Al, Ti, which means that these oxides are more expensive than salts or hydroxides.

In the first stage of the synthesis at a temperature of 600-800 ° C, all uniformly distributed decomposable components are converted into oxides, forming after 3-5 hours LiCoO ₂ particles doped with one or more metals. Surface morphology, size, shape of particles, the distribution of elements over the volume has not yet been completely formed. The resulting intermediate product is quite easily destroyed when exposed to a powder of the required size.

The disadvantage of highly dispersed materials in view of their developed surface is side reactions with the electrolyte. This disadvantage is partially eliminated by smoothing the surface roughness using different methods. So the additive up to 3 mass. % lithium-containing solution to the total molar ratio Li: (Co _(1-x-yz) Me _x Me _y Me _z ) = (1.0-1.04): 1, where the sum of x + y + z is less than 0.07 , x changes from 0 to 0.07, and y, z change from 0 to 0.05 allows you to tightly pack the powder particles of LiCoO ₂ before re-annealing. With the introduction of more than 3 masses. % of lithium-containing solution, a liquid, difficult to process consistency is formed, which does not allow tightly packing the particles before re-annealing.

This solution is applied to the powder particles evenly by spraying while stirring the particles. _{LiOH or LiHCO 3} compounds act as a source of lithium, the concentration of lithium in the solution depends on how much it needs to be added in order to obtain the required ratio of lithium and metal oxides, as a rule, for LiOH does not exceed 5%. It is possible to reapply the solutions after drying the first layer. The sprayed liquid solution evenly covers the entire surface of the powder particles with a thin layer of lithium compounds, which decompose when heated to form lithium oxide on the surface. During the second annealing at temperatures of 800-960 ° C, this oxide is incorporated into the structure of the particle, forming a lithium-rich layer closer to its surface.

The crystal structure of LiCoO ₂ has no noticeable change after surface modification. The chemical and structural stability of the modified surface treated by the proposed method improves the electrochemical behavior of LiCoO ₂ by reducing the active centers, which served as a catalyst for the decomposition of the electrolyte on the particle surface. FIG. 1 shows doped LiCoO ₂ particles obtained according to the prototype, many particles stuck together in the process of surface modification. FIG. 2 shows the doped LiCoO ₂ particles obtained in Example 11 with a surface modified solution with LiHCO ₃ . FIG. 3 shows doped LiCoO ₂ particles obtained in Example 12 with a surface modified solution with LiOH.

The temperature-time regime of the second annealing of 800-960 ° C, for 6-10 hours, ensures the preparation of the LiCoO _{2 compound of the} required structure (high-temperature stable phase). The reaction of solid-phase synthesis of LiCoO ₂ proceeds most fully with an increase in temperature over 800 ° C and a process duration of more than 6 hours. With an increase in the heat treatment temperature over 960 ° C and a time of more than 10 hours, the synthesis is accompanied by a decrease in the quality of synthesized LiCoO ₂ due to an increased release of lithium (evaporation of lithium), which leads to a decrease in the lithium content in the product and adversely affects its electrochemical parameters.

The specified set of features has an inventive step, since it allows to improve the electrochemical characteristics of cathode materials and allows you to solve the set tasks.

Table 1 - Temperatures of decomposition of reagents used for alloying LiCoO _{2 particles.}

Reagent Decomposition reaction T decomposition, ° С Ti (OH) ₄ Ti (OH) ₄ → TiO ₂ + 2H ₂ O 500 Al (OH) ₃ 2Al (OH) ₃ → Al ₂ O ₃ + 3H ₂ O 575 Mg (CO) ₃ Mg (CO ₃ ) → MgO + CO ₂ 650 Mg (OH) ₂ Mg (OH) ₂ → MgO + H ₂ O 360 Mg (C ₂ O ₄ ) 2Mg (C ₂ O ₄ ) + О ₂ → 2MgО + 4СО ₂ 620

The influence of dopants on the structure of LiCoO _{2 was} investigated using a DRON-7 X-ray diffractometer, Cu Kα radiation λ = 1.54186.

LiCoO ₂ powder was tested by two methods.

Method 1. Specific discharge capacities of doped and surface-modified LiCoO _{2 were} determined using button-type dummies; the weight of the electrode with the test material was 40 ± 5 mg. Ready-made button-type dummies (CR2032) with a diameter of 16.2 mm were connected to a stand to test the discharge capacity. Charging and discharging were carried out under normal climatic conditions.

- charge: stage 1: with a constant current of 0.65 A to a voltage of 4.2 V;

Stage 2: with a constant voltage of 4.2 V and a falling current up to a value of 0.04 A;

- a pause of 30 minutes;

- discharge: with a constant current of 1.3 mA up to a voltage of 3.0 V;

- a pause of 30 minutes.

The number of charge-discharge cycles is 1, 5, 20, the discharge capacity of the breadboards after 1, 5, 20 cycles and the specific capacity are shown in Table 2.

The table shows values for three dimensions.

Method 2. The resource characteristics of the LiCoO ₂ powder as a cathode material were determined on the models when determining the values of the degradation of the discharge energy in% of the initial one, on the control cycles of the full capacity (charge C / 10 up to 4.15 V, discharge with current C / 2 up to 2.7 C) from the number of sweep cycles with a depth of discharge of 70%. The numbers of examples of specific performance and the data obtained are shown in table 4.

All alloying powders were calcined before use.

Examples of specific implementation.

Example 1 of the implementation of the method.

To obtain LiCoO ₂ , a mixture of powders with a particle size of less than 25 microns of lithium carbonate (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ) in a lithium to cobalt ratio of 1.02 and a powder of nanostructured magnesium hydroxide Mg (OH) ₂ in an atomic ratio Mg : Co = 0.07: 0.93 or 5.25% Mg (OH) ₂ , in terms of magnesium oxide 3.6% by weight MgO. The mixture was mixed and processed in a mechanical activator at a specific power of 5 W / g for 10 minutes, followed by heat treatment in an oven in air. The first stage of annealing at 750 ° C for 5 hours, the cooled cake is ground to a powder of the required size, moistened in an amount of 3% of the batch weight by spraying with a LiHCO ₃ solution with a concentration of 1.2 g / 100 ml and subjected to a second heat treatment at 950 ° C for 10 hours. The powder was wetted by spraying the LiHCO ₃ solution while stirring the powder. The cooled cake is crushed, classified, analyzed and subjected to electrochemical testing. The test result obtained is shown in table 2, line 1, in table 3, line 1.

Example 2 implementation of the method outside the proposed values of the method.

Under the conditions of example 1, a powder of nanostructured magnesium hydroxide Mg (OH) _{2 was} taken in the atomic ratio Mg: Co = 0.14: 0.86, or 10.6% Mg (OH) ₂ in terms of magnesium oxide, 7.47% by weight of MgO. The obtained result of measuring the parameters of the crystal lattice is shown in table 2, line 2, in table 3, line 2.

Significant change in the parameters of the crystal lattice of the LiCoO ₂ powder upward. Low value of the initial specific capacity.

Example 3 of the implementation of the method.

In the conditions of example 1, taken nano powder of magnesium carbonate MgCO ₃ in atomic ratio Mg: Co = 0.01: 0.99 or 0.77% MgCO ₃ in terms of magnesium oxide 0.5% by weight MgO. After the first annealing at 800 ° C, the powder was moistened in an amount of 1% of the batch weight by spraying a LiOH solution with a concentration of 0.5 g of lithium per 100 ml of water and subjected to a second heat treatment at 960 ° C for 10 hours. The test result obtained is shown in table 2, line 3, in table 3, line 3.

Example 4 of the implementation of the method.

Under the conditions of example 1, nano powder of aluminum hydroxide Al (OH) _{3 was} taken in the atomic ratio Al: Co = 0.05: 0.95 or 4.9% Al (OH) ₃ , or in terms of aluminum oxide 3.2% massive. The test result obtained is shown in table 2, line 4, in table 3, line 4.

Example 5 of the method.

To obtain LiCoO ₂ , a mixture of powders with a particle size of less than 25 microns of lithium carbonate (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ) in the ratio of lithium to cobalt 1.00 and calcined nano powder of aluminum hydroxide Al (OH) ₃ in an atomic ratio Al: Co = 0.005: 0.995 or 0.48% Al (OH) ₃ , in terms of aluminum oxide 0.31% by weight. The mixture was mixed and processed in a mechanical activator at a specific power of 30 W / g for 2 minutes, followed by heat treatment in an oven in air. The first stage of annealing at 600 ° C for 3 hours, the cooled cake was ground to a powder of the required size, moistened in an amount of 3% of the batch weight by spraying a LiHCO ₃ solution with a concentration of 1.2 g / 100 ml and subjected to a second heat treatment at 800 ° C for 10 hours. The powder was moistened with 2% by weight by spraying the LiHCO ₃ solution three times while stirring the powder. The ratio Li: (Co _0.99 Al _0.01 ) was 1.04. The cooled cake is crushed, classified, analyzed and subjected to electrochemical testing. The test result obtained is shown in table 2, line 5, in table 3, line 5.

Example 6 of the implementation of the method.

Under the conditions of example 5, the calcined nano powder of titanium hydroxide Ti (OH) _{4 was} taken in the atomic ratio Ti: Co = 0.05: 0.95 or 7.19% by weight Ti (OH) ₄ , in terms of titanium oxide 4.91 % mass. The Li: (Co _0.95 Ti _0.05 ) ratio was 1.01.

The test result obtained is shown in table 2, line 6, in table 3, line 6.

Example 7 of the implementation of the method.

Under the conditions of example 5, a calcined nanosized powder of titanium hydroxide Ti (OH) _{4 was} taken in an atomic ratio Ti: Co = 0.01: 0.99 or 1.45 wt% Ti (OH) ₄ , in terms of titanium oxide 0.98 % mass. The powder was moistened in an amount of 2% by weight of the charge by spraying a LiHCO ₃ solution with a concentration of 1.2 g / 100 ml and subjected to a second heat treatment at 950 ° C for 8 hours. The ratio Li: (Co _0.99 Ti _0.01 ) was 1.02.

The test result obtained is shown in table 2, line 6, in table 3, line 6.

Example 8 of the implementation of the method outside the proposed values of the method.

Under the conditions of example 5, powder of nanostructured magnesium hydroxide was taken 0.75% by weight in terms of magnesium oxide, aluminum hydroxide 0.48% by weight in terms of aluminum oxide and titanium hydroxide 1.19% by weight in terms of titanium oxide, to the total atomic ratio (Mg _0.07 Al _0.05 Ti _0.05 Co _0.83 ).

The ratio Li: (Mg _0.0041 , Al _0.0013 , Ti _0.0029 Co _0.917 ) was 1: 1.

The obtained test result is shown in table 2, line 8, in table 3, line 8. Significant change in the parameters of the crystal lattice of powder LiCoO ₂ in the direction of increase. Low value of the initial specific capacity.

Example 9 of the implementation of the method.

Under the conditions of example 5, the calcined nano powder of magnesium carbonate MgCO _{3 was} taken in the atomic ratio Mg: Co = 0.01: 0.99 or 0.948% by weight of MgCO ₃ in terms of magnesium oxide, 0.498% by weight. The powder was moistened with 0.2% of the total weight of the powder by spraying a LiOH solution with a concentration of 5 g / L while stirring the powder. The ratio Li: (Co _0.99 Mg _0.011 ) was 1.03. The first stage of annealing at 800 ° C for 3 hours.

The test result obtained is shown in table 2, line 9, in table 3, line 9.

Example 10.

Powders of lithium carbonate (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ) and dopants based on magnesium oxides 0.75% by weight, aluminum 0.48%, titanium 1.19% (total content 2.73% by weight in recalculated to the mass of LiCoO ₂ ). stirred until a homogeneous initial mixture of reagents was obtained and annealed in two stages: at 750 ° C for 5 hours and at 970 ° C for 8 hours.

Surface modification was carried out as follows.

By dissolving Al isopropoxide, a 25% solution in ethanol was prepared, and LiCoO ₂ powder was placed in the resulting solution so that the Al ₂ O ₃ content, based on the LiCoO ₂ weight, was 4.3 wt%. The resulting mixture was heated with stirring to 60 ° C to distill off ethanol. Thereafter, the treated lithium cobaltite was annealed at a temperature of 600 ° C for 1.0 hour. The ratio of lithium to cobalt is 0.98: 1.00.

The appearance and surface morphology of the obtained powder particles are shown in Fig. 1. the data of long-term tests for the degradation of specific capacity in table 4, line 1.

Example 11 of the implementation of the method.

To obtain LiCoO ₂ , a mixture of powders with a particle size of less than 25 microns of lithium carbonate (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ) in the ratio of lithium to cobalt 1.00 was taken. Powder of nanostructured magnesium hydroxide was taken 0.75% by weight in terms of magnesium oxide, aluminum hydroxide 0.48% by weight in terms of aluminum oxide and titanium hydroxide 1.19% by weight in terms of titanium oxide, up to the total atomic ratio (Mg _0.015 , Al _0.0075 , Ti _0.012 ): Co _0.9655 . The mixture was mixed and processed in a mechanical activator at a specific power of 5 W / g for 5 minutes, followed by heat treatment in an oven in air. The first stage of annealing at 740 ° C for 4 hours, the cooled cake was ground to a powder of the required size, moistened twice in an amount of 0.2% of the batch weight by spraying a LiHCO ₃ solution with a concentration of 1.2 g / 100 ml of water and subjected to a second heat treatment at 950 ° C for 10 hours. The cooled cake is crushed, classified, analyzed and subjected to electrochemical testing. The ratio Li: (Mg _0.015 , Al _0.0075 , Ti _0.012 Co _0.9655 ) was 1: 1.

The appearance and surface morphology of the obtained powder particles are shown in FIG. 2, the data of long-term tests for the degradation of specific capacity in table 4, line 2.

Example 12 of the implementation of the method.

To obtain LiCoO ₂ , a mixture of powders with a particle size of less than 25 microns of lithium carbonate (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ) in the ratio of lithium to cobalt 1.00, powder of nanostructured magnesium hydroxide 0.204% by weight in terms of magnesium oxide , aluminum hydroxide 0.08% by weight in terms of aluminum oxide and titanium hydroxide 0.285% by weight in terms of titanium oxide, up to the total atomic ratio Li: (Mg _0.0041 , Al _0.0013 , Ti _0.0029 Co _0.9917 ). The mixture was mixed and processed in a mechanical activator at a specific power of 10 W / g for 10 minutes, followed by heat treatment in an oven in air. The first stage of annealing at 740 ° C for 4 hours, the cooled cake is ground to a powder of the required size, moistened in an amount of 1.2% of the batch weight by spraying a LiHCO ₃ solution with a concentration of 1.2 g / 100 ml of water and subjected to a second heat treatment at 900 ° From within 10 hours. The cooled cake is crushed, classified, analyzed and subjected to electrochemical testing. The ratio Li: (Mg _0.0041 , Al _0.0013 , Ti _0.0029 Co _0.917 ) was 1: 1.

The appearance and surface morphology of the obtained powder particles are shown in FIG. 3, the data of long-term tests for the degradation of specific capacity in table 4, line 3.

Table 2 - Values of the specific discharge capacity of LiCoO ₂ powders from the test cycle and examples of specific performance. Tests according to method 1.

No.
Strings Example No. Specific discharge capacity, mAh / g 1 cycle 5 cycle Cycle 20 1 1 156.9 152.2 146.2 2 2 143.8 139.5 138.2 3 3 160.2 149.5 144.1 4 4 155.4 148.3 144.9 5 5 157.1 148.9 144.8 6 6 148.1 144.2 142.8 7 7 150.6 145.8 141.0 eight eight 132.7 130.9 128.3 nine nine 152.8 146.1 141.7

Table 3 - Parameters of the crystal lattice structure of LiCoO ₂ .

No.
example Lattice parameters Notes (edit) a with s / a 1 2.813 14.043 4.992 Mg (OH) ₂ Mg _0.07 Co _0.93 2 2.819 14.099 5,001 Mg (OH) ₂ Mg _0.14 Co _0.86 3 2.812 14.041 4.993 MgCO ₃ Mg _0.01 Co _0.99 4 2.815 14,052 4.992 Al (OH) ₃ Al _0.05 Co _0.95 5 2.812 14.037 4.992 Al (OH) ₃ Al _0.005 Co _0.995 6 2.816 14,064 4,994 Ti (OH) ₄ Ti _0.05 Co _0.95 7 2.814 14.049 4.993 Ti (OH) ₄ Ti _0.01 Co _0.99 eight 2.827 14,130 4.998 Mg (OH) ₂ Al (OH) ₃ Ti (OH) ₄ Mg _0.07 Al _0.05 Ti _0.05 Co _0.83 nine 2.811 14.028 4,990 MgC ₂ O ₄ Mg _0.01 Co _0.99 ten 2.810 14.034 4,994 Prototype
MgO, Al ₂ O ₃ , TiO ₂ ,
Al ₂ O ₃ coating eleven 2.813 14.051 4.995 Mg _0.015 Al _0.0075 Ti _0.0012 Co _0.9758 12 2.812 14,048 4.996 Mg _0.0041 Al _0.0013 Ti _0.0029 Co _0.9917

Table 4 - Values of the specific discharge capacity of LiCoO ₂ powders from the test cycle and examples of specific performance. Tests according to method 2.

No.
example degradation of the discharge energy in% of the initial and the number of test cycles 100
cycles 200
cycles 300
cycles 400
cycles 500
cycles 10 (Prototype) 4.2 6.5 7.2 8.9 10.5 eleven 2,3 3.8 5.1 6.1 7.2 12 2.5 3.6 5.1 6.2 7.5

Claims (2)

1. A method of obtaining a powder of lithiated cobalt oxide with an alloyed structure and a modified surface, including mixing the initial components of lithium salts, cobalt oxide and additives, annealing in two stages, cooling and surface modification, characterized in that one or more alloying agents are introduced into the mixture of initial components. additives of nanostructured thermally decomposable compounds based on salts or hydroxides of metals Mg, Al, Ti with a decomposition temperature below 660 ° C in the atomic ratio of metal or the sum of metals to Co up to 0.07, while the mixture is subjected to dispersion using a mechanochemical activator at a specific power of 5 -30 W / g, for 2-10 minutes, the initial components of lithium salts and cobalt oxide are taken in the molar ratio Li: Co = (1.0-1.02): 1.0, the resulting cake after the first annealing is ground to the required fractional composition, add up to 3 wt.% lithium-containing solution to the total molar ratio Li: (Co _(1-x-yz) Mg _x Al _y Ti _z ) = (1.0-1.04): 1, where the sum x + y + z is less than 0.07, x changes from 0 to 0.07, while - y, z change from 0 to 0, 05, the crushed powder is mixed and re-annealed. 2. The method according to claim 1, characterized in that the annealing in the first stage is carried out preferably at a temperature of 660-800 ° C for 3-4 hours, and the re-annealing in the second stage is carried out preferably at a temperature of 800-960 ° C for 6 -10 hours.

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