JPWO2016038716A1 - Nonaqueous electrolyte secondary battery and battery pack provided with the same - Google Patents

Abstract

A positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the negative electrode contains a niobium-titanium composite oxide as a negative electrode active material, and the content of Nb5 + in the non-aqueous electrolyte is 0.5 ppm or more A nonaqueous electrolyte secondary battery having a concentration of 200 ppm or less.

Description

Embodiments described herein relate generally to a nonaqueous electrolyte secondary battery and a battery pack including the same.

In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been developed as high energy density batteries. Nonaqueous electrolyte secondary batteries are expected as a power source for hybrid vehicles and electric vehicles. Nonaqueous electrolyte secondary batteries are also expected as uninterruptible power supplies for mobile phone base stations. Therefore, the nonaqueous electrolyte secondary battery is also required to have other characteristics such as rapid charge / discharge performance and long-term reliability. A non-aqueous electrolyte secondary battery capable of rapid charging / discharging has the advantage that the charging time is significantly short. Further, the nonaqueous electrolyte secondary battery can improve the power performance in a hybrid vehicle. Furthermore, the nonaqueous electrolyte secondary battery can efficiently recover the regenerative energy of power.

Rapid charge / discharge is enabled by the rapid movement of electrons and lithium ions between the positive and negative electrodes. In a battery using a carbon-based negative electrode, metal lithium dendrite may be deposited on the electrode by repeated rapid charge and discharge. The dendrite can cause an internal short circuit, resulting in heat generation and / or ignition.

  Therefore, batteries using metal composite oxides as negative electrode active materials instead of carbonaceous materials have been developed. In particular, a battery using titanium oxide as a negative electrode active material has characteristics that it can be stably charged and discharged quickly and has a longer life than a carbon-based negative electrode.

  However, titanium oxide has a higher potential (noble) with respect to metallic lithium than carbonaceous material. In addition, titanium oxide has a low capacity per mass. Therefore, a battery using titanium oxide has a problem of low energy density.

For example, the electrode potential of titanium oxide is about 1.5 V with respect to metallic lithium, and is higher (noble) than the potential of the carbon-based negative electrode. The electrode potential of titanium oxide is electrochemically restricted because it is due to an oxidation-reduction reaction between Ti ³⁺ and Ti ⁴⁺ when electrochemically inserting and releasing lithium. In addition, there is a fact that rapid charge / discharge of lithium ions can be stably performed at a high electrode potential of about 1.5V. Therefore, it is substantially difficult to reduce the electrode potential of titanium oxide in order to improve the energy density of a battery using titanium oxide.

Regarding the capacity per unit mass, the theoretical capacity of titanium dioxide (anatase type structure) is about 165 mAh / g, and the theoretical capacity of a lithium titanium composite oxide such as Li ₄ Ti ₅ O ₁₂ is also about 180 mAh / g. It is. On the other hand, the theoretical capacity of a general graphite electrode material is 385 mAh / g or more. Therefore, the capacity density of the titanium oxide is significantly lower than that of the carbon-based negative electrode. This is due to the fact that there are few sites that occlude lithium in the crystal structure of the titanium oxide, and that the lithium is easily stabilized in the structure, so that the substantial capacity is reduced.

In view of the above, new electrode materials containing titanium and niobium have been studied. Such an electrode material is expected to have a high charge / discharge capacity. In particular, the composite oxide represented by TiNb ₂ O ₇ has a high theoretical capacity exceeding 300 mAh / g. However, a complex oxide such as TiNb ₂ O ₇ has a problem of low productivity.

JP 2008-91079 A JP 2010-287496 A

C.M.Reich et.al., FUEL CELLS No.3-4,1 pp249-255 (2001) M. Gasperin, Journal of Solid State Chemistry 53, pp144-147 (1984)

The problem to be solved by the present invention is to provide a non-aqueous electrolyte secondary battery having excellent rapid charge / discharge performance, high energy density, and long life, and a battery pack including the same.

The nonaqueous electrolyte secondary battery of the embodiment includes a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator.
The negative electrode includes a niobium-titanium composite oxide as a negative electrode active material.
The Nb ⁵⁺ content in the nonaqueous electrolyte is 0.5 ppm or more and 200 ppm or less.

It is a schematic view showing the crystal structure of the monoclinic form TiNb ₂ O _7. It is the schematic diagram which looked at the crystal structure of FIG. 1 from the other direction. It is a schematic diagram which shows the nonaqueous electrolyte secondary battery which concerns on 2nd Embodiment. It is a schematic diagram which shows the nonaqueous electrolyte secondary battery which concerns on 2nd Embodiment. It is a schematic diagram which shows the nonaqueous electrolyte secondary battery which concerns on 2nd Embodiment. It is a schematic diagram which shows the nonaqueous electrolyte secondary battery which concerns on 2nd Embodiment. It is a schematic perspective view which shows the battery pack which concerns on 3rd Embodiment. It is a schematic diagram which shows the battery pack which concerns on 3rd Embodiment. It is a graph which shows the result of the electrochemical measurement of Example 1-3. It is a graph which shows the result of the electrochemical measurement of Example 1-3. It is a graph which shows the result of the electrochemical measurement of Example 1-3. It is a graph which shows the result of the electrochemical measurement of Example 4-6. 10 is a graph showing the results of electrochemical measurement of Example 7.

(First embodiment)
In the first embodiment, a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator is provided.

The negative electrode includes niobium-titanium composite oxide as a negative electrode active material.
The content of Nb ⁵⁺ in the nonaqueous electrolyte is 0.5 ppm or more and 200 ppm or less.

The niobium-titanium composite oxide mainly has a monoclinic crystal structure. An example of the niobium-titanium composite oxide having a monoclinic crystal structure is monoclinic TiNb ₂ O ₇ . 1 and 2 are schematic views showing the crystal structure of monoclinic TiNb ₂ O ₇ .

As shown in FIG. 1, in the crystal structure of monoclinic TiNb ₂ O ₇ , metal ions 101 and oxide ions 102 constitute a skeleton structure portion 103. Note that niobium (Nb) ions and titanium (Ti) ions are randomly arranged in the metal ions 101 at a ratio of Nb ions: Ti ions = 2: 1 (ratio of the number of ions). The skeletal structure portions 103 are alternately arranged three-dimensionally, so that void portions 104 exist between the skeleton structure portions 103. This void portion 104 becomes a host for lithium ions.

In FIG. 1, a region 105 and a region 106 are portions having two-dimensional channels in the [100] direction and the [010] direction. As shown in FIG. 2, in the crystal structure of monoclinic TiNb ₂ O ₇ , there are voids 107 in the [001] direction. This void portion 107 has a tunnel structure that is advantageous for lithium ion conduction. As a result, the gap portion 107 becomes a conduction path in the [001] direction that connects the region 105 and the region 106. The existence of this conduction path allows lithium ions to move back and forth between the region 105 and the region 106.

Thus, the crystal structure of monoclinic TiNb ₂ O ₇ is a two-dimensional channel that has a large equivalent insertion space for lithium ions, is structurally stable, and has a fast diffusion of lithium ions. Therefore, the insertion and removal of lithium ions into the insertion space is improved, and the insertion and removal space of lithium ions is effectively increased. Thereby, the monoclinic TiNb ₂ O ₇ can realize a nonaqueous electrolyte secondary battery having high capacity and high rate performance.

In the nonaqueous electrolyte secondary battery according to the present embodiment, the niobium-titanium composite oxide is not limited to monoclinic TiNb ₂ O ₇ but has a symmetry of the space group C2 / m, and is not patented. It preferably has a crystal structure having atomic coordinates described in Document 2.

Furthermore, the crystal structure of the monoclinic TiNb ₂ O ₇ is such that when lithium ions are inserted into the voids 104, the metal ions 101 that constitute the skeleton are reduced to trivalent, thereby reducing the electrical neutrality of the crystals. Kept. In the nonaqueous electrolyte secondary battery according to the present embodiment, the niobium-titanium composite oxide not only reduces Ti ions from tetravalent to trivalent, but also reduces Nb ions from pentavalent to trivalent. . Therefore, the niobium-titanium composite oxide has a large reduction valence per mass of the negative electrode active material. Therefore, the niobium-titanium composite oxide can maintain the electrical neutrality of the crystal even when many lithium ions are inserted. Therefore, the niobium-titanium composite oxide has a higher energy density than a compound such as titanium oxide containing only a tetravalent cation. In the non-aqueous electrolyte secondary battery according to this embodiment, the theoretical capacity of the niobium-titanium composite oxide is about 387 mAh / g, which is a value more than twice that of the titanium oxide having a spinel structure.

The niobium-titanium composite oxide has an occlusion / release potential of lithium of about 1.5 V (vs. Li / Li ⁺ ). Therefore, by using this negative electrode active material, a non-aqueous electrolyte secondary battery that can be stably and repeatedly charged and discharged can be realized.

From the above, by using a niobium-titanium composite oxide as the negative electrode active material, a nonaqueous electrolyte secondary battery having excellent rapid charge / discharge performance and high energy density can be realized.

However, the niobium-titanium composite oxide contained in the negative electrode elutes niobium ions (Nb ⁵⁺ ) by moisture in the nonaqueous electrolyte and hydrogen fluoride (HF) generated during charge / discharge. Therefore, in the non-aqueous electrolyte secondary battery according to the present embodiment, niobium-titanium contained in the negative electrode is added in advance or added to the non-aqueous electrolyte in an appropriate amount, that is, 0.5 ppm to 200 ppm of Nb ^5+. Elution of Nb ⁵⁺ from the composite oxide can be suppressed. Further, the content of Nb ⁵⁺ in the nonaqueous electrolyte is preferably 1 ppm or more and 50 ppm or less.
When the content of Nb ⁵⁺ in the non-aqueous electrolyte is less than 0.5 ppm, the reaction represented by the following reaction formula (1) proceeds in the right direction due to moisture and hydrogen fluoride in the non-aqueous electrolyte, Nb ⁵⁺ is eluted from the niobium-titanium composite oxide contained in the negative electrode, and the deterioration of the niobium-titanium composite oxide is accelerated.
TiNb ₂ O ₇ (solid) + 14HF⇔7H ₂ O + 2Nb ⁵⁺ + Ti ⁴⁺ + 14F ⁻ (1)
On the other hand, if the content of Nb ^{5+ in} the non-aqueous electrolyte exceeds 200 ppm, the content of Nb ^{5+ in} the non-aqueous electrolyte is too large, and the ionic conductivity of the non-aqueous electrolyte is lowered and the reaction resistance is increased. The life of the nonaqueous electrolyte secondary battery is shortened.

In the nonaqueous electrolyte secondary battery according to this embodiment, the content of water in the nonaqueous electrolyte is preferably 1 ppm or more and 100 ppm or less. Nb ⁵⁺ is eluted from the niobium-titanium composite oxide contained in the negative electrode by adding or generating 0.5 ppm or more and 200 ppm or less of Nb ⁵⁺ to a nonaqueous electrolyte having a water content of 1 ppm to 100 ppm. Can be suppressed. Thereby, the lifetime of the nonaqueous electrolyte secondary battery using the niobium-titanium composite oxide as the negative electrode active material for the negative electrode can be improved.

In the non-aqueous electrolyte secondary battery according to the present embodiment, the niobium-titanium composite contained in the negative electrode is suppressed by suppressing the generation of hydrogen fluoride in the non-aqueous electrolyte by extremely removing water in the non-aqueous electrolyte. Elution of Nb ⁵⁺ from the oxide can be suppressed. Thereby, the lifetime of the nonaqueous electrolyte secondary battery using the niobium-titanium composite oxide as the negative electrode active material for the negative electrode can be improved.

In the non-aqueous electrolyte secondary battery according to the present embodiment, by using an electrolyte that hardly generates hydrogen fluoride in the non-aqueous electrolyte, generation of hydrogen fluoride in the non-aqueous electrolyte can be suppressed and included in the negative electrode. Elution of Nb ⁵⁺ from the niobium-titanium composite oxide. Thereby, the lifetime of the nonaqueous electrolyte secondary battery using the niobium-titanium composite oxide as the negative electrode active material for the negative electrode can be improved.

Niobium-titanium composite oxide is Li _x TiNb _2-y M _y O _{7 ± δ} (where M is B, Na, Mg, Al, Si, S, P, K, Ca, Mo, W, Cr, A compound represented by at least one selected from the group consisting of Mn, Co, Ni, and Fe, 0 ≦ x ≦ 5, 0 ≦ y ≦ 0.5, and 0 ≦ δ ≦ 0.3) is preferable. . The niobium-titanium composite oxide represented by Li _x TiNb _2-y M _y O _{7 ± δ} has one cation that can be reduced from tetravalent to trivalent per chemical formula, and can be reduced to pentavalent or trivalent. It is theoretically possible to insert a maximum of five lithium ions because it has a maximum of two cations. Therefore, in the above chemical formula, x is 0 or more and 5 or less. When all the elements M contained in the niobium-titanium composite oxide are present in a state where Nb in the crystal lattice of the niobium-titanium composite oxide is substituted and dissolved, y = 0.5. On the other hand, when the element M contained in the niobium-titanium composite oxide does not exist uniformly in the crystal lattice and segregates, y = 0. δ varies depending on the reduction state of the niobium-titanium composite oxide having a monoclinic crystal structure. If δ exceeds −0.3, niobium is reduced in advance to deteriorate electrode performance, and phase separation may occur. On the other hand, up to δ = + 0.3 is the measurement error range.

Li _x TiNb _2-y M _y O _{7 ± δ} (where M is from B, Na, Mg, Al, Si, S, P, K, Ca, Mo, W, Cr, Mn, Co, Ni and Fe) In the composite oxide represented by at least one selected from the group consisting of 0 ≦ x ≦ 5, 0 ≦ y ≦ 0.5, and 0 ≦ δ ≦ 0.3), a part of niobium is substituted with the element M Even if it is dissolved, the capacity is not substantially reduced, and it is preferable because improvement in electronic conductivity can be expected by substitution with a different element.

Furthermore, in the nonaqueous electrolyte secondary battery according to the present embodiment, the melting point of the niobium-titanium composite oxide is preferably 1350 ° C. or less, and more preferably 1250 ° C. or less.
If the melting point of the niobium-titanium composite oxide is 1350 ° C. or lower, a niobium-titanium composite oxide having high crystallinity can be obtained even when fired at a low firing temperature. Therefore, niobium-titanium composite oxide can be synthesized using existing equipment. Further, since the niobium-titanium composite oxide can be synthesized at a low firing temperature, there is an advantage that the productivity of the niobium-titanium composite oxide is high.

The average particle size of the primary particles of the niobium-titanium composite oxide is preferably 0.001 μm or more and 3 μm or less. By setting the average particle size to 0.001 μm or more, the distribution of the nonaqueous electrolyte relative to the negative electrode can be made uniform, and depletion of the nonaqueous electrolyte at the negative electrode can be suppressed. By making the average particle size 3 μm or less, when the specific surface area of the negative electrode is 3 m ² / g or more and 50 m ² / g or less, a decrease in the porosity of the negative electrode can be suppressed.

The niobium-titanium composite oxide preferably has an average primary particle size of 1 μm or less and a specific surface area of 3 m ² / g or more and 200 m ² / g or less by the BET method by N ₂ adsorption. Thereby, the affinity with the nonaqueous electrolyte of the negative electrode can be further increased.

  It does not specifically limit as a positive electrode, a separator, and a nonaqueous electrolyte, What is applicable to a lithium secondary battery can be used.

<Method for producing niobium-titanium composite oxide>
In this embodiment, a niobium-titanium composite oxide can be produced by the following method.
First, the starting materials are mixed.
As starting materials for the elements Li, Ti and Nb, oxides or salts containing Li, Ti and Nb are used.
The starting material for the element M is at least one selected from the group consisting of B, Na, Mg, Al, Si, S, P, K, Ca, Mo, W, Cr, Mn, Co, Ni, and Fe. An oxide or a salt containing an element is used. For example, when synthesizing Li _x TiNb _2-y (Mo _0.75y Mg _0.25y ) O _{7 ± δ} , MgO and MoO ₂ or MoO ₃ are used as starting materials for Mg and Mo. The salt used as a starting material is preferably a salt that decomposes at a relatively low temperature to form an oxide, such as carbonate and nitrate.

Here, the starting materials of the elements Li, Ti and Nb and the starting material of the element M are mixed at a ratio such that the molar ratio of M to Ti (M / Ti) is 0 <M / Ti ≦ 0.5. . Further, it is preferable to mix at a molar ratio (M / Ti) so that the total charge of the crystal in which a part of Nb is substituted with the element M is kept neutral. _Thus, crystal maintaining the crystal structure of Li x TiNb ₂ O ₇ are obtained. On the other hand, even when the element M is added so that the total charge of the crystal in which a part of Nb is substituted with the element M is kept neutral, by adjusting the amount of the element M added, A crystal maintaining the crystal structure of Li _x TiNb ₂ O _{7 in} a part is obtained.

Next, the mixture of starting materials is pulverized to obtain a mixture that is as uniform as possible.
The pulverized mixture is then fired. In firing the mixture, the firing temperature is preferably 500 ° C. or more and 1200 ° C. or less, the firing time is preferably 10 hours or more and 40 hours or less, the firing temperature is 800 ° C. or more and 1000 ° C. or less, and the firing time is 10 hours or more and 40 hours or less. The following is more preferable. According to the method for producing a niobium-titanium composite oxide according to this embodiment, a niobium-titanium composite oxide having high crystallinity can be obtained even when the firing temperature is 1200 ° C. or lower. Moreover, if a calcination temperature is 1000 degrees C or less, the conventional installation can be utilized.

Li _x TiNb _2-y M _y O _{7 ± δ} (where M is B, Na, Mg, Al, Si, S, P, K, Ca, At least one selected from the group consisting of Mo, W, Cr, Mn, Co, Ni and Fe, 0 ≦ x ≦ 5, 0 ≦ y ≦ 0.5, 0 ≦ δ ≦ 0.3) A niobium-titanium composite oxide comprising the compound is obtained.

Note that lithium ions may be inserted into the niobium-titanium composite oxide synthesized by the above manufacturing method by charging a nonaqueous electrolyte secondary battery. Alternatively, the niobium-titanium composite oxide may be synthesized as a composite oxide containing lithium by using a compound containing lithium such as lithium carbonate as a starting material.

A non-aqueous electrolyte having a Nb ⁵⁺ content of 0.5 ppm to 200 ppm includes, for example, Nb such as niobium chloride (V) (NbCl ₅ ) as a Nb ⁵⁺ source in the non-aqueous electrolyte. To prepare an appropriate amount of a substance that liberates Nb ⁵⁺ .

  A negative electrode is produced using the niobium-titanium composite oxide synthesized by the above production method, and a nonaqueous electrolyte secondary battery is produced by combining the negative electrode, the positive electrode, a separator, and a nonaqueous electrolyte.

<Inductively coupled plasma (ICP) measurement of Nb ⁵⁺ content in non-aqueous electrolyte>
The non-aqueous electrolyte in the non-aqueous electrolyte secondary battery is transferred to a general-purpose spectrometer, and multi-elements with extremely high speed and low interference are measured by inductively coupled plasma (ICP) measurement.
By this inductively coupled plasma (ICP) measurement, the content (ppm) of Nb ⁵⁺ in the nonaqueous electrolyte can be measured.

(Second Embodiment)
In the second embodiment, a non-aqueous electrolyte that includes a negative electrode including the niobium-titanium composite oxide in the first embodiment described above as a negative electrode active material, a positive electrode, a non-aqueous electrolyte, a separator, and an exterior material. A secondary battery is provided.
More specifically, the nonaqueous electrolyte secondary battery according to the present embodiment includes an exterior material, a positive electrode housed in the exterior material, a spatially separated space from the positive electrode in the exterior material, and a separator interposed therebetween. And the non-aqueous electrolyte filled in the exterior material.

Hereinafter, the negative electrode, the positive electrode, the nonaqueous electrolyte, the separator, and the exterior material, which are constituent members of the nonaqueous electrolyte secondary battery according to the present embodiment, will be described in detail.

(1) The negative electrode includes a negative electrode current collector and a negative electrode layer formed on one or both surfaces of the negative electrode current collector and including a negative electrode active material, a conductive agent, and a binder. The conductive agent and the binder are optional components.

As the negative electrode active material, the niobium-titanium composite oxide described in the first embodiment is used. Thereby, the nonaqueous electrolyte secondary battery which is excellent in productivity and has excellent rapid charge / discharge performance and high energy density can be provided.

As the negative electrode active material, the niobium-titanium composite oxide described in the first embodiment may be used alone, or a niobium-titanium composite oxide and another negative electrode active material may be used in combination. As other negative electrode active materials, for example, titanium dioxide having an anatase structure (TiO ₂ ), lithium titanate having a ramsdellite structure (for example, Li ₂ Ti ₃ O ₇ ), lithium titanate having a spinel structure (for example, Li ₄ Ti ₅ O ₁₂ ) and the like.

The specific surface area of the negative electrode is preferably 3 m ² / g or more and 50 m ² / g or less, and more preferably 5 m ² / g or more and 50 m ² / g or less. Thereby, the output performance and charge / discharge cycle performance of the nonaqueous electrolyte secondary battery can be further improved. Here, the specific surface area of the negative electrode means the surface area per 1 g of the negative electrode layer (excluding the current collector mass). The negative electrode layer is a porous layer containing a negative electrode active material, a conductive agent, and a binder formed on the negative electrode current collector.

The porosity (excluding the current collector) of the negative electrode is preferably 20% or more and 50% or less, and more preferably 25% or more and 40% or less. As a result, a negative electrode having excellent affinity with the nonaqueous electrolyte and a high density can be obtained.

For the negative electrode current collector, a material that is electrochemically stable at the lithium insertion and extraction potential of the negative electrode active material is used. The negative electrode current collector was made of copper, nickel, stainless steel or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu and Si. A current collector is preferred.
The thickness of the negative electrode current collector is preferably 5 μm or more and 20 μm or less. A negative electrode current collector having a thickness in this range can achieve both strength and weight reduction of the negative electrode.

The conductive agent improves the current collecting performance of the negative electrode active material and suppresses the contact resistance between the negative electrode active material and the negative electrode current collector.
Examples of the conductive agent include acetylene black, carbon black, coke, carbon fiber, graphite, metal compound powder, and metal powder. More preferable examples of the conductive agent include coke, graphite, or a metal powder such as TiO, TiC, TiN, Al, Ni, Cu, and Fe having a heat treatment temperature of 800 ° C. to 2000 ° C. and an average particle size of 10 μm or less. It is done.

The binder fills the gap between the dispersed negative electrode active materials, binds the negative electrode active material and the conductive agent, and binds the negative electrode active material and the negative electrode current collector.
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene butadiene rubber, core-shell binder, and organic matter containing polyacrylic acid.

The content of the negative electrode active material in the negative electrode layer is preferably 68% by mass or more and 96% by mass or less. Moreover, it is preferable that content of the electrically conductive agent in a negative electrode layer is 2 to 30 mass%. Moreover, it is preferable that content of the binder in a negative electrode layer is 2 mass% or more and 30 mass% or less.
By making content of a electrically conductive agent 2 mass% or more, the current collection performance of a negative electrode layer can be improved, and the large current characteristic of a nonaqueous electrolyte secondary battery can be improved.
Further, by setting the content of the binder to 2% by mass or more, the binding property between the negative electrode layer and the negative electrode current collector can be improved, and the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved.
On the other hand, it is preferable from the viewpoint of increasing the capacity of the non-aqueous electrolyte secondary battery that the contents of the conductive agent and the binder are 28% by mass or less, respectively.

For example, the negative electrode is prepared by suspending a negative electrode active material, a conductive agent and a binder in a widely used solvent to prepare a slurry, and applying this slurry to a negative electrode current collector and drying to form a negative electrode layer Then, it is manufactured by applying a press. Further, the negative electrode may be produced by forming a negative electrode active material, a conductive agent, and a binder into a pellet shape to form a negative electrode layer, which is disposed on the negative electrode current collector.

(2) The positive electrode includes a positive electrode current collector and a positive electrode layer formed on one or both surfaces of the positive electrode current collector and including a positive electrode active material, a conductive agent, and a binder. The conductive agent and the binder are optional components.

For example, an oxide or a sulfide is used as the positive electrode active material. Examples of the oxide and sulfide include manganese dioxide (MnO ₂ ) that stores lithium, iron oxide, copper oxide, nickel oxide, and lithium manganese composite oxide (for example, Li _x Mn ₂ O ₄ or Li _x MnO ₂ ). , Lithium nickel composite oxide (for example, Li _x NiO ₂ ), lithium cobalt composite oxide (for example, Li _x CoO ₂ ), lithium nickel cobalt composite oxide (for example, LiNi _1-y Co _y O ₂ ), lithium manganese Cobalt composite oxide (for example, Li _x Mn _y Co _1-y O ₂ ), lithium manganese nickel composite oxide having a spinel structure (eg, Li _x Mn _2-y Ni _y O ₄ ), lithium phosphorus having an olivine structure oxides _{(e.g., Li x FePO 4, Li x} Fe 1-y Mn y PO 4 Li _x CoPO _4), iron sulfate _{[Fe 2 (SO 4) 3} ], vanadium oxide _(e.g., V _{2 O} 5), and include lithium-nickel-cobalt-manganese composite oxide. In the above chemical formula, 0 <x ≦ 1 and 0 <y ≦ 1. As the positive electrode active material, these compounds may be used alone, or a plurality of compounds may be used in combination.

More preferable positive electrode active materials include, for example, a lithium manganese composite oxide (eg, Li _x Mn ₂ O ₄ ), a lithium nickel composite oxide (eg, Li _x NiO ₂ ), a lithium cobalt composite oxide ( For example, Li _x CoO ₂ ), lithium nickel cobalt composite oxide (eg, LiNi _1-y Co _y O ₂ ), lithium manganese nickel composite oxide having a spinel structure (eg, Li _x Mn _2-y Ni _y O ₄₎ ), Lithium manganese cobalt composite oxide (for example, Li _x Mn _y Co _1-y O ₂ ), lithium iron phosphate (for example, Li _x FePO ₄ ), and lithium nickel cobalt manganese composite oxide. In the above chemical formula, 0 <x ≦ 1 and 0 <y ≦ 1.

When a room temperature molten salt is used as the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery, preferred examples of the positive electrode active material include lithium iron phosphate, Li _x VPO ₄ F (0 ≦ x ≦ 1), and lithium manganese composite oxide. , Lithium nickel composite oxide, and lithium nickel cobalt composite oxide. Since these compounds have low reactivity with the room temperature molten salt, the cycle life of the nonaqueous electrolyte secondary battery can be improved.

The average particle size of primary particles of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material having an average primary particle size of 100 nm or more is easy to handle in industrial production. In addition, a positive electrode active material having an average primary particle size of 1 μm or less can smoothly diffuse lithium ions in a solid.

The specific surface area of the positive electrode active material is measured by a BET method using N ₂ adsorption, and is preferably 0.1 m ² / g or more and 10 m ² / g or less. The positive electrode active material having a specific surface area of 0.1 m ² / g or more can sufficiently secure the lithium ion storage / release site. Moreover, the positive electrode active material having a specific surface area of 10 m ² / g or less is easy to handle in industrial production and can improve the cycle characteristics of the nonaqueous electrolyte secondary battery.

The positive electrode current collector is formed from an aluminum foil or an aluminum alloy foil containing at least one element selected from the group consisting of Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si. It is preferable.
The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

The thickness of the positive electrode current collector is preferably 5 μm or more and 20 μm or less, and more preferably 5 μm or more and 15 μm or less.

The conductive agent improves the current collection performance of the positive electrode active material and suppresses the contact resistance between the positive electrode active material and the positive electrode current collector. Examples of the conductive agent include those containing acetylene black, carbon black, artificial graphite, natural graphite, carbon fiber, conductive polymer, and the like.
The type of the conductive agent can be one type or two or more types.

As the conductive agent, vapor grown carbon fiber having a fiber diameter of 1 μm or less is particularly preferable. By using this carbon fiber, the network of electron conduction inside the positive electrode is improved, and the output performance of the positive electrode can be greatly improved.

The binder fills the gap between the dispersed positive electrode active materials, binds the positive electrode active material and the conductive agent, and binds the positive electrode active material and the positive electrode current collector.
Examples of the binder include organic substances including polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, and polyacrylic acid.
The type of the binder can be one type or two or more types.
Moreover, as an organic solvent for dispersing the binder, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), or the like is used.

The content of the positive electrode active material in the positive electrode layer is preferably 80% by mass or more and 98% by mass or less. Moreover, it is preferable that content of the binder in a positive electrode layer is 2 mass% or more and 20 mass% or less.
By setting the content of the binder to 2% by mass or more, sufficient electrode strength can be obtained for the positive electrode layer. Further, by setting the binder content to 20% by mass or less, the amount of the insulator in the positive electrode can be reduced, and the internal resistance of the positive electrode can be reduced.

When the conductive agent is added, the content of the positive electrode active material in the positive electrode layer is preferably 77% by mass or more and 95% by mass or less. Moreover, it is preferable that content of the binder in a positive electrode layer is 2 mass% or more and 20 mass% or less. Moreover, it is preferable that content of the electrically conductive agent in a positive electrode layer is 3 to 15 mass%.
By setting the content of the conductive agent to 3% by mass or more, the current collecting performance of the positive electrode can be improved, and the contact resistance between the positive electrode active material and the positive electrode current collector can be suppressed. On the other hand, by setting the content of the conductive agent to 15% by mass or less, decomposition of the non-aqueous electrolyte on the surface of the positive electrode conductive agent under high temperature storage can be reduced.

For example, the positive electrode is prepared by suspending a positive electrode active material, a binder, and a conductive agent blended as necessary in a widely used solvent to prepare a slurry, and applying the slurry to the positive electrode current collector and then drying the slurry. And after forming a positive electrode layer, it produces by giving a press. Further, the positive electrode may be produced by forming a positive electrode active material, a binder, and a conductive agent blended as necessary into a pellet shape to form a positive electrode layer, which is disposed on the positive electrode current collector. .

(3) Non-aqueous electrolyte As the non-aqueous electrolyte, a liquid organic electrolyte prepared by dissolving an electrolyte in an organic solvent, a gel organic electrolyte obtained by combining a liquid organic solvent and a polymer material, or lithium Examples thereof include a solid nonaqueous electrolyte (polymer solid electrolyte) in which a salt electrolyte and a polymer material are combined, and a solid nonaqueous electrolyte (inorganic solid electrolyte) in which a lithium salt electrolyte and an inorganic material are combined. Moreover, you may use the normal temperature molten salt (ionic melt) containing lithium ion as a non-aqueous electrolyte.

The non-aqueous electrolyte is preferably liquid or gel, has a boiling point of 100 ° C. or higher, and contains an organic electrolyte or a room temperature molten salt.

The liquid organic electrolyte is prepared by dissolving the electrolyte in an organic solvent at a concentration of 0.5 mol / L or more and 2.5 mol / L or less. Thereby, a high output can be taken out even in a low temperature environment. A more preferable range of the concentration of the electrolyte in the organic electrolyte is 1.5 mol / L or more and 2.5 mol / L or less.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and trifluorometa. Examples include lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ], and mixtures thereof. The electrolyte is preferably one that is not easily oxidized even at a high potential, and lithium hexafluorophosphate is most preferred.

Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate; chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); Cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN) and sulfolane (SL). These organic solvents can be used alone or in the form of a mixture of two or more.

A room temperature molten salt (ionic melt) is a compound that can exist as a liquid at room temperature (15 ° C. to 25 ° C.) among organic salts composed of combinations of organic cations and anions. Examples of the room temperature molten salt include a room temperature molten salt that exists alone as a liquid, a room temperature molten salt that becomes a liquid when mixed with an electrolyte, and a room temperature molten salt that becomes a liquid when dissolved in an organic solvent. In general, the melting point of a room temperature molten salt used for a non-aqueous electrolyte secondary battery is 25 ° C. or less. The organic cation generally has a quaternary ammonium skeleton.

The polymer solid electrolyte is prepared by dissolving an electrolyte in a polymer material and solidifying it. The inorganic solid electrolyte is a solid material having lithium ion conductivity.

  Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), and the like.

The non-aqueous electrolyte can further include an additive.
Although it does not specifically limit as an additive, For example, vinylene carbonate (VC), vinylene acetate (VA), vinylene butyrate, vinylene hexanate, vinylene crotonate, catechol carbonate, propane sultone etc. are mentioned.
The concentration of the additive is preferably in the range of 0.1% by mass to 3% by mass with respect to 100% by mass of the nonaqueous electrolyte, and more preferably in the range of 0.5% by mass to 1% by mass. is there.

The content of Nb ⁵⁺ in the nonaqueous electrolyte is 0.5 ppm or more and 200 ppm or less, and preferably 1 ppm or more and 50 ppm or less.
The water content in the non-aqueous electrolyte is preferably 1 ppm or more and 100 ppm or less.

A non-aqueous electrolyte having a Nb ⁵⁺ content of 0.5 ppm to 200 ppm includes, for example, Nb such as niobium chloride (V) (NbCl ₅ ) as a Nb ⁵⁺ source in the non-aqueous electrolyte. To prepare an appropriate amount of a substance that liberates Nb ⁵⁺ .

(4) The separator separator is disposed between the positive electrode and the negative electrode.
The separator is formed of, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. Among these, the porous film formed from polyethylene or polypropylene can be melted at a constant temperature and can interrupt the current, so that safety can be improved.

The separator preferably has a thickness of 30 μm or less. The separator preferably has a thickness of 20 μm to 100 μm and a density of 0.2 g / cm ^{3 to} 0.9 g / cm ³ . When the thickness and density of the separator are within this range, it is possible to balance the mechanical strength and the reduction of battery resistance, and it is possible to provide a battery that is high in output and hardly short-circuited internally. In addition, good thermal storage performance can be exhibited with little heat shrinkage in a high temperature environment.

(5) Exterior material As the exterior material in which the positive electrode, the negative electrode, and the nonaqueous electrolyte are accommodated, a metal container or a laminate film exterior container is used.
As the metal container, a metal can made of aluminum, aluminum alloy, iron, stainless steel or the like having a square or cylindrical shape is used. Moreover, it is preferable that the thickness of a metal container is 1 mm or less, More preferably, it is 0.5 mm or less, More preferably, it is 0.2 mm or less.
As the aluminum alloy, an alloy containing elements such as magnesium, zinc and silicon is preferable. When the aluminum alloy contains a transition metal such as iron, copper, nickel, or chromium, the content is preferably 100 ppm or less. A metal container made of an aluminum alloy has a strength that is dramatically higher than that of a metal container made of aluminum, so that the thickness of the metal container can be reduced. As a result, a non-aqueous electrolyte secondary battery that is thin, lightweight, has high output, and has excellent heat dissipation can be realized.

Examples of the laminate film include a multilayer film in which an aluminum foil is covered with a resin film. As the resin constituting the resin film, polymer compounds such as polypropylene (PP), polyethylene (PE), nylon, polyethylene terephthalate (PET) are used. Moreover, it is preferable that the thickness of a laminate film is 0.5 mm or less, and it is more preferable that it is 0.2 mm or less. The purity of the aluminum foil is preferably 99.5% or more.

The present embodiment can be applied to various forms of nonaqueous electrolyte secondary batteries such as a flat type (thin type), a square type, a cylindrical type, a coin type, and a button type.
In addition, the nonaqueous electrolyte secondary battery according to this embodiment can further include a lead electrically connected to the electrode group including the positive electrode and the negative electrode. The nonaqueous electrolyte secondary battery according to the present embodiment can include, for example, two leads. In that case, one lead is electrically connected to the positive current collecting tab, and the other lead is electrically connected to the negative current collecting tab.
The lead material is not particularly limited, and for example, the same material as the positive electrode current collector and the negative electrode current collector is used.

The nonaqueous electrolyte secondary battery according to the present embodiment may further include a terminal that is electrically connected to the lead and is drawn out from the exterior material. The nonaqueous electrolyte secondary battery according to the present embodiment can include, for example, two terminals. In that case, one terminal is connected to a lead electrically connected to the positive electrode current collector tab, and the other terminal is connected to a lead electrically connected to the negative electrode current collector tab.
The material of the terminal is not particularly limited, and for example, the same material as the positive electrode current collector and the negative electrode current collector is used.

(6) Non-aqueous electrolyte secondary battery Next, as an example of the non-aqueous electrolyte secondary battery according to the present embodiment, a flat non-aqueous electrolyte secondary battery (non-aqueous electrolyte secondary battery) shown in FIGS. 200 will be described. FIG. 3 is a schematic cross-sectional view of the flat type nonaqueous electrolyte secondary battery 200. FIG. 4 is an enlarged cross-sectional view of a portion A shown in FIG. Each of these figures is a schematic diagram for explaining the non-aqueous electrolyte secondary battery according to the present embodiment, and the shape, dimensions, ratio, etc. thereof are different from those of the actual device. The design can be changed as appropriate in consideration of the above description and known techniques.

A non-aqueous electrolyte secondary battery 200 shown in FIG. 3 is configured such that a flat wound electrode group 201 is housed in an exterior material 202. The exterior material 202 may be a laminate film formed in a bag shape or a metal container. Further, the flat wound electrode group 201 is formed by winding a laminate in which the negative electrode 203, the separator 204, the positive electrode 205, and the separator 204 are laminated in this order from the outside, that is, the exterior material 202 side, and press-molding. It is formed by. As shown in FIG. 4, the negative electrode 203 located on the outermost periphery has a configuration in which a negative electrode layer 203b is formed on one surface on the inner surface side of the negative electrode current collector 203a. A portion of the negative electrode 203 other than the outermost periphery has a configuration in which the negative electrode layer 203b is formed on both surfaces of the negative electrode current collector 203a. The positive electrode 205 has a structure in which a positive electrode layer 205b is formed on both surfaces of a positive electrode current collector 205a. Note that the above-described gel-like nonaqueous electrolyte may be used instead of the separator 204.

In the wound electrode group 201 shown in FIG. 3, the negative electrode terminal 206 is electrically connected to the negative electrode current collector 203 a of the outermost negative electrode 203 in the vicinity of the outer peripheral end. The positive electrode terminal 207 is electrically connected to the positive electrode current collector 205 a of the inner positive electrode 205. The negative electrode terminal 206 and the positive electrode terminal 207 are extended to the outside of the exterior material 202 or connected to a take-out electrode provided in the exterior material 202.

When manufacturing the non-aqueous electrolyte secondary battery 200 having an exterior material made of a laminate film, the wound electrode group 201 to which the negative electrode terminal 206 and the positive electrode terminal 207 are connected is replaced with a bag-shaped exterior material 202 having an opening. The liquid non-aqueous electrolyte is injected from the opening of the exterior material 202, and the opening of the bag-shaped exterior material 202 is heat-sealed with the negative electrode terminal 206 and the positive electrode terminal 207 sandwiched therebetween. The wound electrode group 201 and the liquid nonaqueous electrolyte are completely sealed.

In addition, when manufacturing the nonaqueous electrolyte secondary battery 200 having an exterior material made of a metal container, the wound electrode group 201 to which the negative electrode terminal 206 and the positive electrode terminal 207 are connected is mounted on a metal container having an opening. The liquid non-aqueous electrolyte is injected from the opening of the exterior material 202, and a lid is attached to the metal container to seal the opening.

As the negative electrode terminal 206, for example, a material having electrical stability and conductivity in a range where the potential with respect to lithium is 1 V or more and 3 V or less can be used. Specifically, aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si can be given. The negative electrode terminal 206 is more preferably made of the same material as the negative electrode current collector 203a in order to reduce contact resistance with the negative electrode current collector 203a.

As the positive electrode terminal 207, a material having electrical stability and conductivity in a range where the potential with respect to lithium is 3 V or more and 4.25 V or less can be used. Specifically, aluminum or an aluminum alloy containing an element such as Mg, Ti, Zn, Mn, Fe, Cu, or Si can be given. The positive electrode terminal 207 is preferably made of the same material as the positive electrode current collector 205a in order to reduce the contact resistance with the positive electrode current collector 205a.
Hereinafter, the exterior material 202, the negative electrode 203, the positive electrode 205, the separator 204, and the nonaqueous electrolyte, which are constituent members of the nonaqueous electrolyte secondary battery 200, will be described in detail.

(1) As the exterior material exterior material 202, the exterior material described above is used.

(2) The negative electrode is used as the negative electrode 203.

(3) The positive electrode is used as the positive electrode 205.

(4) As the separator separator 204, the above separator is used.

(5) Nonaqueous electrolyte As the nonaqueous electrolyte, the above nonaqueous electrolyte is used.

The nonaqueous electrolyte secondary battery according to the second embodiment is not limited to the one shown in FIGS. 3 and 4 described above, and may be a battery shown in FIGS. 5 and 6, for example. FIG. 5 is a partially cutaway perspective view schematically showing another flat type nonaqueous electrolyte secondary battery according to the second embodiment, and FIG. 6 is an enlarged cross-sectional view of a portion B in FIG.

A non-aqueous electrolyte secondary battery 210 shown in FIGS. 5 and 6 is configured such that a laminated electrode group 211 is accommodated in an exterior material 212. As shown in FIG. 6, the stacked electrode group 211 has a structure in which positive electrodes 213 and negative electrodes 214 are alternately stacked with separators 215 interposed therebetween.

There are a plurality of positive electrodes 213, each including a positive electrode current collector 213 a and a positive electrode layer 213 b supported on both surfaces of the positive electrode current collector 213 a. The positive electrode layer 213b contains a positive electrode active material.

There are a plurality of negative electrodes 214, each including a negative electrode current collector 214a and a negative electrode layer 214b supported on both surfaces of the negative electrode current collector 214a. The negative electrode layer 214b contains a negative electrode active material. One side of the negative electrode current collector 214 a of each negative electrode 214 protrudes from the negative electrode 214. The protruding negative electrode current collector 214 a is electrically connected to the strip-shaped negative electrode terminal 216. The tip of the strip-shaped negative electrode terminal 216 is drawn out from the exterior material 212. Although not shown, the positive electrode current collector 213a of the positive electrode 213 has a side protruding from the positive electrode 213 on the side opposite to the protruding side of the negative electrode current collector 214a. The positive electrode current collector 213 a protruding from the positive electrode 213 is electrically connected to the belt-like positive electrode terminal 217. The front end of the strip-like positive electrode terminal 217 is located on the opposite side to the negative electrode terminal 216, and is drawn out from the side of the exterior material 212.

The materials, blending ratios, dimensions, etc. of the members constituting the nonaqueous electrolyte secondary battery 210 shown in FIGS. 5 and 6 are the same as those of the components of the nonaqueous electrolyte secondary battery 200 described in FIGS. 3 and 4. It is the composition.

According to this embodiment described above, a nonaqueous electrolyte secondary battery can be provided.
The nonaqueous electrolyte secondary battery according to the present embodiment includes a negative electrode including the niobium-titanium composite oxide in the first embodiment as a negative electrode active material, a positive electrode, a nonaqueous electrolyte, and a separator. The negative electrode includes niobium-titanium composite oxide as a negative electrode active material. The content of Nb ⁵⁺ in the nonaqueous electrolyte is 0.5 ppm or more and 200 ppm or less. Such a non-aqueous electrolyte secondary battery elutes niobium ions (Nb ⁵⁺ ) from the niobium-titanium composite oxide contained in the negative electrode by moisture in the non-aqueous electrolyte and hydrogen fluoride (HF) generated during charging and discharging. Can be suppressed. Thereby, the nonaqueous electrolyte secondary battery according to the present embodiment has excellent rapid charge / discharge performance, a high energy density, and a long life.

(Third embodiment)
Next, the battery pack according to the third embodiment will be described in detail.
The battery pack according to the present embodiment has a plurality (two or more) of nonaqueous electrolyte secondary batteries (that is, single cells) according to the first embodiment or the second embodiment. In the battery pack according to the present embodiment, the plurality of single cells are electrically connected in series, in parallel, or connected in series and in parallel.

With reference to FIG. 7 and FIG. 8, the battery pack 300 which concerns on this embodiment is demonstrated concretely. In the battery pack 300 shown in FIG. 7, the flat type nonaqueous electrolyte battery 200 shown in FIG. 3 is used as the unit cell 301.
The plurality of unit cells 301 are stacked such that the negative electrode terminal 206 and the positive electrode terminal 207 extending to the outside are aligned in the same direction, and are fastened with an adhesive tape 302 to constitute an assembled battery 303. These unit cells 301 are electrically connected to each other in series as shown in FIGS.

The printed wiring board 304 is disposed to face the side surface of the unit cell 301 from which the negative electrode terminal 206 and the positive electrode terminal 207 extend. As shown in FIG. 7, a thermistor 305 (see FIG. 8), a protection circuit 306, and a terminal 307 for energizing external devices are mounted on the printed wiring board 304. An insulating plate (not shown) is attached to the surface of the printed wiring board 304 facing the assembled battery 303 in order to avoid unnecessary connection with the wiring of the assembled battery 303.

The positive electrode side lead 308 is connected to the positive electrode terminal 207 located at the lowermost layer of the assembled battery 303, and the tip thereof is inserted into the positive electrode side connector 309 of the printed wiring board 304 and electrically connected thereto. The negative electrode side lead 310 is connected to the negative electrode terminal 206 located in the uppermost layer of the assembled battery 303, and the tip thereof is inserted into and electrically connected to the negative electrode side connector 311 of the printed wiring board 304. These connectors 309 and 311 are connected to the protection circuit 306 through wirings 312 and 313 (see FIG. 8) formed on the printed wiring board 304.

The thermistor 305 is used to detect the temperature of the unit cell 301 and is not shown in FIG. 7, but is provided in the vicinity of the unit cell 301 and its detection signal is transmitted to the protection circuit 306. . The protection circuit 306 can cut off the plus side wiring 314a and the minus side wiring 314b between the protection circuit 306 and the terminal 307 for energizing external devices under a predetermined condition. Here, the predetermined condition is, for example, when the temperature detected by the thermistor 305 is equal to or higher than a predetermined temperature. Furthermore, the predetermined condition is when an overcharge, overdischarge, overcurrent, or the like of the unit cell 301 is detected. Such detection of overcharge or the like is performed for each single cell 301 or the entire single cell 301. In addition, when detecting an overcharge or the like in each unit cell 301, 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 unit cell 301. In the case of FIG. 7 and FIG. 8, the voltage detection wiring 315 is connected to each of the single cells 301, and the detection signal is transmitted to the protection circuit 306 through these wirings 315.

As shown in FIG. 7, protective sheets 316 made of rubber or resin are arranged on three side surfaces of the assembled battery 303 excluding the side surfaces from which the positive electrode terminal 207 and the negative electrode terminal 206 protrude.

The assembled battery 303 is stored in the storage container 317 together with each protective sheet 316 and the printed wiring board 304. That is, the protective sheet 316 is disposed on both the inner side surface in the long side direction and the inner side surface in the short side direction of the storage container 317, and the printed wiring board 304 is disposed on the inner side surface opposite to the protective sheet 316 in the short side direction. Be placed. The assembled battery 303 is located in a space surrounded by the protective sheet 316 and the printed wiring board 304. The lid 318 is attached to the upper surface of the storage container 317.

For fixing the assembled battery 303, a heat shrink tape may be used instead of the adhesive tape 302. In this case, protective sheets are arranged on both side surfaces of the assembled battery, the heat shrinkable tape is circulated, and then the heat shrinkable tape is heat shrunk to bind the assembled battery.

Here, FIGS. 7 and 8 show the configuration in which the cells 301 are connected in series. However, in order to increase the battery capacity, the cells 301 may be connected in parallel or in parallel with the series connection. It is good also as a structure which combined connection. In addition, the assembled battery packs can be further connected in series and in parallel.

According to this embodiment described above, a battery pack can be provided. The battery pack according to the present embodiment includes a plurality of nonaqueous electrolyte secondary batteries according to the first embodiment or the second embodiment. Such a battery pack has excellent rapid charge / discharge performance, high energy density, and long life.

In addition, the aspect of a battery pack is changed suitably by a use. As a use of the battery pack according to the present embodiment, one that is required to exhibit excellent cycle characteristics when a large current is taken out is preferable. Specific examples include a power source for a digital camera, a two-wheel or four-wheel hybrid electric vehicle, a two-wheel or four-wheel electric vehicle, an in-vehicle device such as an assist bicycle. In particular, a battery pack using a nonaqueous electrolyte secondary battery having excellent high temperature characteristics is suitably used for in-vehicle use.

According to the above embodiment, it is possible to provide a battery pack having excellent productivity and excellent rapid charge / discharge performance and high energy density.

Hereinafter, based on an Example, said embodiment is described further in detail.
Note that the identification of the crystal phase and the estimation of the crystal structure of the synthesized niobium-titanium composite oxide were performed by a powder X-ray diffraction method using Cu-Kα rays. Further, the composition of the product was analyzed by ICP (Inductively Coupled Plasma) emission spectroscopic analysis to confirm that the target product was obtained. Further, TEM (Transmission Electron Microscope) and EPMA (Electron Probe Micro Analyzer) measurements were performed, and the niobium-titanium composite oxide Li _x TiNb _{2- y My} O _{7 ± δ was} measured. The state of element M was confirmed. Moreover, DSC (differential scanning calorimeter) measurement of the obtained sample was performed, and melting | fusing point was investigated from the vertex position of the endothermic peak.

<Example 1-Example 4>
The niobium-titanium composite oxide of Example 1 to Example 4 was produced by the following procedure.

"Evaluation of electrochemical properties"
(Production of electrochemical measurement cell)
The niobium-titanium composite oxide synthesized above was mixed with acetylene black as a conductive agent. The mixing ratio of the niobium-titanium composite oxide and acetylene black was 10 parts by mass of acetylene black with respect to 100 parts by mass of the niobium-titanium composite oxide. This mixture was dispersed in NMP (N-methyl-2-pyrrolidone). Polyvinylidene fluoride (PVdF) as a binder was mixed with the obtained dispersion to prepare an electrode slurry. 10 parts by mass of PVdF was mixed with 100 parts by mass of the niobium-titanium composite oxide.
Next, the electrode slurry was applied to both surfaces of a current collector made of aluminum foil using a blade. Then, it dried at 130 degreeC under vacuum for 12 hours, and obtained the electrode.

Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 2: 1 to prepare a mixed solvent. In this mixed solvent, lithium hexafluorophosphate as an electrolyte was dissolved at a concentration of 1M to prepare a non-aqueous electrolyte. In the obtained non-aqueous electrolyte, 0.7 ppm, 50 ppm, 100 ppm, and 180 ppm of Nb ⁵⁺ were dissolved to obtain the non-aqueous electrolytes of Example 1 to Example 4. NbCl ₅ was used as the Nb ⁵⁺ source.

An electrochemical measurement cell was fabricated using the above electrode, a metal lithium foil as a counter electrode, and a non-aqueous electrolyte.

(Electrochemical measurement)
A charge / discharge test was performed at room temperature using the electrochemical measurement cell. Charging / discharging was performed at a charge / discharge current value of 0.2 C (time discharge rate) in a potential range of 1.0 V to 3.0 V on the basis of a metal lithium electrode.

  The rate performance was also investigated. The discharge capacities at 0.2C, 1C, 2C, 5C, and 10C were measured, and the discharge capacity ratio was calculated when the 0.2C capacity was 1.0C capacity.

Next, 50 cycles were repeatedly charged / discharged at room temperature (one cycle for charging / discharging), and the 50-time discharge capacity retention rate was examined. Charging / discharging was performed at room temperature with a current value of 1 C (time discharge rate) in a potential range of 1.0 V to 3.0 V based on a metal lithium electrode.

After 50 cycles, charge and discharge were performed again at 0.2 C (time discharge rate), and the discharge capacity was measured. The capacity retention rate (%) after 50 cycles was calculated with the initial discharge capacity as 100%.
The results are shown in FIGS. FIG. 9 is a graph showing measurement results of initial charge / discharge capacities of the electrochemical measurement cells of Example 1 to Example 3. FIG. 10 is a graph showing measurement results of rate characteristics of the electrochemical measurement cells of Example 1 to Example 3. FIG. 11 is a graph showing changes in cycle capacity of the electrochemical measurement cells of Example 1 to Example 3. FIG. 12 is a graph showing changes in cycle capacity of the electrochemical measurement cell of Example 4.
Table 1 shows the content of Nb ⁵⁺ in the nonaqueous electrolyte, the content of water, and the electrochemical characteristics. In Table 1, the measurement results of the electrochemical characteristics are obtained when the discharge capacity maintenance rate (%) after 50 cycles at 45 ° C. and 1C exceeds 80%, ◎, after 45 cycles at 45 ° C. and 1C. When the discharge capacity maintenance rate (%) exceeds 70% and is 80% or less, ○, when the discharge capacity maintenance rate (%) after 50 cycles at 45 ° C. and 1C exceeds 60% and 70% or less Δ, the case where the discharge capacity retention rate (%) after 50 cycles was 60% or less was evaluated as x.

<Example 5>
An electrochemical measurement cell was produced in the same manner as in Example 1 to Example 4 except that activated alumina was added to the nonaqueous electrolyte.
About the obtained electrochemical measurement cell, it carried out similarly to Example 1-Example 4, and performed the electrochemical measurement.
The results are shown in FIG. FIG. 12 is a graph showing changes in cycle capacity of the electrochemical measurement cell of Example 5.

<Example 6>
Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 2: 1 to prepare a mixed solvent. An electrochemical measurement cell was produced in the same manner as in Example 1 to Example 4 except that LiClO ₄ was dissolved as an electrolyte in this mixed solvent at a concentration of 1 M to prepare a nonaqueous electrolyte.
About the obtained electrochemical measurement cell, it carried out similarly to Example 1-Example 4, and performed the electrochemical measurement.
The results are shown in FIG. FIG. 12 is a graph showing changes in cycle capacity of the electrochemical measurement cell of Example 6.

<Example 7>
A compound in which the niobium-titanium composite oxide is represented by Li _x TiNb _2-y M _y O _{7 ± δ} (where 0 ≦ x ≦ 5, 0 ≦ y ≦ 0.5, 0 ≦ δ ≦ 0.3) When the element M is Mo or Fe, an electrochemical measurement cell was produced in the same manner as in Example 1 to Example 3 except that 50 ppm of Nb ⁵⁺ was added to the nonaqueous electrolyte. Note that the Mo content was 0.03 mol and the Fe content was 0.06 mol with respect to 1 mol of Ti in the niobium-titanium composite oxide.
About the obtained electrochemical measurement cell, it carried out similarly to Example 1-Example 4, and performed the electrochemical measurement. The results are shown in Table 1 and FIG. FIG. 13 is a graph showing changes in the discharge capacity retention rate of the electrochemical measurement cell of Example 7.

<Comparative Example 1>
An electrochemical measurement cell was produced in the same manner as in Example 1 to Example 4 except that Nb ⁵⁺ was not added to the nonaqueous electrolyte.
About the obtained electrochemical measurement cell, it carried out similarly to Example 1-Example 4, and performed the electrochemical measurement. The results are shown in Table 1.

<Comparative example 2>
An electrochemical measurement cell was produced in the same manner as in Example 1 to Example 4 except that 10000 ppm of Nb ⁵⁺ was added to the nonaqueous electrolyte.
About the obtained electrochemical measurement cell, it carried out similarly to Example 1-Example 4, and performed the electrochemical measurement. The results are shown in Table 1.

From the results of Table 1, in Example 1 to Example 7, the discharge capacity retention rate after 50 cycles at 45 ° C. and 1 C by setting the content of Nb ⁵⁺ in the nonaqueous electrolyte to 0.7 ppm to 180 ppm. (%) Was found to exceed 60%. Furthermore, by setting the content of Nb ⁵⁺ in the non-aqueous electrolyte to 50 ppm to 100 ppm, the discharge capacity retention rate (%) after 50 cycles at 45 ° C. and 1 C exceeds 70% and becomes 80% or less. I understood.
In Example 5, the content of Nb ⁵⁺ in the non-aqueous electrolyte was 0.7 ppm, and activated alumina was added to the non-aqueous electrolyte so that the water content in the non-aqueous electrolyte was less than 3 ppm. It was found that the discharge capacity retention ratio (%) after 50 cycles at 1 ° C. exceeded 80%.
In Example 6, the content of Nb ⁵⁺ in the nonaqueous electrolyte was 0.7 ppm, and LiClO ₄ was used as the electrolyte, whereby the discharge capacity retention rate (%) after 50 cycles at 45 ° C. and 1 C was 80%. It turned out that it exceeds.
In Example 7, the content of Nb ⁵⁺ in the non-aqueous electrolyte was 50 ppm, and as the niobium-titanium composite oxide, Li _x TiNb _{2 -y} M _y O _{7 ± δ} (where 0 ≦ x ≦ 5, 0 ≦ y ≦ 0.5, 0 ≦ δ ≦ 0.3), and by using a compound in which the element M is Mo or Fe, the discharge capacity retention rate (%) after 50 cycles at 45 ° C. and 1 C is obtained. It was found to exceed 80%.

On the other hand, in Comparative Example 1, it was found that the discharge capacity retention rate (%) after 50 cycles at 45 ° C. and 1 C was less than 60% by setting the content of Nb ⁵⁺ in the nonaqueous electrolyte to 0 ppm. It was.
In Comparative Example 2, it was found that the discharge capacity retention rate (%) after 50 cycles at 45 ° C. and 1 C was less than 60% by setting the content of Nb ⁵⁺ in the nonaqueous electrolyte to 10000 ppm.
In Comparative Example 1, the electrochemical measurement cell expired immediately after repeated charge and discharge.

From the results of FIG. 9, it was found that in Example 1 to Example 3, the initial charge capacity and the initial discharge capacity were substantially equal.
From the results of FIG. 10, it was found that the rate characteristics were substantially the same in Example 1 to Example 3.
From the result of FIG. 11, when the content of Nb ⁵⁺ in the non-aqueous electrolyte is 50 ppm (Example 2) and the content of Nb ⁵⁺ in the non-aqueous electrolyte is 100 ppm (Example 3), the cycle capacity is almost equivalent. It was found that the content of Nb ⁵⁺ in the non-aqueous electrolyte was superior to that in the case of 0.7 ppm (Example 1).
From the results of FIG. 12, in Example 5, the content of Nb ⁵⁺ in the non-aqueous electrolyte was 0.7 ppm, activated alumina was added to the non-aqueous electrolyte, and the water content in the non-aqueous electrolyte was less than 3 ppm. In Example 6, the content of Nb ⁵⁺ in the non-aqueous electrolyte was 0.7 ppm, and LiClO ₄ was used as the electrolyte, so that Example 5 and Example 6 had almost the same cycle capacity, It was found that the content of Nb ⁵⁺ in the electrolyte was superior to that in the case of 180 ppm (Example 4).
From the result of FIG. 13, when the content of Nb ⁵⁺ in the non-aqueous electrolyte is 50 ppm and the niobium-titanium composite oxide containing Mo is used as the negative electrode active material, Nb ⁵⁺ is not added to the non-aqueous electrolyte. It was found that the discharge capacity retention rate was higher than (Comparative Example 1). Further, when the content of Nb ⁵⁺ in the non-aqueous electrolyte is 50 ppm and a niobium-titanium composite oxide containing Fe is used as the negative electrode active material, Nb ⁵⁺ is not added to the non-aqueous electrolyte (Comparative Example 1). ), The discharge capacity retention rate was high until the 42nd cycle, but the capacity was almost zero at the 43rd cycle.

Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

101 ... Metal ion, 102 ... Oxide ion, 103 ... Frame structure portion, 104 ... Void portion, 105,106 ... Area, 107 ... Void portion, 200 ... Non Water electrolyte secondary battery, 201 ... wound electrode group, 202 ... exterior material, 203 ... negative electrode, 204 ... separator, 205 ... positive electrode, 206 ... negative electrode terminal, 207 ...・ Positive electrode terminal, 210... Nonaqueous electrolyte secondary battery, 211... Stacked electrode group, 212. ... Negative electrode terminal, 217 ... Positive electrode terminal, 300 ... Battery pack, 301 ... Single cell, 302 ... Adhesive tape, 303 ... Battery pack, 304 ... Printed wiring board, 305 ... Thermistor, 306 ... Protection 307... Positive electrode side lead 309... Positive electrode side connector 310. Negative electrode side lead 311... Negative electrode side connector 312 and 313. 314a: plus side wiring, 314b: minus side wiring, 315 ... wiring, 316 ... protective sheet, 317 ... storage container, 318 ... lid.

Claims (6)

A positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator;
The negative electrode includes a niobium-titanium composite oxide as a negative electrode active material,
The nonaqueous electrolyte secondary battery in which the content of Nb ⁵⁺ in the nonaqueous electrolyte is 0.5 ppm or more and 200 ppm or less. The niobium-titanium composite oxide is Li _x TiNb _2-y M _y O _{7 ± δ} (where M is B, Na, Mg, Al, Si, S, P, K, Ca, Mo, W, Cr) And at least one selected from the group consisting of Mn, Co, Ni and Fe, 0 ≦ x ≦ 5, 0 ≦ y ≦ 0.5, 0 ≦ δ ≦ 0.3) 2. The nonaqueous electrolyte secondary battery according to 1.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein a content of water in the nonaqueous electrolyte is 1 ppm or more and 100 ppm or less. The non-aqueous electrolyte secondary battery according to claim 1, wherein the niobium-titanium composite oxide is monoclinic TiNb ₂ O ₇ .   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode includes a lithium nickel composite oxide or a lithium manganese composite oxide as a positive electrode active material. A battery pack formed by electrically connecting a plurality of nonaqueous electrolyte secondary batteries according to claim 1 in series or in parallel.

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