JP2017168255A - Nonaqueous electrolyte secondary battery, battery pack, and vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nonaqueous electrolyte secondary battery which enables the formation of a coating on the surface of a negative electrode without causing the degradation of a positive electrode, and which has a high energy density and superior cycle characteristics; a battery pack; and a vehicle.SOLUTION: A nonaqueous electrolyte secondary battery according to an embodiment comprises: a positive electrode which includes a positive electrode active material including a metal oxide, and a positive electrode additive including one or more kinds of oxides selected from a lithium copper oxide, a lithium iron oxide and a lithium manganese oxide; a negative electrode including a negative electrode active material including a titanium-containing oxide; and a nonaqueous electrolyte. When the battery is charged to 4.3 V based on Li and then discharged to 3.0 V to measure an initial charge/discharge efficiency, the positive electrode additive is 10% or less in the initial charge/discharge efficiency.SELECTED DRAWING: Figure 1

Description

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

  Rechargeable batteries can be used repeatedly for charging and discharging, helping to reduce waste, and widely used as portable devices that cannot use AC power, or as backup power when AC power is cut or stopped. It is used. In recent years, there has been an increasing demand for performance enhancement such as expansion of the range of use and accompanying capacity, temperature characteristics, and safety.

As secondary batteries, lead storage batteries, nickel cadmium secondary batteries, nickel metal hydride secondary batteries, nonaqueous electrolyte secondary batteries, and the like have been developed and used worldwide. Among these, non-aqueous electrolyte secondary batteries are small and light and have a large capacity, and thus are widely used in small personal computers, mobile phones, digital cameras, video cameras, and the like.
In addition to the use as a power source for small electronic devices, this non-aqueous electrolyte battery is also expected to be used as a medium-to-large power source for in-vehicle use and stationary use. In such medium and large-sized applications, the non-aqueous electrolyte battery is required to have high energy density and cycle characteristic life characteristics.

Currently used non-aqueous electrolyte secondary batteries use lithium-containing cobalt composite oxide or lithium-containing nickel composite oxide as a positive electrode material, and use a carbon-based material such as graphite or coke as a negative electrode active material. As an electrolytic solution, a lithium salt such as LiPF ₆ or LiBF ₄ is used by dissolving it in an organic solvent such as a cyclic carbonate or a chain carbonate. The positive electrode and the negative electrode are formed into a sheet shape, hold the electrolyte, and face each other through a separator that electrically insulates the positive and negative electrodes, and are housed in various shaped containers to form a battery.

In recent years, lithium iron phosphate (LiFePO ₄ ) is used as a positive electrode material, or a titanium-containing oxide such as lithium titanate (Li ₄ Ti ₅ O) is used as a negative electrode material as a battery superior in safety and durability to energy density. ₁₂ ) has been attempted. However, when conventional graphite-based carbon is used as the negative electrode active material, the working potential is about 0.2 to 0.05 V with respect to the lithium metal potential, whereas lithium titanate or iron sulfide is used as the negative electrode active material. When used as, the working potential is 1 V or more with respect to the lithium metal potential. Therefore, when lithium titanate or iron sulfide is used as the negative electrode active material, the energy density of the entire battery is lowered. In addition, when lithium titanate, iron sulfide, or the like is used as the negative electrode active material, the negative electrode potential does not decrease to 1 V or less even in a charged state, and thus the reduction reaction of the lithium salt or solvent constituting the electrolytic solution can be suppressed. On the other hand, the formation of the negative electrode surface film formed on the graphite surface by the reduction reaction of the solvent and additives at 1 V or less was not performed.

  In order to solve this, it is possible to increase the maximum charging voltage of the battery and lower the potential of the negative electrode at the end of charging. However, in this method, the charging depth of the positive electrode may become too deep, or the positive electrode potential at the end of charging may increase, leading to deterioration of the positive electrode and reduced safety. Furthermore, if only the voltage between the positive and negative electrodes is controlled to lower the negative electrode potential, the negative electrode potential may fluctuate even if the voltage is the same due to the deterioration state of the positive electrode.

A. D. Robertson, L.M. Trevino, H.M. Tukamoto, J. et al. T.A. S. Irvine, J.M. Power Sources 81-82, 352 (1999).

  The problem to be solved by the present invention is to provide a non-aqueous electrolyte secondary battery, a battery pack, and a vehicle having a high energy density and excellent cycle characteristics by forming a coating on the surface of the negative electrode without causing deterioration of the positive electrode. It is to be.

  The nonaqueous electrolyte secondary battery according to the embodiment includes a positive electrode active material containing a metal oxide and a positive electrode containing one or more of oxides selected from lithium copper oxide, lithium iron oxide, and lithium manganese oxide A positive electrode containing a product. The nonaqueous electrolyte secondary battery further includes a negative electrode having a negative electrode active material containing a titanium-containing oxide and a nonaqueous electrolyte. When the positive electrode additive is charged to 4.3 V on the basis of Li and then discharged to 3.0 V and the initial charge / discharge efficiency is measured, the initial charge / discharge efficiency is 10% or less.

It is a cross-sectional schematic diagram which shows an example of the nonaqueous electrolyte battery which concerns on 2nd Embodiment. It is an expanded sectional schematic diagram of the A section of FIG. It is a disassembled perspective view which shows the battery pack which has the above-mentioned nonaqueous electrolyte battery. It is a block diagram which shows the electric circuit with which the battery pack of FIG. 3 was equipped.

  Hereinafter, a nonaqueous electrolyte secondary battery and a battery pack according to embodiments will be described with reference to the drawings.

(First embodiment)
The nonaqueous electrolyte battery according to this embodiment includes at least a positive electrode, a negative electrode, and a nonaqueous electrolyte.

The positive electrode of the present embodiment includes at least a positive electrode active material, a positive electrode additive, a positive electrode conductive agent, and a binder.
Various metal oxides can be used for the positive electrode active material. In particular, the positive electrode active material has the initial charge and discharge efficiency when it is charged to 4.3 V on the basis of Li and then discharged to 3.0 V. , 80% or more of the compound is used. Examples of the positive electrode active material include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, iron phosphate lithium oxide, and manganese phosphate oxide.

The positive electrode additive includes one or more oxides selected from the group consisting of lithium copper oxide, lithium iron oxide, and lithium manganese oxide. Examples of the lithium copper oxide include Li ₂ CuO ₂ , LiCuO, Li ₆ CuO ₄ , Li ₂ Cu ₂ O ₃ , LiCu ₃ O ₃ , LiCu ₂ O ₂ , LiCuO ₂ , Li ₃ Cu ₂ O ₄ , and Li ₃ CuO. ₃ and one or more oxides selected from the group consisting of LiCu ₃ O ₃ and the lithium iron oxide include, for example, Li ₅ FeO ₄ , LiFeO ₂ , LiFe ₅ O ₈ , Li ₃ Fe ₅ O ₈ , Li One or more oxides selected from the group consisting of ₂ Fe ₃ O ₄ , Li ₅ Fe ₅ O ₈ , and Li ₂ Fe ₃ O ₅ , as lithium manganese oxide, for example, LiMnO ₂ , Li ₂ MnO ₃ , One or more oxides selected from the group consisting of Li ₃ MnO ₄ , LiMn ₃ O ₄ , Li ₄ Mn ₅ O ₁₂ , and LiMnO _4; Can be mentioned. These positive electrode active materials can be used alone or in combination.

In addition, the positive electrode additive is selected so that the initial charge / discharge efficiency is 10% or less when the initial charge / discharge efficiency is measured by charging to 4.3V on the basis of Li and then discharging to 3.0V. Is preferred. As a guide, the initial charge / discharge efficiency is preferably in the range of 0 to 10%. If it is out of this range, the positive electrode may be deteriorated in the first charge / discharge. The initial charge / discharge efficiency is particularly preferably 0 to 5%, and this initial charge / discharge efficiency can be achieved by using Li ₂ CuO ₂ described later as a positive electrode additive.

Furthermore, after charging the positive electrode additive to 4.3 V with the Li counter electrode, the difference between the initial charge capacity per unit weight and the initial discharge capacity when discharging to 3.0 V is Q1, and the negative electrode active material is the Li counter electrode. When the charge capacity per unit weight when initially charged to 0.5 V is Q2, and then the charge capacity per unit weight when discharged to 2 V and charged again to 1 V is Q3, the weight W1 of the additive And the weight W2 of the negative electrode active material is expressed by the following formula (1),
0.9 <Q1W1 / (Q3-Q2) W2 <1.1 (1)
It is preferable to satisfy.
Further, in the above relationship, it is particularly preferable that the value of Q1W1 / (Q3-Q2) W2 is about 1.0.

Specifically, a compound contained in the positive electrode additive is selected from the above-mentioned lithium copper oxide, lithium iron oxide, or lithium manganese oxide, and the initial charge efficiency is set to 10% or less by appropriately combining the formulas, The condition (1) can be satisfied. For example, among the above oxides, a positive electrode additive substantially consisting of any of Li ₂ CuO ₂ , LiMnO ₂ or Li ₅ FeO ₂ satisfies the above conditions. In particular, Li ₂ CuO ₂ can be preferably used.

  The weight of the positive electrode additive with respect to the mass of the positive electrode active material is preferably 1% or more and 10% or less. In other words, the positive electrode includes 1 to 10 parts by mass of the positive electrode additive with respect to 100 parts by mass of the positive electrode active material.

  The positive electrode conductive agent enhances the current collecting performance of the positive electrode active material and suppresses the contact resistance with the current collector. Examples of the conductive agent include carbonaceous materials such as acetylene black, carbon black, or graphite.

  The binder binds the positive electrode active material and the conductive agent. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or fluorine-based rubber.

  The positive electrode active material, the positive electrode conductive agent, and the binder in the positive electrode may be blended at a ratio of 80% by mass to 95% by mass, 3% by mass to 18% by mass, and 2% by mass to 17% by mass, respectively. preferable. A positive electrode electrically conductive agent can exhibit the effect mentioned above by making it the quantity of 3 mass% or more. By making the amount of the positive electrode conductive agent 18% by mass or less, the decomposition of the nonaqueous electrolyte on the surface of the conductive agent under high temperature storage can be reduced. A sufficient positive electrode strength can be obtained by adjusting the amount of the binder to 2% by mass or more. By setting the binder to an amount of 17% by mass or less, the amount of the binder, which is an insulating material in the positive electrode, can be reduced, and the internal resistance can be reduced.

The negative electrode of the present embodiment includes at least a negative electrode active material, a negative electrode conductive agent, and a binder.
As an example of a negative electrode active material, you may contain various titanium containing oxides. Examples of the titanium-containing oxide include lithium titanate, titanium dioxide, or niobium titanium oxide.
The negative electrode conductive agent improves the current collection performance of the negative electrode active material and suppresses contact resistance with the current collector. Examples of the conductive agent include acetylene black, carbon black, or graphite.

  As the binder, a binder capable of binding the negative electrode active material and the negative electrode conductive agent can be used. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, or styrene butadiene rubber.

  The negative electrode active material, the negative electrode conductive agent, and the binder in the negative electrode may be blended in a proportion of 70% by mass to 96% by mass, 2% by mass to 28% by mass, and 2% by mass to 28% by mass, respectively. preferable. By setting the amount of the negative electrode conductive agent to 2% by mass or more, the current collecting performance in the negative electrode can be improved, and the characteristics of the nonaqueous electrolyte secondary battery 100 at a large current can be improved. Further, by setting the amount of the binder to 2% by mass or more, in addition to a layer in which the negative electrode includes a negative electrode active material, a negative electrode conductive agent, and a binder (a negative electrode layer described below), a current collector described below is further described. When it is provided, the binding property between the negative electrode layer and the current collector can be improved, and the cycle characteristics can be improved. On the other hand, the negative electrode conductive agent and the binder are each preferably 28% by mass or less in order to increase the capacity.

  As the non-aqueous electrolyte of this embodiment, a liquid non-aqueous electrolyte prepared by, for example, dissolving an electrolyte in an organic solvent is used. The liquid non-aqueous electrolyte is preferably formed by dissolving the electrolyte in an organic solvent at a concentration of 0.5M to 2.5M.

Examples of the electrolyte are lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), trifluorometasulfone Lithium salt of lithium acid (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ], or a mixture thereof. The electrolyte is preferably one that is difficult to oxidize even at a high potential, and LiPF ₆ is most preferred.

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

  A preferable organic solvent is a mixed solvent in which at least two of the group consisting of propylene carbonate (PC), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed, or a mixed solvent containing γ-butyrolactone (GBL). is there. By using these mixed solvents, a nonaqueous electrolyte secondary battery having excellent high temperature characteristics can be obtained.

The element composition of the nonaqueous electrolyte secondary battery of this embodiment can be confirmed using the following method even after the first charge and discharge. The nonaqueous electrolyte secondary battery of the present embodiment is discharged to 1.0 V at a discharge rate of 0.1 C, and then disassembled in a glove box, and the positive electrode is taken out. The taken out positive electrode is sufficiently washed with ethyl methyl carbonate. The positive electrode active material and the elemental composition of the additive are measured by electron energy loss spectroscopy. At this time, the content of Li element in the positive electrode active material and the additive is decreased as compared with the uncharged state as the battery is charged and discharged. In the non-aqueous electrolyte secondary battery of the present embodiment, the element composition of the positive electrode additive in the above measurement is represented by the following formula (2),
Li _x MO ₂ (2)
(Here, M indicates any element of Fe, Cu, or Mn)
X = 1.0 to 1.2. For example, when Li ₂ CuO ₂ is used as the positive electrode additive, the elemental composition of the electrode after charge / discharge is about x = 1.0 to 1.2 in Li _x CuO ₂ . The additive weight relative to the positive electrode active material weight can be measured by the ICP / MS method. The current collector is removed from the positive electrode, and ICP / MS measurement is performed after dissolving in aqua regia as a pretreatment. The additive weight relative to the positive electrode active material weight can be calculated from the transition metal content in the positive electrode active material and additive measured by electron energy loss spectroscopy with respect to the transition metal content measured by ICP / MS.

  Further, in the nonaqueous electrolyte secondary battery of the present embodiment, after charging and discharging for the first time, when the elemental composition of the negative electrode is examined, a film containing the electrolyte and the positive electrode additive is formed on the surface of the negative electrode. Therefore, it can confirm that the compound containing M of said Formula (2) has adhered to the surface of a negative electrode.

Regarding the action of the non-aqueous electrolyte secondary battery of the present embodiment, since a compound selected so that the initial charge and discharge efficiency is low is used for the positive electrode additive, even if the battery voltage is increased during the initial charge, the positive electrode The potential does not rise excessively. Specifically, when the above-mentioned compound, for example, Li ₂ CuO ₂ among lithium copper oxides, is used for the positive electrode additive, it is released from the positive electrode additive during the first charge and returned to the positive electrode additive during the discharge. There is no Li. That is, in the initial charging, charging is performed but discharging cannot be performed sufficiently (the initial charging / discharging efficiency is low), and the potential of the positive electrode is hardly increased while the potential of the negative electrode is decreased. Therefore, the potential of the positive electrode does not increase excessively, so that the positive electrode active material does not deteriorate. Therefore, even if the battery voltage is increased to form a coating film on the negative electrode during the initial charge, the positive electrode active material is not deteriorated, so that the battery performance is not lowered and the battery life is extended.
According to this embodiment described above, a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance can be provided.

(Second Embodiment)
As a second embodiment, a nonaqueous electrolyte battery 100 shown in FIGS. 1 and 2 will be described. FIG. 1 is a schematic cross-sectional view of a nonaqueous electrolyte battery 100. FIG. 2 is an enlarged cross-sectional view of a part A shown in FIG. Each of these drawings is a schematic diagram for explaining the nonaqueous electrolyte battery according to the present embodiment, and there are places where the shape, dimensions, ratio, and the like are different from those of the actual device. The design can be changed as appropriate in consideration of known techniques.

  A non-aqueous electrolyte battery 100 shown in FIG. 1 is configured such that a flat wound electrode group 1 is housed in an exterior material 2. The exterior material 2 may be a laminate film formed in a bag shape or a metal container. Further, as shown in FIG. 2, the flat wound electrode group 1 is formed by spirally laminating a laminate in which the negative electrode 3, the separator 4, the positive electrode 5, and the separator 4 are laminated in this order from the outside, that is, the exterior material 2 side. It is formed by winding and press molding. The negative electrode 3 located on the outermost periphery has a configuration in which a negative electrode layer 3b is formed on one surface on the inner surface side of the negative electrode current collector 3a. A portion of the negative electrode 3 other than the outermost periphery has a configuration in which the negative electrode layer 3b is formed on both surfaces of the negative electrode current collector 3a. The positive electrode 5 has a configuration in which positive electrode layers 5b are formed on both surfaces of a positive electrode current collector 5a.

  In the wound electrode group 1 shown in FIG. 1, the negative electrode terminal 6 is electrically connected to the negative electrode current collector 3a of the outermost negative electrode 3 in the vicinity of the outer peripheral end thereof. The positive electrode terminal 7 is electrically connected to the positive electrode current collector 5a of the inner positive electrode 5 shown in FIG. The negative electrode terminal 6 and the positive electrode terminal 7 are extended to the outside of the bag-shaped exterior material 2 or connected to a take-out electrode provided in the exterior material 2.

  When manufacturing the nonaqueous electrolyte battery 100 including the exterior material made of a laminate film, the wound electrode group 1 to which the negative electrode terminal 6 and the positive electrode terminal 7 are connected is mounted on the bag-shaped exterior material 2 having an opening. The liquid non-aqueous electrolyte is injected from the opening of the outer packaging material 2, and the opening of the bag-shaped outer packaging material 2 is heat-sealed with the negative electrode terminal 6 and the positive electrode terminal 7 sandwiched therebetween, The rotary electrode group 1 and the liquid nonaqueous electrolyte are completely sealed.

  Moreover, when manufacturing the nonaqueous electrolyte battery 100 provided with the exterior material which consists of metal containers, the winding electrode group 1 to which the negative electrode terminal 6 and the positive electrode terminal 7 were connected was inserted into the metal container which has an opening part. The liquid non-aqueous electrolyte is injected from the opening of the exterior material 2, and a lid is attached to the metal container to seal the opening.

  For the negative electrode terminal 6, 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, in addition to aluminum (Al) or aluminum, magnesium (Mg), titanium (Ti), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), or silicon (Si) An aluminum alloy containing an element such as The negative electrode terminal 6 is more preferably made of the same material as the negative electrode current collector 3a in order to reduce the contact resistance with the negative electrode current collector 3a. As the positive electrode terminal 7, a known material having electrical stability and conductivity can be used. The positive electrode terminal 7 is preferably made of the same material as the positive electrode current collector 5a in order to reduce the contact resistance with the positive electrode current collector 5a.

(1) Exterior material The exterior material 2 is formed from a laminate film having a thickness of 0.5 mm or less. Alternatively, a metal container having a thickness of 1.0 mm or less is used as the exterior material. The metal container is more preferably 0.5 mm or less in thickness.
The shape of the exterior material 2 can be selected from a flat type (thin type), a square type, a cylindrical type, a coin type, or a button type. Examples of the exterior material include, for example, an exterior material for a small battery that is loaded on a portable electronic device or the like, an exterior material for a large battery that is loaded on a two- to four-wheeled vehicle, etc., depending on the battery size.

  As the laminate film, a multilayer film in which a metal layer is interposed between resin layers is used. The metal layer is preferably an aluminum foil or an aluminum alloy foil for weight reduction. For the resin layer, for example, a polymer material such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET) can be used. The laminate film can be molded into the shape of an exterior material by sealing by heat sealing.

  The metal container is made of aluminum or an aluminum alloy. The aluminum alloy is preferably an alloy containing an element such as magnesium, zinc, or silicon in addition to aluminum. When a transition metal such as iron, copper, nickel, or chromium is included in the alloy, the amount is preferably 100 ppm by mass or less.

(2) Negative electrode The negative electrode 3 includes the structure of the negative electrode of the first embodiment described above. Specifically, the negative electrode 3 includes a current collector 3a and a negative electrode layer 3b formed on one or both surfaces of the current collector 3a and including a negative electrode active material, a negative electrode conductive agent, and a binder.

  As an example of a negative electrode active material, you may contain various titanium containing oxides. Examples of the titanium-containing oxide include lithium titanate, titanium dioxide, or niobium titanium oxide. Specifically, the negative electrode active material described in the first embodiment can be used.

  The negative electrode conductive agent improves the current collection performance of the negative electrode active material and suppresses contact resistance with the current collector. Examples of the negative electrode conductive agent include acetylene black, carbon black, or graphite. Specifically, the negative electrode conductive agent described in the first embodiment can be used.

  As the binder, a binder capable of binding the negative electrode active material and the negative electrode conductive agent can be used. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, or styrene butadiene rubber. Specifically, the binder described in the first embodiment can be used.

  The current collector 3a includes an aluminum foil that is electrochemically stable in a potential range nobler than 1 V, or an element such as Mg, Ti, Zn, Mn, Fe, Cu, or Si in addition to aluminum. An aluminum alloy foil is preferred.

  For example, the negative electrode 3 is prepared by suspending a negative electrode active material, a negative electrode conductive agent, and a binder in a conventionally used solvent to prepare a slurry, applying the slurry to the current collector 3a, drying, and then pressing the slurry. It is produced by giving. The negative electrode 3 may also be produced by forming an active material, a negative electrode conductive agent, and a binder in the form of pellets to form a negative electrode layer 3b, which is formed on the current collector 3a.

(3) Positive electrode The positive electrode 5 contains the structure of the positive electrode of the above-mentioned 1st Embodiment. Specifically, the positive electrode 5 includes a current collector 5a and a positive electrode layer 5b formed on one or both surfaces of the current collector 5a and including a positive electrode active material, a positive electrode additive, a positive electrode conductive agent, and a binder. Prepare.

  Various metal oxides can be used for the positive electrode active material. In particular, the positive electrode active material has the initial charge and discharge efficiency when it is charged to 4.3 V on the basis of Li and then discharged to 3.0 V. , 80% or more of the compound is used. Examples of the positive electrode active material include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, iron phosphate lithium oxide, and manganese phosphate oxide. Specifically, the positive electrode active material described in the first embodiment can be used.

  The positive electrode additive includes one or more oxides selected from the group consisting of lithium copper oxide, lithium iron oxide, and lithium manganese oxide. Specifically, the positive electrode additive described in the first embodiment can be used.

  The positive electrode conductive agent improves the current collecting performance of the active material and suppresses the contact resistance with the current collector. Examples of the conductive agent include carbonaceous materials such as acetylene black, carbon black, or graphite. Specifically, the positive electrode conductive agent described in the first embodiment can be used.

  The binder binds the positive electrode active material and the conductive agent. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or fluorine-based rubber. Specifically, the binder described in the first embodiment can be used.

  The current collector is preferably, for example, an aluminum foil or an aluminum alloy foil containing an element such as Mg, Ti, Zn, Mn, Fe, Cu, or Si in addition to aluminum.

  For example, the positive electrode 5 is prepared by suspending a positive electrode active material, a positive electrode conductive agent, and a binder in a commonly used solvent to prepare a slurry. The slurry is applied to the current collector 5a, dried, and then pressed. It is produced by this. The positive electrode 5 may also be produced by forming a positive electrode active material, a positive electrode conductive agent, and a binder in the form of a pellet to form the positive electrode layer 5b, and forming this on the current collector 5a.

(4) Nonaqueous electrolyte In this embodiment, the nonaqueous electrolyte uses the liquid nonaqueous electrolyte prepared by melt | dissolving electrolyte in the organic solvent, for example. The liquid non-aqueous electrolyte is preferably formed by dissolving the electrolyte in an organic solvent at a concentration of 0.5M to 2.5M.
Specifically, the liquid non-aqueous electrolyte described in the first embodiment can be used.

  A gel-like non-aqueous electrolyte obtained by combining a liquid non-aqueous electrolyte and a polymer material may be used in place of the separator described later. Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), or polyethylene oxide (PEO).

(5) Separator As the separator 4, for example, a porous film containing polyethylene, polypropylene, cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric can be used. A preferred porous film is made of polyethylene or polypropylene, and can be melted at a constant temperature to cut off the current, thereby improving safety.

  Next, the battery pack provided with the nonaqueous electrolyte battery according to the present embodiment will be described in detail. The battery pack according to this embodiment has one or more of the above-described nonaqueous electrolyte batteries. In addition, description is abbreviate | omitted about the structure similar to the above-mentioned nonaqueous electrolyte battery.

The battery pack 200 will be specifically described with reference to FIGS. 3 and 4. In the battery pack 200 shown in FIG. 3, the nonaqueous electrolyte battery 100 shown in FIG. 2 is used as the unit cell 21.
The plurality of unit cells 21 are laminated so that the negative electrode terminal 6 and the positive electrode terminal 7 extending to the outside are aligned in the same direction, and are fastened with an adhesive tape 22 to constitute an assembled battery 23. These unit cells 21 are electrically connected to each other in series as shown in FIG. In this embodiment, the nonaqueous electrolyte battery 100 shown in the first embodiment is used as the unit cell 21, and the unit cells 21 are alternately connected in series. In the example shown in FIG. 3, four unit cells 21 are alternately connected in series to form an assembled battery 23 including a total of eight unit cells 21. As a modification, the battery cells 21 may be connected in series, in parallel, and appropriately combined according to the purpose of use to constitute the assembled battery 23.

  The printed wiring board 24 is disposed to face the side surface of the unit cell 21 from which the negative electrode terminal 6 and the positive electrode terminal 7 extend. As shown in FIG. 4, a thermistor 25, a protection circuit 26, and a terminal 27 for energizing external devices are mounted on the printed wiring board 24. An insulating plate (not shown) is attached to the surface of the protection circuit board 24 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 7 positioned at the lowermost 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 thereto. The negative electrode side lead 30 is connected to the negative electrode terminal 6 located in 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 thereto. These connectors 29 and 31 are connected to the protection circuit 26 through wirings 32 and 33 formed on the printed wiring board 24.

  The thermistor 25 is used to detect the temperature of the unit cell 21, and the detection signal is transmitted to the protection circuit 26. The protection circuit 26 can cut off the plus side wiring 34a and the minus side wiring 34b between the protection circuit 26 and the energization terminal 27 to the external device under a predetermined condition. The predetermined condition is, for example, when the temperature detected by the thermistor 25 is equal to or higher than a predetermined temperature. The predetermined condition is when the overcharge, overdischarge, overcurrent, or the like of the cell 21 is detected. The detection of overcharge or the like is performed for each individual cell 21 or the entire plurality of unit cells 21. When detecting each single 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 unit cell 21. In the case of FIGS. 3 and 4, the voltage detection wiring 35 is connected to each of the single cells 21, and the detection signal is transmitted to the protection circuit 26 through the wiring 35.

  Protective sheets 36 made of rubber or resin are disposed on the three side surfaces of the assembled battery 23 excluding the side surfaces from which the positive electrode terminal 7 and the negative electrode terminal 6 protrude.

  The assembled battery 23 is stored in a storage container 37 together with each protective sheet 36 and the printed wiring board 24. That is, the protective sheet 36 is disposed on each of the inner side surface in the long side direction and the inner side surface in the short side direction of the storage container 37, and the printed wiring board 24 is disposed on the inner side surface on the opposite side in the short side direction. 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.

  In addition, instead of the adhesive tape 22, a heat shrink tape may be used for fixing 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 shrunk to bind the assembled battery.

  3 and 4 show the configuration in which the unit cells 21 are connected in series, but in order to increase the battery capacity, they may be connected in parallel, or a combination of series connection and parallel connection may be used. The assembled battery packs can be further connected in series and in parallel.

  According to this embodiment described above, a battery pack having excellent charge / discharge cycle performance is provided by including the nonaqueous electrolyte battery having excellent charge / discharge cycle performance by having the configuration of the first embodiment. Can be provided.

In addition, the aspect of a battery pack is changed suitably by a use. The battery pack is preferably one that exhibits excellent cycle characteristics when a large current is taken out. Specific examples include a power source for a digital camera, a vehicle mounted on a vehicle such as a two-wheel to four-wheel hybrid electric vehicle, a two-wheel to four-wheel electric vehicle, or 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. For example, it is possible to improve the power performance of a vehicle such as a hybrid vehicle and to efficiently recover the regenerative energy of the power.
And it can have the outstanding characteristic in the vehicle carrying these battery packs.

Examples will be described in detail below.
Example 1
88% by weight of Nb ₂ TiO ₇ as a negative electrode active material, 6% by weight of acetylene black as a negative electrode conductive material, and 6% by weight of polyvinylidene fluoride (PVdF) are added to N-methylpyrrolidone (NMP) and mixed to form a slurry. Was prepared. The slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm, dried, and pressed to prepare a negative electrode.

88% by weight of LiCoO ₂ as a positive electrode active material and Li ₂ CuO ₂ as a positive electrode additive, 6% by weight of acetylene black as a positive electrode conductive material, and 6% by weight of polyvinylidene fluoride (PVdF) as N-methylpyrrolidone A slurry was prepared by mixing in addition to (NMP). This slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm, then dried and pressed to produce a positive electrode. The weight W1 of the positive electrode additive is the weight W2 of the negative electrode active material, the initial charge capacity per unit weight when the positive electrode additive is charged to 4.3 V with the Li counter electrode, and then discharged to 3.0 V. Q1 is the difference from the initial discharge capacity, Q2 is the charge capacity per unit weight when the negative electrode active material is initially charged to 0.5 V with the Li counter electrode, and then the unit weight is discharged to 2 V and then charged to 1 V again. When the charge capacity per unit is Q3, the weight W1 of the additive and the weight W2 of the negative electrode active material are expressed by the following formula (3),
Q1W1 / (Q3-Q2) W2 = 1.0 (3)
It was set as the value which satisfy | fills.

A test cell was obtained by storing a laminate of a positive electrode and a negative electrode with a polypropylene separator in an aluminum-containing laminate film container together with an electrolytic solution. The capacity of the test cell was 1 Ah. The electrolytic solution was prepared by dissolving 1 mol / L of LiPF ₆ as an electrolyte in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 2).

(Examples 2-3)
A test cell was produced under the same conditions as in Example 1 except that the value of the weight of the positive electrode additive relative to the positive electrode active material was changed as shown in Table 1 below.

(Examples 4 to 5)
A test cell was produced under the same conditions as in Example 1 except that the positive electrode additive was changed as shown in Table 1 below.

(Examples 6 to 7)
A test cell was produced under the same conditions as in Example 1 except that the negative electrode active material was changed as shown in Table 1 below.

(Comparative Example 1)
For comparison, a test cell was produced under the same conditions as in Example 1 except that a positive electrode containing no positive electrode additive was used.

(Comparative Example 2)
For comparison, a test cell was produced under the same conditions as in Example 6 except that the positive electrode not containing the positive electrode additive was used.

(Comparative Example 3)
For comparison, a test cell was produced under the same conditions as in Example 7 except that a positive electrode containing no positive electrode additive was used.

About the battery of the obtained Example and the comparative example, the capacity | capacitance maintenance factor after the first charge / discharge and 500 cycles was measured on condition of the following. The results are shown in Table 1.
_{Incidentally, Li 2 CuO 2, LiMnO 2} , Li 5 FeO 2 charge-discharge efficiency, respectively 5% of the positive electrode additives in the case of using as a positive electrode additive, 10% was 3%. For the examples, the values of Q1W1 / (Q3-Q2) W2 were all in the range of 0.9 to 1.1.

Conditions for measuring discharge capacity:
The battery is charged at a constant current of 0.2 C rate to a voltage of 3.8 V in an environment of 45 ° C. and then charged in a constant voltage mode for 12 hours. From a fully charged state to a constant current of 0.2 C rate to 1.5 V Discharged.
Measurement conditions for capacity retention after 500 cycles:
The battery was charged at a constant current of 1 C rate to a voltage of 3.3 V in an environment of 45 ° C., then charged until the current value converged in the constant voltage mode, and the battery was charged at a constant current of 0.2 C rate from the fully charged state. The capacity when discharged to 5 V was taken as the capacity of the first cycle. Except for setting the rate at the time of discharge to 1C, after charging and discharging for 498 cycles by the same method as the first cycle, charging and discharging were performed again by the same method as the first cycle, and the capacity at the 500th cycle was measured.
The capacity retention rate after 500 cycles was calculated from the capacity ratio at the 500th cycle to the capacity at the first cycle.

  As shown in Table 1, the discharge capacity maintenance ratios after 500 cycles of the batteries according to Comparative Examples 1 to 3 are all 90% or less, whereas the capacity maintenance ratios of the batteries according to Examples 1 to 7 are A high value of 95% or more was exhibited. This is because in the batteries according to Comparative Examples 1 to 3, the battery was charged to 3.8 V in order to form a film by charging the negative electrode to about 0.5 V with respect to Li at the time of initial charge. The potential is higher than the design potential, and the positive electrode active material is deteriorated. On the other hand, in the batteries according to Examples 1 to 7, the positive electrode contains a positive electrode additive having a low initial charge / discharge efficiency. Even if the voltage is increased to 3.8 V, the positive electrode potential does not become higher than the design and no deterioration occurs. In addition, as shown in Examples 1 to 7, a good capacity retention ratio was observed when the weight of the positive electrode additive relative to the mass of the positive electrode active material was in the range of 1 to 10%.

  According to at least one embodiment described above, the positive electrode includes a positive electrode additive having a low initial charge / discharge efficiency, thereby forming a coating on the negative electrode surface without causing a deterioration of the positive electrode, and high energy. The density and cycle characteristics can be realized.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of 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.

  According to this embodiment, a nonaqueous electrolyte secondary battery and a battery pack having a high energy density and excellent cycle characteristics can be obtained by forming a film on the negative electrode surface without causing deterioration of the positive electrode.

  DESCRIPTION OF SYMBOLS 1 ... Winding electrode group, 2 ... Exterior material, 3 ... Negative electrode, 4 ... Separator, 5 ... Positive electrode, 6 ... Negative electrode terminal, 7 ... Positive electrode terminal, 21 ... Single cell, 22 ... Adhesive tape, 23 ... Assembly battery, 24 DESCRIPTION OF SYMBOLS ... Printed circuit board, 25 ... Thermistor, 26 ... Protection circuit, 27 ... Current supply terminal, 28 ... Positive electrode side lead, 29 ... Positive electrode side connector, 30 ... Negative electrode side lead, 31 ... Negative electrode side connector, 32 ... Wiring, 33 ... Wiring, 34a ... plus side wiring, 34b ... minus side wiring, 35 ... wiring, 36 ... protection sheet, 37 ... storage container, 38 ... lid, 100 ... nonaqueous electrolyte battery, 200 ... battery pack

Claims (14)

A positive electrode comprising a positive electrode active material including a metal oxide, and a positive electrode additive including at least one of oxides selected from lithium copper oxide, lithium iron oxide, and lithium manganese oxide;
A negative electrode having a negative electrode active material comprising a titanium-containing oxide;
With a non-aqueous electrolyte,
The positive electrode additive is charged to 4.3 V on a Li basis, then discharged to 3.0 V, and the initial charge / discharge efficiency is measured. . The positive electrode additive is Li ₂ CuO ₂ , LiCuO, Li ₆ CuO ₄ , Li ₂ Cu ₂ O ₃ , LiCu ₃ O ₃ , LiCu ₂ O ₂ , LiCuO ₂ , Li ₃ Cu ₂ O among the lithium copper oxides. _4. The nonaqueous electrolyte secondary battery according to claim 1, comprising one or more oxides selected from the group consisting of: ₄ , Li ₃ CuO ₃ , and LiCu ₃ O ₃ . The positive electrode additive includes Li ₅ FeO ₄ , LiFeO ₂ , LiFe ₅ O ₈ , Li ₃ Fe ₅ O ₈ , Li ₂ Fe ₃ O ₄ , Li ₅ Fe ₅ O ₈ , and Li ₂ among the lithium iron oxides. The nonaqueous electrolyte secondary battery according to claim 1, comprising at least one oxide selected from the group consisting of Fe ₃ O ₅ . The positive electrode additive is one selected from the group consisting of LiMnO ₂ , Li ₂ MnO ₃ , Li ₃ MnO ₄ , LiMn ₃ O ₄ , Li ₄ Mn ₅ O ₁₂ , and LiMnO ₄ among the lithium manganese oxides. The nonaqueous electrolyte secondary battery according to claim 1, comprising the above oxide. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode additive is substantially made of any one of Li ₂ CuO ₂ , LiMnO _{2, and} Li ₅ FeO ₂ . When the initial charge capacity and the initial discharge capacity when the positive electrode additive was charged to 4.3 V on the basis of Li and then discharged to 3.0 V were measured, the difference between the initial charge capacity and the initial discharge capacity was Q1. ,
The charge capacity per unit weight when the negative electrode active material is initially charged to 0.5 V with the Li counter electrode is Q2, and then the charge capacity per unit weight when discharged to 2 V and charged again to 1 V is Q3. When
The weight W1 of the positive electrode additive and the weight W2 of the negative electrode active material are expressed by the following formula (1).
0.9 <Q1W1 / (Q3-Q2) W2 <1.1 (1)
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein   The said positive electrode active material is charged to 4.3V on the basis of Li, then discharged to 3.0V, and when the initial charge / discharge efficiency was measured, the initial charge / discharge efficiency was 80% or more. The nonaqueous electrolyte secondary battery according to any one of the above. When the nonaqueous electrolyte secondary battery was discharged to 1.0 V at a discharge rate of 0.1 C and the elemental composition of the positive electrode active material and the additive was measured,
The element composition of the positive electrode additive is represented by the following formula (2)
Li _x MO ₂ (2)
(Here, M indicates any element of Fe, Cu, or Mn)
X = 1.0 to 1.2,
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein a compound containing M in the formula (2) is attached to a surface of the negative electrode.   A battery pack provided with one or more of the nonaqueous electrolyte secondary batteries according to claim 1.   The battery pack according to claim 9, comprising the non-aqueous electrolyte secondary battery, and at least a terminal for energizing a protection circuit and an external device.   The nonaqueous electrolyte secondary battery according to claim 6, comprising a plurality of the nonaqueous electrolyte secondary batteries, wherein the plurality of nonaqueous electrolyte secondary batteries are electrically connected in series and / or in parallel. Battery pack provided.   A battery pack provided with the nonaqueous electrolyte secondary battery according to claim 6, comprising a plurality of the nonaqueous electrolyte secondary batteries, wherein the plurality of nonaqueous electrolyte secondary batteries are connected in combination in series or in parallel.   A vehicle equipped with the battery pack according to claim 9.   The vehicle according to claim 13, wherein the battery pack according to any one of claims 9 to 13 recovers regenerative energy of power of the vehicle.

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