JP7008275B2 - Power storage element - Google Patents

Description

The present invention relates to a power storage element such as a lithium ion secondary battery.

Conventionally, a lithium ion battery having a positive electrode, a negative electrode, and a non-aqueous electrolytic solution is known. As a battery of this type, a battery in which the negative electrode has a negative electrode active material containing at least one of graphite and amorphous carbon, a conductive auxiliary material containing graphite, and a binder is known (for example,). Patent Document 1).

In the battery described in Patent Document 1, the negative electrode active material has a spherical or massive shape, the conductive auxiliary material has a plate-like shape, and one of the edge surfaces of the conductive auxiliary material is on the surface of the negative electrode active material. The parts are in contact.

International Publication No. 2013/008524

An object of the present embodiment is to provide a power storage element capable of having a relatively high initial output and suppressing the generation of lithium electrodeposition even when repeated charging and discharging are repeated at a high rate.

The power storage element of the present embodiment includes a positive electrode and a negative electrode, and has a positive electrode and a negative electrode.
The positive electrode has a positive electrode active material layer containing a positive electrode active material, and has a positive electrode active material.
The negative electrode has a negative electrode active material layer containing a negative electrode active material, and has a negative electrode active material.
The positive electrode active material contains secondary particles in which primary particles are aggregated, and the positive electrode active material contains secondary particles.
When the average particle size of the primary particles constituting the secondary particles of the positive electrode active material is FP μm and the average particle size D50 of the negative electrode active material of the negative electrode active material layer is DN μm, the FP and DN are determined.
Satisfying the relational expression (1) of 0.070 ≤ FP / DN ≤ 0.875,
When the average particle size D50 of the positive electrode active material is DP μm, DP and DN satisfy the relational expression (2) of 0.7 ≦ DP / DN ≦ 5.0.
When the thickness of the positive electrode active material layer is TP μm and the thickness of the negative electrode active material layer is TN μm, TP and TN satisfy the relational expression (3) of 0.7 ≦ TP / TN ≦ 1.05.

According to this embodiment, it is possible to have a relatively high initial output, and it is possible to suppress the generation of lithium electrodeposition even if charging and discharging are repeated at a high rate.

FIG. 1 is a perspective view of a power storage element according to the present embodiment. FIG. 2 is a cross-sectional view taken along the line II-II of FIG.

Hereinafter, an embodiment of the power storage element according to the present invention will be described with reference to FIGS. 1 and 2. The power storage element includes a secondary battery, a capacitor, and the like. In this embodiment, a rechargeable secondary battery will be described as an example of the power storage element. The names of the constituent members (each constituent element) of the present embodiment are those in the present embodiment, and may be different from the names of the respective constituent members (each constituent element) in the background art.

The power storage element 1 of the present embodiment is a non-aqueous electrolyte secondary battery. More specifically, the power storage element 1 is a lithium ion secondary battery that utilizes the electron movement generated by the movement of lithium ions. This type of power storage element 1 supplies electrical energy. The power storage element 1 is used alone or in a plurality. Specifically, the power storage element 1 is used alone when the required output and the required voltage are small. On the other hand, when at least one of the required output and the required voltage is large, the power storage element 1 is used in a power storage device in combination with another power storage element 1. In the power storage device, the power storage element 1 used in the power storage device supplies electric energy.

As shown in FIGS. 1 and 2, the power storage element 1 is an electrode body 2 including a positive electrode and a negative electrode, a case 3 accommodating the electrode body 2, and an external terminal 7 arranged outside the case 3. An external terminal 7 that conducts with the electrode body 2 is provided. Further, the power storage element 1 has, in addition to the electrode body 2, the case 3, and the external terminal 7, a current collecting member 5 and the like for conducting the electrode body 2 and the external terminal 7.

The electrode body 2 is formed by winding a laminated body 22 in which a positive electrode and a negative electrode are laminated so as to be insulated from each other by a separator.

The positive electrode has a metal foil (positive electrode base material) and an active material layer superimposed on the surface of the metal foil and containing an active material. In this embodiment, the active material layer overlaps both surfaces of the metal foil, respectively. The thickness of the positive electrode may be 20 μm or more and 150 μm or less.

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

The positive electrode active material layer contains a particulate active material (positive electrode active material), a particulate conductive auxiliary agent, and a binder. The positive electrode active material includes secondary particles in which primary particles are aggregated. In other words, the positive electrode active material layer contains secondary particles in which the primary particles of the positive electrode active material are aggregated. In the secondary particles, the primary particles may be fixed to each other. The secondary particles may be hollow. When the secondary particles are hollow, the electrolytic solution enters the inside of the secondary particles, so that the charge / discharge characteristics at a high rate are further improved.

The average value (hereinafter, also referred to as FP) of the primary particles constituting the secondary particles may be 0.1 μm or more and 3.0 μm or less. The average value of such primary particles is obtained by measuring the diameters of at least 100 primary particle diameters in a scanning electron microscope observation image of a cross-sectional view obtained by cutting the positive electrode active material layer in the thickness direction and averaging the measured values. Demanded by. If the primary particle is not spherical, the longest diameter is measured as the diameter. Details of the measuring method are described in Examples.

The thickness (hereinafter, also referred to as TP) of the positive electrode active material layer (for one layer) may be 5 μm or more and 100 μm or less. The thickness is an average value obtained by measuring the thickness at at least 5 randomly selected points. Specifically, before measuring the thickness, for example, the battery is discharged to 2.0 V with a current of 5 A and then held at 2.0 V for 5 hours. After holding, the battery is allowed to rest for 5 hours, and the electrode body 2 is taken out from the container with the battery placed in a dry room or a glove box having an argon atmosphere. The positive electrode is taken out from the electrode body 2, washed with dimethyl carbonate (DMC) having a purity of 99.9 mass or more and a water content of 20 ppm or less three times or more, and then the DMC is removed by vacuum drying. Further, the thickness of at least five randomly selected points including the metal leaf of the positive electrode and the active material layer overlapping on both sides of the metal leaf is measured. The thickness TP for one layer is calculated by subtracting the thickness of the metal leaf from the average value and halving the thickness after the subtraction. The basis weight of the positive electrode active material layer (for one layer) may be 1 mg / cm ² or more and 100 mg / cm ² or less. The density of the positive electrode active material layer may be 0.5 g / cm ³ or more and 5.0 g / cm ³ or less. The density is the density in one layer arranged so as to cover one surface of the metal foil.

The positive electrode active material is a compound that can occlude and release lithium ions. The average particle size D50 (hereinafter, also referred to as DP) of the positive electrode active material may be 1 μm or more and 50 μm or less. The average particle size D50 of the active material is an average particle size (also referred to as a median size) in which the volume accumulation distribution is drawn from the small diameter side in the particle size distribution and the volume accumulation frequency is 50%. The average particle size D50 is obtained by a laser diffraction method using a laser diffraction / scattering type particle size distribution measuring device. The measurement conditions will be described in detail in Examples. When measuring the average particle size D50 of the active material of the manufactured battery, for example, after discharging the battery, the battery is disassembled in a dry atmosphere. Next, the active material layer is taken out, washed with dimethyl carbonate, crushed, and then vacuum dried for 2 hours or more. Then, the particles are dispersed by ultrasonic waves in N-methyl-2-pyrrolidone (NMP). The dispersion liquid after the dispersion treatment can be measured using a particle size distribution measuring device to obtain an average particle size D50. The active material and the conductive auxiliary agent can be separated by a difference in specific gravity or the like.

As the positive electrode active material, for example, lithium represented by a composition formula of Li _x MO _n (M represents at least one kind of transition metal, 0.95 ≦ x ≦ 1.2, and n is an integer of 2 or more and 4 or less). Examples include metal composite oxides. Examples of such lithium metal composite oxides include Li _x CoO ₂ , Li _x NiO ₂ , Li _x Mn ₂ O ₄ , Li _x MnO ₃ , Li _x Coy Ni _{(1-y) O 2} , and Li _{x Coy} Ni. Examples thereof include _z Mn _(1-y-z) O ₂ and Li _x Ni _z Mn _(2-z) O ₄ (0 <y <1, 0 <z <1).
Examples of the positive electrode active material include Li _a Me _b (AO _c ) _d (Me represents at least one kind of transition metal, A is, for example, P, Si, B, V, and 0.95 ≦ a ≦ 1.2. , B is 1 or 2, c is 4, and d is an integer of 1 or more and 3 or less). Examples of such polyanionic compounds include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F and the like.
Some of the elements or polyanions in the above compounds may be substituted with other elements or other anion species. The surface of the particulate active material may be coated with a metal oxide such as ZrO ₂ , MgO, Al ₂ O ₃ or carbon. As the positive electrode active material, conductive polymer compounds such as disulfide, polypyrrole, polyaniline, polyparastyrene, polyacetylene, and polyacene-based materials, pseudographite-structured carbonaceous materials, and the like can also be used. The material of the positive electrode active material is not limited to these. The positive electrode active material may be a single substance of one of these compounds or a mixture of two or more of these compounds.

In this embodiment, the positive electrode active material is a lithium metal composite oxide. Such a lithium metal composite oxide is Li _x Coy Ni _z Mn _{(1-yz) O 2} (where 0.95 ≦ x ≦ 1.2, 0.1 ≦ y ≦ 0.34, 0 < It is preferably expressed by the composition formula of z, 1-y-z> 0). By the lithium metal composite oxide represented by such a composition formula, the generation of lithium electrodeposition can be more sufficiently suppressed even if charging and discharging are repeated at a high rate.

Lithium metal composite oxides represented by the chemical composition of Li _p Ni _q Mn _{r Cos Ot} as described above are, for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiNi _1/6 Co _{1 / 6} Mn _2/3 O ₂ , LiCoO ₂ , etc.

The binder used for the positive electrode active material layer is, for example, polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, methyl polymethacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid. , Styrene butadiene rubber (SBR). The binder of this embodiment is polyvinylidene fluoride.

The conductive auxiliary agent of the positive electrode active material layer is a carbonaceous material containing 98% by mass or more of carbon. The carbonaceous material is, for example, Ketjen Black (registered trademark), acetylene black, graphite and the like. The positive electrode active material layer of the present embodiment has acetylene black as a conductive auxiliary agent.

The negative electrode has a metal foil (negative electrode base material) and a negative electrode active material layer formed on the metal foil. In the present embodiment, the negative electrode active material layer is laminated on both sides of the metal foil. The metal leaf is strip-shaped. The metal leaf of the negative electrode of the present embodiment is, for example, a copper foil. The negative electrode has a non-coated portion (a portion where the negative electrode active material layer is not formed) of the negative electrode active material layer at one edge portion in the width direction, which is the lateral direction of the band shape. The thickness of the negative electrode may be 5 μm or more and 100 μm or less.

The negative electrode active material layer contains a particulate active material (negative electrode active material) and a binder. The negative electrode active material layer is arranged so as to face the positive electrode via the separator. The width of the negative electrode active material layer is larger than the width of the positive electrode active material layer.

In the negative electrode active material layer, the ratio of the binder may be 5% by mass or more and 10% by mass or less with respect to the total mass of the negative electrode active material and the binder.

The negative electrode active material can contribute to the electrode reaction of the charge reaction and the discharge reaction in the negative electrode. For example, the negative electrode active material is a carbon material such as graphite or amorphous carbon (non-graphitized carbon, easily graphitized carbon), or a material that undergoes an alloying reaction with lithium ions such as silicon (Si) and tin (Sn). Is. The negative electrode active material of the present embodiment is preferably amorphous carbon, and more preferably graphitized carbon. The amorphous carbon in the present specification is the average surface of the (002) plane obtained by a wide-angle X-ray diffraction method using CuKα ray as a radiation source in a state after being disassembled in a discharged state, washed with water and dried. The interval d002 is 0.340 nm or more and 0.390 nm or less. Further, the graphitized carbon has an average surface spacing d002 of 0.360 nm or more and 0.390 nm or less. Since the negative electrode active material is amorphous carbon, the number of Li ion insertion sites varies more depending on the particle size of the active material. That is, as the particle size of the active material becomes smaller and the surface area per unit volume becomes larger, the number of Li ion insertion sites increases. Therefore, the generation of lithium electrodeposition can be further suppressed.

The average particle size D50 (hereinafter, also referred to as DN) of the negative electrode active material may be 1 μm or more and 10 μm or less. The average particle size D50 is preferably 1.0 μm or more and 5.9 μm or less. When the DN (average particle size D50 of the negative electrode active material) is 1.0 μm or more and 5.9 μm or less, it is possible to more reliably have a relatively high initial output, and repeated charging and discharging are repeated at a high rate. Even so, the generation of lithium electrodeposition can be suppressed. The average particle size D50 of the negative electrode active material is measured in the same manner as the average particle size D50 of the positive electrode active material as described above.

The thickness (hereinafter, also referred to as TN) of the negative electrode active material layer (for one layer) may be 5 μm or more and 100 μm or less. The thickness is measured in the same manner as the thickness of the positive electrode active material layer described above. The basis weight (for one layer) of the negative electrode active material layer may be 1 mg / cm ² or more and 100 mg / cm ² or less. The density of the negative electrode active material layer (for one layer) may be 0.5 g / cm ³ or more and 5.0 g / cm ³ or less.

The binder used for the negative electrode active material layer is the same as the binder used for the positive electrode active material layer. The binder of this embodiment is polyvinylidene fluoride.

The negative electrode active material layer may further have a conductive auxiliary agent such as Ketjen Black (registered trademark), acetylene black, and graphite.

When the average particle size of the primary particles constituting the secondary particles of the positive electrode active material is FP μm and the average particle size D50 of the negative electrode active material is DN μm, the FP and DN are determined.
The relational expression (1) of 0.070 ≦ FP / DN ≦ 0.875 is satisfied.
Since 0.070 ≦ FP / DN in the relational expression (1), Li ions transferred from the positive electrode active material are easily inserted into the negative electrode active material even during charging at a high rate. Therefore, it is unlikely that Li ions are reduced on the surface of the negative electrode active material to cause Li electrodeposition. As a result, the generation of lithium electrodeposition can be suppressed even if charging and discharging are repeated at a high rate. Further, by setting FP / DN ≦ 0.875, it is possible to have a relatively high initial output.

When the average particle size D50 of the positive electrode active material is DP μm, DP and DN satisfy the relational expression (2) of 0.7 ≦ DP / DN ≦ 5.0. It may be 0.7 <DP / DN, or 0.75 ≦ DP / DN. Since 0.7 ≦ DP / DN in the above relational expression (2), the current density per negative electrode active material can be larger than the current density per positive electrode active material during charging. As a result, Li ions are less likely to be reduced on the surface of the negative electrode active material to cause Li electrodeposition. Therefore, even if charging and discharging are repeated at a high rate, the generation of lithium electrodeposition can be more sufficiently suppressed. On the other hand, when DP / DN ≦ 5.0, variation in the charging depth in the negative electrode active material layer can be suppressed even when charging is performed at a high rate. In addition, it is possible to suppress the occurrence of Li electrodeposition in a portion where the charging depth is deep when cycle charging / discharging is performed with a high load. Further, by setting DP / DN ≦ 5.0, it is possible to have a relatively high initial output.

When the thickness of the positive electrode active material layer is TP μm and the thickness of the negative electrode active material layer is TN μm, TP and TN satisfy the relational expression (3) of 0.7 ≦ TP / TN ≦ 1.05. It may be 0.9 ≦ TP / TN ≦ 1.0. As shown in the relational expression (3), the ratio of the thickness of the positive electrode active material layer to the thickness of the negative electrode active material layer is close, so that the reaction is biased in the thickness direction of the active material layer during charging and discharging. Is suppressed. Li electrodeposition may occur when the charging depth is high during charging, but when the relational expression (3) is satisfied, the charging depth is higher on the separator side than on the metal foil side of the negative electrode active material layer. It can be suppressed from being stored. As a result, the generation of lithium electrodeposition can be suppressed even if charging and discharging are repeated at a high rate.

As described above, by satisfying all of the relational expressions (1) to (3), the power storage element 1 of the present embodiment can have a relatively high initial output and is repeatedly charged and discharged at a high rate. Is repeated, the generation of lithium electrodeposition can be suppressed.

In the electrode body 2 of the present embodiment, the positive electrode and the negative electrode configured as described above are wound in a state of being insulated by a separator. That is, in the electrode body 2 of the present embodiment, the laminated body 22 of the positive electrode, the negative electrode, and the separator is wound. The separator is a member having an insulating property. The separator is arranged between the positive electrode and the negative electrode. As a result, in the electrode body 2 (specifically, the laminated body 22), the positive electrode and the negative electrode are insulated from each other. Further, the separator holds the electrolytic solution in the case 3. As a result, when the power storage element 1 is charged and discharged, lithium ions move between the positive electrode and the negative electrode which are alternately laminated with the separator in between.

In the electrode body 2, the positive electrode active material layer and the negative electrode active material layer face each other, and the rated capacity (detailed later) is divided by the area of the portion where the positive electrode active material layer and the negative electrode active material layer overlap each other in the thickness direction. The value of 1CA current density may be 0.8 mA / cm ² or more. The 1CA current density may be 1.4 mA / cm ² or less. If the 1CA current density is less than 0.8 mA / cm ² , it is difficult to generate Li electrodeposition, while if it is 0.8 mA / cm ² or more, Li electrodeposition is likely to occur. In the power storage element 1 of the present embodiment, even if the 1CA current density is 0.8 mA / cm ² or more, all of the above relational expressions (1) to (3) are satisfied, so that lithium electrodeposition is generated. Can be sufficiently suppressed.

The separator is strip-shaped. The separator has a porous separator base material. The separator of the present embodiment has only a separator base material. The separator is arranged between the positive electrode and the negative electrode to prevent a short circuit between the positive electrode and the negative electrode.

The separator substrate is porous. The separator substrate is, for example, a woven fabric, a non-woven fabric, or a porous membrane. Examples of the material of the separator base material include polymer compounds, glass, and ceramics. Examples of the polymer compound include polyesters such as polyacrylonitrile (PAN), polyamide (PA) and polyethylene terephthalate (PET), polyolefins (PO) such as polypropylene (PP) and polyethylene (PE), and cellulose. ..

The width of the separator (dimension of the strip shape in the lateral direction) is slightly larger than the width of the negative electrode active material layer. The separator is arranged between the positive electrode and the negative electrode which are overlapped with each other in a state where the positive electrode active material layer and the negative electrode active material layer are displaced in the width direction so as to overlap each other.

The electrolytic solution is a non-aqueous electrolyte solution. The electrolytic solution is obtained by dissolving an electrolyte salt in an organic solvent. The organic solvent is, for example, cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate. Electrolyte salts are LiClO ₄ , LiBF ₄ , LiPF ₆ , and the like. The electrolytic solution of the present embodiment is obtained by dissolving 0.5 to 1.5 mol / L of LiPF ₆ in a mixed solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a predetermined ratio.

The case 3 has a case main body 31 having an opening and a lid plate 32 that closes (closes) the opening of the case main body 31. The case 3 houses the electrolytic solution in the internal space together with the electrode body 2, the current collector member 5, and the like. Case 3 is formed of a metal that is resistant to the electrolytic solution.

The case 3 is formed by joining the opening peripheral portion of the case main body 31 and the peripheral edge portion of the rectangular lid plate 32 in a superposed state. Further, the case 3 has an internal space defined by the case main body 31 and the lid plate 32. In the present embodiment, the peripheral edge of the opening of the case body 31 and the peripheral edge of the lid plate 32 are joined by welding.

The lid plate 32 has a gas discharge valve 321 capable of discharging the gas in the case 3 to the outside. The gas discharge valve 321 discharges gas from the inside of the case 3 to the outside when the internal pressure of the case 3 rises to a predetermined pressure. The gas discharge valve 321 is provided in the central portion of the lid plate 32.

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

The external terminal 7 is a portion electrically connected to the external terminal 7 of another lithium ion secondary battery 1, an external device, or the like. The external terminal 7 is formed of a conductive member. The external terminal 7 has a surface 71 to which a bus bar or the like can be welded. The surface 71 is a flat surface.

The current collector member 5 is arranged in the case 3 and is directly or indirectly connected to the electrode body 2 so as to be energized. The current collecting member 5 of the present embodiment is formed of a member having conductivity. The current collector member 5 is arranged along the inner surface of the case 3. The current collector member 5 is electrically conducted to the positive electrode and the negative electrode of the lithium ion secondary battery 1, respectively.

In the lithium ion secondary battery 1 of the present embodiment, the electrode body 2 in a state of being housed in a bag-shaped insulating cover 6 that insulates the electrode body 2 and the case 3 (specifically, the electrode body 2 and the current collecting member 5). Is housed in the case 3.

The power storage element 1 of the present embodiment may have a rated capacity of 4 Ah or more and 10 Ah or less. The rated capacity can be increased, for example, by increasing the amount of active material, and can be decreased by decreasing the amount of active material.

Next, a method for manufacturing the power storage element 1 according to the above embodiment will be described.

In the method for manufacturing the power storage element 1, a mixture containing an active material is applied to a metal foil (electrode base material) to form an active material layer, and electrodes (positive electrode and negative electrode) are manufactured. Next, the positive electrode, the separator, and the negative electrode are superposed to form the electrode body 2. Subsequently, the electrode body 2 is put into the case 3, and the electrolytic solution is put into the case 3 to assemble the power storage element 1.

In the production of the electrode (positive electrode), a positive electrode active material layer is formed by applying a mixture containing an active material, a binder and a solvent to both surfaces of the metal foil. By adjusting the coating amount of the mixture, the basis weight of the positive electrode active material layer can be adjusted. As a coating method for forming the positive electrode active material layer, a general method is adopted. The applied positive electrode active material layer is roll-pressed at a predetermined pressure. By adjusting the press pressure, the thickness and density of the positive electrode active material layer can be adjusted. The negative electrode is also manufactured in the same manner.

In the formation of the electrode body 2, the electrode body 2 is formed by winding the laminated body 22 having the separator sandwiched between the positive electrode and the negative electrode. Specifically, the positive electrode, the separator, and the negative electrode are superposed so that the positive electrode active material layer and the negative electrode active material layer face each other via the separator to form the laminated body 22. Subsequently, the laminated body 22 is wound to form the electrode body 2.

In assembling the power storage element 1, the electrode body 2 is placed in the case body 31 of the case 3, the opening of the case body 31 is closed with the lid plate 32, and the electrolytic solution is injected into the case 3. When closing the opening of the case body 31 with the lid plate 32, the electrode body 2 is inserted inside the case body 31, the positive electrode and one external terminal 7 are made conductive, and the negative electrode and the other external terminal 7 are made conductive. In this state, the opening of the case body 31 is closed with the lid plate 32. When the electrolytic solution is injected into the case 3, the electrolytic solution is injected into the case 3 through the injection hole of the lid plate 32 of the case 3.

It should be noted that the power storage element of the present invention is not limited to the above embodiment, and it is needless to say that various changes can be made within a range not deviating from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment. In addition, some of the configurations of certain embodiments can be deleted.

In the above embodiment, the positive electrode in which the active material layer containing the active material is in direct contact with the metal foil has been described in detail, but in the present invention, the positive electrode contains the binder and the conductive auxiliary agent and does not contain the active material. May have.

In the above embodiment, the electrodes in which the active material layer is arranged on both sides of the metal leaf of each electrode have been described, but in the power storage element of the present invention, the positive electrode or the negative electrode has the active material layer on one side of the metal leaf. May only be prepared.

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

In the above embodiment, the case where the power storage element 1 is used as a non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) capable of charging and discharging has been described, but the type and size (capacity) of the power storage element 1 are arbitrary. be. Further, in the above embodiment, the lithium ion secondary battery has been described as an example of the power storage element 1, but the present invention is not limited to this. For example, the present invention can be applied to various secondary batteries and other storage elements of capacitors such as electric double layer capacitors.

The power storage element 1 (for example, a battery) may be used in a power storage device (a battery module when the power storage element is a battery). The power storage device includes at least two power storage elements 1 and a bus bar member that electrically connects two (different) power storage elements 1 to each other. In this case, the technique of the present invention may be applied to at least one power storage element.

A non-aqueous electrolyte secondary battery (lithium ion secondary battery) was manufactured as shown below.

(Test Example 1)
(1) Preparation of Positive Electrode As the positive electrode active material, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having an average particle size D50 (DP) of 5.0 μm was used. Acetylene black was used as the conductive auxiliary agent. PVdF was used as a binder. The positive electrode paste for producing the positive electrode active material layer uses N-methyl-2-pyrrolidone (NMP) as a solvent, the conductive auxiliary agent is 4.5% by mass, the binder is 4.5% by mass, and the positive electrode active material is. It was prepared by mixing and kneading the solvent, the conductive auxiliary agent and the binder so as to be 91% by mass. The prepared positive electrode paste was applied onto an aluminum foil having a thickness of 15 μm. After coating, the positive electrode paste was applied so that the width of the active material layer was 83 mm, the width of the uncoated portion (non-formed region of the active material layer) was 11 mm, and the basis weight was 6.9 mg / cm ² . After drying, a roll press was performed so that the active material packing density of the active material layer was 2.48 g / cm ³ , and water was removed by vacuum drying to prepare a positive electrode. The thickness (TP) of one layer of the positive electrode active material layer was 32 μm.
-As for the active material, secondary particles in which primary particles were aggregated were used. The average particle diameter (FP) of the primary particles constituting the secondary particles was 0.18 μm. Such an average particle diameter was determined by measuring the diameters of 100 primary particle diameters in a scanning electron microscope observation image and averaging the measured values. If the primary particles were not spherical, the longest diameter was measured as the diameter.

(2) Preparation of Negative Electrode As the negative electrode active material, non-graphitizable carbon having an average particle size D50 (DN) of 2.5 μm was used. PVdF was used as the binder. The negative electrode paste was prepared by using NMP as a solvent and mixing and kneading the solvent, the binder and the active material so that the binder was 7% by mass and the negative electrode active material was 93% by mass. The prepared negative electrode paste was applied onto a copper foil having a thickness of 8 μm. After coating, the negative electrode paste was applied so that the width of the active material layer was 87 mm, the width of the uncoated portion (non-formed region of the active material layer) was 9 mm, and the basis weight was 3.3 mg / cm ² . After drying, a roll press was performed so that the active material packing density of the active material layer was 1.01 g / cm ³ , and water was removed by vacuum drying to prepare a negative electrode. The thickness (TN) of one layer of the negative electrode active material layer was 35 μm.

(3) Separator A polyethylene microporous membrane having a thickness of 21 μm was used as the separator. The air permeability of the polyethylene microporous membrane was 100 seconds / 100 cc.

(4) Preparation of electrolytic solution As the electrolytic solution, the one prepared by the following method was used. As the non-aqueous solvent, a solvent obtained by mixing 1 part by volume of propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was used, and LiPF ₆ was dissolved in this non-aqueous solvent so that the salt concentration was 1.2 mol / L. And prepared an electrolytic solution.

(5) Arrangement of Electrode Body in Case Using the above positive electrode, the above negative electrode, the above electrolytic solution, the separator, and the case, a battery was assembled by a general method.
First, a sheet-like material in which the separator was arranged between the positive electrode and the negative electrode and laminated was wound. The area of the portion where the positive electrode active material layer and the negative electrode active material layer overlapped was 5775 cm ² . Next, the wound electrode body was placed inside the case body of an aluminum square electric tank can as a case. Subsequently, the positive electrode and the negative electrode were electrically connected to each of the two external terminals. Furthermore, a lid plate was attached to the case body. The above electrolytic solution was injected into the case through a liquid injection port formed on the lid plate of the case. Finally, the case was sealed by sealing the injection port of the case.
(6) Confirmation of the capacity of the manufactured battery First, the initial discharge capacity was measured by the following method. Specifically, each battery is charged to 4.2 V at a constant current of 5 A at 25 ° C., further charged at a constant voltage of 4.2 V for a total of 3 hours, and then discharged at a constant current of 5 A under the condition of a cutoff voltage of 2.4 V. By doing so, the initial discharge capacity was measured. From this result, the 1CA current density, which is the area where the positive electrode active material layer and the negative electrode active material layer overlap each other in the thickness direction and is the value obtained by dividing the rated capacity, was 0.88 mA / cm ² .

-About the average particle diameter D50 of the positive electrode active material and the negative electrode active material Each electrode plate of the positive electrode and the negative electrode was taken out from the manufactured battery. Each electrode plate was placed in N-methyl-2-pyrrolidone (NMP) or water and subjected to a dispersion treatment in which particles were dispersed by ultrasonic waves. By filtering after the dispersion treatment, active substances were obtained. A laser diffraction type particle size distribution measuring device (“SALD2200” manufactured by Shimadzu Corporation) was used as the measuring device, and the dedicated application software DMS ver2 was used as the measurement control software. As a specific measurement method, a scattering type measurement mode is adopted, and a wet cell in which a dispersion liquid in which a measurement sample (active material) is dispersed is placed in an ultrasonic environment for 2 minutes and then irradiated with laser light. , Scattered light distribution was obtained from the measurement sample. Then, the scattered light distribution is approximated by a lognormal distribution, and the particle size corresponding to a cumulative degree of 50% (D50) within the range in which the minimum is 0.021 μm and the maximum is 2000 μm in the particle size distribution (horizontal axis, σ). The average particle size was used. The dispersion also contains a surfactant and SN Dispersant 7347-C (product name) or Triton X-100 (product name) as a dispersant. A few drops of dispersant were added to the dispersion.

(Test Examples 2 to 25)
A lithium ion secondary battery was manufactured in the same manner as in Test Example 1 except that the FP / DN value, DP / DN value, and TP / TN value were changed to the values shown in Table 1, respectively. The values of DP, FP, TP, TN, and DN were also changed as appropriate.

<Output confirmation test>
With respect to the battery after the capacity confirmation test, the SOC (State Of Charge) of the battery was adjusted to 20% by charging 20% of the discharge capacity obtained in the above-mentioned capacity confirmation test. Then, it was held at −10 ° C. for 4 hours, and a constant voltage discharge of 2.3 V was performed for 1 second, and the low temperature output (initial output) was calculated from the current value at the 1st second. The results of some of the above test examples are shown in Table 1. Test Examples 2 to 5 are based on the results of Test Example 1, Test Examples 7 to 14 are based on the results of Test Example 6, and Test Examples 15 to 19 are based on the results of Test Example 15. Based on this, the initial output is also expressed as a relative value (ratio). Since the initial output tends to fluctuate depending on the size of the average particle size D50 (DN) of the negative electrode active material, in the test example with the same DN, the initial output is shown not only as a calculated value but also as a relative value (ratio). did.

<Evaluation of electrodeposition>
In order to determine the test conditions for the charge / discharge cycle test, the battery adjusted to SOC 50% was held at 55 ° C. for 4 hours, and was charged with a constant current of 40 A until SOC was 80%. Then, by performing a constant current discharge of 40 A from SOC 80% to SOC 20%, a charge voltage V80 with an SOC of 80% and a discharge voltage V20 with an SOC of 20% were determined.
The 55 ° C. cycle test was carried out at a constant current of 40 A, the cutoff voltage at the time of charging was V80, the cutoff voltage at the time of discharging was V20, and the cycle test was continuously performed without setting a pause time. The total cycle time was 3000 hours. After the cycle test of 3000 hours was completed, the temperature was maintained at 25 ° C. for 4 hours, and the above-mentioned capacity confirmation test and low temperature output confirmation test were performed. Then, the battery was discharged to 2.0 V with a current of 5 A and then held at 2.0 V for 5 hours. After holding, the battery was allowed to rest for 5 hours, and the electrode body was taken out from the container with the battery placed in a dry room or a glove box with an argon atmosphere. The presence or absence of Li electrodeposition was confirmed by visually observing the surface of the negative electrode plate.

The batteries of the examples were able to have a relatively high initial output and lithium electrodeposition was sufficiently suppressed. On the other hand, the battery of the comparative example could not always have a relatively high initial output and suppress lithium electrodeposition. Further, when the FP / DN is larger than 0.875 or the DP / DN is larger than 5, the initial output tends to be low.

1: Power storage element (non-aqueous electrolyte secondary battery),
2: Electrode body,
3: Case, 31: Case body, 32: Cover plate,
5: Current collector member,
6: Insulation cover,
7: External terminal, 71: Surface.

Claims (4)

Equipped with a positive electrode and a negative electrode,
The positive electrode has a positive electrode active material layer containing a positive electrode active material.
The positive electrode active material is Li _x Coy Ni z Mn ( ₁ - _{yz) O} 2 ₍ where 0.95 ≦ x ≦ 1.2, 0.1 ≦ y ≦ 0.34, 0 <z, 1 It is a lithium metal composite oxide represented by the composition formula of −yz> 0).
The negative electrode has a negative electrode active material layer containing a negative electrode active material.
The negative electrode active material is carbon difficult to graphitize, and the negative electrode active material is carbon difficult to graphitize.
The positive electrode active material contains secondary particles in which primary particles are aggregated, and the positive electrode active material contains secondary particles.
When the average particle size of the primary particles constituting the secondary particles of the positive electrode active material is FP μm and the average particle size D50 of the negative electrode active material of the negative electrode active material layer is DN μm.
The DN is 1.0 μm or more and 5.9 μm or less.
The FP and the DN
Satisfying the relational expression (1) of 0.070 ≤ FP / DN ≤ 0.875,
When the average particle size D50 of the positive electrode active material is DP μm, the DP and the DN are
Satisfy the relational expression (2) of 0.7 ≤ DP / DN ≤ 5.0,
When the thickness of the positive electrode active material layer is TP μm and the thickness of the negative electrode active material layer is TN μm, the TP and the TN are
A power storage element satisfying the relational expression (3) of 0.7 ≦ TP / TN ≦ 1.05. The power storage element according to claim 1 , wherein the positive electrode active material layer contains the positive electrode active material, a conductive auxiliary agent, and a binder, and the negative electrode active material layer contains the negative electrode active material and a binder . The power storage element according to claim 1 or 2 , wherein the FP is 0.1 μm or more and 3.0 μm or less, and the DP is 1 μm or more and 50 μm or less . The power storage element according to any one of claims 1 to 3 , wherein the TP is 5 μm or more and 100 μm or less, and the TN is 5 μm or more and 100 μm or less .

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