WO2015033666A1

WO2015033666A1 - Secondary battery charging method and charging device

Info

Publication number: WO2015033666A1
Application number: PCT/JP2014/068335
Authority: WO
Inventors: 荻原　航
Original assignee: 日産自動車株式会社
Priority date: 2013-09-06
Filing date: 2014-07-09
Publication date: 2015-03-12

Abstract

A method for charging a secondary battery using, as a positive electrode material, a positive electrode active material consisting of a solid solution material has: a first charging step of charging the secondary battery to a first predetermined voltage (V₀); and a second charging step of, after the first charging step, charging the secondary battery by setting a second predetermined voltage (V₁) lower than the first predetermined voltage as an upper limit voltage. In the first charging step, charging is performed at a constant current. In the second charging step, charging is performed at a constant voltage.

Description

Secondary battery charging method and charging device

The present invention relates to a secondary battery charging method and a charging device.

A secondary battery such as a lithium secondary battery, for the purpose of high _{^{_{capacity, Li y [M 1 (1}}} -b) Mn b] O 2 or _{^{_{Li y [M 1 (1-}}} b) Mn b] O 1. _A positive electrode active material made of a solid solution material such as _{5 + c} (M ¹ is a metal element) has been studied (Patent Document 1).

JP-T-2004-538610

However, since the battery using the above conventional solid solution positive electrode is used at a high voltage, there is a problem that the transition metal is eluted from the positive electrode and the cycle characteristics are inferior.

The problem to be solved by the present invention is to provide a charging method and a charging device for a secondary battery capable of suppressing deterioration of cycle characteristics.

According to the present invention, a secondary battery using a positive electrode active material made of a solid solution material is charged up to a first predetermined voltage, and then charged with a second predetermined voltage lower than the first predetermined voltage as an upper limit voltage. Solve the above problems.

According to the present invention, after charging to the first predetermined voltage, charging is performed using the second predetermined voltage lower than this as the upper limit voltage, thereby shortening the time during which the charge amount is kept high while maintaining the high voltage. Thereby, since elution of a transition metal can be suppressed, deterioration of cycle characteristics can be suppressed.

It is a top view which shows an example of the secondary battery which is the charging object of the charging method and charging device of this invention. It is sectional drawing which follows the II-II line of FIG. It is a graph explaining the definition of a spinel structure change rate. It is a block diagram which shows the charging device which concerns on one embodiment of this invention. It is a flowchart which shows the charging method which concerns on one embodiment of this invention. It is FIG. (1) explaining the subject of the secondary battery using a solid solution positive electrode. It is FIG. (2) explaining the subject of the secondary battery using a solid solution positive electrode. It is FIG. (3) explaining the subject of the secondary battery using a solid solution positive electrode. It is FIG. (4) explaining the subject of the secondary battery using a solid solution positive electrode. It is a graph which shows the relationship between the battery capacity at the time of charging with the charging method of FIG. 5, and an applied voltage / current. It is a graph which shows the relationship between the charging time at the time of charging with the charging method of FIG. 5, and an applied voltage / current. It is a flowchart which shows the charging method which concerns on other embodiment of this invention. It is a graph which shows an example of the relationship between the battery capacity at the time of charging with the charging method of FIG. 8, and an applied voltage / current. It is a graph which shows an example of the relationship between the charging time at the time of charging with the charging method of FIG. 8, and an applied voltage / current. It is a graph which shows the other example of the relationship between the battery capacity at the time of charging with the charging method of FIG. 8, and an applied voltage / current. It is a graph which shows the other example of the relationship between the charging time at the time of charging with the charging method of FIG. 8, and an applied voltage / current. It is a graph which shows the result of having verified the relationship between the number of charging / discharging cycles and a capacity | capacitance retention rate about the Example and comparative example of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, an example of a secondary battery to be charged will be described, and then a charging method and a charging device according to an embodiment of the present invention will be described.

<Configuration example of secondary battery>
FIG. 1 is a plan view showing an example of a secondary battery to be charged by the charging method and the charging device of the present invention, and FIG. 2 is a sectional view taken along the line II-II in FIG. Examples of the secondary battery 10 to be charged include a lithium secondary battery such as a lithium ion secondary battery. However, the secondary battery shown below is an example of a charging target of the charging method and the charging device of the present invention, and a secondary battery having a structure other than this is also included in the charging target of the present invention.

The secondary battery 10 shown in FIGS. 1 and 2 is connected to an electrode laminate 101 having three positive plates 102, seven separators 103, and three negative plates 104, and the electrode laminate 101, respectively. The positive electrode tab 105 and the negative electrode tab 106, the electrode laminate 101, the positive electrode tab 105, the upper exterior member 107 and the lower exterior member 108 that enclose and seal the negative electrode tab 106, and an electrolyte solution that is not particularly illustrated. Yes. Note that the number of constituents of the positive electrode plate 102, the separator 103, and the negative electrode plate 104 is not particularly limited, and the electrode laminate 101 is configured by one positive electrode plate 102, three separators 103, and one negative electrode plate 104. Alternatively, the number of the positive electrode plate 102, the separator 103, and the negative electrode plate 104 may be appropriately selected as necessary.

The positive electrode plate 102 constituting the electrode laminate 101 includes a positive electrode side current collector 102a extending to the positive electrode tab 105 and a positive electrode active material layer formed on both main surfaces of a part of the positive electrode side current collector 102a. And have. The positive electrode side current collector 102a constituting the positive electrode plate 102 can be formed of an electrochemically stable metal foil such as an aluminum foil, an aluminum alloy foil, a copper titanium foil, or a stainless steel foil having a thickness of about 20 μm.

The positive electrode active material layer constituting the positive electrode plate 102 is a mixture of a positive electrode active material, a conductive agent such as carbon black, and a binder such as an aqueous dispersion of polyvinylidene fluoride or polytetrafluoroethylene, It is formed by applying to a part of the main surface of the positive electrode side current collector 102a, drying and pressing. In particular, in the secondary battery 10 according to this example, the positive electrode active material layer is formed of a positive electrode active material made of a solid solution material. Although it does not specifically limit as a solid solution material used for such a positive electrode active material, For example, the solid solution lithium containing transition metal oxide represented by following General formula (1) is mentioned.
Li _1.5 [Ni _a Co _b Mn _c [Li] _d ] O ₃ (1)
(In the formula (1), Li is lithium, Ni is nickel, Co is cobalt, Mn is manganese, O is oxygen, and a, b, c, and d are 0 <a <1.4, 0 ≦ b <. 1.4, 0 <c <1.4, 0.1 <d ≦ 0.4, a + b + c + d = 1.5, 1.1 ≦ a + b + c <1.4.

The solid solution lithium-containing transition metal oxide of this example has a layered structure part and a part (a layered structure Li ₂ MnO ₃ ) that changes to a spinel structure by charging or charging / discharging in a predetermined potential range. In the solid solution lithium-containing transition metal oxide, the layered structure Li ₂ MnO ₃ was changed to the spinel structure LiMn ₂ O ₄ , and the portions that changed to the spinel structure were all changed to the spinel structure LiMn ₂ O ₄ . When the case ratio is 1, the spinel structure change ratio of the solid solution lithium-containing transition metal oxide is 0.25 or more and less than 1.0.

"Spinel structure change ratio" means that Li ₂ MnO ₃ having a layered structure in the solid solution lithium-containing transition metal oxide is changed to LiMn ₂ O ₄ having a spinel structure by charging or charging / discharging in a predetermined potential range. The ratio of the spinel structure when the layered structure Li ₂ MnO ₃ in the solid solution lithium-containing transition metal oxide is all changed to the spinel structure LiMn ₂ O ₄ is defined as 1. . Specifically, it is defined by the following formula.

Regarding the definition of “spinel structure change ratio”, for a battery assembled using a positive electrode in which the solid solution lithium-containing transition metal oxide is used as a positive electrode active material, a charge charged from initial state A before charging to 4.5 V A case as shown in FIG. 3 will be described as an example, in which the state is set to state B, further passed through a plateau region, overcharged state C charged to 4.8V, and discharged state D further discharged to 2.0V. To do. The “actual capacity of the plateau region” in the above formula is the plateau region in FIG. 3 (specifically, the region from 4.5 V to 4.8 V (the actual capacity V _BC of the region BC from the charged state B to the overcharged state C) The actual capacity of the plateau region), which is the region resulting from the change in the crystal structure.

Further, in practice, in the solid solution lithium-containing transition metal oxide of the composition formula (1), the practical amount V _{AB in} the region AB from the initial state A to the charged state B charged to 4.5 V is a layered structure part. It corresponds to the composition (y) and the theoretical capacity (V _L ) of LiMO ₂ , and the actual capacity V _BC of the region BC in the overcharged state C charged from 4.5 to 4.8 V is charged to spinel. Since it corresponds to the composition ratio (x) and the theoretical capacity (V _S ) of Li ₂ MnO ₃ which is a structural site, the actual capacity (V _T ) measured from the initial state A to a predetermined plateau region is (V _T = V _AB + V _BC ) Since V _AB = y (V _L ) and V _BC = x (V _S ) K, it can also be calculated using the following formula (M is nickel (Ni), cobalt) From (Co) and manganese (Mn) That represents at least one selected from the group.).

Further, the “composition ratio of Li ₂ MnO _{3 in} the solid solution” can be calculated from the composition formula of the solid solution lithium-containing transition metal oxide. In addition, the presence or absence of the layered structure site and the spinel structure site in the solid solution lithium-containing transition metal oxide can be determined by the presence of a peculiar peak in the layered structure and the spinel structure by X-ray diffraction analysis (XRD), and the ratio is It can be determined from the measurement and calculation of the capacity as described above.

In addition, the spinel structure change ratio does not become 1.0, and when it is less than 0.25, a discharge capacity and capacity retention comparable to those of a conventional solid solution lithium-containing transition metal oxide can be realized even if high. Only a solid solution lithium-containing transition metal oxide is obtained.

In the solid solution lithium-containing transition metal oxide of this example, in the composition formula (1), a, b, c and d are 0 <a <1.4, 0 ≦ b <1.4, 0 <c <1.4. , 0.1 <d ≦ 0.4, a + b + c + d = 1.5, 1.1 ≦ a + b + c <1.4, the structure in the solid solution is not stabilized.

Further, in the solid solution lithium-containing transition metal oxide of this example, in the composition formula (1), a, b, c, and d are 0 <a <1.35, 0 ≦ b <1.35, 0 <c <. 1.35, 0.15 <d ≦ 0.35, a + b + c + d = 1.5, 1.15 ≦ a + b + c <1.35 are satisfied, and charging or charging / discharging in a predetermined potential range is performed. The spinel structure change ratio of the solid solution lithium-containing transition metal oxide is more preferably 0.4 or more and less than 0.9.
Further, in the solid solution lithium-containing transition metal oxide of this example, in the composition formula (1), a, b, c, and d are 0 <a <1.3, 0 ≦ b <1.3, 0 <c <. 1.3, 0.15 <d ≦ 0.35, a + b + c + d = 1.5, 1.2 ≦ a + b + c <1.3, satisfying the relationship, charging or charging / discharging in a predetermined potential range Most preferably, the spinel structure change ratio of the solid solution lithium-containing transition metal oxide is 0.6 or more and 0.8 or less.

Such a solid solution lithium-containing transition metal oxide can achieve a high discharge capacity and capacity retention when used as a positive electrode active material of a lithium ion secondary battery. It is suitably used for secondary batteries. As a result, it can be suitably used as a lithium-ion secondary battery for vehicle drive power or auxiliary power. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for home use and portable devices.

The production method of the solid solution lithium-containing transition metal oxide of this example will be described. First, as an example of the production method of the solid solution lithium-containing transition metal oxide precursor, lithium compounds such as sulfates and nitrates, nickel compounds, cobalt compounds And a raw material containing a manganese compound are mixed to obtain a mixture, and then the resulting mixture is baked in an inert gas atmosphere at 800 ° C. to 1000 ° C. for 6 hours to 24 hours. Can be mentioned.

As another example of the method for producing a solid solution lithium-containing transition metal oxide precursor, a mixture is obtained by mixing raw materials including lithium compounds such as sulfates and nitrates, nickel compounds, cobalt compounds and manganese compounds, The obtained mixture is fired at 800 ° C. or higher and 1000 ° C. or lower for 6 hours or longer and 24 hours or shorter to obtain a fired product, and then the obtained fired product is heated at 600 ° C. or higher and 800 ° C. or lower in an inert gas atmosphere. The manufacturing method of the solid solution lithium containing transition metal oxide to heat-process can be mentioned.

The binder (binder) to be added to the positive electrode active material layer as necessary is not particularly limited. For example, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile (PAN), polyimide (PI), polyamide (PA), cellulose, carboxymethylcellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride (PVC), styrene-butadiene rubber (SBR) , Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Heat Plastic polymer, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene- Fluororesin such as tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene Fluoro rubber (VDF-HFP fluoro rubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluoro rubber (VDF-HFP-TFE fluoro rubber), vinylidene full Ride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether -Vinylidene fluoride fluorine rubber such as tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine rubber (VDF-CTFE fluorine rubber), epoxy resin, etc. Can be mentioned. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable at both the positive electrode potential and the negative electrode potential, and can be used for the positive electrode (and negative electrode) active material layer.
However, the material is not limited to these, and a known material conventionally used as a binder for a lithium ion secondary battery can be used. These binders may be used alone or in combination of two or more.

The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it can bind the positive electrode active material, but preferably 0.5 to 15 mass with respect to the positive electrode active material layer. %, More preferably 1 to 10% by mass.

The conductive auxiliary agent added to the positive electrode active material layer as necessary is blended to improve the conductivity of the positive electrode active material layer. As a conductive support agent, carbon materials, such as carbon black, such as acetylene black, a graphite, and a vapor growth carbon fiber, can be mentioned, for example. When the positive electrode active material layer contains a conductive additive, an electronic network inside the positive electrode active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery. However, it is not limited to these, The conventionally well-known material used as a conductive support agent for lithium ion secondary batteries can be used. These conductive assistants may be used alone or in combination of two or more.

In addition, the conductive binder having the functions of the conductive assistant and the binder may be used in place of the conductive assistant and the binder, or one or both of the conductive assistant and the binder. You may use together. As the conductive binder, for example, commercially available TAB-2 (manufactured by Hosen Co., Ltd.) can be used.

Furthermore, the density of the positive electrode active material layer is preferably 2.5 g / cm ³ or more and 3.0 g / cm ³ or less. When the density of the positive electrode active material layer is less than 2.5 g / cm ³ , it is difficult to improve the discharge capacity because the weight (filling amount) per unit volume cannot be improved. Further, when the density of the positive electrode active material layer exceeds 3.0 g / cm ³ , the amount of voids in the positive electrode active material layer is remarkably reduced, and the permeability of the non-aqueous electrolyte and the lithium ion diffusibility may be reduced. is there.

1 and 2, each positive electrode side current collector 102 a constituting the three positive electrode plates 102 having such a solid solution positive electrode active material layer is joined to the positive electrode tab 105. As the positive electrode tab 105, for example, an aluminum foil having a thickness of about 0.2 mm, an aluminum alloy foil, a copper foil, or a nickel foil can be used.

The negative electrode plate 104 constituting the electrode laminate 101 includes a negative electrode current collector 104a extending to the negative electrode tab 106, and a negative electrode active material layer formed on both main surfaces of a part of the negative electrode current collector 104a. And have. The negative electrode side current collector 104a of the negative electrode plate 104 is an electrochemically stable metal foil such as a nickel foil, a copper foil, a stainless steel foil, or an iron foil having a thickness of about 10 μm.

The negative electrode active material layer constituting the negative electrode plate 104 includes, as the negative electrode active material, lithium, a lithium alloy, or a negative electrode material capable of occluding and releasing lithium, and if necessary, a binder or a conductive material. An auxiliary agent may be included. In addition, what was demonstrated above can be used for a binder and a conductive support agent. The negative electrode active material layer is prepared, for example, by adding a binder such as polyvinylidene fluoride and a solvent such as N-2-methylpyrrolidone to a negative electrode active material such as non-graphitizable carbon, graphitizable carbon, or graphite. Then, it is formed by applying to both main surfaces of a part of the negative electrode side current collector 104a, drying and pressing. In the secondary battery 10 of this example, the three negative electrode plates 104 are configured such that each negative electrode side current collector 104 a constituting the negative electrode plate 104 is joined to a single negative electrode tab 106. Yes. That is, in the secondary battery 10 of this embodiment, each negative electrode plate 104 is configured to be joined to a single common negative electrode tab 106.

Examples of the negative electrode material capable of inserting and extracting lithium include graphite (natural graphite, artificial graphite, etc.), which is highly crystalline carbon, low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen) Carbon materials such as black, acetylene black, channel black, lamp black, oil furnace black, thermal black), fullerenes, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon fibrils (containing 10% by mass or less of silicon nanoparticles) Silicon (Si), germanium (Ge), tin (Sn), lead (Pb), aluminum (Al), indium (In), zinc (Zn), hydrogen (H), calcium (Ca), strontium( r), barium (Ba), ruthenium (Ru), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), cadmium (Cd), mercury ( Hg), gallium (Ga), thallium (Tl), carbon (C), nitrogen (N), antimony (Sb), bismuth (Bi), oxygen (O), sulfur (S), selenium (Se), tellurium ( Te), elemental elements that form an alloy with lithium, such as chlorine (Cl), and oxides containing these elements (silicon monoxide (SiO), SiO _x (0 <x <2), tin dioxide (SnO ₂ )) , SnO _x (0 <x <2), SnSiO ₃ etc.) and carbide (silicon carbide (SiC) etc.), etc .; metal materials such as lithium metal; lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O _12), etc. Lithium - can be exemplified transition metal composite oxide. However, it is not limited to these, The conventionally well-known material used as a negative electrode active material for lithium ion secondary batteries can be used. These negative electrode active materials may be used alone or in combination of two or more.

Further, in this example, the carbon material is made of a graphite material that is coated with an amorphous carbon layer and is not scaly, and the BET specific surface area of the carbon material is 0.8 m ² / g or more and 1.5 m ^2. It is preferable that the tap density is 0.9 g / cm ³ or more and 1.2 g / cm ³ or less. A carbon material made of a graphite material that is coated with an amorphous carbon layer and is not scale-like is preferable because of its high lithium ion diffusibility into the graphite layered structure. Moreover, it is preferable that the BET specific surface area of such a carbon material is 0.8 m ² / g or more and 1.5 m ² / g or less because the capacity retention can be further improved. Furthermore, when the tap density of such a carbon material is 0.9 g / cm ³ or more and 1.2 g / cm ³ or less, the weight (filling amount) per unit volume can be improved, and the discharge capacity is improved. be able to.

Furthermore, in this example, it is preferable that the negative electrode active material layer containing at least the carbon material and the binder has a BET specific surface area of 2.0 m ² / g or more and 3.0 m ² / g or less. When the BET specific surface area of the negative electrode active material layer is 2.0 m ² / g or more and 3.0 m ² / g or less, the permeability of the non-aqueous electrolyte can be improved, and the capacity retention is further improved. Gas generation due to decomposition of the non-aqueous electrolyte can be suppressed. In this example, the BET specific surface area of the negative electrode active material layer containing at least a carbon material and a binder after pressure molding is preferably 2.01 m ² / g or more and 3.5 m ² / g or less. is there. By setting the BET specific surface area of the negative electrode active material layer after pressure molding to 2.01 m ² / g or more and 3.5 m ² / g or less, the permeability of the non-aqueous electrolyte can be improved and the capacity can be maintained. The rate can be improved and gas generation due to decomposition of the non-aqueous electrolyte can be suppressed. Furthermore, in this example, the increase in the BET specific surface area before and after pressure press molding of the negative electrode active material layer containing at least the carbon material and the binder is 0.01 m ² / g or more and 0.5 m ² / g or less. Is preferred. Since the BET specific surface area after pressure forming of the negative electrode active material layer can be 2.01 m ² / g or more and 3.5 m ² / g or less, the permeability of the non-aqueous electrolyte can be improved. Capacity retention can be improved and gas generation due to decomposition of the non-aqueous electrolyte can be suppressed.

Also, the thickness of each active material layer (active material layer on one side of the current collector) is not particularly limited, and conventionally known knowledge about the battery can be referred to as appropriate. As an example, the thickness of each active material layer is usually about 1 to 500 μm, preferably 2 to 100 μm, taking into consideration the intended use of the battery (emphasis on output, energy, etc.) and ion conductivity. Furthermore, when the optimum particle size is different for expressing the unique effect of each active material, the optimum particle size for expressing each unique effect may be mixed and used. There is no need to make the particle size of the material uniform. For example, when an oxide in the form of particles is used as the positive electrode active material, the average particle size of the oxide may be approximately the same as the average particle size of the positive electrode active material included in the existing positive electrode active material layer, and is not particularly limited. . From the viewpoint of higher output, it is preferably in the range of 1 to 20 μm. In the present specification, the “particle diameter” refers to the outline of active material particles (observation surface) observed using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It means the maximum distance among any two points. The value of “average particle size” is the average value of the particle size of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted. The particle diameters and average particle diameters of other components can be defined in the same manner. However, it is not limited to such a range at all, and it goes without saying that it may be outside this range as long as the effects of the present embodiment can be expressed effectively.

The separator 103 of the electrode laminate 101 prevents the short circuit between the positive electrode plate 102 and the negative electrode plate 104 described above, and may have a function of holding an electrolyte. The separator 103 is a microporous film made of, for example, a polyolefin such as polyethylene (PE) or polypropylene (PP) having a thickness of about 25 μm. When an overcurrent flows, the pores of the layer are generated by the heat generation. It is also blocked and has a function of cutting off current. As shown in FIG. 2, the positive electrode plates 102 and the negative electrode plates 104 are alternately stacked via the separators 103, and the separators 103 are stacked on the uppermost layer and the lowermost layer. Is formed.

The electrolyte contained in the secondary battery 10 includes an electrolyte solution held in the separator 103, a polymer gel electrolyte, a solid polymer electrolyte, and a layer structure, and further includes a polymer gel electrolyte and a solid polymer. The thing etc. which formed the laminated structure using electrolyte can be mentioned. Here, the electrolyte solution is preferably one that is usually used in a lithium ion secondary battery, and specifically has a form in which a supporting salt (lithium salt) is dissolved in an organic solvent. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), six Inorganic acid anion salts such as lithium fluorotantalate (LiTaF ₆ ), lithium tetrachloroaluminate (LiAlCl ₄ ), lithium decachlorodecaborate (Li ₂ B ₁₀ Cl ₁₀ ), lithium trifluoromethanesulfonate (LiCF ₃₎ Organic acids such as SO ₃ ), lithium bis (trifluoromethanesulfonyl) imide (Li (CF ₃ SO ₂ ) ₂ N), lithium bis (pentafluoroethanesulfonyl) imide (Li (C ₂ F ₅ SO ₂ ) ₂ N) List at least one lithium salt selected from anionic salts Can. Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC); chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC). Ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane; lactones such as γ-butyrolactone; nitriles such as acetonitrile; methyl propionate Esters such as amides; Amides such as dimethylformamide; One using at least one selected from methyl acetate and methyl formate, or a mixture using an organic solvent such as an aprotic solvent can be used. .

Examples of the polymer gel electrolyte include those containing a polymer constituting the polymer gel electrolyte and an electrolytic solution in a conventionally known ratio. For example, from the viewpoint of ionic conductivity, it is desirable that the content be about several mass% to 98 mass%. The polymer gel electrolyte is a solid polymer electrolyte having ion conductivity containing the above-described electrolytic solution usually used in a lithium ion secondary battery. However, the present invention is not limited to this, and includes a structure in which a similar electrolyte solution is held in a polymer skeleton having no lithium ion conductivity. Examples of the polymer having no lithium ion conductivity used for the polymer gel electrolyte include polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). Can be used. However, it is not necessarily limited to these. In addition, since polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and the like are in a class that has almost no ionic conductivity, it can be a polymer having the ionic conductivity. Here, the polymer used for the polymer gel electrolyte is exemplified as a polymer having no lithium ion conductivity.

Examples of the solid polymer electrolyte include a structure in which the lithium salt is dissolved in polyethylene oxide (PEO), polypropylene oxide (PPO), and the like, and does not contain an organic solvent. Therefore, when the electrolyte layer is composed of a solid polymer electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

The thickness of the electrolyte layer of the secondary battery 10 is preferably thin from the viewpoint of reducing internal resistance. The thickness of the electrolyte layer is usually 1 to 100 μm, preferably 5 to 50 μm. A polymer gel electrolyte or a solid polymer electrolyte matrix polymer can exhibit excellent mechanical strength by forming a cross-linked structure. In order to form a crosslinked structure, a suitable polymerization initiator is used to polymerize a polymer for forming a polymer electrolyte (for example, polyethylene oxide (PEO) or polypropylene oxide (PPO)) by thermal polymerization, ultraviolet polymerization, A polymerization treatment such as radiation polymerization or electron beam polymerization may be performed.

The electrode laminate 101 configured as described above is housed and sealed in the upper exterior member 107 and the lower exterior member 108. The upper exterior member 107 and the lower exterior member 108 for sealing the electrode laminate 101 are laminated with a resin film such as polyethylene or polypropylene or a metal foil such as aluminum laminated with a resin such as polyethylene or polypropylene. It is made of a material having flexibility such as a resin-metal thin film laminate material, and the upper exterior member 107 and the lower exterior member 108 are heat-sealed to lead the positive electrode tab 105 and the negative electrode tab 106 to the outside. In this state, the electrode laminate 101 is sealed.

The positive electrode tab 105 and the negative electrode tab 106 are provided with a seal film 109 in order to ensure adhesion between the upper exterior member 107 and the lower exterior member 108 at a portion in contact with the upper exterior member 107 and the lower exterior member 108. Is provided. Although it does not specifically limit as the sealing film 109, For example, it can comprise from the synthetic resin material excellent in electrolyte solution resistance and heat-fusion properties, such as polyethylene, modified polyethylene, a polypropylene, a modified polypropylene, or an ionomer.

<Charging method and charging device>
The secondary battery using the solid solution positive electrode such as Li ₂ MnO ₃ described above has a technical problem that although it has a large discharge capacity, it has poor cycle characteristics and is likely to deteriorate when repeated charging and discharging at a high potential. . The cause of such deterioration of cycle characteristics is considered as follows. That is, in a secondary battery using a solid solution positive electrode, when a constant voltage charge is performed for a long time at a high voltage as shown in FIG. 6A, transition metal ions such as Mn ions and Ni ions are eluted from the positive electrode. Since the deposition potential of these Mn ions and Ni ions is higher than that of Li ions, Mn ions and Ni ions eluted from the positive electrode are electrodeposited on the negative electrode as shown in FIG. 6B. Then, as shown in FIG. 6C, the electrolytic solution is decomposed by Mn or Ni electrodeposited on the negative electrode, and the decomposition product is deposited on the negative electrode. As a result, the deposit causes the movement of Li ions as shown in FIG. 6D. This causes inhibition of the battery (which increases internal resistance).

For this reason, in the charging method and the charging device of the present example, when charging the secondary battery, the secondary battery is charged to the first predetermined voltage (first charging step), and then the second predetermined voltage lower than the first predetermined voltage. The voltage is charged as the upper limit voltage (second charging step). FIG. 4 is a block diagram showing a charging apparatus according to an embodiment of the present invention, and FIG. 5 is a flowchart showing a charging method according to an embodiment of the present invention.

As shown in FIG. 4, the charging device of this example includes the secondary battery 10, the battery control device 20, the power supply 30, the current sensor 40, and the voltage sensor 50 described above. The power source 30 of this example is composed of a commercial power source and / or a motor generator that supplies charging power to the secondary battery 10. For example, when the secondary battery of this example is applied to an electric vehicle or a hybrid vehicle, the power source 30 can be configured from a power plug for connecting to a commercial power source, an inverter, and a motor generator. When the power supply 30 is composed of an inverter and a motor generator, regenerative AC power generated by the rotation of the motor generator is converted into DC power via the inverter and used for charging the secondary battery 10. The DC power supplied from the secondary battery 10 is converted into AC power by the inverter and supplied to the motor generator. Therefore, when the power supply 30 is composed of an inverter and a motor generator, the power supply 30 of this example also functions as a load of the secondary battery 10. However, in the charging method and the charging device of the present invention, the power source 30 may be any one that supplies at least the charging power to the secondary battery 10.

The battery control device 20 of this example is a control device for controlling charging / discharging of the secondary battery 10, and is detected by the charge / discharge current flowing in the secondary battery 10 detected by the current sensor 40 or the voltage sensor 50. Based on the terminal voltage of the secondary battery 10, the charging and discharging of the secondary battery 10 are controlled and the SOC (State of Charge) of the secondary battery 10 is calculated. In this example, in order to execute the charging method described below, the current flowing through the secondary battery 10 is detected by the current sensor 40, the terminal voltage of the secondary battery 10 is detected by the voltage sensor 50, the power supply 30 and the secondary battery The battery 10 is controlled.

Next, a charging method according to an embodiment of the present invention will be described with reference to FIG. First, in step S <b> 1, when the battery control device 20 receives a charge command for the secondary battery 10, the battery control device 20 starts detecting the value of the current flowing through the secondary battery 10 by the current sensor 40, while Detection of the voltage value applied to both terminals is started. Next, control of the power supply 30 is started so that the constant current I ₀ flows through the secondary battery 10 in step S2. The first charging step by the constant current charging, the current value detected by the current sensor 40 is performed by controlling the power supply 30 so as to maintain a predetermined value I _0. For example, when the power supply 30 is composed of an inverter and a motor generator, constant current charging is executed by controlling the switching drive of the inverter by the battery control device 20.

In step S3, it is determined whether or not reached a first predetermined voltage value greater than or equal _to V ₀ that is the voltage between the two terminals (the applied voltage) V of the secondary battery 10 detected by the voltage sensor 50 is set in advance, it has been reached If not, the process returns to step S1, and the current value and voltage value are read again and constant current charging is continued. As a result, as shown in the capacity C ₀ to C ₁ in FIG. 7A and the time T ₀ to T ₁ in FIG. 7B, the secondary battery 10 is charged to the first predetermined voltage value V ₀ to ensure a sufficient charge capacity. can do. In FIGS. 7A and 7B, the battery capacity at time T ₁ corresponds to C ₁ . Further, in this example, the first charging step is set to constant current charging, so that the charging time to the first predetermined voltage value V ₀ is shortened. However, the first charging step in the charging method of the present invention uses a constant voltage. The charging method may be a constant voltage charging to be applied or a combination of constant current charging and constant voltage charging. The first predetermined voltage V ₀ is not particularly limited, but in the lithium ion secondary battery represented by Li _1.5 [Ni _a Co _b Mn _c [Li] _d ] O ₃ described above, one secondary battery is included. On the other hand, it is preferably 4.3 to 4.8V.

In step S3, When the voltage between the two terminals V of the secondary battery 10 detected reaches equal to or more than the first predetermined voltage value V ₀ by a voltage sensor 50, the process proceeds to step S4, the power source 30 so as to interrupt the constant current charging The power supply to the secondary battery 10 is interrupted. In this battery voltage relaxation step, the power supply from the power source 30 and the discharge of the secondary battery 10 are temporarily stopped so that no current flows through the secondary battery 10, and the time T ₁ to T ₂ in FIG. leaving the only rechargeable battery 10 a predetermined time t ₀ in step S5 as. The battery voltage relaxation process of this example is performed in order to suppress the concentration distribution of the electrolytic solution inside the battery and the uneven charging state of lithium ions in the electrode in the charging process performed in the first charging process of step S2. Thereby, elution of transition metals, such as manganese and nickel, can be suppressed by suppressing a potential difference between the positive electrode and the negative electrode and normalizing the battery voltage. This battery voltage relaxation step is particularly effective when relatively rapid charging (constant current charging) is performed in the first charging step, but may be omitted as necessary, such as when quick charging is not required. May be.

If a battery voltage relaxation process is complete | finished, it will progress to step S6 and will implement a 2nd charge process. In the second charging step of this example, constant voltage charging is executed with the second predetermined voltage value V ₁ lower than the first predetermined voltage value V ₀ being the target voltage in the first charging step as the upper limit voltage. Here, it is desirable that the second predetermined voltage value V ₁ is lower by 50 mV or more than the first predetermined voltage value V ₀ . If the second predetermined voltage value V ₁ is less than 50 mV compared to the first predetermined voltage value V ₀ , elution of transition metal ions such as manganese ions and nickel ions shown in FIG. 6A cannot be effectively suppressed. is there. In this example, the second charging step is performed by constant voltage charging. However, if the upper limit voltage is lower than the first predetermined voltage value V ₀ , constant current charging or a combination of constant voltage charging and constant current charging is performed. It may be a charging process.

The second charging step is continuously performed until the open circuit voltage V of the secondary battery 10 (the voltage between both terminals of the secondary battery 10 in the no-load state) reaches, for example, a fully-charged voltage V _SOC100 that is known in advance. When the open circuit voltage V reaches the full charge voltage V _SOC100 in step S7, the charging process of this example is terminated. As a result, as shown by the capacities C ₁ to C ₂ in FIG. 7A and the times T ₂ to T ₃ in FIG. 7B, the secondary battery 10 is charged to the fully charged battery capacity C ₂ . At this time, in the second charging step of the present example, constant voltage charging is executed with the second predetermined voltage value V ₁ lower than the first predetermined voltage value V ₀ in the first charging step as the upper limit voltage, so the charge amount As a result, it is possible to reduce the time for the high voltage while ensuring the above, and as a result, it is possible to suppress the elution of the transition metal and suppress the deterioration of the cycle characteristics.

Incidentally, in the second charging step shown in FIGS. 7A and 7B, constant voltage charging with the second predetermined voltage value V ₁ lower than the first predetermined voltage value V ₀ being the target voltage in the first charging step as the upper limit voltage. Is executed once, but this may be executed a plurality of times. FIG. 8 is a flowchart showing a charging method according to another embodiment of the present invention, FIG. 9A is a graph showing an example of the relationship between the battery capacity and the applied voltage / current when charged by the charging method of FIG. 8, and FIG. It is a graph which shows an example of the relationship between the charging time at the time of charging with the charging method of FIG. 8, and an applied voltage / current.

Steps S11 to S15 in FIG. 8 are the same as steps S1 to S5 in FIG. 5 and are therefore omitted here. However, in step S16, the 2-1 charging process (the first constant voltage in the second charging process) is omitted. Charge). In the 2-1 charging step of the present example, constant voltage charging is executed with the second predetermined voltage value V ₁ lower than the first predetermined voltage value V ₀ being the target voltage in the first charging step as the upper limit voltage. The 2-1 charging step is continuously performed until the open circuit voltage V of the secondary battery 10 reaches, for example, a previously known SOC 90% charge voltage V _SOC90 . In step S17, the open circuit voltage V is changed to the charge voltage. When V _SOC90 is reached, the process proceeds to step S18. In step S18, the 2-2 charging step (second constant voltage charging in the second charging step) is performed. In the 2-1 charging process of the present example, constant voltage charging is executed with the third predetermined voltage value V ₂ lower than the first predetermined voltage value V ₀ being the target voltage in the first charging process as the upper limit voltage. The 2-2 charging step is continuously performed until the open circuit voltage V of the secondary battery 10 reaches, for example, a previously known full charge voltage V _SOC100, and the open circuit voltage V is changed to the full charge voltage V in step S19. _{When SOC100} is reached, the charging process of this example is terminated.

Note that the second predetermined voltage value V ₁ in the 2-1 charging step and the third predetermined voltage value V _{2 in} the 2-2 charging step are V ₂ <V ₁ in the example shown in FIGS. 9A and 9B. There may be V ₂ > V ₁ as shown in FIGS. 10A and 10B. In the examples shown in FIGS. 8 to 10B, the second charging process is configured by two constant voltage charging processes, but may be configured by three or more constant voltage charging processes.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples.
Example 1
(Preparation of negative electrode)
Graphite powder, acetylene black as a conductive additive, and polyvinylidene fluoride PVDF as a binder are blended in a mass ratio of 90: 5: 5, and N-methylpyrrolidone is added as a solvent and mixed. A negative electrode slurry was prepared. A copper foil was used as a current collector, and the negative electrode slurry obtained above was applied to each current collector and dried under vacuum for 24 hours to obtain a target negative electrode.

(Preparation of positive electrode)
As a positive electrode active material, Li _1.85 Ni _0.18 Co _0.10 Mn _0.87 O ₃ (in the above formula (1), a = 0.18, b = 0.10, c = 0.87, d = 0.35), acetylene black as a conductive aid, and polyvinylidene fluoride PVDF as a binder in a mass ratio of 90: 5: 5, and N-methylpyrrolidone is added to this as a solvent. Mixing was performed to prepare a positive electrode slurry. An aluminum foil was used as a current collector, and the positive electrode slurry obtained above was applied and dried under vacuum for 24 hours to obtain a target positive electrode.

(Production of battery)
The negative electrode and the positive electrode prepared above were opposed to each other, and a polyolefin separator having a thickness of 20 μm was disposed therebetween. This negative electrode / separator / positive electrode laminate is placed in an aluminum laminate cell, and 1M lithium hexafluorophosphate LiPF ₆ as a lithium salt is used as an electrolyte in an organic solvent composed of ethylene carbonate EC and diethyl carbonate DEC. The mixture in 2 was poured into the cell and sealed to obtain a lithium ion secondary battery.

(Cycle characteristic evaluation test)
About the lithium ion secondary battery produced as mentioned above, the charge / discharge cycle test was done and the discharge capacity retention rate was verified. That is, in an atmosphere of 30 ° C., after performing constant current charging in the first charging step with an upper limit voltage of 4.45 V corresponding to a current density of 1 C, after resting for 5 minutes (battery voltage relaxation step), the upper limit voltage 4 The constant voltage charge of the 2nd charge process was implemented as .40V. Thereafter, after resting for 1 minute, the current density is equivalent to 1C by the constant current discharge method (1C is a current value at which discharge is terminated when a cell having a nominal capacity value a [Ah] is constant current discharged for 1 hour, 1C = a [ A]) to 2V. The battery capacity before starting this charge / discharge cycle and the capacity after repeating the charge / discharge cycle 100 times were measured, and the capacity retention was calculated. The results are shown in Table 1 and FIG.

Example 2
In Example 1, except that the upper limit voltage of the second charging step was set to 4.35 V, the battery was charged under the same conditions as in Example 1, and the capacity retention rate was calculated when the charge / discharge cycle under the same conditions was repeated 100 times. . The results are shown in Table 1 and FIG.

Example 3
In Example 1, except that the upper limit voltage of the second charging step was 4.30 V, charging was performed under the same conditions as in Example 1, and the capacity retention rate was calculated when the charge / discharge cycle under the same conditions was repeated 100 times. . The results are shown in Table 1 and FIG.

Example 4
In Example 1, except that the upper limit voltage of the second charging step was 4.43 V, charging was performed under the same conditions as in Example 1, and the capacity retention rate was calculated when the charge / discharge cycle under the same conditions was repeated 100 times. . The results are shown in Table 1 and FIG.

<< Comparative Example 1 >>
In Example 1, except that the upper limit voltage of the second charging step was 4.45 V, charging was performed under the same conditions as in Example 1, and the capacity retention rate was calculated when the charge / discharge cycle under the same conditions was repeated 100 times. . The results are shown in Table 1 and FIG.

<Discussion>
In Comparative Example 1 in which the target voltage of the first charging step and the upper limit voltage of the second charging voltage are equal, the capacity retention starts to decrease from 50 cycles and finally decreases significantly to 14%, whereas the second charging In the secondary batteries of Examples 1 to 4 in which the upper limit voltage of the process was lower than the target voltage of the first charging process, it was confirmed that the capacity retention after 100 cycles was as high as 65% to 95%. In particular, the first to third embodiments in which the difference between the target voltage of the first charging step and the upper limit voltage of the second charging voltage is 50 mV or more have a slower capacity reduction start cycle than the fourth embodiment in which the difference is less than 50 mV. It was confirmed that the final capacity retention was also high.

As described above, according to the charging method and the charging device of the present example, after charging to the first predetermined voltage value V ₀ in the first charging step, charging is performed using the second predetermined voltage value V ₁ lower than this as the upper limit voltage. As a result, the time during which the charge amount is kept high while the high voltage is maintained is shortened. Thereby, since elution of a transition metal can be suppressed, there is an effect that deterioration of cycle characteristics can be suppressed. Further, according to the charging method and the charging device of this example, since the first charging step is charged to the first predetermined voltage value by constant current charging, the charging can be performed in a short time.

Further, according to the charging method and the charging device of the present example, the second charging step is performed with the second predetermined voltage value that is 50 mV or more lower than the first predetermined voltage value of the first charging step as the upper limit voltage. As in Examples 1 to 3, the capacity retention is extremely high, and deterioration of cycle characteristics can be remarkably suppressed.

Further, according to the charging method and the charging device of the present example, since the battery voltage relaxation step for interrupting the charging without flowing the charging current to the secondary battery is provided between the first charging step and the second charging step, It is possible to suppress the concentration distribution of the electrolytic solution inside the battery and the uneven charging state of lithium ions in the electrode in the charging process by constant current charging performed in one charging step. Thereby, elution of transition metals, such as manganese and nickel, can be suppressed by suppressing a potential difference between the positive electrode and the negative electrode and normalizing the battery voltage.

Further, according to the charging method and the charging device of the present example, the second charging step is charged with a plurality of charging voltages having the second predetermined voltages V ₁ and V ₂ lower than the first predetermined voltage value V ₀ as upper limit voltages. Since a plurality of charging steps are included, the time during which the high voltage is maintained can be further shortened, whereby the elution of the transition metal can be suppressed, and the deterioration of the cycle characteristics can be further suppressed.

Further, according to the charging method and the charging device of this example, the solid solution material is a solid solution lithium-containing transition metal oxide represented by Li _1.5 [Ni _a Co _b Mn _c [Li] _d ] O ₃ , as the positive electrode active material. Since it uses, the secondary battery which can implement | achieve a high discharge capacity and capacity | capacitance retention can be provided.

The battery control device 20 corresponds to the control means according to the present invention.

DESCRIPTION OF SYMBOLS 10 ... Secondary battery 101 ... Electrode laminated body 102 ... Positive electrode plate 102a ... Positive electrode side collector 103 ... Separator 104 ... Negative electrode plate 104a ... Negative electrode side collector 105 ... Positive electrode tab 106 ... Negative electrode tab 107 ... Upper exterior member 108 ... Lower exterior member 109 ... Seal film 20 ... Battery control device 30 ... Power source 40 ... Current sensor 50 ... Voltage sensor

Claims

In a secondary battery charging method using a positive electrode active material made of a solid solution material as a positive electrode material,
A first charging step of charging to a first predetermined voltage;
And a second charging step of charging the second predetermined voltage lower than the first predetermined voltage as an upper limit voltage after the first charging step.
The charging method of the secondary battery according to claim 1, wherein the first charging step is charged with a constant current.
The charging method of the secondary battery according to claim 1 or 2, wherein the second charging step charges at a constant voltage.
The method for charging a secondary battery according to any one of claims 1 to 3, wherein a difference between the first predetermined voltage and the second predetermined voltage is 50 mV or more.
The battery voltage relaxation step according to any one of claims 1 to 4, further comprising a battery voltage relaxation step that interrupts charging without flowing a charging current to the secondary battery between the first charging step and the second charging step. Rechargeable battery charging method.
The secondary battery charging method according to any one of claims 1 to 5, wherein the second charging step includes a plurality of charging steps of charging at a plurality of charging voltages having the second predetermined voltage as an upper limit voltage. .
The solid solution material is
Composition formula Li 1.5 [Ni a Co b Mn c [Li] d ] O 3
(In the composition formula, Li is lithium, Ni is nickel, Co is cobalt, Mn is manganese, O is oxygen, and a, b, c, and d are 0 <a <1.4, 0 ≦ b <1. 4, 0 <c <1.4, 0.1 <d ≦ 0.4, a + b + c + d = 1.5, 1.1 ≦ a + b + c <1.4.) A metal oxide,
It has a layered structure part and a part that changes to a spinel structure by charging or discharging in a predetermined potential range,
When the spinel structure change ratio when the Li 2 MnO 3 of the layered structure in the solid solution lithium-containing transition metal oxide is all changed to the spinel structure LiMn 2 O 4 is 1, the spinel of the solid solution lithium-containing transition metal oxide The method for charging a secondary battery according to any one of claims 1 to 6, wherein the structural change ratio is 0.25 or more and less than 1.0.
In a charging device for charging a secondary battery using a positive electrode active material made of a solid solution material as a positive electrode material,
A first charging step for charging to a first predetermined voltage;
A charging device for a secondary battery, comprising: a control unit that executes, after the first charging step, a second charging step of charging a second predetermined voltage lower than the first predetermined voltage as an upper limit voltage.