JP4237785B2 - Nonaqueous electrolyte secondary battery and battery pack - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and an assembled battery.

Non-aqueous electrolyte batteries using lithium metal, lithium alloys, lithium compounds, or carbon materials as negative electrodes are expected as high energy density batteries and high power density batteries, and research and development are being actively promoted. So far, lithium ion batteries comprising a positive electrode containing LiCoO ₂ or LiMn ₂ O ₄ as an active material and a negative electrode containing a carbon material that occludes and releases lithium have been widely put into practical use. In the negative electrode, metal oxides or alloys that replace the carbon material have been studied.

  In a nonaqueous electrolyte battery, a copper foil is generally used as a negative electrode current collector. Copper or nickel is generally used for the lead and the terminal to which the lead is connected. In a secondary battery including a negative electrode including a copper foil current collector, the potential of the negative electrode increases in an overdischarged state. For this reason, the dissolution reaction of the negative electrode of the copper foil is promoted, and the discharge capacity is rapidly reduced. Further, in the assembled battery, a battery that is over-discharged due to a loss of battery capacity balance is generated as the long-term cycle continues. For this reason, the collector which consists of copper foil integrated in the battery of an overdischarge state melt | dissolves. Therefore, the secondary battery is equipped with a protection circuit for preventing an overdischarge state.

  However, the energy density of such a secondary battery is reduced by the amount of the protection circuit. Also, when using an outer container having a thin metal can for reducing the weight of the battery, for example, the copper constituting the current collector, lead and terminal of the negative electrode is dissolved during the overdischarge cycle, and the battery swells. Becomes larger.

  For this reason, Patent Document 1 discloses a nonaqueous electrolyte secondary battery that uses an aluminum foil or an aluminum alloy foil as a negative electrode current collector in the use of a negative electrode active material that occludes lithium ions at a specific potential. Yes. According to such a configuration, it is possible to realize a nonaqueous electrolyte secondary battery with improved energy density and overdischarge cycle performance. In addition, since this non-aqueous electrolyte secondary battery can have a discharge capacity of several Ah or more, especially several tens of Ah or more, in addition to power storage, assist bicycles, electric scooters, electric cars, hybrid cars, trains, etc. It is considered promising as a square nonaqueous electrolyte secondary battery for in-vehicle use.

  By the way, the in-vehicle secondary battery needs to have a low internal resistance, a high energy density and a high output density for the purpose of taking out a high output. Furthermore, excellent cycle performance and long-term high strength and corrosion resistance are required under conditions such as high temperature, high humidity, vibration, rapid charge, high output discharge and overdischarge. Therefore, for the purpose of keeping the internal resistance of the battery small, the connection between the lead and the terminal where the current inside the battery is concentrated is mechanical strength, electrochemical stability, chemical stability under high temperature and high humidity environment for a long time. Therefore, it is required to maintain a low resistance excellent in corrosion resistance.

  However, if the negative electrode lead and the terminal are formed of copper having excellent conductivity in the above-described invention, the battery is corroded / dissolved at the connection portion between the lead and the terminal in a high-temperature and high-humidity environment over a long period of use. The reaction proceeds and the resistance increases. For this reason, it becomes difficult to take out high output with a battery and an assembled battery. In addition, since the impedance increases, the discharge reaction of the positive electrode and the negative electrode cannot sufficiently proceed during high output discharge, and the utilization factor of the active material decreases.

  On the other hand, Patent Document 2 discloses a highly safe non-aqueous electrolyte battery having a terminal structure that can prevent or suppress a spark that may occur in a terminal portion due to leakage of the non-aqueous electrolyte. It is disclosed. In the paragraph [0036] of the present invention, the negative electrode terminal 40 made of a copper alloy is composed of a current collecting part 40a serving as an internal terminal and a bolt-shaped external terminal part 40b, and the current collecting part 40a is an electrode body. 10 is joined to a strip-like negative electrode lead 12a extending from the outer peripheral portion 40, and the external terminal portion 40b is located outside the negative electrode side cover plate 23 of the battery case 20, and aluminum for preventing the occurrence of sparks in the exposed portion. It is described that plating is applied.

However, since the current collector 40a of the negative electrode terminal 40 to which the negative electrode lead is connected is made of a copper alloy in the present invention, as described above, the lead and the terminal can be used in a battery overdischarge operation or a high temperature and high humidity environment for a long period of use. Corrosion / dissolution reaction proceeds at the connecting portion of the, and the resistance increases, making it difficult to take out a high output from the battery and the assembled battery.
JP 2004-296256 A JP2003-36825A

  The present invention relates to the connection reliability between the negative electrode terminal and the lead under the conditions of long-term high-temperature and high-humidity environment, rapid charge, overdischarge, and high-output discharge, or the connection reliability between the outer container and the lead that also serves as the negative electrode terminal. An object of the present invention is to provide a nonaqueous electrolyte secondary battery and an assembled battery with improved performance.

According to the first aspect of the present invention, a non-aqueous electrolyte secondary battery having an internal resistance with an AC impedance value of 1 kHz or less of 1 kHz,
Metal outer container;
A non-aqueous electrolyte housed in the container;
A positive electrode housed in the container, a negative electrode having an active material that occludes lithium ions at a potential of 0.4 V or more with respect to the electrode potential of lithium, and a separator interposed between the negative electrode and the positive electrode;
A negative electrode lead having one end connected to the negative electrode and made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more; and being attached to the outer container to be electrically connected to the other end of the negative electrode lead A negative electrode terminal formed of an aluminum alloy containing at least one metal component selected from Mg , Cr, Mn, Cu, Si, Fe and Ni and having an aluminum purity of 90 wt% or more and less than 99 wt%;
A nonaqueous electrolyte secondary battery is provided.

  According to the second aspect of the present invention, there is provided an assembled battery in which a plurality of the nonaqueous electrolyte secondary batteries of the first aspect are connected.

  According to the present invention, the connection reliability between the negative electrode terminal and the lead under the conditions of long-term high-temperature and high-humidity environment, rapid charging, overdischarge and high-output discharge, or the outer container and the lead serving as the negative electrode terminal By improving the connection reliability, it is possible to provide a nonaqueous electrolyte secondary battery and an assembled battery excellent in cycle performance and output performance.

  In the following, embodiments of the present invention will be described in detail mainly with respect to rectangular non-aqueous electrolyte secondary batteries and assembled batteries, but cylindrical non-aqueous electrolyte secondary batteries are also within the scope of the present invention.

(First embodiment)
The rectangular nonaqueous electrolyte secondary battery according to the first embodiment includes a metal outer container, a nonaqueous electrolyte accommodated in the container, a positive electrode accommodated in the container, and an electrode potential of lithium. In contrast, a negative electrode having an active material that occludes lithium ions at a potential of 0.4 V or more and a separator interposed between the negative electrode and the positive electrode are provided. The negative electrode lead is made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more, and one end is connected to the negative electrode. The negative electrode terminal is attached to the container so as to be connected to the other end of the negative electrode lead. The negative electrode terminal has a composition with an aluminum purity of less than 99% by weight, at least the surface connected to the negative electrode lead contains at least one metal component selected from Mg, Cr, Mn, Cu, Si, Fe and Ni. It is formed with the aluminum alloy which has. For example, the positive electrode is connected to a positive electrode terminal attached to the container through a lead. Such a secondary battery has an internal resistance with an AC impedance value of 1 kHz or less at 1 kHz. That is, this secondary battery has a large discharge capacity of 2 Ah or more, for example.

  Hereinafter, the negative electrode, the positive electrode, the separator, the nonaqueous electrolyte, and the outer container will be described in detail.

1) Negative electrode The negative electrode includes a negative electrode current collector and a negative electrode layer that is supported on one or both surfaces of the negative electrode current collector and includes a negative electrode active material, a conductive agent, and a binder.

  The negative electrode current collector is made of, for example, an aluminum foil or aluminum alloy foil having a purity of 99% by weight or more. As the aluminum alloy, for example, an alloy containing a metal component such as Mg, Zn, Mn, and Si is preferable. This aluminum alloy preferably contains a transition metal such as Fe, Cu, Ni, Cr in addition to the metal component in an amount of 100 ppm or less.

The aluminum foil or aluminum alloy foil preferably has an average diameter of crystal grains of 50 μm or less. A more preferable average diameter of crystal grains is 10 μm or less. Here, the average diameter d of the crystal grains of aluminum and aluminum alloy indicates the average diameter of the grains, the structure of the surface of the target substance is observed with a metal microscope, the number n of crystal grains existing within 1 mm × 1 mm is counted, and the crystal The average area S of the particles is determined from S = (1 × 10 ⁶ ) / n (μm ² ). In the metal microscope observation, the crystal particles are counted at five locations, the average area of the crystal particles is substituted into the following formula (1), and the average value d (μm) of the crystal particles is calculated by calculating the average value. Asked. The assumed error is about 5% by weight.

d = 2 (S / π) ^1/2 (1)
The size of the crystal grains of the aluminum foil or aluminum alloy foil is complicatedly influenced by many factors such as material composition, impurities, processing conditions, heat treatment history and annealing heating conditions and cooling conditions. However, it becomes possible to produce an aluminum foil or an aluminum alloy foil having an average diameter of crystal grains of 50 μm or less by organically adjusting the above factors in the production process. In addition, you may produce a negative electrode electrical power collector from PACAL21 (trade name) made from Nippon Foil.

  Such an aluminum foil or aluminum alloy foil having an average diameter of crystal grains of 50 μm or less can dramatically increase the strength. The increase in the strength of the negative electrode current collector improves physical and chemical resistance and makes it difficult for the negative electrode current collector to break. In particular, deterioration due to dissolution and corrosion of the negative electrode current collector can be remarkably prevented in an overdischarge long-term cycle under a high temperature environment (40 ° C. or higher), and an increase in resistance of the negative electrode can be suppressed. Furthermore, the suppression of the increase in resistance of the negative electrode reduces Joule heat, and the heat generation of the negative electrode can be suppressed.

  In addition, by using a negative electrode current collector made of an aluminum foil or an aluminum alloy having an average diameter of crystal particles of 50 μm or less, water intrudes in a long-term cycle under high temperature and high humidity (40 ° C. or higher, humidity 80% or higher). Degradation due to dissolution and corrosion of the negative electrode current collector can be suppressed.

  Furthermore, due to the increase in strength of the negative electrode current collector, the negative electrode active material, the conductive agent and the binder are suspended in a suitable solvent, and this suspension is applied to the current collector, dried, and pressed to apply the negative electrode. When producing the above, even if the press pressure is increased, the current collector can be prevented from being broken. As a result, a high-density negative electrode can be manufactured, and the capacity density can be improved. In addition, increasing the density of the negative electrode increases the thermal conductivity and improves the heat dissipation of the negative electrode. In addition, an increase in battery temperature can be suppressed by a synergistic effect of suppressing the heat generation of the battery and improving the heat dissipation of the electrode.

  The thickness of the negative electrode current collector is preferably 20 μm or less.

  The negative electrode active material occludes lithium ions at a potential of 0.4 V or higher with respect to the lithium electrode potential. That is, the open circuit potential for occluding lithium ions of the negative electrode active material is 0.4 V with respect to the open circuit potential of lithium metal. By using such a negative electrode active material, even if a member around the negative electrode such as a current collector, a lead, or a terminal is formed of aluminum (or aluminum alloy), the aluminum (or aluminum alloy) and lithium are alloyed. It is possible to suppress the formation of fine particles by the chemical reaction. In other words, aluminum (or an aluminum alloy) can be used as the material of the member around the negative electrode in place of conventional copper. In addition, the battery voltage can be further improved. In particular, the open circuit potential for occluding lithium ions of the negative electrode active material is desirably 0.4 to 3 V, more preferably 0.4 to 2 V, relative to the open circuit potential of the lithium metal.

Examples of the negative electrode active material include metal oxides, metal sulfides, metal nitrides, and metal alloys that occlude lithium ions at the specific potential. Specifically, tungsten oxide (WO ₃ ), amorphous tin oxide such as SnB _0.4 P _0.6 O _3.1 , tin silicon oxide (SnSiO ₃ ), silicon oxide (SiO), etc. are used as metal oxides as metal oxides. Examples of the material include lithium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), iron sulfide (FeS, FeS ₂ , Li _x FeS ₂ ), and the like, and the metal nitride includes lithium cobalt nitride (Li _x Co _y N, 0 <X <4.0, 0 <y <0.5) and the like.

  In particular, the negative electrode active material is preferably a titanium-containing oxide such as a titanium-containing metal composite oxide or a titanium-based oxide.

Examples of the titanium-containing metal composite oxide include lithium-titanium composite oxide in which some of the constituent elements of lithium-containing titanium-based oxide, lithium titanium oxide, and lithium titanium oxide are substituted with different elements during oxide synthesis. Things can be mentioned. Examples of the lithium titanium oxide include lithium titanate having a spinel structure (for example, Li _{4 + x} Ti ₅ O ₁₂ (x is 0 ≦ x ≦ 3)), ramsteride type lithium titanate (for example, Li _{2 + y} Ti ₃ O ₇ (where y is 0 ≦ y ≦ 3), etc. These lithium titanates occlude lithium ions at a potential of about 1.5 V with respect to the electrode potential of lithium, and aluminum foil or aluminum This is preferable because it is an electrochemically very stable material with respect to the current collector of the alloy foil.

Examples of the titanium-based oxide include metal composite oxides containing at least one element selected from the group consisting of TiO ₂ , Ti and P, V, Sn, Cu, Ni, Co, and Fe. TiO ₂ is preferably anatase type and low crystalline having a heat treatment temperature of 300 to 500 ° C. Examples of the metal composite oxide containing at least one element selected from the group consisting of Ti and P, V, Sn, Cu, Ni, Co and Fe include TiO ₂ —P ₂ O ₅ and TiO ₂ —V. ₂ O ₅ , TiO ₂ —P ₂ O ₅ —SnO ₂ , TiO ₂ —P ₂ O ₅ —MeO (Me is at least one element selected from the group consisting of Cu, Ni, Co and Fe). be able to. This metal composite oxide preferably has a microstructure in which a crystalline phase and an amorphous phase coexist or exist alone. With such a microstructure, the cycle performance can be greatly improved. Among these, a lithium titanium oxide, a metal composite oxide containing at least one element selected from the group consisting of Ti and P, V, Sn, Cu, Ni, Co, and Fe is preferable.

  The negative electrode active material desirably has an average primary particle size of 1 μm or less, more preferably 0.3 μm or less. Here, the particle size of the negative electrode active material can be measured by the following method using a laser diffraction particle size distribution measuring apparatus (manufactured by Shimadzu Corporation; SALD-300). That is, about 0.1 g of a sample, a surfactant, and 1 to 2 mL of distilled water are added to a beaker and sufficiently stirred, and then poured into a stirred water tank, and the laser diffraction particle size distribution measuring device is used at intervals of 2 seconds. The light intensity distribution is measured 64 times, and the average particle diameter of primary particles of the negative electrode active material is measured by a method of analyzing the particle size distribution data.

  The negative electrode active material having an average primary particle size of 1 μm or less is preferably made into a powder of 1 μm or less as an active material precursor when reacting and synthesizing active material raw materials, for example, a ball mill, a jet mill, etc. The pulverization process is performed to 1 μm or less using a pulverizer.

  By using such a negative electrode active material composed of primary particles having an average particle size of 1 μm or less, cycle performance can be improved. In particular, since this effect becomes remarkable at the time of quick charge and high output discharge, it is optimal as a secondary battery for vehicles having high input / output performance. This is because, for example, the negative electrode active material that occludes and releases lithium ions has a smaller specific particle surface area, and the specific surface area of the secondary particles in which the primary particles are aggregated increases and the diffusion distance of lithium ions inside the active material decreases. This is because lithium ions can be quickly occluded and released.

  Further, when the negative electrode including the pressing step described above is manufactured, the load on the negative electrode current collector increases as the average particle size of the primary particles of the negative electrode active material decreases. For this reason, when an aluminum foil or an aluminum alloy foil is used as the negative electrode current collector, the current collector is broken in the pressing step, and the negative electrode performance is reduced. However, since the strength of the current collector can be improved by making the negative electrode current collector from an aluminum foil or aluminum alloy foil having an average diameter of the crystal particles of 50 μm or less, the average particle diameter of the primary particles is 1 μm or less. Even when a negative electrode is produced using a negative electrode active material, the current collector is prevented from being broken during the pressing process, thereby improving reliability and improving cycle characteristics during rapid charging and high-power discharge. Is possible.

  For example, a carbon material can be used as the conductive agent. Examples of the carbon material include acetylene black, carbon black, coke, carbon fiber, and graphite.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, and styrene butadiene rubber.

  The mixing ratio of the negative electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the negative electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

  The lead electrically connected to the negative electrode current collector is made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more. In particular, the purity of aluminum is preferably 99.9% by weight or more. The aluminum alloy preferably has a composition in which, for example, Mg, Fe, and Si are 0.7% by weight or less in total, and the balance is substantially aluminum. The lead is preferably a flexible foil or plate having a thickness of 100 to 500 μm and a width of 2 to 20 mm. Such a lead does not react and dissolve in the electrolyte in an overdischarged state, and can flow a large current without disconnection even during long-term vibration, so the long-term reliability and high output of the secondary battery Can be maintained.

  The negative electrode terminal has an aluminum purity of less than 99% by weight, preferably containing at least one metal component selected from Mg, Cr, Mn, Cu, Si, Fe and Ni at least on the surface connected to the lead. It is formed of an aluminum alloy having an aluminum purity of 90% by weight or more and less than 99% by weight. Such an aluminum alloy can improve strength and corrosion resistance as compared with aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more. Among the metal components, Mg and Cr further improve the corrosion resistance of the aluminum alloy, and Mn, Cu, Si, Fe and Ni further improve the strength of the aluminum alloy.

  Specifically, the negative electrode terminal has the following form.

  (1) The negative electrode terminal has a terminal body made of at least one metal selected from copper, iron and nickel, and at least a surface of the terminal body to which the lead is connected, for example, the entire surface of the terminal body. And an aluminum alloy layer. Since this negative electrode terminal has a terminal body such as iron having higher strength than the aluminum alloy layer, it is possible to increase the strength.

  (2) The negative electrode terminal has a single structure made of an aluminum alloy having the above composition.

  The aluminum alloy layer (1) preferably has a thickness of 10 to 300 μm. If the thickness of the aluminum alloy layer is less than 10 μm, the connection reliability with the negative electrode lead may be reduced. On the other hand, if the thickness of the aluminum alloy layer exceeds 300 μm, the smoothness and uniformity of the aluminum alloy layer may be reduced. As the method for forming the aluminum alloy layer, for example, a method of immersing the terminal body in an aluminum alloy melt, a method of spraying an aluminum alloy on the terminal body, or a method of plating an aluminum alloy on the terminal body is adopted. Is done. When an aluminum alloy layer is formed only on the lead connection surface of the terminal body by these methods, a method of masking the region other than the lead connection surface of the terminal body is employed.

  The aluminum alloy layer is composed of Mg 0.5 to 5 wt%, Cr 0.5 wt% or less, Mn 0.3 to 2.0 wt%, Cu 5 wt% or less, Si 1 wt% or less, Fe 1 wt% or less, and Ni 1 wt% or less. It is preferable that the composition has at least one metal component selected from the group consisting of Al. In particular, in order to realize an aluminum alloy layer with better corrosion resistance, it is preferable to use an Al—Mg alloy (Mg: 0.5 to 5% by weight). In order to realize an aluminum alloy layer having higher corrosion resistance and strength, a composition containing at least one metal component selected from Mn, Cu, Si, Fe and Ni in the above amount in addition to Mg is preferable. Such an aluminum alloy layer is composed of 0.5 to 5% by weight of Mg, 0.3 to 2.0% by weight of Mn, 0.1% by weight or less of at least one metal selected from Cu, Fe, Si and Cr, and the balance Most preferably, it has a composition consisting essentially of Al. In this way, a terminal having an aluminum alloy layer with higher corrosion resistance and strength can reduce the resistance of the connection part with the lead in a high temperature and high humidity environment, and can reduce the connection resistance between adjacent batteries even when it is an assembled battery. It becomes possible to maintain a low state.

  However, in the case where the aluminum alloy layer is formed by plating, at least one metal selected from Cu, Fe, Si, and Cr is not more than 1.0% by weight, and the balance is substantially made of Al due to restrictions on the plating component. It preferably has a composition.

  The negative electrode terminal having a single structure made of the aluminum alloy (2) is Mg 0.5-5 wt%, Cr 0.5 wt% or less, Mn 0.3-2.0 wt%, Cu 5 wt% or less, Si 1 wt. % Or less, Fe 1% by weight or less, and Ni 1% by weight or less, and the balance is preferably substantially Al. In particular, the negative electrode terminal has at least one metal selected from Mg (Mg: 0.5 to 5 wt%) and the above amounts of Mn, Cu, Si, Fe and Ni from the viewpoint of increasing strength in addition to corrosion resistance. It is preferable to make it from an aluminum alloy having a composition containing components. In the negative electrode terminal of this system, Mg is 0.5 to 5% by weight, Mn is 0.3 to 2.0% by weight, at least one metal selected from Cu, Fe, Si, and Cr is 0.1% by weight or less, and the balance is substantially Most preferably, it is made from an aluminum alloy having a composition of Al. The negative electrode terminal made of an aluminum alloy with higher corrosion resistance and strength can maintain sufficient strength in a high-temperature and high-humidity environment, reduce the resistance of the connection portion with the negative electrode lead, and can be an assembled battery. Even at times, the connection resistance between adjacent batteries can be kept low.

  The negative electrode terminal is preferably a bolt having a diameter of 3 to 30 mm.

2) Positive electrode The positive electrode includes a positive electrode current collector and a positive electrode layer that is supported on one or both surfaces of the positive electrode current collector and includes a positive electrode active material, a conductive agent, and a binder.

  The current collector is made of an aluminum foil or an aluminum alloy foil, and the average diameter of the crystal particles is preferably 50 μm or less, more preferably 10 μm or less, as with the negative electrode current collector described above. Such an aluminum foil or aluminum alloy foil having an average diameter of crystal grains of 50 μm or less can dramatically increase the strength. Therefore, when the positive electrode active material, the conductive agent and the binder are suspended in an appropriate solvent, the suspension is applied to the current collector, dried and pressed to produce the positive electrode. Even if the height is increased, breakage of the current collector can be prevented. As a result, a high-density positive electrode can be manufactured, and the capacity density can be improved.

  The current collector preferably has a thickness of 20 μm or less.

  Examples of the positive electrode active material include oxides, sulfides, and polymers.

Examples of the oxide include manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (for example, Li _x Mn ₂ O ₄ or Li _x MnO ₂ ), and lithium nickel composite oxide (for example, Li _x NiO ₂ ), lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel cobalt composite oxide (eg, Li _x Ni _1-y Co _y O ₂ ), lithium nickel manganese cobalt composite oxide (eg, Li _x Co) _{1-yz Mn y Ni z O} 2), spinel type lithium-manganese-nickel composite oxide _{(Li x Mn 2-y Ni} y O 4), lithium phosphate oxide having an olivine structure (e.g., Li _x FePO _4, Li _x Fe _{1-y Mn y PO 4,} Li x CoPO 4), iron sulfate _{(Fe 2 (SO 4) 3} ), vanadium oxide (e.g. V ₂ O ₅₎ and elevation It is. Note that x, y, and z are preferably in the range of 0 to 1 unless otherwise specified. In particular, the composition of the lithium nickel cobalt manganese composite oxide is Li _a Ni _b Co _c Mn _d O ₂ (where the molar ratios a, b, c and d are 0 ≦ a ≦ 1.1, 0.1 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.9, 0.1 ≦ d ≦ 0.5).

  Examples of the polymer include conductive polymer materials such as polyaniline and polypyrrole, and disulfide polymer materials. In addition, sulfur (S), carbon fluoride, and the like can be used.

  Examples of the positive electrode active material include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, spinel type lithium manganese nickel composite oxide, and lithium manganese cobalt composite oxide with high battery voltage. And lithium nickel cobalt manganese composite oxide having a layered crystal structure.

  Examples of the conductive agent include acetylene black, carbon black, and graphite.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber.

  The mixing ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

3) Separator Examples of the separator include a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, and an aramid porous film.

4) Exterior container This exterior container is comprised from the bottomed cylindrical metal can and the metal cover body joined and fixed to the opening part of this metal can by welding, for example. These metal cans and lids are preferably made of aluminum or an aluminum alloy from the viewpoints of weight reduction and corrosion resistance. The aluminum or aluminum alloy preferably has an average crystal grain size of 50 μm or less, more preferably 10 μm or less. Such a metal can made of aluminum or an aluminum alloy having an average diameter of 50 μm or less can drastically increase the strength, so that the wall thickness can be reduced. As a result, since heat dissipation can be improved, an increase in battery temperature can be suppressed. In addition, the metal can can be reduced in thickness, and the deposition of the electrode group consisting of the positive electrode, separator, and negative electrode accommodated can be effectively increased, so that the energy density is improved and the battery weight and size are reduced accordingly. It becomes possible. These features are suitable for batteries that require high temperature conditions, high energy density, etc., such as in-vehicle secondary batteries.

  The aluminum alloy used for the outer container preferably contains at least one metal component selected from Mg, Mn and Fe. The metal can of the outer container made of such an aluminum alloy is further enhanced in strength and can be thinned to 0.3 mm or less.

  In the prismatic non-aqueous electrolyte secondary battery according to the first embodiment, the negative electrode and positive electrode terminals are respectively electrically insulated and attached to a lid of an outer container, for example. However, it is also possible to attach the terminal of the negative electrode electrically connected to the outer container.

5) Non-aqueous electrolyte As this non-aqueous electrolyte, a liquid non-aqueous electrolyte prepared by dissolving an electrolyte in an organic solvent, a gel-like non-aqueous electrolyte obtained by combining the liquid electrolyte and a polymer material, or a lithium salt electrolyte And a solid non-aqueous electrolyte in which a polymer material is combined. The non-aqueous electrolyte may be a room temperature molten salt (ionic melt) containing lithium ions.

  The liquid non-aqueous electrolyte is prepared by dissolving an electrolyte in an organic solvent at a concentration of 0.5 to 3 mol / L.

Examples of the electrolyte include LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₃ C, LiB [(OCO) ₂ ] At least one selected from ₂ can be mentioned. Among these electrolytes, LiBF ₄ is preferable because it is highly corrosive but has excellent thermal and chemical stability and is difficult to decompose. Furthermore, it is preferable to use an electrolyte that is electrochemically stable at a high potential. Such an electrolyte is at least one selected from the group of LiBF ₄ and LiPF ₆ .

  Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC). , Chain ethers such as dimethoxyethane (DME) and dietoethane (DEE), cyclic ethers such as tetrahydrofuran (THF) and dioxolane (DOX), γ-butyrolactone (GBL), acetonitrile (AN), sulfolane (SL), etc. Can be mentioned. These organic solvents can be used alone or in the form of a mixture. It is desirable to use at least one organic solvent selected from polypropylene carbonate, ethylene carbonate, and γ-butyrolactone because it has a high boiling point, a high ignition point, and excellent thermal stability. It is more desirable to use γ-butyrolactone as the organic solvent.

From the group of at least one organic solvent selected from polypropylene carbonate, ethylene carbonate and γ-butyrolactone, and LiBF ₄ and LiPF ₆ because they have a high boiling point, a high ignition point, and excellent thermal and electrochemical stability. It is desirable to use a non-aqueous electrolyte containing at least one selected electrolyte.

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

  The room temperature molten salt (ionic melt) is composed of lithium ions, organic cations and organic anions, and is in a liquid state at 100 ° C. or lower, and in some cases even at room temperature or lower.

  Next, the prismatic nonaqueous electrolyte secondary battery according to the first embodiment will be specifically described with reference to FIGS.

  The square nonaqueous electrolyte secondary battery 20 includes an exterior container 1 made of, for example, an aluminum alloy. This exterior container 1 is comprised from the bottomed rectangular cylindrical metal can 2 and the rectangular plate-shaped cover body 3 airtightly joined to the upper-end opening part of this metal can 2 by laser welding, for example. Holes 4 and 5 for holding a negative electrode terminal and a positive electrode terminal, which will be described later, are opened in the lid body 3.

  The laminated electrode group 6 is housed in the metal can 2 of the outer container 1. As shown in FIG. 3, the laminated electrode group 6 is formed by alternately inserting a plurality of negative electrodes 8 and positive electrodes 9 into a folded portion of a separator 7 folded into a ninety-nine shape, and the end of the separator 7 is rectangular. It has the structure wound so that the outer peripheral side surface of a columnar laminated body might be covered. Such a laminated electrode group 6 is inserted and accommodated in the metal can 2 so that the surfaces of the separator 7 folded into a ninety-nine shape are the upper and lower end surfaces. The insulating plate 10 is disposed between the inner surface of the bottom of the metal can 2 and the lower end surface of the multilayer electrode group 6. The nonaqueous electrolyte is accommodated in the metal can 2 in which the laminated electrode group 6 is located.

  A cylindrical insulating member 11 having disc-shaped ridges at both ends is fitted into the hole 4 of the lid 3. For example, the bolt-shaped negative electrode terminal 12 is inserted into the tubular insulating member 11 such that the head thereof is positioned in the metal can 2, and the screw portion protrudes from the lid 3 to the outside. For example, a nut 13 made of an aluminum alloy is screwed into a protruding thread portion of the negative electrode terminal 12 via a washer made of an aluminum alloy (not shown), and the negative electrode terminal 12 is insulated and fixed to the lid 3. The negative electrode terminal 12 is made of an aluminum alloy having an aluminum purity of less than 99% by weight containing at least one metal component selected from Mg, Cr, Mn, Cu, Si, Fe and Ni.

  Cylindrical insulating members 14 having disc-shaped ridges at both ends are fitted into the holes 5 of the lid 3. For example, the bolt-shaped positive electrode terminal 15 is inserted into the cylindrical insulating member 14 such that the head thereof is positioned in the metal can 2, and the screw portion protrudes from the lid 3 to the outside. For example, a nut 16 made of an aluminum alloy is screwed into a protruding thread portion of the positive electrode terminal 15 via a washer made of an aluminum alloy (not shown), and the positive electrode terminal 15 is insulated and fixed to the lid 3. The positive electrode terminal 15 is made of an aluminum alloy containing metal components such as Mg, Cr, Mn, Cu, Si, Fe and Ni.

  The negative electrode lead 17 composed of a plurality of foils or plates has one end connected to each negative electrode 8 of the laminated electrode group 6 by, for example, resistance welding, and the other end gathered to the lower end surface of the negative electrode terminal 12 by, for example, resistance welding. It is connected. As with the negative electrode lead 17, the positive electrode lead 18 made of a plurality of foils or plates has one end connected to each positive electrode 9 of the laminated electrode group 6 by, for example, resistance welding, and the other end assembled to the lower side of the positive electrode terminal 15. It is connected to the end face by, for example, resistance welding. The negative electrode lead 17 and the positive electrode lead 18 are made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more.

  In addition, the said negative electrode terminal 12 is not limited to the form of the single structure made from the aluminum alloy of the said composition, as shown in FIG. 1, FIG. For example, as shown in FIG. 4A, the negative electrode terminal 12 is formed on the entire outer periphery of a bolt-shaped terminal body 12a made of at least one metal selected from copper, iron, and nickel, with Mg, Cr, Mn, Cu, Si, You may make it the structure which coat | covered the aluminum alloy layer 12b whose aluminum purity containing at least 1 or more metal component chosen from Fe and Ni is less than 99 weight%. Further, as shown in FIG. 4B, the negative electrode terminal 12 may have a structure in which the lead connection surface (lower end surface) of the bolt-shaped terminal body 12a is covered with the aluminum alloy layer 12b.

  Next, the assembled battery according to the first embodiment will be described.

  The assembled battery according to the first embodiment has a structure in which a plurality of the aforementioned prismatic nonaqueous electrolyte secondary batteries are connected.

  For the connection of the secondary battery, a series connection, a parallel connection, or a combination of series and parallel can be adopted.

  The assembled battery according to the first embodiment will be specifically described with reference to FIG. In this assembled battery, a plurality of, for example, five prismatic non-aqueous electrolyte secondary batteries 20 shown in FIGS. 1 and 2 are arranged adjacent to each other in one direction, and positive and negative terminals 15 of the secondary batteries, 12 is connected in series with connection leads 21 to 24 made of Cu, for example. A positive electrode lead 15 is connected to the positive terminal 15 of the secondary battery 20 at the left end, and a negative electrode lead 26 is connected to the negative terminal 12 of the secondary battery 20 at the right end.

  As described above, the prismatic nonaqueous electrolyte secondary battery according to the first embodiment has an AC impedance value with an internal resistance of 1 kHz of 10 mΩ or less, that is, a discharge capacity of 2 Ah or more, and 0.4 V with respect to the electrode potential of lithium. A negative electrode having an active material that occludes lithium ions at the above potential is provided. Further, a lead for electrically connecting the negative electrode and the negative electrode terminal is formed from aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more, and at least the surface of the negative electrode terminal connected to the lead is Mg, It is formed from an aluminum alloy having an aluminum purity of less than 99% by weight containing at least one metal component selected from Cr, Mn, Cu, Si, Fe and Ni.

  By using a negative electrode having an active material that occludes lithium ions at a specific potential, even if a member around the negative electrode such as a current collector, a lead, or a terminal is formed of aluminum (or an aluminum alloy), It is possible to suppress aluminum (or aluminum alloy) and lithium from being alloyed and being pulverized. That is, the negative electrode lead can be made of low-resistance aluminum or an aluminum alloy, and at least the lead connection portion of the negative electrode terminal can be formed of a low-resistance aluminum alloy containing a specific metal component.

  An aluminum alloy having an aluminum purity of less than 99% by weight containing at least one metal component selected from Mg, Cr, Mn, Cu, Si, Fe and Ni at least on the surface connected to the lead of the negative electrode terminal Therefore, the strength and corrosion resistance of the connecting portion with the negative electrode lead can be improved as compared with the case where the connecting portion is made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more. In particular, at least the surface of the negative electrode terminal connected to the lead is 0.5 to 5% by weight of Mg, 0.3 to 2.0% by weight of Mn, 0.1% by weight of at least one metal selected from Cu, Fe, Si, and Cr. %, And the balance and the corrosion resistance of the connecting portion between the negative electrode terminal and the lead can be further improved.

  As a result, even when the secondary battery is subjected to vibration and impact, it is possible to suppress the disconnection of the connecting portion between the negative electrode terminal and the lead, and high reliability can be ensured.

  Further, even when the connection portion between the negative electrode terminal and the lead is exposed to an overdischarge operation or a high-temperature and high-humidity environment during long-term use, corrosion / dissolution reaction at the connection portion can be prevented and a low-resistance connection can be maintained. For this reason, high output can be taken out, and sufficient positive electrode and negative electrode discharge reactions are performed without causing an increase in impedance during high output discharge, thereby improving the utilization rate of the active material.

Furthermore, since the corrosion resistance of the connecting portion between the negative electrode terminal and the lead can be improved, LiBF ₄ is used as the electrolyte of the non-aqueous electrolyte, but has excellent thermal and chemical stability and hardly decomposes. Therefore, it becomes possible to take out a high output more stably.

  Therefore, by improving the connection reliability between the negative electrode terminal and the lead under the conditions of long-term high-temperature and high-humidity environment, rapid charging, over-discharge and high-output discharge, it has excellent cycle performance and output performance, and high reliability It is possible to provide a prismatic non-aqueous electrolyte secondary battery.

  In addition, by connecting and combining the plurality of prismatic nonaqueous electrolyte secondary batteries described above, each secondary battery is good under the conditions of long-term high-temperature and high-humidity environment, rapid charge, overdischarge, and high-output discharge. Therefore, an assembled battery excellent in cycle performance and output performance can be provided.

(Second Embodiment)
The rectangular nonaqueous electrolyte secondary battery according to the second embodiment includes a metal outer container also serving as a negative electrode terminal, a nonaqueous electrolyte housed in the container, a positive electrode housed in the container, A negative electrode having an active material that occludes lithium ions at a potential of 0.4 V or more with respect to the lithium electrode potential; and a separator interposed between the negative electrode and the positive electrode. The negative electrode lead is made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more, and has one end connected to the negative electrode and the other end connected to the inner surface of the exterior container. In the outer container to which the negative electrode lead is connected, at least the inner surface connected to the negative electrode lead contains at least one metal component selected from Mg, Cr, Mn, Cu, Si, Fe, and Ni. It is formed of an aluminum alloy having a composition with an aluminum purity of less than 99% by weight, preferably an aluminum purity of 90% by weight or more and less than 99% by weight. The positive electrode is connected through a lead to a positive electrode terminal attached to the outer container, for example. Such a secondary battery has an internal resistance with an AC impedance value of 1 kHz or less at 1 kHz. That is, this secondary battery has a large discharge capacity of 2 Ah or more, for example.

  Hereinafter, the exterior container will be described in detail. The negative electrode, the positive electrode, the separator, and the nonaqueous electrolyte are the same as those described in the first embodiment.

  The exterior container is composed of a bottomed cylindrical metal can and a metal lid joined and fixed to the opening of the metal can, for example, by welding. That is, the negative electrode lead is connected to the inner surface of one of a metal can and a lid constituting the outer container. The exterior container having such a configuration has an aluminum purity of 99 wt.%, At least the inner surface to which the negative electrode lead is connected contains at least one metal component selected from Mg, Cr, Mn, Cu, Si, Fe and Ni. %, Preferably an aluminum alloy having an aluminum purity of 90% by weight or more and less than 99% by weight. Such an aluminum alloy can improve strength and corrosion resistance as compared with aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more. Among the metal components, Mg and Cr further improve the corrosion resistance of the aluminum alloy, and Mn, Cu, Si, Fe and Ni further improve the strength of the aluminum alloy.

  Specifically, the exterior container has the following form.

  (1) The exterior container is made of aluminum or an aluminum alloy, and at least an inner surface to which the negative electrode lead is connected, for example, the entire inner surface is formed with an aluminum alloy layer having the above composition containing a metal component such as Mn. In particular, when the negative electrode lead is connected to the lid of the outer container in consideration of the assembly property of the secondary battery, it is preferable to have a structure having an aluminum alloy layer having the above composition on the inner surface.

  (2) The exterior container is composed of a metal can and a metal lid joined to the opening of the metal can, and at least the lid of the metal can and the lid has a metal component such as Mn. It is made from an aluminum alloy of the above composition.

  The aluminum alloy layer (1) preferably has a thickness of 10 to 300 μm. If the thickness of the aluminum alloy layer is less than 10 μm, the connection reliability with the lead may be reduced. On the other hand, if the thickness of the aluminum alloy layer exceeds 300 μm, the smoothness and uniformity of the aluminum alloy layer may be reduced. As a method for forming the aluminum alloy layer, for example, a method of immersing an aluminum alloy in a melt, a method of spraying an aluminum alloy, or a method of plating an aluminum alloy is employed. When the aluminum alloy layer is formed only on the inner surface of the lead connection of the outer container by these methods, a method of masking the region other than the lead connection surface of the outer container is employed.

  The aluminum alloy layer is composed of Mg 0.5 to 5 wt%, Cr 0.5 wt% or less, Mn 0.3 to 2.0 wt%, Cu 5 wt% or less, Si 1 wt% or less, Fe 1 wt% or less, and Ni 1 wt% or less. It is preferable that the composition has at least one metal component selected from the group consisting of Al. In particular, in order to realize an aluminum alloy layer with better corrosion resistance, it is preferable to use an Al—Mg alloy (Mg: 0.5 to 5% by weight). In order to realize an aluminum alloy layer having higher corrosion resistance and strength, a composition containing at least one metal component selected from Mn, Cu, Si, Fe and Ni in the above amount in addition to Mg is preferable. Such an aluminum alloy layer is composed of 0.5 to 5% by weight of Mg, 0.3 to 2.0% by weight of Mn, 0.1% by weight or less of at least one metal selected from Cu, Fe, Si and Cr, and the balance Most preferably, it has a composition consisting essentially of Al. Thus, the outer container having an aluminum alloy layer having higher corrosion resistance and strength can reduce the resistance of the connection portion with the negative electrode lead in a high-temperature and high-humidity environment, and can be connected between adjacent batteries even when an assembled battery is used. The resistance can be kept low.

  However, in the case where the aluminum alloy layer is formed by plating, at least one metal selected from Cu, Fe, Si, and Cr is not more than 1.0% by weight, and the balance is substantially made of Al due to restrictions on the plating component. It preferably has a composition.

  In the outer container made of the aluminum alloy of the above (2), when both the metal can and the lid, which are the constituent members, are made of the aluminum alloy having the above composition containing a metal component such as Mn, the metal can and the lid May have the same composition or different compositions. The outer container is composed of Mg 0.5 to 5 wt%, Cr 0.5 wt% or less, Mn 0.3 to 2.0 wt%, Cu 5 wt% or less, Si 1 wt% or less, Fe 1 wt% or less and Ni 1 wt% or less. It is preferable that the composition has at least one metal component selected and the balance is substantially composed of Al. In particular, from the viewpoint of increasing strength in addition to corrosion resistance, the outer container is made of Al (Mg: 0.5 to 5 wt%) and at least one metal selected from the above-mentioned amounts of Mn, Cu, Si, Fe and Ni. It is preferable to make it from an aluminum alloy having a composition containing components. This alloy-based outer container is composed of 0.5 to 5% by weight of Mg, 0.3 to 2.0% by weight of Mn, 0.1% by weight or less of at least one metal selected from Cu, Fe, Si and Cr, and the balance Most preferably, it is made from an aluminum alloy having a composition substantially consisting of Al. Such an outer container made of an aluminum alloy with higher corrosion resistance and strength can maintain sufficient strength in a high-temperature and high-humidity environment, reduce the resistance of the connection portion with the negative electrode lead, and can be used as an assembled battery. Even when this is done, the connection resistance between adjacent batteries can be kept low.

  In addition to the corrosion resistance and strength, it is preferable to determine the composition of the aluminum alloy in consideration of workability for making the metal can into the can shape in addition to the corrosion resistance and strength.

  The negative terminal for connection to the external lead allows direct electrical connection to the outer container. In such a configuration, the negative electrode terminal can be installed at any position of the outer container. However, it is preferable in terms of secondary battery design that the negative electrode terminal is directly connected to the lid of the outer container.

  In the prismatic non-aqueous electrolyte secondary battery according to the second embodiment, the positive electrode terminal is electrically insulated and attached to, for example, a lid of an outer container.

  Next, a prismatic nonaqueous electrolyte secondary battery according to the second embodiment will be specifically described with reference to FIGS.

  The square nonaqueous electrolyte secondary battery 50 includes an outer container 31. The outer casing 31 is a bottomed rectangle made of an aluminum alloy containing at least one metal component selected from, for example, Mg, Cr, Mn, Cu, Si, Fe and Ni and having an aluminum purity of less than 99% by weight. A cylindrical metal can 32 and a rectangular plate-like lid body 33 made of the same aluminum alloy and hermetically joined to the upper end opening of the metal can 32 by laser welding, for example. The lid 33 has a hole 34 for holding a positive electrode terminal described later.

  The laminated electrode group 35 is accommodated in the metal can 32 of the outer container 31. The stacked electrode group 35 has the same form as that of FIG. That is, a plurality of negative electrodes 37 and positive electrodes 38 are alternately inserted and stacked in the folded portion of the separator 36 folded into a ninety-nine-fold shape of the stacked electrode group 35, and the end of the separator 36 is connected to the outer periphery of the rectangular columnar stack. It has a structure wound so as to cover the side surface. Such a laminated electrode group 35 is inserted and accommodated in the metal can 32 so that the surface of the separator 36 folded in a ninety-nine shape becomes the upper and lower end surfaces. The insulating plate 39 is disposed between the bottom inner surface of the metal can 32 and the lower end surface of the multilayer electrode group 35. The nonaqueous electrolyte is accommodated in the metal can 32 in which the laminated electrode group 35 is located.

  The negative electrode lead 40 made of a plurality of foils or plates has one end connected to each negative electrode 37 of the laminated electrode group 35 by, for example, resistance welding, and the other end gathered, for example, on the inner surface of the lid 33 of the outer container 31, for example Connected by resistance welding. The negative electrode lead 40 is made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more.

  A cylindrical insulating member 41 having disk-shaped ridges at both ends is fitted in the hole 34 of the lid 33. For example, the bolt-shaped positive electrode terminal 42 is inserted into the cylindrical insulating member 41 so that the head thereof is located in the metal can 32, and the screw portion protrudes from the lid 33 to the outside. For example, a nut 43 made of an aluminum alloy is screwed to a protruding thread portion of the positive electrode terminal 42 via a washer made of an aluminum alloy (not shown), and the positive electrode terminal 42 is insulated and fixed to the lid 33. One end of the positive electrode lead 44 made of a plurality of foils or plates is connected to each positive electrode 38 of the stacked electrode group 35 by, for example, resistance welding, and the other end is gathered to the lower end surface of the positive electrode terminal 42 by, for example, resistance welding. It is connected. The positive electrode lead 44 is made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more.

  Next, an assembled battery according to the second embodiment will be described.

  The assembled battery according to the second embodiment has a structure in which a plurality of the aforementioned prismatic nonaqueous electrolyte secondary batteries are connected.

  For the connection of the secondary battery, a series connection, a parallel connection, or a combination of series and parallel can be adopted.

  The assembled battery according to such an embodiment will be specifically described with reference to FIG. In this assembled battery, a plurality of, for example, five prismatic nonaqueous electrolyte secondary batteries 50 shown in FIGS. 6 and 7 are arranged adjacent to each other in one direction, and the positive terminal 42 and the negative electrode of the secondary batteries 50 are arranged. The lid 33 of the outer container 31 that also serves as a terminal has a structure in which the connection leads 51 to 54 made of Cu, for example, are connected in series. The positive electrode terminal 42 of the left end secondary battery 50 is connected to the positive electrode take-out lead 55, and the lid 33 that also serves as the negative electrode terminal of the right end secondary battery 50 is connected to the negative electrode take-out lead 56.

  As described above, the prismatic nonaqueous electrolyte secondary battery according to the second embodiment has an alternating current impedance of 1 kHz or less, that is, a discharge capacity of 2 Ah or more with an internal resistance of 1 kHz, and 0.4 V with respect to the electrode potential of lithium. A negative electrode having an active material that occludes lithium ions at the above potential is provided. Further, a negative electrode lead for electrically connecting the negative electrode and the outer container serving also as the negative electrode terminal is formed from aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more, and further connected to at least the lead of the outer container. The inner surface is formed from an aluminum alloy having an aluminum purity of less than 99% by weight containing at least one metal component selected from Mg, Cr, Mn, Cu, Si, Fe and Ni.

  By using a negative electrode having an active material that occludes lithium ions at a specific potential, a member around the negative electrode such as a current collector or lead is formed of aluminum (or an aluminum alloy). (Alternatively, it is possible to suppress the alloying reaction between aluminum alloy) and lithium into fine powder. That is, since the negative electrode lead can be made of low resistance aluminum or aluminum alloy, the outer container is also made of aluminum or aluminum alloy to enable connection with the negative electrode lead. That is, the exterior container can be configured to also serve as the negative electrode terminal. As a result, it is possible to ensure that in the exterior container, at least the lead connection portion is formed of a low-resistance aluminum alloy containing a specific metal component, similarly to the negative electrode terminal of the first embodiment described above.

  An aluminum alloy having an aluminum purity of less than 99% by weight containing at least one metal component selected from Mg, Cr, Mn, Cu, Si, Fe and Ni on the inner surface connected to at least the lead of the outer container Therefore, the strength and corrosion resistance of the connecting portion with the negative electrode lead can be improved as compared with the case where the connecting portion is made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more. In particular, at least the inner surface of the outer container connected to the lead is 0.5 to 5% by weight of Mg, 0.3 to 2.0% by weight of Mn, 0.1% by weight of at least one metal selected from Cu, Fe, Si, and Cr. %, And the balance and the corrosion resistance of the connecting portion between the outer container and the negative electrode lead can be further improved. In particular, the strength of the metal can can be improved and the thickness of the metal can can be reduced as the strength is improved by making the metal can constituting the exterior container with the aluminum alloy having the above composition.

  As a result, even when the secondary battery is subjected to vibration and impact, it is possible to suppress disconnection of the connection portion between the outer container serving also as the negative electrode terminal and the negative electrode lead, and high reliability can be ensured.

  In addition, even if the connection between the outer container and the negative electrode lead is exposed to an overdischarge operation or high temperature and high humidity environment over a long period of time, corrosion / dissolution reaction at the connection can be prevented and a low resistance connection can be maintained. . For this reason, high output can be taken out, and sufficient positive electrode and negative electrode discharge reactions are performed without causing an increase in impedance during high output discharge, thereby improving the utilization rate of the active material.

Furthermore, since the corrosion resistance of the connection portion between the outer container and the negative electrode lead can be improved, LiBF ₄ having a high corrosion resistance as an electrolyte of the non-aqueous electrolyte, but having excellent thermal and chemical stability and difficult to decompose is used. It can be used, and a high output can be taken out more stably.

  Therefore, by improving the connection reliability between the negative electrode terminal and the lead under the conditions of long-term high-temperature and high-humidity environment, rapid charging, over-discharge and high-output discharge, it has excellent cycle performance and output performance, and high reliability It is possible to provide a prismatic non-aqueous electrolyte secondary battery.

  In addition, by connecting and combining the plurality of prismatic nonaqueous electrolyte secondary batteries described above, each secondary battery is good under the conditions of long-term high-temperature and high-humidity environment, rapid charge, overdischarge, and high-output discharge. Therefore, an assembled battery excellent in cycle performance and output performance can be provided.

  Embodiments of the present invention will be described below with reference to the drawings described above. It should be noted that the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

Example 1
<Production of negative electrode>
Lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having an average primary particle diameter of 0.5 μm as an active material and a BET specific surface area of 20 m ² / g by N ₂ gas and a carbon powder having an average particle diameter of 4 μm as a conductive agent. Polyvinylidene fluoride (PVdF) was blended in a weight ratio of 90: 7: 3 as an adhesive, and dispersed in an n-methylpyrrolidone (NMP) solvent to prepare a slurry. This slurry was applied to an aluminum alloy foil (current collector) having a thickness of 15 μm, an average diameter of crystal particles of 50 μm, and a purity of 99% by weight, dried, pressed, and further cut to a size of 140 mm × 330 mm, an electrode density of 2.4 g / Sixty cm3 negative electrodes were produced. Leads made of an aluminum foil having a width of 10 mm, a length of 30 mm, a thickness of 200 μm, and a purity of 99.9 wt% were joined to one end of the negative electrode current collector by resistance welding.

<Preparation of positive electrode>
Lithium cobalt oxide (LiCoO2) as an active material, graphite powder as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are blended in a weight ratio of 87: 8: 5, and n-methylpyrrolidone (NMP) A slurry was prepared by dispersing in a solvent. This slurry was applied to an aluminum alloy foil (current collector) having a thickness of 15 μm, an average diameter of crystal particles of 10 μm, and a purity of 99% by weight, dried, pressed, and further cut to a size of 140 mm × 330 mm, an electrode density of 3.5 g / Sixty-one cm3 negative electrodes were produced. Leads made of an aluminum foil having a width of 10 mm, a length of 30 mm, a thickness of 200 μm, and a purity of 99.9 wt% were joined to one end of the positive electrode current collector by resistance welding.

<Production of lid with terminal attached>
A lid made of an aluminum alloy having a length of about 141.6 mm, a width of about 14.6 mm, a thickness of 0.3 mm, Mg 1.6 wt%, Mn 1 wt%, Fe 0.4 wt%, and the balance being substantially Al. Holes for holding the negative electrode terminal and the positive electrode terminal were opened. Cylindrical insulating members having disk-shaped ridges at both ends were fitted in the holes of the lid. A bolt-shaped negative electrode terminal having a head diameter of 10 mm was inserted into the cylindrical insulating member of the lid, and the threaded portion was projected to the lid side opposite to the head. The negative electrode terminal was fixed to the lid via one cylindrical insulating member by screwing an aluminum alloy bolt into the threaded portion via an aluminum alloy washer. The negative electrode terminal was made of an aluminum alloy consisting of Mg 1% by weight, Si 0.6% by weight, Cu 0.25% by weight, and the balance substantially consisting of Al. Subsequently, a bolt-shaped positive terminal having a head having a diameter of 10 mm was inserted into the other tubular insulating member of the lid, and the screw portion was projected to the lid side opposite to the head. The positive electrode terminal was fixed to the lid via a cylindrical insulating member by screwing an aluminum alloy bolt into the threaded portion via an aluminum alloy washer. The positive electrode terminal was made of an aluminum alloy consisting of 1 wt% Mg, 0.6 wt% Si, 0.25 wt% Cu, and the balance substantially consisting of Al.

  The bolts and washers were made of an aluminum alloy having a composition of Mg 1 wt%, Si 0.6 wt%, Cu 0.25 wt%, and the balance being substantially Al.

<Assembly of secondary battery>
60 negative electrodes joined with the negative electrode lead and 61 positive electrodes joined with the positive electrode lead were alternately inserted into the folded portion of the separator made of a polyethylene porous film having a thickness of 12 μm and folded into a 99-cell shape. Then, the electrode group 2 shown in FIG. 3 described above was produced by winding the end portions of the separator so as to cover the outer peripheral side surface of the rectangular columnar laminate. The laminated electrode group was further press-molded and then inserted into a bottomed rectangular cylindrical metal can. This metal can is made of an aluminum alloy having 1.6 wt% Mg, 1 wt% Mn, 0.4 wt% Fe, and the balance being substantially Al, and has a height of 335 mm, a length of 142 mm, a width of 15 mm, and a wall thickness of 0.1 mm. It has a dimension of 2 mm. Subsequently, an electrolyte prepared by dissolving 1.5 mol / L of lithium salt LiBF ₄ in a mixed solvent of EC and GBL (volume ratio 1: 2) as a non-aqueous electrolyte was injected into the metal can. Next, the head of the negative electrode and the positive electrode terminal is positioned on the opening side of the metal can, and the tip of the negative electrode lead connected to each negative electrode of the laminated electrode group in the metal can is continuously connected to the head of the negative electrode terminal. While gathering on the lower surface and resistance welding, the tip of the positive electrode lead connected to each positive electrode of the laminated electrode group was gathered on the lower surface of the head of the positive electrode terminal and resistance welded. Thereafter, the lid body is fitted into the opening of the metal can, and the outer peripheral edge of the lid body and the opening of the metal can are laser welded to form the outer container, whereby the height shown in FIG. 1 and FIG. A rectangular nonaqueous electrolyte secondary battery having a length of 335 mm, a length of 142 mm, a width of 15 mm, and a discharge capacity of 40 Ah was manufactured. This secondary battery had a resistance value of 1 kHz AC impedance of 0.5 mΩ.

(Examples 2 to 7)
A rectangular non-aqueous electrolyte 2 having the same structure as in Example 1 except that a negative electrode terminal made of an aluminum alloy having the composition shown in Table 1 and a negative electrode lead made of an aluminum alloy having the composition shown in Table 1 were used. A secondary battery was manufactured.

( Reference Example 1 )
The same structure as in Example 1 was used except that the negative electrode terminal in which the entire surface of the copper terminal body shown in FIG. 4A was coated with a 100 μm thick aluminum alloy plating layer having the composition shown in Table 1 below was used. A square non-aqueous electrolyte secondary battery was manufactured.

( Reference Example 2 )
The same structure as in Example 1 except that the negative electrode terminal in which the entire surface of the iron terminal main body shown in FIG. 4A is coated with a 100 μm thick aluminum alloy plating layer having the composition shown in Table 1 below is used. A square non-aqueous electrolyte secondary battery was manufactured.

( Reference Example 3 )
The same structure as that of Example 1 except that the negative electrode terminal in which the entire surface of the nickel terminal main body shown in FIG. 4A is coated with a 100 μm thick aluminum alloy plating layer having the composition shown in Table 1 below is used. A square nonaqueous electrolyte secondary battery was manufactured.

(Example 8 )
A square nonaqueous electrolyte secondary battery having the same configuration as that of Example 1 was manufactured except that anatase TiO ₂ heat-treated at 350 ° C. was used as the negative electrode active material.

(Example 9 )
The assembled battery shown in FIG. 5 was manufactured by connecting five square non-aqueous electrolyte secondary batteries similar to Example 1 in series with copper connection leads.

(Comparative Examples 1-5)
A square nonaqueous electrolyte secondary battery having the same configuration as that of Example 1 was manufactured except that a negative electrode terminal made of a metal shown in Table 1 was used. However, Comparative Examples 1, 4 and 5 used negative electrode leads made of an aluminum alloy having the composition shown in Table 1 below.

(Comparative Example 6)
An assembled battery was manufactured by connecting five square non-aqueous electrolyte secondary batteries similar to Comparative Example 1 in series with copper connection leads.

For the obtained prismatic nonaqueous electrolyte secondary batteries of Examples 1 to 9, Reference Examples 1 to 3 and Comparative Examples 1 to 5 and the assembled batteries of Example 12 and Comparative Example 6, long-term charge / discharge cycle tests were conducted. The output performance after cycling was evaluated.

  The prismatic non-aqueous electrolyte secondary battery was evaluated by performing 2.8V constant voltage charging (maximum current 400A) in 6 minutes in an environment of a temperature of 60 ° C. and a humidity of 90%, followed by a constant current of 400A up to 0V. The power density (kW / kg) obtained from the maximum current that can be taken out to 1.5 V end in 10 seconds was measured after repeating the high-temperature and high-humidity rapid charge overdischarge cycle test repeated 1000 times.

  Evaluation of the assembled battery is performed under a temperature of 60 ° C. and a humidity of 90% at a high temperature of 14 V constant voltage charging (maximum current 400 A) in 6 minutes, followed by repeated 400 A constant current discharge up to 7.5 V. The power density (kW / kg) obtained from the maximum current that can be taken out to 7.5V end in 10 seconds was measured after repeating the high-humidity rapid charge cycle test 1000 times.

  These results are also shown in Table 1 below.

As apparent from Table 1, a negative electrode lead made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more, and at least the surface connected to the negative electrode lead has Mg, Cr, Mn, Cu, The rectangular non-electrodes of Examples 1 to 8 and Reference Examples 1 to 3 having negative electrode terminals formed from an aluminum alloy having an aluminum purity of less than 99% by weight containing at least one metal component selected from Si, Fe and Ni It can be seen that the water electrolyte secondary battery is superior in output performance after a quick charge overdischarge cycle at a high temperature of 60 ° C. and a high humidity of 90% as compared with Comparative Examples 1 to 5.

Further, the assembled battery of Example 9 in which 5 prismatic nonaqueous electrolyte secondary batteries of Example 1 are connected in series is the assembled battery of Comparative Example 6 in which 5 prismatic nonaqueous electrolyte secondary batteries of Comparative Example 1 are connected in series. It can be seen that the output performance after the rapid charge overdischarge cycle at a high temperature of 60 ° C. and a high humidity of 90% is superior to the battery.

( Reference Example 4 )
Example 13 has a structure in which a square nonaqueous electrolyte secondary battery includes an outer container that also serves as a negative electrode terminal.

<Preparation of lid with positive terminal attached>
A hole for holding the terminal was opened in the lid constituting the exterior container that also served as the negative electrode terminal together with the metal can described later. This lid has a length of about 141.6 mm, a width of about 14.6 mm, a thickness of 0.3 mm, Mg 0.3 wt%, Mn 1.2 wt%, Fe 0.4 wt%, and the balance being substantially Al. Made from aluminum alloy. Cylindrical insulating members having disc-shaped ridges at both ends were fitted into the holes of the lid. A bolt-shaped positive terminal having a head diameter of 10 mm was inserted into the cylindrical insulating member of the lid, and the screw portion was projected to the lid side opposite to the head. The positive electrode terminal was fixed to the lid via a cylindrical insulating member by screwing an aluminum alloy bolt into the threaded portion via an aluminum alloy washer. The positive electrode terminal was made of an aluminum alloy consisting of 1 wt% Mg, 0.6 wt% Si, 0.25 wt% Cu, and the balance substantially consisting of Al.

  The bolts and washers were made of an aluminum alloy having a composition of Mg 1 wt%, Si 0.6 wt%, Cu 0.25 wt%, and the balance being substantially Al.

<Assembly of secondary battery>
In the same manner as in Example 1, a laminated electrode group was prepared, the laminated electrode group was inserted into a bottomed rectangular cylindrical metal can, and an electrolyte was injected into the metal can. This metal can is made of an aluminum alloy having 1.2% by weight of Mn, 0.1% by weight of Si, 0.4% by weight of Fe, and the balance being substantially Al, and has a height of 335 mm, a length of 142 mm, a width of 15 mm, and a meat. It has a thickness of 0.2 mm. Next, the head of the positive electrode terminal is positioned on the opening side of the metal can, and the tip of the negative electrode lead connected to each negative electrode of the laminated electrode group in the metal can is gathered on the lower surface of the cover body to make resistance. While welding, the tip of the positive electrode lead connected to each positive electrode of the laminated electrode group was assembled on the lower surface of the head of the positive electrode terminal and resistance welded. Then, the lid is fitted into the opening of the metal can, and the outer peripheral edge of the lid and the opening of the metal can are laser-welded to form the outer container that also serves as the negative electrode terminal. A rectangular nonaqueous electrolyte secondary battery having a height of 335 mm, a length of 142 mm, a width of 15 mm, and a discharge capacity of 40 Ah shown in FIG. This secondary battery had a resistance value of 1 kHz AC impedance of 0.5 mΩ.

(Reference Examples 5 and 6)
The same as Reference Example 4 except that an exterior container (metal can and lid) made from an aluminum alloy having the composition shown in Table 2 below and a negative electrode lead made from the aluminum alloy having the composition shown in Table 2 were used. A prismatic non-aqueous electrolyte secondary battery having the structure was manufactured.

( Reference Example 7 )
The assembled battery shown in FIG. 8 was manufactured by connecting five square non-aqueous electrolyte secondary batteries similar to those in Reference Example 4 in series with copper connection leads.

For the obtained square nonaqueous electrolyte secondary batteries of Reference Examples 4 to 6 and the assembled battery of Reference Example 7 , a long-term charge / discharge cycle test was conducted in the same manner as in Example 1 to evaluate the output performance after the cycle. did.

  These results are also shown in Table 2 below.

As apparent from Table 2, a negative electrode lead made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more, and at least an inner surface connected to the negative electrode lead has Mg, Cr, Mn, Cu, Square type non-aqueous electrolytes of Reference Examples 4 to 6 having an outer container (lid) formed of an aluminum alloy having an aluminum purity of less than 99% by weight and containing at least one metal component selected from Si, Fe and Ni It can be seen that the secondary battery is superior in output performance after a rapid charge overdischarge cycle at a high temperature of 60 ° C. and a high humidity of 90% as compared with Comparative Examples 1 to 5 in Table 1.

Further, the assembled battery of Example 16 in which five square nonaqueous electrolyte secondary batteries of Reference Example 7 were connected in series had a higher temperature of 60 ° C. and 90% higher humidity than the assembled battery of Comparative Example 6 in Table 1 above. It can be seen that the output performance after the rapid charge overdischarge cycle is excellent.

1 is a cross-sectional view showing a prismatic nonaqueous electrolyte secondary battery according to a first embodiment of the present invention. Sectional drawing which crosses the negative electrode terminal of the secondary battery of FIG. The perspective view which shows the laminated electrode group accommodated in the exterior container of FIG. Sectional drawing which shows another form of the negative electrode terminal used for the square nonaqueous electrolyte secondary battery which concerns on 1st Embodiment of this invention. The perspective view which shows the assembled battery which concerns on 1st Embodiment of this invention. Sectional drawing which shows the square type nonaqueous electrolyte secondary battery which concerns on 2nd Embodiment of this invention. FIG. 8 is a cross-sectional view across the negative electrode lead of the secondary battery of FIG. 7. The perspective view which shows the assembled battery which concerns on 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,31 ... Exterior container, 2,32 ... Metal can, 3,33 ... Lid body, 6,35 ... Laminated electrode group, 7, 36 ... Separator, 8, 37 ... Negative electrode, 9, 38 ... Positive electrode, 12 ... Negative electrode Terminal, 12a ... Terminal body, 12b ... Aluminum alloy layer, 15 ... Positive electrode terminal, 17, 40 ... Negative electrode lead, 18, 44 ... Positive electrode lead, 20, 50 ... Square nonaqueous electrolyte secondary battery, 21-24, 51 54 connection lead.

Claims (9)

A non-aqueous electrolyte secondary battery having an internal resistance of 1 kHz AC impedance value of 10 mΩ or less,
Metal outer container;
A non-aqueous electrolyte housed in the container;
A positive electrode housed in the container, a negative electrode having an active material that occludes lithium ions at a potential of 0.4 V or more with respect to the electrode potential of lithium, and a separator interposed between the negative electrode and the positive electrode;
A negative electrode lead having one end connected to the negative electrode and made of aluminum having a purity of 99% by weight or more or an aluminum alloy having a purity of 99% by weight or more; and being attached to the outer container to be electrically connected to the other end of the negative electrode lead A negative electrode terminal formed of an aluminum alloy containing at least one metal component selected from Mg , Cr, Mn, Cu, Si, Fe and Ni and having an aluminum purity of 90 wt% or more and less than 99 wt%;
A non-aqueous electrolyte secondary battery comprising: The negative electrode terminal is composed of Mg 0.5 to 5 wt%, Cr 0.5 wt% or less, Mn 0.3 to 2.0 wt%, Cu 5 wt% or less, Si 1 wt% or less, Fe 1 wt% or less and Ni 1 wt% or less. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is formed of an aluminum alloy containing at least one metal component selected and having an aluminum purity of 90 wt% or more and less than 99 wt%. The negative electrode terminal is composed of 0.5 to 5% by weight of Mg, 0.3 to 2.0% by weight of Mn, 0.1% by weight or less of at least one metal selected from Cu, Fe, Si, and Cr, and the balance substantially. The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is formed of an aluminum alloy made of Al. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is titanium-containing oxide particles having an average particle diameter of 1 μm or less. The non-aqueous electrolyte includes at least one organic solvent selected from the group consisting of propylene carbonate, ethylene carbonate, and γ-butyrolactone, and LiPF. ₆ And LiBF _Four 5. The nonaqueous electrolyte secondary battery according to claim 1, comprising at least one electrolyte selected from the group consisting of: 6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode has a current collector made of an aluminum foil or aluminum alloy foil having a purity of 99% by weight or more. The outer container is composed of a metal can and a metal lid joined to the opening of the metal can, and at least the metal can of the metal can and the lid is at least selected from Mg, Mn and Fe. 7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is made of an aluminum alloy containing one metal component. The positive electrode active material includes lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, spinel type lithium manganese nickel composite oxide, lithium manganese cobalt composite oxide, lithium phosphorus The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the nonaqueous electrolyte secondary battery is selected from iron oxide or lithium nickel cobalt manganese composite oxide having a layered structure. 9. A battery pack comprising a plurality of nonaqueous electrolyte secondary batteries according to claim 1 connected.

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