JP7467162B2 - Nonaqueous electrolyte battery and battery pack - Google Patents

Description

Embodiments of the present invention relate to non-aqueous electrolyte batteries and battery packs.

Secondary batteries, including lithium-ion secondary batteries, are widely used in portable devices, vehicles such as automobiles, and storage batteries. Secondary batteries are power storage devices whose market size is expected to expand.

The secondary battery includes electrodes including a positive electrode and a negative electrode. The secondary battery may further include an electrolyte. A design of the electrode of the secondary battery includes a current collector and an active material-containing layer provided on a main surface of the current collector. The active material-containing layer of the electrode may be, for example, a layer composed of active material particles, a conductive agent, and a binder, and may be a porous body capable of retaining an electrolyte.

One example of an active material used in the positive electrode of a lithium-ion battery or secondary battery is lithium-containing manganese oxide. A lithium-ion secondary battery that uses lithium-containing manganese oxide in the positive electrode and lithium titanate in the negative electrode has excellent low-temperature output and life performance.

International Publication No. 2016/132436 International Publication No. 2016/143123

The objective is to provide a non-aqueous electrolyte battery with excellent charge/discharge cycle life, and a battery pack equipped with this battery.

According to an embodiment, there is provided a non-aqueous electrolyte battery including a positive electrode, a negative electrode including a negative electrode active material containing layer containing lithium titanate having a spinel structure as a lithium titanium-containing oxide, and a non-aqueous electrolyte, and satisfying the following formula (1): The positive electrode includes a positive electrode active material containing layer containing a positive electrode active material including a lithium-containing manganese oxide and a lithium-containing nickel cobalt manganese oxide. The content of the lithium-containing nickel cobalt manganese oxide in the positive electrode active material is 3 wt % or more and 20 wt % or less.
0.005≦(G _Co /S _Co )/(G _Ti /S _Ti )≦0.15 (1)
Here, G _Co is the weight (mg) of Co contained in the positive electrode active material-containing layer, S _Co is the area (cm ² ) of the positive electrode active material-containing layer, G _Ti is the weight (mg) of Ti contained in the negative electrode active material-containing layer, and S _Ti is the area (cm ² ) of the negative electrode active material-containing layer.
In addition, the open circuit voltage of the positive electrode when the nonaqueous electrolyte battery is discharged at 0.2 C to 1.8 V is 3.6 V (vs. Li/Li ⁺ ) or more and 3.9 V (vs. Li/Li ⁺ ) or less.

According to another embodiment, a battery pack including the nonaqueous electrolyte battery according to the above embodiment is provided.

FIG. 2 is a partially cutaway perspective view showing an example of a battery according to an embodiment. FIG. 2 is an enlarged cross-sectional view of a portion A of the battery shown in FIG. 1 . FIG. 4 is a partially cutaway perspective view showing another example of a battery according to an embodiment. FIG. 13 is a partially cutaway perspective view showing still another example of a battery according to an embodiment. FIG. 5 is an enlarged cross-sectional view of a portion B of the battery shown in FIG. 4 . FIG. 2 is an exploded perspective view showing an example of a battery pack according to an embodiment. FIG. 7 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 6 . 1 is a graph showing a discharge potential curve of a positive electrode A including only a first positive electrode active material as an active material. 13 is a graph showing a discharge potential curve of a positive electrode B including only a second positive electrode active material as an active material. 1 is a graph showing a discharge potential curve of a positive electrode C including a first positive electrode active material and a second positive electrode active material as active materials. 4 is a graph showing charge/discharge potential curves of the positive electrode and negative electrode of a nonaqueous electrolyte battery according to an embodiment including a positive electrode C. 4 is a graph showing charge/discharge potential curves of the positive electrode and negative electrode of a nonaqueous electrolyte battery according to an embodiment including a positive electrode C.

Lithium-ion secondary batteries, which use lithium-containing manganese oxide for the positive electrode and lithium titanate for the negative electrode, have excellent low-temperature output and life performance. However, such batteries have the problem of gas generation. In addition, there is the problem of deterioration of battery performance due to Mn elution from the positive electrode.

As a countermeasure against gas generation, active materials with layered structures can be added. Among such active materials, lithium-containing cobalt oxide acts as a gas adsorbent, so gas generation can be reduced by using both lithium-containing manganese oxide and lithium-containing cobalt oxide as the positive electrode active material.

However, lithium-containing cobalt oxide has the problem of being significantly degraded at high potential. Therefore, the use of lithium-containing nickel-cobalt-manganese oxide as an alternative to lithium-containing cobalt oxide is being considered. Lithium-containing nickel-cobalt-manganese oxide has a problem with cycle life performance because it expands and contracts significantly when absorbing and releasing lithium ions.

The following describes the embodiments with reference to the drawings. Note that common components throughout the embodiments are given the same reference numerals, and duplicate explanations will be omitted. Also, each figure is a schematic diagram to facilitate the explanation and understanding of the embodiments, and the shapes, dimensions, ratios, etc. may differ from the actual device in some places, but these can be appropriately modified in design by taking into account the following explanation and known technology.

First Embodiment
According to a first embodiment, a non-aqueous electrolyte battery is provided that includes a positive electrode including a positive electrode active material-containing layer, a negative electrode including a negative electrode active material-containing layer, and a non-aqueous electrolyte. The positive electrode active material-containing layer includes a positive electrode active material including a lithium-containing manganese oxide as a first positive electrode active material and a lithium-containing nickel-cobalt-manganese oxide as a second positive electrode active material. The content of the second positive electrode active material in the positive electrode active material is 3 wt% or more and 20 wt% or less. The negative electrode active material-containing layer includes a lithium titanium-containing oxide. The non-aqueous electrolyte battery satisfies the following formula (1).

0.005≦(G _Co /S _Co )/(G _Ti /S _Ti )≦0.15 (1)
Here, G _Co is the weight (mg) of Co contained in the positive electrode active material-containing layer, S _Co is the area (cm ² ) of the positive electrode active material-containing layer, G _Ti is the weight (mg) of Ti contained in the negative electrode active material-containing layer, and S _Ti is the area (cm ² ) of the negative electrode active material-containing layer.

The reasons for setting the content of the second positive electrode active material in the positive electrode active material within the above range and for specifying the ratio (G _Co /S _Co )/(G _Ti /S _Ti ) within the range of formula (1) will be explained below.
If the content is less than 3 wt%, or if the ratio value represented by ( _GCo / _SCo )/( _GTi / _STi ) is less than 0.005, the gas generated by the reduction decomposition of the non-aqueous electrolyte in the negative electrode cannot be absorbed by the positive electrode, resulting in poor cycle performance. If the content exceeds 20 wt%, the cycle performance is poor. On the other hand, if the ratio value represented by ( _GCo / _SCo )/( _GTi / _STi ) exceeds 0.15, the cycle performance is poor regardless of the magnitude of deviation between the initial charge potential curve and the discharge potential curve of the positive electrode.

For the reasons explained above, by setting the content of the second positive electrode active material in the positive electrode active material within the above range and specifying the ratio of (G _Co /S _Co )/(G _Ti /S _Ti ) within the range of formula (1), it is possible to improve the cycle performance.

The content of the second positive electrode active material in the positive electrode active material is more preferably in the range of 4 wt % to 10 wt %. The ratio represented by (G _Co /S _Co )/(G _Ti /S _Ti ) is more preferably in the range of 0.01 to 0.08. By specifying the content or ratio of the second positive electrode active material in this range, or specifying both values, the cycle performance can be further improved.

The (G _Co /S _Co )/(G _Ti /S _Ti ) value can be set to a desired value by adjusting the composition of each of the first and second positive electrode active materials, the weight ratio of the second positive electrode active material in the positive electrode active material, the composition of the negative electrode active material, the composition of the negative electrode active material-containing layer, or the basis weight (g/m ² ) of each of the positive and negative electrodes.

It is desirable to set the open circuit voltage of the positive electrode when the nonaqueous electrolyte battery is discharged to 1.8 V at 0.2 C to 3.6 V (vs. Li/Li ⁺ ) or more and 3.9 V (vs. Li/Li ⁺ ) or less. By setting the open circuit voltage to 3.6 V (vs. Li/Li ⁺ ) or more, it is possible to suppress the deterioration of the positive electrode due to overdischarge. In addition, by setting the open circuit voltage to 3.9 V (vs. Li/Li ⁺ ) or less, it is possible to use the range in which the open circuit voltage of the positive electrode is higher than 3.9 V (vs. Li/Li ⁺ ) as the charge/discharge region, so that a high capacity can be obtained. A more preferable range of the open circuit voltage of the positive electrode when the nonaqueous electrolyte battery is discharged to 1.8 V at 0.2 C is 3.65 V (vs. Li/Li ⁺ ) or more and 3.80 V (vs. Li/Li ⁺ ) or less.

8 to 12 show the discharge potential curves or charge/discharge potential curves of the electrodes. The positive electrode potential is that when the positive electrode is charged to 4.25 V at 0.2 C by constant current constant voltage (CCCV) and then discharged to 3.1 V at 0.2 C. The negative electrode potential is that when the negative electrode is charged to 1.4 V at 0.2 C by CCCV and then discharged to 2 V at 0.2 C. FIG. 8 shows the discharge potential curve of a positive electrode (hereinafter, cathode A) including a positive electrode active material consisting of only a first positive electrode active material, FIG. 9 shows the discharge potential curve of a positive electrode (hereinafter, cathode B) including a positive electrode active material consisting of only a second positive electrode active material, and FIG. 10 shows the discharge potential curve of a positive electrode (hereinafter, cathode C) including a positive electrode active material consisting of a first positive electrode active material and a second positive electrode active material, the content of the second positive electrode active material being 10 wt%. In the graphs of FIG. 8 to FIG. 10, the horizontal axis indicates DOD (degree of discharge), and the vertical axis indicates the positive electrode potential V (vs. Li/Li ⁺ ). As shown in FIG. 8, the potential of the positive electrode A is 4.0 V (vs. Li/Li ⁺ ) or more until the DOD reaches about 90%, and drops steeply to about 3.0 V (vs. Li/Li ⁺ ) when the DOD reaches about 100%. As shown in FIG. 9, the potential of the positive electrode B drops almost continuously as the DOD progresses. Also, as shown in FIG. 10, the potential of the positive electrode C is 3.8 V or more until the DOD reaches about 90%, and drops steeply near 100%. A positive electrode having such a characteristic potential can be obtained, for example, by mixing a first positive electrode active material and a second positive electrode active material, and setting the content of the second positive electrode active material in the positive electrode active material to 3 wt % or more and 20 wt % or less. By using this positive electrode and a negative electrode containing a lithium-titanium-containing oxide and adjusting the manufacturing conditions such as the composition of the non-aqueous electrolyte and the aging conditions, the open circuit voltage of the positive electrode when the non-aqueous electrolyte battery is discharged to 1.8 V at 0.2 C can be made to be 3.6 V (vs. Li/Li ⁺ ) or more and 3.9 V (vs. Li/Li ⁺ ) or less.

Among the nonaqueous electrolyte batteries according to the embodiment including the positive electrode C and the negative electrode containing a lithium titanium-containing oxide, the charge/discharge potential curves of the nonaqueous electrolyte battery that satisfies the above open circuit voltage are shown in Fig. 11, and the charge/discharge potential curves of the nonaqueous electrolyte battery that does not satisfy the above open circuit voltage are shown in Fig. 12. The horizontal axis of Fig. 11 and Fig. 12 indicates the battery capacity (Ah), and the vertical axis indicates the potential V (vs. Li/Li ⁺ ).
11, the charge/discharge potential curve of the positive electrode C is indicated by _P1 , and the charge/discharge potential curve of the negative electrode is indicated by _N1 . When the potential difference between _P1 and _N1 is 1.8 V, the open circuit voltage of the positive electrode is, for example, 3.64 V (vs. Li/Li ⁺ ). As overdischarge progresses, the positive electrode potential _P1 decreases while the negative electrode potential _N1 also increases, so that overdischarge can be stopped before the positive electrode potential _P1 drops too far.

12, the charge/discharge potential curve of the positive electrode A is indicated by _P2 , and the charge/discharge potential curve of the negative electrode is indicated by _N2 . When the potential difference between _P2 and _N2 is 1.8 V, the open circuit voltage of the positive electrode is smaller than 3.6 V (vs. Li/Li ⁺ ) (e.g., 3.55 V (vs. Li/Li ⁺ )). In this case, as overdischarge progresses, the positive electrode potential _P2 tends to decrease.
In addition, when the charge capacity per unit area when the charge/discharge range of the positive electrode is 3.0 V (vs. Li/Li ⁺ ) to 4.25 V (vs. Li/Li ⁺ ) is A (mAh/m ² ), and when the charge/discharge range of the negative electrode is 1.4 V (vs. Li/Li ⁺ ) to 2.0 V (vs. Li/Li ⁺ ) is B (mAh/m ² ), it is desirable that the nonaqueous electrolyte battery satisfies 0.9≦A/B≦1.1 (2). Increasing the charge capacity ratio (A/B) has little effect on the overdischarge of the positive electrode, but the positive electrode potential is less likely to increase, making it less likely to be overcharged and improving the cycle characteristics. Therefore, by the battery satisfying the formula (2): 0.9≦A/B≦1.1, the cycle performance of the battery can be improved.

The battery according to the embodiment will be described in detail below.
(1) Positive Electrode The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer supported on one or both surfaces of the positive electrode current collector.

The positive electrode active material-containing layer contains lithium-containing manganese oxide as a first positive electrode active material and lithium-containing nickel-cobalt-manganese oxide as a second positive electrode active material. The content of lithium-containing nickel-cobalt-manganese oxide in the positive electrode active material-containing layer is 3 wt% or more and 20 wt% or less.

The lithium-containing manganese oxide includes, for example, lithium manganese oxide _spinel , which is a compound represented by the chemical formula LiMn2 _{- xMxO4} , where M is at least one selected from the group consisting of Mg, Ti, Cr, Fe, Co, Zn, Al, and Ga. The subscript x is 0.22 or more and 0.7 or less. Hereinafter, the lithium-containing manganese oxide may be referred to as "LMO".

Lithium-containing nickel cobalt _{manganese oxides} include, for example, LiNi1 _{-yzCoyMnzO2 ,} where 0<y<1, 0<z<1, and 0<y+z<1.

The positive electrode active material may include other positive electrode active materials other than the first and second positive electrode active materials. The other positive electrode active materials may include, for example, one or more compounds selected from the group consisting of lithium-containing cobalt oxide, lithium-containing nickel cobalt composite oxide, and lithium-containing manganese cobalt oxide. An example of the lithium-containing cobalt oxide includes Li _w CoO _2. The range of the subscript w in the chemical formula Li _w CoO ₂ is 0<w≦1. An example of the lithium nickel cobalt composite oxide includes LiNi _1-y Co _y O ₂ (where 0<y<1). An example of the lithium manganese cobalt oxide includes LiMn _y Co _1-y O ₂ (where 0<y<1).

The positive electrode active material is, for example, particulate. If particulate, the positive electrode active material may be primary particles or secondary particles formed by agglomeration of primary particles.

The average particle size of the particles of the first positive electrode active material is preferably 0.01 μm or more and 10 μm or less. The average particle size of the particles of the second positive electrode active material is preferably 0.05 μm or more and 30 μm or less.

The positive electrode active material-containing layer may contain a binder and a conductive agent as necessary.

The binder can bind the active material and the conductive agent. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or fluorine-based rubber. The type of binder used can be one or more types.

The conductive agent can increase electronic conductivity and reduce contact resistance with the current collector. Examples of conductive agents include carbon materials such as acetylene black, carbon black, graphite, carbon nanofibers, and carbon nanotubes. One or more types of conductive agents can be used.

The mixing ratio of the positive electrode active material, conductive agent, and binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 18% by weight of the conductive agent, and 2 to 7% by weight of the binder.

For example, a sheet containing a material with high electrical conductivity can be used as the current collector. For example, an aluminum foil or an aluminum alloy foil can be used as the current collector. When an aluminum foil or an aluminum alloy foil is used, the thickness is preferably 20 μm or less. The aluminum alloy foil can contain magnesium (Mg), titanium (Ti), zinc (Zn), manganese (Mn), silicon (Si), and the like. The aluminum alloy foil may also contain other transition metals. The content of the transition metal in the aluminum alloy foil is preferably 1 mass% or less. Examples of transition metals include iron (Fe), copper (Cu), nickel (Ni), and chromium (Cr). The current collector is preferably an aluminum foil or an aluminum alloy foil containing aluminum and one or more elements selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si.

The current collector may include a portion on its surface that does not carry an active material-containing layer. This portion may, for example, serve as an electrode current collecting tab. Alternatively, the electrode may further include an electrode current collecting tab that is separate from the electrode current collector. The separate electrode current collecting tab may be electrically connected to the electrode.

The thickness of the positive electrode is preferably 100 μm or less. Here, the thickness of the positive electrode is the total thickness of the positive electrode active material-containing layer and the positive electrode current collector. When the positive electrode active material-containing layer is supported on both sides of the positive electrode current collector, the total thickness of the two positive electrode active material-containing layers and the positive electrode current collector is the positive electrode thickness. By making the thickness of the positive electrode 100 μm or less, the resistance of the positive electrode can be reduced, and therefore the overvoltage applied to the positive electrode can be reduced. This can suppress the decrease in the positive electrode potential at the end of discharge, and therefore the deterioration due to overdischarge of the positive electrode can be suppressed. In order to ensure a practical battery capacity, the thickness of the positive electrode is preferably 30 μm or more.

The density of the positive electrode active material-containing layer is preferably 2.5 g/cc or more and 3.1 g/cc or less. This ensures that the positive electrode capacity can be used in practical applications even if the positive electrode is thin, for example, 100 μm or less.

The basis weight of the positive electrode active material-containing layer, that is, the weight per unit area (g/m ² ), can be set to 30 g/m ² or more and 130 g/m ² or less.

In the manufacture of the positive electrode, for example, a positive electrode active material, a positive electrode conductive agent, and a binder are first suspended in a suitable solvent, and the resulting slurry is applied to a positive electrode current collector and dried to form a positive electrode active material-containing layer, which is then pressed. Alternatively, the positive electrode active material, the positive electrode conductive agent, and the binder may be formed into pellets to be used as the positive electrode active material-containing layer.
(2) Negative Electrode The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer supported on one or both surfaces of the negative electrode current collector. The negative electrode active material-containing layer includes a lithium-titanium-containing oxide.

The negative electrode current collector may include a portion that does not carry a negative electrode active material-containing layer on its surface. This portion may act as a negative electrode tab. Alternatively, the negative electrode may include a negative electrode tab that is separate from the negative electrode current collector.

Examples of the lithium titanium-containing oxide include lithium titanium oxide, lithium titanium composite oxide in which a part of the constituent elements of the lithium titanium oxide is replaced with a different element, orthorhombic lithium titanium-containing oxide, and monoclinic lithium niobium titanium-containing oxide. Examples of the lithium titanium oxide include lithium titanate having a spinel structure (e.g., Li _4+x Ti ₅ O ₁₂ (x is a value that changes with charging and discharging, 0≦x≦3)), lithium titanate of ramsdellite structure (e.g., Li _2+y Ti ₃ O ₇ (y is a value that changes with charging and discharging, 0≦y≦3)), and the like. On the other hand, the molar ratio of oxygen is formally shown as 12 in the spinel type Li _4+x Ti ₅ O ₁₂ and 7 in the ramsdellite type Li _2+y Ti ₃ O ₇ , but these values may change due to the influence of oxygen nonstoichiometry and the like. The type of the negative electrode active material can be one or more types.

Examples of orthorhombic lithium titanium-containing oxides include compounds represented by the general formula Li2 _{+wNa2 - xM1yTi6 - zM2zO14 +δ} , where M1 is Cs and/or K, and M2 is at least one of Zr, Sn, V, Nb, Ta, Mo, W, Fe, Co, Mn, and Al, and 0≦w≦4, 0≦x≦2, 0≦y≦2, 0≦z<6, and −0.5≦δ≦0.5.

Examples of the monoclinic lithium niobium titanium-containing oxide include compounds represented by the general formula Li _x Ti _1-y M3 _y Nb _2-z M4 _z O _7+δ , where M3 is at least one selected from the group consisting of Zr, Si, Sn, Fe, Co, Mn, and Ni, and M4 is at least one selected from the group consisting of V, Nb, Ta, Mo, W, and Bi, and where 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

The lithium titanium-containing oxide is, for example, in particulate form. When in particulate form, the lithium titanium-containing oxide may be primary particles or secondary particles formed by agglomeration of the primary particles.

The average particle size of the lithium titanium-containing oxide particles is preferably 0.01 μm or more and 10 μm or less.

The negative electrode active material-containing layer may contain a conductive agent and a binder as necessary.

Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide, polyamide, etc. One or more types of binders can be used.

Examples of negative electrode conductive agents include carbon black such as acetylene black and ketjen black, graphite, carbon fiber, carbon nanotubes, fullerenes, etc. The conductive agent may be one type or two or more types.

The mixing ratio of the negative electrode active material, conductive agent, and binder in the negative electrode active material-containing layer is preferably 70% by weight or more and 96% by weight or less of the negative electrode active material, 2% by weight or more and 28% by weight or less of the conductive agent, and 2% by weight or more and 28% by weight or less of the binder.

The density of the negative electrode active material-containing layer is preferably 2.0 g/cm ³ or more.

The current collector is preferably an aluminum foil or an aluminum alloy foil. When an aluminum foil or an aluminum alloy foil is used, the thickness is preferably 20 μm or less. The aluminum alloy foil may contain magnesium (Mg), titanium (Ti), zinc (Zn), manganese (Mn), silicon (Si), and the like. The aluminum alloy foil may also contain other transition metals. The content of the transition metal in the aluminum alloy foil is preferably 1 mass% or less. Examples of transition metals include iron (Fe), copper (Cu), nickel (Ni), and chromium (Cr). The current collector is preferably an aluminum foil or an aluminum alloy foil containing aluminum and one or more elements selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si.

The negative electrode is produced, for example, by suspending the negative electrode active material, the negative electrode conductive agent, and the binder in a suitable solvent, applying the resulting slurry to the negative electrode current collector, drying it, and producing a layer containing the negative electrode active material, followed by pressing. Alternatively, the negative electrode active material, the negative electrode conductive agent, and the binder may be formed into pellets and used as the layer containing the negative electrode active material.

The thickness of the negative electrode can be in the range of 20 μm to 80 μm. Here, the thickness of the negative electrode is the total thickness of the negative electrode active material-containing layer and the negative electrode current collector. When the negative electrode active material-containing layer is supported on both sides of the negative electrode current collector, the total thickness of the two negative electrode active material-containing layers and the negative electrode current collector is the negative electrode thickness.

The negative electrode active material-containing layer can have a basis weight, that is, a weight per unit area (g/m ² ), of 10 g/m ² or more and 80 g/m ² or less.
(3) Nonaqueous Electrolyte Examples of the nonaqueous electrolyte include a liquid nonaqueous electrolyte prepared by dissolving an electrolyte in a nonaqueous solvent, and a gel-like nonaqueous electrolyte prepared by combining a liquid nonaqueous electrolyte with a polymer material.

Examples of the electrolyte include lithium salts such as lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium trifluoromethasulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN(CF ₃ SO ₂ ) ₂ ], lithium aluminum tetrafluoride (LiAlF ₄ ), and lithium difluorobisoxalate phosphate (LiDFBOP) shown in Chemical Formula 1 below. These electrolytes may be used alone or in combination of two or more. The electrolyte preferably contains lithium hexafluorophosphate. A more preferred electrolyte contains lithium hexafluorophosphate as the first electrolyte and at least one of lithium tetrafluoroborate and lithium difluorobisoxalate phosphate as the second electrolyte. A non-aqueous electrolyte containing an electrolyte of this composition can form a lithium ion conductive protective film on the surface of the negative electrode. The formation of the protective film can shift the charge/discharge potential of the negative electrode at the end of discharge to the noble side.

It is preferable that the electrolyte be dissolved in the non-aqueous solvent in a range of 0.5 mol/L to 2.5 mol/L.

When the second electrolyte is contained in the non-aqueous electrolyte, the second electrolyte is preferably dissolved in the non-aqueous solvent in a range of 0.01 mol/L or more and 0.5 mol/L or less. By making the concentration of the second electrolyte 0.01 mol/L or more, a lithium ion conductive protective film can be formed uniformly on the negative electrode surface. By making the concentration of the second electrolyte 0.5 mol/L or less, an increase in negative electrode resistance due to the formation of the protective film can be suppressed.

Examples of non-aqueous solvents include organic solvents such as cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC); chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC); cyclic ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2MeTHF); chain ethers such as dimethoxyethane (DME); cyclic esters such as γ-butyrolactone (BL); chain esters such as methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate; acetonitrile (AN); and sulfolane (SL). These organic solvents can be used alone or in the form of a mixture of two or more kinds.

Examples of polymer materials used for the gel-like non-aqueous electrolyte include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

The positive electrode and the negative electrode can form an electrode group. In the electrode group, the positive electrode active material-containing layer and the negative electrode active material-containing layer can face each other, for example, via a separator.

The electrode group can have various structures. For example, the electrode group can have a stacked structure. An electrode group with a stacked structure can be obtained, for example, by stacking multiple positive electrodes and multiple negative electrodes alternately with a separator sandwiched between a positive electrode active material-containing layer and a negative electrode active material-containing layer. Alternatively, the electrode group can have a wound structure. A wound electrode group can be obtained, for example, by stacking one separator, one negative electrode, another separator, and one positive electrode in this order to create a laminate, and then winding this laminate.

The material of the separator is not particularly limited. It is desirable for the separator to have electrical insulation properties. For example, a porous film, a microporous film, a woven fabric, a nonwoven fabric, or a laminate of the same or different materials among these can be used as the separator. For example, the material forming the separator can be polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene copolymer, polyolefin, cellulose, polyethylene terephthalate, vinylon, and other polymers. The separator may be made of one type of material, or a combination of two or more types.

The thickness of the separator is preferably 2 μm or more and 30 μm or less.

The nonaqueous electrolyte battery according to the embodiment may further include a positive electrode terminal and a negative electrode terminal. The positive electrode terminal may function as a conductor for the transfer of electrons between the positive electrode and an external terminal by being electrically connected to a portion of the positive electrode. The positive electrode terminal may be connected, for example, to a positive electrode current collector, particularly a positive electrode tab. Similarly, the negative electrode terminal may function as a conductor for the transfer of electrons between the negative electrode and an external terminal by being electrically connected to a portion of the negative electrode. The negative electrode terminal may be connected, for example, to a negative electrode current collector, particularly a negative electrode tab.

The exterior member contains the electrode group and the non-aqueous electrolyte. The non-aqueous electrolyte may be impregnated into the electrode group within the exterior member. A portion of each of the positive electrode terminal and the negative electrode terminal may extend from the exterior member.

The exterior member may be formed from a laminate film or may be a metal container. When a metal container is used, the lid may be integrated with the container or may be a separate member. The thickness of the metal container is preferably 0.5 mm or less, more preferably 0.2 mm or less. The shape of the exterior member may be flat, rectangular, cylindrical, coin, button, sheet, laminated, etc. In addition to small batteries to be loaded on portable electronic devices, etc., large batteries to be loaded on two- or four-wheeled automobiles may also be used.

The thickness of the laminate film exterior component is desirably 0.2 mm or less. An example of a laminate film is a multilayer film including a resin film and a metal layer disposed between the resin films. The metal layer is preferably aluminum foil or aluminum alloy foil for weight reduction. The resin film may be made of a polymer material such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET). The laminate film can be sealed by heat fusion to form it into the shape of the exterior component.

The metal container is made of aluminum or an aluminum alloy. The aluminum alloy is preferably an alloy containing elements such as magnesium, zinc, and silicon. In aluminum or an aluminum alloy, it is preferable to keep the content of transition metals such as iron, copper, nickel, and chromium to 100 ppm or less in order to dramatically improve long-term reliability and heat dissipation in high-temperature environments.

It is desirable that the metal container made of aluminum or an aluminum alloy has an average crystal grain size of 50 μm or less, more preferably 30 μm or less, and even more preferably 5 μm or less. By making the average crystal grain size 50 μm or less, the strength of the metal container made of aluminum or an aluminum alloy can be dramatically increased, and the container can be made even thinner. As a result, a nonaqueous electrolyte battery that is lightweight, has high output, and has excellent long-term reliability, making it suitable for use in vehicles, etc. can be realized.

Next, specific examples of nonaqueous electrolyte batteries according to embodiments will be described with reference to the drawings.

First, a nonaqueous electrolyte battery according to a first embodiment will be described with reference to Figures 1 and 2.

Figure 1 is a partially cutaway perspective view of an example of a nonaqueous electrolyte battery according to an embodiment. Figure 2 is an enlarged cross-sectional view of part A of the nonaqueous electrolyte battery shown in Figure 1.

The nonaqueous electrolyte battery 100 shown in Figures 1 and 2 includes a flat electrode group 1 and an exterior member 7 made of a laminate film. The flat electrode group 1 includes a negative electrode 2, a positive electrode 3, and a separator 4. The flat electrode group 1 is formed by winding the negative electrode 2 and the positive electrode 3 in a flat shape with the separator 4 between them.

As shown in FIG. 2, the negative electrode 2 comprises a negative electrode collector 2a and a negative electrode active material-containing layer 2b supported on the negative electrode collector 2a. As shown in FIG. 2, in the outermost portion of the negative electrode 2, the negative electrode active material-containing layer 2b is not supported on the main surface of the two main surfaces of the negative electrode collector 2a that does not face the positive electrode 3. In the other portions of the negative electrode 2, the negative electrode active material-containing layer 2b is supported on both main surfaces of the negative electrode collector. As shown in FIG. 2, the positive electrode 3 comprises a positive electrode collector 3a and a positive electrode active material-containing layer 3b supported on the two main surfaces of the positive electrode collector 3a.

A strip-shaped negative electrode terminal 5 is electrically connected to the negative electrode 2. A strip-shaped positive electrode terminal 6 is electrically connected to the positive electrode 3.

The electrode group 1 is housed in an exterior member 7 made of laminate film with the ends of the negative electrode terminal 5 and the positive electrode terminal 6 extending from the exterior member 7. A non-aqueous electrolyte (not shown) is housed in the exterior member 7 made of laminate film. The non-aqueous electrolyte is impregnated into the electrode group 1. The exterior member 7 made of laminate film is sealed by heat fusing one end of the exterior member 7, with the negative electrode terminal 5 and the positive electrode terminal 6 sandwiched therebetween, and the end and two ends perpendicular to the end.

Next, another example of a battery according to an embodiment will be described in detail with reference to FIG. 3. FIG. 3 is a partially cutaway perspective view showing another example of a battery according to an embodiment.

The battery 100 shown in FIG. 3 differs from the battery 100 shown in FIG. 1 and FIG. 2 in that the exterior member is composed of a metal container 17a and a sealing plate 17b.

The flat electrode group 1 includes a negative electrode, a positive electrode, and a separator, similar to the electrode group 1 in the battery 100 shown in Figures 1 and 2. The electrode group 1 has a similar structure between Figures 1 and 3. However, in Figure 3, instead of the negative electrode terminal 5 and the positive electrode terminal 6, a negative electrode lead 15a and a positive electrode lead 16a are electrically connected to the negative electrode and the positive electrode, respectively, as described below.

In the battery 100 shown in FIG. 3, such an electrode group 1 is housed in a metal container 17a. The metal container 17a further houses an electrolyte (not shown). The metal container 17a is sealed by a metal sealing plate 17b. The metal container 17a and the sealing plate 17b constitute, for example, an exterior can as an exterior member.

One end of the negative electrode lead 15a is electrically connected to the negative electrode collector, and the other end is electrically connected to the negative electrode terminal 15. One end of the positive electrode lead 16a is electrically connected to the positive electrode collector, and the other end is electrically connected to the positive electrode terminal 16 fixed to the sealing plate 17b. The positive electrode terminal 16 is fixed to the sealing plate 17b via an insulating member 17c. The positive electrode terminal 16 and the sealing plate 17b are electrically insulated by the insulating member 17c.

Figures 4 and 5 show a battery including a stacked electrode group as yet another example of a battery. Figure 4 is a partially cutaway perspective view showing yet another example of a battery according to an embodiment. Figure 5 is an enlarged cross-sectional view of part B of the battery shown in Figure 4.

The battery 100 of the example shown in Figures 4 and 5 includes an electrode group 1 shown in Figures 4 and 5, an outer container 7 shown in Figures 4 and 5, a positive electrode terminal 6 shown in Figures 4 and 5, and a negative electrode terminal 5 shown in Figure 4.

The electrode group 1 shown in Figures 4 and 5 includes multiple positive electrodes 3, multiple negative electrodes 2, and one separator 4.

As shown in FIG. 5, each positive electrode 3 includes a positive electrode collector 3a and a positive electrode active material-containing layer 3b formed on both sides of the positive electrode collector 3a. As shown in FIG. 5, the positive electrode collector 3a includes a portion on its surface where the positive electrode active material-containing layer 3b is not formed. This portion functions as a positive electrode collector tab 3c.

Each negative electrode 2 comprises a negative electrode current collector 2a and a negative electrode active material-containing layer 2b formed on both sides of the negative electrode current collector 2a. The negative electrode current collector 2a also includes a portion on its surface where the negative electrode active material-containing layer 2b is not formed (not shown). This portion functions as a negative electrode current collector tab.

As shown in FIG. 5, the separator 4 is zigzag folded. A positive electrode 3 or a negative electrode 2 is disposed in the space defined by the opposing faces of the zigzag folded separator 4. As a result, the positive electrode 3 and the negative electrode 2 are stacked such that the positive electrode active material-containing layer 3b and the negative electrode active material-containing layer 2b face each other with the separator 4 interposed therebetween, as shown in FIG. 5. In this way, an electrode group 1 is formed.

As shown in FIG. 5, the positive electrode current collector tab 3c of the electrode group 1 extends beyond the ends of the positive electrode active material-containing layer 3b and the negative electrode active material-containing layer 2b. As shown in FIG. 5, these positive electrode current collector tabs 3c are joined together and connected to the positive electrode terminal 6. Although not shown, the negative electrode current collector tab of the electrode group 1 also extends beyond the other ends of the positive electrode active material-containing layer 3b and the negative electrode active material-containing layer 2b. Although not shown, these negative electrode current collector tabs are joined together and connected to the negative electrode terminal 5 shown in FIG. 4.

As shown in Figures 4 and 5, such an electrode group 1 is housed in an exterior member consisting of an exterior container 7 made of a laminate film.

The outer container 7 is formed of an aluminum-containing laminate film consisting of an aluminum foil 71 and resin films 72 and 73 formed on both sides of the aluminum foil. The aluminum-containing laminate film forming the outer container 7 is folded at the folding portion 7d so that the resin film 72 faces inward, and contains the electrode group 1. As shown in Figs. 4 and 5, at the peripheral portion 7b of the outer container 7, the facing portions of the resin film 72 sandwich the positive electrode terminal 6 therebetween. Similarly, at the peripheral portion 7c of the outer container 7, the facing portions of the resin film 72 sandwich the negative electrode terminal 5 therebetween. The positive electrode terminal 6 and the negative electrode terminal 5 extend in opposite directions from the outer container 7.

At the peripheral portions 7a, 7b, and 7c of the outer container 7, except for the portions sandwiching the positive electrode terminal 6 and the negative electrode terminal 5, the opposing portions of the resin film 72 are heat-sealed.

In addition, in the battery 100, in order to improve the bonding strength between the positive terminal 6 and the resin film 72, as shown in FIG. 5, an insulating film 9 is provided between the positive terminal 6 and the resin film 72. In addition, at the peripheral portion 7b, the positive terminal 6 and the insulating film 9 are heat-sealed, and the resin film 72 and the insulating film 9 are heat-sealed. Similarly, although not shown, an insulating film 9 is provided between the negative terminal 5 and the resin film 72. In addition, at the peripheral portion 7c, the negative terminal 5 and the insulating film 9 are heat-sealed, and the resin film 72 and the insulating film 9 are heat-sealed. That is, in the battery 100 shown in FIG. 5, all of the peripheral portions 7a, 7b, and 7c of the outer container 7 are heat-sealed.

The outer container 7 further contains an electrolyte (not shown). The electrolyte is impregnated into the electrode group 1.

In the battery 100 shown in Figures 4 and 5, as shown in Figure 5, multiple positive electrode current collector tabs 3c are grouped together in the lowest layer of the electrode group 1. Similarly, although not shown, multiple negative electrode current collector tabs are grouped together in the lowest layer of the electrode group 1. However, for example, multiple positive electrode current collector tabs 3c and multiple negative electrode current collector tabs can be grouped together near the middle of the electrode group 1 and connected to the positive electrode terminal 6 and negative electrode terminal 5, respectively.

According to the nonaqueous electrolyte battery of the first embodiment described above, the battery includes a positive electrode active material-containing layer including a positive electrode active material containing a lithium-containing manganese oxide and a lithium-containing nickel-cobalt manganese oxide, and a negative electrode active material-containing layer including a lithium-titanium-containing oxide. The content of the lithium-containing nickel-cobalt manganese oxide in the positive electrode active material is 3 wt% or more and 20 wt% or less. The nonaqueous electrolyte battery satisfies the following formula (1).

0.005≦(G _Co /S _Co )/(G _Ti /S _Ti )≦0.15 (1)
According to the nonaqueous electrolyte battery, overdischarge of the positive electrode can be suppressed, and the charge/discharge cycle life performance can be improved.

Second Embodiment
According to a second embodiment, a battery pack is provided, the battery pack including the battery according to the first embodiment.

The battery pack according to the embodiment may include a plurality of batteries. The plurality of batteries may be electrically connected in series or in parallel. Alternatively, the plurality of batteries may be electrically connected in a combination of series and parallel. That is, the battery pack according to the embodiment may include a battery assembly. There may be a plurality of battery assemblies. The plurality of battery assemblies may be electrically connected in series, in parallel, or in a combination of series and parallel.

Below, an example of a battery pack according to an embodiment will be described with reference to Figs. 6 and 7. Fig. 6 is an exploded perspective view showing an example of a battery pack according to an embodiment. Fig. 7 is a block diagram showing an example of an electrical circuit of the battery pack shown in Fig. 6.

The battery pack 20 shown in Figures 6 and 7 includes a plurality of cells 21. The cells 21 may be, for example, a flat-type battery 100 according to an embodiment described with reference to Figure 1.

The multiple single cells 21 are stacked so that the negative electrode terminals 5 and positive electrode terminals 6 extending outward are aligned in the same direction, and are fastened together with adhesive tape 22 to form a battery pack 23. These single cells 21 are electrically connected in series with each other as shown in FIG. 7.

The printed wiring board 24 is disposed so as to face the side from which the negative terminal 5 and positive terminal 6 of the single battery 21 extend. As shown in FIG. 7, the printed wiring board 24 is equipped with a thermistor 25, a protection circuit 26, and a terminal 27 for supplying current to an external device. An insulating plate (not shown) is attached to the surface of the printed wiring board 24 facing the assembled battery 23 to prevent unnecessary connection with the wiring of the assembled battery 23.

The positive electrode lead 28 is connected to the positive electrode terminal 6 located on the bottom layer of the battery pack 23, and its tip is inserted into and electrically connected to the positive electrode connector 29 of the printed wiring board 24. The negative electrode lead 30 is connected to the negative electrode terminal 5 located on the top layer of the battery pack 23, and its tip is inserted into and electrically connected to the negative electrode connector 31 of the printed wiring board 24. These connectors 29 and 31 are connected to the protection circuit 26 through wiring 32 and 33 formed on the printed wiring board 24.

The thermistor 25 detects the temperature of the cell 21, and the detection signal is sent to the protection circuit 26. The protection circuit 26 can cut off the positive side wiring 34a and the negative side wiring 34b between the protection circuit 26 and the terminal 27 for supplying electricity to the external device under a predetermined condition. An example of the predetermined condition is when the temperature detected by the thermistor 25 reaches a predetermined temperature or higher. Another example of the predetermined condition is when overcharging, overdischarging, or overcurrent of the cell 21 is detected. This detection of overcharging, etc. is performed for each cell 21 or the entire battery pack 23. When detecting each cell 21, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 21. In the battery pack 20 of FIG. 6 and FIG. 7, wiring 35 for voltage detection is connected to each cell 21. A detection signal is transmitted to the protection circuit 26 through these wirings 35.

A protective sheet 36 made of rubber or resin is disposed on each of the three sides of the battery pack 23, excluding the side from which the positive electrode terminal 6 and the negative electrode terminal 5 protrude.

The battery pack 23 is housed in a container 37 together with each protective sheet 36 and the printed wiring board 24. That is, protective sheets 36 are arranged on both inner surfaces along the long sides and the inner surface along the short side of the container 37, and the printed wiring board 24 is arranged on the inner surface along the other short side on the opposite side across from the battery pack 23. The battery pack 23 is located in a space surrounded by the protective sheets 36 and the printed wiring board 24. A lid 38 is attached to the top surface of the container 37.

In addition, heat shrink tape may be used instead of adhesive tape 22 to secure the battery pack 23. In this case, protective sheets are placed on both sides of the battery pack, the heat shrink tape is wrapped around it, and then the heat shrink tape is thermally shrunk to bind the battery pack.

Although Figures 6 and 7 show a configuration in which the cells 21 are electrically connected in series, they may be electrically connected in parallel to increase the battery capacity. Furthermore, the assembled battery pack may be electrically connected in series and/or parallel.

The configuration of the battery pack according to the embodiment may be changed as appropriate depending on the application. The battery pack according to the embodiment is preferably used in applications where cycle performance in large current charging and discharging is desired. Specific applications include power sources for digital cameras, and in-vehicle applications such as two- to four-wheel hybrid electric vehicles, two- to four-wheel electric vehicles, and power-assisted bicycles. In-vehicle applications are particularly suitable for the battery pack according to the embodiment.

The battery pack according to the second embodiment includes the battery according to the first embodiment. Therefore, the battery pack according to the embodiment has excellent life performance.

Hereinafter, methods for measuring the content of the second positive electrode active material in the positive electrode active material, the (G _Co /S _Co )/(G _Ti /S _Ti ) value, the open circuit voltage of the positive electrode, and the thickness and density of the positive electrode and negative electrode will be described. First, a method for removing the positive electrode will be described.

<How to remove the positive electrode>
The battery is fully discharged to bring the state of charge (SOC) to 0%. The battery is disassembled, and the positive electrode is cut into a size of about 2 cm square. The cut positive electrode is immersed in 50 cc (cm ³ ) of ethyl methyl carbonate and left for 1 hour. The positive electrode is then vacuum dried for 1 hour to obtain a measurement sample. The operations up to this point are carried out in a glove box with an argon atmosphere.

<Measurement of active material composition>
The composition of the active material contained in the electrode can be determined as follows.

The active material-containing layer is peeled off from the electrode to be measured using, for example, a spatula to obtain a powdered sample.

The crystal structure of the active material is identified by powder X-ray diffraction (XRD) measurement of the powdered sample. The measurement is performed using CuKα radiation as the radiation source, with 2θ ranging from 10° to 90°. This measurement makes it possible to obtain the X-ray diffraction pattern of the compound contained in the selected particles.

As an apparatus for powder X-ray diffraction measurement, for example, SmartLab manufactured by Rigaku Co., Ltd. is used. The measurement conditions are as follows:
X-ray source: Cu target Output: 45 kV, 200 mA
Soller slit: 5° for both incidence and reception
Step width: 0.02 deg
Scan speed: 20 deg/min Semiconductor detector: D/teX Ultra 250
Sample plate holder: Flat glass sample plate holder (thickness 0.5 mm)
Measurement range: 10°≦2θ≦90°.

When using other equipment, measurements should be performed using standard Si powder for powder X-ray diffraction to obtain results equivalent to those above, and the conditions should be adjusted so that the peak intensity and peak top position match those of the above equipment.

Next, the sample containing the active material is observed using a scanning electron microscope (SEM). Even during SEM observation, it is desirable to prevent the sample from coming into contact with the air and to perform the observation in an inert atmosphere such as argon or nitrogen.

For example, several particles having the form of primary particles or secondary particles that can be confirmed within the field of view in a 3000x SEM observation image are selected. In this case, the selected particles are selected so that the particle size distribution is as wide as possible. The type and composition of the constituent elements of the active material are identified by EDX analysis of the observed active material particles. This makes it possible to identify the type and amount of elements other than Li contained in each of the selected particles. The same operation is performed on each of the multiple active material particles to determine the mixed state of the active material particles.

Then, the powder sample collected from the active material-containing layer as described above is washed with acetone and dried. The resulting powder is dissolved in hydrochloric acid, the conductive agent is removed by filtration, and then the measurement sample is prepared by diluting with ion-exchanged water. The metal content ratio in the measurement sample is calculated by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis.

When there are multiple types of active materials, the mass ratio is estimated from the content ratio of elements specific to each active material. The ratio of the mass of the specific elements to the active material is determined from the composition of the constituent elements obtained by EDX analysis. For example, the measurement sample obtained from the active material-containing layer may contain lithium-containing nickel-cobalt-manganese oxide as the second active material together with lithium-containing manganese oxide as the first active material. In this case, the chemical formula and formula weight of each of the first and second active materials are calculated from the obtained metal ratio, and the weight ratio of the first and second active materials contained in the active material-containing layer of a predetermined weight taken is obtained. The content of the second active material in the positive electrode active material is obtained from the weight ratio of the first and second active materials.
<Method of measuring (G _Co /S _Co )/(G _Ti /S _Ti ) value>
Method for Analyzing Co in Positive Electrode 1) S _Co (cm ² ) is cut out from the positive electrode and sampled in a beaker.
2) The active material is dissolved using hydrochloric acid and hydrogen peroxide.
3) Filter the solution, collect the filtrate and washings in a measuring flask, and add water up to the mark. This is the sample solution.
4) Preliminary quantification of Co is performed using ICP emission spectrometry, and based on the results, the sample solution is diluted so that the Co concentration becomes 5 to 10 μg/ml (D).
5) Quantify Co by ICP emission spectrometry. At this time, standard solutions with Co concentrations of 0 μg/ml, 5 μg/ml, and 10 μg/ml are used, and quantification is performed by the calibration curve method (C).
6) Calculate the amount of Co using the following formula (2).

G _Co (mg) = C × D × V × 10 ⁻³ (2)
where C is the Co concentration in the diluted solution (μg/ml), D is the dilution ratio, V is the volume of the measuring flask (ml), and 10 ^-3 is the coefficient for converting μg to mg.

Method for Analyzing Ti in a Negative Electrode (1) S _Ti (cm ² ) is cut out from the negative electrode and sampled in a beaker.
(2) The aluminum foil is dissolved using hydrochloric acid.
(3) Sulfuric acid is added and heated to dissolve most of the active material.
(4) After diluting with water, filter the solution, collect the filtrate and washings in a measuring flask A, and add water up to the mark. This is sample solution A. The insoluble portion will be used in the step (5) and subsequent steps.
(5) The insoluble matter is transferred to a platinum crucible together with the filter paper, and then heated using a gas burner and an electric furnace to convert it to ash.
(6) Potassium disulfate is added, and the mixture is heated in an electric furnace to melt the mixture.
(7) Dissolve 10 ml of a solution diluted with 20 volumes of water for every 1 volume of sulfuric acid.
(8) Filter through type 5 C filter paper, collect the filtrate and washings in a measuring flask B, and add water up to the mark. This is sample solution B.
(9) A preliminary quantitative analysis of sample solution A is carried out using ICP emission spectrometry, and based on the results, the sample solution is diluted so that the Ti concentration becomes 5 to 10 μg/ml (DA).
(10) Quantify Ti by ICP emission spectrometry using standard solutions with Ti concentrations of 0 μg/ml, 5 μg/ml, and 10 μg/ml, and quantify using a calibration curve method (CA).
(11) A preliminary quantitative analysis of sample solution B is performed using ICP emission spectrometry, and based on the results, the sample solution is diluted so that the Ti concentration becomes 10 μg/ml or less (DB).
(12) Quantify Ti by ICP emission spectrometry. At this time, use standard solutions containing potassium disulfate at Ti concentrations of 0 μg/ml, 5 μg/ml, and 10 μg/ml, and quantify using the calibration curve method (CB).
(13) Calculate the amount of Ti using the following formula (3).

G _Ti (mg) = CA × DA × VA × 10 ⁻³ + CB × DB × VB × 10 ⁻³ (3)
where CA is the Ti concentration (μg/ml) in the diluted solution of sample solution A, DA is the dilution ratio of sample solution A, VA is the volume of measuring flask A (ml), 10 ^-3 is the coefficient for converting μg to mg, CB is the Ti concentration (μg/ml) in the diluted solution of sample solution B, DB is the dilution ratio of sample solution B, and VB is the volume of measuring flask B (ml).

Calculation method of (G _Co /S _Co )/(G _Ti /S _Ti ) value S _Co (cm ² ) of the positive electrode is calculated by summing the area of the positive electrode active material-containing layer formed on each surface of the positive electrode current collector, and S _Ti (cm ² ) of the negative electrode is calculated by summing the area of the negative electrode active material-containing layer formed on each surface of the negative electrode current collector.

From the values of G _Co , S _Co , G _Ti and S _Ti obtained above, (G _Co /S _Co )/(G _Ti /S _Ti ) is calculated.
<Measurement of open circuit voltage of positive electrode>
The nonaqueous electrolyte battery is charged at 0.2 C to 4.25 V at constant current constant voltage (CCCV), and then discharged at 0.2 C to 1.8 V. Next, the nonaqueous electrolyte battery is disassembled in an Ar atmosphere, and the electrode group is removed. The positive electrode is cut out from the removed electrode group. This positive electrode and metallic Li as the counter electrode are immersed in an electrolyte solution in which 1 mol/L of LiPF ₆ is dissolved in a mixed solvent of ethyl methyl carbonate (EMC) and ethylene carbonate (EC), and the positive electrode potential relative to metallic Li is measured with a tester, and the open circuit voltage V (vs. Li/Li ⁺ ) of the positive electrode when discharged to 1.8 V at 0.2 C is taken as the current value. 1 C is a current value that can charge and discharge the nominal capacity of the nonaqueous electrolyte battery in 1 hour.
<Method of measuring thickness of positive electrode and negative electrode and density of active material-containing layer>
First, the thickness of the electrode is measured using a thickness measuring device, and the obtained value is regarded as the thickness of the positive electrode or negative electrode.
Next, the electrode is punched out to a size of 1 cm x 1 cm using a cutter to obtain an electrode sample. The mass of this electrode sample is then measured. Next, the electrode sample is immersed in a solvent such as N-methylpyrrolidone to remove the active material-containing layer from the electrode sample. The solvent used to peel off the active material-containing layer is not particularly limited as long as it does not corrode the current collector and can peel off the active material-containing layer. Next, the thickness and mass of the current collector sample are measured.

Next, the thickness of the active material-containing layer is calculated by subtracting the thickness of the current collector sample from the thickness of the electrode sample. The volume of the active material-containing layer is calculated from this thickness. The mass of the active material-containing layer is also calculated by subtracting the mass of the current collector sample from the mass of the electrode sample. Next, the density (g/ ^cm3 ) of the active material-containing layer is calculated by dividing the mass of the active material-containing layer by the volume of the active material-containing layer.

The embodiments will be described in detail below.
Example 1
Preparation of Positive Electrode As the positive electrode active material, 90% by weight _of a first positive electrode active material made of lithium-containing manganese oxide particles having an average particle size of 5 μm represented by _{LiMn1.7Al0.3O4} and _{10 %} by _weight of a _second positive electrode active material made of lithium-containing nickel cobalt manganese oxide particles having an average particle size of 5 μm represented by _{LiNi0.5Co0.2Mn0.3O2} were prepared. Acetylene black as a conductive agent and polyvinylidene fluoride (PVdF) as a binder were dispersed in N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5 in the positive electrode active material. The obtained dispersion was applied to a current collector made of aluminum foil having a thickness of 15 μm, dried, and pressed to provide a positive electrode active material-containing layer. The basis weight of one side of the positive electrode, the density of the positive electrode, and the thickness of the positive electrode are shown in Table 1 below.

Preparation of the negative electrode As the negative electrode active material, lithium titanate particles having an average particle size of 3 μm, represented by Li ₄ Ti ₅ O _12, were prepared. The negative electrode active material was dispersed in N-methylpyrrolidone (NMP) at a weight ratio of 95:3:2 with graphite as a conductive agent and polyvinylidene fluoride as a binder. The obtained dispersion was applied to a current collector made of aluminum foil having a thickness of 15 μm, dried, and pressed to provide a negative electrode active material-containing layer. The basis weight of one side of the negative electrode, the density of the negative electrode, and the thickness of the negative electrode are shown in Table 2 below.
A cellulose nonwoven separator with a thickness of 15 μm was prepared as a separator. The separator was wound between the positive and negative electrodes to prepare a spiral electrode group. The electrode group was stored in an aluminum container. This was placed in a dryer and vacuum dried at 95 ° C for 6 hours. After drying, it was transported to a glove box controlled to a dew point of -50 ° C or less. 70 cc of electrolyte solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of ethyl methyl carbonate (MEC) and ethylene carbonate (EC) was poured into the container. The ratio of MEC in the mixed solvent was 70 vol. %, and the ratio of EC was 30 vol. %.
The outer container containing the electrolyte was sealed in a reduced pressure environment of -90 kPa. After the electrolyte was poured in, the battery was initially charged at 1C (10A) to a state of charge (SOC) of 80%, and aged for 24 hours in a thermostatic chamber at 70°C. After aging, the can was opened and sealed again in a reduced pressure environment of -90 kPa to prepare a nonaqueous electrolyte battery.
(Examples 2 to 12)
A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the first positive electrode active material, the second positive electrode active material, the weight ratio between the first and second positive electrode active materials, and the density, basis weight per one side, thickness, and Co/Ti weight ratio for each of the positive electrode and negative electrode were set as shown in Tables 1 to 3.
(Example 13)
As a non-aqueous electrolyte, an electrolyte solution was prepared by dissolving 1 mol/L LiPF ₆ (first electrolyte) and 0.1 mol/L LiBF ₄ (second electrolyte) in a mixed solvent of ethyl methyl carbonate (MEC) and ethylene carbonate (EC). The ratio of MEC in the mixed solvent was 70 vol. %, and the ratio of EC was 30 vol. %.

Using the above nonaqueous electrolyte, a nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the first positive electrode active material, the second positive electrode active material, the weight ratio between the first and second positive electrode active materials, the density, the basis weight and thickness of one side of the positive electrode and the negative electrode, and the Co/Ti weight ratio were set as shown in Tables 1 to 3.
(Examples 14 to 16)
A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the first positive electrode active material, the second positive electrode active material, the weight ratio between the first and second positive electrode active materials, the density, the basis weight and thickness of one side of each of the positive electrode and negative electrode, the type and concentration of the second electrolyte in the nonaqueous electrolyte, and the Co/Ti weight ratio were set as shown in Tables 1 to 3.
(Example 17)
A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the type of the negative electrode active material was changed to an orthorhombic lithium titanium-containing oxide represented by Li ₂ Na _1.5 Ti _5.5 Nb _0.5 O ₁₄ , and the first positive electrode active material, the second positive electrode active material, the weight ratio of the first and second positive electrode active materials, the density, the basis weight and thickness of one side of each of the positive electrode and negative electrode, the type and concentration of the second electrolyte of the nonaqueous electrolyte, and the Co/Ti weight ratio were set as shown in Tables 1 to 3.
(Comparative Example 1)
A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the second positive electrode active material and the second electrolyte were not used, and the density, basis weight and thickness of one side, and Co/Ti weight ratio of each of the positive electrode and the negative electrode were set as shown in Tables 1 to 3.
(Comparative Example 2)
A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the first positive electrode active material, the second positive electrode active material, the weight ratio between the first and second positive electrode active materials, the density, the basis weight and thickness of one side of each of the positive electrode and negative electrode, the type and concentration of the second electrolyte in the nonaqueous electrolyte, and the Co/Ti weight ratio were set as shown in Tables 1 to 3.
<Cycle characteristic evaluation>
A 1C constant current charge/discharge cycle was carried out in a voltage range of 1.8 V to 2.8 V in an environment of 45° C. The capacity retention rate after 3000 cycles is shown in Table 3 below.
<Open circuit voltage of positive electrode>
The open circuit voltage V (vs. Li/Li ⁺ ) of the positive electrode when the nonaqueous electrolyte battery was discharged to 1.8 V at 0.2 C was measured by the above-mentioned method. The results are shown in Table 3.

As shown in Tables 1 to 3, the capacity retention rate after 3000 cycles of the batteries of Examples 1 to 17 is higher than that of Comparative Examples 1 and 2 which do not satisfy 0.005≦(G _Co /S _Co )/(G _Ti /S _Ti )≦0.15. Examples 1 to 11 and 13 to 17 in which the thickness of the positive electrode is 100 μm or less have a higher capacity retention rate after 3000 cycles than Example 12 in which the thickness of the positive electrode is more than 100 μm. In addition, by comparing Example 4 and Examples 13 to 15 in which the values of (G _Co /S _Co )/(G _Ti /S _Ti ) are the same, it can be seen that using a second electrolyte is advantageous for cycle performance. On the other hand, by comparing Example 1 and Example 17 in which the values of (G _Co /S _Co )/(G _Ti /S _Ti ) are the same, it can be seen that Example 1 in which lithium titanate is used as the negative electrode active material has better cycle performance than Example 17.

The nonaqueous electrolyte battery according to at least one of the embodiments and examples described above satisfies 0.005≦(G _Co /S _Co )/(G _Ti /S _Ti )≦0.15, and therefore can suppress overdischarge of the positive electrode and improve the charge/discharge cycle life.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention.
The invention as originally claimed in the present application is set forth below.
[1] A positive electrode including a positive electrode active material containing a lithium-containing manganese oxide and a lithium-containing nickel-cobalt-manganese oxide, the content of the lithium-containing nickel-cobalt-manganese oxide in the positive electrode active material being 3 wt % or more and 20 wt % or less;
a negative electrode including a negative electrode active material-containing layer that contains a lithium-titanium-containing oxide;
and a nonaqueous electrolyte, and the nonaqueous electrolyte battery satisfies the following formula (1):
0.005≦(G _Co /S _Co )/(G _Ti /S _Ti )≦0.15 (1)
Here, G _Co is the weight (mg) of Co contained in the positive electrode active material-containing layer, S _Co is the area (cm ² ) of the positive electrode active material-containing layer , G _Ti is the weight (mg) of Ti contained in the negative electrode active material-containing layer, and S _Ti is the area (cm ² ) of the negative electrode active material-containing layer .
[2] The nonaqueous electrolyte battery according to [1], wherein the open circuit voltage of the positive electrode when the nonaqueous electrolyte battery is discharged at 0.2 C to 1.8 V is 3.6 V (vs. Li/Li ⁺ ) or more and 3.9 V (vs. Li/Li ⁺ ) or less.
[3] The nonaqueous electrolyte battery according to [1] or [2], wherein the positive electrode has a thickness of 100 μm or less.
[4] The nonaqueous electrolyte battery according to any one of [1] to [3], wherein the density of the positive electrode is 2.5 g/cc or more and 3.1 g/cc or less.
[5] The nonaqueous electrolyte battery according to any one of [1] to [4], wherein the nonaqueous electrolyte battery satisfies the following formula (2):
0.9≦A/B≦1.1 (2)
Here, A is the charge capacity (mAh/ ^m2 ) per unit area when the charge/discharge range of the positive electrode is 3.0 V (vs. Li/Li ⁺ ) or more and 4.25 V (vs. Li/Li ⁺ ) or less, and B is the charge capacity (mAh/ ^m2 ) per unit area when the charge/discharge range of the negative electrode is 1.4 V (vs. Li /Li ⁺ ) or more and 2.0 V (vs. Li /Li ⁺ ) or less .
[6] A battery pack comprising the nonaqueous electrolyte battery according to any one of [1] to [5].

1...electrode group, 2...negative electrode, 2a...negative electrode current collector, 2b...negative electrode active material-containing layer, 3...positive electrode, 3a...positive electrode current collector, 3b...positive electrode active material-containing layer, 3c...positive electrode current collector tab, 4...separator, 5...negative electrode terminal, 6...positive electrode terminal, 7...exterior member, 15...negative electrode terminal, 15a...negative electrode lead, 16...positive electrode terminal, 16a...positive electrode lead, 17a...metallic container, 17b...sealing plate, 17c...insulating member, 20...battery pack, 23...battery assembly, 24...printed wiring board, 25...thermistor, 26...protective circuit, 27...current-carrying terminal, 28...positive electrode side lead, 30...negative electrode side lead, 36...protective sheet, 37...container, 38...lid.

Claims (5)

a positive electrode including a positive electrode active material containing a lithium-containing manganese oxide and a lithium-containing nickel-cobalt-manganese oxide, the content of the lithium-containing nickel-cobalt-manganese oxide in the positive electrode active material being 3 wt % or more and 20 wt % or less;
a negative electrode including a negative electrode active material-containing layer containing lithium titanate having a spinel structure as a lithium-titanium- containing oxide;
A non-aqueous electrolyte battery comprising :
the open circuit voltage of the positive electrode when the nonaqueous electrolyte battery is discharged to 1.8 V at 0.2 C is 3.6 V (vs. Li/Li ⁺ ) or more and 3.9 V (vs. Li/Li ⁺ ) or less, and the following formula (1) is satisfied:
0.005≦(G _Co /S _Co )/(G _Ti /S _Ti )≦0.15 (1)
Here, G _Co is the weight (mg) of Co contained in the positive electrode active material-containing layer, S _Co is the area (cm ² ) of the positive electrode active material-containing layer, G _Ti is the weight (mg) of Ti contained in the negative electrode active material-containing layer, and S _Ti is the area (cm ² ) of the negative electrode active material-containing layer. 2. The nonaqueous electrolyte battery according to claim 1 , wherein the positive electrode has a thickness of 100 μm or less. 3. The nonaqueous electrolyte battery according to claim 1 , wherein the density of the positive electrode is 2.5 g/cc or more and 3.1 g/cc or less. The nonaqueous electrolyte battery according to any one of claims 1 to 3 , which satisfies the following formula (2):
0.9≦A/B≦1.1 (2)
Here, A is the charge capacity (mAh/ ^m2 ) per unit area when the charge/discharge range of the positive electrode is 3.0 V (vs. Li/Li ⁺ ) or more and 4.25 V (vs. Li/Li ⁺ ) or less, and B is the charge capacity (mAh/ ^m2 ) per unit area when the charge/discharge range of the negative electrode is 1.4 V (vs. Li/Li ⁺ ) or more and 2.0 V (vs. Li/Li ⁺ ) or less. A battery pack comprising the nonaqueous electrolyte battery according to any one of claims 1 to 4 .