JP2017103141A - Secondary battery device, and method for discharging nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery device which enables the improvement of a secondary battery in output characteristic in charging subsequent to discharge; and a method for discharging the nonaqueous electrolyte secondary battery.SOLUTION: A secondary battery device 1 according to the present invention comprises: a nonaqueous electrolyte secondary battery 20 having a positive electrode 21 including a positive electrode active material showing two-phase coexisting type reaction, a negative electrode 22, and a nonaqueous electrolyte 23 including alkali-metal ions and a nonaqueous solvent; and a charge-discharge controller 3 for controlling the charge and discharge of the nonaqueous electrolyte secondary battery 20. In the secondary battery device 1, the charge-discharge controller 3 performs the discharge of the nonaqueous electrolyte secondary battery 20 after the charge thereof. The crystallite diameter (X[nm]) and volume change rate (Y[%]) of the positive electrode active material satisfy a relation given by the expression (1) below. A discharging method according to the invention comprises the step of discharging the nonaqueous electrolyte secondary battery 20 after the charge thereof.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a secondary battery device and a discharge method for a nonaqueous electrolyte secondary battery, and more particularly, a secondary battery device that discharges a nonaqueous electrolyte secondary battery including a positive electrode active material that exhibits a two-phase coexistence type reaction. And a discharge method.

  With the spread of notebook computers, mobile phones, digital cameras, etc., the demand for secondary batteries for driving these small electronic devices is increasing. And since these electronic devices can be increased in capacity, the use of nonaqueous electrolyte secondary batteries (particularly lithium ion secondary batteries) is being promoted.

  Non-aqueous electrolyte secondary batteries are used in small electronic devices, as well as vehicles such as electric vehicles (EV vehicles), hybrid vehicles (HV vehicles), plug-in hybrid vehicles (PHV vehicles), and home energy management systems ( Application to a use requiring high power such as a household power source such as HEMS) is also being studied. In this case, a large amount of power can be generated by means such as increasing the size of the electrode plate of the nonaqueous electrolyte secondary battery, stacking a large number of electrode plates to form an electrode body, or combining a large number of battery cells into an assembled battery. I try to get it.

A lithium ion secondary battery, which is one form of a non-aqueous electrolyte secondary battery, can be used repeatedly for charge and discharge because each electrode active material has excellent reversibility of insertion and extraction of lithium.
For example, Patent Document 1 describes a secondary battery device using a lithium ion secondary battery.

  Patent Document 1 discloses a secondary battery device comprising: a secondary battery having a positive electrode active material that performs charge and discharge in a two-phase coexistence type; and a control unit that controls charge and discharge of the secondary battery, When the amount of electricity required to increase the SOC of the secondary battery by 5% is set as the first reference value, the control means performs control for discharging the secondary battery, and then controls the secondary battery. On the other hand, there is described a secondary battery device that performs control for charging an amount of electricity equal to or higher than the first reference value.

JP 2010-73498 A

  In conventional lithium ion secondary batteries (secondary battery devices), it is considered to reduce the particle size of the positive electrode active material in order to enable quick charge / discharge at high power (to improve charge / discharge characteristics). Has been. And in the conventional lithium ion secondary battery, when the particle diameter of the positive electrode active material was reduced, there was a problem that the resistance in charging after discharging increased. This problem is particularly caused by the difference in the diffusion rate of Li ions diffusing the two-phase coexisting positive electrode active material. That is, the conventional secondary battery (secondary battery device) has a problem that the battery characteristics are deteriorated under specific charge / discharge conditions.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the secondary battery apparatus which can improve the output characteristic of the secondary battery in charge after discharge, and the discharge method of a nonaqueous electrolyte secondary battery. .

  In order to solve the above problems, the present inventors have completed the present invention as a result of repeated studies on a secondary battery device and a discharge method using a positive electrode active material having a two-phase coexistence type reaction.

  The secondary battery device of the present invention is a non-aqueous battery comprising a positive electrode including a positive electrode active material exhibiting a two-phase coexistence reaction, a negative electrode, and a non-aqueous electrolyte including an alkali metal ion and a non-aqueous solvent. An electrolyte secondary battery and a charge / discharge control device that controls charge / discharge of the nonaqueous electrolyte secondary battery, and the charge / discharge control device discharges after the nonaqueous electrolyte secondary battery is charged. A secondary battery device, wherein the crystallite diameter (X [nm]) of the positive electrode active material and the volume change rate (Y [%]) satisfy the relationship of the formula (1).

X-((1-0.01Y) X ³ ) ^1/3 ≧ 0.96 (1)

  The secondary battery device of the present invention discharges after charging a nonaqueous electrolyte secondary battery using an active material having a two-phase coexistence type reaction. Then, when the crystallite diameter (X) and the volume change rate (Y) of the positive electrode active material satisfy the relationship of the expression (1), the resistance (specifically, discharge resistance) increases in the discharge after charging. Is suppressed. As a result, the output characteristics of the secondary battery are improved.

  In the secondary battery device of the present invention, the charge / discharge control device discharges immediately after the nonaqueous electrolyte secondary battery is charged. According to this configuration, since the discharge is performed before the change in the state of the positive electrode active material due to charging is eliminated (relaxation behavior is completed), an increase in resistance can be reliably suppressed.

The nonaqueous electrolyte secondary battery discharge method of the present invention includes a positive electrode including a positive electrode active material exhibiting a two-phase coexistence reaction, a negative electrode, a nonaqueous electrolyte including an alkali metal ion and a nonaqueous solvent, A discharge method for a non-aqueous electrolyte secondary battery that controls discharge of a non-aqueous electrolyte secondary battery including a crystallite diameter (X [nm]) of a positive electrode active material and a volume change rate (Y [%]) Is discharged after the non-aqueous electrolyte secondary battery is charged, satisfying the relationship of formula (1).
The discharge method of the present invention is a discharge method in the above secondary battery device, and can exhibit the above effects.

1 is a diagram illustrating a configuration of a secondary battery device according to Embodiment 1. FIG. 1 is a diagram illustrating a configuration of a secondary battery according to Embodiment 1. FIG. 3 is a diagram showing a configuration in a state where Li ions form a solvate in the secondary battery of Embodiment 1. FIG. It is a figure which shows the state which the solvate of Embodiment 1 entered into the crack of the positive electrode active material. FIG. 3 is a diagram illustrating a discharging operation of the secondary battery device according to the first embodiment. 4 is a diagram illustrating a configuration of a secondary battery device according to Embodiment 2. FIG. It is a figure which shows the structure of the secondary battery apparatus of Embodiment 3. 6 is a perspective view illustrating a configuration of a secondary battery according to Embodiment 4. FIG. 6 is a cross-sectional view illustrating a configuration of a secondary battery according to Embodiment 4. FIG.

Hereinafter, the present invention will be described using specific embodiments.
As the secondary battery device and discharge method of the present invention, this embodiment will be described using a secondary battery device formed using a lithium ion secondary battery as a secondary battery and a discharge method thereof.

[Embodiment 1]
The secondary battery device 1 of the present embodiment includes an assembled battery 2 in which a plurality of lithium ion secondary batteries 20 are combined, a charge / discharge control device 3, and an external load unit 4. The structure of the secondary battery device 1 of this embodiment is shown in FIG.

[Battery]
The assembled battery 2 is charged and discharged with respect to the external load unit 4 via the charge / discharge control device 3. The assembled battery 2 is configured by combining a plurality of lithium ion secondary batteries 20. In the assembled battery 2, the combination of the plurality of secondary batteries 20 may be connected in series, connected in parallel, or combined in series and parallel. In this embodiment, it is a series connection.
In this embodiment, the assembled battery 2 is used as a battery that charges and discharges with respect to the external load unit 4 via the charge / discharge control device 3, but a single battery may be used.

[Lithium ion secondary battery]
The lithium ion secondary battery 20 is a secondary battery using a positive electrode active material having a two-phase coexistence type reaction. The secondary battery 20 is not limited to the configuration other than the positive electrode active material, and can be configured in the same manner as a conventional lithium ion secondary battery.
The secondary battery 20 includes a positive electrode 21, a negative electrode 22, and a nonaqueous electrolyte 23. The configuration of the secondary battery 20 is shown in FIG.

[Positive electrode]
The positive electrode 21 has a positive electrode active material layer 211 containing a positive electrode active material on the surface of the positive electrode current collector 210. The positive electrode active material layer 211 is formed by applying a positive electrode mixture obtained by mixing a positive electrode active material, a conductive material, and a binder to the surface of the positive electrode current collector 210 and drying (coating). It is formed). That is, the positive electrode active material layer 211 has a layer shape in which the positive electrode active material, the conductive material, and the binder are uniformly dispersed. Here, the conductive material and the binder are arbitrary and may not be mixed. The positive electrode mixture is made into a paste (slurry) with an appropriate solvent.

[Positive electrode active material]
As the positive electrode active material, a compound capable of occluding and releasing lithium ions (electrolyte ions and alkali metal ions of nonaqueous electrolyte secondary batteries) is used. Examples thereof include various oxides, sulfides, lithium-containing oxides, and conductive polymers. As the positive electrode active material, it is preferable to use a lithium-transition metal composite oxide.

  As the lithium-transition metal composite oxide of the positive electrode active material, it is more preferable to use a composite oxide having a layered structure, a composite oxide having a spinel structure, or a composite oxide having a polyanion structure.

  As the positive electrode active material of this embodiment, a compound showing a two-phase coexistence type reaction is used. And it is more preferable that it is a compound of the olivine structure which is 1 type of a polyanion structure as a compound which shows a two-phase coexistence type reaction.

Examples of the olivine structure compound include LiFePO ₄ and Li _x Mn _y M _1-y X _z O _{5 -z} (M: one or more selected from transition metals except M: Mn, X: P, As, Si, One or more selected from Mo and one or more selected from X: Al, Mg, Ca, Zn, Ti can be optionally contained, 0 <x ≦ 1.0, 0 ≦ y <1.0, 0 ≦ z ≦ 1.5). In this composition, y is preferably 0.4 or more, and more preferably 0.6 or more.

The composite oxide having a layered structure is, for example, LiNi _x Co _y Mn _z O ₂ (x + y + z = 1, 0 ≦ x, y, z ≦ 1), LiNi _x Al _w Mn _z O ₂ (x + w + z = 1, 0 ≦ x, w, z ≦ 1), LiNi _x Co _y Al _w Mn _z O ₂ (x + y + w + z = 1, 0 ≦ x, y, w, z ≦ 1), specifically, LiNi _0.4 An example is Co _0.4 Mn _0.2 O ₂ .
Examples of the composite oxide having spinel include LiNi _x M _y Mn _z O ₄ (x + y + z = 2, 0 ≦ x, y, z ≦ 2).

  In the positive electrode active material, the crystallite diameter (X [nm]) and the volume change rate (Y [%]) satisfy the relationship of the above formula (1). In addition, the numerical value 0.96 on the right side in the equation (1) is a value obtained by rounding off the third digit after the decimal point, and the value calculated from the left side is similarly rounded.

  A compound exhibiting a two-phase coexistence reaction (positive electrode active material) undergoes a volume change when charged and discharged (when Li ions are occluded / desorbed). A compound having a large volume change rate (Y) has a large volume change. In particular, when charging is performed, Li ions are desorbed and volume reduction (shrinkage) occurs. This volume reduction occurs for each crystallite. Then, separation occurs at the crystallite interface, and cracks are generated in the positive electrode active material particles. As a result, the surface area of the positive electrode active material particles is increased, the contact area with Li ions (electrolyte ions) is increased, and the surface area capable of storing Li ions is increased. That is, battery characteristics are improved.

  When the positive electrode active material satisfies the relationship of the above formula (1), a crack having a size that allows Li ions to enter the inside is formed. Furthermore, Li ions can enter the cracks in a solvated state. If it becomes so, the effect that the contact area of Li ion increases reliably can be exhibited.

  As for the crystallite diameter (X [nm]) and the volume change rate (Y [%]) of the positive electrode active material, it is preferable that Z represented by the formula (2) is 0.96 ≦ Z ≦ 20. More preferably, 96 ≦ Z ≦ 10, and more preferably 0.96 ≦ Z ≦ 5. Z corresponds to the left side of the above equation (1).

Z = X − ((1-0.01Y) X ³ ) ^1/3 (2)

Specific examples of the positive electrode active material include LiFePO ₄ , LiMn _0.7 Fe _0.3 PO ₄ , LiMnPO ₄ , and LiMn ₂ O ₄ .
LiFePO ₄ is a compound having an olivine structure, the volume change rate (Y) is 7 [%], and the crystallite diameter (X) is in the range of 40 [nm] or more. The upper limit of the crystallite diameter (X) is not limited, but is preferably 100 [nm] or less.
LiMn _0.7 Fe _0.3 PO ₄ is a compound having an olivine structure, the volume change rate (Y) is 9 [%], and the crystallite diameter (X) is in the range of 31 [nm] or more. . The upper limit of the crystallite diameter (X) is not limited, but is preferably 100 [nm] or less.
LiMnPO ₄ is a compound having an olivine structure, the volume change rate (Y) is 10 [%], and the crystallite diameter (X) is 28 [nm] or more. The upper limit of the crystallite diameter (X) is not limited, but is preferably 100 [nm] or less.
LiMn ₂ O ₄ is a compound having a spinel structure, the volume change rate (Y) is 5 [%], and the crystallite diameter (X) is 57 [nm] or more. The upper limit of the crystallite diameter (X) is not limited, but is preferably 500 [nm] or less.

Note that the crystallite diameter (X [nm]) of the positive electrode active material can be measured and calculated using an XRD apparatus. For example, it can be measured by the measuring method described in the examples described later.
Regarding the volume change rate (Y [%]), the lattice volume in the fully discharged state and the fully charged state may be measured by XRD, or a known numerical value may be used.

  The positive electrode active material is preferably a two-phase coexisting compound (hereinafter referred to as the compound of the present invention) that satisfies the relationship of the above formula (1), but with a known positive electrode active material other than the compound of the present invention. It may be a mixture. In this case, the Li diffusion coefficient is preferably larger than that of the compound of the present invention.

  When the positive electrode active material is a mixture, the mixing ratio is not limited, but the compound of the present invention is rich, that is, the total number of Li atoms of the positive electrode active material is 100 [%]. Sometimes, it is preferable that the number of Li atoms in the compound of the present invention is 50% or more. In addition, when the total mass of the positive electrode active material is 100 [mass%], the mass of the compound of the present invention is preferably 50 [mass%] or more.

  The production method of the positive electrode active material is not limited, and can be produced using a conventionally known production method. The positive electrode active material may form secondary particles in which primary particles are aggregated. The shape of the primary particles is not limited, and examples thereof include scaly, spherical, and potato-like shapes. The olivine-structured positive electrode active material preferably has a crystallite diameter of 100 [nm] or less. The spinel-type positive electrode active material preferably has a crystallite diameter of 500 [nm] or less. The primary particles preferably have a minor axis of 1 [μm] or less, and more preferably 500 [μm] or less. The primary particles are more preferably substantially spherical particles having a particle size (for example, average particle size, D50) of 1 [μm] or less, and the particle size is 0.5 [μm] (500 [nm]) or less. More preferably.

[Conductive material, binder, composite material, positive electrode current collector]
The conductive material ensures the electrical conductivity of the positive electrode 21. Examples of the conductive material include graphite fine particles, carbon black (CB) such as acetylene black (AB), ketjen black (KB), and carbon nanofiber (CNF), and amorphous carbon fine particles such as needle coke. However, it is not limited to these.

  The binder of the positive electrode mixture binds the positive electrode active material particles and the conductive material. Examples of the binder include, but are not limited to, polyvinylidene fluoride (PVDF), EPDM, SBR, NBR, and fluororubber.

  As the solvent for the positive electrode mixture, an organic solvent that dissolves the binder is usually used. Examples include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like. Although it can, it is not limited to these. In some cases, a positive electrode active material is slurried with polytetrafluoroethylene (PTFE) by adding a dispersant, a thickener, or the like to water.

  As the positive electrode current collector 210, a conventional current collector can be used, and a processed metal such as aluminum, for example, a foil processed into a plate shape, a net, a punched metal, a foam metal, or the like can be used. However, it is not limited to these.

  The thickness of the positive electrode current collector 210 is not limited. The thickness can be the same as that of the positive electrode current collector that has been used. The thickness of the positive electrode current collector 210 is preferably 20 [μm] or less. For example, it is preferable to use a foil having a thickness of about 15 [μm].

[Negative electrode]
The negative electrode 22 contains a negative electrode active material. The negative electrode 22 has a negative electrode active material layer 221 on the surface of the negative electrode current collector 220. The negative electrode active material layer 221 is formed by applying a negative electrode mixture obtained by mixing a negative electrode active material, a conductive material, and a binder to the surface of the negative electrode current collector 220 and drying (coating). It is formed). That is, the negative electrode active material layer 221 has a layer shape in which the negative electrode active material, the conductive material, and the binder are uniformly dispersed. Here, the conductive material and the binder are arbitrary and may not be mixed. The negative electrode mixture is made into a paste (slurry) with an appropriate solvent.

[Negative electrode active material]
A conventional negative electrode active material can be used as the negative electrode active material of the negative electrode 22. A negative electrode active material containing at least one element of Sn, Si, Sb, Ge, and C can be given. Among these negative electrode active materials, C is preferably a carbon material capable of occluding and releasing electrolyte ions of a lithium ion secondary battery (having Li storage ability), and more preferably graphite.

  Of these negative electrode active materials, Sn, Sb, and Ge are alloy materials having a large volume change. These negative electrode active materials may form an alloy with another metal such as Ti—Si, Ag—Sn, Sn—Sb, Ag—Ge, Cu—Sn, and Ni—Sn. Furthermore, titanium-containing metal oxides such as lithium titanium oxide, titanium oxide, and niobium titanium composite oxide containing Ti can be cited as these negative electrode active materials.

[Conductive material, binder, composite material, negative electrode current collector]
As the conductive material of the negative electrode 22, a carbon material, metal powder, conductive polymer, or the like can be used. From the viewpoint of conductivity and stability, it is preferable to use a carbon material such as AB, KB, or CB.

As the binder of the negative electrode 22, PTFE, PVDF, fluororesin copolymer (tetrafluoroethylene / hexafluoropropylene copolymer), SBR, acrylic rubber, fluororubber, polyvinyl alcohol (PVA), styrene -Maleic acid resin, polyacrylate, carboxymethyl cellulose (CMC), etc. can be mentioned.
Examples of the solvent for the composite material of the negative electrode 22 include an organic solvent such as NMP, water, or an aqueous solvent.

  As the negative electrode current collector 220, a conventional current collector can be used, which is obtained by processing a metal such as copper, stainless steel, titanium, or nickel, for example, a foil processed in a plate shape, a net, a punched metal, a foam metal, or the like However, it is not limited to these.

[Nonaqueous electrolyte]
The nonaqueous electrolyte 23 can be a conventional nonaqueous electrolyte. Examples of the non-aqueous electrolyte 23 include those in which the supporting electrolyte is dissolved in a non-aqueous solvent. Moreover, the conventional additive may be added.

The supporting electrolyte is not limited except that it contains lithium. For example, inorganic salts selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , derivatives of these inorganic salts, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₃ and LiN (SO ₂ CF ₃ ) ₂ , LiN An organic salt selected from (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and a derivative of these organic salts are preferred. These supporting electrolytes can further improve the battery performance, and can maintain the battery performance higher even in a temperature range other than room temperature. The concentration of the supporting electrolyte is not particularly limited, and it is preferable to select appropriately in consideration of the types of the supporting electrolyte and the organic solvent.

  The non-aqueous solvent dissolves the supporting electrolyte. The non-aqueous solvent is not limited except that it dissolves the supporting electrolyte. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like can be used. In particular, propylene carbonate, ethylene carbonate (EC), 1,2-dimethoxyethane, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), and a mixed solvent thereof are preferable. . Among these organic solvents, the use of at least one nonaqueous solvent selected from the group consisting of carbonates and ethers is particularly excellent in the solubility, dielectric constant and viscosity of the supporting electrolyte, and is a lithium ion secondary battery. This is preferable because the charge / discharge efficiency of 20 is increased.

  As a conventional additive, when a battery is assembled, it is decomposed on the surface of an electrode (for example, positive electrode), and a film (for example, Solid Electrolyte Interface: SEI film) is formed on the surface of the electrode (positive electrode, particularly positive electrode active material). Generate. The coating produced on the surface of this electrode (positive electrode) exhibits high stability. And even if a positive electrode becomes a high electric potential (for example, even if a charge reaction advances with a high electric potential), a film does not decompose | disassemble and coat | covers the surface of an electrode (positive electrode). As a result, a decrease in the capacity of the electrode (positive electrode) is suppressed by the coating.

As described above, the positive electrode active material of the present embodiment generates a crack due to a volume change caused by charging, and Li ions enter the inside thereof. At this time, the Li ions are preferably in a state solvated with the solvent of the nonaqueous electrolyte 23. That is, as shown in FIG. 3, Li ions (Li ⁺ ) may be in a state of forming a solvate by binding with a nonaqueous solvent molecule (SOL) by electrostatic force or hydrogen bond. preferable. When the solvate is formed, the solvent preferably has such a size that can enter a crack formed in the positive electrode active material as shown in FIG. 4, and is preferably not an excessively bulky compound.
As a solvent for such a non-aqueous electrolyte 23, propylene carbonate, ethylene carbonate (EC), 1,2-dimethoxyethane, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), vinylene carbonate ( VC) and other solvents can be used alone or mixed.

[Other configurations]
The secondary battery 20 accommodates the positive electrode 21 and the negative electrode 22 in the battery case 25 together with the nonaqueous electrolyte 23 with the separator 24 interposed, with the positive electrode active material layer 211 and the negative electrode active material layer 221 facing each other. Is done.

[Separator]
The separator 24 plays a role of electrically insulating the positive electrode 21 and the negative electrode 22 and holding the nonaqueous electrolyte 23. As the separator 24, for example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film is preferably used.

[Battery case]
The battery case 25 accommodates (encloses) the positive electrode 21 and the negative electrode 22 together with the nonaqueous electrolyte 23 with the separator 24 interposed therebetween.

  The battery case 25 is made of a material that inhibits moisture permeation between the inside and the outside. An example of such a material is a material having a metal layer. Examples of the material having a metal layer include the metal itself and a laminate film provided with the metal layer.

[Charging / Discharging Control Device]
The charge / discharge control device 3 controls charge / discharge of the assembled battery 2. The charging / discharging control device 3 includes a battery detection unit 30 that detects a charging / discharging state of the assembled battery 2, a calculation unit 31 that determines charging / discharging conditions of the assembled battery 2, and charging / discharging of the assembled battery 2 based on the charging / discharging conditions. A charge / discharge control unit 32 for controlling the battery pack and a storage unit 33 for storing the state of the assembled battery 2.

The battery detection unit 30 detects the charge / discharge state of the assembled battery 2. The battery detection unit 30 detects the charge / discharge voltage and the charge / discharge current of the assembled battery 2 when the charge / discharge control device 3 charges / discharges the assembled battery 2. The specific configuration is not limited as long as the device can detect the charge / discharge voltage and the charge / discharge current. The detection result of the battery detection unit 30 is output to the calculation unit 31 and the storage unit 33.
In addition, although the battery detection part 30 of this form detects the charging / discharging state of the assembled battery 2, you may detect each charging / discharging state of the secondary battery 20 which comprises the assembled battery 2. FIG.

The calculation unit 31 receives the detection result of the battery detection unit 30 and calculates the charge / discharge conditions of the assembled battery 2. The charging / discharging conditions determined by the calculation unit 31 are charging / discharging conditions for charging / discharging the assembled battery 2, and are conditions for charging / discharging the external load unit 4.
The calculation unit 31 performs control so that the battery pack 2 is discharged after being charged.

The calculation unit 31 determines the discharge resistance as shown in FIG. 5 and controls the discharge of the assembled battery 2. That is, the discharge conditions are determined. When the assembled battery 2 discharges, it is determined whether or not the resistance (discharge resistance) of the assembled battery 2 (secondary battery 20) when the discharge is performed is equal to or less than a predetermined threshold value. Is determined to be less than or equal to the threshold value, the battery pack 2 is controlled to start discharging. When it is determined that the discharge resistance is greater than the threshold value, charging is performed at a predetermined rate, and immediately after that, control for starting discharging the assembled battery 2 is performed.
The calculation unit 31 performs the discharge control illustrated in FIG. 5, but the charge control is not limited, and a conventionally known control can be performed.

  The discharge resistance of the assembled battery 2 (secondary battery 20) can be determined (calculated) from the state of the assembled battery 2. For example, determination (calculation) can be made based on various conditions such as the immediately preceding charge / discharge operation and the elapsed time since that operation, the past charge / discharge operation history (SOC change history), the current and past temperature changes, and the like. Specifically, when the immediately preceding operation is discharging, the discharge resistance can be determined (calculated) based on the elapsed time from the end of the immediately preceding discharging operation.

The predetermined rate of charging can be arbitrarily set. The predetermined charge rate is, for example, preferably about 1/100 C to 5 C, and more preferably 1 C to 5 C. Moreover, the charge amount (charge time) of charge at a predetermined rate can also be set arbitrarily.
The predetermined rate of charging is preferably a high rate. This means that when charging is performed at a high rate, the reaction on the surface layer of the positive electrode active material further proceeds. If it does so, it will become easy to produce the below-mentioned crack. If the predetermined charging rate becomes excessively high, the charging power for the formation of cracks becomes excessively large, and it becomes difficult to obtain an effect commensurate with the charging rate.

The charging / discharging conditions such as a predetermined rate, the threshold value, and the discharge resistance can be calculated by the calculation unit 31, but the values calculated in advance are stored in the storage unit 33 and called from the storage unit 33. May be used. That is, a database of threshold values and charging conditions at a predetermined rate corresponding to the threshold values is stored, and the calculation unit 31 refers to the detection result of the input battery detection unit 30 to determine the charge / discharge conditions. Also good.
The calculation unit 31 also calculates the state of the assembled battery 2 such as calculation of SOC. And the calculation result about the states of the assembled battery 2 such as SOC also contributes to the determination of the charging condition.

  The calculation unit 31 determines the charging / discharging conditions so as to start discharging immediately after charging at a predetermined rate. The term “immediately” refers to the diffusion of Li in the positive electrode active material described later (the uneven distribution of Li). This is the time during which the cancellation is not completed. In other words, it is preferable to start discharging without any time after charging at a predetermined rate, but after several minutes to several hours have elapsed after charging at the predetermined rate, Discharging may be started.

The calculation unit 31 is not limited to a specific configuration as long as it is a device capable of calculating. A computer (or MCU (micro control unit)) can be exemplified.
The charge / discharge control unit 32 charges / discharges the assembled battery 2 based on the charge / discharge conditions from the calculation unit 31.

  The memory | storage part 33 memorize | stores data, such as charging / discharging conditions of the above-mentioned assembled battery 2, a threshold value, the discharge conditions of a predetermined rate. The storage unit 33 is not limited to a specific configuration as long as it is a device capable of storing data. A memory can be exemplified.

[External load section]
The external load unit 4 includes a device (hereinafter referred to as an external load device 40) on which the secondary battery device 1 operates and an external power source 41. The external load device 40 operates with electric power from the secondary battery device 1. That is, the discharge power of the secondary battery device 1 is used as a power source. Examples of the external load device 40 include electric devices such as various motors of the vehicle. The external power source 41 is a power source for charging the secondary battery device 1. The external power supply 41 can exemplify another battery mounted on the vehicle, a power generation motor, or a regenerative motor.

[Function and effect of this embodiment]
As an operation of the secondary battery device 1 of the present embodiment, an operation in discharging to the external load unit 4 will be specifically described. The operation chart is shown in FIG. In addition, about the charge to the external load part 4, it can perform by the operation | movement (control method) similar to the conventional secondary battery apparatus 1. FIG.

[Discharge to external load unit 4]
(Step S1)
First, an energization start (discharge start) signal (input signal) to the assembled battery 2 is input to the charge / discharge control device 3 with respect to the external load unit 4 (specifically, the external load device 40).

(Step S2)
When the charge / discharge control device 3 receives the input signal, the charge / discharge control device 3 determines the resistance (discharge resistance) of the assembled battery 2 (secondary battery 20).

The calculation of the discharge resistance by the charge / discharge control device 3 is performed by determining the state of the assembled battery 2 (secondary battery 20) after receiving the input signal. Specifically, the charging / discharging control device 3 (calculation unit 31) determines whether or not the immediately preceding charging / discharging operation is a discharging operation, obtains an elapsed time from the immediately preceding operation, and stores the corresponding discharging resistance in the storage unit. Call from 33 and decide.
In this step, the discharge resistance for determining in the subsequent step (step S3) is determined. By this process, determination can be performed in the subsequent process (step S3).

(Step S3)
The charge / discharge control device 3 (calculation unit 31) determines whether or not the discharge resistance determined in the previous step S2 is equal to or less than a predetermined threshold. The threshold is determined by calling from the storage unit 33.
If it is determined that the discharge resistance is greater than the threshold value, it is determined that if the discharge is performed as it is, the battery performance is degraded due to the discharge resistance, and the process proceeds to the next step S4.
When the discharge resistance is less than or equal to the threshold value, it is determined that the discharge with the low resistance is possible, and the process proceeds to step S5 to be described later, and the discharge by the input signal is performed.

  In this step, it is determined whether or not the discharge resistance is equal to or less than a predetermined threshold value. According to this determination, when discharging is performed in a state where the discharge resistance is large, the battery performance is degraded by the resistance. If it is determined that the discharge resistance is high, charging is performed in the subsequent process (step S4) in order to suppress the deterioration of the battery performance. If it is determined that the discharge resistance is not large, since the deterioration of the battery performance at the time of discharge is suppressed, the discharge process of step S5 is performed as it is.

(Step S4)
The charge / discharge control device 3 performs charging at a predetermined rate.
The calculating part 31 determines the conditions for charging at a predetermined rate. The charging condition is determined by calling from the storage unit 33.

  In this step, charging is performed at a predetermined rate. When this charging is performed, Li ions are desorbed from the positive electrode active material of the positive electrode 21 of the secondary battery 20. As a result, the positive electrode active material undergoes volume change (shrinkage). Shrinkage of the positive electrode active material occurs for each crystallite. When each crystallite shrinks, separation occurs at the crystallite interface, and a crack is generated in the positive electrode active material particles. As a result, the surface area of the positive electrode active material particles is increased, the contact area with Li ions (electrolyte ions) is increased, and the surface area capable of storing Li ions is increased.

  Further, when charging is performed at a predetermined rate, the amount of occlusion of Li is reduced in the vicinity of the surface of the positive electrode active material particles as compared with the central part of the positive electrode active material particles. This is because the amount of Li moving (moving speed, diffusion speed) in the positive electrode active material particles is smaller than the amount of Li desorbing from the positive electrode active material particles by charging (desorption rate). That is, Li is desorbed from the vicinity of the surface of the positive electrode active material particles to the outside, but the amount of Li diffusing from the central portion of the positive electrode active material particles to the surface portion is smaller than the amount of Li to be desorbed. As a result, the vicinity of the surface portion is partially in a Li poor state. The state of Li poor is a state in which many sites capable of storing Li exist, and can store a large amount of Li ions. In other words, by increasing the amount of occlusion of Li ions in the Li poor state, an increase in discharge resistance in the subsequent discharge can be suppressed.

(Step S5)
Discharge corresponding to the input signal.
Discharging is performed immediately after charging in step S4. Further, when it is determined in step S3 that the discharge resistance is not large, the determination is performed immediately after the determination.
The discharge corresponding to the input signal is a discharge to the external load unit 4 (specifically, the external power supply 41), and this discharge condition is the same as the conventional one.

In this step, the battery pack 2 (secondary battery 20) can be discharged by performing discharge corresponding to the input signal.
The charging is performed immediately after the discharge in step S4, so that the discharge is performed in a state where cracks are generated in the positive electrode active material particles. In a state where cracks are generated in the positive electrode active material particles, Li ions of the nonaqueous electrolyte 23 enter, and the insertion of Li ions is also performed from the inner surface of the cracks. That is, the surface area where Li ions can be occluded is increased.

Further, as described above, the discharge is performed immediately after the charging in step S4, so that the Li poor state is maintained in the vicinity of the surface of the positive electrode active material particles, and the occlusion amount of Li ions can be increased. .
In this step, as described above, the amount of Li that can be occluded by the positive electrode active material is increased, and an increase in discharge resistance can be suppressed.

(Step S6)
The discharge corresponding to the input signal is terminated.
Through the above steps, the secondary battery device 1 of the present embodiment can perform discharge in which the rise in discharge resistance is suppressed from the assembled battery 2 (secondary battery 20).

(1) First Effect The secondary battery device 1 of the present embodiment includes a positive electrode active material that includes a crystallite diameter (X) and a volume change rate (Y) within a predetermined range and exhibits a two-phase coexistence type reaction. The charging / discharging control device 3 discharges after the secondary battery 20 performs charging.

According to this configuration, a positive electrode active material that includes a crystallite diameter (X) and a volume change rate (Y) within a predetermined range and exhibits a two-phase coexistence type reaction is used. When this positive electrode active material is charged, the positive electrode active material undergoes volume change (shrinkage), and cracks are generated. As a result, the surface area of the positive electrode active material particles is increased, the contact area with Li ions (electrolyte ions) is increased, and the surface area capable of storing Li ions is increased.
Furthermore, when charging is performed, the vicinity of the surface of the positive electrode active material is in a Li poor state, the amount of occlusion of Li ions can be increased, and an increase in discharge resistance in the subsequent discharge can be suppressed.

  And the secondary battery apparatus 1 of this form can suppress the increase in discharge resistance from discharging the assembled battery 2 (secondary battery 20) in which the positive electrode active material is in this state. That is, the assembled battery 2 (secondary battery 20) can exhibit high battery performance.

(2) Second effect The positive electrode active material is made of at least one selected from lithium iron phosphate, lithium manganese phosphate, and lithium manganate.
By selecting the positive electrode active material from these, the first effect can be surely exhibited.

(3) Third Effect The assembled battery 2 having a plurality of secondary batteries 20 is formed.

  Even when the assembled battery 2 is formed by combining a plurality of secondary batteries 20, the above-described effects can be exhibited. Further, by forming the assembled battery 2, the secondary battery device 1 of the present embodiment can be charged / discharged with high power.

(4) Fourth to Fifth Effects The secondary battery device 1 of the present embodiment includes a crystallite diameter (X) and a volume change rate (Y) within a predetermined range, and exhibits a two-phase coexistence type reaction. The secondary battery 20 having the positive electrode 21 including the positive electrode active material is charged and then discharged.
By performing discharge using this discharge method, the above-described excellent effects can be exhibited.

[Embodiment 2]
The secondary battery device 1 of the present embodiment is a form in which the secondary battery device 1 of the first embodiment is applied to a drive system of an HV vehicle. Among the specific configurations of the present embodiment, configurations not particularly mentioned are the same as those of the first embodiment. The structure of the secondary battery device 1 of this embodiment is shown in FIG.
The secondary battery device 1 of this embodiment is the same as that of Embodiment 1 except that the configuration of the external load unit 4 is different.
In the secondary battery device 1 of this embodiment, the assembled battery 2 and the drive unit 5 are connected via the charge / discharge control device 3.

  The drive unit 5 includes an engine 50, a generator 51, a starter motor 52, a front motor 53, and a rear motor 54. The drive unit 5 may be arranged with an inverter between the assembled battery 2. The secondary battery device 1 according to the present embodiment is a device that is driven by using the engine 50, the front motor 53, and the rear motor 54 together to run the HV vehicle.

  In the secondary battery device 1 of the present embodiment, the engine 50 is connected to the charge / discharge control device 3 via the generator 51 or the starting motor 52. The engine 50 is a vehicle engine (internal combustion engine). The generator 51 is a device that generates electric power using the rotation of the engine 50 as a power source, and is also referred to as an alternator or a generator. The starter motor 52 rotates using the electric power of the assembled battery 2 as a power source, and starts the engine 50. The starter motor 52 is also referred to as a cell motor.

  The front motor 53 and the rear motor 54 are also connected to the charge / discharge control device 3. The front motor 53 and the rear motor 54 function not only as motors but also as generators.

  When the HV vehicle is stopped, secondary battery device 1 of the present embodiment discharges starter motor 52 and starts engine 50. Then, power generation is started by the generator 51 by the operation of the engine 50. The generated power is supplied to the assembled battery 2 (secondary battery 20), and each secondary battery 20 is charged.

When the HV vehicle is stopped, the secondary battery device 1 of the present embodiment also discharges the front motor 53 and the rear motor 54 to run (start) the HV vehicle. When the HV vehicle is decelerated, the electric power generated by the regenerative brake is supplied to the assembled battery 2 (secondary battery 20) to charge each secondary battery 20.
In addition, the secondary battery apparatus 1 of this form performs charging / discharging with high electric power. For this reason, it is preferable that the assembled battery 2 has a configuration in which a plurality of secondary batteries 20 are connected in series.

[Effect of this embodiment]
The secondary battery device 1 of the present embodiment is the same as that of the first embodiment except that the configuration of the external load unit 4 is different, and exhibits the same effect.
In particular, in the secondary battery device 1 that charges and discharges a large amount of power as in a drive system of an HV vehicle, even a slight increase in discharge resistance has a great effect. Specifically, when discharging with high power is performed in a state where the discharge resistance is increased, the assembled battery 2 (secondary battery 20) generates heat. If it does so, not only battery performance will fall, but the assembled battery 2 (secondary battery 20) itself will be exposed to high heat, and a thermal damage will arise.
However, the secondary battery device 1 of the present embodiment has an effect of suppressing an increase in discharge resistance and suppressing the occurrence of these problems.

[Embodiment 3]
The secondary battery device 1 of the present embodiment includes two assembled batteries 2A and 2B, and the embodiment is configured except that external loads 6A and 6B are further connected to the two assembled batteries 2A and 2B. 2 is the same configuration as the secondary battery device 1 of FIG. Among the specific configurations of the present embodiment, configurations not particularly mentioned are the same as those of the second embodiment. The configuration of the secondary battery device 1 of this embodiment is shown in FIG.
In the secondary battery device 1 of this embodiment, the charge / discharge control device 3 controls the charge / discharge of the two assembled batteries 2A, 2B.

The assembled battery 2 </ b> A is connected to the engine 50 via the generator 51 or the starter motor 52. The assembled battery 2A is also connected to the external load 6A.
The assembled battery 2 </ b> B is connected to each of the front motor 53 and the rear motor 54. The assembled battery 2B is also connected to the external load 6B.

  The external loads 6A and 6B are electrical devices mounted on the vehicle, and examples thereof include an audio device and a lighting device mounted in the vehicle interior. The external loads 6 </ b> A and 6 </ b> B are driven with power saving as compared with the drive unit 5.

[Effect of this embodiment]
The secondary battery device 1 of the present embodiment is substantially the same as the second embodiment except that the configuration of the assembled battery 2 is different, and exhibits the same effect.
Furthermore, in the secondary battery device 1 of the present embodiment, the two assembled batteries 2A and 2B are connected to the drive unit 5 that consumes a large amount of power. In this configuration, the charge / discharge power of each of the assembled batteries 2A and 2B can be reduced as compared with the second embodiment. This can reduce the influence of the increase in the discharge resistance, and can exert the effect of further suppressing the deterioration of the battery performance.

[Embodiment 4]
Although each said form was the secondary battery apparatus 1 provided with the assembled battery 2 which combined several lithium ion secondary battery 20, you may comprise from one secondary battery 20. FIG.
Examples of the lithium ion secondary battery 20 include a laminate-type secondary battery 20. FIG. 8 is a perspective view of the configuration of the laminate-type secondary battery 20, and FIG. 9 is a cross-sectional view taken along line IX-IX in FIG.

  In this embodiment, the secondary battery 20 of the first embodiment is applied to a laminated battery, and the configuration of the positive electrode 21, the negative electrode 22, the nonaqueous electrolyte 23, and the like is the same as that of the first embodiment.

  The secondary battery 20 of this embodiment is configured by housing (sealing) a positive electrode 21 and a negative electrode 22 in a battery case 7 made of a laminate case. In addition, the structure which is not specifically limited by this form is the same as that of each above-mentioned form (Embodiment 1).

  The positive electrode 21 is formed by forming a positive electrode active material layer 211 on the surface (both sides) of a substantially square positive electrode current collector 210. The positive electrode 21 has an uncoated portion 212 on one side of a square shape where the positive electrode current collector 210 is exposed (the positive electrode active material layer 211 is not formed).

  The negative electrode 22 is formed by forming a negative electrode active material layer 221 on the surface (both surfaces) of a substantially square negative electrode current collector 220. The negative electrode 22 has an uncoated portion 222 on one side of the square shape where the negative electrode current collector 220 is exposed (the negative electrode active material layer 221 is not formed).

  In the negative electrode 22, the negative electrode active material layer 221 is formed wider than the positive electrode active material layer 211 of the positive electrode 21. When the negative electrode active material layer 221 of the negative electrode 22 is stacked on the positive electrode active material layer 211, the positive electrode active material layer 211 is formed in a size that can be completely covered without being exposed.

The positive electrode 21 and the negative electrode 22 are accommodated (enclosed) in a battery case 7 formed of a laminate film together with the non-aqueous electrolyte 23 in a state of being laminated via a separator 24.
The separator 24 is formed with a larger area than the negative electrode active material layer 221.

  The positive electrode 21 and the negative electrode 22 are stacked in a state where the centers of the positive electrode active material layer 211 and the negative electrode active material layer 221 overlap with the separator 24 interposed therebetween. At this time, the uncoated portion 212 of the positive electrode 21 and the uncoated portion 222 of the negative electrode 22 are arranged so as not to overlap.

[Battery case]
The battery case 7 is formed from a laminate film 70. The laminate film includes a plastic resin layer 701, a metal foil 702, and a plastic resin layer 703 in this order. The battery case 7 is adhered by pressing the laminate film 70 bent in advance into a predetermined shape against another laminate film or the like in a state where the plastic resin layers 701 and 703 are softened by heat or some solvent.

  The battery case 7 has a laminate film 70 that is pre-molded (embossed) into a shape that can accommodate the positive electrode 21 and the negative electrode 22, and the outer peripheral edge is bonded to the entire periphery to connect the positive electrode 21 and the negative electrode 22. It is sealed inside. A sealing part is formed by adhesion of the outer periphery. Adhesion of the outer periphery in this form was made by fusion.

  The battery case 7 is formed by overlaying another laminate film 70 on the laminate film 70. Here, another laminate film 70 indicates a laminate film to be bonded (fused). That is, the battery case 7 includes not only an embodiment formed from two or more laminate films 70 but also an embodiment formed by folding one laminate film.

  Bonding (assembling) the outer periphery of the battery case 7 is performed under a reduced pressure atmosphere (preferably vacuum). Thereby, only the electrode body is enclosed in the battery case 7 without containing air (water contained therein).

  As shown in FIGS. 8 to 9, the pre-formed laminate film 70 includes a flat plate portion 71 that forms a sealing portion 72 with another laminate film 70 when overlapped, and the flat plate portion 71. And a tank-like portion 73 that can accommodate the positive electrode 21 and the negative electrode 22 formed in the center portion.

  As shown in FIGS. 8 to 9, the laminate films 70 and 70 are bent (formed) so as to have a concave shape that can accommodate the positive electrode 21 and the negative electrode 22. The laminate films 70 and 70 have the same shape, and the flat plate portions 71 and 71 are completely overlapped when they are overlapped in directions facing each other.

  In the laminate film 70, the flat plate portion 71 and the bottom portion 73A of the tank-like portion 73 (the portion forming the end portion in the stacking direction of the secondary battery 20) are formed in parallel. The flat plate portion 71 and the bottom portion 73A of the tank-like portion 73 are connected by a standing portion 73B. The standing portion 73B extends in a direction (inclined direction) intersecting the parallel direction of the flat plate portion 71 and the bottom portion 73A. The bottom 73A is formed smaller than the opening of the tank-like portion 73 (the inner end of the flat plate portion 71).

In the battery case 7, a sealing portion 72 is formed at the peripheral portion of the flat plate portions 71, 71, and the flat plate portions 71, 71 are overlapped on the inner side of the sealing portion 72 (in the direction close to the electrode body). The part of is formed. The unbonded portion where the flat plate portions 71 and 71 are overlapped may be in a contact state or in a state where a gap is formed. Further, uncoated portions 212 and 222 of the electrode plates (the positive electrode plate 21 and the negative electrode plate 22) and the separator 24 may be interposed.
Laminate films 70 and 70 are previously formed in the shape shown in FIGS. For forming into this shape, a conventionally known forming method is used.
In the secondary battery 20, each of the positive electrode 21 and the negative electrode 22 is connected to electrode terminals (a positive electrode terminal 75 and a negative electrode terminal 76).

[Electrode terminal]
The positive terminal 75 is electrically connected to the uncoated part 212 of the positive electrode 21. The negative electrode terminal 76 is electrically connected to the uncoated part 222 of the negative electrode 22. In this embodiment, uncoated portions 212 and 222 of the electrodes 21 and 22 are joined to the electrode terminals 75 and 76 by welding (vibration welding), respectively. The center portions in the width direction of the uncoated portions 212 and 222 of the electrodes 21 and 22 are joined to the electrode terminals 75 and 76.

  Each of the electrode terminals 75 and 76 is joined via a sealant 74 so that the plastic resin layer 701 of the laminate films 70 and 70 and the electrode terminals 75 and 76 are kept in a sealed state at a portion penetrating the battery case 7. ing.

  The electrode terminals 75 and 76 are made of sheet-like (foil-like) metal, and the sealant 74 is made of resin that covers the sheet-like electrode terminals 75 and 76. The sealant 74 covers a portion where the electrode terminals 75 and 76 overlap the flat plate portion 71. By forming the electrode terminals 75 and 76 into a sheet shape, it is possible to reduce the deformation stress of the laminate film 70 due to the electrode terminals 75 and 76 being interposed at the portion penetrating the battery case 7. Further, welding (vibration welding) of the electrodes 21 and 22 to the uncoated portions 212 and 222 can be easily performed.

  The laminate-type secondary battery 20 preferably has a restraining member that restricts the positive electrode 21 and the negative electrode 22 from shifting in a direction away from each other. By having a restraining member, it can suppress that the distance of the lamination direction of the positive electrode 21 and the negative electrode 22 becomes long. When the distance between the positive electrode 21 and the negative electrode 22 is increased, the moving distance of the electrolyte ions is increased, leading to an increase in internal resistance. The restraining member can suppress an increase in the distance.

  Examples of the restraining member include a member provided with a pair of jigs that are in contact with both outer peripheral surfaces of the laminated secondary battery 20 in the stacking direction. Even if the restraining member is a member that pressurizes the outer peripheral surface of the laminate-type secondary battery 20 in a compressing direction, the restraining member is a member that restricts only an increase in thickness by fixing the distance between the pair of jigs. Either. The restraining member may be a rigid outer case that houses the laminate-type secondary battery 20.

[effect]
The secondary battery device 1 of the present embodiment has the same configuration as that of the first embodiment except that the number of secondary batteries 20 constituting the assembled battery 2 is different, and exhibits the same effect as that of the first embodiment.

Hereinafter, the present invention will be specifically described with reference to examples.
As an example for specifically explaining the present invention, the secondary battery device 1 shown in the fourth embodiment was manufactured.

(Configuration of the secondary battery 20)
The positive electrode 21 was prepared by applying a positive electrode mixture obtained by mixing positive electrode active material: 91 parts by mass, acetylene black: 4 parts by mass, and PVDF: 6 parts by mass to a positive electrode current collector 210 made of aluminum foil. What formed the material layer 211 was used.

  As the negative electrode, a negative electrode mixture obtained by mixing graphite as a negative electrode active material: 98 parts by mass, SBR: 1 part by mass, and CMC: 1 part by mass with a solvent was prepared. The negative electrode mixture was applied to both surfaces of a negative electrode current collector 220 made of a copper foil having a thickness of 0.01 mm and dried to form a negative electrode active material layer 221.

As the non-aqueous electrolyte 23, a solution obtained by dissolving LiPF ₆ to 1 mol% in a mixed solvent in which EC: DEC was mixed at a ratio of 30:70 (vol%) was used. VC as an additive is added to the non-aqueous electrolyte 23 at 2 mass% when the whole is 100 mass%.

  The secondary battery 20 is formed by housing a positive electrode 21, a negative electrode 22, and a nonaqueous electrolyte 23 in a laminate type battery case 7. The positive electrode 21 and the negative electrode 22 were assembled so that the capacity ratio (positive electrode capacity / negative electrode capacity) was 1.3. The secondary battery 20 has a capacity of 5 Ah.

(Measurement of crystallite diameter of positive electrode active material)
The crystallite diameter of the positive electrode active material was calculated using an X-ray diffractometer (XRD apparatus, manufactured by Rigaku, RINT-TTR2) under the following conditions.
Detector: Semiconductor detector Measurement angle: 10 ° -80 °
Sampling width: 0.01
Scan speed: 5
Voltage: 50 Current: 300
Operation axis: 2θ / θ
Measurement method: Continuous Counting: cps
Integration count: 3
Slit width Divergence slit: Open Divergence length restriction slit: 1.2mm
Scattering slit: 2 °
Receiving slit: 0.15mm
Crystallite size calculation method: Halder-Wagner method

Example 1
In this example, LiFePO ₄ (hereinafter referred to as LFP) having a crystallite diameter of 42 [nm] was used as the positive electrode active material. The volume change rate of this positive electrode active material is 7 [%].
Z in the above formula (2) of this example was 1.00 (≧ 0.96).

(Example 2)
In this example, LFP having a crystallite diameter of 72 nm was used as the positive electrode active material. Z in the above formula (2) of this example was 1.72 (≧ 0.96).

(Example 3)
In this example, LFP having a crystallite diameter of 152 [nm] was used as the positive electrode active material. Z in the above formula (2) of this example was 3.63 (≧ 0.96).

Example 4
In this example, LFP having a crystallite diameter of 300 nm was used as the positive electrode active material. Z in the above formula (2) of this example was 7.17 (≧ 0.96).

(Example 5)
In this example, LFP having a crystallite diameter of 500 [nm] was used as the positive electrode active material. Z in the above formula (2) of this example was 11.95 (≧ 0.96).

(Example 6)
In this example, LiMn ₂ O ₄ (hereinafter referred to as LMO) having a crystallite diameter of 57 [nm] was used as the positive electrode active material. The volume change rate of this positive electrode active material is 5 [%].
Z in the above formula (2) of this example was 0.97 (≧ 0.96).

(Comparative Example 1)
In this example, LFP having a crystallite diameter of 38 [nm] was used as the positive electrode active material. Z in the above formula (2) of this example was 0.91 (≦ 0.96).

(Comparative Example 2)
In this example, LMO having a crystallite diameter of 49 [nm] was used as the positive electrode active material. Z in the above formula (2) of this example was 0.83 (≦ 0.96).

[Evaluation]
As the evaluation of the secondary battery device 1 of each example described above, the discharge resistance when discharging was performed after charging was measured and evaluated. The evaluation results are shown in Table 1.

(Measurement of discharge resistance)
The secondary battery 20 is charged to SOC 50% at a rate of 1 / 5C.
After charging, take a 30-minute pause.
After rest, charge for 10 seconds at 1C rate. This charging corresponds to the charging in step S4 in FIG.
After discharge, a 30 minute rest period is taken.

After the rest, the battery is discharged to SOC 50% at a rate of 0.1C (1 / 10C). This discharge corresponds to the discharge corresponding to the input signal in step S5 of FIG. This discharge discharges the charging power charged at the time of the charge in the previous step S4.
Measure the IV relationship during discharge.
These steps are performed at the discharge rates of 2C, 3C, and 5C in step S5, and the discharge resistance is calculated from the respective IV relationship.

(Measurement of reference discharge resistance)
The secondary battery 20 is charged to SOC 100% at a rate of 1 / 5C.
After charging, take a 30-minute pause.
After rest, the battery is discharged to SOC 50% at a rate of 0.1C.
Thereafter, the battery is discharged at a rate of 1C for 10 seconds, and the IV relationship at the time of discharge is measured.
In these steps, discharge is performed at each rate of 2C, 3C, and 5C, and a discharge resistance (reference discharge resistance) is calculated from each IV relationship.

(Calculation of discharge resistance ratio)
The ratio (percentage) of the calculated discharge resistance to the corresponding reference discharge resistance was determined and used as the discharge resistance ratio. The discharge resistance ratio is shown in Table 1.

(Evaluation)
The secondary battery device 1 of each example was evaluated from the calculated discharge resistance ratio. In the evaluation, an example in which the discharge resistance ratio is less than 100% is “◯”, an example in which the discharge resistance ratio is less than 80% is “◎”, and an example in which the discharge resistance ratio is 100% or more is “x”.

  Here, the discharge resistance in each example is measured immediately after the charging in step S4. That is, the discharge resistance in a state where Li is desorbed from the positive electrode active material (the state where the surface is Li poor) is measured. On the other hand, the reference discharge resistance is measured immediately after the discharge is performed. That is, the discharge resistance is measured in a state where Li is occluded in the positive electrode active material (the surface vicinity is Li-rich).

  First, when the discharge resistance ratio of each example is confirmed, all are less than 100%. On the other hand, the discharge resistance ratio of each comparative example is a value exceeding 100%. From this, for the secondary battery 20 in which the positive electrode active material in which the crystallite diameter and the volume change rate satisfy a predetermined relationship (Z ≧ 0.96) and exhibits a two-phase coexistence type reaction is used, By discharging after charging, an increase in discharge resistance can be suppressed.

  And when each Example is compared, it can confirm that discharge resistance ratio can be reduced more, so that the relationship (Z) of a crystallite diameter and volume change rate approaches 2.00. That is, it can be confirmed that the battery performance of the secondary battery 20 can be improved.

1: assembled battery device 2: assembled battery 20: lithium ion secondary battery 21: positive electrode 210: positive electrode current collector 211: positive electrode active material layer 22: negative electrode 220: negative electrode current collector 221: negative electrode active material layer 23: non-aqueous Electrolyte 24: Separator 25: Battery case 3: Charge / discharge control device 30: Battery detection unit 31: Current detection unit 32: Calculation unit 33: Storage unit 4: External load unit 40: External load unit 41: External power supply 5: Drive unit 50: Engine 51: Generator 52: Motor for starting 53: Front motor 54: Rear motor 6: External loads 6A and 6B
7: Battery case 70: Laminate film 71: Flat plate part 72: Sealing part 73: Tank-like part 74: Sealant 75: Positive electrode terminal 76: Negative electrode terminal

Claims (5)

Nonaqueous comprising a positive electrode (21) having a positive electrode active material exhibiting a two-phase coexistence reaction, a negative electrode (22), and a nonaqueous electrolyte (23) comprising an alkali metal ion and a nonaqueous solvent. An electrolyte secondary battery (20);
A charge / discharge control device (3) for controlling charge / discharge of the non-aqueous electrolyte secondary battery (20);
A secondary battery device (1) in which the charge / discharge control device (3) discharges after the non-aqueous electrolyte secondary battery (20) is charged,
A secondary battery device in which the crystallite diameter (X [nm]) of the positive electrode active material and the volume change rate (Y [%]) satisfy the relationship of the formula (1).
X-((1-0.01Y) X ³ ) ^1/3 ≧ 0.96 (1)   The secondary battery device according to claim 1, wherein the positive electrode active material is at least one selected from lithium iron phosphate, lithium manganese phosphate, and lithium manganate.   The secondary battery device according to claim 1, comprising a plurality of the non-aqueous electrolyte secondary batteries (20). Nonaqueous comprising a positive electrode (21) having a positive electrode active material exhibiting a two-phase coexistence reaction, a negative electrode (22), and a nonaqueous electrolyte (23) comprising an alkali metal ion and a nonaqueous solvent. A non-aqueous electrolyte secondary battery discharge method for controlling discharge of an electrolyte secondary battery (20), comprising:
The crystallite diameter (X [nm]) of the positive electrode active material and the volume change rate (Y [%]) satisfy the relationship of the formula (1),
And the discharge method of the nonaqueous electrolyte secondary battery which discharges after this nonaqueous electrolyte secondary battery (20) charges.   The method for discharging a non-aqueous electrolyte secondary battery according to claim 4, wherein discharging is performed immediately after the non-aqueous electrolyte secondary battery (20) is charged.

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