WO2021186601A1

WO2021186601A1 - Secondary battery and battery pack

Info

Publication number: WO2021186601A1
Application number: PCT/JP2020/011896
Authority: WO
Inventors: 将司服部; 泰章村司; 尚己西尾
Original assignee: 株式会社東芝
Priority date: 2020-03-18
Filing date: 2020-03-18
Publication date: 2021-09-23

Abstract

An embodiment of the present invention provides a secondary battery which comprises a positive electrode, a negative electrode and a nonaqueous electrolyte, while satisfying formula (1) to formula (3). The positive electrode comprises a positive electrode active material-containing layer that contains a lithium-containing manganese oxide and a lithium-containing nickel cobalt manganese oxide. The negative electrode comprises a negative electrode active material-containing layer that contains a lithium titanium oxide and an Li intercalation/deintercalation oxide which is different from the lithium titanium oxide.　(1): E_p > E_n (2): E_n ≥ 94% (3): 1.0 ≤ C_p/C_n ≤ 1.2 In the formulae, E_p represents the charge/discharge efficiency of the positive electrode within the range of from 3.0 V to 4.25 V (vs. Li/Li⁺); E_n represents the charge/discharge efficiency of the negative electrode within the range of from 1.4 V to 2.0 V (vs. Li/Li⁺); C_p represents the charge capacity per unit area of the positive electrode when the charge/discharge range is from 3.0 V to 4.25 V (vs. Li/Li⁺); and C_n represents the charge capacity per unit area of the negative electrode when the charge/discharge range is from 1.4 V to 2.0 V (vs. Li/Li⁺).

Description

Rechargeable batteries and battery packs

The embodiment of the present invention relates to a secondary battery and a battery pack.

Secondary batteries, including lithium-ion secondary batteries, are widely used in vehicles such as mobile devices and 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 contain an electrolyte. The electrodes of a secondary battery of a certain design include a current collector and an active material-containing layer provided on the main surface of the current collector. The active material-containing layer of the electrode can be, for example, a layer composed of active material particles, a conductive agent, and a binder, and can be a porous body capable of holding an electrolyte.

Lithium-containing manganese oxide is an example of an active material used for the positive electrode of a lithium ion battery or a secondary battery. A lithium ion secondary battery using lithium-containing manganese oxide for the positive electrode and lithium titanate for the negative electrode has excellent low-temperature output and longevity performance.

International Publication No. 2016/132436

It is an object of the present invention to provide a secondary battery having an excellent charge / discharge cycle life and a battery pack equipped with this battery.

According to the embodiment, a secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte and satisfying the following equations (1), (2), and (3) is provided. The positive electrode 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. The negative electrode includes a negative electrode active material-containing layer comprising a negative electrode active material containing a lithium titanium oxide and a Li-inserted-desorbed oxide different from the lithium titanium oxide.

_E _p> E n (1)
E _n ≧ 94% (2)
1.0 ≤ C _p / C _n ≤ 1.2 (3)
However, _{E p} is 3.0V (vs.Li/Li ⁺⁾ or 4.25V (vs.Li/Li ⁺⁾ The following charge-discharge efficiency of the positive electrode in charging and discharging range, _{E n} is 1.4V (vs.Li / Li ⁺⁾ or higher 2.0V (vs.Li/Li ⁺⁾ the following charge-discharge efficiency of the negative electrode in charging and discharging range, _{C p} is the charge-discharge range of the positive electrode 3.0V (vs.Li/Li ⁺⁾ or 4 Charging capacity per unit area (mAh / m ² ) when it is .25V (vs.Li ^/ Li +) or less, and Cn _means that the negative electrode charge / discharge range is 1.4V (vs.Li / Li ⁺ ) or more 2 It is the charge capacity (mAh / m ² ) per unit area when the voltage is 0.0 V (vs. Li / Li ^{+) or less.}

According to another embodiment, a battery pack containing a secondary battery according to the above embodiment is provided.

FIG. 1 is a partially cutaway perspective view showing an example of the battery according to the embodiment. FIG. 2 is an enlarged cross-sectional view of part A of the battery shown in FIG. FIG. 3 is a partially cutaway perspective view showing another example of the battery according to the embodiment. FIG. 4 is a partially cutaway perspective view showing still another example of the battery according to the embodiment. FIG. 5 is an enlarged cross-sectional view of a portion B of the battery shown in FIG. FIG. 6 is an exploded perspective view showing an example of the battery pack according to the embodiment. FIG. 7 is a block diagram showing an example of the electric circuit of the battery pack shown in FIG. FIG. 8 is a graph showing an example of the charge / discharge curve of the battery according to the embodiment.

Embodiment

A lithium-ion secondary battery that uses lithium-containing manganese oxide for the positive electrode and lithium titanate for the negative electrode has excellent low-temperature output and longevity performance. On the other hand, such a battery has a problem that gas is generated. Further, there is a problem that the battery performance is deteriorated due to the elution of Mn from the positive electrode.

As a countermeasure against gas generation, an active material with a layered structure can be added. Among such active materials, the lithium-containing cobalt oxide plays the role of a gas adsorbent, and therefore, the amount of gas generated is reduced by using both the lithium-containing manganese oxide and the lithium-containing cobalt oxide as the positive electrode active material.

However, the lithium-containing cobalt oxide has a problem that it is significantly deteriorated at a high potential. Therefore, the use of lithium-containing nickel-cobalt-manganese oxide as an alternative to lithium-containing cobalt oxide has been studied. Lithium-containing nickel-cobalt-manganese oxide is resistant to high potentials. However, the lithium-containing nickel-cobalt-manganese oxide has a large expansion and contraction when lithium ions are inserted and removed, and has a problem in cycle life performance. Further, the lithium-containing nickel-cobalt-manganese oxide has a low working potential. Moreover, at a potential of 3.6 V (vs. Li ^/ Li +) or less, the cycle life performance of the lithium-containing nickel-cobalt-manganese oxide tends to deteriorate.

The embodiment will be described below with reference to the drawings. In addition, the same reference numerals are given to common configurations throughout the embodiment, and duplicate description will be omitted. In addition, each figure is a schematic view for facilitating the explanation of the embodiment and its understanding, and the shape, dimensions, ratio, etc. of the figure may differ from those of the actual device. The design can be changed as appropriate by taking into consideration.

(First Embodiment)
According to the first embodiment, a secondary battery including 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 is provided. The positive electrode active material-containing layer contains a positive electrode active material containing 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 negative electrode active material-containing layer contains lithium titanium oxide as the first negative electrode active material, and also contains Li-inserted-desorbed oxide different from the lithium titanium oxide as the second negative electrode active material. The secondary battery satisfies the following equations (1), (2), and (3).

_E _p> E n (1)
E _n ≧ 94% (2)
1.0 ≤ C _p / C _n ≤ 1.2 (3).

Here, _{E p} is the charge-discharge efficiency of the positive electrode in the following charge-discharge range 3.0V (vs.Li/Li ⁺⁾ or 4.25V (vs.Li/Li ^+). E _n is the charge-discharge efficiency of 1.4V (vs.Li/Li ⁺⁾ or 2.0V (vs.Li/Li ⁺⁾ anode in the following charge-discharge range. In C _p is the charge capacity per unit area when the charge-discharge range of the positive electrode is not more than 3.0V (vs.Li/Li ⁺⁾ or ^{4.25V (vs.Li/Li +) (mAh /} m 2) be. In C _n the charge capacity per unit area when the charge-discharge range of the negative electrode is less than 1.4V (vs.Li/Li ⁺⁾ or ^{2.0V (vs.Li/Li +) (mAh /} m 2) be.

The secondary battery can be, for example, a lithium ion battery. Specific examples of the secondary battery include a non-aqueous electrolyte secondary battery. A non-aqueous electrolyte secondary battery may be simply referred to as a non-aqueous electrolyte battery.

And reasons for specifying the E _p and _{E n} the range of relation and (2) formula (1), and reasons for specifying the ratio of _{C p} for _{C n} and (Cp / Cn) (3) in the range formula explain.

The fact that meets the above-mentioned (1) reacting a _{(E p>} E _n), indicates a low charge-discharge efficiency of the negative electrode as compared with the charge-discharge efficiency of the positive electrode. (2) The fact that satisfies formula (E _n ≧ 94%), indicating that the charge-discharge efficiency of the negative electrode moderately high, not too low. Satisfying both the equations (1) and (2) indicates that the charge / discharge balance is appropriately adjusted between the positive electrode and the negative electrode. In a battery in such a state, the positive electrode potential does not easily drop when the state of charge (SOC) is 0%. As a specific example, in a secondary battery including a positive electrode of a system in which the first positive electrode active material and the second positive electrode active material are combined, when the battery is discharged to a battery voltage of 1.8 V at a current value of 0.2 C. open circuit voltage of the positive electrode may be the 3.6V (vs.Li/Li ⁺⁾ or 3.9V (vs.Li/Li ⁺⁾ within the following range. Since the positive electrode potential in the discharged state does not easily drop, it is possible to greatly improve the cycle life performance of the battery. Further, since the charge / discharge efficiency of the negative electrode is lower than that of the positive electrode, the range of use of the two-phase coexistence reaction region for the negative electrode active material is narrowed, so that the cycle life performance is improved.

FIG. 8 is a graph showing an example of the charge / discharge curve of the battery according to the embodiment. In the graph of FIG. 8, the horizontal axis represents the battery capacity (Ah), and the vertical axis represents the electrode potential (vs. Li ^/ Li +). The graph shows the charge curve 83 and the discharge curve 93 of the positive electrode, and the charge curve 82 and the discharge curve 92 of the negative electrode. The difference in length of the respective transverse axis direction of the charging curve 83 and the discharge curve 93 of the positive electrode is small, it can be seen that the charge-discharge efficiency E _p of the positive electrode is high. On the other hand, from the horizontal axis direction of the difference in length is greater than that for the positive electrode, the charge-discharge efficiency E _p it is the positive electrode of the charge-discharge efficiency E _n of the negative electrode between the charge curve 82 and the discharge curve 92 of the negative electrode It turns out that is also low. Since the charge / discharge efficiency of the negative electrode is lower, the negative electrode potential rises just before the discharge end voltage is reached, before the positive electrode potential drops significantly. Therefore, the discharge end voltage of the battery, for example, 1.8 V, can be reached before the positive electrode potential drops significantly with the discharge. _{In this way, the positive electrode potential P 0} in the discharged state (for example, when SOC = 0%) does not decrease, and the discharge can be terminated in a state where the positive electrode potential does not drop extremely.

A more preferred range of values of E _n is less 96.5% or more 94.0%. The values of E _n by specifying this range, it is possible to further improve the cycle performance.

Satisfying the above equation (3) (1.0 ≤ C _p / C _n ≤ 1.2) indicates that the positive electrode capacity is equivalent to about 1.2 times the negative electrode capacity. When the positive electrode capacity is equal to or larger than the negative electrode capacity, it is possible to reduce the decrease in the positive electrode potential. When the ratio of the positive electrode capacity to the negative electrode capacity (C _p / C _n ) is 1.2 or less, a high energy density can be ensured.

The reason described above, as well as specific to a range of related and (2) of the E _p and E _n (1) where, by specifying the ratio of C _p and C _n in the range of (Formula 3) , It is possible to improve the cycle performance.

The composition of each of the first and second positive electrode active materials, the mixing ratio of the first and second positive electrode active materials in the positive electrode active material, the respective compositions of the first and second negative electrode active materials, and the negative electrode active material. The design at the time of battery manufacturing is appropriately set, including the mixing ratio of the first and second negative electrode active materials, the thickness of the positive positive active material-containing layer, the thickness of the negative negative active material-containing layer, and the aging conditions for the assembled battery. By combining them, a secondary battery satisfying all of the equations (1), (2) and (3) can be obtained. A specific example will be shown in the latter embodiment. For example, for E _p, a large influence of the weight ratio of the second positive electrode active material in the positive electrode active material. For E _n, is greater influence of the weight ratio of the second negative electrode active material of the negative electrode active material.

A positive electrode using a combination of lithium-containing manganese oxide (first positive electrode active material) and lithium-containing nickel cobalt manganese oxide (second positive electrode active material; hereinafter, NCM), and Li having a spinel structure, for example. _{4 In} a battery that combines a negative electrode using lithium titanium oxide such as lithium titanate represented by Ti ₅ O ₁₂ , if the ratio of NCM used for the positive electrode is low, the reduction gas generated at the negative electrode is less suppressed. .. On the other hand, NCM has a low operating potential and low initial charge / discharge efficiency. Therefore, if the ratio of NCM used for the positive electrode is high, the operating potential of the positive electrode decreases. Furthermore, if the ratio of NCM is high, the charge / discharge efficiency at the initial stage of the positive electrode is low, so that the positive electrode potential at SOC = 0% can be low. That is, the higher the NCM ratio in the positive electrode, the wider the operating range of the positive electrode is to a lower potential, and the potential at which the cycle life of the NCM deteriorates is likely to be included in the charge / discharge range. As described above, a high NCM ratio becomes a factor of accelerating the deterioration of the positive electrode, and the cycle life of the battery may be shortened due to the influence thereof.

The content of the second positive electrode active material in the positive electrode active material is preferably 2 wt% or more and 20 wt% or less. When the content of the second positive electrode active material (NCM) among the positive electrode active materials is 2 wt% or more, the effect of absorbing the gas generated by the reductive decomposition of the non-aqueous electrolyte in the negative electrode can be exhibited by the positive electrode. When the content of the second positive electrode active material is 20 wt% or less, the operating potential of the positive electrode can be maintained sufficiently high. In addition, the charge / discharge efficiency of the positive electrode can be kept good. A more preferable range of 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.

As the first negative electrode active material, for example, the above-mentioned lithium titanate having a spinel structure (Li ₄ Ti ₅ O ₁₂ ) can be mentioned, and the lithium titanate has high charge / discharge efficiency and can be charged / discharged. There is very little expansion and contraction due to the insertion-desorption of lithium ions. The cycle life performance can be improved by using the first negative electrode active material together with the Li insertion-desorption oxide, which is different from the lithium titanium oxide of the first negative electrode active material, as the second negative electrode active material. can. The Li insertion-desorption oxide (second negative electrode active material), which is different from the above-mentioned lithium titanium oxide, is a metal capable of inserting and removing Li ions, which are carrier ions of charges between the positive and negative electrodes. Among oxides such as oxides and metal-containing composite oxides, oxides other than the above lithium titanium oxide as the first negative electrode active material are included. Specific examples include one or more Li-inserted-eliminating oxides selected from the group consisting of niobium-titanium composite oxides and titanium oxide. In the negative electrode using lithium titanium oxide (first negative electrode active material) alone such as lithium titanate, the lithium diffusion inside the oxide is not so good at the end of discharge due to the high charge / discharge efficiency at the time of discharge. Via. In the negative electrode using the second negative electrode active material together with the first negative electrode active material, the charge / discharge efficiency is lower than that in the negative electrode using the first negative electrode active material alone. As a result, it is possible to avoid passing through the end of discharge of the first negative electrode active material.

On the other hand, if the proportion of the second negative electrode active material is large, the cycle life performance may be deteriorated due to the expansion and contraction of the negative electrode during charging and discharging. For example, a negative electrode using niobium-titanium composite oxide alone tends to have lower cycle performance than a negative electrode using lithium titanate because the volume expansion and contraction during charging and discharging are large.

From these facts, it is preferable that the content of the second negative electrode active material among the negative electrode active materials is 3 wt% or more and 30 wt% or less. A more preferable range of the content of the second negative electrode active material in the negative electrode active material is 3 wt% or more and 20 wt% or less.

When the secondary battery is discharged to 1.8V at 0.2C, the open circuit voltage of the positive electrode should be 3.6V (vs.Li ^/ Li +) or more and 3.9V (vs.Li ^/ Li +) or less. desirable. A secondary battery thus discharged can be in a 0% charge state (SOC). By setting the open circuit voltage to 3.6 V (vs. Li ^/ Li +) or more, the positive electrode potential is less likely to decrease, so that deterioration of the positive electrode can be suppressed. In addition, by setting the open circuit voltage to 3.9 V (vs.Li ^/ Li +) or less, the range where the open circuit voltage of the positive electrode ^{is higher than 3.9 V (vs.Li /} Li +) is used as the charge / discharge region. Therefore, a high capacity can be obtained. The more preferable range of the open circuit voltage of the positive electrode when the secondary battery is discharged to 1.8 V at 0.2 C is 3.69 V (vs.Li ^/ Li +) or more and 3.80 V (vs.Li ^/ Li +). It is as follows.

Hereinafter, the battery according to the embodiment will be described in detail.

(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 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 lithium-containing manganese oxide includes, for example, spinel-type lithium manganate, which is a compound represented by _{the chemical formula LiMn 2-x} M _x O _4. Here, 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 oxide, for _{_{example, LiNi 1-yz Co y Mn}} z O 2 ( where, 0 <y <1,0 <z <1 and 0 <y + z <1) including.

The positive electrode active material may contain other positive electrode active materials other than the first and second positive electrode active materials. The other positive electrode active material can 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. Examples of lithium-containing cobalt oxides include Li _w CoO ₂ . The range of the subscript w in the chemical formula Li _w CoO _{2 is 0 <w ≦ 1.} Examples of the lithium-nickel-cobalt composite _{_{oxide, LiNi 1-y Co y O}} 2 ( where, 0 <y <1) including. Examples of lithium manganese cobalt oxide include LiMn _y Co _1-y O ₂ (where 0 <y <1).

The positive electrode active material is, for example, in the form of particles. When it is in the form of particles, the positive electrode active material may be primary particles or may be secondary particles in which primary particles are aggregated.

The average particle size of the particles of the first positive electrode active material is preferably 8.0 μm or more and 11.0 μm or less. The average particle size of the particles of the second positive electrode active material is preferably 5.2 μm or more and 6.8 μm or less.

The positive electrode active material-containing layer can contain a binder and a conductive agent, if necessary.

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

The conductive agent can enhance the electron conductivity and suppress the contact resistance with the current collector. The conductive agent includes, for example, a carbon material such as acetylene black, carbon black, graphite, carbon nanofibers or carbon nanotubes. The type of the conductive agent used may be one type or two or more types.

The compounding ratio of the positive electrode active material, the conductive agent and the binder shall be in the range of 80% by weight to 95% by weight of the positive electrode active material, 3% by weight to 18% by weight of the conductive agent, and 2% by weight to 7% by weight of the binder. Is preferable.

As the current collector, for example, a sheet containing a material having high electrical conductivity can be used. 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 thereof 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. Further, the aluminum alloy foil may contain other transition metals. The content of the transition metal in the aluminum alloy foil is preferably 1% by mass or less. Examples of the transition metal 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 positive electrode current collector can include a portion that does not support an active material-containing layer on its surface. This portion can serve, for example, as a positive electrode current collector tab. Alternatively, the positive electrode may further include a positive electrode current collector tab that is separate from the positive electrode current collector. A separate positive electrode current collector tab can be electrically connected to the positive electrode.

It is desirable that the thickness of the positive electrode is 80 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 80 μm or less, the resistance of the positive electrode can be lowered, so that the overvoltage applied to the positive electrode can be reduced. As a result, it is possible to suppress a decrease in the positive electrode potential at the end of discharge, so that deterioration due to over-discharge of the positive electrode can be suppressed. In order to secure a practical battery capacity, it is desirable that the thickness of the positive electrode is 65 μm or more.

The density of the positive electrode active material-containing layer ^{is preferably 2.5 g / cm 3} or more and 3.1 g / cm ³ or less. As a result, even if the thickness of the positive electrode is as thin as 80 μm or less, it is possible to secure a positive electrode capacity that can withstand practical use.

The basis weight of the positive electrode active material-containing layer, that is, the weight per unit area (g / m ² ) can be, for example, 80 g / m ² or more and 130 g / m ² or less.

In the production of a positive electrode, for example, a positive electrode active material, a positive electrode conductive agent, and a binder are suspended in an appropriate solvent, and the obtained slurry is applied to a positive electrode current collector and dried to obtain a positive electrode active material-containing layer. After making the above, press it. In addition, the positive electrode active material, the positive electrode conductive agent, and the binder may be formed in pellet form and 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 contains lithium titanium oxide as the first negative electrode active material and the second negative electrode active material, and Li insertion-desorption oxide different from the lithium titanium oxide.

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

The lithium titanium oxide as the first negative electrode active material includes, for example, lithium titanate having a spinel-type structure (for example, _{a compound represented by Li 4 + v} Ti ₅ O ₁₂ ; where v changes with charge and discharge. In value, 0 ≦ v ≦ 3), and _{a compound represented by rams delite type lithium titanate (for example, Li 2 + v} Ti ₃ O ₇ ; where v is a value that changes with charge and discharge, 0 ≦ v ≦. 3) and the like can be mentioned. On the other hand, the molar ratio of oxygen is formally shown as 12 _{for spinel type Li 4 + v} Ti ₅ O ₁₂ _{and 7 for rams delite type Li 2 + v} Ti ₃ O ₇ , but these are due to the influence of oxygen non-stoikiometry and the like. The value can change. It is desirable that the first titanium-containing oxide has a spinel structure and contains a compound (0 ≦ v ≦ 3) represented by _{Li 4 + v} Ti ₅ O _12.

For Li insertion-desorption oxides other than the above lithium titanium oxide, that is, the second negative electrode active material, for example, 1.4V (vs.Li ^/ Li +) or more and 2.0V (vs.Li ^/ Li +) Oxides having a Li insertion-desorption potential can be used in the following range. Specific examples include titanium oxide (titania), hollandite-type titanium composite oxide, lithium titanium composite oxide in which some of the constituent elements of the lithium titanium oxide are replaced with different elements, orthorhombic titanium-containing composite oxidation. Titanium-containing oxides such as materials and niobium titanium composite oxides are included. As another example, a metal composite oxide containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, Nb and Fe can be mentioned. The type of the second negative electrode active material can be one type or two or more types.

As titanium oxide, monoclinic titanium dioxide ( _{a compound represented by Li u} TiO ₂ (B); where u is a value that changes depending on the charge / discharge state, 0 ≦ u ≦ 1), anatase type titanium dioxide, And rutile type titanium dioxide.

The rectangular lithium-titanium-containing oxide is represented by the general formula Li _{2 + q} Na _2-r M1 _s Ti _6-t M2 _t O _{14 + δ} , M1 is Cs and / or K, and M2 is Zr, Sn, V. , Nb, Ta, Mo, W, Fe, Co, Mn, and Al. The range of each subscript is 0 ≦ q ≦ 4, 0 ≦ r ≦ 2, 0 ≦ s ≦ 2, 0 ≦ t <6, −0.5 ≦ δ ≦ 0.5, respectively.

Examples of the niobium-titanium composite oxide include a monoclinic lithium-niobium-titanium-containing oxide and a rectangular Na-containing niobium-titanium composite oxide. The monoclinic form lithium niobate titanium-containing oxide is expressed by a general formula _{_{_{_{Li m Ti 1-n M3 n}}}} Nb 2-p M4 p O 7 + σ, M3 is Zr, Si, Sn, Fe, Co, Mn and Ni Examples include at least one compound selected from the group consisting of, and M4 being at least one compound selected from the group consisting of V, Nb, Ta, Mo, W and Bi, 0≤m≤5,0. ≦ n <1, 0 ≦ p <2, −0.3 ≦ σ ≦ 0.3. Examples of the orthorhombic Na-containing niobium-titanium composite oxide include compounds represented by the general formula Li _{2 + g} Na _2-j M5 _h Ti _6-j-k Nb _j M6 _k O _{14 + δ} . In the general formula, M5 is at least one selected from the group consisting of Cs, K, Sr, Ba and Ca, and M6 is Zr, Sn, V, Ta, Mo, W, Fe, Co, Mn, And at least one selected from the group consisting of Al, 0 ≦ g <2, 0 ≦ h <2, 0 <j <2, 0 ≦ k <3, −0.5 ≦ δ ≦ 0.5. .. It is preferable that M6 is at least one selected from the group consisting of Sn, V, Ta, Mo, W, Fe, Co and Mn.

The negative electrode active material-containing layer may contain one or more selected from the group consisting of niobium-titanium composite oxide and titanium oxide as the second negative electrode active material. In particular, the second negative electrode active material can be, for example, a monoclinic lithium niobate-containing oxide and / or a monoclinic titanium dioxide.

The negative electrode active material may contain other negative electrode active materials other than the first and second negative electrode active materials. Other negative electrode active materials include, for example, metals, metal alloys, metal sulfides, metal nitrides, graphitic materials, carbonaceous materials. Examples of the metal include aluminum and lithium. Examples of the metal alloy include aluminum alloys, magnesium alloys, lithium alloys and the like. In addition to the metal, for example, a metalloid such as silicon can be used as the negative electrode active material. As the metal sulfide, for example, titanium sulfide such as TiS _2, molybdenum sulfide such as MoS _2, FeS, FeS _2, and _Li d FeS ₂ (subscript d is 0.9 ≦ d ≦ 1.2) of Such as iron sulfide. Examples of the metal nitride include lithium nitride such as lithium cobalt nitride (for example, Li _e Co _f N, where 0 <e <4 and 0 <f <0.5). .. Examples of the graphitic material and the carbonaceous material include graphite (for example, natural graphite or artificial graphite), coke, vapor-grown carbon fiber, mesophase-pitch carbon fiber, spherical carbon, and resin-fired carbon.

The negative electrode active material is, for example, in the form of particles. When it is in the form of particles, the negative electrode active material may be primary particles or may be secondary particles in which primary particles are aggregated.

The average particle size of the particles of the first and second negative electrode active materials is preferably 0.8 μm or more and 1.2 μm or less.

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

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide, and polyamide. The type of binder can be one or more.

Examples of the negative electrode conductive agent include carbon black such as acetylene black and ketjen black, graphite, carbon fiber, carbon nanotube, and fullerene. The type of the conductive agent can be one type or two or more types.

The blending ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode active material-containing layer is 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 of the binder. It is preferably 28% by weight or more.

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 thereof 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. Further, the aluminum alloy foil may contain other transition metals. The content of the transition metal in the aluminum alloy foil is preferably 1% by mass or less. Examples of the transition metal 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.

For the negative electrode, for example, a negative electrode active material, a negative electrode conductive agent, and a binder are suspended in an appropriate solvent, and the obtained slurry is applied to a negative electrode current collector and dried to prepare a negative electrode active material-containing layer. It is produced by pressing. In addition, the negative electrode active material, the negative electrode conductive agent, and the binder may be formed in pellet form and used as the negative electrode active material-containing layer.

The thickness of the negative electrode can be in the range of 44 μm or more and 50 μm or less. 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 layers are 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 basis weight of the negative electrode active material-containing layer, that is, the weight per unit area (g / m ² ) can be 40 g / m ² or more and 65 g / m ² or less.

(3) Non-aqueous electrolyte Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte prepared by dissolving the electrolyte in a non-aqueous solvent, a gel-like non-aqueous electrolyte obtained by combining a liquid non-aqueous electrolyte and a polymer material, and the like.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), and difluorophosphate. Lithium salts such as lithium (LiPO ₂ F ₂ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₂ ) ₂ ], lithium tetrafluorofluoride (LiAlF ₄ ) Can be mentioned. These electrolytes may be used alone or in admixture of two or more. The electrolyte preferably contains lithium hexafluorophosphate.

The electrolyte is preferably dissolved in a non-aqueous solvent in the range of 0.5 mol / L or more and 2.5 mol / L or less.

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

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

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 via, for example, a separator.

The electrode group can have various structures. For example, the electrode group can have a stack type structure. The electrode group having a stack type structure can be obtained, for example, by alternately stacking a plurality of positive electrodes and a plurality of negative electrodes with a separator sandwiched between the positive electrode active material-containing layer and the negative electrode active material-containing layer. Alternatively, the electrode group can have a wound structure. In the winding type electrode group, for example, one separator, one negative electrode, another separator, and one positive electrode are laminated in this order to form a laminated body, and this laminated body is formed. It can be obtained by turning.

The material of the separator is not particularly limited. The separator is preferably electrically insulating. As the separator, for example, a porous film, a microporous film, a woven fabric, or a non-woven fabric, or a laminate of the same material or a different material among them can be used. Examples of the material for forming the separator include polymers such as polyethylene, polypropylene, ethylene-propylene copolymer polymer, ethylene-butene copolymer polymer, polyolefin, cellulose, polyethylene terephthalate, and vinylon. The material of the separator may be one kind, or two or more kinds may be used in combination.

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

The secondary battery according to the embodiment can further include a positive electrode terminal and a negative electrode terminal. A part of the positive electrode terminal is electrically connected to a part of the positive electrode, so that the positive electrode terminal can function as a conductor for electrons to move between the positive electrode and the external terminal. The positive electrode terminal can be connected to, for example, a positive electrode current collector, particularly a positive electrode tab. Similarly, the negative electrode terminal can act as a conductor for electrons to move between the negative electrode and the external terminal by electrically connecting a part of the negative electrode terminal to a part of the negative electrode. The negative electrode terminal can be connected to, for example, a negative electrode current collector, particularly a negative electrode tab.

The exterior member accommodates the electrode group and the non-aqueous electrolyte. The non-aqueous electrolyte can be impregnated in the electrode group within the exterior member. A part of each of the positive electrode terminal and the negative electrode terminal can also be extended from the exterior member.

The exterior member may be formed of a laminated film or may be composed of a metal container. When using a metal container, the lid can be integral with or separate from the container. The wall thickness of the metal container is more preferably 0.5 mm or less and 0.2 mm or less. Examples of the shape of the exterior member include a flat type, a square type, a cylindrical type, a coin type, a button type, a sheet type, and a laminated type. In addition to a small battery mounted on a portable electronic device or the like, a large battery mounted on a two-wheeled or four-wheeled automobile may be used.

It is desirable that the wall thickness of the laminated film exterior member is 0.2 mm or less. An example of a laminated film is a multilayer film containing a resin film and a metal layer arranged between the resin films. The metal layer is preferably an aluminum foil or an aluminum alloy foil for weight reduction. As the resin film, for example, a polymer material such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET) can be used. The laminated film can be sealed into the shape of an exterior member by heat fusion.

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

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 further preferably 5 μm or less. By setting the average crystal grain size to 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 further thinned. As a result, it is possible to realize a secondary battery suitable for in-vehicle use, which is lightweight, has high output, and has excellent long-term reliability.

Next, a specific example of the secondary battery according to the embodiment will be described with reference to the drawings.

First, the secondary battery of the first example according to the embodiment will be described with reference to FIGS. 1 and 2.

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

The secondary battery 100 shown in FIGS. 1 and 2 includes a flat electrode group 1 and an exterior member 7 made of a laminated film. The flat electrode group 1 includes a negative electrode 2, a positive electrode 3, and a separator 4. In the flat electrode group 1, the negative electrode 2 and the positive electrode 3 are wound in a flat shape with a separator 4 interposed therebetween.

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

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

The electrode group 1 is housed in the exterior member 7 made of a laminated film in a state where the ends of the negative electrode terminal 5 and the positive electrode terminal 6 extend from the exterior member 7. A non-aqueous electrolyte (not shown) is housed in the exterior member 7 made of a laminated film. The non-aqueous electrolyte is impregnated in the electrode group 1. The exterior member 7 made of a laminated film is sealed by heat-sealing each of the end portion and the two ends orthogonal to the end portion with the negative electrode terminal 5 and the positive electrode terminal 6 sandwiched between one end portions. ing.

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

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

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

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 contains 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 form, for example, an outer can as an outer member.

One end of the negative electrode lead 15a is electrically connected to the negative electrode current 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 current 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 an insulating member 17c.

4 and 5 show a battery including a stack-type electrode group as yet another example of the battery. FIG. 4 is a partially cutaway perspective view showing still another example of the battery according to the embodiment. FIG. 5 is an enlarged cross-sectional view of a portion B of the battery shown in FIG.

The battery 100 of the example shown in FIGS. 4 and 5 includes an electrode group 1 shown in FIGS. 4 and 5, an exterior member 7 shown in FIGS. 4 and 5, and a positive electrode terminal 6 shown in FIGS. 4 and 5. It is provided with the negative electrode terminal 5 shown in 4.

The electrode group 1 shown in FIGS. 4 and 5 includes a plurality of positive electrodes 3, a plurality of negative electrodes 2, and a single separator 4.

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

Each negative electrode 2 includes 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. Further, the negative electrode current collector 2a includes a portion where the negative electrode active material-containing layer 2b is not formed on the surface (not shown). This part acts as a negative electrode current collector tab.

As shown in part in FIG. 5, the separator 4 is zigzag. A positive electrode 3 or a negative electrode 2 is arranged in a space defined by faces of the zigzag separators 4 facing each other. As a result, as shown in FIG. 5, the positive electrode 3 and the negative electrode 2 are laminated so 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. Thus, the electrode group 1 is formed.

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

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

The exterior member 7 is formed of an aluminum-containing laminated film composed of an aluminum foil 71 and

resin films

72 and 73 formed on both sides thereof. The aluminum-containing laminated film forming the exterior member 7 is bent so that the resin film 72 faces inward with the bent portion 7d as a crease, and accommodates the electrode group 1. Further, as shown in FIGS. 4 and 5, in the peripheral edge portion 7b of the exterior member 7, the portions of the resin film 72 facing each other sandwich the positive electrode terminal 6 between them. Similarly, in the peripheral edge portion 7c of the exterior member 7, the portions of the resin film 72 facing each other sandwich the negative electrode terminal 5 between them. The positive electrode terminal 6 and the negative electrode terminal 5 extend from the exterior member 7 in opposite directions.

At the

peripheral edges

7a, 7b and 7c of the exterior member 7 excluding the portions sandwiching the positive electrode terminal 6 and the negative electrode terminal 5, the portions of the resin film 72 facing each other are heat-sealed.

Further, in the battery 100, in order to improve the bonding strength between the positive electrode terminal 6 and the resin film 72, an insulating film 9 is provided between the positive electrode terminal 6 and the resin film 72 as shown in FIG. Further, at the peripheral edge portion 7b, the positive electrode 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 also provided between the negative electrode terminal 5 and the resin film 72. Further, in the peripheral edge portion 7c, the negative electrode 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 exterior member 7 are heat-sealed.

The exterior member 7 further contains an electrolyte (not shown). The electrolyte is impregnated in the electrode group 1.

In the battery 100 shown in FIGS. 4 and 5, as shown in FIG. 5, a plurality of positive electrode current collecting tabs 3c are grouped in the lowermost layer of the electrode group 1. Similarly, although not shown, a plurality of negative electrode current collecting tabs are grouped in the lowermost layer of the electrode group 1. However, for example, a plurality of positive electrode current collecting tabs 3c and a plurality of negative electrode current collecting tabs can be combined into one near the middle stage of the electrode group 1 and connected to each of the positive electrode terminal 6 and the negative electrode terminal 5.

According to the secondary battery of the first embodiment described above, a positive electrode active material-containing layer containing a positive electrode active material containing a lithium-containing manganese oxide and a lithium-containing nickel cobalt manganese oxide, a lithium titanium oxide, and the like. Includes a negative electrode active material-containing layer containing a negative electrode active material containing Li insertion-desorbed oxide other than. The secondary battery satisfies the following equations (1), (2), and (3):
_E _p> E n (1)
E _n ≧ 94% (2)
1.0 ≤ C _p / C _n ≤ 1.2 (3).

According to the above secondary battery, a decrease in the positive electrode potential can be suppressed. Therefore, the charge / discharge cycle life performance of the secondary battery can be improved.

(Second Embodiment)
According to the second embodiment, a battery pack is provided. This battery pack includes the secondary battery according to the first embodiment.

The battery pack according to the embodiment may include a plurality of batteries. Multiple batteries can be electrically connected in series or electrically in parallel. Alternatively, a plurality of batteries can be electrically connected in a combination of series and parallel. That is, the battery pack according to the embodiment may include an assembled battery. The number of assembled batteries can be multiple. Multiple battery packs can be electrically connected in series, in parallel, or in a combination of series and parallel.

An example of the battery pack according to the embodiment will be described below with reference to FIGS. 6 and 7. FIG. 6 is an exploded perspective view showing an example of the battery pack according to the embodiment. FIG. 7 is a block diagram showing an example of the electric circuit of the battery pack shown in FIG.

The battery pack 20 shown in FIGS. 6 and 7 includes a plurality of cell cells 21. The cell 21 may be, for example, an example flat battery 100 according to the embodiment described with reference to FIG.

The plurality of cells 21 are laminated so that the negative electrode terminals 5 and the positive electrode terminals 6 extending to the outside are aligned in the same direction, and are fastened with the adhesive tape 22 to form the assembled battery 23. These cell cells 21 are electrically connected in series with each other as shown in FIG.

The printed wiring board 24 is arranged so as to face the side surface on which the negative electrode terminal 5 and the positive electrode terminal 6 of the cell 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 energizing an external device. An insulating plate (not shown) is attached to the printed wiring board 24 on the surface facing the assembled battery 23 in order to avoid unnecessary connection with the wiring of the assembled battery 23.

The positive electrode side lead 28 is connected to the positive electrode terminal 6 located at the bottom layer of the assembled battery 23, and the tip thereof is inserted into the positive electrode side connector 29 of the printed wiring board 24 and electrically connected. The negative electrode side lead 30 is connected to the negative electrode terminal 5 located on the uppermost layer of the assembled battery 23, and the tip thereof is inserted into the negative electrode side connector 31 of the printed wiring board 24 and electrically connected. These

connectors

29 and 31 are connected to the protection circuit 26 through the

wirings

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 transmitted 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 energizing terminal 27 to the external device under predetermined conditions. An example of the predetermined condition is when the detection temperature of the thermistor 25 becomes equal to or higher than the predetermined temperature. Further, another example of the predetermined condition is the case where an overcharge, an overdischarge, an overcurrent, or the like of the cell 21 is detected. The detection of overcharging or the like is performed on the individual cell 21 or the entire assembled battery 23. When detecting the individual 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 FIGS. 6 and 7, a wiring 35 for voltage detection is connected to each of the cell 21. The detection signal is transmitted to the protection circuit 26 through these wires 35.

Protective sheets 36 made of rubber or resin are arranged on the three side surfaces of the assembled battery 23 except for the side surfaces on which the positive electrode terminal 6 and the negative electrode terminal 5 protrude.

The assembled battery 23 is housed in the storage container 37 together with the protective sheet 36 and the printed wiring board 24. That is, the protective sheet 36 is arranged on both inner side surfaces along the long side direction and the inner side surface along the short side direction of the storage container 37, and the inside along the other short side direction on the opposite side via the assembled battery 23. The printed wiring board 24 is arranged on the side surface. The assembled battery 23 is located in a space surrounded by the protective sheet 36 and the printed wiring board 24. The lid 38 is attached to the upper surface of the storage container 37.

A heat-shrinkable tape may be used instead of the adhesive tape 22 to fix the assembled battery 23. 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-shrinked to bind the assembled battery.

Although FIGS. 6 and 7 show a form in which the cells 21 are electrically connected in series, they may be electrically connected in parallel in order to increase the battery capacity. Further, the assembled battery packs can be electrically connected in series and / or in parallel.

Further, the mode of the battery pack according to the embodiment is appropriately changed depending on the application. As the use of the battery pack according to the embodiment, those in which cycle performance in charging / discharging a large current is desired are preferable. Specific applications include power supplies for digital cameras, two-wheeled to four-wheeled hybrid electric vehicles, two-wheeled to four-wheeled electric vehicles, and in-vehicle use such as assisted bicycles. As the use of the battery pack according to the embodiment, it is particularly suitable for in-vehicle use.

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, the second in the positive electrode active material content in the positive electrode active material, the content of the second negative electrode active material of the negative electrode active material in the charge-discharge efficiency E _p of the positive _electrode, the negative electrode charge-discharge efficiency E _n, the positive electrode A method for measuring the open circuit voltage, the thickness of the positive electrode and the negative electrode, and the density will be described. First, a method of taking out the electrodes will be described.

<How to take out the electrode>
The battery is completely discharged and the charged state (SOC) is set to 0%. For example, it discharges to a battery voltage of 1.8 V with a current value of 1 C. This battery is disassembled and the electrode group is taken out. Cut out about 2 cm square each of the positive electrode and the negative electrode from the electrode group. Each of the cut electrodes is ^{immersed in 50 cc (cm 3} ) of ethyl methyl carbonate and left for 1 hour. Then, in order to dry the electrode, it is vacuum dried for 1 hour to obtain a measurement sample. The operations up to this point are performed in a glove box with an argon atmosphere. Note that 1C is a current value capable of charging and discharging the nominal capacity of the secondary battery in one hour.

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

The active material-containing layer is peeled off from the electrode as the measurement sample using, for example, a spatula to obtain a powdery sample.

The crystal structure of the active material is identified by powder X-ray diffraction (XRD) measurement on the powdered sample. The measurement is performed using CuKα ray as a radiation source in a measurement range in which 2θ is 10 ° or more and 90 ° or less. By this measurement, the X-ray diffraction pattern of the compound contained in the selected particles can be obtained.

As a device for measuring powder X-ray diffraction, for example, SmartLab manufactured by Rigaku Co., Ltd. is used. The measurement conditions are as follows:
X-ray source: Cu target Output: 45kV, 200mA
Solar slit: 5 ° for both incident and light 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: Range of 10 ° ≤ 2θ ≤ 90 °.

When using other equipment, measure using standard Si powder for powder X-ray diffraction so that the same measurement results as above can be obtained, and make sure that the peak intensity and peak top position match those of the above equipment. Adjust and measure.

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

For example, select some particles having the form of primary particles or secondary particles confirmed in the field of view in a 3000 times SEM observation image. At this time, the selected particles are selected so that the particle size distribution is as wide as possible. The types and compositions of the constituent elements of the active material are identified by EDX analysis of the observed active material particles. This makes it possible to specify the type and amount of elements other than Li among the elements contained in each of the selected particles. Perform the same operation for each of the plurality of active material particles to determine the mixed state of the active material particles.

Subsequently, as described above, the powdered sample collected from the active material-containing layer is washed with acetone and dried. The obtained powder is dissolved in hydrochloric acid, the conductive agent is filtered off, and then diluted with ion-exchanged water to prepare a measurement sample. The metal content ratio in the measurement sample is calculated by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis method.

If there are multiple types of active materials, the weight ratio is estimated from the content ratio of the elements unique to each active material. The ratio of the unique element to the weight of the active material is judged from the composition of the constituent elements obtained by EDX analysis. For example, the measurement sample obtained from the active material-containing layer of the positive electrode may contain lithium-containing manganese oxide as the first active material and lithium-containing nickel cobalt manganese oxide as the second active material. In this case, the chemical formulas and formula amounts of the first and second active materials are calculated from the obtained metal ratios, and the weight ratios of the first and second active materials contained in the collected active material-containing layer of a predetermined weight are obtained. From the weight ratio of the first and second active materials, the content of the second active material in the positive electrode active material is obtained. Similarly, the measurement sample obtained from the active material-containing layer of the negative electrode may contain lithium titanate as the first active material and other Li-inserted-desorbed oxides as the second active material. As for the negative electrode, similarly to the positive electrode, the chemical formulas and formula amounts of the first and second active materials are calculated from the metal ratio, the weight ratio is obtained, and the content of the second active material in the negative electrode active material is obtained.

<Measurement of positive electrode open circuit voltage>
After charging the secondary battery to 2.8 V at 0.2 C, the secondary battery is discharged to 1.8 V at 0.2 C. Next, the secondary battery is disassembled in an Ar atmosphere, and the electrode group is taken out. A positive electrode is cut out from the taken-out electrode group. _{The positive electrode and the counter electrode metal Li are immersed in an electrolytic solution in which 1 mol / L LiPF 6} is dissolved in a mixed solvent of ethyl methyl carbonate (EMC) and ethylene carbonate (EC), and the metal Li is immersed by a tester. The positive electrode potential is measured with respect to the positive electrode open circuit voltage V (vs. Li ^/ Li +) at the time of discharging to 1.8 V at 0.2 C.

<Measurement method of charge capacity and charge / discharge efficiency of positive and negative electrodes>
According to the procedure described above, the positive electrode and the negative electrode are cut out from the electrode group taken out from the discharged battery to obtain a measurement sample. For each electrode as a measurement sample, a test cell is independently prepared, and the charge capacity and the discharge capacity are measured. The charge / discharge efficiency of each electrode is calculated from the charge capacity and discharge capacity.

_{Specifically, 1 mol / L LiPF 6} of an electrode (either positive electrode or negative electrode) as a measurement sample and a metal Li as a counter electrode in a mixed solvent of ethyl methyl carbonate (EMC) and ethylene carbonate (EC). A test cell is prepared using the electrolytic solution in which the above is dissolved.

For cells using a positive electrode, first, a constant current-constant voltage (CCCV) is charged at 1C until the ^{positive electrode potential reaches 4.25V (vs.Li / Li +), and then 3.0V (vs).} Discharge at 1C to a potential of .Li / Li ^+). The capacity charged at the time of charging is measured and recorded as the charging capacity. Similarly, the capacity discharged at the time of discharge is measured and recorded as the discharge capacity. From the measured charge capacity and discharge capacity, the charge / discharge efficiency E _p of the positive electrode is calculated (E _p = [discharge capacity of the positive electrode sample] / [charge capacity of the positive electrode sample] × 100%). _{Further, the charge capacity C p} (mAh / m ² ) per unit area of the positive electrode is calculated by dividing the obtained charge capacity (mAh) by the area (m ² _{) of the measurement sample (C p} = [positive electrode sample). Charging capacity] / [Area of positive electrode sample]).

For cells using a negative electrode, first, CCCV is charged at 1C until ^{the negative electrode potential reaches 2.0V (vs.Li /} Li +), and then discharged at 1C to a potential of ^{1.4V (vs.Li / Li +).} do. The capacity charged at the time of charging is measured and recorded as the charging capacity. Similarly, the capacity discharged at the time of discharge is measured and recorded as the discharge capacity. From the measured charge capacity and the discharge capacity, and calculates the charge and discharge efficiency E _n of the negative electrode ([charge capacity of the negative electrode sample] × 100% E n _{= [discharge} capacity of the anode sample] /). _{Further, the charge capacity C n} (mAh / m ² ) per unit area of the negative electrode is calculated by dividing the obtained charge capacity (mAh) by the area (m ² _{) of the measurement sample (C n} = [negative electrode sample). Charging capacity] / [Area of negative electrode sample]).

Based on the result of the above measurement, it can be determined whether or not the above-described equations (1), (2) and (3) are satisfied.

<Measurement method of the thickness of each of the positive electrode and the negative electrode and the density of the active material-containing layer>
First, the thickness of the electrode is measured using a thickness measuring machine. The obtained value is taken as the thickness of the positive electrode or the negative electrode.

Next, using a cutting machine, the electrodes are punched to a size of 1 cm x 1 cm to obtain an electrode sample. Next, the weight of this electrode sample is measured. Next, the active material-containing layer is removed from the electrode sample by immersing the electrode sample in a solvent such as N-methylpyrrolidone. The solvent used for peeling off the active material-containing layer is not particularly limited as long as it does not erode the current collector and can peel off the active material-containing layer. Next, the thickness and weight 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. From this thickness, the volume of the active material-containing layer is calculated. Further, the weight of the active material-containing layer is calculated by subtracting the weight of the current collector sample from the weight of the electrode sample. ^{Next, the density (g / cm 3} ) of the active material-containing layer is calculated by dividing the weight of the active material-containing layer by the volume of the active material-containing layer.

Hereinafter, examples will be described in detail.
(Example 1)
Preparation of positive electrode As the positive electrode active material, 95% by weight of the first positive electrode active material composed of lithium-containing manganese oxide particles having an average particle size of 9.0 μm represented by _{LiMn 2} O ₄ _{and LiNi 0.33} Co _0.33 Mn _0.33 O _{A second} positive electrode active material composed of lithium-containing nickel-cobalt-manganese oxide particles having an average particle size of 6.0 μm represented by 2 was prepared in an amount of 5% by weight. In the positive electrode active material, acetylene black as a conductive agent and polyvinylidene fluoride (PVDF) as a binder were dispersed in N-methylpyrrolidone (NMP) at a weight ratio of 100: 3: 4: 1.5. The obtained dispersion was applied to both sides of a current collector made of an aluminum foil having a thickness of 12 μm and dried. After drying, a press treatment was performed to provide a positive electrode active material-containing layer. The basis weight and press pressure per one side of the positive electrode were adjusted so that the electrode density (excluding the current collector) was 2.90 g / cm ³ and the electrode thickness was 70 μm.

Preparation of Negative Electrode As the negative electrode active material, the first negative electrode active material composed of lithium titanate particles having an average particle size of 0.9 μm represented by _{Li 4} Ti ₅ O ₁₂ _{is represented by 90% by weight and TiNb 2} O _7. A second negative electrode active material composed of niobium titanium composite oxide particles having an average particle size of 1.1 μm was prepared in an amount of 10% by weight. In the negative electrode active material, acetylene black as a conductive agent and PVDF as a binder were dispersed in N-methylpyrrolidone (NMP) at a weight ratio of 100: 4: 2. The obtained dispersion was applied to both sides of a current collector made of an aluminum foil having a thickness of 12 μm and dried. After drying, a press treatment was performed to provide a negative electrode active material-containing layer. The basis weight and press pressure per one side of the negative electrode were adjusted so that the electrode density (excluding the current collector) was 2.15 g / cm ³ and the electrode thickness was 44 μm.

As a separator, a cellulose non-woven fabric separator having a thickness of 15 μm was prepared. A group of spiral electrodes was prepared by winding so that a separator was arranged between the positive electrode and the negative electrode. The electrode group was housed in an aluminum container. This was put into a dryer and vacuum dried at 95 ° C. for 6 hours. After drying, it was carried to a glove box controlled to have a dew point of -50 ° C or lower. Into the container, 70 cc of an electrolytic solution prepared by dissolving _{1.2 mol / L LiPF 6} in a mixed solvent of ethyl methyl carbonate (MEC) and propylene carbonate (PC) was injected. The proportion of MEC in the mixed solvent was 51.9% by volume, and the proportion of PC was 30.8% by volume.

The outer container containing the electrolytic solution was sealed under a reduced pressure environment of -90 kPa. After the injection, the battery was first charged to 80% of the charged state (State of Charge; SOC) at 1C (0.5A), and aged for 24 hours in a constant temperature bath at 75 ° C. Here, the above initial charging was performed with SOC = 0% when the battery voltage was 1.8 V and SOC = 100% when the battery voltage was 2.8 V. After aging, the can was opened and sealed again in a reduced pressure environment of −90 kPa to prepare a non-aqueous electrolyte battery.

(Example 2)
As the second negative electrode active material, monooblique titanium dioxide particles having an average particle size of 0.3 μm represented by _{TiO 2 were used instead of the niobium titanium composite oxide particles.} The basis weight per one side of the negative electrode was adjusted so that the thickness of the negative electrode was 45 μm. A non-aqueous electrolyte battery was produced in the same manner as described in Example 1 except for these changes.

(Example 3-12, Comparative Example 1-8)
Weight ratio of first positive electrode active material, second positive electrode active material, first and second positive electrode active materials, first negative electrode active material, second negative electrode active material, weight ratio of first and second negative electrode active materials, A non-aqueous electrolyte battery was produced in the same manner as in Example 1 except that the thicknesses of each of the positive electrode and the negative electrode were set as shown in Table 1. The thickness of each of the positive electrode and the negative electrode was adjusted by changing the basis weight.

In Table 1, the column of "positive electrode composition" shows the types of the first positive electrode active material and the second positive electrode active material, and their weight ratios. “LMO” refers to lithium-containing manganese oxide (LiMn ₂ O ₄ ) as the first positive electrode active material, and “NMC” refers to lithium-containing nickel cobalt manganese oxide (LiNi _0.33 Co _{0.33) as the second positive electrode active material.} Mn _0.33 O ₂ ) is shown. The column of "negative electrode composition" shows the types of the first negative electrode active material and the second negative electrode active material, and their weight ratios. “LTO” refers to lithium titanate (Li ₄ Ti ₅ O ₁₂ ) as the first negative electrode active material. “NTO” indicates a niobium titanium composite oxide (TiNb ₂ O ₇ ) as a second negative electrode active material, and “TiO ₂ _{” indicates titanium dioxide (TiO 2} ) as a second negative electrode active material.

[Measurement and evaluation]
<Open circuit voltage of positive electrode>
^{By the above method, the open circuit voltage V (vs. Li /} Li +) of the positive electrode when the non-aqueous electrolyte battery was discharged to 1.8 V at 0.2 C was measured. The measurement results are shown in Table 2.

<Cycle performance evaluation>
A 1C constant current charge / discharge cycle was carried out in a voltage range of 1.8V to 2.8V in a 45 ° C. environment. The capacity retention rate after 3000 cycles is shown in Table 2 below.

<Charging capacity and charge / discharge efficiency of positive and negative electrodes>
The charge capacity and the discharge capacity were measured for each of the positive electrode and the negative electrode by the above-mentioned method. Result of calculation based on the measurement result (the charge-discharge efficiency E _p of the positive _electrode, the charge-discharge efficiency E _n of the negative _electrode, and the unit capacitance ratio C _{p /} C n per area of the positive and negative _electrodes) are shown in Table 2.

As shown in Table 2, in all of the batteries of Examples 1 to 12, towards the charge-discharge capacity E _p of the positive electrode is higher than the charge and discharge capacity E _n of the negative electrode, charging and discharging capacity E _n is more than 94% of the negative electrode, _{Moreover, the capacitance ratio C p} / C _n between the positive electrode and the negative electrode per unit area was 1.0 or more and 1.2 or less. That is, in Examples 1 to 12, all of the above-mentioned equations (1), (2), and (3) were satisfied. In Examples 1 to 12, the capacity is maintained after 3000 cycles as compared with the batteries of Comparative Examples 1 to 8 which do not satisfy at least one of the equations (1), (2), and (3). The rate was high.

Since the secondary batteries according to at least one embodiment and the above-described embodiments satisfy all of the equations (1), (2), and (3), when the SOC is 0%. The positive electrode potential does not drop, and the charge / discharge cycle life can be improved.

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 embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

Claims

A positive electrode containing a positive electrode active material-containing layer comprising a positive electrode active material containing a lithium-containing manganese oxide and a lithium-containing nickel cobalt manganese oxide, and a positive electrode containing a positive electrode active material.
A negative electrode including a negative electrode active material-containing layer comprising a negative electrode active material containing a lithium titanium oxide and a Li-insertion-desorption oxide different from the lithium titanium oxide, and a negative electrode.
A secondary battery containing a non-aqueous electrolyte and satisfying the following equations (1), (2), and (3) below.
E p> E n (1)
E n ≧ 94% (2)
1.0 ≤ C p / C n ≤ 1.2 (3)
However, E p is 3.0V (vs.Li/Li +) or 4.25V (vs.Li/Li +) following the in charge-discharge range the positive electrode of the charge-discharge efficiency, E n is 1.4V (vs. Li / Li +) or higher 2.0V (vs.Li/Li +) the following charge-discharge efficiency of the negative electrode in charging and discharging range, C p is the charge-discharge range of the positive electrode is 3.0V (vs.Li/Li + ) or 4.25 V (the charge capacity per unit area when Vs.Li/Li +) or less (mAh / m 2), C n is the charge-discharge range of the negative electrode 1.4V (vs.Li/Li + ) Is the charge capacity (mAh / m 2 ) per unit area when the voltage is 2.0 V (vs. Li / Li +) or less.
When the secondary battery is discharged to 1.8 V at 0.2 C, the open circuit voltage of the positive electrode is 3.6 V (vs.Li / Li +) or more and 3.9 V (vs.Li / Li + ) or less. , The secondary battery according to claim 1.
When the content of the lithium-containing nickel-cobalt manganese oxide in the positive electrode active material is 2 wt% or more and 20 wt% or less, and the content of the Li-inserted-desorbed oxide in the negative electrode active material is 3 wt% or more and 30 wt% or less. The secondary battery according to claim 1 or 2.
The secondary battery according to any one of claims 1 to 3, wherein the thickness of the positive electrode is 80 μm or less.
The secondary battery according to any one of claims 1 to 4, wherein the Li insertion-elimination oxide contains one or more selected from the group consisting of niobium-titanium composite oxide and titanium oxide.
A battery pack containing the secondary battery according to any one of claims 1 to 5.