JP7139056B2 - Spinel-type lithium titanate and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a spinel-type lithium titanate having a ratio (CO ₂ /NH ₃ ) of the amount of desorbed CO ₂ and the amount of NH ₃ desorbed, which is equal to or greater than a certain level.

Spinel-type lithium titanate (Li ₄ Ti ₅ O ₁₂ ) undergoes only a slight volume change due to the insertion and extraction of lithium ions. ⁺ ), it is attracting attention as an electrode material for electric storage devices because it is less likely to cause side reactions such as decomposition of the electrolytic solution. Also, it is known that the chemical reaction formula of Li ₄ Ti ₅ O ₁₂ during charging and discharging is the following formula (1).

In the above formula (1), when Li ₇ Ti ₅ O ₁₂ is generated during charging, it is necessary to pass a current through Li ₄ Ti ₅ O ₁₂ to insert lithium ions, but Li ₄ Ti ₅ O ₁₂ is insulating. Therefore, there was a problem that the energy barrier required for the structural change was high and the reaction was difficult to proceed. For this reason, it is necessary to charge the battery with a weak current over a long period of time, which has been an obstacle to the practical use of power storage devices that perform high-speed charging, such as electric vehicles.

In Patent Document 1, a mixture of one or more lithium compounds selected from lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxide and titanium oxide is calcined to form TiO ₂ and Li ₂ TiO ₃ . or a composition composed of TiO ₂ , Li ₂ TiO ₃ and Li ₄ Ti ₅ O ₁₂ , and then sintering. . According to this, it is possible to produce lithium titanate having excellent characteristics as a lithium secondary battery.

Patent Document 2 describes a method for producing lithium titanate (Li ₄ Ti ₅ O ₁₂ ) by mixing raw material powder made of a lithium compound and raw material powder made of a titanate compound and firing the mixture, wherein the lithium compound is lithium carbonate, and the titanate compound is metatitanic acid or orthotitanic acid. According to this, lithium titanate which is excellent in rate performance and easy to handle can be obtained, and lithium titanate which can satisfy the high required characteristics of lithium ion secondary batteries typified by batteries for vehicles, and a method for producing the same are provided. It is said that it can be done. However, the lithium titanate obtained by Patent Documents 1 and 2 does not necessarily enable high-speed charging, and a lithium titanate having an excellent charge capacity retention rate has been desired.

JP-A-2000-302547 WO2013/137381

The present invention has been made to solve the above problems, and the amount of CO ₂ desorption and NH ₃ desorption that can be suitably used as an electricity storage device that enables high-speed charging and has an excellent charge capacity retention rate. It is an object of the present invention to provide a spinel-type lithium titanate having a certain or more ratio (CO ₂ /NH ₃ ).

The above problem is that the ratio (CO ₂ /NH ₃ ) of the amount of CO ₂ desorbed at 200 to 400° C. by CO ₂ -TPD and the amount of NH ₃ desorbed by NH ₃ -TPD at 200 to 400° C. is 1.0 or more. It is solved by providing a spinel-type lithium titanate characterized by:

At this time, it is preferable that the CO ₂ desorption amount is 4 μmol/g or more and the NH ₃ desorption amount is 4 μmol/g or more. It is preferable that the specific surface area is 10 to 150 m ² /g, and the electrode containing the spinel-type lithium titanate is a preferable embodiment. A preferred embodiment is an electrode in which the spinel-type lithium titanate is a negative electrode active material, and a power storage device including the electrode is also a preferred embodiment.

Further, the above-mentioned problem is a method for producing spinel-type lithium titanate obtained by mixing and firing a titanium raw material and a lithium raw material, wherein the titanium raw material is hydrous titanium oxide having a water content of 18 to 40%. wherein the lithium raw material is at least one selected from lithium hydroxide and lithium carbonate, and the titanium raw material and the lithium The problem can also be solved by providing a method for producing spinel-type lithium titanate, performing a step of mixing raw materials to prepare a slurry, followed by a step of firing at 500 to 900°C.

At this time, after performing the step of preparing the slurry, it is a preferred embodiment to perform the step of drying and pulverizing, and then performing the step of firing.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a spinel-type lithium titanate in which the ratio (CO ₂ /NH ₃ ) of the amount of desorbed CO ₂ and the amount of NH ₃ desorbed is above a certain level. The spinel-type lithium titanate obtained in this way attracts lithium ions, which are cations, and promotes the charging reaction, so that it can be suitably used as an electricity storage device that enables high-speed charging and has an excellent charge capacity retention rate.

It is the figure which showed the result of the Raman spectroscopy. It is the figure which showed the result of the X-ray-diffraction measurement.

The _{spinel -} type lithium titanate of the present invention has a ratio _{(CO 2 / NH 3} ) is 1.0 or more. As described above, when the ratio (CO ₂ /NH ₃ ) is at least a certain value, it can be suitably used as an electricity storage device that can be charged at high speed and has an excellent charge capacity retention rate.

TPD (temperature-programmed desorption) involves adsorbing _NH3 gas or _CO2 gas (hereinafter sometimes referred to as gas when both are shown) on a solid, and then controlling the rate of temperature increase at a constant rate. This is a method of measuring the amount of desorbed gas and the desorption temperature of the gas by raising the temperature continuously. With NH ₃ -TPD, it is possible to measure the acid sites on the solid surface, and with CO ₂ -TPD, it is possible to measure the basic sites on the solid surface. , gases adsorbed at strong acid sites and basic sites are desorbed at high temperatures exceeding 200°C. _When the temperature exceeds 400°C, surface hydroxyl groups related to solid acidity and basicity _are eliminated.・Base content and acid/base strength can be evaluated.

As is clear from the comparison between Examples and Comparative Examples, which will be described later, when the ratio (CO ₂ /NH ₃ ) is less than 1.0, the charge/discharge test was performed using a full cell at a charge/discharge rate of 300C. The inventors found that the value of the charge capacity (mAh) when the battery was charged and the value of the charge capacity (mAh/g) when the charge/discharge rate was 50 C using a half cell were low, and the value of the charge capacity retention rate was also low. have confirmed. On the other hand, it was found that when the ratio (CO ₂ /NH ₃ ) was 1.0 or more, the charge capacity value and the charge capacity retention rate also increased. That is, by setting the ratio (CO ₂ /NH ₃ ) between the amount of CO ₂ desorbed, which indicates solid basicity, and the amount of NH ₃ desorbed, which indicates solid acidity, to a certain value or more, cations are formed on the spinel-type lithium titanate surface. The present inventors have found that the charging reaction is promoted by attracting lithium ions. The spinel-type lithium titanate obtained in this way enables high-speed charging and can be suitably used as an electricity storage device having an excellent charge capacity retention rate, so the present invention is of great significance.

In the spinel-type lithium titanate of the present invention, the CO ₂ desorption amount is preferably 4 μmol/g or more. If the CO ₂ desorption amount is less than 4 μmol/g, it may be difficult to accelerate the charging reaction, and the CO ₂ desorption amount is more preferably 6 μmol/g or more, and 8 μmol/g or more. is more preferable, and 11 μmol/g or more is particularly preferable. The amount of CO ₂ desorption is usually 60 μmol/g or less.

In the spinel-type lithium titanate of the present invention, the NH ₃ desorption amount is preferably 4 μmol/g or more. If the NH ₃ elimination amount is less than 4 μmol/g, it may be difficult to promote the charging reaction, and the NH ₃ elimination amount is more preferably 6 μmol/g or more, and 8 μmol/g or more. is more preferable, and 11 μmol/g or more is particularly preferable. The NH ₃ elimination amount is usually 60 μmol/g or less.

The spinel-type lithium titanate of the present invention preferably has a specific surface area of 10 to 150 m ² /g. If the specific surface area is less ^than 10 ^{m 2} /g, it may be difficult to accelerate the charging reaction. ² /g or more is particularly preferred, and 50 m ² /g or more is most preferred. On the other hand, if the specific surface area exceeds 150 m ² /g, the charge capacity may significantly decrease, and it is more preferably 135 m ² /g or less, particularly preferably 100 m ² /g or less.

The method for producing the spinel-type lithium titanate of the present invention is not particularly limited. A spinel-type lithium titanate can be obtained by mixing and firing a titanium raw material and a lithium raw material. Among them, the titanium raw material is hydrous titanium oxide having a water content of 18 to 40%, the lithium raw material is at least one selected from lithium hydroxide and lithium carbonate, and the Li/Ti (molar ratio) is 0. After performing a step of mixing the titanium raw material and the lithium raw material to prepare a slurry (hereinafter sometimes abbreviated as a “mixing step”) so that the slurry becomes more than 0.80 and 0.88 or less, The spinel-type lithium titanate of the present invention can be suitably obtained by performing the step of firing at 900° C. (hereinafter sometimes abbreviated as “firing step”).

The titanium raw material used in the present invention is not particularly limited. Hydrous titanium oxide having a water content of 18 to 40% is preferably used. When using hydrous titanium oxide with a water content of less than 18%, the present inventors conducted a charge/discharge test using a full cell at a charge/discharge rate of 300C. It was confirmed that the value of charge capacity (mAh/g) was low when the charge/discharge rate was 50C, and the value of charge capacity retention rate was also low. Therefore, as the titanium raw material, hydrous titanium oxide with a water content of 18 to 40% is preferably used, hydrous titanium oxide with a water content of 20% or more is more preferably used, and hydrous titanium oxide with a water content of 24% or more is further used. It is preferably used. On the other hand, if the water content of the hydrous titanium oxide exceeds 40%, the cycle characteristics may deteriorate, and the water content is more preferably 38% or less, and even more preferably 35% or less.

As the titanium raw material used in the present invention, the excitation laser wavelength is 532 nm, the grating is 1800 l / mm, the slit width is 100 × 1000 μm, the exposure time is 60 seconds, and the number of exposures is 2 times. A hydrous titanium oxide that does not show a peak at ^-1 is preferably used. When the hydrous titanium oxide having a peak at 2800 to 3000 cm ⁻¹ was used, the present inventors conducted a charge/discharge test using a full cell at a charge/discharge rate of 300C. It was also confirmed that the value of charge capacity (mAh/g) was low when the charge/discharge rate was 50 C using half cells, and the value of charge capacity retention rate was also low. Therefore, as the titanium raw material, hydrous titanium oxide, which does not show a peak at 2800 to 3000 cm ⁻¹ in the Raman spectroscopy, is preferably used.

As the titanium raw material used in the present invention, when performing X-ray diffraction measurement with Cu Ka line, no peak is observed at the diffraction angle 2θ = 24 to 26°, or at the diffraction angle 2θ = 24 to 26° A hydrous titanium oxide having a peak half width of 2 or more is preferably used. As is clear from the comparison between Examples and Comparative Examples, which will be described later, when the half width of the peak at the diffraction angle 2θ = 24 to 26° is less than 2, a charge/discharge test is performed using a full cell at a charge/discharge rate of 300C. It was confirmed that the charge capacity (mAh) value when the battery was charged and the charge capacity (mAh/g) value when the charge/discharge rate was 50C using a half cell were low, and the charge capacity retention rate was also low. . Therefore, as a titanium raw material, when the X-ray diffraction measurement is performed, no peak is observed at the diffraction angle 2θ = 24 to 26°, or the half width of the peak at the diffraction angle 2θ = 24 to 26° is 2 or more. Hydrous titanium oxide is preferably used. The half width is more preferably 2.5 or more, and most preferably no peak is observed.

The titanium raw material used in the present invention preferably has an N content of 0.75 parts by weight or more with respect to 100 parts by weight of hydrous titanium oxide. As is clear from the comparison between Examples and Comparative Examples to be described later, when the N content is less than 0.75 parts by weight, the charge capacity ( mAh), the charge capacity (mAh/g) when the charge/discharge rate was 50C using a half cell, and the charge capacity retention rate were also low. Therefore, with respect to 100 parts by weight of hydrous titanium oxide, the N content is preferably 0.75 parts by weight or more, more preferably 1 part by weight or more, and further preferably 1.2 parts by weight or more. preferable. On the other hand, the N content is usually 10 parts by weight or less.

Although the lithium raw material used in the present invention is not particularly limited, it is preferably at least one selected from lithium hydroxide and lithium carbonate. By using such a lithium raw material, the spinel-type lithium titanate of the present invention can be obtained by mixing with the titanium raw material in the mixing step described later and performing the firing step. Lithium hydroxide is more preferable as the lithium raw material.

The mixing step in the present invention is a step of preparing a slurry by mixing the titanium raw material and the lithium raw material so that the Li/Ti (molar ratio) is more than 0.80 and 0.88 or less. This is the preferred embodiment. As is clear from the comparison between Examples and Comparative Examples to be described later, when the Li/Ti (molar ratio) is 0.80 or less, the charge/discharge test is performed using a full cell at a charge/discharge rate of 300C. It was confirmed that the value of the capacity (mAh) and the value of the charge capacity (mAh/g) when charging/discharging at a charge/discharge rate of 50 C using a half cell were low, and the value of the charge capacity retention rate was also low. Therefore, the Li/Ti (molar ratio) is preferably greater than 0.80, more preferably 0.81 or more, still more preferably 0.82 or more, and preferably 0.83 or more. Especially preferred. On the other hand, if the Li/Ti (molar ratio) exceeds 0.88, Li ₂ TiO ₃ that does not contribute to the charge/discharge reaction may be mixed, and the charge capacity may decrease, so it is more preferably 0.87 or less. , 0.86 or less. The method for preparing the slurry is not particularly limited, and water may be added to the titanium raw material and then mixed with the lithium raw material, or water may be added to the lithium raw material and then mixed with the titanium raw material. However, water may be added when mixing the titanium raw material and the lithium raw material.

In the present invention, it is a preferred embodiment to perform a firing step of firing at 500 to 900° C. after performing the mixing step. If the firing temperature is lower than 500°C, the charging capacity may be lowered, so it is more preferably 520°C or higher, and even more preferably 540°C or higher. On the other hand, if the firing temperature exceeds 900° C., it may be difficult to promote the charging reaction, so it is more preferably 790° C. or lower, still more preferably 740° C. or lower, and 690° C. or lower. is particularly preferred.

In a preferred embodiment of the present invention, after performing the step of preparing the slurry, the step of drying and pulverizing is performed, and then the step of firing is performed. By performing the step of drying and pulverizing, the raw materials can be uniformly mixed, thereby obtaining high-purity lithium titanate. The drying temperature is not particularly limited, and is preferably 80 to 200°C, more preferably 90 to 150°C. From the viewpoint of productivity and handling, it is preferable to dry to the extent that water is evaporated to dryness.

The spinel-type lithium titanate of the present invention obtained as described above attracts lithium ions, which are cations, to promote the charging reaction, enabling high-speed charging and exhibiting the effect of being excellent in the charge capacity retention rate. . Therefore, it can be suitably used as an electrode for electric storage devices such as lithium ion secondary batteries and lithium ion capacitors. Among them, a more preferred embodiment is that the electrode is a negative electrode, and a further preferred embodiment is that the spinel-type lithium titanate of the present invention is a negative electrode active material. In particular, it is suitably used as an electricity storage device that enables high-speed charging and has an excellent charge capacity retention rate, and is particularly suitably used as an electricity storage device that performs high-speed charging such as electric vehicles.

EXAMPLES The present invention will be described in more detail below using Examples, but the present invention is not limited to these Examples.

[Evaluation of physical properties of hydrous titanium oxide]
After preparation of the following (1) measurement samples, water content measurement, Raman spectroscopic measurement, X-ray diffraction measurement, and N content measurement of hydrous titanium oxide used in Examples and Comparative Examples were carried out. Table 1 shows the results.

(1) Preparation of Samples for Measurement Physical properties of hydrous titanium oxide used as a raw material were measured by using dried ones by the following methods. The synthesized hydrated titanium compound slurry was filtered to obtain a cake. The resulting cake was placed in a glass beaker, placed in a vacuum dryer, adjusted to 1 hPa or less using a vacuum pump, and dried at 60° C. for 20 hours. After 20 hours had passed, the pressure was returned to normal, and it was quickly placed in a desiccator adjusted to a humidity of less than 20% to lower the temperature to room temperature.

(2) Water content measurement Using "TG/DTA7300" manufactured by Hitachi High-Tech Science Co., Ltd., using alumina as a reference sample, each sample when heated from 30 ° C to 400 ° C at a heating rate of 10 ° C / min was measured. 25 to 30 mg of the sample was weighed into a Pt container, and the water content was calculated from the weight of the sample at 30°C and the weight of the sample at 400°C by the following formula.
Moisture content (%): [(Sample weight (mg) at 30 ° C.-Sample weight (mg) at 400 ° C.
) / sample weight at 30 ° C. (mg)] × 100

(3) Raman spectroscopic measurement Using a microscopic Raman device "NRS-7100" manufactured by JASCO Corporation, the excitation laser wavelength is 532 nm, the grating is 1800 l / mm, the slit width is 100 × 1000 μm, the exposure time is 60 seconds, and the number of exposures is 2 times. A hydrous titanium oxide in which no peak was observed at 2800 to 3000 cm ⁻¹ was evaluated as having no peak, and a hydrous titanium oxide having a peak was evaluated as having a peak.

(4) X-ray diffraction measurement Using a Philips XRD device "X'pert-PRO", each powder sample was subjected to X-ray diffraction measurement with the Ka line of Cu, and the peak position and intensity of the sample were analyzed. . As the hydrous titanium oxide in Examples 1 to 6, one having no crystal peak or having low crystallinity of anatase-type TiO ₂ was used. The crystallinity was evaluated by the half width of the peak seen at 2θ=24-26° corresponding to (110) of anatase TiO ₂ .

(5) N content measurement The N content contained in the hydrous titanium oxide is measured by using an organic elemental analyzer (Macrocoder, JMA1000CN, manufactured by J Science Lab Co., Ltd.) to measure 50 mg ± 10 mg of hydrous titanium oxide. It was measured. In addition, from the measurement results of 5, 10, 15, and 20 mg of hippuric acid whose N content is known as a standard sample, a calibration curve of N detection value and N content was prepared, and the N detection value when measuring hydrous titanium oxide was calculated. The N content (wt%) was calculated by applying the calibration curve.

Comparative example 7
Hydrous titanium oxide (water content: 26.3%, product name: IP499, manufactured by Tayca Corporation) was used as the titanium source, and lithium hydroxide (manufactured by FMC) was used as the lithium source. These were weighed so that the Li/Ti (molar ratio) was 0.83, and then wet-mixed using water as a medium to obtain a lithium titanate precursor slurry. Then, the resulting slurry was held at 120° C. in the atmosphere to evaporate the medium water to dryness. Next, after pulverizing the obtained dried body with a pulverizer, it was fired in the atmosphere at 720° C. for 2 hours using a firing furnace to obtain lithium titanate.

Example 2
In Comparative Example 7 , lithium titanate was obtained in the same manner as in Comparative Example 7 , except that the sintering temperature was changed to 700°C.

Example 3
In Comparative Example 7 , lithium titanate was obtained in the same manner as in Comparative Example 7 , except that the sintering temperature was changed to 670°C.

Example 4
In Comparative Example 7 , lithium titanate was obtained in the same manner as in Comparative Example 7 , except that the sintering temperature was changed to 620°C.

Example 5
In Comparative Example 7 , lithium titanate was obtained in the same manner as in Comparative Example 7 , except that the sintering temperature was changed to 550°C.

Example 6
Hydrous titanium oxide (water content: 19.9%, product name: IP459, manufactured by Tayca Corporation) was used as the titanium source, and lithium hydroxide (manufactured by FMC) was used as the lithium source. These were weighed so that the Li/Ti (molar ratio) was 0.83, and then wet-mixed using water as a medium to obtain a lithium titanate precursor slurry. Then, the resulting slurry was held at 120° C. in the atmosphere to evaporate the medium water to dryness. Next, after pulverizing the obtained dried body with a pulverizer, it was fired in the atmosphere at 670° C. for 2 hours using a firing furnace to obtain lithium titanate.

Comparative example 1
Hydrous titanium oxide (water content: 15.1%, product name: IP448, manufactured by Tayca Corporation) was used as the titanium source, and lithium carbonate (manufactured by FMC) was used as the lithium source. These are weighed so that the Li/Ti (molar ratio) is 0.80, mixed for 30 minutes using a Henschel mixer, fired in the atmosphere at 750 ° C. for 2 hours using a firing furnace, and then pulverized. Lithium titanate was thus obtained.

Comparative example 2
Hydrous titanium oxide (water content: 13.8%, product name: IP308, manufactured by Tayca Corporation) was used as the titanium source, and lithium hydroxide (manufactured by FMC) was used as the lithium source. These were weighed so that the Li/Ti (molar ratio) was 0.80, mixed for 30 minutes using a Henschel mixer, and then calcined in the atmosphere at 450° C. for 2 hours using a firing furnace. After mixing 50 parts by weight of granular polyvinyl alcohol (manufactured by Sigma-Aldrich Co., Ltd.) as a grain growth inhibitor with 100 parts by weight of the obtained calcined powder, nitrogen atmosphere firing furnace was used at a flow rate of 2 L / min. Main firing was carried out at 950° C. for 2 hours while gas was circulated. Further, the obtained main calcined powder was calcined in the atmosphere at 550° C. for 1 hour in a rotary kiln, and then pulverized to obtain lithium titanate.

Comparative example 3
In Comparative Example 2, lithium titanate was obtained in the same manner as in Comparative Example 2, except that the calcination temperature was changed to 600°C.

Comparative example 4
In Comparative Example 2, lithium titanate was obtained in the same manner as in Comparative Example 2, except that the calcination temperature was set to 500°C.

Comparative example 5
In Comparative Example 2, lithium titanate was obtained in the same manner as in Comparative Example 2, except that the calcination temperature was changed to 400°C.

Comparative example 6
Hydrous titanium oxide (water content: 15.1%, product name: IP448, manufactured by Tayca Corporation) was used as the titanium source, and lithium carbonate (manufactured by FMC) was used as the lithium source. These were weighed so that the Li/Ti (molar ratio) was 0.80, and then wet-mixed using water as a medium to obtain a lithium titanate precursor slurry. Then, the resulting slurry was held at 120° C. in the atmosphere to evaporate the medium water to dryness. Next, after pulverizing the obtained dried body with a pulverizer, it was fired in the atmosphere at 670° C. for 2 hours using a firing furnace to obtain lithium titanate.

[Measurement of _NH3 desorption amount and _CO2 desorption amount]
Solid acidity and solid basicity in Examples 2 to 6 and Comparative Examples 1 to 7 were measured by NH ₃ -TPD measurement or CO It was obtained by ₂ -TPD measurement. Specifically, first, 50±5 mg of the powders of Examples 2 to 6 and Comparative Examples 1 to 7 were weighed and filled in a quartz cell. Next, the temperature was raised to 400° C. in He over 40 minutes, held for 1 hour, and then lowered to 100° C. in He over 10 minutes to remove adsorbed moisture. Furthermore, after adsorbing NH ₃ or CO ₂ by circulating NH ₃ or CO ₂ gas at 100 ° C. at a flow rate of 20 mL / min for 30 minutes, the gas is switched to He, and while circulating at a flow rate of 30 mL / min, NH ₃ or CO ₂ was desorbed by raising the temperature to 400° C. at a temperature rate of 10° C./min. At this time, a calibration curve is created using NH ₃ /He balance gas or CO 2 /He balance gas with a known concentration (each concentration of 5%) or CO ₂ /He balance gas as standard gas, and NH ₃ or CO ₂ is desorbed based on this calibration curve. Desorption amount and desorption temperature were measured. Peak detection of NH ₃ and CO ₂ was performed using fragments of NH ₃ (m/e=17) and CO ₂ (m/e=44) in the mass spectrum.

From the TPD measurement results obtained above, the amount of gas desorption per 1 g at a high temperature section (200 to 400 ° C) that greatly affects the acid strength or base strength is calculated, and the amount of CO ₂ desorption and NH ₃ desorption The CO ₂ /NH ₃ ratio of the amount was calculated. When this value exceeds 1, it can be said that the basic strength is greater than the acid strength. Table 1 shows the results.

[Measurement of specific surface area]
The specific surface area was measured by the BET one-point method using a nitrogen adsorption measuring device (“Macsorb HM model-1208” manufactured by Mountec Co., Ltd.). As pre-drying conditions for the measurement sample, the sample was vacuum-dried at 150° C. for 20 minutes and then cooled for 4 minutes. Table 1 shows the results.

[Power storage device evaluation (full-cell evaluation)]
(Preparation of negative electrode)
Lithium titanate of Examples 2 to 6 and Comparative Examples 1 to 7 as a negative electrode active material, acetylene black (“Denka black powder” manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive aid, polyvinylidene fluoride (Co., Ltd. Kureha's "KF Polymer") was used, these were mixed at a ratio of 80:10:10, and N-methyl-2-pyrrolidone was used as a dispersion medium to prepare an electrode mixture slurry. This electrode mixture slurry was coated on an etched aluminum foil (“20CB” manufactured by Nippon Electric Capacitor Industry Co., Ltd.) as a current collector, dried, and roll-pressed to prepare a negative electrode having a film thickness of 40 μm.

(Preparation of positive electrode)
Activated carbon ("YP-50F" manufactured by Kuraray Co., Ltd.) as a positive electrode active material, acetylene black ("Denka black powder" manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive agent, polyvinylidene fluoride ("KF" manufactured by Kureha Co., Ltd.) as a binder polymer"), these were mixed at a ratio of 77:9:14, and N-methyl-2-pyrrolidone was used as a dispersion medium to prepare an electrode mixture slurry. This electrode mixture slurry was coated on an etched aluminum foil (“20CB” manufactured by Nippon Dendenki Kogyo Co., Ltd.) as a current collector, dried, and roll-pressed to prepare a positive electrode having a thickness of 101 μm.

(Production of power storage device)
When the positive electrode and the negative electrode prepared above were punched into 3.0 cm×4.0 cm (12.0 cm ² ) and 3.3 cm×4.3 cm (14.2 cm ² ) pieces, respectively, the weight of the activated carbon contained in the positive electrode was 50. .5 mg, and the weight of lithium titanate contained in the negative electrode was 41.7 mg. Assuming that the actual capacity of activated carbon is 40 mAh/g and the actual capacity of lithium titanate is 130 mAh/g, the capacity of the positive electrode is 2.02 mAh and the capacity of the negative electrode is 5.43 mAh. was 2.69. The above positive electrode and negative electrode were opposed to each other with a cellulose separator interposed therebetween, and 1.0 M LiBF ₄ /PC was injected as an electrolytic solution, followed by lamination sealing to produce an electricity storage device.

(Charging and discharging test)
A charge/discharge test was performed at a charge/discharge rate of 1C and 300C using the electricity storage device produced above. From the obtained results, the charge capacity retention rate (%) was calculated using the following formula. The measurement was performed using a charge/discharge test device (HJ0610SD8Y manufactured by Hokuto Denko Co., Ltd.). Table 1 shows the results.
Charging capacity at 300C (mAh)/Charging capacity at 1C (mAh) x 100 = Charging capacity maintenance rate (%)

[Power storage device evaluation (half-cell evaluation)]
(Preparation of coin cell)
The negative electrode prepared above was punched out by electrode punching, and a coin cell of 2032 type was formed together with lithium metal as a counter electrode and 1.0 M LiBF ₄ /PC as a non-aqueous electrolyte.

(Charging and discharging test)
Charge/discharge tests were performed at charge/discharge rates of 1C and 50C using the coin cells produced above. From the obtained results, the charge capacity retention rate (%) was calculated using the following formula. The measurement was performed using a charge/discharge test device (HJ1001SD8A manufactured by Hokuto Denko Co., Ltd.). Table 1 shows the results.
Charge capacity at 50C (mAh/g)/Charge capacity at 1C (mAh/g) x 100 = Charge capacity maintenance rate (%)

Claims (6)

The ratio (CO ₂ /NH ₃ ) of the amount of CO ₂ desorbed at 200 to 400° C. by CO ₂ -TPD to the amount of NH ₃ desorbed by NH ₃ -TPD at 200 to 400° C. is 1.0 or more , A spinel-type lithium titanate having a specific surface area of 35 to 150 m ² /g . 2. The spinel-type lithium titanate according to claim 1, wherein the _CO2 elimination amount is 4 μmol/g or more, and the _NH3 elimination amount is 4 μmol/g or more. An electrode comprising the spinel-type lithium titanate according to claim 1 or 2 . 4. The electrode according to claim 3 , wherein the spinel-type lithium titanate is a negative electrode active material. An electricity storage device comprising the electrode according to claim 3 or 4 . A method for producing a spinel-type lithium titanate obtained by mixing and firing a titanium raw material and a lithium raw material,
The titanium raw material is hydrous titanium oxide with a water content of 18 to 40%, and when X-ray diffraction measurement is performed with the Ka line of Cu, no peak is observed at the diffraction angle 2θ = 24 to 26 °. or hydrous titanium oxide having a peak half width of 2 or more at a diffraction angle of 2θ = 24 to 26°,
The lithium raw material is at least one selected from lithium hydroxide and lithium carbonate,
After performing a step of preparing a slurry by mixing the titanium raw material and the lithium raw material so that the Li/Ti (molar ratio) is more than 0.80 and 0.88 or less, a step of drying and pulverizing is performed. 3. The method for producing spinel-type lithium titanate according to claim 1 or 2 , wherein the step of firing at 500 to 700 ° C. is performed after heating.

Images