JP2009238656A - Active material for nonaqueous electrolyte battery and nonaqueous electrolyte battery having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high performance nonaqueous electrolyte battery using lithium titanate as an active material. <P>SOLUTION: This invention uses the active material for the nonaqueous electrolyte battery having carbon in at least a part of a surface and including a lithium titanate particle on which a value of the atomic ratio (C/Ti) of the carbon to titanium determined by an X-ray photoelectric spectroscopic analysis is 6 or more. 6.3≤(C/Ti)≤8 is further desirable. Ethanol is desirably used as a carbon source. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolyte battery active material containing lithium titanate and a nonaqueous electrolyte battery.

In recent years, non-aqueous electrolyte batteries represented by lithium ion secondary batteries have been put into practical use as electrochemical devices with high energy density. Various materials can be applied to the positive electrode active material and the negative electrode active material constituting the lithium ion secondary battery, and they are properly used depending on the application. For example, for small portable electronic devices typified by mobile phones, high energy density is required. Therefore, LiCoO ₂ is applied as a positive electrode active material capable of obtaining a high voltage and high capacity, and a carbon material is applied as a negative electrode active material. Has been. On the other hand, long-term reliability is required for backup and HEV because the use period is longer. Therefore, in recent years, lithium titanate has attracted attention as an active material for non-aqueous electrolyte batteries used in these applications. The charge / discharge potential of this material is nobler than the potential of the carbon material, and is about 1.56 V (vs. Li / Li ⁺ ) in spinel type lithium titanate represented by, for example, Li ₄ Ti ₅ O _12. .

  When lithium titanate is used as the negative electrode active material, the volume change associated with lithium insertion / extraction is smaller than when carbon materials are used, and the potential for lithium ion insertion / extraction reaction is noble. It is known that the lifetime of the battery is prolonged because the solvent decomposition reaction on the surface of the negative electrode active material is suppressed. On the other hand, depending on the application, high rate discharge performance is required in addition to the lifetime. In order to increase this performance, it is important to reduce the DC resistance of the negative electrode. Therefore, a method of coating the surface of the active material particles with carbon for the purpose of reducing the direct current resistance of the negative electrode using lithium titanate is known.

  Patent Document 1 uses lithium titanate having carbon on the surface for the purpose of providing an electrochemical device that suppresses gas generation and is excellent in charge / discharge cycle performance and storage characteristics at high temperatures. A non-aqueous electrolyte battery is described that includes a negative electrode that may have been below 1.0 V relative to the potential. Patent Document 1 describes a method for supporting carbon by pyrolysis of a lower alcohol, and describes an example using methanol as the lower alcohol.

Non-patent document 1 describes that toluene was allowed to act, and as a result of TEM observation, Li ₄ Ti ₅ O ₁₂ powder coated with carbon to cover the entire particle surface (“over the entire particle surface”) was obtained. The schematic diagram is shown in Figure 9.

However, neither Patent Document 1 nor Non-Patent Document 1 has a specific description about the degree of coverage or uniformity of carbon provided on the surface of lithium titanate particles, and is obtained by X-ray photoelectron spectroscopy. There is no description that the capacity retention rate during high rate discharge can be remarkably improved by setting the atomic ratio of carbon to titanium within a specific range.
JP 2007-323958 A Journal of The Electrochemical Society, 154, A692 (2007)

  An object of the present invention is to provide a high-performance nonaqueous electrolyte battery using lithium titanate as an active material.

  The technical configuration and operational effects of the present invention are as follows. However, the action mechanism includes estimation, and its correctness does not limit the present invention. The present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiment or experimental example is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the scope of claims, and is not restricted to the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  The present invention is characterized in that carbon is provided on at least a part of the surface of the lithium titanate particles, and the value of the atomic ratio of carbon to titanium (C / Ti) obtained by X-ray photoelectron spectroscopy is 6 or more. It is an active material for a non-aqueous electrolyte battery.

  Moreover, this invention is a nonaqueous electrolyte battery provided with the electrode containing the said active material for nonaqueous electrolyte batteries.

  Moreover, this invention is a manufacturing method of the active material for nonaqueous electrolyte batteries which manufactures the said active material for nonaqueous electrolyte batteries using ethanol for a carbon source.

  X-ray photoelectron spectroscopy (XPS) is a well-known elemental analysis method, and Japanese Patent Laid-Open No. 2001-305082 has the following description. XPS irradiates a sample with X-rays, detects the energy of photoelectrons emitted from the sample at that time, obtains an energy spectrum, and performs elemental analysis based on information on the peak of the energy spectrum. There are two types of measurement methods using XPS: a method with constant relative resolution and a method with constant absolute resolution. In the latter method, the resolution is constant on both the low energy side and the high energy side. Therefore, when the chemical state is analyzed, measurement by the latter method is performed.

In the diagram showing the energy spectrum of photoelectrons emitted from the sample surface, a peak appears at the energy position corresponding to the element contained in the sample. Since the kinetic energy of the photoelectrons emitted from the sample has a certain range, the energy spectrum becomes a continuous spectrum. The spectral intensity in the energy spectrum indicates the concentration of each element contained in the sample, and the peak having a large intensity suggests that there are many elements having the corresponding kinetic energy. Therefore, the concentration of each element can be quantified by determining the area of each peak. However, the relationship between the element concentration in the sample and the peak area is not linear. This is because the ease of excitation of photoelectrons is different. As described above, since the easiness of emission of photoelectrons varies from one atom to another, in order to perform quantitative analysis, a correction in consideration of the easiness of emission of photoelectrons is necessary. A relative sensitivity factor (RSF) is used to perform this correction. The relative sensitivity factor RSF is defined as follows.
RSF = σ · λ · T · β (3)

  Here, σ is a photoionization cross-sectional area, which is a factor relating to the generation probability of photoelectrons. λ is an inelastic scattering mean free path (IMFP), and T is an analyzer transmission function (hereinafter simply referred to as a transmission function). Β is an asymmetric parameter and is a factor relating to the ease of generation of photoelectrons when X-rays are irradiated. IMFPλ is sometimes referred to as escape depth. Thus, in order to quantify the concentration of elements in the sample from the energy spectrum, the relative sensitivity factor RSF must be known, and in order to know the relative sensitivity factor RSF, the photoionization cross section σ, IMFPλ, transmission function Four factors, T and asymmetric parameter β, must be known. Among these four factors, the value of the photoionization cross section σ can be obtained using a Scofield table, and IMFPλ can be obtained using an equation formulated by Tanuma et al. The asymmetric parameter β can be obtained using a known table.

  The transmission function T is generally provided by the XPS manufacturer. The transmission function T provided by this manufacturer is theoretically obtained as a physical constant. However, the transmission function T is different for each XPS apparatus, and changes over time. Therefore, it is not desirable to always use the transmission function T provided by the manufacturer as it is, and it is preferable to accurately determine the transmission function T for each XPS apparatus in order to more accurately determine the element.

  The energy spectrum is preferably subjected to baseline correction by the Shirley method. The Shirley method is described in detail in “The Surface Science Society of Japan: X-ray photoelectron spectroscopy, Maruzen Co., Ltd. (1998)”.

  ADVANTAGE OF THE INVENTION According to this invention, the active material for nonaqueous electrolyte batteries which can be used as a high performance nonaqueous electrolyte battery can be provided. In addition, a high-performance nonaqueous electrolyte battery can be provided. Moreover, the manufacturing method of the active material for nonaqueous electrolyte batteries which can be used as a high performance nonaqueous electrolyte battery can be provided.

Examples of the lithium titanate particles according to the present invention, the general formula _Li x _Ti y _{O 4} can be used (1.0 ≦ x ≦ 2.4,1 ≦ y ≦ 2) in those represented.

  The higher the coverage of lithium titanate particles with carbon, the greater the atomic ratio of carbon to titanium (C / Ti) required by X-ray photoelectron spectroscopy analysis. When carbon completely covers the particle surface, The value of (C / Ti) is theoretically infinite.

  Lithium titanate is generally formed by agglomerating primary particles to form secondary particles, but the “lithium titanate particles” referred to in the claims of the present application refer to primary particles. In performing X-ray photoelectron spectroscopic analysis, the secondary particles may be used for measurement as they are, and no special attention is required such as disassembling the primary particles for measurement.

  When the value of (C / Ti) is less than 6, the electronic conductivity of the lithium titanate particles decreases, and the lithium insertion / extraction reaction to the lithium titanate hardly occurs. The value of (C / Ti) is more preferably 6.3 ≦ (C / Ti) ≦ 8. By setting the value of (C / Ti) to 8 or less, the coverage with carbon does not become too high, and the possibility that the lithium insertion / extraction reaction to lithium titanate hardly occurs can be reduced. This is because the potential at which lithium insertion / extraction reaction occurs in carbon is lower than that in lithium titanate, so at the potential at which lithium insertion / extraction from lithium titanate occurs, carbon is inserted / extracted from lithium. This is presumed to be an obstacle to reaction. Accordingly, it is preferable that the coverage with carbon is not too high, and the ease of the lithium insertion / extraction reaction to lithium titanate takes a maximum value when the coverage with carbon is within the above range.

  It is preferable that the thickness of the carbon layer in the part provided with carbon on the surface of the active material according to the present invention is 5 nm or less. The thickness of the carbon layer is determined by randomly selecting five secondary particles of the active material and observing each of them using a transmission electron microscope (TEM), and at least one carbon layer is observed. The thickness is estimated for the primary particles, and the thickness of the carbon generated in each primary particle is estimated by simple averaging.

  Carbon thickness may be estimated from energy dispersive X-ray fluorescence analysis (EDS) or electron energy loss spectroscopy (EELS).

  A method using FIB is preferable as a method for preparing a thin piece sample used in the analysis method using an electron beam.

  In addition, when TEM observation is performed in such a procedure, a portion where carbon is observed and a portion where carbon is not observed may be seen on the surface of lithium titanate. The part where carbon is not observed is considered to be a part not including carbon, but it is also possible that the carbon is peeled off during the process of FIB or the like. When estimating the thickness of the carbon layer provided on the surface of the lithium titanate, it is appropriate to perform it in a portion where the carbon layer is observed.

  The reason why the thickness of the carbon layer is preferably 5 nm or less is considered as follows. That is, the current collection with the active material in the battery includes electronic conduction through the active material particles other than through the conductive agent added to the electrode. In the latter electronic conduction, the electronic conductivity of carbon is better than that of lithium titanate, and therefore surface conduction through carbon is dominant. In order to improve the surface conductivity, it is preferable to increase the cross-sectional area. That is, it is effective to increase the thickness of the carbon layer. On the other hand, the lithium insertion reaction into lithium titanate through the carbon layer is suppressed as the thickness of the carbon layer increases.

The presence of carbon can also be confirmed by Raman spectroscopy. Even if the thickness of carbon is extremely thin and difficult to confirm using a transmission electron microscope, the peak derived from carbon is about 1600 cm by using, for example, Raman spectroscopic analysis using an argon ion laser. ^-1 and about 1360 cm ^-1 .

The average particle size of the lithium titanate according to the present invention is preferably 20 μm or less. When the average particle size is 20 μm or less, it is possible to reduce the possibility that the resistance derived from lithium diffusion in the particles becomes dominant. Therefore, the effect of the present invention is not remarkable when the carbon coat is applied under certain conditions. The risk of becoming a thing can be reduced. In the specification of the present application, the average particle diameter of the particles is represented by D ₅₀ (μm), which is the particle diameter of the total number of 50% accumulated from the smaller particle diameter in the cumulative distribution curve. Further, the cumulative particle diameter is measured by a laser method after ultrasonically dispersing the particles in a solvent.

  As a method for synthesizing the active material for a non-aqueous electrolyte battery of the present invention, a method of supplying a carbon source after raising the temperature of the firing furnace to a high temperature after putting lithium titanate into the firing furnace, a raw material of lithium titanate There is a method of, for example, supplying a carbon source after the temperature of the baking furnace is increased to a high temperature to synthesize lithium titanate.

  Examples of the carbon source include alcohols, hydrocarbons, and aromatic carbon materials. Examples of the alcohol include ethanol, propanol, butanol and the like.

  As a method of supplying alcohol to the baking furnace, there are a method of directly supplying a liquid, a method of supplying the liquid by vaporizing, and the like. In the latter method, it is preferable that the alcohol is gasified and supplied as a mixed gas with an inert gas such as nitrogen, argon or helium. In order to obtain the active material of the present invention using alcohol as a carbon source, assuming that the carbon production rate is V (mass% / h), the value should be within a range satisfying the relationship of V <0.8. preferable.

  According to the finding of the present inventor, the form of carbon generated on the surface of the lithium titanate particles greatly changes depending on the generation rate of carbon, and the atomic ratio (C / Ti) determined by X-ray photoelectron spectroscopy is also obtained. Different. By setting the generation rate to less than 0.8 (mass% / h), it is possible to reduce the possibility that (C / Ti) is remarkably lowered.

  When methanol is used as the carbon source, this is gasified and supplied as a mixed gas with an inert gas such as nitrogen, argon, or helium to generate carbon on the lithium titanate particle surface, the carbon is lithium titanate. The particle surface may be coated unevenly. In such a case, even if the carbon generation rate is limited to the above range, the (C / Ti) value of the obtained active material is smaller than 6. There is a risk. Therefore, it is preferable to use an alcohol other than methanol when synthesizing the active material of the present invention.

  The active material for a nonaqueous electrolyte battery of the present invention may be used as a positive electrode active material or a negative electrode active material.

When applying a non-aqueous electrolyte battery active material of the present invention as the positive electrode active material, as an anode active material, metal _{lithium, Li 3-P M P N} (M is a transition metal, 0 ≦ P ≦ 0.8) such as Nitride and lithium alloy are exemplified. Examples of the lithium alloy include alloys of lithium and aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

When the active material for a nonaqueous electrolyte battery of the present invention is applied as a negative electrode active material, examples of the positive electrode active material include lithium manganese composite oxide (for example, Li _x Mn ₂ O ₄ or Li _x MnO ₂ ), lithium nickel composite. Oxides (eg, Li _x NiO ₂ ), lithium cobalt composite oxides (eg, Li _x CoO ₂ ), lithium nickel cobalt composite oxides (eg, LiNi _1-y Co _y O ₂ ), lithium transition metal composite oxides (eg, LiNi _x Co _y Mn _1-yz O ₂ ), spinel-type lithium manganese nickel composite oxide (for example, Li _x Mn _2-y Ni _y O ₄ ), lithium phosphorous oxide having an olivine structure (for example, Li _x FePO ₄ , _{Li x Fe 1-y Mn y} PO 4, Li , etc. _{x CoPO 4), Li x MVO} 4 (M Is a transition metal), LiVOPO ₄ , Li _x MSiO ₄ (M is a transition metal), Li _x V ₂ (PO ₄ ) ₃ , Li _x MBO ₃ (M is a transition metal), manganese dioxide (MnO ₂ ), iron oxide, Iron sulfate (Fe ₂ (SO ₄ ) ₃ ), vanadium oxide (eg, V ₂ O ₅ ), copper oxide, nickel oxide, or the like can be used. Various sulfides can be used. In addition, conductive polymer materials such as polyaniline and polypyrrole, disulfide polymer materials, organic materials such as carbon fluoride, and inorganic materials can also be used. Furthermore, substances containing Al, P, B, or other typical nonmetallic elements or typical metal elements in these compounds can be used.

  The positive electrode includes a positive electrode layer containing a positive electrode active material and a positive electrode current collector. The positive electrode layer can be produced by mixing a positive electrode active material, a conductive agent and a binder in a solvent, applying the resulting slurry to a positive electrode current collector, and further drying.

  The negative electrode includes a negative electrode layer containing a negative electrode active material and a negative electrode current collector. The negative electrode layer can be produced by mixing a negative electrode active material and a binder in a solvent, applying the resulting slurry to a negative electrode current collector, and further drying. The negative electrode layer may contain a conductive agent separately from the negative electrode active material.

  As the current collector used for the positive electrode or the negative electrode, aluminum, iron, stainless steel, nickel, copper, or an alloy thereof can be used. Examples of the shape include a sheet, a foam, a sintered porous body, and an expanded lattice. Furthermore, as the current collector, a current collector having a hole in an arbitrary shape may be used.

  As a conductive agent used for the positive electrode or the negative electrode, various carbon materials can be used. Examples of the carbon material include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke. Also in the electrode using the active material of the present invention having carbon on the surface, it is preferable to use these conductive agents in combination because it can help bring out good battery performance. The amount of the carbon material as the conductive agent is preferably 5% by mass or less with respect to the active material. In particular, in an electrode using the active material of the present invention having carbon on the surface, the amount of these conductive agents used can be suppressed to a low level, for example, 1% by mass or less based on the active material. In particular, the effect of the present invention is more noticeably observed when the content is 0.6% by mass or less based on the active material.

  As the solvent or solution used for mixing the positive electrode active material or the negative electrode active material and the binder, a solvent or a solution in which the binder is dissolved or dispersed can be used. As the solvent or solution, a non-aqueous solvent or an aqueous solution can be used. Non-aqueous solvents include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. Can do. On the other hand, as the aqueous solution, water or an aqueous solution to which a dispersant, a thickener, or the like is added can be used. In the latter aqueous solution, latex such as SBR and an active material can be mixed and slurried.

  Examples of the binder used for the positive electrode or the negative electrode include PVdF (polyvinylidene fluoride), P (VdF / HFP) (polyvinylidene fluoride-hexafluoropropylene copolymer), PTFE (polytetrafluoroethylene), and fluorination. Polyvinylidene fluoride, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, Or these derivatives can be used individually or in mixture.

  As the separator, a microporous polymer membrane, a synthetic resin non-woven fabric, or the like can be used, and the materials thereof are nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, and polypropylene, polyethylene, polybutene. And the like. Of these, polyolefin microporous membranes are particularly preferred. Alternatively, a microporous film in which polyethylene and polypropylene are laminated may be used.

  As the non-aqueous electrolyte, a non-aqueous electrolyte, a polymer solid electrolyte, a gel electrolyte, or an inorganic solid electrolyte can be used. The electrolyte may have pores. The non-aqueous electrolyte is composed of a non-aqueous solvent and a solute.

Examples of the electrolyte salt include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and trifluoro Examples thereof include lithium salts such as lithium metasulfonate (LiCF ₃ SO ₃ ), bistrifluoromethylsulfonylimitolithium [LiN (CF ₃ SO ₂ ) ₂ ], and boron-based oxalate (for example, LiBOB).

  Examples of the organic solvent used in the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl. Chain carbonates such as carbonate (DEC), cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), chain ethers such as dimethoxyethane (DME), γ-butyrolactone (BL) acetonitrile (AN), sulfolane ( SL), and sultone such as 1,3-propane sultone and 1,3-propene sultone. These organic solvents can be used alone or in the form of a mixture of two or more.

Moreover, a room temperature molten salt containing lithium ions can be used as the non-aqueous electrolyte.
As an exterior material used for the battery of the present invention, a metal container or a laminate film can be used. As the metal container, a metal can made of aluminum, aluminum alloy, iron, stainless steel or the like can be used. The laminate film is a multilayer film in which a metal foil is coated with a resin film, and a polymer such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET) can be used as the resin.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, unless it exceeds the main point of invention, it is not limited at all.

<Production of carbon-coated lithium titanate>
A spinel type lithium titanate (Li ₄ Ti ₅ O ₁₂ ) powder having an average particle size of 18 μm was placed in a reaction vessel of a 20 liter baking furnace (externally heated batch rotary kiln manufactured by Takasago Industry Co., Ltd.), under a nitrogen atmosphere, Hold at 600 ° C. Thereafter, alcohol heated in a water bath at a predetermined temperature was bubbled with nitrogen gas to supply the reaction vessel at a flow rate of 5 liters / minute for a predetermined time. Thereafter, the firing furnace was cooled to produce active materials SA1 to SA9 shown in Table 1.

(XPS analysis conditions)
Device name: Quantera SXM manufactured by PHI
Excitation X-ray: AlKα ray (1486.6 eV)
X-ray diameter: 200 μm
Photoelectron escape angle: 45 ° (inclination of detector with respect to sample surface)

  In the production of the active materials SA1 to SA9, the type of alcohol used as the carbon source, the temperature at which the alcohol was heated in a water bath, the time during which the alcohol was supplied to the firing furnace, the atomic ratio of carbon to titanium determined by XPS analysis (C / Ti) is shown in Table 1. Here, in obtaining the value of (C / Ti), it is necessary to consider the relative sensitivity factor. In the examples of the present specification, the value of the sensitivity factor ratio of Ti2p when C1s is 1.00. 7.29 was adopted. The energy spectrum was baseline corrected by the Shirley method.

  About the produced active material SA1-SA9, when the quantity of carbon with which particle | grains were equipped was calculated | required by thermogravimetry (TG), all turned out to be 1.0 mass%.

  Moreover, about the produced active material SA1-SA9, the mode of the carbon produced | generated on the particle | grain surface of lithium titanate was observed with the transmission electron microscope (TEM). During TEM observation, a thin piece sample was prepared using FIB. FIGS. 1 and 2 show representative TEM observation results for SA4 and SA9.

  FIG. 1 is a TEM observation result in the vicinity of the particle surface of the active material SA4 produced using ethanol as a carbon source. The length of the scale shown at the upper right of the screen is 40 nm. The portion observed with a smooth appearance occupying the lower right portion of the screen corresponds to the lithium titanate particles, and the cross section of the lithium titanate particles cut by the FIB is directed to the observation screen. The black streaks that cross diagonally and diagonally from the lower left to the upper right of the screen are platinum coated on the sample as a pretreatment. And the thin white line between the platinum part and the lithium titanate particle part is carbon derived from the raw material ethanol. From this figure or a further enlarged figure, the thickness of the carbon layer provided on the surface of the lithium titanate particles in the active material SA4 was estimated to be 3 to 4 nm.

  FIG. 2 shows a TEM observation result in the vicinity of the particle surface of the active material SA9 produced using methanol as a carbon source. The length of the scale shown at the upper right of the screen is 100 nm. The portion observed with a smooth appearance in the upper left corner corresponds to the lithium titanate particles, and the cross section of the lithium titanate particles cut by the FIB is directed to the observation screen. The bulky object observed in the circled part in the center of the screen is carbon derived from the raw material methanol. As described above, in the active material SA9, it was observed that the carbon adhered to the surface of the lithium titanate particles in a bulky size of 100 nm or more.

  As a result of TEM observation, the thickness of the carbon layer formed on the surface of the negative electrode active material particles SA1 to SA6 was 5 nm or less. Further, when methanol was used as the carbon source (active material SA9), the uniformity of the carbon coat was lower and the ratio of (C / Ti) was smaller than when ethanol was used.

<Production of negative electrode>
The produced active materials SA1 to SA9 were each used as a negative electrode active material to produce a negative electrode. A slurry containing N-methylpyrrolidone (NMP) as a solvent and containing the negative electrode active material, acetylene black and polyvinylidene fluoride (PVdF) in a mass ratio of 91.5: 0.5: 8 is obtained from a copper foil having a thickness of 10 μm. The negative electrode was prepared by applying the mixture to both sides of the current collector so that the electrode mixture density was 8.4 mg / cm ² (excluding the current collector), and then drying and pressing. The mass of the electrode coated on both sides was 26 mg / cm ² including the current collector.

<Preparation of positive electrode>
Lithium transition metal composite oxide (LiNi _1/6 Co _2/3 Mn _1/6 ) powder was used as the positive electrode active material. A slurry containing NMP as a solvent and containing the positive electrode active material, acetylene black and PVdF in a mass ratio of 91: 4.5: 4.5 on both surfaces of a current collector made of an aluminum foil having a thickness of 20 μm. After coating so that the density was 10.6 mg / cm ² (not including the current collector), the positive electrode was produced by drying and pressing. The mass of the electrode coated on both sides was 27 mg / cm ² including the current collector.

<Preparation of nonaqueous electrolyte>
As the nonaqueous electrolyte, a solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate in a volume ratio of 6: 7: 7 at a concentration of 1 mol / liter was used.

<Production of nonaqueous electrolyte battery>
The electrode group formed by winding the positive electrode, the polyethylene porous separator, and the negative electrode is housed in an aluminum battery case having a height of 49.3 mm, a width of 33.7 mm, and a thickness of 5.17 mm. After 3.2 g of nonaqueous electrolyte was poured into the vacuum, constant current charging was performed for 1 hour at a current value of 80 mA in an opened state, and finally a sealing operation was performed to produce a battery. The nonaqueous electrolyte batteries using the negative electrode active materials SA1 to SA6 shown in Table 1 are referred to as Example Battery 1 to Example Battery 6, respectively, and the nonaqueous electrolytes using SA7 to SA9 are respectively used as Comparative Example Battery 1 to Comparative Example Battery. It was set to 3.

<Battery performance test>
All the following charge / discharge tests were carried out in a thermostatic chamber maintained at 25 ° C. The battery of Examples 1 to 6 and Comparative Examples 1 to 3 were subjected to constant current and constant voltage charging with a charging voltage of 2.5 V and a current value of 80 mA for 8 hours, and left for 10 minutes. Was carried out at a constant current of 1.0 V and a current value of 80 mA. Next, constant current and constant voltage charging with a charging voltage of 2.5 V and a current value of 400 mA were performed for 3 hours, and after standing for 10 minutes, a constant current discharge with a discharge end voltage of 1.0 V and a current value of 400 mA was performed. went. The capacity of all the batteries obtained in this discharge process was 400 mAh.

  Next, for each battery, constant current and constant voltage charging with a charging voltage of 2.5 V and a current value of 400 mA were performed for 3 hours, and after leaving for 10 minutes, the discharge end voltage was 1.0 V and the current value was A constant current discharge of 4.8 A (12 ItmA) was performed. The ratio (percentage) of the discharge capacity at 4.8 A (12 ItmA) to the discharge capacity (400 mAh) at 400 mA (1 ItmA) is also shown in Table 1 as the discharge capacity maintenance rate.

  As is apparent from the results in Table 1, the example battery using the sample having a (C / Ti) value of 6 or more is a comparative battery using the sample having a (C / Ti) value of less than 6. Compared with, it showed excellent high rate discharge performance. In particular, it is understood that the high rate discharge performance is particularly excellent when a sample having a (C / Ti) ratio of 6.3 or more and 8 or less is used.

<Preparation of samples with different carbon layer thickness>
Next, a sample was produced in which the thickness of the carbon layer formed on the surface of the lithium titanate particles was changed by changing the alcohol supply time under the SA3 preparation conditions. Table 2 summarizes the alcohol supply time, the thickness of the carbon layer, and the (C / Ti) ratio determined by XPS analysis.

  Next, the nonaqueous electrolyte batteries using SA10, SA11, and SA12 were designated as Example Battery 7 to Example Battery 9, respectively, and a charge / discharge test was performed under the same conditions as described above to confirm the capacity. The capacity of each battery was 400 mAh. Subsequently, a 12 ItmA high rate discharge test was performed on each battery under the same conditions as described above, and the discharge capacity retention rate was calculated. The results are shown in Table 2 together with the results of Example Battery 3.

  From Table 2, when the thickness of the carbon layer produced | generated on the lithium titanate particle surface was 5 nm or less, it turned out that the high rate discharge performance of the battery using it is excellent.

  In the above description, the carbon layer thickness was changed based on the SA3 conditions, but the alcohol supply time was changed in the same manner for SA1, SA2, SA4, SA5, and SA6. As a result of comparing the high-rate discharge performance of the battery using the obtained active material by changing the thickness of the carbon layer according to the results, the battery using the active material having a carbon layer thickness of 5 nm or less in any case It was found that the high rate discharge performance was excellent.

It is a figure which shows the TEM observation result of the active material which concerns on an Example. It is a figure which shows the TEM observation result of the active material which concerns on a comparative example.

Claims (3)

A non-aqueous electrolyte comprising carbon on at least a part of the surface of lithium titanate particles and having a carbon to titanium atomic ratio (C / Ti) value of 6 or more determined by X-ray photoelectron spectroscopy Battery active material. A nonaqueous electrolyte battery comprising an electrode containing the active material for a nonaqueous electrolyte battery according to claim 1. The manufacturing method of the active material for nonaqueous electrolyte batteries which manufactures the active material for nonaqueous electrolyte batteries of Claim 1 using ethanol for a carbon source.