TW201603371A - Nonaqueous-electrolyte secondary battery - Google Patents

Abstract

This invention provides a nonaqueous-electrolyte secondary battery that, while exhibiting excellent cycle characteristics due to the use of a carbonaceous material that exhibits little expansion and contraction during charging and discharging, exhibits both the low internal resistance and the charging-curve shape with a large sloped region that are in demand for HEV applications and the like, resulting in excellent input characteristics. Said nonaqueous-electrolyte secondary battery is provided with the following: a positive electrode containing a positive-electrode active material that comprises a lithium-containing transition-metal composite oxide; a negative electrode containing a negative-electrode active material that contains a carbonaceous material; and a nonaqueous electrolyte. This nonaqueous-electrolyte secondary battery has a positive-electrode capacity (the capacity with metallic lithium used as the other electrode) of at most 3.0 mAh/cm2; the true density of the carbonaceous material, as determined using a butanol method, is between 1.45 and 1.70 g/cm3, inclusive; and the ratio (A/B) of the positive-electrode capacity (A) to the negative-electrode capacity (B) is between 0.4 and 0.8, inclusive.

Description

Nonaqueous electrolyte secondary battery

The present invention relates to a nonaqueous electrolyte secondary battery.

In recent years, a large-scale lithium ion secondary battery having a high energy density and excellent output characteristics has been studied in an electric vehicle due to an increase in attention to environmental issues. In a small mobile device such as a mobile phone or a notebook computer, capacitance per unit volume becomes important. Therefore, a graphite material having a large density is mainly used as a negative electrode active material. However, in the case of a lithium ion secondary battery for a vehicle, since it is large and expensive, replacement in the middle is difficult. Therefore, it is necessary to have the same durability as that of a car, for example, it is required to achieve life performance (high durability) of 10 years or more. Further, since the weight of the vehicle is required to be light, the battery characteristics per unit weight are also emphasized.

Moreover, the use form of the battery is not a method of repeating full charge and full discharge of a small mobile device, but a method of using a large current charging and discharging. In such a form, it is preferable to adopt a configuration in which the battery is held in a region where the input characteristics and the output characteristics are balanced, that is, when the full-charge is 100%, the charging region is half or 50%. And repeat the input and output. In the case of assuming such a use form, it is not a positive and negative electrode combination that exhibits a substantially fixed potential with respect to a change in capacitance under use conditions as in the case of a battery for a small mobile device, and is used in an HEV (Hybrid Electric Vehicle, In a battery for use in a hybrid electric vehicle, the battery is designed such that the potential change of the negative electrode changes with respect to the change in capacitance under the use condition, whereby the input characteristics can be improved.

For example, in a small mobile device power supply, it is required to be charged in a self-discharge state for a charging load of 1 to 2 hours and a charging load of 0.5 to 1 hour. On the other hand, in the power supply for hybrid electric vehicles (HEV), if energy regeneration is performed in consideration of braking, a large current charger capable of being around 5 to 50 hours is required. In addition, regarding the discharge, it is required to be able to discharge with a large current at the same level, and it is required to be able to discharge and discharge at the same level as the lithium ion secondary battery which is absolutely superior in speed (input). Output) characteristics.

As described above, in the battery used for the HEV application, the input/output characteristics, particularly the input characteristics equivalent to charging, are taken into consideration, and it is important that the charging capacitance in the region where the charging curve is inclined is large.

In order to improve the input characteristics, it is preferable that a carbonaceous material which exhibits a shape in which the charging curve is inclined in a wide area is used for the negative electrode active material. Specifically, it is proposed to select an active material which is largely changed with respect to a capacitance potential, that is, a non-graphitizable carbon or an easily graphitizable carbon as a negative electrode material.

Further, as described above, since durability or cycle characteristics are required for a vehicle-mounted secondary battery, improvement in durability or cycle characteristics has been proposed. For example, in the case of the negative electrode active material, a low-crystalline carbon material having a lattice spacing (d ₀₀₂ ) of 0.37 nm or more and 0.40 nm or less is used, and the potential at the time of occlusion of lithium is set to 30 mV or more (vs. Li/). Li ⁺ ), thereby improving the cycle life characteristics, but even if the ratio of the inclined region in the charging process can be increased, the electrode resistance can not be lowered, and the improvement effect of the input/output characteristics is not sufficient. Patent Document 2 proposes to use a low crystallinity carbon having a lattice spacing (d ₀₀₂ ) of 0.37 nm or more and 0.385 nm or less, and a capacitance density of a negative electrode when fully charged is a chargeable discharge when metal lithium is set as a counter electrode. When the capacitance is 40% or more and 60% or less, the long-term durability and the high-temperature stability are improved. However, the electrode resistance cannot be lowered, and the improvement effect of the input/output characteristics is not sufficient. Further, in the examples of Patent Documents 1 and 2, a carbon material having an average particle diameter of 10 μm or more is exemplified. However, if the particles have an average particle diameter of about 10 μm or more, the negative electrode cannot be sufficiently thin-coated, and input and output characteristics cannot be obtained. Improvement.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 4,951,825

[Patent Document 2] Japanese Patent No. 4961649

An object of the present invention is to provide a nonaqueous electrolyte secondary battery in which a carbonaceous material having less expansion and contraction during charge and discharge is used to achieve excellent battery cycle characteristics, and to meet the requirements of HEV use and the like. The shape of the charging curve with a large slope area and a low internal resistance make the input characteristics excellent.

The present inventors have found that it is possible to provide a battery which is excellent in cycle characteristics and which has both a charging curve shape having a large inclined region and an input characteristic having a low internal resistance, and the battery system is provided to contain lithium-containing A positive electrode of a positive electrode active material composed of a transition metal composite oxide, a negative electrode including a negative electrode active material containing a carbonaceous material, and a nonaqueous electrolyte secondary battery. In the nonaqueous electrolyte secondary battery, the positive electrode capacitance is 3.0 mAh. /cm ² or less (capacitance when the opposite electrode is Li metal), the true density of the carbonaceous material obtained by the butanol method is 1.45 to 1.70 g/cm ³ , and the opposite of the positive electrode capacitor A and the negative electrode capacitor B The ratio (A/B) is 0.4 to 0.8. Specifically, the present invention provides the following.

(1) A nonaqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material composed of a transition metal complex oxide containing lithium, a negative electrode including a negative electrode active material containing a carbonaceous material, and a nonaqueous electrolyte. The positive electrode capacitance is 3.0 mAh/cm ² or less (the capacitance when the counter electrode is Li metal), and the true density of the carbonaceous material obtained by the butanol method is 1.45 to 1.70 g/cm ³ , which is opposite The ratio (A/B) of the positive electrode capacitor A to the negative electrode capacitor B is 0.4 to 0.8.

(2) The nonaqueous electrolyte secondary battery according to the above (1), wherein the negative electrode active material layer in the negative electrode has a thickness of 45 μm or less.

(3) The nonaqueous electrolyte secondary battery according to the above (1) or (2), wherein the carbonaceous material has an average particle diameter (Dv ₅₀ ) of 4.5 μm or less.

According to the invention, there is provided a battery comprising a positive electrode comprising a positive electrode active material composed of a transition metal-containing composite oxide containing lithium, a negative electrode comprising a negative electrode active material containing a carbonaceous material, and a non-aqueous electrolyte of a non-aqueous electrolyte In the non-aqueous electrolyte secondary battery, the positive electrode capacitance is 3.0 mAh/cm ² or less (the capacitance when the counter electrode is Li metal), and the true density of the carbonaceous material obtained by the butanol method is 1.45 to 1.70 g. /cm ³ , the ratio of the positive electrode capacitor A to the negative electrode capacitor B (A/B) is 0.4 to 0.8, thereby achieving excellent cycle characteristics and taking into account the shape of the charging curve and the lower internal portion of the inclined region. Resistance, which makes the input characteristics excellent.

Increasing the tilt region not only suppresses the precipitation of lithium during charging but also contributes to the improvement of the charge-discharge cycle characteristics, and enables charging at a higher load. Further, in the battery of the present invention, the thickness of the negative electrode active material layer is thinner than that of the conventional negative electrode, and the electric resistance in the thickness direction of the negative electrode is low, so that the internal resistance of the battery can be lowered to provide a battery with high input and output.

Fig. 1 is a view showing input and output current pulses used in the embodiment.

Hereinafter, embodiments of the present invention will be described.

Preferably, the nonaqueous electrolyte secondary battery of the present invention includes a positive electrode including a positive electrode active material composed of a transition metal complex oxide containing lithium, a negative electrode including a negative electrode active material containing a carbonaceous material, and a nonaqueous electrolyte. In the water-electrolyte secondary battery, the positive electrode capacitance is 3.0 mAh/cm ² or less (the capacitance when the counter electrode is Li metal), and the true density of the carbonaceous material obtained by the butanol method is 1.45 to 1.70 g/cm ³ . The ratio of the positive electrode capacitor A to the negative electrode capacitor B (A/B) is 0.4 to 0.8.

The positive electrode capacitance means a discharge capacity per unit area in the positive electrode, and is set to achieve a charge and discharge capacitance necessary for input and output of the secondary battery. On the other hand, since the negative electrode absorbs lithium ions during charging, it is necessary to increase the negative electrode capacitance according to an increase in the positive electrode capacitance so as not to precipitate excess lithium as lithium metal. However, since the increase in the negative electrode capacitance causes the thickness of the electrode of the negative electrode to become large, the diffusion distance of lithium becomes long and the electric resistance increases, so that the input/output characteristics are lowered. Further, there is a case where the influence of expansion and contraction due to repetition of charge and discharge is increased, and the capacity retention rate is lowered. Therefore, the positive electrode capacitance must be fixed to be within a suitable range, preferably 3.0 mAh/cm ² or less. More preferably, it is 2.7 mAh/cm ² or less. Moreover, since the necessary capacitance can be appropriately set in accordance with the cruising distance of the HEV or the like, it is also possible to set it to 0.8 mAh/cm ² or more. It is preferably 1 mAh/cm ² or more.

Preferably, the non-aqueous electrolyte secondary battery of the present invention has a true density of the carbonaceous material determined by a butanol method of 1.45 to 1.70 g/cm ³ , and a ratio of the positive electrode capacitor A to the negative electrode capacitor B (A/B). ) is 0.4~0.8.

As a carbonaceous material having a true density of 1.45 to 1.70 g/cm ³ , a non-graphitizable material having a non-graphitizable carbon is representative. This non-graphite material has a capacitance in a region where the potential change near the full charge is small, but has a large capacitance in a slope region where the potential gradually changes, and is therefore suitable for use in an HEV application. When the true density exceeds 1.70 g/cm ³ , the expansion shrinkage of the carbonaceous material in charge and discharge becomes large, the capacity retention rate after the charge and discharge cycle decreases, and when it is less than 1.45 g/cm ³ , carbonization is insufficient. The tendency of irreversible capacitance to become large is not good.

When the ratio (A/B) of the positive electrode capacitor A to the negative electrode capacitor B is less than 0.4, the decrease in the battery capacity is remarkable, thus causing a decrease in input and output characteristics. On the other hand, when it exceeds 0.8, the thickness of the active material layer of the negative electrode becomes relatively large, due to an increase in electrical resistance or expansion and contraction. This results in a decrease in input/output characteristics or a decrease in capacitance maintenance rate. Therefore, the ratio (A/B) is preferably from 0.4 to 0.8.

The thickness of the negative electrode active material layer in the negative electrode of the nonaqueous electrolyte secondary battery of the present invention is preferably 45 μm or less. When the thickness of the negative electrode active material layer is present on both surfaces of the current collector of the negative electrode, it corresponds to one half of the thickness obtained by subtracting the thickness of the current collector from the negative electrode, and the negative electrode is present only on one side of the current collector. In the case of the active material layer, it corresponds to the thickness obtained by subtracting the thickness of the current collector from the negative electrode. When the thickness of the negative electrode active material layer is too large, the input/output characteristics are lowered and the capacity retention rate is lowered. Therefore, the thickness of the negative electrode active material layer is preferably 45 μm or less per one surface, and more preferably 40 μm or less.

The nonaqueous electrolyte secondary battery of the present invention preferably has a negative electrode active material containing a carbonaceous material having an average particle diameter (Dv ₅₀ and a cumulative volume of 50%) of 6 μm or less. When the average particle diameter of the carbonaceous material is too large, a large particle increases, and it is difficult to apply a thin coating to the electrode, and further, since the diffusion distance of lithium in the particle increases, it is difficult to perform rapid charge and discharge. Input and output characteristics are reduced. Therefore, the average particle diameter is preferably 4.5 μm or less, more preferably 4 μm or less. Further, when the average particle diameter is too small, the ratio of the fine powder increases, and the irreversible capacitance increases. Therefore, it may be 1 μm or more, and preferably 1.5 μm or more.

In the negative electrode active material contained in the negative electrode which is opposed to the positive electrode including the positive electrode active material, the average layer spacing (d ₀₀₂ ) of the 002 surface obtained by the X-ray diffraction method is preferably 0.365 nm or more and 0.40 nm or less. The layered carbonaceous material is constructed. The higher the crystal completeness, the smaller the average layer spacing exhibits, which is 0.3354 nm in the graphite structure, and the more the graphite structure is disordered, the more the value tends to increase. The graphite material is expanded by about 10% due to the doping of lithium and the dedoping, so that the crystal structure is easily broken. Therefore, in the present invention, a carbonaceous material having a disordered layer structure having an average surface spacing larger than that of a graphite structure is used as the negative electrode active material, and the average layer spacing of the 002 plane is preferably 0.365 nm or more and 0.400 nm or less. If the average surface spacing is less than 0.365 nm, the doping capacitance per unit weight becomes small. More preferably, it is 0.368 nm or more. When the average surface spacing exceeds 0.400 nm, it means that carbonization is insufficient and the irreversible capacitance becomes large, which is not preferable. More preferably, it is 0.395 nm or less.

The nonaqueous electrolyte secondary battery of the present invention preferably has a negative electrode active material having a specific surface area (BET) of 6 m ² /g or more as determined by a BET method using adsorption of nitrogen. When the specific surface area of the negative electrode active material is too small, the reaction area with the electrolytic solution is small, and the input/output characteristics tend to be lowered. Therefore, it may be 7 m ² /g or more. It is preferably 8 m ² /g or more. When the specific surface area of the negative electrode active material is too large, the irreversible capacitance of the obtained battery tends to increase, and therefore it may be 20 m ² /g or less. It is preferably 15 m ² /g or less.

(non-aqueous electrolyte secondary battery)

The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte. The other material constituting the battery such as a separator is not particularly limited, and may be used as a nonaqueous electrolyte. Various materials used or proposed for secondary batteries.

(positive electrode active material)

As the positive electrode active material, a positive electrode active material used in the art can be used. For example, lithium iron phosphate (LiFePO ₄ ), lithium manganese phosphate (LiMnPO ₄ ), lithium manganese iron phosphate (LiMn _1-x Fe _x PO ₄ ), lithium cobalt phosphate (LiCoPO ₄ ), lithium cobaltate composite oxide are preferred. (LiCoO ₂ ), spinel-type lithium manganate composite oxide (LiMn ₂ O ₄ ), lithium manganate composite oxide (LiMnO ₂ , Li ₂ MnO ₃ ), lithium nickelate composite oxide (LiNiO ₂ ), ruthenium lithium composite oxide (LiNbO _2), lithium iron composite oxides (LiFeO _2), magnesium, lithium composite oxide (LiMgO _2), calcium, lithium composite oxide (LiCaO _2), copper lithium composite oxide ( LiCuO ₂ ), lithium zincate composite oxide (LiZnO ₂ ), lithium molybdate composite oxide (LiMoO ₂ ), lithium niobate composite oxide (LiTaO ₂ ), lithium tungstate composite oxide (LiWO ₂ ), lithium- Nickel-cobalt-aluminum composite oxide (LiNi _0.8 Co _0.15 Al _0.05 O ₂ ), lithium-nickel-cobalt-manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), Li excess nickel - a composite metal chalcogen compound such as a cobalt-manganese composite oxide (Li _x Ni _A Co _B Mn _C O ₂ solid solution), manganese oxide (MnO ₂ ), vanadium, sulfur or citrate It is necessary to mix these chalcogen compound compounds. These positive electrode materials are formed together with a suitable binder and a carbon material for imparting conductivity to the electrodes, and a layer is formed on the conductive collector to form a positive electrode.

(negative electrode active material)

The carbonaceous material used in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, but can be based on a production method similar to that of the carbonaceous material of the prior nonaqueous electrolyte secondary battery, and the firing condition is optimized. Thereby, it can be manufactured well. Carbonaceous materials made from carbon precursors can be used. As the carbon precursor, petroleum pitch or tar, coal pitch or tar, a thermoplastic resin, or a thermosetting resin can be cited. Further, examples of the thermoplastic resin include polyacetal, polyacrylonitrile, styrene/divinylbenzene copolymer, polyimine, polycarbonate, modified polyphenylene ether, polybutylene terephthalate, and poly Aryl ester, polyfluorene, polyphenylene sulfide, fluororesin, polyamidoximine, or polyetheretherketone. Examples of the thermosetting resin include a phenol resin, an amine resin, an unsaturated polyester resin, a diallyl phthalate resin, an alkyd resin, an epoxy resin, and a urethane resin. For example, it is specifically a furan resin.

Further, in the negative electrode active material, as the carbonaceous material, in addition to the difficult graphitized carbon, easily graphitizable carbon, graphite or the like may be mixed. Further, a negative electrode active material other than the carbonaceous material may be mixed.

In the present invention, a non-graphitizable carbonaceous material can be used, and therefore, petroleum pitch or tar, coal pitch or tar, or thermoplastic resin must be subjected to a non-melting treatment in the manufacturing process so as not to melt with respect to heat. . The non-melting treatment can be carried out by crosslinking the carbon precursor by oxidation. The non-melting treatment can be carried out by methods well known in the art of the present invention.

The carbon precursor is fired in order to form a carbonaceous material for a negative electrode. In the present invention, it is preferably carried out by preliminary calcination at a temperature of 300 ° C or higher and less than 900 ° C, and calcination at a temperature of 900 to 1500 ° C. If the pre-firing temperature is too low, the de-tarred oil is insufficient, and a large amount of tar is generated during calcination, which causes a deterioration in battery performance, which is not preferable. Pre The calcination temperature is preferably 300 ° C or higher, more preferably 500 ° C or higher, and particularly preferably 600 ° C or higher. On the other hand, if the preliminary firing temperature is too high, the tar generation temperature region is exceeded, and the energy efficiency of use is lowered, which is not preferable. Further, the generated tar causes a secondary decomposition reaction, and the like, which adheres to the carbon precursor, may cause a decrease in performance, which is not preferable. The pulverization step can be carried out after the non-melting step, but is preferably carried out after the preliminary calcination. If the preliminary firing temperature is too high, the carbon precursor becomes hard, and the pulverization efficiency may be lowered, which is not preferable. The preliminary firing is preferably carried out at less than 900 °C. In the case of preliminary calcination and calcination, the temperature may be lowered temporarily after preliminary calcination, and pulverized and calcined.

The calcination step can be carried out in the order of usual calcination. The calcination temperature is preferably from 900 to 1500 °C. When the calcination temperature is less than 900 ° C, carbonization is insufficient, and a large amount of functional groups remain in the carbonaceous material to increase the value of H/C, and the irreversible capacitance increases due to the reaction with lithium, which is not preferable. The lower limit of the calcination temperature of the present invention is 900 ° C or higher, more preferably 950 ° C or higher. On the other hand, when the calcination temperature exceeds 1500 ° C, the selective orientation of the carbon hexagonal plane is increased, and the discharge capacity is lowered, and the true density is increased, the expansion shrinkage in charge and discharge is increased, and the charge and discharge cycle characteristics are deteriorated, so that it is not good. . The upper limit of the calcination temperature of the present invention is 1,500 ° C or lower, more preferably 1450 ° C or lower, and still more preferably 1400 ° C or lower. When the calcination temperature exceeds 1500 ° C, the true density becomes large, and the expansion and contraction during charging and discharging become large, and the charge and discharge cycle characteristics are deteriorated, which is not preferable. When the temperature is lower than 900 ° C, the carbonization is insufficient and the irreversible capacitance becomes large, which is not preferable. The calcination is preferably carried out at 900 ° C to 1450 ° C, more preferably at 950 ° C to 1400 ° C.

(Manufacture of electrodes)

In the electrode of the nonaqueous electrolyte secondary battery of the present invention, a binder (adhesive) may be added to the positive electrode active material or the negative electrode active material, and an appropriate amount of a solvent may be added and kneaded. After the electrode mixture is formed, the metal plate or the like may be contained. The current collector is coated and dried, and then produced by press molding.

The current collecting system uses a metal material such as aluminum, copper, nickel, or stainless steel, or a conductive polymer material.

Further, for the purpose of imparting high conductivity, a conductive auxiliary agent may be added as needed in the preparation of the electrode mixture. As the conductive auxiliary agent, conductive carbon black, vapor-grown carbon fiber (VGCF), a nanotube, or the like can be used, and the amount of addition varies depending on the type of the conductive auxiliary agent to be used, but if the amount added is too small, it cannot be used. It is not preferable to obtain the desired conductivity, and if it is too large, the dispersion in the electrode mixture is deteriorated, which is not preferable. From this point of view, a preferred ratio of the conductive auxiliary agent to be added is 0.5 to 10% by weight (here, the active material mass + the bonding amount + the conductive auxiliary agent amount = 100% by weight), and further preferably 0.5 to 7 The weight % is particularly preferably 0.5 to 5% by weight.

As a binder, as long as it is PVDF (Polyvinylidene fluoride, polyvinylidene fluoride), polytetrafluoroethylene, and SBR (styrene-butadiene rubber, styrene ‧ butadiene rubber) and CMC (carboxymethyl cellulose, carboxymethyl fiber The mixture of the compound and the like is not particularly limited as long as it does not react with the electrolyte. Among them, the PVDF attached to the surface of the active material of PVDF does not hinder the movement of lithium ions, and is advantageous for obtaining good input and output characteristics. In order to dissolve the PVDF forming slurry, a polar solvent such as N-methylpyrrolidone (NMP) is preferably used, but an aqueous emulsion such as SBR or CMC may be dissolved in water and used. When the amount of the binder added is too large, the electric resistance of the obtained electrode becomes large. Therefore, the internal resistance of the battery becomes large, and the battery characteristics are lowered, which is not preferable. Further, when the amount of the binder added is too small, the bonding of the negative electrode material particles to each other and the bonding with the current collector are insufficient, which is not preferable. The preferred addition amount of the binder varies depending on the type of the binder to be used, but it is preferably from 3 to 13% by weight, and more preferably from 3 to 10% by weight, based on the PVDF-based binder. On the other hand, in the solvent-based water-based adhesive, a plurality of kinds of binders such as a mixture of SBR and CMC are often used in combination, and the total amount of all the binders used is preferably 0.5 to 5% by weight. Further, it is preferably from 1 to 4% by weight. The electrode active material layer is formed substantially on both sides of the current collector plate, but may be one side as needed.

(non-aqueous electrolyte)

The nonaqueous electrolyte used in the combination of the positive electrode and the negative electrode is generally formed by dissolving an electrolyte in a nonaqueous solvent. As the nonaqueous solvent, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2 may be combined. One type or two or more types of organic solvents such as methyltetrahydrofuran, cyclobutane or 1,3-dioxolane are used. Further, as the electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr, LiB(C ₆ H ₅ ) ₄ , or LiN(SO ₃ CF ₃ ) ₂ or the like is used. Further, a gel electrolyte or a solid electrolyte can be used in the nonaqueous electrolyte secondary battery of the present invention.

In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode active material layer and the negative electrode active material layer which are formed as described above are generally opposed to each other via a liquid-permeable separator including a nonwoven fabric or another porous material. It is formed by immersing in an electrolyte solution.

As the separator, a transmissive separator which is generally used for a secondary battery and which includes a nonwoven fabric or other porous material can be used. Alternatively, a solid electrolyte in which a polymer gel impregnated with an electrolyte is used may be used instead of or in combination with the separator.

The nonaqueous electrolyte secondary battery of the present invention is preferably used as a secondary battery mounted on a vehicle such as an electric car or an HEV. The electric vehicle or the fuel cell or the hybrid electric vehicle of the internal combustion engine, which is generally known, may be specifically targeted, but includes at least a power supply device including the battery and an electric motor driven by the power supply from the power supply device. The drive mechanism and the control device that controls it. Further, it is also possible to provide a power generating brake or a regenerative brake, and a mechanism for converting the braking energy into electricity and charging the lithium ion secondary battery.

[Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the scope of the invention is not limited thereto.

The physical properties (ρ _Bt , BET specific surface area, average particle diameter (Dv ₅₀ ), d ₀₀₂ , active material layer thickness, positive electrode capacitance, and positive electrode active material of the positive electrode active material and the negative electrode active material in the nonaqueous electrolyte secondary battery of the present invention are described below. The measurement method of the negative electrode capacitance, the input density per unit weight at the time of SOC 50%, and the capacity retention rate) is included in the present specification, and the physical property values described in the present specification are based on the values obtained by the following methods.

(true density (ρ _Bt ) obtained by the butanol method)

The true density was measured by the butanol method according to the method specified in JIS R 7212. The mass (m ₁ ) of the pycnometer with the inner tube of about 40 mL was measured accurately. Next, after the sample was smoothly added to the bottom portion in such a manner as to have a thickness of about 10 mm, the mass (m ₂ ) was accurately measured. 1-butanol was slowly added thereto to a depth of about 20 mm from the bottom. Next, a slight vibration was applied to the pycnometer, and it was confirmed that no large bubbles were generated, and then placed in a vacuum drier, and slowly vented to 2.0 to 2.7 kPa. Hold at this pressure for 20 minutes or more, take out after the generation of the bubble, and then fill 1-butanol, plug it with a stopper, and immerse it in a constant temperature water tank (adjusted to 30 ± 0.03 ° C) for 15 minutes or more. The level of 1-butanol is aligned with the marking. Next, it was taken out, the outside was carefully wiped, and cooled to room temperature, after which the mass (m ₄ ) was accurately measured.

Next, the same pycnometer was filled with 1-butanol, and immersed in a constant-temperature water tank in the same manner as described above, and after being aligned with the reticle, the mass (m ₃ ) was measured. Further, the distilled water which was boiled before use and the dissolved gas was removed, and extracted into a pycnometer, and immersed in a constant temperature water tank in the same manner as described above, and aligned with the reticle, the mass (m ₅ ) was measured. The ρ _Bt system is calculated by the following formula.

At this time, d is the specific gravity (0.9946) at 30 ° C of water.

(Using nitrogen adsorption specific surface area (SSA))

The approximate expression derived from the BET equation is described below.

Using the above approximate expression, v _{m was} determined by a one-point method (relative pressure x = 0.3) using nitrogen adsorption at a liquid nitrogen temperature, and the specific surface area of the sample was calculated by the following formula.

[Number 3] specific surface area (SSA) = 4.35 × V _m (m ² /g)

At this time, v _m is an adsorption amount (cm ³ /g) necessary for forming a monomolecular layer on the surface of the sample, and v is an actually measured adsorption amount (cm ³ /g), and x is a relative pressure.

Specifically, the amount of nitrogen adsorbed to the carbonaceous material at the liquid nitrogen temperature was measured by using "Flow Sorb II 2300" manufactured by MICROMERITICS. The carbonaceous material pulverized to a particle diameter of about 5 to 50 μm was filled in the sample tube, and the sample tube was cooled to -196 ° C while flowing a helium gas: nitrogen gas of 70:30, and nitrogen gas was adsorbed to the carbonaceous material. Next, return the sample tube to room temperature. At this time, the amount of nitrogen gas that has escaped from the sample is measured by a thermal conductivity type detector, and the amount of adsorbed gas v is set.

(Average slice interval (d ₀₀₂ ) obtained by X-ray diffraction method)

The carbonaceous material powder was filled in the sample holder, and the CuKα line monochromated by the Ni filter was used as a line source to obtain an X-ray diffraction pattern. The peak position of the diffraction pattern is obtained by the center of gravity method (the method of obtaining the position of the center of gravity of the ray, and determining the peak position by using the corresponding 2θ value), and using the (111) surface of the high-purity bismuth powder using the standard substance. The diffraction peak is corrected. The wavelength of the CuKα line was set to 0.15418 nm, and d _{002 was} calculated by the Bragg formula described below.

λ: wavelength of X-ray, θ: diffraction angle

(Average particle size (Dv ₅₀ ) obtained by laser diffraction method)

A dispersant (surfactant SN WET 366 (manufactured by SAN NOPCO Co., Ltd.)) was added to the sample and allowed to be affinity. Then, after adding deionized water and dispersing it by ultrasonic waves, the particle size distribution measuring instrument ("SALD-3000S" manufactured by Shimadzu Corporation) was used to set the refractive index to 2.0-0.1i, and the particle diameter was 0.5 to 3000 μm. The particle size distribution of the range. According to the obtained particle size distribution, the particle diameter of 50% of the cumulative volume was set as the average particle diameter Dv ₅₀ .

An electrode was produced using the positive electrode active material containing a lithium transition metal composite oxide and the negative electrode active material containing a carbonaceous material in Examples 1 to 10 and Comparative Examples 1 to 9, and a non-electrolyte secondary battery for testing was prepared. Battery, test battery) and evaluate the battery performance.

(Example 1)

Perform the following operations (a) to (j) and measure specific items.

(a) Production of positive electrode

As the positive electrode active material, a lithium-nickel-cobalt-manganese composite oxide (NCM) having an atomic ratio of nickel, cobalt and manganese of 1:1:1 was used.

In the positive electrode, 3 parts by mass of acetylene black as a conductive material is added to 100 parts by mass of the above-mentioned positive electrode active material, and the following solution is kneaded in the mixture to form a paste, which is based on N-methylpyrrolidone (NMP). The solvent was dissolved in polyvinylidene fluoride (PVDF) ("KF #1100" manufactured by KUREHA Co., Ltd.) as a binder. Joined PVDF The amount is prepared in an amount of 4 parts by mass based on 100 parts by mass of the active material. Then, the paste was uniformly coated on an aluminum foil. After drying, it was punched from an aluminum foil into a disk shape having a diameter of 15 mm, and pressed to form a positive electrode.

(b) Production of negative electrode

The negative electrode active material is a non-graphitizable carbon obtained by heat-treating an isotropic pitch as a raw material. The average particle diameter was 4.2 μm, (d ₀₀₂ ) was 0.390 nm, and the true density was 1.48 g/cm ³ .

In the same manner as in the production of the positive electrode, the negative electrode was prepared by kneading the following solution in 100 parts by mass of the carbonaceous powder, and the solution was prepared by dissolving PVDF as a binder in a solvent of NMP. The amount of PVDF added was prepared in an amount of 8 parts by mass based on 100 parts by mass of the carbon powder. Then, the paste was uniformly applied onto the copper foil. After drying, it was punched from a copper foil into a disk shape having a diameter of 15 mm, and pressed to form a negative electrode.

(c) Determination of the thickness of the anode active material layer

When the thickness of the negative electrode active material layer is such that the negative electrode active material layer exists on both surfaces of the current collector of the negative electrode, it is equivalent to one half of the thickness obtained by subtracting the thickness of the current collector from the negative electrode, and is only in the current collector. In the case where the negative electrode active material layer is present on one side, it corresponds to the thickness obtained by subtracting the thickness of the current collector from the negative electrode.

Specifically, the thickness is measured by a thickness measuring device.

(d) Production of full battery

In order to measure the input characteristics of the lithium secondary battery and the capacity retention rate after the cycle, the above positive electrode and negative electrode were combined to form a full battery for testing. The positive and negative active materials are laminated to form a positive electrode, a separator of a fine pore film made of boron silicate glass fiber having a diameter of 19 mm, and a negative electrode, and the positive and negative electrodes and the separator are filled with an electrolyte. . The electrolytic solution was used to add LiPF ₆ at a ratio of 1.4 mol/L in a mixed solvent in which ethylene carbonate, dimethyl carbonate, and methyl carbonate were mixed at a capacitance ratio of 1:2:2. Further, an aluminum plate having a thickness of 0.2 mm was placed on the positive electrode side, and a full-size battery of 2016 size was assembled in an Ar glove box using a gasket made of polyethylene.

(e) Determination of initial discharge capacitance

The charge and discharge test was performed by the constant current constant voltage method using the charge and discharge tester ("TOSCAT" manufactured by Toyo Corp.). Specifically, the entire battery was charged with a constant current of 0.3 mA and a constant voltage of 4.2 V, and the charging was terminated when the current was attenuated to 0.03 mA. Thereafter, the battery circuit was opened and a constant current discharge was performed until it reached 0.3 mA and 2.5 V. At this time, the initial discharge capacity (mAh) was measured by the amount of discharge.

(f) Determination of input density per unit weight

The charge and discharge current was changed to 0.6 mA using the above-described full battery in which the initial discharge capacity was measured, and the charge and discharge were performed once under the same conditions as above. The entire battery is charged with a constant current of 0.6 mA and a constant voltage of 4.2 V until one half of the initial discharge capacitance.

Then, for the whole battery, an input/output current pulse as shown in FIG. 1 is applied, and the voltage before the application of the charging (input) pulse and the voltage after each charging (input) pulse is applied for 10 seconds (for each voltage reading) This is done in Figure 1 before the rise of the current pulse and before the fall. As a voltage reading point, the voltage measured at four points as shown in FIG. 1 is plotted against the applied current value. The approximate straight line of the curves was extrapolated, and the product of the current value at the intersection of the charging upper limit voltage of 4.2 V and the charging upper limit voltage was calculated as an input value (W: watt). The input value is divided by the sum of the weights of the constituent elements including the positive electrode, the separator, and the negative electrode disposed inside the test cell, and the input density per unit weight is calculated.

(g) Determination of capacitance maintenance rate

The full battery after the above input density was evaluated was charged by a constant current constant voltage method. Set the charging upper limit voltage to 4.2V, set the charging current value to 5mA, and after charging to 4.2V, charge at a fixed voltage, when the current is attenuated to 0.5mA. The point ends charging. Thereafter, constant current discharge was performed at 5 mA, and the end was reached at the time of reaching 2.5 V. The discharge capacity at this time was measured. This charge and discharge cycle was repeated for 300 cycles, and the discharge capacity of the 300th cycle was divided by the discharge capacity of the first cycle, and the ratio was calculated as the capacitance retention ratio (%).

Further, the initial discharge capacity, the input density per unit weight, the positive electrode capacitance, the negative electrode capacitance, and the capacity retention ratio were all measured in a thermostatic chamber at 25 ° C in the charge and discharge test and measurement.

(h) Production of test battery

Another full battery was fabricated in the same manner as in the above (d), and after charging in the same manner as in the above "(e) Measurement of initial discharge capacitance", the entire battery was disassembled and the positive electrode and the negative electrode were taken out. The preparation of the lithium electrode was carried out in a glove box in an Ar environment. A stainless steel wire mesh disk having a diameter of 16 mm was spot-welded in advance on a coin-type battery can of 2016 size, and a metal lithium plate having a thickness of 0.8 mm was punched into a disk having a diameter of 15 mm. The resultant was crimped to a stainless steel wire mesh. Disc, as an electrode (counter electrode). Using a pair of lithium electrodes and a positive electrode fabricated in this manner, or a pair of the lithium and the negative electrodes, as an electrolytic solution, using ethylene carbonate, dimethyl carbonate, methyl methyl carbonate at a capacitance ratio of 1:2 : In the mixed solvent of 2, LiPF ₆ was added at a ratio of 1.4 mol/L, and a separator made of a fine pore film made of borosilicate glass fiber having a diameter of 19 mm was made of a gasket made of polyethylene in an Ar glove box. Assemble the 2016 size coin type test battery.

(i) Determination of positive electrode capacitance

Using the test cell comprising the pair of lithium electrode and the positive electrode of the above (h), discharge was performed at a constant current of 0.3 mA, and the discharge was terminated at a point when the voltage was lowered to 80% of the voltage at the start of discharge. The discharge capacity was measured based on the discharge amount at this time, and the discharge capacity was divided by the area of the positive electrode, and the positive electrode capacitance A (mAh/cm ² ) was calculated.

(j) Determination of negative electrode capacitance

Using the test battery of the above (h) containing the pair of lithium and the negative electrode, charging was performed at a constant current of 0.3 mA (the process of doping Li into the carbon material), and after reaching 0 V, charging was performed at a constant voltage of 0 V, at a current At the time of attenuation to 0.03 mA, the charging is terminated. Then, discharge was performed at a constant current of 0.3 mA (the process of de-doping Li from the carbon material), and discharge was performed until 1.5 V was reached. The discharge capacity was measured based on the discharge amount at this time, and the discharge capacity was divided by the area of the negative electrode to calculate the negative electrode capacitance B (mAh/cm ² ). Thereby, the capacitance ratio A/B is calculated.

(Examples 2 to 3)

An NCM positive electrode was used in the same manner as in Example 1. The negative electrode active material is a non-graphitizable carbon obtained by changing the degree of non-melting using an isotropic pitch as a raw material to prepare a precursor, and pulverizing and heat-treating the precursor. A test battery and a full battery including a negative electrode of NCM and a negative electrode of a carbonaceous material were produced under the same production conditions as in Example 1 except that the thickness of the negative electrode and the thickness of the positive electrode were changed, and the same evaluation items were measured.

In Example 2, the potential of the test cell prepared by disassembling the entire battery in a charged state was 27 mV.

(Example 4)

A test battery and a full battery were produced in the same manner as in Example 3 except that the pulverization conditions of the carbon precursor of Example 3 were changed to obtain non-graphitizable carbon having different average particle diameters, and the thickness of the negative electrode and the thickness of the positive electrode were changed. And determine the same assessment item.

(Example 5)

The LCO was produced by using the same negative electrode active material as the positive electrode active material (LiCoO ₂ ) (LCO) as the positive electrode active material and changing the thickness of the positive electrode, in the same manner as in Example 3 except that the negative electrode prepared in Example 3 was used. The test battery and the full battery of the positive electrode and the negative electrode of the carbonaceous material were measured, and the same evaluation items were measured.

(Example 6)

Using the negative electrode prepared in Example 3, using lithium iron phosphate (LiFePO ₄ ) (LFP) as a positive electrode active material and changing the thickness of the positive electrode, a positive electrode and carbon having LFP were produced under the same production conditions as in Example 3. Test battery and full battery of the negative electrode of the material. The constant voltage at the time of charging the entire battery was changed from 4.2 V to 3.6 V, the charging upper limit voltage was changed to 3.6 V, and the discharge end voltage was changed to 2.0 V, and the same as Example 1 (NCM positive electrode). In the case of the same conditions, a charge and discharge test is performed, and a specific evaluation item is measured.

(Example 7)

In the same manner as in Example 3, the negative electrode prepared in Example 3 was used, and the spinel-type lithium manganate composite oxide (LiMn ₂ O ₄ ) (LMO) was used as the positive electrode active material to change the thickness of the positive electrode. Production conditions: A test battery and a full battery including a positive electrode of LMO and a negative electrode of a carbonaceous material were produced. The charge and discharge test was carried out under the same conditions as in the case of Example 1 (NCM positive electrode) except that the constant voltage at the time of charging the entire battery was changed from 4.24 V to 4.15 V and the charge upper limit voltage was changed to 4.15 V. And determine the specific evaluation item.

(Example 8)

A test battery and a full battery including a negative electrode of a positive electrode and a carbonaceous material of NCM were produced by using the same conditions as in Example 3 except that the thickness of the positive electrode and the thickness of the negative electrode were changed using the non-graphitizable carbon obtained in Example 3. And determine the same assessment item.

(Example 9)

The negative electrode active material is a non-graphitizable carbon obtained by using an isotropic pitch as a raw material to produce a precursor having a non-melting degree and pulverizing and heat-treating the precursor. A test battery and a full battery including a negative electrode of NCM and a negative electrode of a carbonaceous material were produced under the same production conditions as in Example 1 except that the thickness of the positive electrode and the thickness of the negative electrode were changed, and the same evaluation items were measured.

(Embodiment 10)

A test cell and a full cell were produced in the same manner as in Example 9 except that the pulverization conditions of the carbon precursor of Example 9 were changed to obtain non-graphitizable carbon having a different average particle diameter, and the same battery was used. Evaluation project.

(Comparative Example 1)

The negative electrode active material is a non-graphitizable carbon obtained by using an isotropic pitch as a raw material to produce a precursor having a non-melting degree and pulverizing and heat-treating the precursor. A test battery and a full battery including a negative electrode of NCM and a negative electrode of a carbonaceous material were produced under the same production conditions as in Example 1 except that the thickness of the positive electrode was changed, and the same evaluation items were measured.

(Comparative Example 2)

A test cell and a full battery of a negative electrode including a positive electrode of LCO and a negative electrode of a carbonaceous material were produced under the same production conditions as in Example 5 except that the thickness of the positive electrode and the thickness of the negative electrode were changed in the same manner as in Example 3. The same evaluation items were measured under the same conditions as in Example 5.

(Comparative Example 3)

A test battery and a full battery including a positive electrode of LFP and a negative electrode of a carbonaceous material were produced by using the same conditions as in Example 6 except that the thickness of the positive electrode and the thickness of the negative electrode were changed in the same manner as in Example 3. The same evaluation items were measured under the same conditions as in Example 6.

(Comparative Example 4)

A test battery and a full battery including a positive electrode of LMO and a negative electrode of a carbonaceous material were produced by using the same conditions as in Example 7 except that the thickness of the positive electrode and the thickness of the negative electrode were changed in the same manner as in Example 3. The same evaluation item was measured under the same conditions as in Example 7.

(Comparative examples 5 to 6)

A test battery and a full battery including a positive electrode of NCM and a negative electrode of a carbonaceous material were produced by using the same conditions as in Example 1 except that the thickness of the positive electrode and the thickness of the negative electrode were changed in the same manner as in Example 3. The same evaluation items were measured under the same conditions as in Example 1.

(Comparative Example 7)

A test battery and a full battery including a negative electrode of a positive electrode of LCO and a negative electrode of a carbonaceous material were produced by using the same conditions as in Example 5 except that the thickness of the positive electrode and the thickness of the negative electrode were changed in the same manner as in Example 3. The same evaluation items were measured under the same conditions as in Example 5.

(Comparative Example 8)

A test cell and a full cell including a negative electrode of a positive electrode and a carbonaceous material of NCM were produced by using the same conditions as in Example 1 except that the thickness of the positive electrode and the thickness of the negative electrode were changed in the same manner as in Example 4. The same evaluation items were measured under the same conditions as in Example 1.

(Comparative Example 9)

The negative electrode active material is a non-graphitizable carbon obtained by using an isotropic pitch as a raw material to change a pre-melting degree precursor and pulverizing and heat-treating the precursor. A test battery and a full battery including a negative electrode of NCM and a negative electrode of a carbonaceous material were produced under the same production conditions as in Example 1 except that the thickness of the negative electrode was changed, and the same evaluation items were measured.

The results of the measurements of the examples and comparative examples are shown in Table 1. The input density has been normalized to the value of Example 1.

In Examples 1 to 10, the true density (ρ _Bt ) of the negative electrode active material is in the range of 1.45 to 1.70 g/cm ³ , and the ratio of the positive electrode capacitance to the negative electrode capacitance (A/B) is in the range of 0.4 to 0.8, and the positive electrode capacitance A It is a battery of 3.0 mAh/cm ² or less. Both exhibit high input density per unit weight and high capacity retention.

On the other hand, since the true density (ρ _Bt ) of the carbonaceous material of the negative electrode active material in Comparative Example 1 was higher than 1.70 g/cm ³ , the capacity retention ratio was low. In Comparative Examples 2 to 6, the capacitance ratio A/B did not reach 0.4 or exceeded 0.8, so the input density per unit weight or the capacity retention ratio was low. In Comparative Examples 7 and 8, the positive electrode capacitance A exceeded 3.0 mAh/cm ² , and therefore, the input density ratio and the capacitance retention ratio per unit weight were low. The carbonaceous material of the negative electrode active material in Comparative Example 9 has a true density (ρ _Bt ) of less than 1.45 g/cm ³ , and thus the capacity retention ratio is low.

Further, in the examples, when the thickness of the negative electrode active material layer is 45 μm or less, or the average particle diameter (Dv ₅₀ ) is 4.5 μm or less, the input/output characteristics and cycle characteristics are particularly good. The thickness of the negative electrode active material layer in Comparative Example 6 was 45 μm or less, but the capacitance ratio (A/B) exceeded 0.8, and thus the cycle characteristics were lowered. In Comparative Examples 2 to 7, and 9, the average particle diameter was 4.5 μm or less. However, the capacitance ratio (A/B), the positive electrode capacitance A, or the true density (ρ _Bt ) were outside the range of the present invention, and thus the cycle characteristics were lowered.

As described above, it was confirmed that Examples 1 to 10 having the configuration of the present invention maintain excellent cycle characteristics and can realize high output characteristics.

Claims (3)

A nonaqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material composed of a transition metal complex oxide containing lithium, a negative electrode including a negative electrode active material containing a carbonaceous material, and a nonaqueous electrolyte, wherein : The positive electrode capacitance is 3.0 mAh/cm ² or less (the capacitance when the counter electrode is Li metal), and the true density of the carbonaceous material obtained by the butanol method is 1.45 to 1.70 g/cm ³ , and the opposite positive electrode capacitor A The ratio (A/B) to the negative electrode capacitance B is 0.4 to 0.8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material layer in the negative electrode has a thickness of 45 μm or less. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the carbonaceous material has an average particle diameter (Dv ₅₀ ) of 4.5 μm or less.