JP2023090118A - Charging method of lithium ion secondary battery, method for controlling charging of the lithium ion secondary battery and control device for charging the lithium ion secondary battery - Google Patents

Abstract

To provide a charging method enabling improvement of a cycle characteristic of a lithium ion secondary battery.SOLUTION: A charging method of a lithium ion secondary battery, performs charging including: at least a step A of performing a charging of a predetermined voltage Va; and a step B of performing a constant voltage changing while gradually reducing a charging current in such a manner that the predetermined voltage Va is maintained after the voltage of the lithium ion secondary battery reaches the predetermined voltage Va. A cathode active material layer of the lithium ion secondary battery, includes at least: a lithium manganese iron phosphate as a first cathode active material; and transition metal lithium having layered structure as a second cathode active material. In the step of performing the charging up to a predetermined voltage, a charging current is increased when a ratio R/Rmin which is a ratio of a current resistance value R obtained by a current value and a voltage value which are successively detected to the minimum value Rmin of a current resistance value in the above step reaches a preset predetermined value or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method of charging a lithium ion secondary battery, a method of controlling charging of a lithium ion secondary battery, and an apparatus for controlling charging of a lithium ion secondary battery.

2. Description of the Related Art In recent years, mobile cordless products such as mobile phones, notebook personal computers, and video cameras are becoming more and more compact and portable. In addition, from the viewpoint of environmental problems such as air pollution and increased carbon dioxide, the development of electric vehicles such as hybrid vehicles, electric vehicles, electric ships, and small aircraft such as drones is being promoted, and is at the stage of practical use. It has become. These electronic devices, electric vehicles, and the like require excellent secondary batteries having characteristics such as high efficiency, high output, high energy density, and light weight. Development and research on secondary batteries having such characteristics have been actively carried out, and various secondary batteries such as lithium batteries and lithium ion batteries have been put to practical use. In order to charge such a secondary battery in a short time, constant-current and constant-voltage charging (CC charging) combined with constant-current charging (CC charging) with high current density up to the charging end voltage is used. CCCV charging) is generally performed.

Conventionally, active materials such as graphite that intercalates lithium ions between layers and silicon and tin that react with lithium ions to form alloys have been favorably used as negative electrode active materials for lithium ion secondary batteries. When a current is applied to such a negative electrode active material, the amount of heat generated may increase and deposition of metallic lithium may occur on the negative electrode, which may shorten the life of the lithium ion secondary battery. . In particular, when using a lithium composite oxide with a layered structure such as nickel, cobalt, manganese, etc. as a positive electrode active material with the aim of increasing the energy density of a lithium ion secondary battery, charge termination is required to obtain a desired capacity. It is necessary to set the voltage to 4.2 V or more, but due to the characteristics of the lithium composite oxide having a layered structure, the CC charging time is long, so there is a problem that the life of the lithium ion secondary battery is shortened. there were.

On the other hand, in a lithium ion secondary battery containing at least an electrode including a positive electrode and a negative electrode and an electrolytic solution, lithium manganese phosphate (LMP) and phosphoric acid, which are composed of elements that are excellent in stability and abundant in terms of resources, Attempts have been made to use lithium iron (LFP) as a positive electrode active material. In particular, lithium manganese iron phosphate (LMFP), in which part of the manganese element that constitutes LMP is replaced with iron element, has high lithium ion conductivity and electronic conductivity, and is excellent in stability, so it is resistant to overcharge and overdischarge. A strong lithium-ion secondary battery with a long cycle life can be provided. Therefore, many efforts have been made to use LMFP positive electrode active materials or mixed positive electrode active materials in which LMFP is mixed with layered lithium transition metal oxides that have been conventionally used as positive electrode active materials.

In Patent Document 1, in a mixed positive electrode active material obtained by blending a lithium transition metal oxide with a layered structure and a lithium oxide with an olivine structure (lithium iron phosphate, etc.), some of the iron atoms are replaced with other atoms such as manganese atoms. Attempts have been made to minimize the reduction in output in the transient region by using elementally substituted lithium manganese iron phosphate to reduce the operating voltage difference with the layered structure lithium transition metal oxide.

On the other hand, Patent Document 2 discloses a method and apparatus for charging a non-aqueous electrolyte secondary battery comprising a positive electrode containing a lithium-containing composite oxide as an active material, a negative electrode containing an alloy-based negative electrode active material, and a non-aqueous electrolyte. is disclosed. The secondary battery charging method disclosed in Patent Document 2 detects the voltage of the secondary battery, and if the detected value is less than a predetermined voltage x, charges with a relatively small current value B, If the detected value is greater than or equal to x and less than z, the battery is charged with a relatively large current value A. If the detected value is greater than or equal to the predetermined voltage z and less than y, the battery is charged with a relatively small current value C. If the detected value is greater than or equal to the predetermined voltage y. For example, it is characterized by charging at a constant voltage or stopping charging (where B<A, C<A, and x<z<y).

Special table 2015-519005 WO2011/033704

When charging a lithium-ion secondary battery using a mixed positive electrode active material, as the remaining capacity (or degree of charge, hereinafter referred to as "SOC") of the battery increases, the direct current resistance of the entire battery increases sharply. Although there is a problem that the load on the negative electrode active material increases and the end-of-charge voltage is quickly reached, Patent Document 1 does not notice such a problem.

In Patent Document 2, charging is performed with a relatively small current value B at the initial stage of charging when the internal resistance of the secondary battery is large, and charging is performed with a relatively large current value A after the internal resistance of the secondary battery has decreased. It is disclosed that it is possible to suppress large fluctuations in charge polarization, which means that when the SOC of the battery is low, it is charged at a low current, and when the SOC is intermediate, it is charged at a high current. , when the SOC is high, the battery is charged again with a low current.

The present inventors found that when charging a lithium ion secondary battery using a positive electrode active material containing at least lithium manganese iron phosphate and a transition metal lithium oxide with a layered structure, only a transition metal lithium oxide with a layered structure Compared to charging a lithium-ion secondary battery using I paid attention. At the timing when the SOC of the lithium ion secondary battery becomes constant and the DC resistance value suddenly increases, the charging current density, that is, the charging rate is increased once to reach the charging end voltage early, and then CC charging to CV The inventors have found that the amount of heat generated from the lithium-ion secondary battery can be suppressed and the deposition of metallic lithium on the negative electrode can also be suppressed by shifting to charging, and have completed the present invention. Therefore, when charging a lithium ion secondary battery using a positive electrode active material containing at least lithium manganese iron phosphate and a transition metal lithium oxide with a layered structure, the present invention is not limited to an alloy-based negative electrode active material but a carbon-based It is an object of the present invention to provide a charging method capable of reducing the load on all negative electrode active materials including negative electrode active materials and metallic lithium and improving the cycle characteristics of lithium ion secondary batteries.

The embodiment of the present invention includes the following steps: (A) charging to a predetermined voltage _Va ; and (B) maintaining the predetermined voltage _Va after reaching the predetermined voltage _Va . and a step of performing constant voltage charging while gradually decreasing the charging current. Here, the lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a current collector, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution, The positive electrode active material layer includes at least lithium manganese iron phosphate as a first positive electrode active material and a transition metal lithium oxide having a layered structure as a second positive electrode active material, and the step (A) In step (A), the ratio R/R _min of the DC resistance value R obtained from the successively detected current value and voltage value to the minimum value R _min of the DC resistance value in step (A) is equal to or greater than a predetermined value. It is characterized by increasing the charging current when it reaches.

Another aspect of the present invention comprises the following steps: (A) charging with a predetermined charging current up to _a predetermined voltage _Va ; and a step of performing constant voltage charging while gradually decreasing the charging current so as to maintain the voltage Va _of . Here, the lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a current collector, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution, The positive electrode active material layer includes at least lithium manganese iron phosphate as a first positive electrode active material and a transition metal lithium oxide having a layered structure as a second positive electrode active material, and the step (A) 3, the charging current is increased when the amount of change in the voltage value with respect to the charging current value reaches a predetermined value or more.

Another aspect of the present invention is the following steps: (A) charging to a predetermined voltage _Va ; and (B) maintaining the predetermined voltage _Va after reaching the predetermined voltage Va. a step of performing constant-voltage charging while gradually decreasing the charging current as above. Here, the lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a current collector, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution, The positive electrode active material layer includes at least lithium manganese iron phosphate as a first positive electrode active material and a transition metal lithium oxide having a layered structure as a second positive electrode active material, and the step (A) In step (A), when the ratio V/V _min of the sequentially detected voltage value V to the minimum value V _min of the voltage value in step (A) reaches a predetermined value or more, the charging current is increased. characterized by

Another aspect of the invention is a method of controlling charging of a lithium-ion secondary battery. In the method of controlling the charging, the charging includes (A) a constant current charging process and (B) a constant voltage charging process, and the charging current value and the voltage value are sequentially changed through the charging. and storing the DC resistance value R and the minimum value _Rmin of the DC resistance value in the charging from the charging current value and the voltage value that are successively detected, and the step (A) stores a predetermined charging current charging with _Ia1 ; and charging with a charging current _Ia2 larger than the predetermined charging current _Ia1 , wherein in the step (A), constant current charging is started with the charging current _Ia1 . , in the step (A), when the ratio R/ _Rmin of the DC resistance value R and the minimum DC resistance value _Rmin reaches a predetermined value or more, the charging current _Ia2 and charge until the voltage reaches a predetermined voltage _Va , and after the voltage reaches the predetermined voltage _Va , the charging current is gradually decreased so as to maintain the predetermined voltage _Va . while performing the step (B).

Another aspect of the present invention is a lithium ion secondary battery comprising at least a detection unit that detects a current value and a voltage value, and a control unit that changes the magnitude of the charging current based on the detected voltage value. It is a control device for charging the battery. Here, the charging of the lithium ion secondary battery includes the following steps: (A) charging to a predetermined voltage _Va , and (B) after reaching the predetermined voltage _Va , the predetermined voltage and performing constant voltage charging while gradually decreasing the charging current so as to maintain _Va , wherein the lithium ion secondary battery has a positive electrode active material layer formed on a current collector. At least a positive electrode, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution are included, and the positive electrode active material layer includes lithium manganese iron phosphate as a first positive electrode active material, and a second positive electrode active material. a transition metal lithium oxide having a layered structure, which is a positive electrode active material; The controller increases the charging current when the ratio V/V _min to _min reaches a predetermined value or more.

Another aspect of the present invention includes a detection unit that detects a current value and a voltage value, a calculation unit that calculates a DC resistance value from the detected values, and a charging current based on a change in the calculated DC resistance value. A controller for charging a lithium-ion secondary battery, comprising at least a controller for changing the size. Here, the charging of the lithium ion secondary battery includes the following steps: (A) a step of charging with a predetermined charging current up to a predetermined voltage _Va , and (B) after reaching the predetermined voltage _Va is charging including at least the step of performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va , wherein the lithium ion secondary battery has a positive electrode active on a current collector. At least a positive electrode having a material layer formed thereon, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution, wherein the positive electrode active material layer contains phosphoric acid as a first positive electrode active material. containing at least lithium manganese iron and a layered structure transition metal lithium oxide, which is a second positive electrode active material; , the calculation unit calculates the DC resistance value R, and when the ratio R/R _min to the minimum value R _min of the DC resistance value in the step (A) reaches a predetermined value or more, the control unit It is characterized by increasing the charging current.

According to the lithium ion secondary battery charging method of the present invention, during charging of a lithium ion secondary battery using a positive electrode active material containing at least lithium manganese iron phosphate and a transition metal lithium oxide having a layered structure, Since the load that can be applied to the negative electrode active material can be reduced, the cycle characteristics of the lithium ion secondary battery can be improved and the battery life can be extended.

When a lithium ion secondary battery using a positive electrode active material containing lithium manganese iron phosphate and a transition metal lithium oxide with a layered structure is charged at constant current, the SOC (horizontal axis) and the DC resistance value (vertical axis) of the battery ).

Embodiments of the present invention are a method of charging a lithium ion secondary battery, a method of controlling charging of a lithium ion secondary battery, and a control device for charging a lithium ion secondary battery. First, lithium ion secondary batteries in all embodiments of the present invention will be described below.

A secondary battery of the embodiment refers to a chargeable/dischargeable chemical battery. An embodiment of the present invention is a lithium ion secondary battery. A lithium ion secondary battery of an embodiment includes at least an electrode including a positive electrode and a negative electrode, and an electrolytic solution as constituent elements. When the lithium ion secondary battery is discharged, the electrode with the higher potential is the positive electrode and the electrode with the lower potential is the negative electrode. In an embodiment, the electrode is formed by forming an electrode active material layer containing an electrode active material on the surface of an electrode current collector. Here, the electrode current collector is usually composed of a metal plate or metal foil, holds the electrode active material on its surface, and plays a role of supplying current to the electrode active material or receiving current from the electrode active material. Fulfill. Further, the electrode active material is a substance that causes a chemical reaction to release energy, particularly a substance that can cause a battery reaction in a lithium ion secondary battery to release electrical energy to the outside. The electrode active material layer is a layer obtained by depositing an electrode active material mixture (electrode mixture) containing the aforementioned electrode active material and optionally a conductive aid and a binder. It is for forming an electrode active material layer by binding conductive aids to each other. The electrode active material layer provides a field for cell reactions. Here, the conductive aid is for assisting electron transfer in the electrode active material layer. On the other hand, the binder is for forming the electrode active material layer by binding the above-described electrode active material and, in some cases, the conductive aid.

In an embodiment, the positive electrode is obtained by forming a positive electrode active material layer containing a positive electrode active material on the surface of a positive electrode current collector. The positive electrode current collector is composed of a metal plate or metal foil, particularly an aluminum plate or aluminum foil, which holds the positive electrode active material on its surface and supplies current to or from the positive electrode active material. play a role in Although the material used as the positive electrode active material is not particularly limited, metal oxides and metal sulfides capable of intercalating and deintercalating lithium ions during charging and discharging are preferable. Such as metal oxides and metal sulfides, vanadium oxides, vanadium sulfides, molybdenum oxides, molybdenum sulfides, manganese oxides, chromium oxides, titanium oxides, titanium sulfides and their composite oxides and composite sulfides. Examples _{of such} compounds include _Cr3O8 , _{V2O5 , V5O18 , VO2} , _{Cr2O5 , MnO2} , _{TiO2 , MoV2O8 , TiS2V2S5MoS2 . , MoS3VS2 , Cr0.25V0.75S2 and Cr0.5V0.5S2 . _} LiMY ₂ (M is a transition metal such as Co or Ni; Y is a chalcogen compound such as O or S); LiM ₂ Y ₄ (M is Mn; Y is O); oxides such as WO ₃ ; Sulfides such as Fe _0.25 V _0.75 S ₂ and Na _0.1 CrS ₂ , phosphorus and sulfur compounds such as NiPS ₈ and FePS ₈ can also be used. Manganese oxides and lithium-manganese composite oxides having a spinel structure are also preferred.

In particular, lithium manganese iron phosphate (hereinafter sometimes referred to as “LMFP”) as the first positive electrode active material and a transition metal lithium oxide having a layered structure, specifically LiCoO ₂ , as the second positive electrode active material. _, LiMnO ₂ , _{LiNixMnyzO 2} , _{LiNixCoyAlzO 2} , _{Li 6} FeO _{4 and} the like.

In the embodiment, the positive electrode active material layer is a layer in which a positive electrode active material mixture (positive electrode mixture) containing the above-described positive electrode active material and optionally a conductive aid and a binder is deposited. The positive electrode active material layer provides a place for battery reaction (positive electrode reaction). Here, the conductive aid is for assisting electron transfer in the positive electrode active material layer. As the conductive aid, carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and Ketjen black, carbon materials such as activated carbon, graphite, mesoporous carbon, fullerenes, and carbon nanotubes can be used. On the other hand, the binder is for forming the positive electrode active material layer by binding the above positive electrode active material and optionally the conductive aid to each other. Fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and polyvinyl fluoride (PVF) as binders, conductive polymers such as polyanilines, polythiophenes, polyacetylenes and polypyrroles, styrene butadiene rubber (SBR) ), synthetic rubber such as butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), or polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin. can be done. In addition, electrode additives generally used for electrode formation, such as thickeners, dispersants, and stabilizers, may be appropriately used in the positive electrode active material layer.

The positive electrode is prepared by applying a slurry obtained by dispersing a positive electrode mixture containing a positive electrode active material, a conductive aid, and a binder in an appropriate solvent onto at least one surface of a generally planar positive electrode current collector, and evaporating the solvent. It can be obtained by forming a positive electrode active material layer.

On the other hand, in the embodiments, the negative electrode is obtained by forming a negative electrode active material layer containing a negative electrode active material on the surface of a negative electrode current collector. The negative electrode current collector is composed of a metal plate or metal foil, particularly a copper plate or copper foil, which holds the negative electrode active material on its surface and supplies current to the negative electrode active material or receives current from the negative electrode active material. play a role. As the negative electrode current collector, a copper or copper alloy with lithium interspersed therein, or a copper or copper alloy with other metals (for example, tin or indium) deposited by plating or vapor deposition can also be used. The thickness of the negative electrode current collector is preferably 5 μm to 20 μm. The material used as the negative electrode active material is not particularly limited, but carbon materials, particularly graphite, can be mentioned. Graphite is a carbon material with hexagonal hexagonal plate crystals, and is sometimes called graphite, graphite, or the like. Preferably, the graphite is in the form of particles. Graphite includes natural graphite and artificial graphite. Natural graphite can be obtained in large quantities at low cost, and has a stable structure and excellent durability. Artificial graphite is graphite that is artificially produced, and has a high purity (almost no impurities such as allotropes are included), and thus has a low electrical resistance. Both natural graphite and artificial graphite can be suitably used as the negative electrode active material in the embodiments. Natural graphite with an amorphous carbon coating or artificial graphite with an amorphous carbon coating can also be used. Amorphous carbon is a carbon material that is amorphous as a whole and has a structure in which microcrystals are randomly networked, which may partially have a structure similar to graphite. . Examples of amorphous carbon include carbon black, coke, activated carbon, carbon fiber, hard carbon, soft carbon, and mesoporous carbon. These negative electrode active materials may optionally be mixed and used. Graphite coated with amorphous carbon can also be used.

In the embodiment, the negative electrode active material layer is a layer formed by depositing a negative electrode active material mixture (negative electrode mixture) containing the aforementioned negative electrode active material and optionally a conductive aid and a binder. The negative electrode active material layer provides a place for battery reaction (negative electrode reaction). Here, the conductive aid is for assisting electron transfer in the negative electrode active material layer. As the conductive aid, carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and Ketjen black, carbon materials such as activated carbon, graphite, mesoporous carbon, fullerenes, and carbon nanotubes can be used. On the other hand, the binder is for forming the negative electrode active material layer by binding the above-described negative electrode active material and, in some cases, the conductive aid. Fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and polyvinyl fluoride (PVF) as binders, conductive polymers such as polyanilines, polythiophenes, polyacetylenes and polypyrroles, styrene butadiene rubber (SBR) ), synthetic rubber such as butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), or polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin. can be done. In addition, electrode additives generally used for electrode formation, such as thickeners, dispersants, and stabilizers, may be appropriately used in the negative electrode active material layer.

The negative electrode is formed by applying a slurry obtained by dispersing a positive electrode mixture containing a negative electrode active material, a conductive aid, and a binder in an appropriate solvent onto at least one surface of a generally planar negative electrode current collector, and evaporating the solvent. It can be obtained by forming a negative electrode active material layer.

A lithium-ion secondary battery of an embodiment includes an electrolytic solution. In an embodiment, the electrolytic solution preferably contains a non-aqueous solvent, an electrolyte, and zeolite. As non-aqueous solvents, acetonitrile (AN), γ-butyrolactone (BL), γ-valerolactone (VL), γ-octanoic lactone (OL), diethyl ether (DEE), 1,2-dimethoxyethane (DME) , 1,2-diethoxyethane (DEE), dimethyl sulfoxide (DMSO), 1,3-dioxolane (DOL), ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC) , ethyl methyl carbonate (EMC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), methyl formate (MF), tetrahydrofuran (THF), 2-methyltetrahydrofuran (MTHF), 3-methyl-1,3-oxaziridine- 2-one (MOX), sulfolane (S), diglyme, triglyme, tetraglyme and the like are preferably used, and these can be used alone or as a mixture of two or more.

Further, the electrolyte contained in the electrolytic solution used in the embodiment preferably contains a lithium salt. Lithium _salts such as _LiPF6 , LiAsF6, _LiClO4 , _LiBF4 , LiB( _C2O4 ) ₂ , LiN( _SO2F ) _{2 ( LiFSI} ), LiN _{( SO2CF3} ) ₂ , _LiCF3SO3 , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ and the like, and one or more of these may be dissolved in the above non-aqueous solvent at a concentration of about 0.5 to 2.0 M. Used.

A separator can be used in the secondary battery of the embodiment. A separator is laminated between the positive electrode and the negative electrode, and separates the positive electrode from the negative electrode to prevent short circuits. It is a member used for the purpose of having a current-blocking characteristic for preventing the passage of electricity and ensuring safety. A polyolefin film can be used as the separator. Polyolefins are compounds obtained by polymerizing or copolymerizing α-olefins such as ethylene, propylene, butene, pentene, and hexene. Copolymers may be mentioned. In addition, polyimide resin, polyamide resin such as nylon, polyester resin such as polyethylene terephthalate and polyethylene naphthalate, polyvinyl chloride resin, polyvinylidene chloride resin, polyurethane resin, polyoxymethylene resin, fluorine resin such as polytetrafluoroethylene, poly Paraphenylene benzbis thiazole resin or the like may also be used. If the resin has a low melting point or a low softening point, the separator tends to melt and shrink when the temperature of the secondary battery rises. Since heat shrinkage of the separator causes a short circuit between the electrodes, the resin preferably has a high melting point or softening point, for example, a melting point or softening point of 140° C. or higher.

When a polyolefin film is used as the separator used in the embodiment, it is advantageous if the structure has pores that are closed when the battery temperature rises, that is, a porous or microporous polyolefin film. Also, a crosslinked polyolefin film can be used as the separator. A heat-resistant fine particle layer may be provided on one side or both sides of the separator. Examples of heat-resistant inorganic fine particles include inorganic oxides such as silica, alumina (α-alumina, β-alumina, θ-alumina), iron oxide, titanium oxide, barium titanate, and zirconium oxide; boehmite, zeolite, apatite, kaolin, Minerals such as spinel, mica, and mullite can be mentioned.

As a separator, it is also preferable to use a porous resin film in which pores are three-dimensionally communicated with each other through communicating pores (such a structure is referred to herein as a “3DOM structure”). By using such a "3DOM structure" separator, the current distribution of lithium ions in a secondary battery (especially a lithium secondary battery or a lithium ion secondary battery) is made uniform, and it is safe without generating lithium dendrites. It is possible to charge and discharge the secondary battery in a short period of time. The diffusion of lithium ions is made uniform, and as a result, the ion current density is made uniform even in the case of a diffusion-controlled reaction, so that the lithium electrodeposition reaction is uniformly controlled. In addition, due to the effect that the 3DOM structure makes the ion current density uniform, the lithium electrodeposition reaction is uniformly controlled even under high current density charging/discharging conditions, improving the cycle characteristics of secondary batteries using metallic lithium anodes. can be made

A power generating element can be formed by stacking the positive electrode and the negative electrode, if necessary, with a separator interposed therebetween. One or more positive electrodes, negative electrodes, and optionally separators can be laminated. Such a power generating element is appropriately provided with members for extracting current, such as a positive electrode tab and a negative electrode tab, and other necessary members such as a gasket, a current collector, a sealing plate, and a cell case, which are other battery components, are added as appropriate. A lithium-ion secondary battery can be obtained by encapsulating in an outer package such as a coin cell or an aluminum laminate film manufactured by the manufacturer and injecting a non-aqueous electrolyte. The shape of the battery is not particularly limited, and may be any shape including conventionally known shapes such as cylindrical, square, coin, etc., in addition to the laminate type. When the lithium ion secondary battery is, for example, a coin-type battery, the negative electrode plate is usually placed on the cell floor plate, the electrolytic solution and the separator are placed thereon, and the positive electrode is placed so as to face the negative electrode. A lithium ion secondary battery is formed by crimping together with the sealing plate. Also, when the lithium ion secondary battery is, for example, a laminate type battery, terminals such as a positive electrode tab and a negative electrode tab are attached to the power generating element, inserted into a bag made of a metal laminate film, and an electrolytic solution is injected. A lithium ion secondary battery can be obtained by sealing the laminate film. The structure or manufacturing method of the lithium ion secondary battery is not limited to these.

One embodiment is a charging method for the above lithium ion secondary battery. The charging method is the following steps:
(A) charging to a predetermined voltage _Va ;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
including at least Start charging the lithium ion secondary battery (that is, perform step (A)), perform step (A) until the voltage of the lithium ion secondary battery reaches a predetermined value _Va , and then perform the predetermined voltage V Constant voltage charging is performed while gradually decreasing the charging current so as to maintain _a . Here, in step (A), the DC resistance value R is obtained from the successively detected current value and voltage value, and the ratio of the DC resistance value R to the minimum value R _min of the DC resistance value in step (A) ( R/R _min ) reaches a predetermined value or more, the charging current is increased. For example, charging in step (A) is started at a constant current ₍ I _a1 ), and the ratio (R/R _min ) reaches a predetermined value, the charging current is raised to _Ia2 . At a certain point in step (A), the charging current is increased from _Ia1 to _Ia2 , so that the voltage of the lithium ion secondary battery reaches a predetermined value _Va compared to charging with the constant current of _Ia1 . shorter time to reach. As the timing for increasing the charging current from _Ia1 to _Ia2 , the DC resistance value R of the lithium ion secondary battery can be used. When charging of the lithium ion secondary battery is started, the DC resistance value of the lithium ion secondary battery usually drops, then rises, and then drops sharply to reach the minimum DC resistance value _Rmin in step (A). and then start to rise. Thereafter, the charging current can be switched when the ratio (R/R _min ) between the DC resistance value R of the lithium ion secondary battery and the minimum DC resistance value R _min in step (A) reaches a predetermined value. . In the present embodiment, the DC resistance value R of the lithium ion secondary battery behaves as described above (that is, it drops once from the start of charging, rises, and then drops sharply to record the minimum DC resistance value. and then rises) is that the positive electrode active materials of the lithium-ion secondary battery using the charging method of the embodiment are lithium manganese iron phosphate, which is the first positive electrode active material, and the second positive electrode active material. It is thought that this is caused by containing a transition metal lithium oxide having a layered structure.

In this way, at a certain point in step (A), the charging is switched to a high charging current density, and when the voltage of the lithium ion secondary battery reaches a predetermined value _Va , the charging current is adjusted so as to maintain the predetermined value _Va . is gradually decreased, and the charging is terminated at a predetermined time. By charging the lithium ion secondary battery with the charging method of the present embodiment, it is possible to quickly switch from CC charging to CV charging. In this way, in the step (A), the reason why the charging is temporarily switched to charging at a high charging current density is that the current density of the CV charging is smaller than that of the CC charging. Since the load voltage to the negative electrode becomes smaller when the current density during charging is smaller, it is considered that deposition of metallic lithium on the negative electrode is suppressed. If the timing of switching to charging at a high charging current density in step (A) is delayed, deposition of metallic lithium on the negative electrode may easily occur. Also, if the timing of switching to charging at a high charging current density is early, the amount of heat generated may increase. In step (A), it is appropriate to switch to charging at a high charging current density when the SOC of the lithium ion secondary battery reaches approximately 78 to 85%. As a measure of the SOC of such a lithium ion secondary battery, the above R/R _min value can be used. In embodiments, charging can be switched to high charging current density when the value of R/R _min is greater than or equal to 1.9. In step (A), charging is continued until the voltage of the lithium ion secondary battery reaches a predetermined value _Va after switching to charging at a high charging current density. Here, the predetermined value V _a is 4.0 V or higher, preferably 4.1 V or higher, more preferably 4.2 V or higher. When the voltage of the lithium ion secondary battery reaches a predetermined value _Va , step (B) of performing CV charging so as to maintain the voltage predetermined value _Va can be performed.

A second embodiment is a method for charging the lithium-ion secondary battery described above. The charging method is the following steps:
(A) charging to a predetermined voltage _Va ;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
including at least Start charging the lithium ion secondary battery (that is, perform step (A)), perform step (A) until the voltage of the lithium ion secondary battery reaches a predetermined value _Va , and then perform the predetermined voltage V Constant voltage charging is performed while gradually decreasing the charging current so as to maintain _a . Here, in step (A), when the amount of change in the voltage value with respect to the charging current value reaches a predetermined value or more, the charging current is increased. For example, the charging in step (A) is started at a constant current (I _a1 ), and when the amount of change in the voltage value with respect to the charging current value of the lithium ion secondary battery reaches a predetermined value, the charging current is increased to I _a2 . . At a certain point in step (A), the charging current is increased from _Ia1 to _Ia2 , so that the voltage of the lithium ion secondary battery reaches a predetermined value _Va compared to charging with the constant current of _Ia1 . shorter time to reach. As the timing for increasing the charging current from _Ia1 to _Ia2 , the amount of change in the voltage value with respect to the charging current value of the lithium-ion secondary battery can be used. When charging of the lithium ion secondary battery is started, the amount of change in the voltage value with respect to the charging current value of the lithium ion secondary battery usually increases, and then the amount of change in the voltage value with respect to the charging current value of the lithium ion secondary battery increases. The charging current can be switched when a predetermined value is reached.

In this way, at a certain point in step (A), the charging is switched to a high charging current density, and when the voltage of the lithium ion secondary battery reaches a predetermined value _Va , the charging current is adjusted so as to maintain the predetermined value _Va . is gradually decreased, and the charging is terminated at a predetermined time. By charging the lithium ion secondary battery with the charging method of the present embodiment, it is possible to quickly switch from CC charging to CV charging. In this way, in the step (A), the reason why the charging is temporarily switched to charging at a high charging current density is that the current density of the CV charging is smaller than that of the CC charging. Since the load voltage to the negative electrode becomes smaller when the current density during charging is smaller, it is considered that deposition of metallic lithium on the negative electrode is suppressed. If the timing of switching to charging at a high charging current density in step (A) is delayed, deposition of metallic lithium on the negative electrode may easily occur. Also, if the timing of switching to charging at a high charging current density is early, the amount of heat generated may increase. In step (A), it is appropriate to switch to charging at a high charging current density when the SOC of the lithium ion secondary battery reaches approximately 78 to 85%. As a measure of the SOC of such a lithium ion secondary battery, the amount of change in the voltage value with respect to the charging current value can be used. In the embodiment, when the amount of change in the voltage value with respect to the charging current value is 0.25 mV/A or more, preferably 0.30 mV/A or more, and more preferably 0.35 mV/A or more, the charging current density is high. can be switched to charging. In step (A), charging is continued until the voltage of the lithium ion secondary battery reaches a predetermined value _Va after switching to charging at a high charging current density. Here, the predetermined value V _a is 4.0 V or higher, preferably 4.1 V or higher, more preferably 4.2 V or higher. When the voltage of the lithium ion secondary battery reaches a predetermined value _Va , step (B) of performing CV charging so as to maintain the voltage predetermined value _Va can be performed.

A third embodiment is a method for charging the lithium-ion secondary battery described above. The charging method is the following steps:
(A) charging to a predetermined voltage _Va ;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
Constant current and constant voltage charging including at least Start charging the lithium ion secondary battery (that is, perform step (A)), perform step (A) until the voltage of the lithium ion secondary battery reaches a predetermined value _Va , and then perform the predetermined voltage V Constant voltage charging is performed while gradually decreasing the charging current so as to maintain _a . Here, in step (A), when the ratio V/V _min of the sequentially detected voltage value V to the minimum voltage value V _min in step (A) reaches a predetermined value or more, Increase the charging current. For example, charging in step (A) is started at a constant current (I _a1 ), and the ratio of the voltage value V of the lithium ion secondary battery to the minimum voltage value V _min in step (A) (V/V _min ) reaches a predetermined value, the charging current is raised to _Ia2 . At a certain point in step (A), the charging current is increased from _Ia1 to _Ia2 , so that the voltage of the lithium ion secondary battery reaches a predetermined value _Va compared to charging with the constant current of _Ia1 . shorter time to reach. The above V/V _min value can be used as the timing for increasing the charging current from _Ia1 to _Ia2 . When charging of a lithium-ion secondary battery is started, the value of V/V _min usually increases, and then the charging current can be switched when the value of V/V _min reaches a predetermined value.

In this way, at a certain point in step (A), the charging is switched to a high charging current density, and when the voltage of the lithium ion secondary battery reaches a predetermined value _Va , the charging current is adjusted so as to maintain the predetermined value _Va . is gradually decreased, and the charging is terminated at a predetermined time. By charging the lithium ion secondary battery with the charging method of the present embodiment, it is possible to quickly switch from CC charging to CV charging. In this way, in the step (A), the reason why the charging is temporarily switched to charging at a high charging current density is that the current density of the CV charging is smaller than that of the CC charging. Since the load voltage to the negative electrode becomes smaller when the current density during charging is smaller, it is considered that deposition of metallic lithium on the negative electrode is suppressed. If the timing of switching to charging at a high charging current density in step (A) is delayed, deposition of metallic lithium on the negative electrode may easily occur. Also, if the timing of switching to charging at a high charging current density is early, the amount of heat generated may increase. In step (A), it is appropriate to switch to charging at a high charging current density when the SOC of the lithium ion secondary battery reaches approximately 78 to 85%. As a measure of the SOC of such a lithium ion secondary battery, the amount of change in the voltage value with respect to the charging current value can be used. In embodiments, charging can be switched to high charging current density when the value of V/V _min is 1.9 or greater. In step (A), charging is continued until the voltage of the lithium ion secondary battery reaches a predetermined value _Va after switching to charging at a high charging current density. Here, the predetermined value V _a is 4.0 V or higher, preferably 4.1 V or higher, more preferably 4.2 V or higher. When the voltage of the lithium ion secondary battery reaches a predetermined value _Va , step (B) of performing CV charging so as to maintain the voltage predetermined value _Va can be performed.

A fourth embodiment is a method of controlling charging of the above lithium ion secondary battery. The control method is that charging
(A) a constant current charging step;
(B) a constant voltage charging step;
Through the charging, the charging current value and the voltage value are successively detected, and from the successively detected charging current value and voltage value, the DC resistance value R and the DC resistance value in the charging store the minimum value R _min and
The step (A) is
charging with a predetermined charging current _Ia1 ;
charging with a charging current _Ia2 greater than the predetermined charging current _Ia1 ;
including at least Start charging the lithium ion secondary battery (that is, perform step (A)), perform step (A) until the voltage of the lithium ion secondary battery reaches a predetermined value _Va , and then perform the predetermined voltage V Constant voltage charging is performed while gradually decreasing the charging current so as to maintain _a . Here, in step (A), the DC resistance value R is obtained from the successively detected current value and voltage value, and the ratio of the DC resistance value R to the minimum value R _min of the DC resistance value in step (A) ( R/R _min ) reaches a predetermined value or more, the charging current is increased. For example, charging in step (A) is started at a constant current ₍ I _a1 ), and the ratio (R/R _min ) reaches a predetermined value, the charging current is raised to _Ia2 . At a certain point in step (A), the charging current is increased from _Ia1 to _Ia2 , so that the voltage of the lithium ion secondary battery reaches a predetermined value _Va compared to charging with the constant current of _Ia1 . shorter time to reach. As the timing for increasing the charging current from _Ia1 to _Ia2 , the DC resistance value R of the lithium ion secondary battery can be used. When charging of the lithium ion secondary battery is started, the DC resistance value of the lithium ion secondary battery usually decreases, reaches the minimum DC resistance value R _min in step (A), and then increases. Thereafter, the charging current can be switched when the ratio (R/R _min ) between the DC resistance value R of the lithium ion secondary battery and the minimum DC resistance value R _min in step (A) reaches a predetermined value. .

In this way, at a certain point in step (A), the charging is switched to a high charging current density, and when the voltage of the lithium ion secondary battery reaches a predetermined value _Va , the charging current is adjusted so as to maintain the predetermined value _Va . is gradually decreased, and the charging is terminated at a predetermined time. By charging the lithium ion secondary battery with the charging method of the present embodiment, it is possible to quickly switch from CC charging to CV charging. In this way, in the step (A), the reason why the charging is temporarily switched to charging at a high charging current density is that the current density of the CV charging is smaller than that of the CC charging. Since the load voltage to the negative electrode becomes smaller when the current density during charging is smaller, it is considered that deposition of metallic lithium on the negative electrode is suppressed. If the timing of switching to charging at a high charging current density in step (A) is delayed, deposition of metallic lithium on the negative electrode may easily occur. Also, if the timing of switching to charging at a high charging current density is early, the amount of heat generated may increase. In step (A), it is appropriate to switch to charging at a high charging current density when the SOC of the lithium ion secondary battery reaches approximately 78 to 85%. As a measure of the SOC of such a lithium ion secondary battery, the above R/R _min value can be used. In embodiments, charging can be switched to high charging current density when the value of R/R _min is greater than or equal to 1.9. In step (A), charging is continued until the voltage of the lithium ion secondary battery reaches a predetermined value _Va after switching to charging at a high charging current density. Here, the predetermined value V _a is 4.0 V or higher, preferably 4.1 V or higher, more preferably 4.2 V or higher. When the voltage of the lithium ion secondary battery reaches a predetermined value _Va , step (B) of performing CV charging so as to maintain the voltage predetermined value _Va can be performed.

A fifth embodiment includes a detection unit that detects a current value and a voltage value,
a control unit that changes the magnitude of the charging current based on the detected voltage value;
A control device for charging a lithium ion secondary battery, comprising at least The control device is used for controlling the charging of the above lithium ion secondary battery, and the charging is performed by the following steps:
(A) charging to a predetermined voltage _Va ;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
including at least Start charging the lithium ion secondary battery (that is, perform step (A)), perform step (A) until the voltage of the lithium ion secondary battery reaches a predetermined value _Va , and then perform the predetermined voltage V Constant voltage charging is performed while gradually decreasing the charging current so as to maintain _a . Here, in step (A), when the ratio V/V _min of the sequentially detected voltage value V to the minimum voltage value V _min in step (A) reaches a predetermined value or more, Increase the charging current. For example, charging in step (A) is started at a constant current (I _a1 ), and the ratio of the voltage value V of the lithium ion secondary battery to the minimum voltage value V _min in step (A) (V/V _min ) reaches a predetermined value, the charging current is raised to _Ia2 . At a certain point in step (A), the charging current is increased from _Ia1 to _Ia2 , so that the voltage of the lithium ion secondary battery reaches a predetermined value _Va compared to charging with the constant current of _Ia1 . shorter time to reach. The above V/V _min value can be used as the timing for increasing the charging current from _Ia1 to _Ia2 . When charging of a lithium-ion secondary battery is started, the value of V/V _min usually increases, and then the charging current can be switched when the value of V/V _min reaches a predetermined value.

In this way, at a certain point in step (A), the charging is switched to a high charging current density, and when the voltage of the lithium ion secondary battery reaches a predetermined value _Va , the charging current is adjusted so as to maintain the predetermined value _Va . is gradually decreased, and the charging is terminated at a predetermined time. By charging the lithium ion secondary battery with the charging method of the present embodiment, it is possible to quickly switch from CC charging to CV charging. In this way, in the step (A), the reason why the charging is temporarily switched to charging at a high charging current density is that the current density of the CV charging is smaller than that of the CC charging. Since the load voltage to the negative electrode becomes smaller when the current density during charging is smaller, it is considered that deposition of metallic lithium on the negative electrode is suppressed. If the timing of switching to charging at a high charging current density in step (A) is delayed, deposition of metallic lithium on the negative electrode may easily occur. Also, if the timing of switching to charging at a high charging current density is early, the amount of heat generated may increase. In step (A), it is appropriate to switch to charging at a high charging current density when the SOC of the lithium ion secondary battery reaches approximately 78 to 85%. As a measure of the SOC of such a lithium ion secondary battery, the amount of change in the voltage value with respect to the charging current value can be used. In embodiments, charging can be switched to high charging current density when the value of V/V _min is 1.9 or greater. In step (A), charging is continued until the voltage of the lithium ion secondary battery reaches a predetermined value _Va after switching to charging at a high charging current density. Here, the predetermined value V _a is 4.0 V or higher, preferably 4.1 V or higher, more preferably 4.2 V or higher. When the voltage of the lithium ion secondary battery reaches a predetermined value _Va , step (B) of performing CV charging so as to maintain the voltage predetermined value _Va can be performed.

A sixth embodiment includes a detection unit that detects a current value and a voltage value,
a calculation unit that calculates a DC resistance value from each detected value;
a control unit that changes the magnitude of the charging current based on the calculated change in the DC resistance;
A control device for charging a lithium ion secondary battery, comprising at least The control device is used for controlling the charging of the above lithium ion secondary battery, and the charging is performed by the following steps:
(A) charging with a predetermined charging current up to _a predetermined voltage Va;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
including at least Start charging the lithium ion secondary battery (that is, perform step (A)), perform step (A) until the voltage of the lithium ion secondary battery reaches a predetermined value _Va , and then perform the predetermined voltage V Constant voltage charging is performed while gradually decreasing the charging current so as to maintain _a . Here, in step (A), the DC resistance value R is obtained from the successively detected current value and voltage value, and the ratio of the DC resistance value R to the minimum value R _min of the DC resistance value in step (A) ( R/R _min ) reaches a predetermined value or more, the charging current is increased. For example, charging in step (A) is started at a constant current ₍ I _a1 ), and the ratio (R/R _min ) reaches a predetermined value, the charging current is raised to _Ia2 . At a certain point in step (A), the charging current is increased from _Ia1 to _Ia2 , so that the voltage of the lithium ion secondary battery reaches a predetermined value _Va compared to charging with the constant current of _Ia1 . shorter time to reach. As the timing for increasing the charging current from _Ia1 to _Ia2 , the DC resistance value R of the lithium ion secondary battery can be used. When charging of the lithium ion secondary battery is started, the DC resistance value of the lithium ion secondary battery usually decreases, reaches the minimum DC resistance value R _min in step (A), and then increases. Thereafter, the charging current can be switched when the ratio (R/R _min ) between the DC resistance value R of the lithium ion secondary battery and the minimum DC resistance value R _min in step (A) reaches a predetermined value. .

In this way, at a certain point in step (A), the charging is switched to a high charging current density, and when the voltage of the lithium ion secondary battery reaches a predetermined value _Va , the charging current is adjusted so as to maintain the predetermined value _Va . is gradually decreased, and the charging is terminated at a predetermined time. By charging the lithium ion secondary battery with the charging method of the present embodiment, it is possible to quickly switch from CC charging to CV charging. In this way, in the step (A), the reason why the charging is temporarily switched to charging at a high charging current density is that the current density of the CV charging is smaller than that of the CC charging. Since the load voltage to the negative electrode becomes smaller when the current density during charging is smaller, it is considered that deposition of metallic lithium on the negative electrode is suppressed. If the timing of switching to charging at a high charging current density in step (A) is delayed, deposition of metallic lithium on the negative electrode may easily occur. Also, if the timing of switching to charging at a high charging current density is early, the amount of heat generated may increase. In step (A), it is appropriate to switch to charging at a high charging current density when the SOC of the lithium ion secondary battery reaches approximately 78 to 85%. As a measure of the SOC of such a lithium ion secondary battery, the above R/R _min value can be used. In embodiments, charging can be switched to high charging current density when the value of R/R _min is greater than or equal to 1.9. In step (A), charging is continued until the voltage of the lithium ion secondary battery reaches a predetermined value _Va after switching to charging at a high charging current density. Here, the predetermined value V _a is 4.0 V or higher, preferably 4.1 V or higher, more preferably 4.2 V or higher. When the voltage of the lithium ion secondary battery reaches a predetermined value _Va , step (B) of performing CV charging so as to maintain the voltage predetermined value _Va can be performed.

In the charging method and control method of the embodiment, the significance of controlling early switching from CC charging to CV charging by switching to charging at a high charging current density at a certain point in step (A) is as follows. to explain. FIG. 1 shows a lithium ion secondary battery using a positive electrode active material containing at least lithium manganese iron phosphate (LMFP) and a transition metal lithium oxide with a layered structure at a charge rate of 1C (in the case of FIG. 1, the charge current density is 2.7 mA/cm ² ) shows the relationship between the SOC (horizontal axis) and the DC resistance value (vertical axis) of the battery when it is charged at a constant current. When charging of a lithium ion secondary battery using a positive electrode active material containing at least lithium manganese iron phosphate and a transition metal lithium oxide having a layered structure is started at a charge rate of 1 C, for example, the DC resistance value R gradually decreases. (up to about 30% SOC) and then increase. After that, the DC resistance value R suddenly decreases, and the minimum value R _min of the DC resistance value is recorded when the SOC reaches about 60%. The DC resistance value R of a lithium ion secondary battery using a positive electrode active material containing at least lithium manganese iron phosphate and a transition metal lithium oxide with a layered structure behaves as described above because lithium manganese iron phosphate This is because the oxidation-reduction reaction of is in two stages, that is, a trivalent/divalent oxidation-reduction reaction of iron (Fe) occurs on the low potential side and manganese (Mn) occurs on the high potential side. CC charging is continued at the 1C rate, and the charging rate (charging current density) is increased when the ratio R/ _Rmin of the DC resistance value R to the minimum DC resistance value _Rmin reaches a predetermined value. (eg 2C). In FIG. 1, it is preferable to switch to high charge current density charging in the range where the SOC is about 78-85%. Switch to high current density charging and continue CC charging as it is, switch to CV charging when the battery voltage reaches a predetermined value (for example, 4.3 V), charge while maintaining the battery voltage, and charge at a predetermined time exit. Thus, it is important to increase the CC charging rate and shorten the CC charging time when the SOC of the battery reaches 78-85. As a result, the amount of heat generated by the lithium ion secondary battery can be suppressed, and deposition of metallic lithium on the negative electrode can be prevented. If the charging is switched to the high charging current density charging before the SOC reaches the above % range, the lithium ion secondary battery may generate a large amount of heat. Also, if the SOC exceeds the above range of 78 to 85% and the charging is switched to the high charging current density charging, the deposition of metallic lithium cannot be effectively prevented. Therefore, switching to high current density charging during CC charging should be performed while the SOC of the battery is 78 to 85%.

In the positive electrode active material containing lithium manganese iron phosphate and a layered structure transition metal lithium oxide, when the mixing ratio of lithium manganese iron phosphate is increased, it is possible to switch to high charging current density charging at a slightly lower SOC. preferable. This is because the higher the mixing ratio of LMFP, the higher the ratio of the reaction region of the Mn plateau of LMFP to the whole, and the higher voltage is reached at a low SOC. If the charging is not switched to the high charging current density charging at a low SOC, the CC charging time at a high voltage becomes longer and the deterioration due to lithium deposition increases. For example, in a positive electrode active material containing lithium manganese iron phosphate and a transition metal lithium oxide with a layered structure, a lithium ion secondary battery using a positive electrode with a mixture ratio of 20% by mass of lithium manganese iron phosphate is charged. In this case, the timing of shifting to high charging current density charging is when the SOC of the battery reaches 78 to 85%. When charging an ion secondary battery, the timing of shifting to high charging current density charging is when the SOC of the battery is lower than the above range. In order to detect that the SOC of the lithium ion secondary battery has reached the above range during charging, for example, a DC resistance value R obtained from the successively detected current value and voltage value, and the DC resistance value The ratio R/ _Rmin of the minimum value _Rmin , the amount of change in the voltage value with respect to the charging current value, and the ratio V/ _Vmin between the sequentially detected voltage value V and the minimum voltage value _Vmin can be used. . Using these values, in step (A) in the charging method of the embodiment, by switching to high charging current density charging at an appropriate timing, the time for CV charging of the lithium ion secondary battery is shortened, thereby Since the amount of heat generated by the battery can be suppressed and the deposition of metallic lithium can also be prevented, the cycle characteristics of the lithium ion secondary battery can be improved and the life can be extended.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited by these.

<Production of secondary battery>
A lithium-nickel-manganese-cobalt composite oxide (LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , “NMC532”), which is a positive electrode active material, and lithium manganese iron phosphate (LiMn _0.7 Fe 0.7 Fe 0.2 O _{2 ). 3} PO ₄ , "LMFP", Taiheiyo Cement Co., Ltd.) at a ratio of 80:20, and 0.6% by weight of carbon nanotubes as a conductive agent and polyvinylidene fluoride (PVDF) (Kureha Co., Ltd.) was mixed with 2.0% by weight to obtain a positive electrode mixture. A slurry obtained by dispersing this positive electrode mixture in N-methyl-2-pyrrolidone (NMP) was applied to an aluminum foil having a thickness of 16 μm, dried and pressed to obtain a basis weight of 19 mg/cm ² and a coating thickness per side. A positive electrode was obtained in which a positive electrode active material layer was formed to have a thickness of 55 μm. Different positive electrodes were produced by changing the mixing ratio of the lithium-nickel-manganese-cobalt composite oxide and the lithium manganese iron phosphate as shown in Table 1 below.
On the other hand, a negative electrode mixture was obtained by mixing graphite with 2.5% by weight of styrene-butadiene rubber (SBR) as a binder and 2.5% by weight of carboxymethyl cellulose (CMC) as a thickener. A slurry obtained by dispersing this negative electrode mixture in water (H ₂ O) is coated on a copper foil with a thickness of 8 μm, dried and pressed to obtain a basis weight of 10 mg/cm ³ and a coating thickness of 72 μm per side. Thus, a negative electrode having a negative electrode active material layer formed thereon was obtained.
The separator used was a polypropylene porous membrane (overall thickness: 24 μm) coated with alumina particles on one side.
As an electrolytic solution, non-aqueous solvent ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:1:1 (volume ratio), electrolyte lithium hexafluorophosphate ( _LiPF6 ) was dissolved at a concentration of 1M.

Each of the above positive electrodes (4 × 3 cm), a separator (4.5 × 3.5 cm), and a negative electrode (4.2 × 3.2 cm) are superimposed to prepare a battery element, which is attached to the positive electrode tab and the negative electrode. Created a tab. Together with the electrolytic solution having a volume twice the sum of the pore volume of the positive electrode and the pore volume of the separator (each unit: milliliters), the battery element provided with a tab was covered with an aluminum laminate film (thickness: 110 μm) (Dainippon Printing Co., Ltd.) and sealed around the exterior to obtain a laminated cell (secondary battery) with a cell capacity of 40 mAh.

<Charge/discharge of secondary battery>
[Initial charge/discharge]
Initial charge/discharge of the laminate type cell produced as described above was performed. In the initial charge and discharge, constant current and constant voltage (CC-CV) charging was performed at an ambient temperature of 25°C, a current of 0.2C, an upper limit voltage of 4.2V, and a cutoff of 0.05C. A constant current (CC) discharge at 2C current was performed.

[Charging conditions after the second cycle]
Charge/discharge was performed on the laminate type cell that had been charged/discharged for the first time as described above. First, charging conditions for each laminate type cell were different as shown in Table 1.
In Example 1, the mixture ratio of LMFP in the positive electrode active material: 20 parts by mass of the battery was charged under the following charging conditions: set temperature: 25 ° C., charging rate at the start of charging: 1 C, charging during high charging current density charging. Rate: 2C (The transition timing to high charging current density charging is the ratio R/R _min of the DC resistance value R to the minimum value R _min in the charging process when the SOC of the laminated cell is 78% (see Table 1 was described as "resistance relative value") and was charged at 1.9.
In Example 2, the mixture ratio of LMFP in the positive electrode active material: 20 parts by mass of the battery was charged under the following charging conditions: set temperature: 25 ° C., charging rate at the start of charging: 1 C, charging during high charging current density charging. Rate: 2C (The timing of transition to high charging current density charging is when the SOC of the laminated cell is 80% and the ratio R/R _min of the DC resistance value R to the minimum value R _min in the charging process of the DC resistance value R (see Table 1 was described as "resistance relative value") and was charged at 2.0.
In addition, in Example 3, the following charging conditions were set for a battery having a mixture ratio of LMFP in the positive electrode active material of 20 parts by mass; Charging rate: 2C (The timing of transition to high charging current density charging is when the SOC of the laminated cell is 85% and the ratio R/R _{min of the DC resistance value R to the minimum value R min} of the DC resistance value in the charging process in the charging process R/R _min (Table 1 described as "resistance relative value") 2.2, charging was performed.

On the other hand, in Comparative Example 1, a battery with a mixture ratio of LMFP in the positive electrode active material: 20 parts by mass was charged under the following charging conditions: set temperature: 25 ° C., charging rate at the start of charging: 1 C (charging no current density switching).
In Comparative Example 2, a battery having a mixture ratio of LMFP in the positive electrode active material of 20 parts by mass was charged under the following charging conditions: set temperature: 25°C, charging rate at the start of charging: 2C (charging current density no switching).
In Comparative Example 3, a battery with a mixture ratio of LMFP in the positive electrode active material: 20 parts by mass was charged under the following charging conditions: set temperature: 25 ° C., charging rate at the start of charging: 1 C, high charging current density charging. Rate: 2C (The timing of transition to high charging current density charging is when the SOC of the laminated cell is 75% and the ratio R/R _min of the DC resistance value R to the minimum value R _min in the charging process of the DC resistance value R (see Table 1 described as "resistance relative value") 1.2, was charged.
Furthermore, in Comparative Example 4, a battery having a mixture ratio of LMFP in the positive electrode active material of 0 parts by mass was charged under the following charging conditions: set temperature: 25°C, charging rate at the start of charging: 1C (charging current without density switching).

[Discharge conditions after the second cycle]
In each example and comparative example, constant-current charging was performed until the battery voltage reached 4.3 V, and then the charging was terminated by switching to constant-voltage charging. After that, constant current discharge (CC discharge) was performed under the following discharge conditions: a set temperature of 25° C. on the cell surface, a lower limit voltage of 2.8 V, and a current density of 2.7 mA/cm ² (1 C).
In each example and comparative example, one cycle was defined as a combination of charging under each of the above conditions and discharging under this condition. Each battery was charged and discharged for 2000 cycles.
The ratio of the cell capacity after 1000 cycles of charge/discharge to the cell capacity after the first charge/discharge and the cell capacity after 2000 cycles of charge/discharge were calculated.
Also, the difference between the maximum cell surface temperature reached during 2000 cycles of charging and discharging and the temperature before the start of charging was recorded.

In the SOC range or resistance relative value range of the present invention, when charging is performed by switching to a high charging current density, heat generation of the battery during charging and discharging can be suppressed and cycle characteristics can be improved. On the other hand, if charging is performed without switching to a high charging current density, the heat generation of the battery can be suppressed, but the decrease in the capacity retention rate cannot be avoided (Comparative Example 1), or the heat generation of the battery can be suppressed. Not possible (Comparative Example 2). In addition, there is a suitable timing for switching to charging at a high charging current density, and even if charging is switched to a high charging current density when this timing is not met, it is possible to avoid heat generation of the battery and a decrease in the capacity retention rate. It turned out that it cannot (comparative example 3).

When a lithium ion secondary battery is charged by the charging method of the present invention, heat generation of the battery during charging and discharging can be suppressed, and deterioration of battery capacity due to cyclic charging and discharging can be suppressed, so that the life of the battery can be extended.

Claims (10)

The following steps:
(A) charging to a predetermined voltage _Va ;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
A method of charging a lithium ion secondary battery by charging at least including
The lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a current collector, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution,
The positive electrode active material layer includes a first positive electrode active material, lithium manganese iron phosphate,
A transition metal lithium oxide having a layered structure, which is the second positive electrode active material;
including at least
In the step (A), the ratio R/R _min of the DC resistance value R obtained from the successively detected current value and voltage value to the minimum value R _min of the DC resistance value in the step (A) is predetermined. increasing the charging current when it reaches a predetermined value or higher;
A method for charging the lithium ion secondary battery. The lithium ion secondary battery according to claim 1, wherein the charging current is increased when the _Va is 4.0 V or more and the R/R _min value is 1.9 or more. charging method. The following steps:
(A) charging to a predetermined voltage _Va ;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
A method of charging a lithium ion secondary battery by charging at least including
The lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a current collector, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution,
The positive electrode active material layer includes a first positive electrode active material, lithium manganese iron phosphate,
A transition metal lithium oxide having a layered structure, which is the second positive electrode active material;
including at least
In the step (A), when the amount of change in the voltage value with respect to the charging current value reaches a predetermined value or more, the charging current is increased;
A method for charging the lithium ion secondary battery. 4. The lithium according to claim 3, wherein the charging current is increased when the _Va is 4.0 V or more and the amount of change in voltage value with respect to the charging current value is 0.25 mV/A or more. A charging method for an ion secondary battery. The following steps:
(A) charging with a predetermined charging current up to _a predetermined voltage Va;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
A method of charging a lithium ion secondary battery by constant current constant voltage charging including at least
The lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a current collector, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution,
The positive electrode active material layer includes a first positive electrode active material, lithium manganese iron phosphate,
A transition metal lithium oxide having a layered structure, which is the second positive electrode active material;
including at least
In the step (A), when the ratio V/V _min of the sequentially detected voltage value V to the minimum voltage value V _min in the step (A) reaches a predetermined value or more, the charging increase the current,
A method for charging the lithium ion secondary battery. 6. The lithium ion secondary battery according to claim 5, wherein the charging current is increased when the _Va is 4.0 V or more and the V/V _min value is 1.9 or more. charging method. A method for controlling charging of a lithium ion secondary battery, comprising:
the charging is
(A) a constant current charging step;
(B) a constant voltage charging step;
Through the charging, the charging current value and the voltage value are successively detected, and from the successively detected charging current value and voltage value, the DC resistance value R and the DC resistance value in the charging store the minimum value R _min and
The step (A) is
charging with a predetermined charging current _Ia1 ;
charging with a charging current _Ia2 greater than the predetermined charging current _Ia1 ;
including
In the step (A),
starting constant current charging with the charging current _Ia1 ,
In the step (A), when the value of the ratio R/ _Rmin of the DC resistance value R and the minimum DC resistance value _Rmin reaches a predetermined value or more, the charging current _Ia2 switching and charging until said voltage reaches a predetermined voltage _Va ;
After the voltage reaches the predetermined voltage _Va , step (B) is performed while gradually decreasing the charging current so as to maintain the predetermined voltage _Va . 8. The method of claim 7, wherein the charging current is switched to _Ia2 when the _Va is greater than or equal to 4.0V and the R/ _Rmin value is greater than or equal to 1.9. a detection unit that detects a current value and a voltage value;
a control unit that changes the magnitude of the charging current based on the detected voltage value;
A control device for charging a lithium ion secondary battery, comprising at least
The charging of the lithium ion secondary battery comprises the following steps:
(A) charging to a predetermined voltage _Va ;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
is a charge that includes at least
The lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a current collector, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution,
The positive electrode active material layer includes a first positive electrode active material, lithium manganese iron phosphate,
A transition metal lithium oxide having a layered structure, which is the second positive electrode active material;
including at least
In the step (A), when the ratio V/V _min of the sequentially detected voltage value V to the minimum voltage value V _min in the step (A) reaches a predetermined value or more, the control increases the charging current;
A control device for charging the lithium ion secondary battery. a detection unit that detects a current value and a voltage value;
a calculation unit that calculates a DC resistance value from each detected value;
a control unit that changes the magnitude of the charging current based on the calculated change in the DC resistance;
A control device for charging a lithium ion secondary battery, comprising at least
The charging of the lithium ion secondary battery comprises the following steps:
(A) charging with a predetermined charging current up to _a predetermined voltage Va;
(B) after reaching the predetermined voltage _Va , performing constant voltage charging while gradually decreasing the charging current so as to maintain the predetermined voltage _Va ;
is a charge that includes at least
The lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a current collector, a negative electrode having a negative electrode active material layer formed on a current collector, and an electrolytic solution,
The positive electrode active material layer includes a first positive electrode active material, lithium manganese iron phosphate,
A transition metal lithium oxide having a layered structure, which is the second positive electrode active material;
including at least
In the step (A), the calculation unit calculates the DC resistance value R from the current value and the voltage value sequentially detected by the detection unit, and the DC resistance value R _min in the step (A) when the ratio R/R _min reaches a predetermined value or more, the control unit increases the charging current;
A control device for charging the lithium ion secondary battery.

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