Method for producing lithium transition metal composite oxide using used lithium ion battery

Abstract

Provided is a method for producing a lithium transition metal composite oxide using a positive electrode recovered from a used lithium ion battery.　This method for producing a lithium transition metal composite oxide includes the following steps for: (1) preparing a cathode composite recovered from a used lithium-ion battery; (2) cleaning the lithium transition metal composite oxide in the prepared cathode composite; (3) kneading the cleaned lithium transition metal composite oxide with a lithium compound; (4) calcining the kneaded material under prescribed conditions; and (5) cooling the calcined lithium transition metal composite oxide.

Description

Manufacturing method for lithium transition metal composite oxide using used lithium ion batteries

[0001] The present invention relates to a method for producing a lithium transition metal composite oxide using a positive electrode mixture recovered from used lithium ion batteries as a raw material.

[0002] In recent years, efforts to combat global warming have called for the realization of a carbon-free society, which requires the effective use of electricity rather than fossil fuels such as oil. Lithium-ion batteries for energy storage are expected to be one promising means of achieving this, and their practical use as power sources for small home appliances such as computers and smartphones, as well as for automobiles, is rapidly expanding.

[0003] This lithium-ion battery contains, in an outer can made of a metal such as aluminum or iron, a negative electrode material in which a negative electrode active material such as graphite is fixed to a negative electrode substrate made of copper foil, a positive electrode in which a positive electrode active material such as lithium-based oxides such as lithium nickel oxide or lithium cobalt oxide is fixed to a current collector such as aluminum foil using a fusing agent, a separator made of a resin film such as a porous polypropylene film, and an electrolytic solution, electrolyte, etc.

[0004] As the practical use of lithium-ion batteries rapidly expands, there is a demand for effective recycling of used lithium-ion batteries, and one method being considered for this purpose is to recover valuable metals from used lithium-ion batteries and make effective use of them.

[0005] As a method for recovering valuable metals from a lithium-ion battery having the above-described structure, for example, dry treatment or incineration treatment as described in Patent Documents 1 and 2 is utilized. However, these methods have drawbacks such as consuming a large amount of thermal energy and being unable to recover lithium (Li) or aluminum (Al). In addition, lithium hexafluorophosphate (LiPF) is used as the electrolyte. ６ ) is contained, there is also a problem that the furnace material is consumed significantly.

[0006] To address these problems associated with dry treatment or incineration, Patent Document 3 proposes a total dissolution method in which disassembled lithium-ion batteries are all dissolved using an acidic or alkaline solution to recover valuable metals. However, in this total dissolution method, chemicals are consumed by elements such as aluminum, copper (Cu), and iron (Fe) that are present in large excess, making it uneconomical for effectively recovering valuable metals such as nickel (Ni), cobalt (Co), and lithium.

[0007] In response to this, Patent Document 4 discloses a method of dismantling a lithium ion secondary battery and then recovering used positive electrode active material from the positive electrode using electric pulse discharge.

[0008] Patent Document 5 also discloses a method for recovering activated positive electrode active material by removing the positive electrode from a used lithium-ion battery, mixing an activation treatment agent containing an alkali metal compound with the positive electrode, and then heating the mixture. This method is considered to be advantageous from the perspective of reducing environmental impact, since the positive electrode active material, which is mainly composed of a lithium transition metal composite oxide, is recovered from the used lithium-ion battery after being activated.

[0009] On the other hand, the method described in Patent Document 4 makes it possible to recover used positive electrode active materials, but does not restore the performance required for reuse as a material for lithium ion batteries. Also, the method described in Patent Document 5 leaves room for further improvement in the heat treatment conditions after mixing with the activation treatment agent in order to impart the recovered positive electrode active materials with the performance required for reuse as a material for lithium ion batteries.

[0010] JP 07-207349 JP 10-330855 JP 08-22846 JP 2023-86494 JP 2012-186150

[0011] The present invention has been proposed in view of the above circumstances, and aims to provide a method for producing a lithium transition metal composite oxide to be used as a positive electrode active material, using a positive electrode mixture recovered from used lithium ion batteries as a raw material.

[0012] As a result of extensive research into achieving the above object, the present inventors have arrived at the following invention.

[0013] That is, the present invention relates to the following inventions.

[0014] A method for producing a lithium transition metal composite oxide, comprising the steps of: preparing a positive electrode composite material containing 80% or more by weight of a lithium transition metal composite oxide (hereinafter sometimes simply referred to as "lithium transition metal composite oxide") having a hexagonal crystal structure and satisfying the following composition (1), which has been recovered from used lithium-ion batteries; washing the lithium transition metal composite oxide in the prepared positive electrode composite material; kneading the washed lithium transition metal composite oxide with a lithium compound; calcining the kneaded material so as to satisfy the following condition (1); and cooling the calcined lithium transition metal composite oxide. <Composition (1)> Lithium, nickel, cobalt, aluminum, and an element M are contained in a substance ratio of Li:Ni:Co:Al:M=a:x:y:z:1-x-y-z. (The conditions 0.5≦a≦0.9, 0.4≦x≦0.95, 0.01≦y≦0.4, 0.01≦z≦0.2, and x+y+z≦1 are satisfied, and M includes one or more elements selected from W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Mn, Nb, Ta, Si, P, B, S, Na, and K.) <Condition (1)> (a) When the heating temperature is Ts (°C) and the heating time is Time (hr), 4000 (°C.hr)≦Ts×Time ≦8000 (°C.hr), and (b) T1 (°C) ≦Ts ≦T1 + 250 (°C) (T1 (°C) = 750 - 500 × substance ratio of Ni shown in composition (1)), and (c) The volume fraction of oxygen in the heating atmosphere is more than 20% and less than 50%.

[0015] The prepared positive electrode mixture may contain a fluororesin as a binder and a conductive carbon material as a conductive material.

[0016] In the step of washing the lithium transition metal composite oxide, a basic solution having a surface tension of 70 (mN / m) or less can be used.

[0017] In the step of kneading the washed lithium transition metal composite oxide with a lithium compound, a lithium compound having a melting point lower than the heating temperature in the subsequent calcination step can be used.

[0018] The dew point of the atmosphere during the calcination can be set to 10°C or lower, preferably -60°C or higher and 0°C or lower, and more preferably -60°C or higher and -10°C or lower.

[0019] In the step of cooling the calcined lithium transition metal composite oxide, the average cooling rate from the end of calcination to 100°C can be set to 5°C / min or less, preferably 3°C / min or less, and more preferably 1°C / min or less.

[0020] According to the present invention, after the lithium transition metal composite oxide in the prepared positive electrode mixture is washed, the lithium compound is kneaded, and then the mixture is roasted under heating conditions and in a predetermined heating atmosphere according to the chemical composition of the lithium transition metal composite oxide, thereby making it possible to efficiently produce a lithium transition metal composite oxide from used lithium ion batteries under conditions with low environmental impact.

[0021] The drawings attached to this specification present preferred embodiments of the present invention and, together with the detailed description of the invention, serve to promote a better understanding of the technical concept of the present invention, and the present invention should not be interpreted as being limited to the matters described in the drawings.

[0022] 1 is a diagram showing the flow of each step of a method for producing a positive electrode active material according to the present invention. 2 is a schematic diagram showing a positive electrode mixture recovered from a used lithium ion battery according to the present invention.

[0023] Hereinafter, the method for producing a positive electrode active material according to the present invention will be described in detail with reference to the drawings.

[0024] First, a positive electrode composite 50 containing 80% by weight or more of a lithium transition metal composite oxide 10 having a hexagonal crystal structure satisfying composition (1) is prepared from a used lithium ion battery (S10). The positive electrode composite 50 in the present invention refers to a positive electrode 1 of a lithium ion battery from which the current collector 40 has been removed, and is composed of the lithium transition metal composite oxide 10, or the lithium transition metal composite oxide 10, a binder 20, a conductive material 30, etc.

[0025] Here, the used lithium transition metal composite oxide can be specifically represented by the following general formula:

[0026] [General formula (1)] Li ａ Ni x Co y Al z M (１-ｘ-ｙ-ｚ) O ２＋α (wherein 0.5≦a≦0.9, 0.4≦x≦0.95, 0.01≦y≦0.4, 0.01≦z≦0.2, x+y+z≦1, and −0.1≦α≦0.2 are satisfied, and M includes one or more elements selected from W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Mn, Nb, Ta, Si, P, B, S, Na, and K.)

[0027] In terms of production efficiency in the subsequent washing step and calcination step, the prepared positive electrode composite preferably contains 80% or more, preferably 90% or more, and more preferably 95% or more by weight of a lithium transition metal composite oxide having a hexagonal crystal structure that satisfies the above composition (1).

[0028] The binder contained in the positive electrode mixture is preferably a fluororesin. Examples of fluororesins include polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber. The conductive material contained in the positive electrode mixture is preferably a conductive carbon material. Examples include graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black materials such as acetylene black and Ketjen Black (registered trademark).

[0029] The positive electrode composite may be recovered from used lithium-ion batteries by a conventional method, which involves discharging the used lithium-ion batteries to render them harmless, then crushing and dismantling the batteries, separating the components of the lithium-ion battery, such as the electrolyte, negative electrode material, and separator, to recover the positive electrode, and then removing the current collector from the positive electrode.

[0030] By cutting out a portion of the prepared cathode composite and chemically analyzing it, it is possible to analyze the weight ratio and composition of the lithium transition metal composite oxide contained in the cathode composite, determine whether the general formula (1) is satisfied, and identify the types of conductive material and binder. As a chemical analysis method, any conventional method may be used, and for example, analysis can be performed using an ICP optical emission spectrometer.

[0031] Furthermore, it is possible to identify the composition of the lithium transition metal composite oxide constituting the positive electrode composite, as well as the type of conductive material and binder, from information about the lithium ion battery that the positive electrode composite was used in, without having to cut out a portion of the prepared positive electrode composite and perform chemical analysis. Examples of information about the lithium ion battery include the identification number assigned to the battery and the model of the automobile in which the battery was installed.

[0032] By the above method, a positive electrode mixture containing 80% or more by weight of a lithium transition metal composite oxide having a hexagonal crystal structure that satisfies the general formula (1) can be prepared (S10).

[0033] Next, the lithium transition metal composite oxide in the prepared positive electrode mixture is washed (S20). Because the prepared positive electrode mixture may contain a binder, a conductive material, and the like in addition to the lithium transition metal composite oxide, the lithium transition metal composite oxide in the positive electrode mixture is separated from the binder and the conductive material, and the surfaces of the lithium transition metal composite oxide particles are cleaned in order to effectively replenish lithium in the subsequent kneading and calcination steps.

[0034] The specific gravity of the lithium transition metal composite oxide is greater than that of the binder and the conductive material, and separation methods utilizing the difference in specific gravity are effective, such as sedimentation or centrifugation. For example, if polyvinylidene fluoride is used as the binder and acetylene black is used as the conductive material, the specific gravity of the lithium transition metal composite oxide is about three times that of the polyvinylidene fluoride and acetylene black. The separated substance will have a composition containing either the lithium transition metal composite oxide or a lithium transition metal composite oxide with a trace amount of the binder and the conductive material.

[0035] Furthermore, since it is necessary to allow the cleaning solution to penetrate between the lithium transition metal composite oxide particles and to suppress the elution of lithium during cleaning, it is preferable to use a basic solution having a surface tension of 70 (mN / m) or less as the cleaning solution. For example, a solution containing a carboxylate such as sodium laurate, sodium myristate, sodium palmitate, sodium stearate, sodium oleate, sodium palm fatty acid, or sodium palm kernel fatty acid can be used.

[0036] In the washing step, separation and washing can be carried out multiple times, and the washed lithium transition metal composite oxide can be subjected to solid-liquid separation by a method such as filtration, and then dried.

[0037] Next, the lithium compound is kneaded with the washed lithium transition metal composite oxide (S30). There are no particular limitations on the kneading method, and conventional methods such as using a mixer can be used.

[0038] It is preferable to select a lithium compound to be kneaded whose melting point is lower than the heating temperature in the subsequent calcination step. For example, the melting points of lithium compounds, lithium nitrate, lithium hydroxide, lithium carbonate, and lithium oxide, are 260°C, 470°C, 720°C, and 1440°C, respectively. Therefore, it is preferable to use lithium nitrate or lithium hydroxide when the heating temperature is 500°C, and lithium hydroxide or lithium carbonate when the heating temperature is 800°C. The lithium compound can be dissolved in a solvent such as water and kneaded with the lithium transition metal composite oxide, but it is preferable to knead it in the form of a powder or solid in order to avoid the influence of evaporation of the solvent in the subsequent calcination step.

[0039] After kneading the lithium compound, the temperature and time are important conditions for calcination in order to fully restore the lithium molar ratio. As a result of extensive investigation, we discovered that by setting the calcination temperature and time according to the nickel molar ratio in the recovered lithium transition metal composite oxide so as to satisfy the following conditions, it is possible to replenish a sufficient amount of lithium while suppressing cation mixing, and restore the performance of the lithium transition metal composite oxide.

[0040] The heating method is not particularly limited, and a combustion furnace using a fossil fuel such as oil or gas, or an electric furnace using electrical energy can be used. Furthermore, operation methods such as continuous or batch systems can be adopted. The heating time refers to the time the lithium transition metal composite oxide is maintained at that temperature after it reaches that temperature. <Conditions> (a) where Ts (°C) is the heating temperature and Time (hr) is the heating time, 4000 (°C·hr)≦Ts×Time≦8000 (°C·hr) and (b) T1 (°C)≦Ts≦T1 + 250 (°C) (T1 (°C)=750−500×the amount of substance ratio of Ni shown in composition (1)), and (c) the volume fraction of oxygen in the heating atmosphere is more than 20% and less than 50%.

[0041] In addition to the temperature and time, the composition of the atmosphere during calcination is also important for replenishing a sufficient amount of lithium and restoring the performance of the lithium transition metal composite oxide. In the present invention, the atmosphere during calcination has an oxygen volume fraction of more than 20% and less than 50%.

[0042] By setting the volume fraction of oxygen in the calcination atmosphere to more than 20%, it is possible to prevent the lithium transition metal composite oxide from undergoing a reduction reaction. If the volume fraction of oxygen is 50% or more, the atmosphere becomes more oxidative, which may react with the lithium transition metal composite oxide and affect the crystal structure. Therefore, the upper limit of the volume fraction of oxygen is set to less than 50%.

[0043] Furthermore, the presence of water vapor in the atmosphere during calcination can inhibit the reaction between the lithium compound and the lithium transition metal composite oxide. For example, when lithium hydroxide is used as the lithium compound, lithium hydroxide reacts with nickel oxide in the lithium transition metal composite oxide to produce water, so a low moisture content in the atmosphere is advantageous in promoting the reaction. Furthermore, high-temperature water vapor is highly reactive with metals, and can react with the lithium transition metal composite oxide to affect the crystal structure. Therefore, the upper limit of the dew point is set to 10°C or less, more preferably 0°C or less, and even more preferably -10°C or less. The lower limit of the dew point is not particularly limited, but is preferably set to -60°C or higher from the viewpoint of atmospheric gas control.

[0044] If the lithium transition metal composite oxide before being kneaded with the lithium compound contains a small amount of binder or conductive material, these will be thermally decomposed or oxidized during calcination, and therefore the lithium transition metal composite oxide after calcination will be in a state in which the binder and conductive material have been completely removed or only a very small amount of binder and conductive material remains attached.

[0045] After calcination, the lithium transition metal composite oxide is cooled so that the average cooling rate from the end of calcination to 100°C is 5°C / min or less, preferably 3°C / min or less, and more preferably 1°C / min or less. If the cooling rate after calcination is too fast, the thermodynamic properties tend to become unstable, which may result in a decrease in cycle characteristics.

[0046] After the cooled lithium transition metal composite oxide is recovered, it can be washed as needed to remove excess lithium remaining in the oxide, such as lithium hydroxide, lithium carbonate, etc. As the washing liquid, for example, a basic solution with a surface tension of 70 (mN / m) or less or a solution with an electrical conductivity of 10 μS / cm or less can be used.

[0047] The washing is preferably carried out by adding a washing solution to the lithium transition metal composite oxide and then forming a slurry. The washing may be carried out by appropriately setting the amount of excess lithium determined by neutralization titration to 0.1% by mass or less, preferably 0.05% by mass or less. "Example (1)"

[0048] <Fabrication of Lithium-ion Battery Module> As shown in Table 1, three types of lithium transition metal composite oxides were prepared, each of which was mixed with polyvinylidene fluoride as a binder and acetylene black as a conductive material in a weight ratio of 90:6:4, and dispersed in N-methyl-2-pyrrolidone to prepare a slurry. Furthermore, aluminum foil was used as a current collector, and the prepared slurry was applied to the aluminum foil. The N-methyl-2-pyrrolidone was then removed by drying at 120°C in air for 30 minutes. A positive electrode mixture consisting of a positive electrode active material, binder, and conductive material was attached to the current collector, and this was used as a positive electrode membrane.

[0049] Next, a negative electrode composite paste, which is a mixture of graphite powder with an average particle size of about 20 μm and polyvinylidene fluoride, was applied to a copper foil to prepare a negative electrode membrane. The separator (SE) was a 20 μm thick polyethylene porous membrane, and the electrolyte was 1 M LiPF ６ A 3:7 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with ethylene carbonate (EC) as the supporting electrolyte was used.

[0050] In a dry room controlled at a dew point of -60°C, the laminate of the positive electrode, separator, and negative electrode film was impregnated with an electrolyte solution and sealed with a laminate to produce multiple lithium-ion battery modules. The capacity of the produced lithium-ion battery modules was measured and found to be 160 to 200 mAh / g, as shown in Table 1.

[0051] <Fabrication of Spent Lithium-ion Battery Modules> The lithium-ion battery modules fabricated above were repeatedly charged and discharged to fabricate a plurality of simulated spent lithium-ion battery modules. The capacity of the simulated spent lithium-ion battery modules was 115 to 140 mAh / g, as shown in Table 1.

[0052] <Recovery of Used Positive Electrode Composite> The simulated used lithium-ion battery module was disassembled, the used positive electrode was removed, and the positive electrode was immersed in N-methyl-2-pyrrolidone. The positive electrode composite was separated from the current collector, and then dried to remove the N-methyl-2-pyrrolidone, and the positive electrode composite was recovered. The weight ratio of the lithium transition metal composite oxide in the recovered positive electrode composite was 92%.

[0053] <Cleaning of Lithium Transition Metal Composite Oxide in Positive Electrode Mixture> The recovered positive electrode mix was immersed in water and stirred, and then the lithium transition metal composite oxide was separated and recovered using a centrifuge, and the surface of the oxide was cleaned.

[0054] In Example 1, the recovered lithium transition metal composite oxide was washed with an aqueous alkali ion solution having a pH of 8.5 and a surface tension of 70 (mN / m), while in Examples 2 to 4, a solution having a pH of 9 and a surface tension of 30 (mN / m) was prepared using sodium laurate as a surfactant, and then washing was carried out. The washing was carried out by adding 2 g of the washing solution per 1 g of the lithium transition metal composite oxide and stirring, followed by solid-liquid separation and drying.

[0055] The lithium transition metal composite oxide composition after the washing was chemically analyzed using an ICP atomic emission spectrometer, and a change in the lithium molar ratio was observed compared to before use, as shown in the chemical composition of the lithium transition metal composite oxide in Table 1. Furthermore, the amount of polyvinylidene fluoride and carbon black was extremely small, and in particular, in Examples 2 to 4, lithium transition metal composite oxides with higher purity than in Example 1 were recovered.

[0056] <Kneading of Lithium Compound> A lithium compound was kneaded with the washed lithium transition metal composite oxide. The amount of the lithium compound to be kneaded was set so that the molar ratio of lithium in the lithium transition metal composite oxide (0.7) would theoretically be 1.1. In Examples 7, 10, 13, and 16 in Table 2, lithium nitrate (melting point 260°C) was used as the lithium compound, while in the other Examples, lithium hydroxide (melting point 470°C) was used.

[0057] <Caloning> The calcination conditions were the heating temperature, heating time, oxygen concentration in the heating atmosphere, and dew point shown in Table 2.

[0058] <Cooling> The calcined lithium transition metal composite oxide was cooled. The time from the end of calcination until cooling to 100°C and the temperature history were measured using a thermocouple, and the cooling rate was calculated. The average cooling rate was 10°C / min.

[0059] <Performance of the produced lithium transition metal composite oxide (capacity recovery)> When the chemical composition of the lithium transition metal composite oxide after cooling was analyzed, the lithium molar ratio was found to be the value shown in Table 2. After calcination, lithium was replenished to the desired value, and a lithium transition metal composite oxide was produced.

[0060] Using each of the lithium-replenished lithium transition metal composite oxides, lithium ion battery modules were manufactured by the method described in paragraphs

[0048] to

[0050] . The capacity of the manufactured battery modules was measured, and it was found that in all of Examples 5 to 16, the performance recovered to 85% or more of the capacity before use (160 to 200 mAh / g) shown in Table 1, compared to the capacity after use (115 to 140 mAh / g) shown in Table 1.

[0061] In particular, in Examples 14 to 16, the volume fraction of oxygen was 45%, which was higher than that in Examples 5 to 13, and the dew point in the calcination atmosphere was lower, at -10 to -50°C, and therefore the capacity recovery rate was further improved.

[0062] <Mixing> In Comparative Examples 1 to 16, as shown in Table 2, the preparation of a positive electrode composite (S10) and the washing of the lithium transition metal composite oxide in the positive electrode composite (S20) were performed under the same conditions as in Examples 5 to 7, and then a lithium compound was mixed (S30) in an amount such that the molar ratio of lithium in the lithium transition metal composite oxide (0.7) would theoretically be 1.1. In Comparative Examples 7, 10, 13, and 16, lithium nitrate (melting point 260°C) was used as the lithium compound, and in the other Comparative Examples, lithium hydroxide (melting point 470°C) was used.

[0063] <Calonization> The kneaded material was calcined (S40) at the heating temperature, heating time, oxygen concentration in the heating atmosphere, and dew point shown in Table 2.

[0064] <Cooling> After calcination, cooling (S50) was carried out at the same cooling rate as in Examples 5 to 16.

[0065] <Performance of Produced Lithium Transition Metal Composite Oxide (Capacity Recovery)> When the chemical composition of the lithium transition metal composite oxide after cooling was analyzed, the molar ratio of lithium was found to be the value shown in Table 2.

[0066] Using the lithium-supplemented lithium transition metal composite oxide, a lithium ion battery module was manufactured in the same manner as in the above example.

[0067] In Comparative Example 1, which was left standing in the air at 25° C. for 10 hours, lithium was not replenished, and therefore no change in capacity was observed even when a battery module was manufactured.

[0068] In Comparative Examples 2 to 4, calcination was performed outside the range of condition (1). When a battery module was manufactured, capacity recovery was observed, but the recovery rate was lower than in the Examples. Analysis of the lithium content of the lithium transition metal composite oxide in these Comparative Examples revealed a molar ratio of 0.95, which is presumed to be due to the fact that lithium was not replenished to the desired value.

[0069] In Comparative Examples 5 to 7, the heating temperature and time were within the range of condition (1), but calcination was performed in an atmosphere with an oxygen volume fraction of 15%. When the battery module was manufactured, capacity recovery was observed, but the recovery rate was lower than in the Examples. Analysis of the lithium content of the lithium transition metal composite oxide in these Comparative Examples revealed a molar ratio of 0.97, which is presumed to be due to the fact that lithium was not replenished to the desired value.

[0070] In Comparative Examples 8 to 10, the heating temperature and time were within the range of condition (1), but calcination was performed in an atmosphere with an oxygen volume fraction of 70%. When the battery module was manufactured, capacity recovery was observed, but the recovery rate was lower than in the Examples. Analysis of the lithium content of the lithium transition metal composite oxide in these Comparative Examples revealed a molar ratio of 0.98, which is presumed to be due to the fact that lithium was not replenished to the desired value.

[0071] In Comparative Examples 11 to 13, calcination was performed for a heating time outside the range of condition (1). When the battery module was manufactured, capacity recovery was observed, but the recovery rate was lower than in the Examples. Analysis of the lithium content of the lithium transition metal composite oxide in these Comparative Examples revealed a molar ratio of 0.97, which is presumed to be due to the fact that lithium was not replenished to the desired value.

[0072] In Comparative Examples 14 to 16, the heating time was outside the range of Condition (1), and calcination was performed in an atmosphere with an oxygen volume fraction of 60%. When the battery module was manufactured, capacity recovery was observed, but the recovery rate was lower than in the Examples. Analysis of the lithium content of the lithium transition metal composite oxide in these Comparative Examples revealed a molar ratio of 0.95, which is presumed to be due to the fact that lithium was not replenished to the desired value. "Example (2)"

[0073] <Performance (cycle characteristics) of the produced lithium transition complex oxide> After carrying out the steps up to calcination under the same conditions as in Examples 8 to 10, the material was cooled to 100°C at the average cooling rate shown in Table 3, and then a battery module was produced in the same manner as in Example (1), and the cycle characteristics were evaluated. The cycle characteristics were measured at 25°C, 0.2 mA / cm ２ The capacity retention rate after 50 cycles was evaluated.

[0074] Examples 17 to 25, in which the average cooling rate was 15°C / min or less, exhibited high cycle characteristics with a capacity retention rate of 85% or more. In particular, Examples 26 to 31, in which the average cooling rate was 5°C / min or less, exhibited high cycle characteristics with a capacity retention rate of 90% or more.

[0075]

[0076]

[0077]

[0078] 1: Positive electrode 10: Lithium transition metal composite oxide 20: Binder 30: Conductive material 40: Current collector 50: Positive electrode mixture

Claims

1. A method for producing a lithium transition metal composite oxide, comprising the steps of: preparing a positive electrode mixture containing 80% or more by weight of a lithium transition metal composite oxide having a hexagonal crystal structure and satisfying the following composition (1), recovered from a used lithium ion battery; washing the lithium transition metal composite oxide in the prepared positive electrode mixture; kneading the washed lithium transition metal composite oxide with a lithium compound; calcining the kneaded material so as to satisfy the following condition (1); and cooling the calcined lithium transition metal composite oxide. <Composition (1)> Lithium, nickel, cobalt, aluminum, and an element M are contained in a substance ratio of Li:Ni:Co:Al:M=a:x:y:z:1-x-y-z. (0.5≦a≦0.9, 0.4≦x≦0.95, 0.01≦y≦0.4, 0.01≦z≦0.2, x+y+z≦1 are satisfied, and M includes one or more elements selected from W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Mn, Nb, Ta, Si, P, B, S, Na, and K.) <Condition (1)> (a) When the heating temperature is Ts (°C) and the heating time is Time (hr), 4000 (°C.hr)≦ Ts × Time ≦8000 (°C.hr) and (b) T1 (°C) ≦ Ts ≦ T1 + 250 (°C) (T1 (°C) = 750 - 500 × substance ratio of Ni shown in composition (1)) and (c) The volume fraction of oxygen in the heating atmosphere is more than 20% and less than 50%.

2. The method for producing a lithium transition metal composite oxide according to claim 1, wherein the prepared positive electrode mixture contains a fluororesin and a conductive carbon material.

3. The method for producing a lithium transition metal composite oxide according to claim 1 or 2, characterized in that a basic solution having a surface tension of 70 (mN / m) or less is used in the step of washing the lithium transition metal composite oxide in the positive electrode mixture.

4. The method for producing a lithium transition metal composite oxide according to any one of claims 1 to 3, characterized in that in the step of kneading the washed lithium transition metal composite oxide with a lithium compound, a lithium compound having a melting point lower than the heating temperature in the calcination step is used.

5. The method for producing a lithium transition metal composite oxide according to any one of claims 1 to 4, wherein the dew point of the atmosphere during the calcination is 10°C or less.

6. The method for producing a lithium transition metal composite oxide according to any one of claims 1 to 5, characterized in that in the step of cooling the calcined lithium transition metal composite oxide, the average cooling rate from the end of calcination to 100°C is 5°C / min or less.

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