[0001 ]

The present disclosure relates to a method for producing a spinel-type lithium-mixed transition metal oxide.

[Background Art]

[0002]

Spinel lithium nickel manganese oxide (LiNio.5Mn1.5O4, referred to below as “LNMO”) has a high operating voltage of up to 4.7 V (versus Li ⁺ /Li class, referred to as “5 V class”) with a theoretical capacity of 147 mAh ■ g- ¹ , and is therefore a desirable cathode material because it is capable of providing high energy density at low cost.

However, a number of inherent technical problems, such as continuous electrolyte degradation above 4.5 V and a reduction in capacity during cycling, are preventing large- scale development of this technology. The latter case is mainly associated with continuous dissolution of Mn into a liquid electrolyte during cycling. In practice, Mn ³⁺ causes a disproportionation reaction, providing Mn ⁴⁺ and Mn ²⁺ which are soluble in the electrolyte, and therefore the dissolution of Mn is caused by the presence of Mn ³⁺ in the lattice structure. Additionally, an Mn ³⁺ /Mn ⁴⁺ redox (oxidation-reduction) reaction occurs at up to 4.2 V (4.7 V for Ni ²⁺ /Ni ⁴⁺ redox), and the energy density of the LNMO cathode material as a whole is reduced. The ratio of Mn ³⁺ /Mn ⁴⁺ is closely related to the LNMO superlattice structure and an ordered or disordered lattice structure, but an ordered structure becomes predominant as the ratio of Mn ³⁺ /Mn ⁴⁺ decreases (the ratio of Mn ⁴⁺ increases). Accordingly, a regular structure (predominantly Mn ⁴⁺ ) has an advantage in terms of energy density. However, this ordered structure is known to cause a lack of flexibility in structures capable of producing a delay in lithium ion migration during charging and discharging, leading to poor long-term cycling properties.

[0003]

Mn ²⁺ (Mn precursor oxidation state) is readily oxidized to Mn ⁴⁺ during firing, but even in the presence of air (instead of pure oxygen), a small proportion of the Mn ⁴⁺ in the LNMO is converted to an Mn ³⁺ oxidation state (in particular converted at >900°C), and this is the conventional temperature for synthesising LNMO. Additionally, at a temperature such as this, the spinel structure of the LNMO tends to undergo an electrochemical transition to an inert rock salt or 03 structure, especially in a region close to the surface, which accordingly causes a reduction in initial capacity and initial Coulombic efficiency.

[0004]

In light of the reasons above, it is very important in the development of LNMO cathode materials to control the Mn ³⁺ ratio (to be greater than Mn ⁴⁺ ) in an optimum ordered/disordered domain within the lattice structure, while also electrochemically reducing an inert impurity phase. Typical approaches which may be cited involve controlling oxygen vacancies by means of doping, surface coating, addition of an electrolyte additive for CEI control (cathode electrolyte interface passivation layer), and replacement of a conventional binder with an Mn ²⁺ chelation binder. In order to improve the electrochemical performance of spinel LNMO cathode materials, it has also been proposed to adjust other synthesis conditions, such as post heat treatment and firing atmosphere.

[0005]

Patent Document 1 reports a method for producing a spinel cathode material comprising Li, Mn, Ni and two other elements selected from Co, Fe, Mg, Ti, Al, Ba, Cr, W, Mo, Y, Zr and Nb. In Patent Document 1 , an ordered lattice structure and a disordered lattice structure are mixed, less gas is generated during cycling, and discharge capacity is improved.

[0006]

Patent Document 2 reports a method for producing a spinel cathode material which operates at a voltage above 4.4 V (vs. Li ⁺ /Li), and comprises a separate element selected from Li, Mn, Ni, Mg, Ti, V, Cr, Fe, Co, Cu and Zn. Al, G a , R b , G e , Mo, N b , Z r , S i and SO ₄ may be used as a dopant. A spinel cathode material doped with SO ₄ can be obtained by means of firing under a reducing atmosphere and an oxygencontaining atmosphere, and by a subsequent post heat treatment under the atmosphere, and this enables improved long-term cycling properties.

[0007]

Non-Patent Document 1 reports a spinel LNMO positive electrode active material obtained by means of a post heat treatment (annealing treatment) under the atmosphere, and reports that an optimum duration is 2 hours-6 hours to enable an improvement in the longterm cycling properties.

[0008]

Non-Patent Document 2 reports a spherical LNMO cathode active material doped with an Mg gradient, wherein an Mg-rich surface suppresses a reaction between the electrolyte and LNMO, and total resistance is reduced.

[0009]

Non-Patent Document 3 reports an over-lithiated LNMO cathode material which compensates lithium loss caused by the presence of an active rock salt phase (converted to an active spinel phase during a first cycle) and a side reaction with an electrolyte. This over-lithiation enables a higher initial capacity and higher long-term cycling properties than a conventional spinel LNMO cathode material.

[0010]

Non-Patent Document 4 reports an AI2O3 coating on LNMO cathode material, and a subsequent post heat treatment. A thin, uniform AI2O3 coating layer prevents direct contact between the electrode and electrolyte, and traps HF from the electrolyte, which accordingly enables improved long-term cycling characteristics.

[Prior Art Documents]

[Patent Documents]

[0011 ]

[Patent Document 1 ] US Patent No. 1046848

[Patent Document 2] WO 2018/036954 A1

[Non-Patent Documents] [0012]

[Non-Patent Document 1 ] Chem. Mater., 2014, No. 26, pp. 4377-4386

[Non-Patent Document 2] Electrochim. Acta, 2014, No. 120, pp. 133-139

[Non-Patent Document 3] J. Electrochem. Soc., 2019, No. 166, pp. A3531-A3538

[Non-Patent Document 4] J. Solid State Chem., 2022, No. 306, p. 122765 [Summary of the Invention]

[Problems to be Solved by the Invention] [0013]

Doping using another element is employed in order to improve electrochemical performance, mainly by suppressing Mn dissolution, and a surface coating method is generally used in order to control the Mn ³⁺ /Mn ⁴⁺ ratio, ordered/disordered structure, and surface characteristics. Such methods are known to be effective, but they require the addition of two or more production processes (e.g., preparation of a doped precursor by means of heat treatment), and this increases the cost of producing the spinel LNMO cathode material.

For application to lithium ion batteries, there is therefore a strong need in this technical field for the development of a method for preparing a spinel cathode material which is capable of demonstrating better chemical and structural stability (controlled Mn ³⁺ /Mn ⁴⁺ ratio), better cycling properties, and improved characteristics such as high capacity.

[0014]

There has been a large amount of research focused on manganese (Mn)-rich cathode materials as substitutes for layered high-Ni cathode active materials used in lithium ion batteries, such as NMC811 (lithium nickel manganese cobalt oxide having a molar ratio of Ni:Mn:Co of 80:10:10) and NCA (lithium nickel cobalt aluminium oxide having a molar ratio of Ni:Co:AI of 85:15:5).

Because of a number of similarities with Mn-rich cathode materials, attention is focusing on spinel lithium nickel manganese oxide (LiNixMnyOz), because it does not contain costly metals such as cobalt and nickel, or has a smaller content thereof, and is capable of achieving a suitable energy density (580 Wh ■ kg ^-1 against 760 Wh ■ kg ^-1 for high-Ni NMC811 ).

Despite the advantages mentioned above, wide-scale commercialisation of spinel lithium nickel manganese oxide (LNMO below) is prevented by a number of inherent technical problems, such as a lack of available electrolytes operating at a high voltage of up to 4.9 V (vs. Li ⁺ /Li), continuous Mn dissolution into the electrolyte arising from the Mn ³⁺ disproportionation reaction, and the presence of an impurity phase (03 and/or rock salt phase in the firing process).

The approaches generally used to alleviate such problems are doping with another element and surface coating. Such approaches are known to be effective, but they require the addition of two or more production processes (e.g., preparation of a doped precursor by means of heat treatment), and this increases the cost of producing the spinel LNMO cathode material. Meanwhile, a post heat treatment (annealing) under air following the firing process has also been proposed, and this can be combined with the approaches mentioned above. Oxygen from the air electrochemically reacts with the inert impurity phase, and these electrochemically convert to an active spinel structure. In addition, the oxygen contained in the air also reacts with Mn ³⁺ and reduces the proportion of Mn ³⁺ (to a greater extent than Mn ⁴⁺ ), and dissolution of Mn into the electrolyte is suppressed accordingly.

However, oxygen in the air (at 20.9% v/v) is insufficient for effective reduction of the majority of the impurity phase and oxidation of Mn ³⁺ to Mn ⁴⁺ .

For application to lithium ion batteries, there is therefore a need for the development of a method for preparing a spinel cathode material which is capable of demonstrating better chemical and structural stability (controlled Mn ³⁺ /Mn ⁴⁺ ratio), superior cycling properties, and improved characteristics such as high capacity.

[0015]

The present disclosure provides a defined annealing mixed gas composition and a defined range for an annealing treatment process duration capable of minimizing the impurity phase and also capable of suppressing a reduction in Mn ³⁺ in proportion to an optimum value in the chemical structure of a spinel-type lithium-mixed transition metal oxide.

By virtue of the defined gas composition and post heat treatment time, the present disclosure makes it possible to provide a method for producing a spinel-type lithium-mixed transition metal oxide which is capable of improving reversibility (Coulombic efficiency) and long-term cycling properties, and achieving higher capacity (energy density) in a lithium ion battery.

The present disclosure provides a lithium ion secondary battery comprising, as a positive electrode active material, a spinel-type lithium-mixed transition metal oxide produced by the abovementioned method for producing a spinel-type lithium-mixed transition metal oxide.

[Means for Solving the Problems]

[0016]

A method for producing a spinel-type lithium-mixed transition metal oxide according to the present disclosure comprises: an annealing treatment step in which a spinel-type lithium-mixed transition metal oxide obtained in a firing step is subjected to an annealing treatment (post heat treatment) at a predetermined temperature and for a predetermined time under an atmosphere of an annealing mixed gas comprising at least oxygen.

The spinel-type lithium-mixed transition metal oxide is defined by the chemical formula (1 ). Li _a NixMn _y A _z O ₄ - _k (D

In the formula, A is a dopant, 0.9<a< 1 .1 , x+ y + z =2, x<0. 5 , and y <1. 5 . x, y, z and k are molar ratios, and a is a molar ratio independent of other elements, k varies correspondingly with x, e.g., k= from 0.0 to 0.2.

[0017]

The annealing treatment step may include a steady temperature treatment comprising heating at a predetermined fixed temperature (e.g., in a range of 650-750°C, more preferably 680°C-720°C).

The annealing treatment step may include an increasing-temperature heating treatment in which the temperature is increased to the fixed temperature at a predetermined heating rate (e.g., 1-10°C/minute), and a cooling treatment comprising cooling from the fixed temperature to a predetermined temperature (e.g., 30°C or room temperature, etc...) at a predetermined cooling rate (e.g., 1-10°C/minute).

In the annealing treatment step:

A time of the steady temperature treatment in the annealing treatment may be 25 minutes- 10 hours, preferably 28 minutes-10 hours, more preferably in a range of from 1 hour to 10 hours, even more preferably in a range of from 1 .5 hours to 8 hours, and especially preferably in a range of from 2 hours to 8 hours.

[0018]

An oxygen concentration of the annealing mixed gas is a concentration exceeding the oxygen concentration in the atmosphere, and may be 30 vol%-99.999 vol%, preferably 32 vol%-99.999 vol%, and more preferably in a range of 34 vol%-99.999 vol%.

[0019]

Gases other than oxygen in the annealing mixed gas may include the gases nitrogen ( N 2) and/or argon (Ar).

A concentration of the N 2 may be in a range of 0 vol%-50 vol%, and preferably in a range of 0 vol%-35 vol%.

A concentration of the Ar may be in a range of 0 vol%-50 vol%, and preferably in a range of 0 vol%-35 vol%.

One or two or more of argon, nitrogen, helium, neon and krypton may be selected as the gases other than oxygen in the annealing mixed gas.

[0020] The firing step is a step in which a cathode precursor containing nickel at a predetermined content or greater, and a metal oxide solid starting material comprising a lithium starting material are fired in a reactor.

The firing step may comprise firing in the reactor under an atmosphere of a firing mixed gas comprising at least oxygen.

The content of oxygen in the firing mixed gas is preferably 95 vol% or greater and 97 vol% or less.

One or two or more of argon, nitrogen, helium and krypton may be selected as gas components other than oxygen in the firing mixed gas.

When the gas component other than the oxygen is argon, the argon content may be in a range of 2 vol%-5 vol%.

When the gas components other than the oxygen are argon and nitrogen, the argon content (vol%) is preferably greater than the nitrogen content.

When the gas components other than the oxygen are argon and nitrogen, the nitrogen content may be in a range of 0 vol%-2 vol%.

[0021 ]

A precursor preparation step for preparing the cathode precursor, and a step of producing a solid starting material of the spinel-type lithium-mixed transition metal oxide may also be included before the firing step.

A washing step for removing excess lithium and impurities from the spinel-type lithium- mixed transition metal oxide obtained in the firing step may also be included after the firing step and before the annealing step, or after the annealing step.

A coating step for coating the spinel-type lithium-mixed transition metal oxide may also be included after the annealing step or after the washing step.

[0022]

A lithium ion secondary battery according to other disclosure comprises, as a positive electrode active material, a spinel-type lithium-mixed transition metal oxide produced by the abovementioned method for producing a spinel-type lithium-mixed transition metal oxide.

[0023]

A method for producing the lithium ion secondary battery according to other disclosure comprises: an electrode production step in which an electrode is produced by using a spineltype lithium-mixed transition metal oxide produced by the abovementioned method for producing a spinel-type lithium-mixed transition metal oxide.

[0024]

A method for producing the lithium ion secondary battery according to other disclosure comprises: an electrode production step in which a cathode electrode is produced by using a spinel- type lithium-mixed transition metal oxide produced by the abovementioned method for producing a spinel-type lithium-mixed transition metal oxide.

[0025]

(Effects)

(1) An impurity phase is minimized and a reduction in Mn ³⁺ in proportion to an optimum value in the chemical structure of the spinel-type lithium-mixed transition metal oxide is suppressed.

(2) By virtue of defining the annealing gas composition and annealing treatment time, it is possible to improve reversibility (Coulombic efficiency) and long-term cycling properties, and to achieve higher capacity (energy density) in a lithium ion battery.

[Brief Description of the Drawings]

[0026]

[Fig. 1 ] Fig. 1 shows a flow of a production method of Embodiment 1 .

[Fig. 2] Fig. 2 shows results of four types of evaluations in the examples.

[Fig. 3] Fig. 3 shows results of differential capacity ( d Q/ d V) in the examples.

[Embodiments of the Invention]

[0027]

Several embodiments of the present invention will be described below. The embodiments described below illustrate examples of the present invention. The present invention is in no way limited by the following embodiments, and also includes a numberof variant modes which may be implemented without altering the gist of the present invention. It should be noted that not all of the components described below are essential components of the present invention.

[0028]

(Definition of Terminology)

In the present specification, standard abbreviations for elements from the Periodic Table of the Elements are used. Elements may therefore be represented by these abbreviations. For example, Li means lithium, Ni means nickel, Mn means manganese, and O means oxygen. The same also applies to other elements.

[0029]

(Embodiment 1)

A spinel-type lithium-mixed transition metal oxide according to embodiment 1 will be described with reference to the flowchart in fig. 1 .

A cathode precursor is prepared in a precursor preparation step (S1 ).

The cathode precursor is a nickel manganese oxide comprising 0.5 nickel and 1.5 manganese, as a molar ratio.

In the precursor preparation step (S1 ), for example, a nickel salt and a manganese salt are dissolved in deionised water, the resulting aqueous solution is added to an alkali solution to form a suspension, and a solid product is obtained. The resulting solid product is dried to produce the cathode precursor. It should be noted that the precursor may also be obtained by other methods.

[0030]

The cathode precursor and a lithium starting material are mixed in a metal oxide solid starting material production step (S2).

For example, the cathode precursor and a lithium salt are mixed and dispersed in an aqueous solvent to form a uniform slurry, which is then dried to obtain a metal oxide solid starting material. The metal oxide solid starting material may also be obtained by other methods.

[0031 ]

In a firing step (S3), the cathode precursor and the metal oxide solid starting material are introduced into a reactor under an atmosphere of a mixed gas comprising oxygen, and fired. A spinel lithium nickel manganese oxide is obtained in this way.

[0032]

In the firing step (S3), a firing mixed gas may be supplied to the reactor either continuously or intermittently.

In the firing step (S3), the firing temperature may be in a range of 600°C-1100°C, preferably in a range of 650°C-900°C, and more preferably in a range of 700°C-800°C.

In the firing step (S3), a firing time may be in a range of 5 hours-24 hours, preferably in a range of 8 hours-16 hours, and more preferably between 11 hours and 13 hours.

[0033]

In an annealing treatment step (S4), the spinel lithium nickel manganese oxide obtained in the firing step (S3) is subjected to an annealing treatment (post heat treatment) at a predetermined temperature and for a predetermined time under an atmosphere of an annealing mixed gas comprising at least oxygen.

The annealing treatment step includes a steady temperature treatment at a predetermined fixed temperature (e.g., in a range of 650-750°C, more preferably 680°C-720°C). An increasing-temperature heating treatment in which the temperature is increased to the fixed temperature at a predetermined heating rate (e.g., 1-10°C/minute), and a cooling treatment comprising cooling from the fixed temperature to a predetermined temperature (e.g., 30°C or room temperature, etc.) at a predetermined cooling rate (e.g., 1-10°C/minute) may further be included.

A time of the steady temperature treatment in the annealing treatment in the annealing treatment step is 25 minutes-9 hours, preferably 28 minutes-9 hours, more preferably in a range of from 29 minutes to 9 hours, and even more preferably in a range of from 29 minutes to 8 hours.

An oxygen concentration of the annealing mixed gas may be 30 vol%-99.999 vol%, preferably 32 vol%-99.999 vol%, and more preferably in a range of 34 vol%-99.999 vol%. Gases other than the oxygen in the annealing mixed gas may include the gases nitrogen ( N2) and/or argon (Ar).

[0034]

A washing step and/or a coating step may further be included. Impurities are removed from the spinel lithium nickel manganese oxide in the washing step. The spinel lithium nickel manganese oxide is coated in the coating step.

[0035]

Furthermore, a method for producing a lithium ion secondary battery comprises an electrode production step in which a cathode electrode is produced by using the spinel lithium nickel manganese oxide.

[0036]

(Examples)

A spinel lithium nickel manganese oxide obtained in a firing step was prepared. The spinel lithium nickel manganese oxide was LiNio ₅ Mni ₅ O ₄ having a discharge capacity of 18.3% from Mn ³⁺ . 1 g of the spinel lithium nickel manganese oxide was introduced into a crucible and subjected to an annealing treatment under an annealing mixed gas atmosphere.

Heating rate: 5°C/minute (136 minutes from 20°C to 700°C)

Steady heating temperature: 700°C

Cooling rate: approximately 5°C/minute (natural cooling from 700°C to 30°C, 136 minutes until cooled)

Gas flow: 100 SCCM

[0037]

Table 1 shows the compositional ratio (vol%) of the annealing mixed gas. Air was used in comparative example 1 and the annealing treatment was not performed in comparative example 2. The annealing treatment times (steady heating temperature time, dwelling time) were set at 30 minutes, 2 hours, 4 hours, 6 hours and 10 hours.

[Table 1 ] [0038]

An electrode was produced. The electrode comprises: spinel lithium nickel manganese oxide (88 wt%), carbon black (product name: C65; manufacturer: TIMCAL; amount: 7 wt%), and polyvinylidene fluoride (abbreviation: PVDF; manufacturer: Solvay; product name: Solef 5130; amount: 5 wt%). The electrode material was dispersed using N-methyl- 2-pyrrolidone (abbreviation: NMP; 1-methyl-2-pyrrolidone, manufactured by FUFIFILM Wako Chemicals) as a solvent, and the ingredients were mixed for 1 hour at 400 rpm in an agate grinding jar. In this way, an electrode slurry was produced.

The resulting electrode slurry was then formed into a uniformly thin layer of 150 pm on an aluminium current collector using a doctor blade (in other words, it was formed by tape casting).

Electrodes (12.7 mm in diameter) were then cut and dried in vacuo for 15 hours at 90°C. CR2032 coin cell batteries were assembled in a glovebox in an argon (Ar) atmosphere using lithium metal as both the reference and counter electrodes.

The electrolyte consisted of 1.0 M LiPF ₆ in ethylene carbonate (EC):methyl ethyl carbonate (MEC) (50:50 [v/v] ).

Lastly, electrochemical galvanostatic measurements were performed on the resulting coin cell batteries. The measurements were performed in the constant current (CC) format under conditions of 25°C within a voltage window of 3.0 to 4.9 V versus Li ⁺ /Li at a different current density (1 C = 1 4 7 m A g ^-1 ). Cells were formed at 0.1 °C for 3 cycles. All data below are average values of the results for three different coin cell batteries.

[0039]

(Evaluation)

The discharge capacity (discharge capacity at 1 C), initial Coulombic efficiency (CE), capacity from Mn ³⁺ /Mn ⁴⁺ redox couple, and long-term capacity retention were each evaluated. The BCS-805 battery cycler manufactured by BioLogic was used for the discharge capacity measurement.

The initial discharge capacity directly determines capacity and energy density, and a higher discharge capacity is always preferred.

The initial Coulombic efficiency (CE) represents reversibility of the cathode material. The proportion of irreversible lithium loss (i.e., the capacity) may be expressed by 100%- Coulombic efficiency (%). In a full cell configuration, this proportion should be as low as possible because the initial Coulombic efficiency does not enable the lithium lost in the first cycle to be compensated or recovered by another means.

In LNMO cathode chemistry, capacity from the Mn ³⁺ /Mn ⁴⁺ redox (oxidation-reduction) couple is important, with Mn ³⁺ /Mn ⁴⁺ redox occurring at a lower potential than Ni ²⁺ /Ni ⁴⁺ , which causes a reduction in energy density, and this capacity should therefore be as low as possible. Additionally, the continuous Mn dissolution caused by Mn ⁴⁺ disproportionation may cause a battery fault and/or continuous capacity reduction. Long-term capacity retention explains how a cathode material can achieve discharge capacity over a large number of cycles. Assuming that a higher capacity retention rate is preferred, it should be noted that a cathode material having a lower initial discharge capacity and lower Coulombic efficiency cannot be used on an industrial level.

[0040]

Fig. 2 shows results of the four types of evaluations. Considering the four types of evaluations, the 6-hour annealing sample of example 1 (pure O2) or example 2 (50% O2) showed the best results. The evaluations for the 6-hour annealing samples were better than for the 10-hour annealing samples.

[0041 ]

In order to systematically evaluate the performance of the LNMO cathode materials, formulae were created to include all the relevant parameters. A relative performance index of the LNMO material after 100 cycles is represented as below.

Initial discharge capacity (m A h ■ g ^-1 )xinitial Coulombic efficiency (%) xcapacity retention rate after 100 cycles (%) x { [capacity from Mn ³⁺ /Mn ⁴⁺ x ( 4. 2 V/ 4. 7 V) ] x [1 — (capacity from Mn ³⁺ /Mn ⁴⁺ ) ] } (%) (formula 1 )

Formula (2) = [formula (1)/value obtained using formula (1) without annealing treatment] xioo

[0042]

[Table 2]

It can be seen from table 2 that the 6-hour annealing treatment in examples 1 , 2 and 3 was better than the 10-hour annealing treatment. The effect of performing the annealing could also be seen in comparative example 1 (air), but examples 1 and 2 were better in the case of the 30-minute annealing treatment, and examples 1 to 3 showed better results in the 2- hour annealing treatment. 0 minutes means that the annealing treatment was not performed, which corresponds to comparative example 2. [0043]

Fig. 3 shows results of differential capacity ( d Q / d V) for different annealing treatment times (30 minutes, 2 hours and 6 hours).

Peaks (arrows) from bulk irregular regions decreased along with an increase in time after the annealing treatment. The 30-minute annealing samples still had bulk irregular domains in a sizeable proportion thereof, but these domains were sufficiently suppressed in the samples that underwent the 6-hour annealing treatment.

[0044]

Table 3 shows electrochemical characteristics of the LNMO cathode materials prepared by means of the 6-hour annealing treatment.

[Table 3]

In table 3, the impurity phase was reduced and bulk irregular domains were suppressed in the samples following the 6-hour annealing treatment. A higher initial Coulombic efficiency (C. E.) was demonstrated as compared to the LNMO of comparative example 2 in which the annealing treatment was not performed. The capacity from Mn ³⁺ decreased as the oxygen content increased, and an increase in the oxygen content in the annealing mixed gas atmosphere was advantageous for oxidation of Mn ³⁺ , and an increase in energy density was shown as a result.

Furthermore, oxidation of Mn ³⁺ led to an increase in ordered domains in the LNMO structure, as can be seen by the shift of the ( d Q / d V) peak in fig. 3 toward a higher voltage (see the 6-hour annealing around 4.72 V (example 1), the 6-hour annealing (examples 2 and 3), and comparative example 1 ). As indicated above, a large amount of disordered domains are reduced from the original state from the point of view of capacity retention.

[0045]

Table 4 shows electrochemical characteristics of the LNMO cathode materials prepared by means of the 30-minute annealing treatment. [Table 4]

In table 4, the same trend of increased discharge capacity was observed in the LNMO after the 30-minute annealing treatment. However, the initial Coulombic efficiency of those samples was lowerthan the sample without the annealing treatment (comparative example 2), and was therefore unsatisfactory. Additionally, improvement in the capacity (better capacity) from Mn ³⁺ was slight, at 3-4%. The 30-minute annealing treatment was therefore unsuitable for an annealing treatment for LNMO cathode active materials.

[0046] Table 5 shows electrochemical characteristics of the LNMO cathode materials prepared by means of the 2-hour annealing treatment.

[Table 5] In table 5, discharge capacity of the LNMO following the 2-hour annealing treatment increased along with an increase in O2 content in the gas atmosphere. However, there was no improvement in initial Coulombic efficiency in comparison with the LNMO of comparative example 2 (no annealing treatment), and the capacity from Mn ³⁺ was markedly higher than the capacity in samples following the 6-hour annealing treatment. In addition, the long-term cycling properties (%) were slightly lower than those of the 6-hour annealing samples. This suggests that the 2-hour annealing treatment starts a phase transition (region-by-region bulk disordering to nano-integrated disordered regions, fig. 3) and is sufficient to remove the impurity phase (as shown by the increased initial capacity), but the reaction cannot be accomplished and therefore faster degradation is demonstrated than in the 6-hour annealing samples.

[0047]

Table 6 shows electrochemical characteristics of the LNMO cathode materials prepared by means of the 4-hour annealing treatment.

[Table 6]

In table 6, the initial Coulombic efficiency was slightly higher than in the 2-hour annealing treatment (table 5), but the capacity retention rate was still lower than in the 6-hour annealing treatment, and therefore there was no advantage to the 4-hour annealing treatment.

[0048]

Table 7 shows electrochemical characteristics of the LNMO cathode materials prepared by means of the 10-hour annealing treatment. [Table 7]

In table 7, the capacity from Mn ³⁺ decreased when the annealing treatment was extended to 10 hours, but the initial Coulombic efficiency also decreased, which suggests that the 10-hour annealing treatment does not have any advantages in regard to cathode performance and energy/time consumption.