WO2018230519A1 - Power storage element, method for manufacturing power storage element, and power storage device provided with method for manufacturing power storage element and power storage element - Google Patents

Abstract

Provided is a power storage element that is capable of reducing variation in the charging depth of a positive electrode in a relatively short time. The present embodiment provides: a power storage element provided with a positive electrode that includes an active material having, as the main ingredient, LiMPO₄ (where M is at least one of transition metals selected from the group consisting of Fe, Mn, and Co) which has an olivine structure, wherein an open circuit potential curve of the positive electrode has a flat region and sloped regions, and the open circuit potential of the positive electrode is located in the sloped regions when the open circuit voltage of the power storage element is 0 V; a method for manufacturing the power storage element; and a power storage device provided with the method for manufacturing the power storage element and the power storage element.

Description

Power storage device, power storage device manufacturing method, power storage device control method, and power storage device including power storage device

The present invention relates to a power storage element such as a lithium ion secondary battery, a method for manufacturing the power storage element, a method for controlling the power storage element, and a power storage device including the power storage element.

Conventionally, a lithium ion secondary battery including a positive electrode in which a positive electrode active material layer is provided on a positive electrode current collector, a negative electrode, and an electrolyte provided between the positive electrode and the negative electrode is known (for example, Patent Document 1). .

In the battery described in Patent Document 1, in the positive electrode active material layer, graphene and lithium-containing composite oxide are alternately stacked, and the lithium-containing composite oxide is a single crystal grain having a flat shape, and the flat shape is The single crystal grains having a length in the b-axis direction are shorter than the lengths in the a-axis direction and the c-axis direction, and the lithium-containing composite oxide has the b-axis direction of the single crystal grains intersecting the surface of the positive electrode current collector. And provided on the positive electrode current collector. The lithium-containing composite oxide is represented by the general formula LiMPO ₄ (M is one or more of Fe (II), Mn (II), Co (II), Ni (II)).

Japanese Patent Laying-Open No. 2015-173071

In a conventional battery using a positive electrode active material such as lithium cobaltate, charging and discharging are repeated, and even when the charging depth varies in the positive electrode, variation can be obtained by leaving the battery without charging / discharging. The difference in the generated open circuit potential of the positive electrode of each part becomes a driving force, and the variation in the charging depth can be reduced relatively quickly. However, in the battery described in Patent Document 1, the difference in the open circuit potential of the positive electrode of each portion where the variation occurs is small and the driving force is small, so the variation in the charging depth does not decrease in a short time. Therefore, there is a demand for a power storage element that can reduce variation in the charging depth of the positive electrode in a relatively short time.

An object of the present invention is to provide a power storage element that can reduce variation in the charging depth in the positive electrode in a relatively short time.

A power storage device according to one aspect of the present invention includes a positive electrode including an active material mainly composed of LiMPO ₄ having an olivine structure (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co). The open circuit potential curve of the positive electrode has a flat region and an inclined region, and when the open circuit voltage is 0 V, the open circuit potential of the positive electrode is located in the inclined region.

According to another aspect of the present invention, there is provided a method for producing a power storage device, comprising: an active mainly composed of LiMPO ₄ having an olivine structure (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co). Providing a positive electrode comprising a substance and having an open circuit potential curve having a flat region and a slope region;
Preparing a negative electrode containing an active material,
In preparing the positive electrode and / or preparing the negative electrode, the irreversible capacity of the negative electrode is made smaller than the irreversible capacity of the positive electrode.
This is a method for manufacturing a storage element in which the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage of the storage element is 0V.

According to one aspect of the present invention, there is provided a power storage device capable of reducing variation in charging depth in a positive electrode in a relatively short time, a method for manufacturing the power storage device, a method for controlling the power storage device, and a power storage device including the power storage device. it can.

FIG. 1 is a perspective view of a power storage device according to this embodiment. 2 is a cross-sectional view taken along the line II-II in FIG. FIG. 3 is a graph schematically showing each potential of the positive electrode and the negative electrode with respect to the capacity in the electricity storage device of the present embodiment. FIG. 4 is a graph schematically showing each potential of the positive electrode and the negative electrode with respect to the capacity in the conventional power storage element. FIG. 5 is a block diagram illustrating a configuration of the power storage device according to the present embodiment. FIG. 6 is a flowchart illustrating a control processing procedure of the charge / discharge control unit.

A power storage device according to one aspect of the present invention includes a positive electrode including an active material mainly composed of LiMPO ₄ having an olivine structure (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co). The open circuit potential curve of the positive electrode has a flat region and a slope region, and the open circuit potential of the positive electrode is located in the slope region when the open circuit voltage of the power storage element is 0V.

The electric storage element can reduce variation in the charging depth of the positive electrode in a relatively short time. LiMPO ₄ (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co) and is represented by a lithium phosphate transition metal lithium compound having a flat region in an open circuit potential curve. When a positive electrode active material containing at least 50% by mass is provided in the positive electrode, the conventional power storage device has the following problems. That is, since the storage element is designed so that the open circuit potential of the positive electrode is located in a flat region when the open circuit voltage of the conventional storage element is set to 0 V, the open circuit potential of the positive electrode is low in the low charge state. Is located in a flat region, the difference in the open circuit potential of the positive electrode of each part where the variation in the charging depth occurs is reduced, and the driving force for equalizing the dispersed potential is reduced. Therefore, when the power storage element is left in a low charge state, the variation in the charge depth does not become small in a short time. On the other hand, the storage element of the present embodiment is designed so that the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage of the storage element is set to 0 V. Since the potential difference with respect to the difference in charge amount (absolute value of the slope of the open circuit potential curve of the positive electrode) is relatively large, the driving force for making the dispersed positive electrode potential uniform is increased. Therefore, by performing charging or discharging in a low charge state, or by leaving it to stand, variation in the charging depth in the positive electrode can be reduced in a relatively short time using the slope region of the potential curve.

In the power storage element, the content of any transition metal in the transition metal M of LiMPO ₄ may be 60 mol% or more. When the proportion of any one transition metal of Fe, Mn, and Co in the transition metal is 60 mol% or more, the flat region of the potential curve becomes wider due to the influence of the one transition metal. As the flat region becomes wider, charging and discharging are often performed in the flat region of the potential curve, and the charge depth tends to vary. However, in the power storage device of this embodiment, even when the positive electrode active material is as described above, the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage is 0V. Therefore, as described above, the variation in the charging depth in the positive electrode can be reduced in a relatively short time.

The electric storage element preferably further includes a negative electrode containing non-graphitic carbon. When the active material of the negative electrode is non-graphitic carbon, the potential change at the end of discharge of the negative electrode is not abrupt and gentle compared to the case where the active material is graphite (graphite) or lithium titanate, and the open circuit voltage is As it approaches 0V, the potential gradually increases. Therefore, when the active material of the negative electrode is non-graphitic carbon, the open circuit potential of the positive electrode when the open circuit voltage is 0 V is not extremely low. Since the potential of the positive electrode does not become extremely low, it is possible to suppress deterioration of a member such as an aluminum metal foil of the positive electrode due to the low potential.

According to another aspect of the present invention, there is provided a method for producing a power storage device, comprising: an active mainly composed of LiMPO ₄ having an olivine structure (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co). Preparing a positive electrode having a material and having an open circuit potential curve having a flat region and an inclined region, and preparing a negative electrode containing an active material, and preparing the positive electrode, and / or the negative electrode In the preparation, the irreversible capacity of the negative electrode is made smaller than the irreversible capacity of the positive electrode, and the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage of the power storage element is 0 V It is.

In the manufacturing method, by making the irreversible capacity of the negative electrode smaller than the irreversible capacity of the positive electrode, the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage of the power storage element is 0V Manufacturing. That is, according to the manufacturing method, it is possible to obtain a power storage element that can reduce the variation in the charging depth of the positive electrode in a relatively short time.

A method for controlling a storage element according to another aspect of the present invention includes setting the storage element to a low charge state and leaving the storage element to stand.

According to the control method, by leaving the power storage element in a low charge state, it is possible to reduce the variation in the charging depth in the positive electrode in a relatively short time by using the slope region of the potential curve of the positive electrode.

A power storage device according to still another aspect of the present invention includes the power storage element and a control device including a reception unit, an SOC calculation unit, and a charge / discharge control unit, wherein the reception unit is configured to output a voltage value of the power storage element or The SOC calculation unit receives the current value, calculates the SOC based on the voltage value or the current value, and the charge / discharge control unit determines whether to perform the neglecting process based on the SOC.

According to the above configuration, since it is possible to determine whether to perform the neglecting process based on the SOC of the power storage element, when the power storage element is in a low charge state (low SOC), that is, the potential of the positive electrode is the slope If it is located in the area, the neglecting process can be performed. Therefore, the variation in the charging depth in the positive electrode can be reduced in a relatively short time.

Hereinafter, a power storage device according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. Examples of power storage elements include secondary batteries and capacitors. In the present embodiment, a chargeable / dischargeable secondary battery will be described as an example of a power storage element. In addition, the name of each component (each component) of this embodiment is a thing in this embodiment, and may differ from the name of each component (each component) in background art.

The electricity storage device 1 of the present embodiment is a nonaqueous electrolyte secondary battery. More specifically, the electricity storage element 1 is a lithium ion secondary battery that utilizes electron movement that occurs in association with movement of lithium ions. This type of power storage element 1 supplies electric energy. The electric storage element 1 is used singly or in plural. Specifically, the storage element 1 is used as a single unit when the required output and the required voltage are small. On the other hand, when at least one of the required output and the required voltage is large, the power storage element 1 is combined with another power storage element 1 and used in the power storage device. In the power storage device, the power storage element 1 used in the power storage device supplies electric energy.

As shown in FIGS. 1 and 2, the storage element 1 includes an electrode body 2 including a positive electrode and a negative electrode, a case 3 that houses the electrode body 2, and an external terminal 7 that is disposed outside the case 3. And an external terminal 7 that is electrically connected to the electrode body 2. In addition to the electrode body 2, the case 3, and the external terminal 7, the power storage element 1 includes a current collector 5 that electrically connects the electrode body 2 and the external terminal 7.

The electrode body 2 is formed by winding a laminated body 22 in which the positive electrode and the negative electrode are laminated with the separator 4 being insulated from each other.

The positive electrode has a metal foil (current collector foil) and an active material layer that is superimposed on the surface of the metal foil and contains active material particles. In the present embodiment, the active material layers are provided on both surfaces of the metal foil.

The metal foil is strip-shaped. The metal foil of the positive electrode of the present embodiment contains aluminum, for example, an aluminum foil. The positive electrode has a non-covered portion of the positive electrode active material layer (a portion where the positive electrode active material layer is not formed) at one end edge in the width direction, which is the short direction of the band shape.

The positive electrode active material layer includes a particulate positive electrode active material (active material particles), a particulate conductive aid, and a binder.

The positive electrode active material is a compound that can occlude and release lithium ions. The positive electrode active material includes a polyanion compound. Specifically, the active material mainly includes a lithium transition metal lithium compound represented by a chemical composition of LiMPO ₄ (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co). . The compound has an olivine type structure. “Mainly contained” means containing at least 50 mass% with respect to the total mass of the active material. The positive electrode active material preferably contains 75% by mass or more, and more preferably 90% by mass or more of the transition metal lithium compound represented by the above chemical composition. Note that the positive electrode active material may include a compound capable of occluding and releasing lithium ions other than the polyanion compound.

The open circuit potential curve of the positive electrode is a curve representing a change in the potential of the positive electrode in the open circuit state with respect to the capacity (charge rate) of the power storage element 1. Such a potential curve is represented by a graph in which the horizontal axis represents capacity (charge rate SOC%) and the vertical axis represents potential (vs. lithium potential). As shown in FIG. 3, such a potential curve has a flat region and an inclined region. Specifically, such a potential curve includes a flat region, a first slope region on a side having a lower capacity than the flat region (low potential side), and a first region on the side having a higher capacity than the flat region (high potential side). And two inclined regions. When the open circuit voltage of the power storage element is 0 V, the positive circuit open circuit potential is preferably in the first slope region. The first inclined region and the second inclined region are regions in which the absolute value of the potential gradient with respect to the capacitance is 3 Vg · Ah ⁻¹ or more. The flat region is a region where the absolute value of the potential gradient with respect to the capacitance is less than 3 Vg · Ah ⁻¹ . A method for measuring the potential curve will be described later. In the open circuit potential curve of the positive electrode, the absolute value of the slope in the open circuit potential curve of the positive electrode when the open circuit voltage of the storage element 1 is 0 V is 3 Vg · Ah ⁻¹ or more, and is 5 Vg · Ah ⁻¹ or more. Preferably there is. The above potential curve may have a first slope region when the storage element 1 is in a low charge state, and when the capacity (charge rate SOC) of the storage element 1 is 0% or more and 15% or less (the end of discharge). May have a first inclined region. The potential curve may have a second slope region when the capacity (charge rate SOC) of the power storage element 1 is 85% or more and 100% or less (end-of-charge stage).

Examples of the binder include polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, and styrene butadiene rubber (SBR). ). The binder is preferably polyvinylidene fluoride.

Examples of the conductive assistant include carbonaceous materials, metals, and conductive ceramics. Examples of the carbonaceous material include ketjen black (registered trademark), acetylene black, and graphite. The positive electrode active material layer of the present embodiment preferably has acetylene black as a conductive additive.

The positive electrode active material layer may contain 1% by mass to 10% by mass of a conductive additive.

The negative electrode has a metal foil (current collector foil) and a negative electrode active material layer formed on the metal foil. In the present embodiment, the negative electrode active material layers are provided on both surfaces of the metal foil. The metal foil is strip-shaped. The metal foil of the negative electrode of this embodiment is a copper foil, for example. The negative electrode has a non-covered portion of the negative electrode active material layer (a portion where the negative electrode active material layer is not formed) at one end edge in the width direction, which is the short direction of the band shape.

The negative electrode active material layer includes a particulate negative electrode active material (active material particles) and a binder. The negative electrode active material layer is disposed so as to face the positive electrode through the separator. The width of the negative electrode active material layer is larger than the width of the positive electrode active material layer.

The negative electrode active material can contribute to the electrode reaction of charge reaction and discharge reaction in the negative electrode. For example, the negative electrode active material is a carbonaceous material such as non-graphitic carbon (non-graphitizable carbon, graphitizable carbon, etc.), which is also called graphite or amorphous carbon, lithium titanate, or silicon (Si ) And tin (Sn), and other materials that cause an alloying reaction with lithium ions. The negative electrode active material of the present embodiment is preferably non-graphitic carbon, and more preferably non-graphitizable carbon. The negative electrode active material may be a mixture of different types of active materials. The open circuit potential curve of the negative electrode is measured in the same manner as the open circuit potential curve of the positive electrode.

The non-graphitic carbon in the present specification means an average interplanar spacing d of (002) planes determined by a wide angle X-ray diffraction method using CuKα rays as a radiation source in a state after being disassembled in a discharge state and washed and dried. ₀₀₂ is from 0.340 nm to 0.390 nm. Further, the non-graphitizable carbon is one having an average interplanar distance d ₀₀₂ of 0.360 nm to 0.390 nm.

The binder used for the negative electrode active material layer is the same as the binder used for the positive electrode active material layer. The binder is preferably polyvinylidene fluoride (PVdF).

The proportion of the binder contained in the negative electrode active material layer may be 1% by mass or more and 10% by mass or less with respect to the total mass of the active material particles and the binder.

The negative electrode active material layer may further include a conductive auxiliary agent such as ketjen black (registered trademark), acetylene black, or graphite. The negative electrode active material layer of this embodiment may not have a conductive additive.

In the electrode body 2 of the present embodiment, the positive electrode and the negative electrode configured as described above are wound in a state of being insulated by a separator. That is, in the electrode body 2 of this embodiment, the laminated body 22 of a positive electrode, a negative electrode, and a separator is wound. The separator is an insulating member. The separator is disposed between the positive electrode and the negative electrode. Thereby, in the electrode body 2 (specifically, the laminated body 22), the positive electrode and the negative electrode are insulated from each other. The separator holds the electrolytic solution in the case 3. Thereby, at the time of charging / discharging of the electrical storage element 1, lithium ion moves between the positive electrode and negative electrode which are laminated | stacked alternately on both sides of a separator.

In the present embodiment, the open circuit potential curve of the positive electrode has a flat region and an inclined region as shown in FIG. When the open circuit voltage of the storage element 1 is 0 V, the positive open circuit potential is located in the inclined region.

In general, in the electricity storage device 1, the charging depth varies in the thickness direction and the surface direction of the positive electrode active material layer as charging and discharging are repeated. As a positive electrode active material, conventional LiMO ₂ having a layered rock salt structure (M is at least one transition metal selected from the group consisting of Ni, Co, and Mn), spinel-type LiMn ₂ O _{4, and the} like are used. In the electric storage element, the open circuit potential curve of the positive electrode has a certain slope. For this reason, even if the state where the charging depth varies is left as it is, the difference in the open circuit potential of the positive electrode of each part where the variation occurs becomes a driving force, and the variation in the charging depth can be gradually reduced.
In contrast, phosphoric acid represented by the chemical composition of LiMPO ₄ (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co) and having a flat region in the open circuit potential curve. When a positive electrode active material containing at least 50% by mass of a transition metal lithium compound is provided in the positive electrode, the open circuit potential of the positive electrode is designed to be located in a flat region when the open circuit voltage of the storage element is set to 0V. In a conventional power storage device, the open circuit potential of the positive electrode is positioned in a flat region in a low charge state, and the difference in the open circuit potential of the positive electrode of each part where the variation in the charging depth occurs becomes small, and the dispersed potential is reduced. A uniform driving force is reduced. Therefore, when the power storage element is left in a low charge state, the variation in the charge depth does not become small in a short time. On the other hand, the storage element of this embodiment is designed so that the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage of the storage element is set to 0 V. The potential difference (absolute value of the slope of the open circuit potential curve of the positive electrode) with respect to the difference in charge amount is relatively large, so that the driving force for equalizing the dispersed potential is increased. Therefore, by performing charging or discharging in a low charge state, or by leaving it to stand, variation in the charging depth in the positive electrode can be reduced in a relatively short time using the slope region of the potential curve.
In the electricity storage device of this embodiment, the positive circuit is charged or discharged via a low charge state or left in a low potential state (for example, SOC 15% or less) so that the open circuit potential of the positive electrode is located in the inclined region. The voltage of the power storage element is not necessarily set to 0V.

In the measurement of each potential curve in the open circuit state of the positive electrode and the negative electrode, after making a hole in a part of the electricity storage element (battery) so that the lithium reference electrode for potential measurement and the positive electrode and the negative electrode are in liquid junction Each potential of the positive electrode and the negative electrode is measured. More specifically, a part of the side surface of the electricity storage element is opened in an inert atmosphere with a dew point of −50 degrees or less, and a lithium reference electrode wrapped in a separator is inserted between the positive and negative electrodes of the electrode group. The portion into which the lithium reference electrode is inserted is stored in an airtight container in a state where the portion is appropriately pressed (the pressing force applied to the lithium reference electrode before insertion). The storage element is measured while changing the voltage of the storage element between the positive electrode and the negative electrode (voltage of the storage element), between the positive electrode and the reference electrode (positive electrode potential), and between the negative electrode and the reference electrode (negative electrode potential). In addition, the measurement of each voltage and potential described above is performed by charging a storage element in a constant current and constant voltage charge to a fully charged state (for example, 4.2 V) in advance from a fully charged state (for example, 4.2 V) to 0 V. After discharging a predetermined amount of electricity so as to be in a range, the voltage and potential are measured by resting for 1 hour. Specifically, the following procedure is used. First, the storage element is discharged at a constant current (CC) to a set lower limit voltage with a discharge current of 0.2 C, and then a constant current constant voltage (CCCV) to a set upper limit voltage (full charge state) with a charge current of 0.2 C. Charge. The charge termination condition is that the total charge time is 8 hours. Next, a constant current discharge with a discharge current of 0.05 C and a discharge time of 1 hour is performed, and each voltage and potential after a pause of 1 hour are measured. By repeating this operation until the voltage reaches 0 V, an open circuit voltage curve of the power storage element and open circuit potential curves of the positive electrode and the negative electrode can be obtained. A current value for discharging the rated capacity of the power storage element in one hour is 1C.
Note that when the open circuit voltage is 0 V in the electricity storage device of the present embodiment, the voltage of the electricity storage device is 0 V when the above-described discharge is completed.

It is confirmed by differentiating the measured potential curve that the open circuit potential curve has a slope region (a region where the absolute value of the potential slope with respect to the capacitance is 3 Vg · Ah ⁻¹ or more).

The fact that the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage of the power storage device 1 is 0 V is confirmed by comparing the voltage transition of the power storage device 1 with the transition of each potential of the positive electrode and the negative electrode. Is done.

In the electricity storage device 1 of the present embodiment, when the open circuit voltage is 0 V, the open circuit potential of the positive electrode is preferably 3 V or less in terms of lithium potential. Thereby, the open circuit potential of the negative electrode when the open circuit voltage is 0 V is also relatively low. Therefore, when the metal foil of the negative electrode is a copper foil, it is possible to prevent the copper foil from being melted due to an increase in the potential of the negative electrode due to overdischarge or the like. Further, when the open circuit voltage is 0 V, the open circuit potential of the positive electrode is preferably 0.5 V or more in terms of lithium potential. Thereby, it is suppressed that the electric potential of the positive electrode at the time of overdischarge falls to the electric potential which aluminum alloyes. Therefore, when the metal foil of the positive electrode is an aluminum foil, it can be suppressed that the aluminum foil is alloyed. When the open circuit voltage is 0 V, the absolute value of the slope of the positive circuit open circuit potential curve (the slope of the potential with respect to the capacitance) is smaller than the absolute value of the slope of the open circuit potential curve of the negative electrode (the slope of the potential with respect to the capacitance). May be large.

In the electricity storage device 1 of the present embodiment, the content of any transition metal in the above-described transition metal M of LiMPO ₄ may be 60 mol% or more, preferably 70 mol% or more, and 100 mol%. There may be. That is, the proportion of any one of Fe, Mn, and Co in the transition metal in the compound represented by LiMPO ₄ may be 60 mol% or more, preferably 70 mol% or more, and preferably 100 mol%. It may be. When the proportion of any one transition metal of Fe, Mn, and Co in the transition metal is 60 mol% or more, the flat region of the potential curve becomes wider due to the influence of the one transition metal. As the flat region becomes wider, charge and discharge are often performed in the flat region of the above-described potential curve, and the charge depth is likely to vary. However, in the electricity storage device 1 of the present embodiment, even when the positive electrode active material is as described above, the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage is 0V. Therefore, as described above, the variation in the charging depth in the positive electrode can be reduced in a relatively short time.

In the electricity storage device 1 of the present embodiment, the transition metal M of LiMPO ₄ described above may be two or more of Fe, Mn, and Co, but it is preferable that M of the transition metal is at least Fe. That is, it is preferable that M contains at least Fe. More preferably, the active material of the positive electrode is lithium iron phosphate (LiFePO ₄ ). When the positive electrode active material is lithium iron phosphate, the positive electrode active material is more than the case where the positive electrode active material is another polyanion compound other than lithium iron phosphate or another active material (LiNiCoMnO ₂ system or LiMn ₂ O ₄ ). The potential in the flat region of the potential curve is lowered. Therefore, when lithium iron phosphate and an active material other than lithium iron phosphate are mixed, the proportion of the flat region on the end of discharge can be increased in the potential curve because the potential is lowered by lithium iron phosphate. As the flat area increases at the end of the discharge, the charge / discharge is performed more frequently in the flat area, so that the variation in the charge depth is more likely to occur. However, even if the active material contains a relatively large amount of lithium iron phosphate, by performing charging or discharging using the inclined region at the end of discharging, the variation in charging depth can be reduced more reliably.

In the electricity storage device 1 of the present embodiment, the negative electrode active material is preferably non-graphitic carbon (amorphous carbon). When the active material of the negative electrode is non-graphitic carbon, the potential change at the end of discharge of the negative electrode is not abrupt and gentle compared to the case where the active material is graphite (graphite) or lithium titanate, and the open circuit voltage is As it approaches 0V, the potential gradually increases. Therefore, when the active material of the negative electrode is non-graphitic carbon, the open circuit potential of the positive electrode when the open circuit voltage is 0 V is not extremely low. Since the potential of the positive electrode does not become extremely low, it is possible to suppress deterioration of a member such as an aluminum metal foil of the positive electrode due to the low potential.

In the electricity storage device 1 of the present embodiment, when the capacity (charge rate SOC) is 100%, the absolute value of the slope of the positive circuit open circuit potential curve (the slope of the potential with respect to the capacity) is the slope of the open circuit potential curve of the negative electrode. It may be larger than the absolute value of (the potential gradient with respect to the capacitance). Further, at the end of charging (when the SOC is close to 100%), the open circuit potential of the positive electrode may be located in the inclined region. With such a configuration, by performing charging or discharging when the SOC is close to 100% (at the end of charging), it is possible to reduce variation in the charging depth at the positive electrode, as in the case of charging or discharging at the end of discharging.

The separator is strip-shaped. The separator has a porous separator substrate. The separator is disposed between the positive electrode and the negative electrode in order to prevent a short circuit between the positive electrode and the negative electrode. The separator of this embodiment has only a separator base material.

The separator substrate is configured to be porous. A separator base material is a textile fabric, a nonwoven fabric, or a porous film, for example. Examples of the material for the separator substrate include polymer compounds, glass, and ceramics. Examples of the polymer compound include a group consisting of polyester such as polyacrylonitrile (PAN), polyamide (PA), polyethylene terephthalate (PET), polyolefin (PO) such as polypropylene (PP) and polyethylene (PE), and cellulose. The at least 1 sort selected from more is mentioned.

The width of the separator (the dimension of the strip shape in the short direction) is slightly larger than the width of the negative electrode active material layer. A separator is arrange | positioned between the positive electrode and the negative electrode which were piled up in the state shifted | deviated in the width direction so that a positive electrode active material layer and a negative electrode active material layer may overlap. At this time, the uncoated portion of the positive electrode and the uncoated portion of the negative electrode do not overlap. That is, the non-covered portion of the positive electrode protrudes in the width direction from the region where the positive electrode and the negative electrode overlap, and the non-covered portion of the negative electrode extends in the width direction (the protruding direction of the non-covered portion of the positive electrode). (Opposite direction). The electrode body 2 is formed by winding the stacked positive electrode, negative electrode, and separator, that is, the stacked body 22.

The case 3 includes a case main body 31 having an opening and a lid plate 32 that closes (closes) the opening of the case main body 31. The case 3 houses the electrolytic solution in the internal space together with the electrode body 2 and the current collector 5. Case 3 is formed of a metal having resistance to the electrolytic solution. The case 3 is made of an aluminum-based metal material such as aluminum or an aluminum alloy, for example. The case 3 may be formed of a metal material such as stainless steel and nickel, or a composite material obtained by bonding a resin such as nylon to aluminum.

The electrolytic solution is a non-aqueous electrolytic solution. The electrolytic solution is obtained by dissolving an electrolyte salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The electrolyte salt is LiClO ₄ , LiBF ₄ , LiPF ₆ or the like. The electrolyte of this embodiment is obtained by dissolving 0.5 mol / L or more and 1.5 mol / L or less of LiPF ₆ in a mixed solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a predetermined ratio. is there.

The lid plate 32 has a gas discharge valve 321 that can discharge the gas in the case 3 to the outside. The gas discharge valve 321 discharges gas from the inside of the case 3 to the outside when the internal pressure of the case 3 rises to a predetermined pressure. The gas discharge valve 321 is provided at the center of the lid plate 32.

Case 3 is provided with a liquid injection hole for injecting an electrolytic solution. The liquid injection hole communicates the inside and the outside of the case 3. The liquid injection hole is provided in the lid plate 32. The liquid injection hole is sealed (closed) by a liquid injection stopper 326. The liquid filling tap 326 is fixed to the case 3 (the cover plate 32 in the example of the present embodiment) by welding.

The external terminal 7 is a part that is electrically connected to the external terminal 7 of another power storage element 1 or an external device. The external terminal 7 is formed of a conductive member. The external terminal 7 has a surface 71 to which a bus bar or the like can be welded. The surface 71 is a flat surface.

The current collector 5 is disposed in the case 3 and is directly or indirectly connected to the electrode body 2 so as to be energized. The current collector 5 of the present embodiment is formed of a conductive member. As shown in FIG. 2, the current collector 5 is disposed along the inner surface of the case 3. The current collector 5 is electrically connected to the positive electrode and the negative electrode of the electricity storage device 1.

In the electricity storage device 1 of the present embodiment, the electrode body 2 (specifically, the electrode body 2 and the current collector 5) housed in a bag-like insulating cover 6 that insulates the electrode body 2 and the case 3 is the case 3. Housed inside.

Next, a method for manufacturing the electricity storage device 1 of the above embodiment will be described.

The method for manufacturing the electricity storage device 1 of the present embodiment includes an active material mainly composed of LiMPO ₄ having an olivine structure (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co). Preparing a positive electrode and preparing a negative electrode containing an active material. At least one of preparing the positive electrode and preparing the negative electrode, the irreversible capacity of the negative electrode is made smaller than the irreversible capacity of the positive electrode. Thus, the above-mentioned electrical storage element 1 is manufactured by preparing a positive electrode and a negative electrode.
The irreversible capacity is a value obtained by subtracting the discharge energization amount (discharge electricity amount) from the charge energization amount (charge electricity amount) when the electrode and each material are charged and discharged.

In the method for manufacturing the electricity storage device 1, first, a mixture containing an active material is applied to a metal foil (current collector foil) to form an active material layer, and a positive electrode and a negative electrode are respectively prepared (manufactured). Next, the positive electrode, the separator, and the negative electrode are overlapped to form the electrode body 2. Subsequently, the electrode body 2 is put in the case 3 and the electrolytic solution is put in the case 3 to assemble the power storage element 1.

In the production of the positive electrode, for example, a relatively large irreversible capacity is generated in the active material in order to increase the irreversible capacity of the positive electrode. For example, a mixture of the active material of LiMPO ₄ having an olivine structure and an active material (such as LiNi _0.8 Co _0.15 Al _0.05 O ₂ ) having a larger irreversible capacity than the active material is used. By using it as a material, a relatively large irreversible capacity is generated in the active material. Further, for example, the irreversible capacity of the positive electrode is increased by a material other than the active material that can be electrolyzed along with charge / discharge of the power storage element (hydrated water attached to the active material, Li ₆ CoO ₄ , Li ₂ O, etc.). . By these, the irreversible capacity | capacitance of a negative electrode can be made smaller than the irreversible capacity | capacitance of a positive electrode, and the electrical storage element 1 of embodiment mentioned above can be manufactured.
In the production of the positive electrode, for example, the positive electrode active material layer is formed by applying a mixture containing active material particles, a binder, a conductive additive, and a solvent to both surfaces of the metal foil. A general method is adopted as a coating method for forming the positive electrode active material layer. The applied positive electrode active material layer is roll-pressed at a predetermined pressure. By adjusting the pressing pressure, the thickness and density of the positive electrode active material layer can be adjusted.

In the production of the negative electrode, in order to reduce the irreversible capacity of the negative electrode (in order to prepare an active material with reduced irreversible capacity), for example, a carbonaceous material (such as non-graphitic carbon) as an active material is doped with lithium ions. . Thereby, the irreversible capacity | capacitance of a negative electrode can be made smaller than the irreversible capacity | capacitance of a positive electrode, and the electrical storage element 1 of embodiment mentioned above can be manufactured.
Preferably, lithium ions having an irreversible capacity or more are doped into a carbonaceous material (such as non-graphitic carbon) as an active material. Specifically, metallic lithium corresponding to an amount of electricity greater than or equal to the irreversible capacity is conducted to the negative electrode. More specifically, if the irreversible capacity of non-graphitic carbon as an active material is 30 mAh / g, metal lithium corresponding to an amount of electricity equal to or greater than the value obtained by multiplying the irreversible capacity by the amount of active material is conducted to the negative electrode. Let Thereby, during the aging after charging the produced electricity storage device 1 for the first time, metallic lithium is dissolved, and the dissolved lithium is occluded in the active material of the negative electrode. The amount of metallic lithium conducted to the negative electrode is preferably larger than the amount of metallic lithium stored in the active material. Thereby, the irreversible capacity | capacitance of a negative electrode can be made small more reliably, and the electrical storage element 1 of this embodiment can be manufactured more reliably. However, in order to prevent lithium electrodeposition, less lithium metal is stored in the active material than the active material can store.
In the production of the negative electrode, a negative electrode active material layer is formed on both surfaces of the metal foil in the same manner as in the production of the positive electrode.

The electric storage element can also be manufactured by adjusting the capacity ratio (N / P ratio) between the positive electrode and the negative electrode. For example, by increasing the capacity ratio (mass ratio) of the positive electrode active material to the negative electrode active material, the irreversible capacity of the positive electrode relative to the irreversible capacity of the negative electrode can be relatively increased, so that the open circuit voltage of the storage element is 0 V In this case, the open circuit potential of the positive electrode can be designed to be located in the inclined region.

Even if the storage element is manufactured without performing the above operations on the active material of the positive electrode or the negative electrode, and the preliminary charge or chemical conversion treatment is simply performed after the manufacture, the positive electrode is opened when the open circuit voltage is 0V. The circuit potential is not located in the slope region of the potential curve. Even if the preliminary charging or the chemical conversion treatment is simply performed, the open circuit potential of the positive electrode when the open circuit voltage is 0 V is higher than 3 V with respect to the lithium potential.

In the formation of the electrode body 2, the electrode body 2 is formed by winding the laminated body 22 with a separator interposed between the positive electrode and the negative electrode. Specifically, the positive electrode, the separator, and the negative electrode are overlapped so that the positive electrode active material layer and the negative electrode active material layer face each other with the separator interposed therebetween, thereby forming the laminate 22. The laminated body 22 is wound to form the electrode body 2.

In assembling the electricity storage element 1, the electrode body 2 is inserted into the case body 31 of the case 3, the opening of the case body 31 is closed with the cover plate 32, and the electrolytic solution is injected into the case 3. When closing the opening of the case body 31 with the cover plate 32, the electrode body 2 is inserted into the case body 31, the positive electrode and the one external terminal 7 are electrically connected, and the negative electrode and the other external terminal 7 are electrically connected. In this state, the opening of the case body 31 is closed with the cover plate 32. When the electrolytic solution is injected into the case 3, the electrolytic solution is injected into the case 3 from the injection hole of the cover plate 32 of the case 3.

In the electricity storage device 1 of this embodiment manufactured as described above, as shown in FIG. 3, when the open circuit voltage of the electricity storage device 1 is 0 V, the open circuit potential of the positive electrode is located in the slope region of the potential curve. To do.
On the other hand, for example, even when lithium iron phosphate is used as the active material for the positive electrode and non-graphitic carbon is used as the active material for the negative electrode, and the power storage device is simply assembled, as shown in FIG. The positive open circuit potential when the circuit voltage is 0 V is not located in the slope region of the potential curve. If further discharging is continued from this state, as can be recognized from FIG. 4, if the metal foil of the negative electrode is made of copper, the metal foil of the negative electrode has a high potential at which copper dissolves. Can dissolve.

Then, the usage method of the electrical storage element 1 of the said embodiment is demonstrated.

The method of using the electricity storage device 1 according to the embodiment includes charging or discharging the electricity storage device 1 through the slope region in the open circuit potential curve of the positive electrode.

In the above usage method, charging or discharging may be performed in the inclined region. Further, the charging and discharging may be repeated a plurality of times. In the above usage method, charging or discharging may be performed through an inclination region where the absolute value of the inclination of the potential with respect to the capacitance is 3 Vg · Ah ⁻¹ or more.

In the above method of use, it is preferable to perform charging and discharging through an inclined region having a lower potential than the flat region of the open circuit potential curve of the positive electrode. That is, charging and discharging may be performed through an inclined region at the end of discharging. Thereby, in the inclined region at the end of discharge, the potential of the positive electrode is not so high, so that the electrolytic solution can be prevented from being decomposed by a high potential. In addition, by performing charging and discharging in the slope region at the end of discharge (on the low potential side), when the active material of the negative electrode is a carbonaceous material, generation of lithium electrodeposition on the active material can be suppressed.

Next, a power storage device according to an embodiment of the present invention will be described with reference to FIG.
The power storage device 10 includes one or more power storage elements 1 and a control device 100. The control device 100 includes a receiving unit 101, an SOC calculating unit 102, a charge / discharge control unit 103, a memory 104, and a time measuring unit 105. The power storage device 10 further includes a voltmeter 11, an ammeter 12, a generator 13, a load 14, and switches 6A and 6B. The charge / discharge control unit 103 performs switch open / close control. The power storage device 10 may include at least two power storage elements 1 and a bus bar member (not shown) that electrically connects the power storage elements 1 to each other. In this case, the technique of the present invention may be applied to at least one power storage element.
The memory 104 stores an SOC-OCV curve. The timer 105 is a counter that measures time. The receiving unit 101 acquires a voltage value from the voltmeter 11 or a current value from the ammeter 12 and transmits the information to the SOC calculation unit 102. The SOC calculation unit 102 calculates the SOC from the SOC-OCV curve stored in the memory 104 using the voltage value acquired from the reception unit 101. Alternatively, the current values acquired from the receiving unit 101 are integrated, the time is acquired from the time measuring unit 105, the charge electricity amount or the discharge electricity amount is obtained, and the SOC is calculated from the charge electricity amount or the discharge electricity amount (current integration). SOC is obtained using the method). The calculated SOC information is transmitted to the charge / discharge control unit 103. The charge / discharge control unit 103 determines whether or not the SOC value acquired from the SOC calculation unit 102 is a predetermined value or less (for example, 15% or less). I do. The neglecting process is continued until a predetermined time elapses based on the time measured by the time measuring unit 105.

As an example, the control flow of the charge / discharge control unit is shown in FIG. In S1, the SOC of the storage element is determined. It is determined whether the SOC is equal to or less than a predetermined value. If the value exceeds the predetermined value, the process ends. If the SOC is equal to or lower than the predetermined value, the process proceeds to a leaving process (S2) for prohibiting charging / discharging. Further, the time is accumulated by a counter (timer) (S3). Next, it is determined whether or not the accumulated time is a predetermined value or more (S4). If the integration time is less than the predetermined value, the process ends and returns to the start. If it is equal to or greater than the predetermined value, the process proceeds to a process of canceling the charge / discharge inhibition (S5). In S5, charging / discharging is permitted, the counter is reset (S6), and the process is terminated.

In addition, the electric storage element of the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention. For example, the configuration of another embodiment can be added to the configuration of a certain embodiment, and a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment. Furthermore, a part of the configuration of an embodiment can be deleted.

In the above embodiment, the positive electrode in which the active material layer containing the active material is in direct contact with the metal foil has been described in detail. However, in the present invention, the positive electrode is a conductive layer containing a binder and a conductive auxiliary agent, and the active material layer And a conductive layer disposed between the metal foil and the metal foil.

In the above embodiment, the power storage element 1 including the electrode body 2 in which the multilayer body 22 is wound has been described in detail. However, the power storage element of the present invention may include the multilayer body 22 that is not wound. Specifically, the storage element may include an electrode body in which a positive electrode, a separator, a negative electrode, and a separator each formed in a rectangular shape are stacked a plurality of times in this order.

In the above embodiment, the case where the power storage element 1 is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described. However, the type and size (capacity) of the power storage element 1 are arbitrary. is there. Moreover, although the lithium ion secondary battery was demonstrated as an example of the electrical storage element 1 in the said embodiment, it is not limited to this. For example, the present invention can be applied to various secondary batteries, and other power storage elements such as electric double layer capacitors.

1: Storage element (non-aqueous electrolyte secondary battery)
10: power storage device 100: control device 101: receiving unit 102: SOC calculating unit 103: charge / discharge control unit 104: memory 105: time measuring unit 11: voltmeter 12: ammeter 13: generator 14: load 15A, 15B: switch 2: Electrode body 22: Laminated body 3: Case 31: Case body 32: Cover plate 5: Current collector 6: Insulating cover 7: External terminal 71: Surface

Claims (6)

A positive electrode including an active material mainly composed of LiMPO ₄ having an olivine structure (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co);
The open circuit potential curve of the positive electrode has a flat region and an inclined region,
The storage element, wherein the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage of the storage element is 0V. The electrical storage element according to claim 1, wherein the content of any transition metal in the transition metal M of LiMPO ₄ is 60 mol% or more. The electricity storage device according to claim 1 or 2, further comprising a negative electrode containing non-graphitic carbon. An open circuit potential curve comprising a flat region and an inclined region containing an active material mainly composed of LiMPO ₄ having an olivine structure (M is at least one transition metal selected from the group consisting of Fe, Mn, and Co). Preparing a positive electrode having,
Preparing a negative electrode containing an active material,
In preparing the positive electrode and / or preparing the negative electrode, the irreversible capacity of the negative electrode is made smaller than the irreversible capacity of the positive electrode.
A method for manufacturing a storage element, wherein the open circuit potential of the positive electrode is located in the inclined region when the open circuit voltage of the storage element is 0V. Putting the electricity storage device according to any one of claims 1 to 3 into a low-charge state;
Leaving the power storage element, and controlling the power storage element. The electricity storage device according to any one of claims 1 to 3,
A control unit including a receiving unit, an SOC calculation unit, and a charge / discharge control unit,
The receiving unit receives a voltage value or a current value of the power storage element,
The SOC calculation unit calculates an SOC based on the voltage value or the current value,
The charge / discharge control unit is a power storage device that determines whether to perform a neglect process based on the SOC.

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