JP5720952B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery that can be used at a higher voltage and has good cycle characteristics.

  A lithium ion secondary battery includes positive and negative electrodes capable of reversibly occluding and releasing lithium ions, and a separator interposed between the two electrodes. The separator is impregnated with a nonaqueous electrolytic solution, and charging and discharging are performed by lithium ions in the electrolytic solution moving between the electrodes. Because it is lightweight and has high energy density, it is widely used as a power source for various portable devices. Moreover, utilization is anticipated also in the field | area which requires large capacity | capacitance power supplies, such as a vehicle, and the higher energy density is calculated | required. Patent documents 1-3 are mentioned as technical literature about a lithium ion secondary battery.

JP 2007-524204 A JP 2009-508309 A JP 2009-545129 A

The increase in energy density can be realized, for example, by increasing the voltage of the battery (increasing the upper limit voltage during use). As a means for increasing the voltage, for example, as a positive electrode material, a potential higher than the upper limit voltage in a typical usage mode of a general lithium ion secondary battery (for example, the positive electrode potential is 4.3 V (vs. Li / Li ⁺ The use of a lithium transition metal compound that can function suitably as a positive electrode active material is also being investigated in the embodiment charged to above). Along with this, improvement in oxidation resistance of electrolyte components (solvents and the like) is also required, and it has been reported that a fluorinated organic solvent is used as the electrolyte solution solvent. However, generally, since the oxidation resistance and reduction resistance of a substance are contradictory properties, if one is improved, the other is lowered. Therefore, an electrolyte solution containing a solvent with high oxidation resistance is in a state where the negative electrode potential is low (typically when the battery is in a fully charged state or a state close thereto, for example, the negative electrode potential is 0.1 V (vs. Li / Li ⁺ )), the solvent tends to undergo reductive decomposition in the negative electrode, and the battery capacity may be significantly reduced by repeated charge / discharge cycles and long-term storage at high temperatures.
In order to suppress the reduction reaction in such a negative electrode, it is also conceivable to use an electrolytic solution to which a material (SEI forming material) capable of forming a coating (SEI) for suppressing the reduction reaction on the negative electrode surface is added. However, when the potential of the positive electrode is high, the SEI forming material is oxidized and decomposed at the positive electrode, and the negative electrode surface is difficult to be properly covered with SEI. For this reason, the effect of adding the SEI forming material may not be sufficiently exerted, and it may be difficult to improve charge / discharge cycle characteristics (for example, improvement in capacity deterioration).

  An object of the present invention is to provide a lithium ion secondary battery having excellent cycle characteristics even when used under conditions of a high upper limit voltage value (for example, 4.3 V or more). Another object of the present invention is to provide a power supply device using such a lithium ion secondary battery.

  According to the present invention, there is provided a lithium ion secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolyte P containing a nonaqueous solvent, a supporting salt, and an SEI forming material. . The battery further includes a non-fluid electrolyte Q interposed between the positive electrode active material and the electrolytic solution P.

  In the lithium ion secondary battery of such an embodiment, the electrolyte solution P is in the form of a solution, while the electrolyte Q is non-fluid (typically gel or solid), so that they are separated without being mixed. Maintained. Therefore, it is possible to separately control the characteristics (oxidation resistance, reduction resistance, etc.) of the electrolytic solution P and the electrolyte Q. In addition, since the non-fluid electrolyte Q is interposed between the electrolytic solution P and the positive electrode active material, direct contact between the electrolytic solution P and the positive electrode active material is prevented, and the SEI contained in the electrolytic solution P is prevented. It is possible to avoid an event in which the forming material is decomposed on the surface of the positive electrode (this consumes the SEI forming material and makes it difficult for the negative electrode surface to be properly covered with SEI). Furthermore, since the electrolytic solution P contains the SEI forming material and is in a liquid state, SEI can be efficiently formed and repaired on the negative electrode surface, and a reduction in capacity due to repeated charge / discharge cycles can be suppressed. Accordingly, for example, a lithium ion secondary battery that can exhibit good cycle characteristics even when used at a higher voltage value (for example, 4.3 V or more) than a conventional general lithium ion secondary battery can be realized.

In a preferred embodiment of the technology disclosed herein, the non-flowable electrolyte Q is an electrolyte composition that forms a gel. This gel electrolyte composition Q typically includes a non-aqueous solvent and a supporting salt. The positive electrode active material is coated with the gel electrolyte composition Q. Since the electrolyte composition Q is in a gel form, it is fixed on the positive electrode, and direct contact with the negative electrode can be prevented. By this, reductive decomposition on the negative electrode surface of the solvent contained in the electrolyte composition Q can be substantially avoided. Preferably, the oxidation potential (vs. Li / Li ⁺ ) of the non-aqueous solvent contained in the electrolyte composition Q is higher than the oxidation potential (vs. Li / Li ⁺ ) of the non-aqueous solvent contained in the electrolyte P ( Typically 0.1V or higher, preferably 0.2V or higher, for example, about 0.3V to 1.0V higher). When the electrolyte Q containing a non-aqueous solvent having a high oxidation potential (not easily oxidized but tends to be reduced) is used, it is particularly meaningful to apply the configuration of the present invention.

Here, “the positive electrode active material is coated with the electrolyte composition Q” means, for example, in the positive electrode having the porous layer containing the positive electrode active material, the composition Q on at least the surface of the porous layer. Is assigned (retained; applied). In a preferred embodiment, the electrolyte composition Q also enters at least a part of the fine pores (pores) of the porous layer (typically, pores at least in the vicinity of the outer surface) ( Soaked). The SEI (Solid Electrolyte Interface: solid electrolyte interface) is a surface coating having a function of suppressing side reactions (such as reductive decomposition) on the negative electrode surface. The SEI-forming material refers to a material that allows the SEI to be formed more easily when the material is contained in the electrolyte solution than when the material is not contained. The electrolyte P is in the form of a solution. “The oxidation potential (vs. Li / Li ⁺ ) of the non-aqueous solvent contained in the electrolyte composition Q is higher than the oxidation potential (vs. Li / Li ⁺ ) of the non-aqueous solvent contained in the electrolyte P”. The oxidation potential measured for the non-aqueous solvent contained in the product Q (which may be a mixture of two or more non-aqueous solvents) is the non-aqueous solvent (mixture of two or more non-aqueous solvents) contained in the electrolyte P. It is higher than the measured oxidation potential. Here, the oxidation potential (which can also be grasped as the oxidative decomposition start potential) is a case where constant voltage charging is performed while gradually increasing the voltage for the evaluation cell in the oxidation potential measurement method described later. The potential when the current value is greater than 0.1 mA. Hereinafter, the gel electrolyte composition may be simply referred to as an electrolyte gel.

  In another preferred embodiment of the technology disclosed herein, the non-fluid electrolyte Q is a solid electrolyte (typically a solid inorganic material). By interposing the solid electrolyte Q between the positive electrode active material and the electrolytic solution P, direct contact between the positive electrode active material and the SEI forming material contained in the electrolytic solution P is more reliably prevented, In the positive electrode, the SEI forming material is less likely to undergo oxidative decomposition, alteration, and the like. Thereby, SEI is appropriately formed and repaired on the surface of the negative electrode, and capacity reduction due to repeated charge / discharge cycles can be suppressed. From this, for example, a lithium ion secondary battery that can exhibit good cycle characteristics even when used at a higher voltage value (for example, 4.3 V or more) than a conventional general lithium ion secondary battery can be realized. In a preferred embodiment, the solid electrolyte Q is coated on the surface of the positive electrode active material. For example, in a lithium ion secondary battery including a particulate positive electrode active material, it is preferable that the surface of the positive electrode active material particle is coated with a solid electrolyte Q. Such a configuration is suitable for preventing direct contact between the electrolyte P and the positive electrode active material by the solid electrolyte Q without greatly increasing the internal resistance of the battery.

Techniques disclosed herein (about positive electrode potential when fully charged (vs. Li / Li ⁺⁾ is 4.1～4.2V) positive electrode potential (vs. Li / Li ⁺⁾ is a general lithium ion secondary battery It can be preferably applied to a lithium ion secondary battery used in a mode (use conditions) that can be charged until it becomes higher. For example, it is suitable for a lithium ion secondary battery used under a condition that the positive electrode potential (vs. Li / Li ⁺ ) is 4.3 V or higher, more preferably 4.5 V or higher (for example, 4.7 V or higher). .

In a preferred embodiment, the nonaqueous solvent contained in the electrolyte gel Q has an oxidation potential (vs. Li / Li ⁺ ) higher than 4.3V. Here, when the non-aqueous solvent contained in the electrolyte gel Q is a mixture (mixed solvent) of two or more kinds of non-aqueous solvents, “the oxidation potential of the non-aqueous solvent contained in the electrolyte gel Q (vs. Li / Li ^“+ ) Is higher than 4.3V” means that the oxidation potential measured for the whole of the non-aqueous solvent is higher than 4.3V. The lithium ion secondary battery of this aspect can be suitably used under the condition that the upper limit voltage is 4.3 V or higher. In a preferred embodiment, the oxidation potential measured for each component (non-aqueous solvent) contained in the mixed solvent is higher than 4.3V.

In another preferred embodiment, the non-aqueous solvent contained in the electrolyte composition Q has an oxidation potential (vs. Li / Li ⁺ ) of the positive electrode active material in a fully charged state of the battery (an operating potential described later). .) (Vs. Li / Li ⁺ ). In such a lithium ion secondary battery, even if the battery is fully charged (even if the SOC (State Of Charge) is 100%), the nonaqueous solvent contained in the electrolyte gel Q is difficult to be oxidized and decomposed. The increase in resistance at can be suppressed. “Fully charged” refers to charging the battery until the SOC reaches 100% at the upper limit voltage for ensuring a desired capacity (typically, the rated capacity determined by the battery design). “Fully charged potential” refers to a state in which the SOC is 100% after charging at the upper limit voltage for securing the desired capacity. Further, “full charge potential (vs. Li / Li ⁺ )” means a positive electrode potential based on metallic lithium at the above upper limit voltage (which can also be grasped as the charge upper limit potential of the charge / discharge control system).

In another preferred embodiment, 95% by volume or more of the non-aqueous solvent contained in the electrolyte composition Q is composed of at least one fluorinated carbonate. Fluorinated carbonates tend to have higher oxidation potentials (vs. Li / Li ⁺ ) than the corresponding carbonates. Therefore, even if this lithium ion secondary battery is used at a higher upper limit voltage setting, it can have good cycle characteristics.

  In another preferred embodiment, the lithium ion secondary battery further includes a porous plastic layer disposed between the electrolyte composition Q and the negative electrode. Typically, the pores of the porous plastic layer are impregnated with the electrolytic solution P. Such plastic layers have physical pores through which lithium ions can efficiently move between the two electrodes. In a preferred embodiment, when the temperature reaches the melting point of the plastic layer, these pores close by melting. That is, the lithium ion secondary battery having such a plastic layer at the predetermined location can be provided with a shutdown function that stops charging / discharging when overheating due to overcharging occurs, as in the conventional battery.

  As another aspect of the technology disclosed herein, a power supply comprising the lithium ion secondary battery disclosed herein and a control circuit electrically connected to the battery and defining at least an upper limit voltage value of the battery An apparatus is provided. Here, the upper limit voltage value is set to 4.3 V or higher. Such a power supply device can be one in which the capacity reduction of the lithium ion secondary battery is small even at the relatively high upper limit voltage value.

  As described above, the lithium ion secondary battery disclosed herein is excellent in cycle characteristics even when used under conditions having a higher upper limit voltage value than conventional general lithium ion secondary batteries, and is therefore used in vehicles. It is suitable as a power source. Therefore, according to this invention, the vehicle provided with one of the lithium ion secondary batteries disclosed here is provided. In particular, a vehicle (for example, an automobile) including such a lithium ion secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is preferable.

It is a perspective view which shows typically the external shape of the lithium ion secondary battery which concerns on one Embodiment. It is the II-II sectional view taken on the line in FIG. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion secondary battery of this invention. It is sectional drawing which shows typically the structural concept of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the structural concept of the lithium ion secondary battery which concerns on other one Embodiment of this invention. It is sectional drawing which shows typically the structural concept of the lithium ion secondary battery which concerns on other one Embodiment of this invention. It is sectional drawing which shows typically the structural concept of the positive electrode active material particle used in embodiment shown by FIG. It is explanatory drawing which shows the power supply system containing the lithium ion secondary battery which concerns on one Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In the following drawings, members / parts having the same action are described with the same reference numerals, and redundant descriptions may be omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  Examples of an aspect provided with a gel-like non-fluidic electrolyte (electrolyte gel) Q will be described with reference to FIGS. 4 and 5 for lithium ion secondary batteries according to some embodiments of the present invention. Moreover, the example of the aspect provided with the solid non-fluid electrolyte (solid electrolyte) Q is demonstrated using FIG. 6 and FIG.

<Configuration example of lithium ion secondary battery provided with gel-like non-fluidic electrolyte Q>
As shown in FIG. 4, a lithium ion secondary battery 500 according to an embodiment of the present invention includes a positive electrode 530 having a positive electrode active material layer 534 on a positive electrode current collector 532, a negative electrode current collector, and a container 510. A negative electrode 540 having a negative electrode active material layer 544 over a body 542, an electrolyte gel 536 (electrolyte composition Q), and a liquid electrolyte (electrolytic solution P) 537 are provided. The positive electrode active material layer 534 is a layer mainly containing the positive electrode active material 534A, and the negative electrode active material layer 544 is a layer mainly containing the negative electrode active material 544A. The positive electrode active material layer 534 is covered with an electrolyte gel 536. The liquid electrolyte 537 is included in the battery so as to contact the negative electrode active material layer 544 but not directly contact the positive electrode active material layer 534. In other words, electrolyte compositions having different phases (electrolyte gel Q, electrolyte P) are on the positive electrode side (meaning “contact with the positive electrode”) and negative electrode side (meaning “contact with the negative electrode”). Each has an arranged configuration. That is, the electrolyte composition Q disposed on the positive electrode side is a gel phase, and the electrolytic solution P disposed on the negative electrode side is a solution phase.

  The lithium ion secondary battery of the present invention can be preferably implemented in a mode in which the battery 500 shown in FIG. 4 is modified. For example, in the battery 500, the positive electrode current collector 532 has the positive electrode active material layer 534 only on one surface (typically, the surface facing the negative electrode), and the electrolyte gel 536 covers the positive electrode active material layer 534. (Typically, also in the negative electrode, the negative electrode active material layer 544 is provided only on one surface of the negative electrode current collector 542 (typically, the surface facing the positive electrode).) Etc. are also included in the battery embodiments disclosed herein.

When using electrolyte compositions having different compositions on the positive electrode side and the negative electrode side, in order to prevent these two types of solutions from mixing and becoming uniform if they are both in the liquid phase, for example, Li ⁺ conduction However, it is required to interpose a liquid phase separation membrane (for example, a layer made of silicon) made of a substance that has the properties of the two kinds of electrolytes but has substantially no permeability to other components. However, such a liquid-tight separation membrane may not have a sufficient Li ⁺ conduction velocity, and the charge / discharge efficiency can be significantly reduced by interposing the separation membrane. On the other hand, in the lithium ion secondary battery disclosed herein, the electrolyte gel Q and the electrolyte solution P are different not only in composition and characteristics (at least oxidation resistance) but also in phase with each other on the positive electrode side and the negative electrode side. Are used respectively. Therefore, since it is not necessary to use a liquid phase separation membrane as described above, a higher Li ⁺ conduction velocity can be realized. As shown in FIG. 5, the technique disclosed herein allows the electrolyte P to permeate between both electrodes in the lithium ion secondary battery 500 shown in FIG. 4 or a battery obtained by modifying the lithium ion secondary battery 500 as described above. An embodiment in which an insulating layer (for example, a porous plastic layer) 550 is further disposed as a separator can be preferably implemented.

In the lithium ion secondary battery disclosed herein, the electrolyte composition Q is applied (held) to the pores in the positive electrode active material layer and the surface of the positive electrode active material layer. This positive electrode active material layer is, for example, a lithium ion secondary battery having a general operating potential (vs. Li / Li ⁺ ) in at least a partial range of SOC 0% to 100% (the upper limit of the operating potential is about 4.1 V). Higher positive electrode active material. For example, a positive electrode active material having an SOC range in which the operating potential (vs. Li / Li ⁺ ) is higher than 4.3V (in other words, the positive electrode active material having the highest operating potential at SOC 0% to 100% higher than 4.3V). Substance) can be preferably used. As an example of the positive electrode active material that can be preferably used, a lithium composite oxide (for example, spinel type lithium nickel manganese oxide) containing Ni and Mn as transition metals can be given. For example, a compound represented by the following formula: LiNi _P Mn _{2 -P} O ₄ (0.2 ≦ P ≦ 0.6); is preferable. A specific example of the spinel type lithium nickel manganese oxide represented by the above formula is LiNi _0.5 Mn _1.5 O ₄ . Examples of other preferable positive electrode active materials include LiNiPO ₄ , LiCoPO ₄ , Li ₂ MnO ₃ , Li ₂ MnPO ₄ F, and compounds obtained by replacing some of transition metal elements contained in these compounds with other elements. Is done.

Here, as the operating potential, a value measured as follows is adopted. That is, a positive electrode containing a positive electrode active material to be measured, metallic lithium as a counter electrode, metallic lithium as a reference electrode, and LiPF ₆ having a concentration of 1 M in a mixed solvent of EC: DMC = 30: 70 (volume basis). A triode cell is constructed using the electrolyte solution. Based on the theoretical capacity of the cell, the SOC is adjusted in increments of 5% from 0% SOC to 100% SOC (for example, adjustment is performed by constant current charging). At this time, after each cell is allowed to stand for 1 hour at each SOC value, the positive electrode potential (vs. Li / Li ⁺ ) is measured to obtain the operating potential at the SOC value of the positive electrode active material.

Normally, the operating potential of the positive electrode active material is highest in a range including SOC 100% between SOC 0% and 100%, so that the operating potential at SOC 100% (that is, fully charged state) is higher than 4.3V. A high positive electrode active material can be grasped as a positive electrode active material having an SOC range in which the operating potential is higher than 4.3V. The operating potential of the positive electrode active material in a fully charged state (vs. Li / Li ⁺ ) (hereinafter sometimes referred to as “the full charge potential of the positive electrode active material”) is more preferably higher than 4.4V. More preferably, the voltage is higher than 0.5 V, more preferably higher than 4.6 V (for example, 4.7 V or higher). The technology disclosed herein is typically preferably applied to a lithium ion secondary battery in which the positive electrode active material has a full charge potential (vs. Li / Li ⁺ ) of 7.0 V or less (for example, 5.0 V or less). The

  The electrolyte composition Q is in a gel form. The electrolyte gel of the aspect provided to the positive electrode active material is, for example, a polymer precursor obtained by adding a polymer precursor Qp, a polymerization initiator, etc. to a nonaqueous electrolytic solution containing a supporting salt in a nonaqueous solvent (organic solvent). After the Qp solution is applied to the positive electrode active material layer, it can be formed by holding it under appropriate conditions to cause gelation (for example, by allowing the polymerization reaction to proceed). Typically, after the positive electrode active material layer is sufficiently impregnated with the polymer precursor Qp solution, and an excess of the polymer precursor Qp solution is appropriately removed from the positive electrode active material layer according to a desired amount of electrolyte gel. The polymer is subjected to a polymerization reaction under suitable conditions (temperature, etc.). What is necessary is just to select superposition | polymerization temperature suitably, for example, it can be set as about 80-140 degreeC. The polymerization time may be appropriately selected and can be set to, for example, about 5 minutes to 3 hours. The “polymerization reaction” herein may be anything that can contribute to gelation (curing) of the polymer precursor Qp solution, and may be, for example, a crosslinking reaction, a condensation reaction, or the like. The impregnation of the polymer precursor Qp solution into the positive electrode active material layer may be performed, for example, under reduced pressure or under vacuum. The removal of the excess of the polymer precursor Qp solution is performed by extruding the excess solution while applying an appropriate pressure (for example, about 0.01 MPa to 0.1 MPa) to the surface of the positive electrode active material layer after the impregnation treatment. Can be implemented in this way.

In the electrolyte composition Q, the thickness of the portion laminated on the surface of the positive electrode active material layer (the distance from the surface of the positive electrode active material layer to the surface of the electrolyte gel layer) is not particularly limited. For example, the function as an insulating layer between both electrodes can be enhanced by making the portion laminated on the positive electrode surface relatively thick. On the other hand, from the viewpoint of increasing the output efficiency (Li ⁺ conductivity) by shortening the moving distance of lithium ions; from the viewpoint of reducing the weight and thickness of the battery, it is preferable that the thickness of the laminated portion is not too large. In consideration of these balances, the thickness can be set to about 10 μm to 100 μm, for example. When the thickness of the laminated portion is relatively thin, a porous insulating layer is preferably interposed as a separator between both electrodes. This porous insulating layer can be, for example, a porous plastic layer interposed between both electrodes. Such a porous plastic layer may be an independent member (separator sheet) like the insulating layer 550 illustrated in FIG. 5, and is a layer integrated with another member (for example, fixed to the surface of the negative electrode active material layer). Layer).

As the non-aqueous solvent, an organic solvent having an oxidation potential (vs. Li / Li ⁺ ) higher than the full charge potential (vs. Li / Li ⁺ ) of the positive electrode active material to be used is preferably selected and used. Preferably, the oxidation potential (vs. Li / Li ⁺ ) is 0.1 V or higher (eg, 0.2 V or higher, 0.3 V or higher) than the full charge potential (vs. Li / Li ⁺ ) of the positive electrode active material. 0.5V or higher.) High organic solvents can be used. Such organic solvents can be used alone or in combination of two or more. In the lithium ion secondary battery having such a configuration, the oxidation potential (vs. Li / Li ⁺ ) of the organic solvent in the electrolyte composition Q in contact with the positive electrode active material is higher than the positive electrode potential when the SOC of the battery is 100%. Can also be expensive. Therefore, the oxidative decomposition of the solvent at the positive electrode can be suppressed to a higher degree. Of the total amount of the nonaqueous solvent contained in the electrolyte composition Q, the amount occupied by the organic solvent having an oxidation potential higher than the full charge potential of the positive electrode active material to be used is preferably more than 50% by volume, more Preferably it is 75 volume% or more, More preferably, it is 90 volume% or more (for example, 95 volume% or more), and substantially all (for example, 98 volume% or more, typically 100 volume%) may be sufficient.

  As the non-aqueous solvent of the electrolyte composition Q, a fluorinated organic solvent is typically used. Preferred fluorinated organic solvents include fluoroethylene carbonate (FEC), trifluorodimethyl carbonate (TFDMC), difluorodimethyl carbonate (methyl difluoromethyl carbonate, di (fluoromethyl) carbonate), fluorinated esters, fluorinated ethers and the like. Examples thereof include carbonates (which may be cyclic, linear, or branched). Of the non-aqueous solvent contained in the electrolyte composition Q, typically 50% by volume or more, for example, 75% by volume or more (more preferably 95% by volume or more, more preferably 99% by volume or more) It is preferable that it is at least one of carbonates. Substantially all of the non-aqueous solvent may be one or more fluorinated carbonates.

In addition, the value measured according to the following method shall be employ | adopted as an oxidation potential (vs. Li / Li ^<+> ) of a nonaqueous solvent.
A working electrode is prepared using LiFePO ₄ . Specifically, LiFePO ₄ , acetylene black (conductive material), and PVDF (binder) are mixed so that the mass ratio thereof is 85: 5: 10, and N-methyl-2-pyrrolidone (NMP To prepare a slurry-like composition. This is applied in the form of an aluminum foil, and dried and roll-pressed to produce a working electrode (positive electrode) sheet. A three-electrode cell is constructed using the working electrode, metallic lithium as a counter electrode, metallic lithium as a working electrode, and an electrolytic solution to be measured. The triode cell is treated to completely desorb Li from the working electrode. Specifically, at a temperature of 25 ° C., constant current charging is performed up to 4.2 V at a current value that is 1/5 of the battery capacity (Ah) predicted from the theoretical capacity of the working electrode, and the current value is initial at 4.2 V. The constant voltage charging is performed until the current value becomes 1/50 of the current value (that is, the current value that is 1/5 of the battery capacity). Next, constant voltage charging is performed for a predetermined time (for example, about 10 hours) at an arbitrary voltage in a voltage range (typically a voltage range higher than 4.2 V) predicted to include the oxidation potential of the electrolyte to be measured. ) And measure the current value at that time. More specifically, the voltage is increased stepwise (for example, in steps of 0.2 V) within the voltage range, and constant voltage charging is performed for a predetermined time (for example, about 10 hours) at each step. Measure the current value. The potential when the current value during constant voltage charging is greater than 0.1 mA is defined as the oxidation potential of the electrolytic solution.

As the supporting salt, a lithium salt used as a supporting salt in a general lithium ion secondary battery can be appropriately selected and used. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO _{3 and the} like. These supporting salts can be used alone or in combination of two or more. A particularly preferred example is LiPF ₆ . The non-aqueous electrolyte is preferably prepared, for example, so that the concentration of the supporting salt is within a range of 0.7 to 1.3 mol / L.

  As the polymer precursor Qp, only one kind of material (which may be a monomer or an oligomer) whose characteristics after gelation (electrochemical stability, thermal stability, etc.) are adapted to the desired battery configuration and use conditions is used. Can be used alone or in combination of two or more. The polymer precursor Qp can be multifunctional or monofunctional. Usually, a polymer precursor (polyfunctional polymer precursor) having two or three or more polymerizable (crosslinkable) functional groups is preferably used. Preferred examples of the polymer precursor Qp include polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF). Typically, a polymer precursor Qp having a thermally polymerizable (thermally crosslinkable) functional group is used. Specific examples of the polymer precursor Qp preferably used in the technology disclosed herein include, for example, product number “TA140” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. and similar products. What is necessary is just to select the usage-amount of the said polymer precursor Qp suitably according to the desired degree of gelation etc., for example, it can be set as about 10-17 mass% of the said polymer precursor Qp solution.

  The said polymerization initiator can be suitably selected and used according to the kind of polymer precursor Qp to be used. Typically, a thermal polymerization initiator is used. As the thermal polymerization initiator, various conventionally known initiators such as azo type and peroxide type can be used. Preferred polymerization initiators include azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO) and the like. What is necessary is just to select the usage-amount of the said polymerization initiator suitably, For example, it can be set as about 0.1-3 mass% with respect to the said polymer precursor Qp.

  In the non-aqueous electrolyte, as other additives, those which are added to the electrolyte of a general lithium ion secondary battery and do not inhibit the polymerization reaction, or contribute to the control of the polymerization reaction and to the positive electrode And electrochemically stable ones may be added.

  As the electrolytic solution P, a non-aqueous electrolytic solution (that is, a solution containing a supporting salt in a non-aqueous solvent (organic solvent)) used in a general lithium ion secondary battery is added. Can be used. This electrolytic solution P is typically disposed so as to be in contact with both the negative electrode and the non-fluid electrolyte (electrolyte gel in the examples shown in FIGS. 4 and 5) Q. Usually, the electrolytic solution P is impregnated in at least the active material layer of the negative electrode, and in a mode in which the separator is disposed between both electrodes, the separator is also impregnated.

  As the non-aqueous solvent contained in the electrolytic solution P, an organic solvent which is used for an electrolytic solution of a general lithium ion secondary battery and hardly undergoes reductive decomposition at the negative electrode can be appropriately selected and used. These organic solvents can be used alone or in combination of two or more. For example, carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) (which may be cyclic, linear or branched). May be used). It is preferable to use at least one of these carbonates. For example, a mixed solvent of EC and DMC can be preferably used.

As the supporting salt contained in the electrolytic solution P, a general supporting salt for a lithium ion secondary battery can be used in the same manner as the supporting salt contained in the electrolyte composition Q. Typically, the same supporting salt as that used in the electrolyte composition Q is used. A particularly preferred example is LiPF ₆ . For example, the electrolytic solution P is preferably prepared so that the concentration of the supporting salt is within a range of 0.7 to 1.3 mol / L.

  As the SEI forming material, when a surface coating is formed on the negative electrode surface (typically, the SEI forming material is reduced and decomposed on the negative electrode surface, and the decomposition product forms a surface coating as SEI), as described above. In addition, a conventionally known compound that is known to exhibit a function of suppressing the reduction reaction on the negative electrode surface can be used without particular limitation. Such compounds may be used singly or in combination of two or more. For example, use of vinylene carbonate (VC), FEC or the like is preferable. That is, FEC can be preferably used as part or all of the nonaqueous solvent in the electrolytic solution composition Q, while it can be preferably used as the SEI forming material in the electrolytic solution P. For example, a configuration in which a gel-like non-fluidic electrolyte (electrolyte gel) Q and an electrolytic solution P containing FEC as an SEI forming material are combined can be preferably employed. What is necessary is just to select the quantity of the SEI formation material contained in the said electrolyte solution P suitably, for example, it can be set as about 1-5 vol% (volume%). Thereby, an SEI film is formed on the negative electrode surface, and side reactions (further reductive decomposition of the electrolyte component, precipitation of metallic lithium, etc.) on the negative electrode surface can be effectively suppressed.

  In the electrolytic solution P after the start of use of the lithium ion secondary battery (for example, after performing the conditioning treatment described in Examples described later), for example, 0.01 to 1.20 wt% of the electrolytic solution P It is preferable that the SEI forming material (more preferably 0.01 to 0.50 wt%) remains. As a result, even if the SEI film on the negative electrode surface is partially damaged (peeled off) due to repeated charge / discharge cycles, the SEI film is repaired by the remaining SEI forming material. For example, capacity reduction can be more effectively suppressed.

Thus, according to the lithium ion secondary battery of the aspect in which the electrolyte gel Q is interposed between the electrolytic solution P containing the SEI forming material and the positive electrode active material, in the corresponding laminated cell type evaluation battery having a theoretical capacity of 30 mAh, Preferably, in an evaluation test in which a predetermined charge / discharge cycle is repeated 300 cycles in a state in which the SOC is adjusted to 60% at a rate of 1/5 C at a temperature of 25 ° C. and restrained by applying a 350 kg / 25 cm ² load. The 300 cyc capacity retention rate (%) obtained as a percentage of the discharge capacity after the end of the cycle with respect to the initial capacity is approximately 80% or more. The predetermined charging / discharging cycle is “constant current charging up to 4.9 V at a rate of 2 C at a temperature of 40 ° C.—pause for 10 minutes—constant current discharge to 3.5 V at a rate of 2 C—pause for 10 minutes”. In a more preferred embodiment, the 300 cyc capacity retention rate is about 85% or more, more preferably about 88% or more (for example, 90% or more).

<Configuration example of a lithium ion secondary battery provided with a solid non-fluid electrolyte Q>
As shown in FIG. 6, a lithium ion secondary battery 500 according to another embodiment of the present invention includes a positive electrode 630 having a positive electrode active material layer 634 on a positive electrode current collector 532, and a negative electrode in a container 510. A negative electrode 540 having a negative electrode active material layer 544 over a current collector 542 and a liquid electrolyte (electrolytic solution P) 537 are provided. Furthermore, it is preferable to include an insulating layer 550 interposed between the positive electrode 630 and the negative electrode 540. The positive electrode active material layer 634 is a layer mainly containing the positive electrode active material 634A, and the negative electrode active material layer 544 is a layer mainly containing the negative electrode active material 544A. As schematically shown in FIG. 7, at least a part of the particle surface of positive electrode active material 634A (the entire surface in the example shown in FIG. 7) is covered with solid electrolyte 634B. That is, the positive electrode active material 634A and the solid electrolyte 634B are combined at the particle level. Therefore, the liquid electrolyte 537 is included in the battery so as to contact the negative electrode active material layer 544 but not directly contact the positive electrode active material 634A.

As the positive electrode active material 634A, the same material as the positive electrode active material in the embodiment including the gel-like non-fluidic electrolyte Q can be preferably used. The solid electrolyte that covers the particle surface of the positive electrode active material is a solid that has higher oxidation resistance than the positive electrode active material and hardly changes electrochemically under the use conditions (full charge potential) of the battery. A substance having lithium ion conductivity is preferable. As a solid electrolyte that can be preferably used, for example, aluminum-substituted lithium germanium phosphate (typically represented by Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ (0.2 ≦ x ≦ 0.8) Solid electrolyte). As another preferable solid electrolyte, a lithium phosphate solid electrolyte (typically Li ₃ PO ₄ , which may have a composition in which a part of Li is substituted with another element), Li ₂ O—B Examples include ₂ O ₃ solid solution. A solid electrolyte having a composition containing lithium is preferred.

  Such a composite of a positive electrode active material and a solid electrolyte is obtained, for example, by coating the particle surface of the positive electrode active material with the precursor Sp of the solid electrolyte, and firing the precursor Sp-coated positive electrode active material particles under predetermined conditions. Can be formed. The coating (coating) of the surface of the positive electrode active material particles with the precursor Sp can be preferably performed using, for example, a device that performs a coating process using a collision energy between particles using a centrifugal force. As such an apparatus, for example, “Nobilta NOB-MINI” manufactured by Hosokawa Micron Co., Ltd. or its equivalent can be used.

The firing temperature for forming the composite is preferably set to a temperature equal to or higher than the temperature at which the precursor Sp (typically amorphous powder) can be crystallized to form a desired solid electrolyte. Such crystallization can improve the lithium ion conductivity of the solid electrolyte. For example, when the solid electrolyte is Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ , the precursor (precursor attached to the surface of the positive electrode active material) has a temperature of 700 ° C. or higher (preferably 700 ° C. to 750 ° C.). It is preferable to fire at. The mass ratio of the positive electrode active material to the solid electrolyte (positive electrode active material: solid electrolyte) is, for example, 99.9: 0.1 to 90:10 (typically 99.8: 0.2 to 95: 5, for example, about 99.5: 0.5 to 97.5: 2.5). This can be achieved, for example, by setting the mass ratio when the positive electrode active material particles are coated with the solid electrolyte precursor Sp to be approximately the same as the mass ratio of the positive electrode active material and the solid electrolyte. . The mass ratio may be about 99.5: 0.5 to 98.5: 1.5. If the mass of the solid electrolyte relative to the mass of the positive electrode active material is too large, the internal resistance of the battery may increase and the output characteristics may tend to be reduced. If the mass of the solid electrolyte is too small relative to the mass of the positive electrode active material, it may be difficult to coat the surface of the positive electrode active material with the solid electrolyte.

The solid electrolyte precursor Sp can be prepared by drying or pre-baking a solution containing each element source contained in the solid electrolyte under predetermined conditions. For example, a precursor of Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ is obtained by mixing a Li source, an Al source, a Ge source, and a P source so that these element ratios have a desired composition ratio. The obtained solution can be preferably prepared by calcination under pressure in an atmosphere containing oxygen (typically in air) by the FCM method (Flash Creation Method) or the like. As a coating apparatus using the FCM method, for example, “Nobilta NOB-MINI” manufactured by Hosokawa Micron Co., Ltd. or an equivalent thereof can be used.

  In the lithium ion secondary battery having such a solid electrolyte Q, as the constituent component of the electrolyte P, the same components as the electrolyte P described in the aspect having the electrolyte gel Q described above can be used. For example, a configuration in which a solid non-flowable electrolyte (solid electrolyte) Q and an electrolytic solution P containing VC as an SEI forming material can be preferably employed. What is necessary is just to select suitably the quantity of the SEI formation material contained in the said electrolyte solution P, for example, can be about 0.1-3 wt% (mass%).

Thus, according to the lithium ion secondary battery having a configuration in which the solid electrolyte Q is interposed between the electrolytic solution P containing the SEI forming material and the positive electrode active material, in the corresponding laminated cell type evaluation battery having a theoretical capacity of 60 mAh, Preferably, in an evaluation test in which a predetermined charge / discharge cycle is repeated 100 cycles in a state where the SOC is adjusted to 60% at a rate of 1/5 C at a temperature of 25 ° C. and then restrained by applying a 350 kg / 25 cm ² load. The 100 cyc capacity retention rate (%) obtained as a percentage of the discharge capacity after the end of the cycle with respect to the initial capacity is approximately 80% or more. The predetermined charging / discharging cycle is “constant current charging at a temperature of 60 ° C. up to 4.9 V at a rate of 2 C—pause for 10 minutes—constant current discharge to 3.5 V at a rate of 2 C—pause for 10 minutes”. In a more preferred embodiment, the 200 cyc capacity retention rate obtained in the same manner after repeating the same cycle for another 100 cycles is about 43% or more, more preferably about 45% or more (for example, 50% or more).

  The matter disclosed in this specification includes any of the lithium ion secondary batteries disclosed herein having an upper limit voltage value of 4.3 V or higher (typically 4.5 V or higher, for example, 4.7 V or higher. ) And a method for use under the charge / discharge conditions set. Further, such a lithium ion secondary battery (may be in the form of an assembled battery in which a plurality of batteries are connected in series and / or in parallel) and the battery is set so as to be the above upper limit voltage value. And a power supply device including a control mechanism (control device) that controls the charging / discharging conditions.

  For example, as in the power supply device 800 shown in FIG. 8, the power supply device operates the load 802 according to the state of the lithium ion secondary battery 500, the load 802 connected thereto, and the lithium ion secondary battery 500. The electronic control unit (ECU) 804 to be adjusted may be included. The load 802 may include a power consumer that consumes the power stored in the lithium ion secondary battery 500 and / or a power supply device (charger) that can charge the battery 500. Based on the predetermined information, the ECU 804 controls the load 802 so that the upper limit voltage value of the battery 500 becomes a predetermined value (for example, 4.5 V) equal to or higher than 4.3V. A typical configuration of the ECU 804 includes at least a ROM (Read Only Memory) storing a program for performing such control, and a CPU (Central Processing Unit) capable of executing the program. As the predetermined information, for example, one or more information among the voltage of the battery 500, each electrode potential, charge / discharge history, and the like can be used. A lithium ion secondary battery 500 disclosed herein includes, for example, a vehicle (typically an automobile, particularly a hybrid automobile or an electric automobile) as shown in FIG. 3 as a component of a power supply device 800 as shown in FIG. , An automobile equipped with an electric motor such as a fuel cell automobile).

  Hereinafter, with reference to the drawings, an example of a lithium ion secondary battery disclosed herein is provided with a gel-like non-fluidic electrolyte (electrolyte gel) Q and an electrode body including positive and negative electrodes The lithium ion secondary battery 100 (FIG. 1) in which the water electrolyte is housed in a rectangular battery case will be described in more detail as an example, but the application target of the present invention is limited to such an embodiment. Is not intended. That is, the shape of the lithium ion secondary battery according to the present invention is not particularly limited, and the battery case, electrode body, and the like can be appropriately selected in terms of material, shape, size, and the like according to the application and capacity. For example, the battery case may have a rectangular parallelepiped shape, a flat shape, a cylindrical shape, or the like.

  As shown in FIGS. 1 and 2, the lithium ion secondary battery 100 includes a wound electrode body 20 and a flat box corresponding to the shape of the electrode body 20 together with the electrolyte P (represented by reference numeral 37). The battery case 10 is housed inside the opening 12 of the battery case 10 and the opening 12 of the case 10 is closed by the lid 14. The lid body 14 is provided with a positive terminal 38 and a negative terminal 48 for external connection so that a part of the terminals protrudes to the surface side of the lid body 14.

  The electrode body 20 includes a positive electrode sheet 30 in which a positive electrode active material layer 34 is formed on the surface of a long sheet-like positive electrode current collector 32 and an electrolyte gel Q (denoted by reference numeral 36) is further provided. The negative electrode sheet 40 in which the negative electrode active material layer 44 was formed on the surface of the sheet-like negative electrode current collector 42 was typically overlapped with two long sheet-like separators 50 and wound. It is formed into a flat shape by squeezing the rolled body from the side direction and causing it to be ablated. As described above, when the electrolyte gel 36 has a thickness that can function as an insulating layer, the use of the separator 50 can be omitted.

  The positive electrode sheet 30 has a positive electrode current collector 32 exposed at one end along the longitudinal direction. Similarly, in the negative electrode sheet 40 to be wound, the negative electrode current collector 42 is exposed at one end portion along the longitudinal direction. Then, the positive electrode terminal 38 is joined to the exposed end portion of the positive electrode current collector 32, and the negative electrode terminal 48 is joined to the exposed end portion of the negative electrode current collector 42, respectively. The positive electrode sheet 30 or the negative electrode sheet 40 is electrically connected. The positive and negative terminals 38 and 48 and the positive and negative current collectors 32 and 42 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

  As described above, the positive electrode sheet 30 is, for example, a paste in which the above-described positive electrode active material is dispersed in an appropriate solvent (for example, NMP) together with a conductive material, a binder (binder), and the like used as necessary. Or a slurry-like composition (positive electrode mixture) is prepared, applied to the positive electrode current collector 32, and dried to form the positive electrode active material layer 34. The positive electrode active material layer is sufficiently impregnated with the polymer precursor Qp solution in accordance with the above-described method, and if there is an excess of the polymer precursor Qp solution, it is removed and then subjected to a polymerization reaction to obtain an electrolyte composition. A gel phase 36 comprising Q is further applied. The amount of the positive electrode active material contained in the positive electrode active material layer can be, for example, about 69 to 98% by mass.

  In the production of a lithium ion secondary battery having a solid non-fluid electrolyte (solid electrolyte) Q or a positive electrode sheet for the battery, a composite of a positive electrode active material and a solid electrolyte is used as necessary. A paste-like or slurry-like composition dispersed in an appropriate solvent together with the conductive material and the binder to be used may be applied to the positive electrode current collector 32. The amount of the composite (that is, the composite of the positive electrode active material and the solid electrolyte) contained in the positive electrode active material layer can be, for example, about 69 to 98% by mass.

As the conductive material, a conductive powder material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. A conductive material can be used alone or in combination of two or more.
What is necessary is just to select suitably the quantity of the electrically conductive material contained in a positive electrode active material layer according to the kind and quantity of a positive electrode active material, for example, can be about 1-30 mass%.

  As the binder, one or two or more selected from various binding polymers can be used. For example, an organic solvent-soluble polymer such as polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene oxide-propylene oxide copolymer (PEO-PPO) is used. It can be preferably used. Examples of other usable binders include carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), hydroxypropylmethylcellulose phthalate (HPMCP), polyvinyl alcohol ( Water-soluble polymers such as PVA); polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoro Fluorine resin such as ethylene copolymer (ETFE), ethylene-vinyl acetate copolymer, styrene butadiene block copolymer (SBR), acrylic acid modified SBR resin (SBR latex) Scan), rubber such as gum arabic (water dispersible polymer); and the like. What is necessary is just to select the quantity of the binder contained in a positive electrode active material layer suitably according to the kind and quantity of a positive electrode active material and a electrically conductive material, for example, it can be set as about 1-10 mass%.

  For the positive electrode current collector 32, a conductive member made of a metal having good conductivity is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector 32 may vary depending on the shape of the lithium ion secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. . In the present embodiment, a sheet-like aluminum positive electrode current collector 32 is used, and can be preferably used for the lithium ion secondary battery 100 including the wound electrode body 20. In such an embodiment, for example, an aluminum sheet having a thickness of about 10 μm to 30 μm can be preferably used.

  The negative electrode sheet 40 includes, for example, a paste or slurry composition (negative electrode mixture) in which a negative electrode active material is dispersed in an appropriate solvent together with a binder (binder) as necessary. And the composition can be preferably prepared by drying.

  As the negative electrode active material, one type or two or more types of materials conventionally used in lithium ion secondary batteries can be used without any particular limitation. For example, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least in part can be used. Any of so-called graphitic (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), and those having a combination of these may be preferably used. Specific examples include natural graphite.

  As the binder, one kind or two or more kinds selected from those similar to the above-described positive electrode can be used. The amount of the binder contained in the negative electrode active material layer is not particularly limited, and may be appropriately selected according to the type and amount of the negative electrode active material.

  As the negative electrode current collector 42, a conductive member made of a metal having good conductivity is preferably used. For example, copper or an alloy containing copper as a main component can be used. In addition, the shape of the negative electrode current collector 42 may vary depending on the shape of the lithium ion secondary battery and the like, and thus is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. possible. In the present embodiment, a sheet-like copper negative electrode current collector 42 is used, and can be preferably used for the lithium ion secondary battery 100 including the wound electrode body 20. In this embodiment, for example, a copper sheet having a thickness of about 6 μm to 30 μm can be preferably used.

  The separator 50 (corresponding to the porous plastic layer described above) is a layer interposed between the positive electrode sheet 30 and the negative electrode sheet 40 and typically has a sheet shape, and the surface of the positive electrode sheet 30 (electrolyte composition). The positive electrode active material layer 34) whose surface is coated with Q and the surface of the negative electrode sheet 40 (negative electrode active material layer 44) are disposed in contact with each other. And prevention of a short circuit accompanying contact of both electrode active material layers 34 and 44 in the positive electrode sheet 30 and the negative electrode sheet 40, or a conductive path between the electrodes by impregnating the electrolyte solution P in the pores of the separator 50 ( It plays a role of forming a conductive path). As this separator 50, a conventionally well-known thing can be especially used without a restriction | limiting. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. A porous polyolefin resin sheet such as polyethylene (PE), polypropylene (PP), and polystyrene is preferred. Either a single layer structure sheet or a multilayer structure sheet may be used. Preferable examples of the porous plastic layer include porous polyolefin films such as polyethylene (PE) single layer film, polypropylene (PP) / PE / PP three layer film and the like. The thickness of the separator is preferably set within a range of approximately 10 μm to 40 μm, for example.

  Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to such examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Example 1>
As a positive electrode mixture, LiNi _0.5 Mn _1.5 O ₄ (positive electrode active material), acetylene black (conductive material), and PVDF (binder) so that the mass ratio thereof becomes 87: 10: 3 And a slurry composition was prepared by dispersing in NMP. This positive electrode mixture slurry was applied to one side of an aluminum foil (positive electrode current collector) having a thickness of 15 μm and then dried to form a positive electrode active material layer, which was roll pressed to produce a positive electrode sheet. The positive electrode sheet was cut into a 5 cm × 5 cm square with a 10 mm wide strip protruding at one corner. The active material layer was removed from the belt-like portion, the aluminum foil was exposed to form a terminal portion, and a positive electrode sheet with a terminal portion was obtained.

  As a negative electrode mixture, natural graphite (negative electrode active material; average particle size 20 μm, graphitization degree ≧ 0.9), CMC (thickener), and SBR (binder) have a mass ratio of 98: 1. : 1 was mixed and dispersed in ion-exchanged water to prepare a slurry composition. This negative electrode mixture slurry was applied to one side of a 10 μm thick copper foil (negative electrode current collector) so that the coating amount after drying was about 1: 1.5 in terms of the theoretical capacity ratio between the positive electrode and the negative electrode. And dried, and then roll pressed to produce a negative electrode sheet. This negative electrode sheet was processed into the same area and shape as the above-described positive electrode sheet with terminal portions to obtain a negative electrode sheet with terminal portions.

Non-aqueous electrolyte A was prepared by dissolving LiPF ₆ in a mixed solvent containing FEC and TFDMC (FH ₂ CO (C═O) CHF ₂ ) at a volume ratio of 1: 1 to a concentration of 1 mol / L. Was prepared. According to the above-described method, the voltage is changed by 0.2 V in the range of 4.2 V to 5.2 V, and constant voltage charging is performed for 10 hours at each voltage value. When the oxidation potential was measured, the oxidation potential of the electrolytic solution A was 5.0 to 5.2V.

  The positive electrode sheet with terminal part, a separator (porous PP / PE / PP three-layer sheet) cut out to an appropriate size and impregnated with the electrolytic solution A, and the negative electrode sheet with terminal part are stacked in this order. Combined and covered with laminate film. The electrolyte solution A was further injected here, and the film was sealed to construct a laminated cell type battery having a theoretical capacity (1C capacity; 1C is a current value that can be fully charged and discharged in 1 hour) of 30 mAh.

<Example 2>
LiPF ₆ was dissolved to a concentration of 1 mol / L in a mixed solvent containing EC and DMC at a volume ratio of 1: 1 to prepare a non-aqueous electrolyte B. A laminated cell battery having a 1 C capacity of 30 mAh was constructed in the same manner as in Example 1 except that the nonaqueous electrolyte B was used instead of the nonaqueous electrolyte A. In addition, the oxidation potential of the electrolytic solution B measured in the same manner as described above was 4.6 to 4.8V.

<Example 3>
Vinylene carbonate (VC) as an SEI forming material was added to the non-aqueous electrolyte B to prepare a non-aqueous electrolyte B / VC. The amount of VC added was 3 parts VC with respect to 100 parts non-aqueous electrolyte B on a volume basis. To a mixture of 90 parts of this electrolytic solution B / VC and 10 parts of a PEO polymer precursor (product number “TA140” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 0.1 part of AIBN (thermal polymerization initiator) was added. Stirring to obtain a polymer precursor solution. The polymer precursor solution was applied onto the negative electrode active material layer of the negative electrode sheet of Example 1 at an extrusion pressure of 0.05 MPa, and then the negative electrode sheet was held in a drying furnace at a temperature of 60 ° C. for 120 minutes to advance the polymerization reaction. The negative electrode sheet | seat with which electrolyte gel pB * VC was provided was produced. After this was cut out in the same area and shape as in Example 1, a terminal portion was provided in the same manner as in Example 1.

  The same positive electrode sheet with a terminal part as in Example 1, a separator (porous PP / PE / PP three-layer sheet) cut out to an appropriate size and impregnated with the electrolytic solution A, and pB · VC with the above terminal part The negative electrode sheet with gel was superposed in this order and covered with a laminate film. The electrolyte solution A was further injected therein, and the film was sealed to produce a laminated cell type battery having a 1 C capacity of 30 mAh.

<Example 4>
Fluoroethylene carbonate (FEC) as a SEI forming material was added to the non-aqueous electrolyte B to prepare a non-aqueous electrolyte B / FEC. The amount of FEC added was 3 parts FEC with respect to 100 parts of non-aqueous electrolyte B on a volume basis. A negative electrode sheet provided with the electrolyte gel pB · FEC was obtained in the same manner as in Example 3 except that the nonaqueous electrolyte B · FEC was used instead of the nonaqueous electrolyte B · VC. A laminated cell type battery having a 1 C capacity of 30 mAh was constructed in the same manner as in Example 3 except that the negative electrode sheet with pB / FEC gel was used instead of the negative electrode sheet with pB / VC gel.

<Example 5>
To a mixture of 90 parts of nonaqueous electrolyte A and 10 parts of PEO polymer precursor (Daiichi Kogyo Seiyaku Co., Ltd., product number “TA140”), 0.1 part of AIBN (thermal polymerization initiator) is added and stirred. As a result, a polymer precursor solution was obtained. The polymer precursor solution was applied onto the positive electrode active material layer of the positive electrode sheet of Example 1 at an extrusion pressure of 0.05 MPa, and then the positive electrode sheet was held in a drying furnace at a temperature of 60 ° C. for 120 minutes to advance the polymerization reaction. A positive electrode sheet to which the electrolyte gel pA was applied was prepared. This was processed into the same area and shape as in Example 1 to provide a terminal portion.

  The positive electrode sheet with pA gel with the terminal part, the separator impregnated with the electrolytic solution B / VC (porous PP / PE / PP three-layer sheet), and the negative electrode sheet with terminal part similar to Example 1 are stacked in this order. Combined and covered with laminate film. The electrolytic solution B / VC was further injected into this, the film was sealed, and a laminated cell type battery having a 1 C capacity of 30 mAh was constructed.

<Example 6>
A laminated cell type battery having a 1 C capacity of 30 mAh was constructed in the same manner as in Example 5 except that the electrolyte B / FEC was used instead of the electrolyte B / VC.

[Conditioning process]
Each battery cell according to Examples 1 to 6 was sandwiched between two plates and restrained in a state where a load of 350 kgf (350 kg / 25 cm ² ) was applied. For each restrained battery cell, an operation of charging a constant current (CC) to 4.9 V at a rate of 1/3 C and an operation of discharging to 3.5 V at a rate of 1/3 C were repeated three times. The following measurements and the like were performed on the battery cells that were restrained unless otherwise specified.

[Initial capacity]
For each battery cell according to Examples 1 to 6, CC charging was performed at a temperature of 25 ° C. at a rate of 1/5 C until the voltage between both terminals became 4.9 V, and then the current value was 1/50 C. The battery was charged at a constant voltage (CV) until it became a fully charged state. Next, CC discharge was performed at a rate of 1/5 C until the voltage reached 3.5 V, and the discharge capacity at this time was measured to obtain an initial capacity. Note that the voltage between both terminals when the charger was removed after completion of charging (the state where the overvoltage was released) was about 4.7 to 4.8 V in all cases.

[Initial DC resistance]
Each battery cell after the initial capacity measurement was CC charged at a temperature of 25 ° C. at a rate of 1/5 C until the SOC reached 60%. Each battery cell adjusted to SOC 60% was charged and discharged at a rate of 1 / 3C, 1C, 3C, and the overvoltage at that time was measured. The resistance was calculated by dividing the measured overvoltage value by the corresponding current value (for example, 10 mA for 1/3 C) to obtain the initial DC resistance.

[Capacity after storage and capacity maintenance ratio]
Each battery cell according to Examples 1 to 6, which was separately prepared and subjected to the conditioning process, was in a fully charged state in the same manner as the initial capacity measurement. Next, after holding at a temperature of 40 ° C. for 10 days, hold at a temperature of 25 ° C. for 5 hours, and CC discharge until the voltage reaches 3.5 V at a rate of 1/5 C. After measuring and storing the discharge capacity at this time The capacity. The percentage of the capacity after storage with respect to the initial capacity was calculated as the capacity maintenance ratio after storage.

[DC resistance after storage]
For each battery cell after storage, the DC resistance was measured in the same manner as the initial DC resistance, and the DC resistance after storage was determined. The resistance increase rate (%) was calculated from the percentage of the DC resistance after the storage to the initial DC resistance.

[Charge / discharge cycle characteristics]
After measuring the initial capacity, each battery adjusted to SOC 60% at a rate of 1/5 C at a temperature of 25 ° C. was CC charged to 4.9 V at a rate of 2 C at a temperature of 40 ° C. and rested for 10 minutes. Thereafter, a charge / discharge cycle of CC discharge to 3.5 V at the same rate and resting for 10 minutes was repeated 300 cycles. Thereafter, the discharge capacity was measured in the same manner as the initial capacity. The percentage of the discharge capacity after the cycle relative to the initial capacity was determined as a 300 cyc capacity retention rate (%).

  Table 1 shows the configurations of the batteries of Examples 1 to 6, and Table 2 shows the results of the evaluation tests.

As shown in Tables 1 and 2, the battery cell of Example 1 using the same oxidation-resistant electrolyte A on both the positive electrode side and the negative electrode side has a relatively low resistance increase rate after storage, and the oxidation-resistant electrolyte solution By using, it is thought that the increase in resistance on the positive electrode surface was suppressed. However, the capacity after storage at 40 ° C. for 10 days in a fully charged state decreased by 30% from the initial capacity, and further decreased by 3% after the cycle test. This is presumably because the organic solvent in the electrolytic solution was reduced and decomposed on the negative electrode surface in the fully charged battery, resulting in a large irreversible capacity.
In addition, the battery cell of Example 2 using the same reduction-resistant electrolyte B on both electrode sides had less capacity reduction after storage than the battery cell of Example 1. This is considered to be because SEI that suppresses side reactions (reductive decomposition) at the negative electrode was effectively formed on the surface of the negative electrode, and the generation of irreversible capacity was suppressed. However, the rate of increase in resistance after storage was as high as 151%. This is considered to be due to the fact that in the fully charged battery, the organic solvent in the electrolytic solution is oxidized on the surface of the positive electrode to form a film, thereby greatly increasing the positive electrode resistance.

  In addition, the battery cells of Examples 3 and 4 using the oxidation-resistant electrolytic solution A on the positive electrode side and the electrolyte gel pB · VC or pB · FEC on the negative electrode side are compared in capacity decrease and resistance increase rate after storage. It was small. This is considered to be due to the fact that the separated state of these electrolyte compositions was maintained by using an oxidation-resistant electrolyte solution on the positive electrode side and an electrolyte gel on the negative electrode side. On the other hand, the capacity decreased by about 25 to 30% after the cycle and was the same as in Examples 1 and 2, because the effect of the SEI forming material added to the electrolyte gel on the negative electrode side was not sufficient. It is considered a thing. Specifically, for example, even if SEI defects (cracks, etc.) occur due to repeated expansion and contraction of the negative electrode during repeated charge / discharge cycles, the mobility of the SEI-forming material is remarkably reduced in the gel. It is thought that this is because the material is difficult to reach the negative electrode surface and repair of SEI becomes difficult.

  For the battery cells of Examples 1 to 4, the battery cells of Examples 5 and 6 using the electrolyte gel pA on the positive electrode side and the electrolyte B · VC or B · FEC on the negative electrode side are 40 in a fully charged state. Both the capacity after storage at 10 ° C. for 10 days and the capacity after the cycle test were as high as 90% or more of the initial capacity. Furthermore, the increase rate of DC resistance was sufficiently suppressed before and after full charge storage at 40 ° C. for 10 days. The rate of increase in resistance was small because the oxidation-resistant electrolyte gel was disposed on the positive electrode side and separated from the electrolyte solution on the negative electrode side, thereby suppressing side reactions (oxidation reaction) on the positive electrode surface. it is conceivable that. Further, it is considered that the electrolyte solution is arranged on the negative electrode side and the SEI forming material is contained in the solution, so that even if SEI is formed on the negative electrode surface and the SEI is lost, it is effectively repaired. .

<Example 7>
A precursor of Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (LAGP) according to the FCM (Flash Creation Method) method using a particle design device “NanoCreator FCM” manufactured by Hosokawa Micron Co., Ltd. Powder) was prepared as a coating material for a positive electrode active material. Specifically, lithium naphthenate solution as a Li source (solvent: white spirit; Li concentration 1.2%), ethyl-acetoacetate-aluminum-di-n-butyrate as an Al source (Ethyl acetateto aluminum di-n-butylate) ) Solution (solvent: mineral spirit; Al concentration: 5.8%), germanium solution as Ge source (solvent: mineral spirit; Ge concentration: 9.8%), diethylphosphonoacetic acid (P concentration: P source) 13.4%) was mixed so that Li: Al: Ge: P = 1.5: 0.5: 1.5: 3 to prepare a LAGP precursor solution. This LAGP precursor solution was pre-fired by the FCM method under the conditions of an oxygen flow rate of 30 L / min and a chamber internal pressure of 10 ⁴ Pa to obtain a LAGP precursor (amorphous powdery coating material for positive electrode active material).

100 parts of LiNi _0.5 Mn _1.5 O ₄ (average particle size 6 μm, specific surface area 0.7 m ² / g) (positive electrode active material) and 1.5 parts of the LAGP precursor were coated with a coating apparatus (Hosokawa Micron Corporation). Manufactured and manufactured by “Nobilta NOB-MINI”; an apparatus for coating by collision energy between particles utilizing centrifugal force), and subjected to a coating treatment for 30 minutes at a rotational speed of 5000 rpm. The obtained positive electrode active material with a coating material was fired in air at a temperature of 700 ° C. for 2 hours to obtain a positive electrode active material-LAGP composite whose surface was coated with LAGP. When this was observed with an SEM (scanning electron microscope), it was confirmed that the primary particle surface of the positive electrode active material was covered with LAGP (having a LAGP layer).

  The positive electrode active material-LAGP composite, acetylene black (conductive material) and PVDF (binder) are mixed so that the mass ratio is 87: 10: 3, and dispersed in NMP to form a slurry composition. A product was prepared. This positive electrode mixture slurry was applied to one side of an aluminum foil (positive electrode current collector) having a thickness of 15 μm and then dried to form a positive electrode active material layer, which was roll pressed to produce a positive electrode sheet. The positive electrode sheet was cut into a 5 cm × 5 cm square with a 10 mm wide strip protruding at one corner. The active material layer was removed from the belt-like portion, the aluminum foil was exposed to form a terminal portion, and a positive electrode sheet with a terminal portion was obtained.

Natural graphite (negative electrode active material; average particle size 20 μm, degree of graphitization ≧ 0.9, specific surface area (BET (nitrogen adsorption) method) 4 m ² / g), CMC (thickener) and SBR (binder) Were mixed so that these mass ratios might become 98: 1: 1, and it was made to disperse | distribute to ion-exchange water, and the slurry-like composition was prepared. This negative electrode mixture slurry was applied to one side of a 10 μm thick copper foil (negative electrode current collector) so that the coating amount after drying was about 1: 1.5 in terms of the theoretical capacity ratio between the positive electrode and the negative electrode. And dried, and then roll pressed to produce a negative electrode sheet. This negative electrode sheet was processed into the same area and shape as the above-described positive electrode sheet with terminal portions to obtain a negative electrode sheet with terminal portions.

LiPF ₆ was dissolved in a mixed solvent containing EC and EMC at a volume ratio of 3: 7 so as to have a concentration of 1 mol / L to prepare a non-aqueous electrolyte C. To this, VC was added to a concentration of 0.5% to obtain a non-aqueous electrolyte C · VC _0.5 . According to the above-described method, the voltage is changed by 0.2 V in the range of 4.2 V to 5.2 V, and constant voltage charging is performed for 10 hours at each voltage value. When the oxidation potential was measured, the oxidation potential of the electrolytic solution C · VC _0.5 was 4.6 to 4.8V.

  The positive electrode sheet with terminal part, a separator (porous PP / PE / PP three-layer sheet) cut out to an appropriate size and impregnated with the electrolytic solution C / VC, and the negative electrode sheet with terminal part, They were stacked one after another and covered with a laminate film. The electrolyte solution A was further injected therein, the film was sealed, and a laminated cell type battery having a theoretical capacity of 60 mAh was constructed.

<Example 8>
To non-aqueous electrolyte C, VC was added to a concentration of 1.0% to obtain non-aqueous electrolyte C · VC _1.0 . A laminated cell type battery having a 1 C capacity of 60 mAh was constructed in the same manner as in Example 7 except that this non-aqueous electrolyte C · VC _1.0 was used.

<Example 9>
To non-aqueous electrolyte C, VC was added to a concentration of 1.5% to obtain non-aqueous electrolyte C · VC _1.5 . A laminated cell type battery having a 1 C capacity of 60 mAh was constructed in the same manner as in Example 7 except that this non-aqueous electrolyte C · VC _1.5 was used.

<Example 10>
To non-aqueous electrolyte C, VC was added to a concentration of 2.0% to obtain non-aqueous electrolyte C · VC _2.0 . A laminated cell type battery having a 1 C capacity of 60 mAh was constructed in the same manner as in Example 7 except that this non-aqueous electrolyte C · VC _2.0 was used.

<Example 11>
A laminated cell type battery having a 1 C capacity of 60 mAh was constructed in the same manner as in Example 7 except that the nonaqueous electrolytic solution C was used.

<Example 12>
A laminated cell type battery having a 1 C capacity of 60 mAh was constructed in the same manner as in Example 7 except that the positive electrode sheet with terminals and the non-aqueous electrolyte C · VC _1.0 of Example 1 were used.

[Conditioning process]
Each battery cell of Examples 7 to 12 was sandwiched between two plates and restrained to a state where a load of 350 kgf (350 kg / 25 cm ² ) was applied. For each battery cell that is restrained, the voltage between both terminals is CC charged at a rate of 1/5 C to 4.9 V, and then the constant voltage (CV) is charged until the current value becomes 1/50 C at the same voltage value. The operation of fully charging and the operation of discharging CC to 3.5 V at a rate of 1/5 C were repeated three times. Except for the measurement of the residual amount of VC, the following measurements and the like were performed on the battery cells remaining restrained unless otherwise specified.

[Residual VC after conditioning]
About the non-aqueous electrolyte sample extract | collected from each battery cell of Examples 7-12 after a conditioning process, VC in non-aqueous electrolyte using gas chromatography (GC) (model "GC-17A" by Shimadzu Corporation) Residual amount (%) was measured.

[Initial capacity]
The initial capacity of each battery cell of Examples 7 to 12 subjected to the conditioning treatment in the same manner as described above was measured in the same procedure as described above. Note that the voltage between both terminals when the charger was removed after completion of charging (the state where the overvoltage was released) was about 4.7 to 4.8 V in all cases.

[Initial DC resistance]
For each battery cell of Examples 7 to 12, the initial DC resistance was measured in the same procedure as described above.

[Charge / discharge cycle characteristics]
About each battery cell which concerns on Examples 7-12, after measuring initial capacity as mentioned above, CC charge to 4.9V at the rate of 2C at the temperature of 60 degreeC, and after resting for 10 minutes, it is 3.5V at the same rate. The charge / discharge cycle in which CC was discharged until 10 minutes was stopped was repeated 100 cycles. Thereafter, the discharge capacity was measured in the same manner as in the initial capacity, and the discharge capacity after 100 cycles was determined, and the percentage with respect to the initial capacity was determined as the 100 cyc capacity retention rate (%). For each battery cell after 100 cycles, the same charge / discharge cycle as the first 100 cycles was further repeated 100 cycles. In addition, for each battery after 200 cycles, the discharge capacity after 200 cycles was measured in the same manner as the 100 cyc capacity retention rate, and the percentage with respect to the initial capacity was determined as 200 cyc capacity retention rate (%). In addition, about the battery cell of Example 12, since the 100 cyc capacity | capacitance maintenance factor was low, the cycle test was complete | finished when 100 cycles were completed.

  Table 3 shows the configurations of the batteries of Examples 7 to 12, and Table 4 shows the results of the evaluation tests.

  As shown in Tables 3 and 4, the battery cells of Examples 7 to 10 in which the electrolyte containing VC as the SEI forming material and the positive electrode active material coated with LAGP were used together had a relatively high temperature of 60 ° C. The capacity retention rate after 100 cycles at a high temperature showed good cycle characteristics of 80% or more. On the other hand, even when the LAGP-coated positive electrode active material was used, the battery cell of Example 11 using the electrolytic solution containing no SEI forming material had a 100 cyc capacity retention rate of less than 80%. This indicates that the effect of improving the cycle characteristics can be exhibited by the SEI formed on the negative electrode surface. Furthermore, the battery cell of Example 12 using the positive electrode active material that was not coated with LAGP while using the electrolytic solution containing the SEI forming material had an extremely low value of about 30% of the 100 cyc capacity retention rate. As a result, despite the use of the electrolyte contained in the SEI forming material, the full charge potential of the positive electrode is high, so that the SEI forming material is oxidized and consumed, and the SEI coating on the negative electrode surface is not sufficient. It suggests that.

  Further, when the battery cells of Examples 8 and 12 in which the addition amount of the SEI forming material at the time of battery construction is the same amount (1.0% in each case) are compared, the residual amount of the SEI forming material after the conditioning treatment is 8 was 0.2%, whereas Example 12 was 0.0%. This indicates that the solid electrolyte coated on the surface of the positive electrode active material particles exhibited the effect of suppressing the oxidative decomposition of the SEI forming material. In addition, in the battery cell of Example 7 in which the residual amount of the SEI forming material after the conditioning treatment was also 0.0%, the SEI forming material formed on the negative electrode surface from the SEI forming material added at 0.5% at the time of battery construction was used. Due to the presence, the 100 cyc capacity retention rate was 83.5%, which was significantly improved compared to Example 12.

Regarding the 200 cyc capacity retention rate, Example 8 was about 10% higher than Example 7 and was a better result. This is considered to be due to the fact that the SEI-forming material remains in the electrolyte after conditioning, and that this SEI-forming material repairs the SEI damaged by peeling or the like during the charge / discharge cycle. It is done.
The battery cell of Example 10 with the largest amount of SEI forming material had a slightly higher initial resistance than Examples 7 to 9 and Example 12. This is considered to be because the thickness of the solid electrolyte layer on the surface of the positive electrode active material in Example 10 increased due to the increase in the amount of addition.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

DESCRIPTION OF SYMBOLS 1 Vehicle 20 Winding electrode body 30 Positive electrode sheet 32 Positive electrode collector 34 Positive electrode active material layer 36 Electrolyte composition Q
37 Electrolyte P
38 Positive electrode terminal 40 Negative electrode sheet 42 Negative electrode current collector 44 Negative electrode active material layer 48 Negative electrode terminal 50 Separator 100, 500 Lithium ion secondary battery 530, 630 Positive electrode 534, 634 Positive electrode active material layer 534A, 634A Positive electrode active material 634B Solid electrolyte 536 Electrolyte gel (electrolyte composition Q)
537 Liquid Electrolyte (Electrolytic Solution P)
540 Negative electrode 544 Negative electrode active material layer 544A Negative electrode active material 550 Insulating layer (separator)
800 Power supply 804 Electronic control unit (control device)

Claims (9)

A positive electrode having a positive electrode active material layer containing a positive electrode active material ;
A negative electrode having a negative electrode active material layer containing a negative electrode active material ;
Look containing a nonaqueous solvent and a supporting salt and a SEI-forming material, a electrolyte P maintained in a liquid, wherein at is impregnated in the negative electrode active material layer on the negative electrode active material layer in contact with the positive electrode active material layer Electrolyte P not touching ,
A non-fluid gel-like or solid electrolyte Q interposed between the positive electrode active material and the electrolyte P;
A lithium ion secondary battery comprising: The non-fluid electrolyte Q is an electrolyte composition Q containing a non-aqueous solvent and a supporting salt, and the positive electrode active material is coated with the electrolyte composition Q, where the electrolyte composition Q is The oxidation potential (vs. Li / Li ⁺ ) of the nonaqueous solvent contained in the composition Q is higher than the oxidation potential (vs. Li / Li ⁺ ) of the nonaqueous solvent contained in the electrolyte P. The lithium ion secondary battery according to claim 1, which is high.   The lithium ion secondary battery according to claim 1, wherein the positive electrode active material includes spinel type lithium nickel manganese oxide. 4. The lithium ion secondary battery according to claim 1, wherein the non-aqueous solvent contained in the electrolyte composition Q has an oxidation potential (vs. Li / Li ⁺ ) higher than 4.3 V. 5. The non-aqueous solvent contained in the electrolyte composition Q has an oxidation potential (vs. Li / Li ⁺ ) higher than the potential of the positive electrode active material (vs. Li / Li ⁺ ) in a fully charged state of the battery. The lithium ion secondary battery as described in any one of 1-4.   The lithium ion secondary battery according to any one of claims 1 to 5, wherein 95% by volume or more of the non-aqueous solvent contained in the electrolyte composition Q is made of at least one kind of fluorinated carbonate.   The lithium ion secondary battery according to any one of claims 1 to 6, further comprising a porous plastic layer disposed between the electrolyte composition Q and the negative electrode.   The lithium ion secondary battery according to any one of claims 1 to 7, wherein the upper limit voltage is 4.3 V or more. A lithium ion secondary battery according to any one of claims 1 to 8,
A control circuit electrically connected to the battery and defining at least an upper limit voltage value of the battery;
With
The power supply device in which the upper limit voltage value is set to 4.3 V or more.

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