JP6701511B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  With the spread of notebook computers, mobile phones, digital cameras, and the like, demand for secondary batteries for driving these small electronic devices is expanding. Further, for these electronic devices, the use of non-aqueous electrolyte secondary batteries (particularly, lithium ion secondary batteries) is being promoted because the capacity can be increased.

  The non-aqueous electrolyte secondary battery is used for small electronic devices, and is also used for electric vehicles (EV vehicles), hybrid vehicles (HV vehicles), plug-in hybrid vehicles (PHV vehicles), and home energy management systems ( It is also considered to be applied to applications requiring large power such as household power sources such as HEMS). In this case, large power can be obtained by means of increasing the size of the electrode plate of the non-aqueous electrolyte secondary battery, forming an electrode body by laminating a large number of electrode plates, and combining a large number of battery cells into an assembled battery. I am trying to get it.

A lithium-ion secondary battery, which is one form of a non-aqueous electrolyte secondary battery, can be used repeatedly by charging and discharging because each electrode active material is excellent in reversibility of absorption and desorption of lithium.
The lithium-ion secondary battery is described in Patent Document 1, for example.

Patent Document 1 includes a positive electrode and a negative electrode using a material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte, and until the potential of the positive electrode reaches 4.5 V (vs. Li ^/ Li ⁺ ). In the non-aqueous electrolyte secondary battery configured such that the opposite charge capacity ratio between the positive electrode and the negative electrode when charged is 1.0 to 1.15, the main material of the positive electrode active material is a chemical formula: Li _a Mn _s Ni _{t. Co u Mo v O 2 (0} ≦ a ≦ 1.2, s + t + u = 1,0 <s ≦ 0.5,0 <t ≦ 0.5,0.45 ≦ s / (s + t) ≦ 0.55,0 .45≦t/(s+t)≦0.55, u≧0, and 0.001≦v≦0.01 are satisfied.), which is a non-aqueous electrolyte secondary battery. Has been done.

  The conventional positive electrode active material (positive electrode material) of a non-aqueous electrolyte secondary battery is insufficient in safety. Specifically, in a lithium-ion secondary battery (non-aqueous electrolyte secondary battery), the crystal structure of the lithium composite oxide used for the positive electrode active material collapses due to long-term use and the like, and the contained oxygen is There was a risk that it would be released.

In order to solve such a problem, the positive electrode active material contains Li _2−x Ni _α M ¹ _β M ² _γ O _4−ε (0.50<α≦1.33, 0≦β<0.67, 0≦γ≦ 1.33, M ¹ : at least one selected from Co, Al and Ga, at least one represented by M ² : Mn, Ge, Sn and Sb, and 0≦x≦2 by occluding and releasing lithium ions. Is reversibly changed) is being studied.

JP, 2007-95443, A

_However, positive electrode using the ^{_{Li 2-x Ni α M 1}} β M 2 γ O 4-ε is the region of the low SOC, of the positive electrode itself resistance is disadvantageously increased. The increase in the resistance of the positive electrode causes the performance of the secondary battery to deteriorate due to the resistance of the positive electrode when the secondary battery using the positive electrode charges and discharges in a low SOC region of the positive electrode. That is, there is a problem that the battery characteristics of the secondary battery deteriorate in the low SOC region.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery in which deterioration of battery characteristics in a low SOC region is suppressed.

  The present inventors have completed the present invention as a result of repeated studies on the configuration of the non-aqueous electrolyte secondary battery in order to solve the above problems.

The non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode using a material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte having lithium ions as electrolyte ions. Then, the positive electrode is Li ₂ Ni _α M ¹ _β M ² _γ Mn _η O _4-ε (0.50<α≦1.33, 0≦β≦0.67, 0.33≦γ≦1.1 , 0≦ε≦1.00, 0≦η≦1.00, M ¹ : at least one selected from Co and Ga, and M ² : at least one selected from Ge, Sn, and Sb). It comprises an oxide, the positive electrode, the resistance at SOC 0%, has a relationship of resistance -SOC to be 2.0 times or more resistance at SOC 10%, the lithium transition metal oxide, ^{Ni, M} 1, M ² and Mn each have a local structure of 6-coordination, and the negative electrode has an average OCP of 50% SOC of the non-aqueous electrolyte secondary battery, an average OCP of −0.10 [V ]) and the average capacitance at (average OCP+0.25[V]) are used as numerator, and the average capacitance at (average OCP+0.25[V]) and the negative OCP A non-aqueous electrolyte secondary battery having a ratio value of 0.05 or more with a denominator of a section electric capacity that is a difference in electric capacity at a large limit value.

  In the non-aqueous electrolyte secondary battery of the present invention, even if an oxide whose resistance increases in the low SOC region is used for the positive electrode, the use in the low SOC region can be avoided by adjusting the electric capacity of the negative electrode. it can. As a result, the non-aqueous electrolyte secondary battery of the present invention has suppressed deterioration of battery characteristics in the low SOC region.

FIG. 3 is a diagram schematically showing the configuration of the secondary battery of Embodiment 1. 3 is a diagram showing the relationship between the electric capacity and the potential of the electrode of the secondary battery of Embodiment 1. FIG. 3 is a diagram showing a relationship between an electric capacity of an electrode of the secondary battery of Embodiment 1 and a potential. FIG. 5 is a perspective view schematically showing the configuration of the secondary battery of Embodiment 2. FIG. 5 is a cross-sectional view schematically showing the configuration of the secondary battery of Embodiment 2. FIG. 6 is a cross-sectional view schematically showing the configuration of the secondary battery of Embodiment 3. FIG.

The present invention will be described below with reference to specific embodiments. The present invention is not limited to these forms.
This form is a form in which the nonaqueous electrolyte secondary battery of the present invention is applied to a lithium ion secondary battery.

[Embodiment 1]
[Lithium-ion secondary battery]
The lithium-ion secondary battery 1 has a positive electrode 11, a negative electrode 12, and a non-aqueous electrolyte 13. Specifically, the positive electrode 11 and the negative electrode 12 are housed in the battery case 15 together with the non-aqueous electrolyte 13 with the positive electrode active material layer 111 and the negative electrode active material layer 121 facing each other with the separator 14 interposed therebetween. The structure of the secondary battery 1 is shown in a schematic diagram in FIG.

[Positive electrode]
The positive electrode 11 has a positive electrode active material layer 111 containing a positive electrode active material on the surface of the positive electrode current collector 110. The positive electrode active material layer 111 is formed by applying a positive electrode mixture material obtained by mixing a positive electrode active material, a conductive material, and a binding material onto the surface of the positive electrode current collector 110 and drying (coating). It is formed). That is, in the positive electrode active material layer 111, the positive electrode active material, the conductive material, and the binder are uniformly dispersed. Here, the conductive material and the binder are optional and may not be mixed. The positive electrode mixture is made into a paste (slurry) with an appropriate solvent. Other known additives may be added to the positive electrode 11 and the positive electrode mixture.

[Cathode active material]
In the present embodiment, as the positive electrode active material, Li _2-x Ni _α M ¹ _β M ² _γ O _4-ε (0.50<α≦1.33, 0≦β≦0.67, 0≦γ≦1. 33, 0≦ε≦1.00, M ¹ : at least one selected from Co, Al, and Ga, at least one represented by M ² : Mn, Ge, Sn, and Sb, by occluding and releasing lithium ions , Reversibly changes in the range of 0≦x≦2)).

  This lithium transition metal oxide contains Ni in its composition. This Ni forms a local structure in which oxygen (O) is six-coordinated (six-coordinated local structure). As a result, stable charging/discharging is performed. Further, a large amount of Ni, which is a redox species, is contained in the range of 0.50<α≦1.33, so that the capacity can be increased.

Further, by containing a large amount of the M ¹ element and the M ² element, the crystal structure becomes more stable and the crystal structure during charge/discharge is kept stable, and as a result, the decrease in battery capacity is suppressed. The M ¹ element is an element having a formal valence of 3, and the addition of the M ¹ element is expected to suppress entry of Li having greatly different valences into the Ni layer. The M ² element strongly fixes oxygen and, as a result, suppresses desorption of oxygen which is a concern during abnormal heat generation, and thus improves the safety of the battery. Furthermore, the amount of M ² element, when became 0.33 or more, on average, all of the oxygen in the Ni layer is adjoin the M ² element, and to have a bond with M ² element Therefore, the oxygen desorption effect is significantly enhanced.

Further, the M ¹ element and the M ² element are also preferably in a 6-coordination state, and by having this configuration, the structural gap with the adjacent transition metal element (coordination structure of Ni or Mn) is reduced. This makes it possible to further improve the durability.

  The lithium transition metal oxide may further include Mn (a ratio of 0 or more and 1.00 or less) that is a transition metal in its composition. Like Mn, this Mn forms a local structure in which oxygen (O) is hexacoordinated (a hexacoordinated local structure). By including it in this ratio, the effect of stabilizing the Ni layer is exhibited.

  Generally, in a non-aqueous electrolyte secondary battery, if overcharging or the like progresses, problems of ignition and smoke may occur. Ignition and smoke in this battery are greatly affected by oxygen released from the positive electrode active material (positive electrode material) in the process of reaching the smoke. Specifically, electrons are deprived from oxygen of the positive electrode active material along with charging, and oxygen is easily released.

The lithium transition metal oxide is added with the M ² element, and the added M ² element is more strongly bonded to oxygen than Ni or Mn (transition metal). That is, the addition of the M ² element makes it possible to minimize oxygen desorption during charge and discharge.

The lithium transition metal oxide has a layered structure including a Li layer and a Ni layer. With this structure, the positive electrode material has excellent Li ion conductivity. The Li layer refers to a layer formed of Li as a main component, and is a layer substantially made of Li. The Ni layer indicates a layer formed mainly of Ni (Ni compound), and is substantially a layer formed mainly of Ni and elements of M ¹ and M ² .

In the present embodiment, the lithium transition metal oxide is Li ₂ Ni _α M ¹ _β M ² _γ Mn _η O _4-ε (0.50<α≦1.33, 0.33≦γ≦1.1, 0≦ η≦1.00, 0≦β≦0.67, 0≦ε≦1.00, M ¹ : at least one selected from Co and Ga, and M ² : at least one selected from Ge, Sn, and Sb). Preferably.
The positive electrode active material is preferably the above lithium transition metal oxide, but may be a mixture with a known positive electrode active material other than this oxide.

  As the known positive electrode active material to be mixed, a compound capable of inserting and extracting lithium ions (electrolyte ions of non-aqueous electrolyte secondary batteries, alkali metal ions) is used. For example, various oxides, sulfides, lithium-containing oxides, conductive polymers and the like can be mentioned. A lithium-transition metal composite oxide is preferably used as the positive electrode active material.

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

  When the positive electrode active material is a mixture, the mixing ratio is not limited, but the lithium transition metal oxide is in a rich state, that is, the total number of Li atoms in the positive electrode active material is 100 [%]. At this time, the number of Li atoms in the lithium transition metal oxide is preferably 50[%] or more. Further, when the total mass of the positive electrode active materials is 100 [mass%], the mass of the lithium transition metal oxide is preferably 50 [mass%] or more.

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

[Conductive material, binder, mixture, positive electrode current collector]
The conductive material ensures the electrical conductivity of the positive electrode 11. As the conductive material, fine particles of graphite, acetylene black (AB), Ketjen black (KB), carbon black (CB) such as carbon nanofiber (CNF), and amorphous carbon fine particles such as needle coke can be used. , But not limited to these.

  The binder of the positive electrode composite material binds the positive electrode active material particles and the conductive material. As the binder, for example, polyvinylidene fluoride (PVDF), EPDM, styrene-butadiene rubber (SBR), NBR, fluororubber and the like can be used, but the binder is not limited thereto.

  As the solvent for the positive electrode mixture, an organic solvent that dissolves the binder is usually used. For example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N-N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like can be mentioned. Yes, but not limited to. In addition, a positive electrode active material may be slurried with water such as polytetrafluoroethylene (PTFE) by adding a dispersant, a thickener and the like to water.

  As the positive electrode current collector 110, a conventional current collector can be used, and a processed metal such as aluminum, for example, a plate-processed foil, net, punched metal, or foam metal can be used. , But not limited to these.

  The thickness of the positive electrode current collector 110 is not limited. The thickness can be similar to that of the positive electrode current collector that has been used previously. The thickness of the positive electrode current collector 110 is preferably 20 [μm] or less. For example, it is preferable to use a foil having a thickness of about 15 [μm].

[Characteristics of positive electrode]
The positive electrode 11 has a resistance at SOC 0% of 2.0 times or more than a resistance at a predetermined SOC or higher. Note that these resistances are the resistances of the single pole of the positive electrode 11. The resistance at the single pole of the positive electrode 11 can be obtained from the current (charge/discharge rate) and voltage when a test cell (half cell) having a lithium counter electrode is assembled and charged and discharged as described later. Further, the resistance at SOC 0% indicates not only the SOC 0% but also the resistance in the region including the vicinity of SOC 0% (about several%). Specifically, it includes an SOC region charged with electric power such that the current (charge/discharge rate) and voltage during charging/discharging can be measured. For example, it is difficult to measure the discharge resistance at SOC 0%. In this case, discharge from SOC several% to SOC 0% is performed, and the measured discharge resistance is taken as SOC 0%.

  The positive electrode 11 of the secondary battery 1 of the present embodiment has a resistance at SOC 0% that is 2.0 times or more the resistance at a SOC equal to or higher than a predetermined SOC. The positive electrode having this resistance characteristic has high resistance in a low region where SOC is around 0%.

  Although the specific numerical value of the predetermined SOC is not limited, it is preferably small. When the predetermined SOC has a large value, the SOC region of the high resistance of the positive electrode 11 is increased, and the chargeable/dischargeable region of the secondary battery 1 relatively decreases. It is preferable that the predetermined SOC is SOC of 10% or less.

  As the predetermined SOC, the characteristic of the resistance value of the positive electrode 11 (relationship between resistance and SOC) is measured in advance, and a predetermined resistance value of 50% of the resistance value at SOC 0% (or a resistance value equal to or lower than the half resistance value) is determined. The SOC that is the resistance value) may be obtained, and the obtained SOC value may be adopted.

[Negative electrode]
The negative electrode 12 contains a negative electrode active material. The negative electrode 12 has a negative electrode active material layer 121 on the surface of the negative electrode current collector 120. The negative electrode active material layer 121 is formed by applying and drying a negative electrode mixture material obtained by mixing the negative electrode active material and a binder on the surface of the negative electrode current collector 120 (formed by coating). ). The negative electrode mixture is made into a paste (slurry) with an appropriate solvent. Other known additives may be added to the negative electrode 12 and the negative electrode mixture.

[Negative electrode active material]
As the negative electrode active material of the negative electrode 12, a conventional negative electrode active material can be used as long as it has an electric capacity ratio described below. A negative electrode active material containing at least one element of C, Si, Ti, Sn, Sb and Ge can be mentioned.

  Among these elements, the negative electrode active material containing C is preferably a carbon material capable of occluding/releasing electrolyte ions of a lithium ion secondary battery (having Li occluding ability). The carbon material of the negative electrode active material is more preferably a carbon material containing non-graphitizable carbon (also called hard carbon) or graphitizable carbon (also called soft carbon).

  When a carbon material containing non-graphitizable carbon or graphitizable carbon is used for the negative electrode active material, the graphitizable carbon or graphitizable carbon is 5 mass% or more when the mass of the entire carbon material is 100 mass %. It is preferable to include a natural carbon.

  When a carbon material containing non-graphitizable carbon or graphitizable carbon is used as the carbon material of the negative electrode active material, conventionally known carbon materials can be used in addition to the graphitizable carbon. For example, graphite (graphite) can be mentioned.

  Further, the negative electrode active material containing Si can increase the capacity of the secondary battery 1. The negative electrode active material containing Si is preferably one containing silicon or silicon oxide. Further, the negative electrode active material containing Si may be alloyed with another metal, such as Ti-Si.

  When using the negative electrode active material containing Si, it is preferable to further contain a carbon material. Here, the carbon material contained in the negative electrode active material containing Si is preferably the above-mentioned carbon material or graphite. When the negative electrode active material containing Si contains a carbon material, the mixing ratio is not limited.

  The negative electrode active material containing Ti can improve the durability of the secondary battery 1. The negative electrode active material containing Ti is preferably a compound capable of occluding/releasing electrolyte ions of a lithium ion secondary battery (having Li occluding ability). Examples of the negative electrode active material containing Ti include titanium-containing metal oxides such as lithium titanium composite oxide, titanium oxide, and niobium titanium composite oxide, and lithium titanium composite oxide is more preferable.

The lithium titanium composite oxide is more preferably TiO ₂ (B). The lithium-titanium composite oxide preferably contains TiO ₂ (B) at 5 mass% or more when the total mass of the composite oxide is 100 mass %.

  Moreover, these negative electrode active materials may contain a compound containing Sn, Sb, and Ge. These compounds are particularly alloy materials that undergo a large volume change. These negative electrode active materials may be alloyed with another metal such as Ti-Si, Ag-Sn, Sn-Sb, Ag-Ge, Cu-Sn, Ni-Sn.

[Conductive material, binder, mixture, negative electrode current collector]
As the conductive material of the negative electrode 12, carbon material, metal powder, conductive polymer, or the like can be used. From the viewpoint of conductivity and stability, it is preferable to use carbon materials such as AB, KB, and CB.

As the binder for the negative electrode 12, PTFE, PVDF, fluororesin copolymer (tetrafluoroethylene/hexafluoropropylene copolymer), SBR, acrylic rubber, fluororubber, polyvinyl alcohol (PVA), styrene -Maleic acid resin, polyacrylic acid salt, carboxymethyl cellulose (CMC) and the like can be mentioned.
Examples of the solvent for the composite material of the negative electrode 12 include organic solvents such as NMP, water, or aqueous solvents.

  As the negative electrode current collector 120, a conventional current collector can be used, and a metal such as copper, stainless steel, titanium, or nickel is processed, for example, a plate-shaped foil, net, punched metal, foam metal, or the like. Can be used, but is not limited thereto.

[Non-aqueous electrolyte]
As the non-aqueous electrolyte 13, a conventional non-aqueous electrolyte can be used. Examples of the non-aqueous electrolyte 13 include those obtained by dissolving a supporting electrolyte in a non-aqueous solvent. Further, conventional additives may be added.

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

  The non-aqueous solvent dissolves the supporting electrolyte. The non-aqueous solvent is not limited except that it dissolves the supporting electrolyte. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like can be used. In particular, propylene carbonate, ethylene carbonate (EC), 1,2-dimethoxyethane, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), vinylene carbonate (VC) and the like and mixed solvents thereof are preferable. . Among these organic solvents, the use of at least one non-aqueous solvent selected from the group consisting of carbonates and ethers is excellent in the solubility, dielectric constant and viscosity of the supporting electrolyte, and is a lithium ion secondary battery. 1 is preferable because the charge/discharge efficiency of No. 1 becomes high.

  As a conventional additive, when a battery is assembled, it is decomposed on the surface of an electrode (in this embodiment, a positive electrode), and a film (for example, Solid Electrolyte Interphase: SEI film) is formed on the surface of the electrode (a positive electrode, particularly a positive electrode active material). ) Is generated. The coating film formed on the surface of this electrode (positive electrode) exhibits high stability. Then, even if the positive electrode has a high potential (for example, even if the charging reaction proceeds at a high potential), the coating does not decompose and covers the surface of the electrode (positive electrode). As a result, the coating film suppresses a decrease in the capacity of the electrode (positive electrode).

[Separator]
The separator 14 plays a role of electrically insulating the positive electrode 11 and the negative electrode 12 and holding the non-aqueous electrolyte 13. For the separator 14, for example, it is preferable to use a porous synthetic resin film, particularly a porous film of a polyolefin-based polymer (polyethylene, polypropylene).

[Battery case]
The battery case 15 accommodates (encloses) the positive electrode 11 and the negative electrode 12 together with the non-aqueous electrolyte 13 in a state of having the separator 14 interposed therebetween.

  The battery case 15 is made of a material that impedes the permeation of water between the inside and the outside. Examples of such a material include a material having a metal layer. Examples of the material having a metal layer include metal itself and a laminated film.

[Other configurations of secondary battery]
In the secondary battery 1 of the present embodiment, the negative electrode 12 is larger than (average OCP−0.10 [V]) and (average OCP+0) when the potential of the negative electrode 12 at SOC 50% of the secondary battery 1 is the average OCP. The ratio of the electric capacity in the range of less than 0.25 [V]) to the electric capacity in the range where the OCP of the negative electrode 12 is larger than (average OCP+0.25 [V]) is 0.05 or more. Note that OCP is an abbreviation for open circuit potential.

  That is, the electric capacity ratio of the negative electrode 12 obtained by (electric capacity of the negative electrode 12 in the vicinity of the average OCP)/(electric capacity of the negative electrode 12 at the average OCP+0.25 [V]) is 0.05 or more. When the electric capacity ratio is 0.05 or more, the secondary battery 1 of the present embodiment does not use the SOC region (low SOC region) where the positive electrode 11 has high resistance. As a result, the secondary battery 1 of the present embodiment can exhibit excellent battery performance in a wide SOC range including the low SOC range. When the electric capacity ratio is less than 0.05, when the secondary battery 1 is charged and discharged, the region where the positive electrode 11 has a high resistance is used.

  The potential of the negative electrode 12 can be obtained from the current (charge/discharge rate) and voltage when a test cell (half cell) having a lithium counter electrode is assembled and charged and discharged as described below. Further, the resistance at SOC 0% indicates not only the SOC 0% but also the resistance in the region including the vicinity of SOC 0% (about several%). Specifically, it includes an SOC region charged with electric power such that the current (charge/discharge rate) and voltage during charging/discharging can be measured. For example, it is difficult to measure the discharge resistance at SOC 0%. In this case, discharge from SOC several% to SOC 0% is performed, and the measured discharge resistance is taken as SOC 0%.

  The upper limit of the electric capacity ratio is not limited, but if the electric capacity ratio becomes excessively large, the SOC range that can be used when the secondary battery 1 is charged and discharged decreases. That is, the battery capacity of the secondary battery 1 is reduced. The electric capacity ratio is preferably 2.0 or less, and more preferably 1.8 or less.

  The adjustment of the electric capacity ratio can be changed by adjusting the sizes of the positive electrode active material layer 111 of the positive electrode 11 and the negative electrode active material layer 121 of the negative electrode 12, and adjusting the content ratio of the positive electrode active material and the negative electrode active material.

[Effect of this embodiment]
(1) First Effect The secondary battery 1 of the present embodiment uses the above lithium transition metal oxide as the positive electrode active material. The electric capacity ratio of the negative electrode 12 is 0.05 or more. According to this configuration, the secondary battery 1 of the present embodiment has an effect of suppressing deterioration of battery characteristics in the low SOC region.

  Specifically, the relationship between the electric capacities (SOC of the positive electrode 11) of the positive electrode 11 and the negative electrode 12 of the secondary battery 1 and the potential is shown in FIGS. 2 to 3 show potential changes based on the SOC of the positive electrode 11. FIG. 3 is an enlarged view of the low SOC region of FIG.

  In the positive electrode 11 of this embodiment, the above lithium transition metal oxide is used as the positive electrode active material. This lithium transition metal oxide has high resistance in the low SOC region as described above. Specifically, the resistance of the positive electrode 11 at 0% SOC is twice or more the resistance at a SOC equal to or higher than a predetermined SOC. In FIG. 3, the predetermined SOC is SOC 15%.

When the SOC increases from zero, the potential of the negative electrode 12 decreases, and when the potential becomes sufficiently low, the negative electrode 12 moves to a region where there is little or little change in potential (region where potential change is small).
The battery voltage of the secondary battery 1 is the difference between the potentials of the two potential change curves (potential difference) when the potential change curves of the positive electrode 11 and the negative electrode 12 are shown in the same figure.

  Then, the electric capacity ratio of the secondary battery 1 of the present embodiment is larger than (average OCP-0.10 [V]) when the potential of the negative electrode 12 at SOC 50% of the secondary battery 1 is the average OCP, and ( It is the ratio of the electric capacity of the negative electrode 12 in the range of less than (average OCP+0.25 [V]) to the electric capacity of the negative electrode 12 in the range of OCP of the negative electrode 12 larger than (average OCP+0.25 [V]). ..

The battery capacity of the secondary battery 1 is a capacity in the range between the lower limit voltage and the upper limit voltage in FIG. Then, the capacity that is half the capacity in the range between the lower limit voltage and the upper limit voltage corresponds to the average OCP capacity. The “potential of the negative electrode 12 at a capacity that is half the capacity in the range between the lower limit voltage and the upper limit voltage” corresponds to the “average OCP”. “A range in which the OCP of the negative electrode 12 is larger than (average OCP+0.25 [V])” corresponds to the low SOC side indicated as “electric capacity of high OCP” in FIGS. This is because the x-axis in the diagrams of FIGS. 2-3 is based on the positive electrode capacity.
The capacitance ratio is 0.05 or more. When the electric capacity ratio of the negative electrode 12 is in this range, the battery voltage (lower limit voltage) of the secondary battery 1 is not included in the low SOC region.

  When the electric capacity ratio is 0.05 or more, the slope of the potential change curve of the negative electrode 12 in the “high OCP electric capacity” becomes gentle. Then, the change in the potential difference (increase in the potential difference), which is the difference between the potential change curve of the negative electrode 12 and the potential change curve of the positive electrode 11, also becomes gentle. This increases the SOC value (SOC value of the positive electrode 11) at which the battery voltage, which is the potential difference between the both electrodes 11 and 12, becomes the lower limit voltage (shifts to the right in FIGS. 2 to 3). When the electric capacity ratio is 0.05 or more, the SOC value as the lower limit voltage (SOC value of the positive electrode 11) becomes larger than that in the low SOC region of the positive electrode 11. As a result, the secondary battery 1 can be charged and discharged in a low resistance state. That is, the secondary battery 1 has an effect of suppressing deterioration of battery characteristics.

(2) Second Effect The negative electrode 12 has a carbon material containing non-graphitizable carbon or easily graphitizable carbon, and the carbon material is 5 mass% when the total mass of the carbon material is 100 mass %. The above includes non-graphitizable carbon or graphitizable carbon.

  By using a carbon material containing non-graphitizable carbon or graphitizable carbon, the negative electrode 12 can surely have the above-mentioned potential capacity ratio. If the non-graphitizable carbon or the easily graphitizable carbon is less than 5 mass%, the effect of addition will not be sufficiently exhibited. A carbon material that does not contain non-graphitizable carbon or graphitizable carbon has a small electric capacity ratio, and tends to be less than 0.05. In particular, the larger the graphite content in the carbon material, the smaller the capacitance ratio.

(3-4) Third and Fourth Effects The negative electrode 12 contains silicon or silicon oxide as a negative electrode active material. With this configuration, the negative electrode 12 can surely have the above-mentioned potential capacity ratio.
The negative electrode active material preferably further contains a carbon material.
By containing the carbon material, it is possible to prevent the electric capacity ratio from becoming excessively large. It also functions as a conductive material and can suppress an increase in the resistance of the negative electrode 12.

(5-6) Fifth to Sixth Effects The negative electrode 12 contains a lithium titanium composite oxide as a negative electrode active material. With this configuration, the negative electrode 12 can surely have the above-mentioned potential capacity ratio.
The lithium titanium composite oxide contains TiO ₂ (B) at 5 mass% or more when the total mass is 100 mass %. By containing TiO ₂ (B), it is possible to prevent the electric capacity ratio from becoming excessively large. If TiO ₂ (B) is less than 5 mass %, the effect of addition is not sufficiently exhibited. The lithium titanium composite oxide containing no TiO ₂ (B) has a small electric capacity ratio, and tends to be less than 0.05.

(7) Seventh Effect The secondary battery 1 of the present embodiment has a predetermined SOC of 10% SOC or less. With this structure, the secondary battery 1 can exhibit the above-described effects.

(8) Eighth effect In the secondary battery 1 of the present embodiment, the above lithium transition metal oxide is Li ₂ Ni _α M ¹ _β M ² _γ Mn _η O _4-ε (0.50<α≦1.33. , 0.33≦γ≦1.1, 0≦η≦1.00, 0≦β≦0.67, 0≦ε≦1.00, M ¹ : At least one selected from Co and Ga, M ² : At least one selected from Ge, Sn, and Sb).
By using this compound as the positive electrode active material of the positive electrode 11, the secondary battery 1 can exhibit the effects described above.

[Embodiment 2]
The present embodiment is a form in which the secondary battery 1 of Embodiment 1 is applied to a laminated battery, and the configurations of the positive electrode 11, the negative electrode 12, the non-aqueous electrolyte 13, etc. are the same as those of the first embodiment. The configuration of the secondary battery 1 of this embodiment is shown in FIGS. FIG. 4 is a perspective view of the secondary battery 1, and FIG. 5 is a sectional view taken along the line VV in FIG.

  The lithium-ion secondary battery 1 of the present embodiment has a positive electrode 11 and a negative electrode 12 housed (enclosed) in a battery case 2 made of a laminated case. Note that configurations that are not particularly limited in this embodiment are similar to those in the first embodiment.

  The positive electrode 11 is formed by forming a positive electrode active material layer 111 on the surface (both sides) of a substantially square positive electrode current collector 110. The positive electrode 11 has, on one side of the rectangular shape, an uncoated portion 112 where the positive electrode current collector 110 is exposed (the positive electrode active material layer 111 is not formed).

  The negative electrode 12 is formed by forming a negative electrode active material layer 121 on the surface (both sides) of a substantially rectangular negative electrode current collector 120. The negative electrode 12 has an uncoated portion 122 where the negative electrode current collector 120 is exposed (the negative electrode active material layer 121 is not formed) on one side of the rectangular shape.

  In the negative electrode 12, the negative electrode active material layer 121 is formed wider than the positive electrode active material layer 111 of the positive electrode 11. The negative electrode active material layer 121 of the negative electrode 12 is formed in such a size that the positive electrode active material layer 111 can be completely covered without being exposed when the negative electrode active material layer 121 is stacked on the positive electrode active material layer 111.

The positive electrode 11 and the negative electrode 12 are housed (enclosed) in a battery case 2 formed of a laminate film together with the non-aqueous electrolyte 13 in a state of being laminated via a separator 14.
The separator 14 is formed in a larger area than the negative electrode active material layer 121.

  The positive electrode 11 and the negative electrode 12 are stacked with the separator 14 in between, with the centers of the positive electrode active material layer 111 and the negative electrode active material layer 121 overlapping. At this time, the uncoated portion 112 of the positive electrode 11 and the uncoated portion 122 of the negative electrode 12 are arranged in opposite directions (directions facing each other).

[Battery case]
The battery case 2 is formed from the laminate film 20. The laminate film includes the plastic resin layer 201/metal foil 202/plastic resin layer 203 in this order. The battery case 2 is adhered by pressing the laminated film 20 bent in advance into a predetermined shape against another laminated film or the like while the plastic resin layers 201 and 203 are softened by heat or some solvent.

  In the battery case 2, the laminate films 20 which are preformed (embossed) into a shape capable of accommodating the positive electrode 11 and the negative electrode 12 are overlapped, and the edge portions of the outer circumference are adhered over the entire circumference to form the positive electrode 11 and the negative electrode 12. It is formed by being enclosed inside. The sealing portion is formed by bonding the outer periphery. The bonding of the outer circumference in this embodiment was performed by fusion.

  The battery case 2 is formed by stacking another laminated film 20 on the laminated film 20. Here, another laminated film 20 is a laminated film that is adhered (fused). That is, the battery case 2 includes not only a mode in which it is formed from two or more laminated films 20, but also a mode in which one laminated film is folded back.

  Bonding (assembling) of the outer periphery of the battery case 2 is performed under a reduced pressure atmosphere (preferably vacuum) or under an inert gas atmosphere (rare gas atmosphere, preferably Ar gas atmosphere). As a result, encapsulation of a substance that deteriorates the performance of the electrode body is hindered, and the electrode body is encapsulated without the atmosphere (water contained therein) in the battery case 2.

  As shown in FIGS. 4 to 5, the preformed laminated film 20 includes a flat plate portion 21 that forms a sealing portion 22 with another laminate film 20 when stacked, and a flat plate portion 21. It has a tank-shaped portion 23 that can store the positive electrode 11 and the negative electrode 12 formed in the central portion.

  As shown in FIGS. 4 to 5, the laminate films 20 and 20 are bent (molded) to have a concave shape capable of accommodating the positive electrode 11 and the negative electrode 12. The laminated films 20 and 20 have the same shape, and the flat plate portions 21 and 21 are completely overlapped with each other when the laminated films 20 and 20 are overlapped with each other so as to face each other.

  In the laminated film 20, the flat plate portion 21 and the bottom portion 23A of the tank-shaped portion 23 (the portion forming the end portion in the stacking direction of the secondary battery 1) are formed in parallel. The flat plate portion 21 and the bottom portion 23A of the tank-shaped portion 23 are connected by a standing portion 23B. The standing portion 23B extends in a direction (inclined direction) intersecting the parallel direction of the flat plate portion 21 and the bottom portion 23A. The bottom portion 23A is formed smaller than the opening of the tank-shaped portion 23 (the inner end of the flat plate portion 21).

In the battery case 2, the sealing portion 22 is formed on the peripheral edge of the flat plate portions 21 and 21, and the flat portions 21 and 21 are overlapped and not bonded inside the sealing portion 22 (direction close to the electrode body). Is formed. The non-bonded portions where the flat plate portions 21 and 21 overlap each other may be in contact with each other or in a state where a gap is formed. Furthermore, the uncoated portions 112 and 122 of the electrode plates (the positive electrode plate 11 and the negative electrode plate 12) and the separator 14 may be interposed.
The laminate films 20 and 20 are preformed in the shapes shown in FIGS. A conventionally known molding method is used for molding into this shape.
In the lithium ion secondary battery 1, each of the positive electrode 11 and the negative electrode 12 is connected to an electrode terminal (positive electrode terminal 25, negative electrode terminal 26).

[Electrode terminal]
The positive electrode terminal 25 is electrically connected to the uncoated portion 112 of the positive electrode 11. The negative electrode terminal 26 is electrically connected to the uncoated portion 122 of the negative electrode 12. In the present embodiment, the uncoated portions 112, 122 of the electrodes 11, 12 are joined to the electrode terminals 25, 26 by welding (vibration welding). The central portions of the uncoated portions 112, 122 of the electrodes 11, 12 in the width direction are joined to the electrode terminals 25, 26.

  Each of the electrode terminals 25 and 26 is joined via a sealant 24 so that the plastic resin layer 201 of the laminate films 20 and 20 and the electrode terminals 25 and 26 are kept in a sealed state at a portion penetrating the battery case 2. ing.

  The electrode terminals 25 and 26 are made of sheet-shaped (foil-shaped) metal, and the sealant 24 is made of a resin that covers the sheet-shaped electrode terminals 25 and 26. The sealant 24 covers the portion where the electrode terminals 25 and 26 overlap the flat plate portion 21. By forming the electrode terminals 25 and 26 into a sheet shape, the stress of deformation of the laminate film 20 due to the interposition of the electrode terminals 25 and 26 at the portion penetrating the battery case 2 can be reduced. Further, welding (vibration welding) of the electrodes 11 and 12 to the uncoated portions 112 and 122 can be easily performed.

  The laminated secondary battery 1 of the present embodiment preferably has a restraint member that regulates the displacement of the positive electrode 11 and the negative electrode 12 in the direction in which they separate from each other. By providing the restraint member, it is possible to prevent the distance between the positive electrode 11 and the negative electrode 12 in the stacking direction from increasing. When the distance between the positive electrode 11 and the negative electrode 12 becomes long, the moving distance of the electrolyte ions becomes long, which leads to increase in internal resistance. The restraint member can suppress the increase in this distance.

  The restraint member may be, for example, a member provided with a pair of jigs that come into contact with both outer peripheral surfaces of the laminated secondary battery 1 in the stacking direction. Even if the restraint member is a member that pressurizes the outer peripheral surface of the laminated secondary battery 1 in a direction of compressing it, the restraint member is a member that fixes the distance between the pair of jigs and restricts only the increase in thickness. Both are good. The restraint member may be a rigid outer case that houses the laminated secondary battery 1.

[effect]
The secondary battery 1 of the present embodiment has the same configuration as that of the first embodiment except that the secondary battery 1 has a different shape, and exhibits the same effect as that of the first embodiment.

[Third Embodiment]
In this embodiment, the secondary battery 1 of Embodiment 1 is applied to a coin-type battery, and the configurations of the positive electrode 11, the negative electrode 12, the nonaqueous electrolyte 13, and the like are the same as those in Embodiment 1. The configuration of the secondary battery 1 of this embodiment is shown in a sectional view in FIG.

  The lithium-ion secondary battery 1 of the present embodiment has a positive electrode 11 and a negative electrode 12 housed (enclosed) in a battery case 3 made of metal. It should be noted that configurations that are not particularly limited in the present embodiment are similar to those in the first and second embodiments.

  Specifically, the lithium ion secondary battery 1 of the present embodiment has a positive electrode 11, a negative electrode 12, a non-aqueous electrolyte 13, a separator 14, a positive electrode case 31, a negative electrode case 32, a sealing material 33, and a holding member 34.

In the lithium-ion secondary battery 1 of the present embodiment, the positive electrode case 31 and the negative electrode case 32 seal the internal components via the insulating seal material 33. The built-in component has a positive electrode 11, a negative electrode 12, a non-aqueous electrolyte 13, a separator 14, and a holding member 34. The seal material 33 can be exemplified by a gasket.
Note that, as shown in FIG. 6, the positive electrode 11 and the negative electrode 12 are arranged with the positive electrode active material layer 111 and the negative electrode active material layer 121 facing each other through the separator 14.

  The positive electrode active material layer 111 is brought into surface contact with the positive electrode case 31 through the positive electrode current collector 110 to be conductive. The negative electrode active material layer 121 is brought into surface contact with the negative electrode case 32 through the negative electrode current collector 120 to conduct electricity.

[effect]
The secondary battery 1 of the present embodiment has the same configuration as that of the first embodiment except that the secondary battery 1 has a different shape, and exhibits the same effect as that of the first embodiment.

The secondary batteries 1 of Embodiments 2 to 3 described above are applied to laminate type or coin type batteries, but the present invention is not limited to these forms. For example, in addition to the laminate type amorphous secondary battery 1 and the coin type secondary battery 1 of the present embodiment, various types of batteries such as a cylindrical type and a square type can be used.
Furthermore, an assembled battery in which the secondary batteries 1 are combined in series and/or in parallel may be formed.

Hereinafter, the present invention will be specifically described with reference to examples.
As an example for specifically explaining the present invention, the lithium-ion secondary battery 1 shown in Embodiment 2 was manufactured.

(Example 1)
(Positive electrode)
First, an aqueous solution containing each of Li, Ni, Mn, and Sn as a metal complex was prepared. The obtained complex solution was mixed so as to have the composition ratio of the intended positive electrode material. That is, the complex solution was mixed so that the atomic ratio of Li:Ni:Mn:Sn was 2:1:0.67:0.33.
The obtained mixed solution was dried in a drying oven to remove organic components by heat treatment, and then heated and fired.
As described above, the positive electrode active material (Li ₂ NiMn _0.67 Sn _0.33 O ₄ powder) of this example was manufactured.

Next, a positive electrode active material: 88 parts by mass, a conductive material: 6 parts by mass, and a binder: 6 parts by mass were added to and mixed with NMP to prepare a slurry-like positive electrode mixture. Acetylene black was used as the conductive material. PVDF was used as the binder. The positive electrode mixture was applied on both sides of a current collector made of an aluminum foil having a thickness of 15 μm, dried, and pressed.
Through the above steps, the positive electrode 11 of this example was manufactured.

Incidentally, the positive electrode active material of the present embodiment, a lithium transition metal oxide described above in _{(Li 2-x Ni α M} 1 β M 2 γ O 4-ε), x = 0, α = 1, β = 0, γ =1 (=0.67+0.33), M ² : Mn and Sn, ε=0.

(Negative electrode)
Graphite powder: 90 parts by mass as the negative electrode active material, non-graphitizable carbon powder: 8 parts by mass, SBR: 1 part by mass as a binder, CMC: 1 part by mass as a binder, added to and mixed with water to form a slurry. A negative electrode mixture was prepared. An aqueous solution was used as the CMC of the binder, and the CMC of the binder was used as parts by mass in terms of solid content. The negative electrode mixture was applied on both sides of a current collector made of a copper foil having a thickness of 10 μm, dried, and pressed.
The negative electrode mixture was applied such that the applied amount was 1.0 with respect to the electric capacity per area of the positive electrode.
As described above, the negative electrode 12 of this example was produced.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte 13, a solution obtained by dissolving LiPF _{6 in an amount} of 1 mol% in a mixed solvent in which EC:DEC was mixed at a ratio of 30:70 (vol %) was used. VC is added as an additive to the non-aqueous electrolyte 13 at 2 mass% when the total amount is 100 mass %.

(Secondary battery)
The secondary battery 1 is formed by accommodating a laminated body in which a positive electrode 11, a separator 14, and a negative electrode 12 are laminated in this order together with a non-aqueous electrolyte 13 in a laminated battery case 2. Specifically, it was manufactured by injecting (injecting) the non-aqueous electrolyte 13 into the battery case 2 accommodating the laminated body and then sealing the battery case 2 by heat sealing. The battery capacity of the stack is 3 [Ah] by adjusting the number of stacks.
A 25 μm-thick polyethylene porous film was used for the separator 14.

  The battery case 2 is formed of a laminate film 20 including a polypropylene layer 201, an aluminum foil 202, and a polyethylene terephthalate layer 203.

  After the secondary battery 1 is assembled, at room temperature, the charge is 4.1 [V] cut CC charge, and the discharge is 2.5 [V] cut CC discharge at 1/3 C×5 cycles. The activation process by charging and discharging was performed.

(Example 2)
In this example, except that the negative electrode mixture was prepared by adding/mixing graphitizable carbon powder: 98 parts by mass, SBR: 1 part by mass, CMC: 1 part by mass to water. The secondary battery 1 is similar to the secondary battery 1.

(Example 3)
In this example, the negative electrode mixture was prepared by adding and mixing graphite powder: 90 parts by mass, graphitizable carbon powder: 8 parts by mass, SBR: 1 part by mass, CMC: 1 part by mass, in water. The secondary battery 1 is the same as that of the example 1 except for the above.

(Example 4)
This example was prepared by adding and mixing the negative electrode mixture material with 90 parts by mass of graphite powder, 8 parts by mass of silicon oxide (SiO ₂ ) powder, 1 part by mass of SBR, and 1 part by mass of CMC. The secondary battery 1 is the same as that of the example 1 except that the secondary battery 1 is used.

(Comparative Example 1)
This example is the same as Example 1 except that the negative electrode mixture was prepared by adding and mixing graphite powder: 98 parts by mass, SBR: 1 part by mass, and CMC: 1 part by mass in water. Secondary battery 1.

(Example 5)
In this example, the negative electrode mixture material is lithium titanate powder represented by Li ₄ Ti ₅ O ₁₂ : 45 parts by mass, TiO ₂ (B) powder: 45 parts by mass, acetylene black as a conductive material: 5 parts by mass, and a binder. It was prepared by adding and mixing PVDF: 5 parts by mass as an adhering material to NMP. Then, the negative electrode mixture was applied on both sides of a current collector made of an aluminum foil having a thickness of 15 μm, dried, and pressed.

In addition, after the secondary battery 1 is assembled, at room temperature, charging is 2.8 [V] cut CC charge and discharge is 2.0 [V] cut CC discharge, and 1/3C×5. The activation process was performed by charging and discharging the cycle.
The present example is a secondary battery 1 having the same configuration as that of Example 1 except for these.

(Comparative example 2)
In this example, the negative electrode composite material was obtained by adding lithium titanate powder represented by Li ₄ Ti ₅ O ₁₂ : 90 parts by mass, acetylene black: 5 parts by mass, and PVDF: 5 parts by mass as a binder to NMP. It was prepared by mixing.
This example is a secondary battery 1 having the same structure as that of Example 5 except for these.

(Example 6)
This example is a secondary battery 1 similar to that of Example 1 except that Li ₂ Ni _0.67 Co _0.67 Mn _0.33 Sn _0.33 O ₄ powder was used as the positive electrode active material.
In manufacturing the positive electrode active material of this example, first, an aqueous solution containing each of Li, Ni, Mn, Co, and Sn as a metal complex was prepared. The obtained complex solution was mixed so as to have the composition ratio of the intended positive electrode material. That is, the complex solution was mixed so that the atomic ratio of Li:Ni:Mn:Mn:Sn was 2:0.67:0.67:0.33:0.33. After that, heating and firing were performed in the same manner as in Example 1 to obtain the positive electrode active material of this example.

Incidentally, the positive electrode active material of the present embodiment, a lithium transition metal oxide described above in _{(Li 2-x Ni α M} 1 β M 2 γ O 4-ε), x = 0, α = 0.67, M 1: This corresponds to the case of Co, β=0.67, M ² : Mn and Sn, γ=0.66 (=0.33+0.33), and ε=0.

(Comparative example 3)
This example is a secondary battery 1 similar to Comparative example 1 except that Li ₂ Ni _0.67 Co _0.67 Mn _0.33 Sn _0.33 O ₄ powder was used as the positive electrode active material. The positive electrode active material is the same as in Example 6.

(Example 7)
This example is a secondary battery 1 similar to that of Example 1 except that Li ₂ NiMn _0.67 Ge _0.33 O ₄ powder was used as the positive electrode active material.
In the production of the positive electrode active material of this example, first, an aqueous solution containing each of Li, Ni, Mn, and Ge as a metal complex was prepared. The obtained complex solution was mixed so as to have the composition ratio of the intended positive electrode material. That is, the complex solution was mixed so that the atomic ratio of Li:Ni:Mn:Ge was 2:1:0.67:0.33. After that, heating and firing were performed in the same manner as in Example 1 to obtain the positive electrode active material of this example.

Incidentally, the positive electrode active material of the present embodiment, a lithium transition metal oxide described above in _{(Li 2-x Ni α M} 1 β M 2 γ O 4-ε), x = 0, α = 1, β = 0, γ =1.00 (=0.67+0.33), M ² : Mn and Ge, and ε=0.

(Comparative example 4)
This example is a secondary battery 1 similar to Comparative example 1 except that Li ₂ NiMn _0.67 Ge _0.33 O ₄ powder was used as the positive electrode active material. The positive electrode active material of this example is the same positive electrode active material as in Example 7.

[Evaluation]
The secondary battery 1 of each example was evaluated. In addition, prior to the evaluation of the secondary battery 1, the positive electrode 11 and the negative electrode 12 were evaluated (confirmation of characteristics). The positive electrode 11 and the negative electrode 12 were evaluated using a half-cell type test cell using a counter electrode made of metallic lithium. In the following measurement method, the characteristics of the positive electrode 11 were measured, but the characteristics of the negative electrode 12 can be obtained by the same method.

  The half cell type test cell has the configuration of the coin type battery of the third embodiment. Then, in the evaluation of the positive electrode 11, metallic lithium was used instead of the negative electrode 12. In the evaluation of the negative electrode 12, metallic lithium was used instead of the positive electrode 11. As the non-aqueous electrolyte 13, the non-aqueous electrolyte of each example was used.

  After being assembled, the half-cell type test cells used for evaluation of the positive electrode 11 of Examples 1 to 4, 6 to 7 and Comparative Example 1 were, at room temperature, charged with CC charge of 4.3 V cut and discharged. The activation treatment was performed by charging/discharging at 1/3C×5 cycles with 2.0V cut CC discharge.

  After being assembled, the half-cell type test cells used for evaluation of the negative electrode 12 of Examples 1 to 4, 6 to 7 and Comparative Example 1 were, at room temperature, discharged by CC discharge of 0.01 V cut and charged. An activation treatment was performed by charging/discharging at 1/10 C×5 cycles with CC charging of 2.0 V cut.

  Further, the secondary battery 1 of each example used for evaluation was assembled into a three-electrode cell in which the positive electrode 11 was the working electrode, the negative electrode 12 was the counter electrode, and the reference electrode made of lithium metal was further assembled.

  After being assembled, the triode cells of Examples 1 to 4, 6 to 7 and Comparative Example 1 were assembled at room temperature, and were charged by 4.1 V cut CC charge and discharged by 2.5 V cut CC discharge. , ⅓C×5 cycles of charge/discharge activation was performed.

  After being assembled, the half-cell type test cells used for evaluation of the positive electrode 11 of Example 5 and Comparative Example 2 were, at room temperature, charged at CC charge of 4.3 V and discharged at CC of 2.0 V. By discharge, an activation treatment was performed by charge/discharge of 1/3 C×5 cycles.

  The half-cell type test cells used for evaluation of the negative electrode 12 of Example 5 and Comparative Example 2 were assembled and then at room temperature, discharge was CC discharge of 0.05 V cut, and charge was CC of 2.0 V cut. Upon charging, an activation treatment was performed by charging/discharging at 1/10 C×5 cycles.

  After being assembled, the triode cells of Example 5 and Comparative Example 2 were assembled at room temperature and charged at a 2.8V cut CC charge and discharged at a 2.0V cut CC discharge at 1/3C×5. The activation process was performed by charging and discharging the cycle.

(Evaluation in test cell)
(Capacity measurement of positive electrode)
The test cell was charged and discharged at a rate of 1/3C. The charging was performed by CC charging of 4.3 V cut, and the discharging was performed by CC discharge of 2.0 V cut. The obtained discharge capacity was used as the battery capacity of the test cell and the electric capacity of the positive electrode 11. The measurement results are shown in Table 1.

(Confirm positive electrode potential-capacity)
The test cell was CC charged at 4.3 V cut at a rate of 1/3 C to be fully charged. After that, CC discharge of a predetermined capacity was performed and the target SOC was adjusted. After adjusting the SOC, the potential at each unipolar SOC was calculated, and the relational expression between the positive electrode potential and the positive electrode unipolar SOC was obtained. In addition, if this relationship is illustrated, a diagram similar to the diagrams shown in FIGS.

(Check positive electrode resistance)
The test cell was CC charged at 4.3 V cut at a rate of 1/3 C to be fully charged. After that, CC discharge of a predetermined capacity was performed and the target SOC was adjusted. After adjusting the SOC, the battery was charged at 1/2 C for 10 seconds, and the voltage value after 10 seconds was measured. Hereinafter, similarly, the voltage value after 10 seconds of 1C and 3C was measured. The resistance was calculated by the least square method from the charging current value and the obtained voltage value.
The obtained resistance was used as the resistance of the test cell and the resistance of the positive electrode 11.

(Check positive electrode resistance ratio)
The input resistance of the test cell (resistance of the positive electrode 11) at the unipolar SOC 0% and the input resistance of the test cell (resistance of the positive electrode 11) at the unipolar SOC 10% were measured, and the ratio of the two input resistances (at SOC 0% Resistance/resistance at SOC 10%) was determined. The obtained resistance ratio is shown in Table 1. It should be noted that this SOC 10% corresponds to "SOC equal to or higher than a predetermined SOC".

(Measurement of negative electrode capacity)
The test cell was charged and discharged at a rate of 1/10C. The discharging was performed by CC discharge of 0.01 V cut and the charging was performed by CC charge of 2.0 V cut. The obtained discharge capacity was used as the battery capacity of the test cell and the electric capacity of the negative electrode 12.

(Confirmation of negative electrode potential-capacity)
The test cell was subjected to 0.01 V cut CC discharge at a rate of 1/10 C. After that, CC charging of a predetermined capacity was performed and the target SOC was adjusted. After adjusting the SOC, the potential at each unipolar SOC was calculated, and the relational expression between the negative electrode potential and the negative unipolar SOC was obtained. In addition, if this relationship is illustrated, a diagram similar to the diagrams shown in FIGS.

(Evaluation with secondary battery)
(Rechargeable battery capacity measurement)
The secondary battery 1 of each example was charged and discharged at a rate of 1/3C. The charging was performed by a 4.1V cut CC charge and the discharge was performed by a 2.5V cut CC discharge. The obtained discharge capacity was used as the battery capacity of the secondary battery 1.

(Check the secondary battery resistance)
The secondary battery 1 of each example was subjected to a CC charge of 4.1 V cut at a 1/3C rate to be fully charged. After that, CC discharge of a predetermined capacity was performed and the target SOC was adjusted. After adjusting the SOC, the battery was charged at 1/2 C for 10 seconds, and the voltage value after 10 seconds was measured. Hereinafter, similarly, the voltage value after 10 seconds of 1C and 3C was measured. The resistance was calculated by the least square method from the charging current value and the obtained voltage value.

(Resistance ratio of secondary battery)
For the secondary battery 1 of each example, the input resistance was measured at SOC 10% and SOC 0%. The resistance value ratio was calculated from the two measured resistance values.

(Evaluation with a triode cell)
(Rechargeable battery capacity measurement)
The triode cell of each example was charged and discharged at a rate of 1/3C. The charging was performed by a 4.1V cut CC charge and the discharge was performed by a 2.5V cut CC discharge. The obtained discharge capacity was used as the battery capacity in the three-electrode cell of the secondary battery 1.

(Bipolar unipolar SOC measurement)
The triode cell of each example was charged and discharged at a rate of 1/3C. Charging was performed by CC charging with 4.3 V cut to full charge. After that, CC discharge of a predetermined capacity was performed and the target SOC was adjusted. After adjusting the SOC, the potentials of the working electrode and the counter electrode with respect to the reference electrode were measured and set as the positive electrode potential and the negative electrode potential.

  The SOC of the positive electrode single electrode was calculated from the relational expression of the positive electrode potential and the positive electrode single electrode SOC measured in advance, and the positive electrode potential. Similarly, the relational expression between the negative electrode potential and the single negative electrode SOC was used to calculate the negative electrode single electrode SOC from the negative electrode potential.

(Measurement of average OCP of negative electrode)
For the three-electrode cell of each example, the SOC of the negative electrode single electrode at SOC 50% was measured.

(Negative electrode capacity ratio)
For the three-electrode cell of each example, the electric capacity in the range of (negative electrode average OCP−0.15 [V]) to (negative electrode average OCP+0.25 [V]) and (negative electrode average OCP+0.25 [V]). [V]) The electric capacity in a larger range is measured. Then, the capacitance ratio is calculated from the two capacitances.

  As shown in Table 1, the positive electrode resistance ratio of the positive electrode 11 used in each example is 2.0 or more. That is, in the positive electrode 11 used in each example, the resistance at SOC 0% is 1.5 times or more the resistance at SOC 10% (SOC equal to or higher than the predetermined SOC).

  Moreover, in the secondary battery 1 of each example, the electric capacity ratio of the negative electrode 12 is 0.05 or more. On the other hand, in the secondary battery 1 of each comparative example, the electric capacity ratio of the negative electrode 12 is less than 0.05 (0.04 or less).

  In the secondary battery 1 of each example, as shown in Table 1, the resistance ratio is as low as 1.2 or less (specifically, 1 to 1.2). In other words, the difference between the input resistance at SOC 0% of the secondary battery 1 and the input resistance at SOC 10% is small. On the other hand, in the secondary battery 1 of each comparative example, the resistance ratio is as large as 2.9 or more (specifically, 2.9 to 4.4). In other words, the difference between the input resistance at SOC 0% of the secondary battery 1 and the input resistance at SOC 10% is small.

  From this, it can be confirmed that the secondary battery 1 of each example can be charged with low resistance when the SOC of the secondary battery 1 is 0% or more. On the other hand, in the secondary battery 1 of each example, the input resistance increases and the characteristics of the secondary battery 1 deteriorate in the low SOC region where the SOC of the secondary battery 1 is 10% or less. I can confirm.

  More specifically, in the secondary battery 1 of each comparative example, the SOC of the positive electrode 11 is 8 to 10% when the SOC of the secondary battery 1 is 0%. A region where the SOC of the positive electrode 11 is 8 to 10% is a region where the resistance of the positive electrode 11 is high.

  On the other hand, in the secondary battery 1 of each example, the SOC of the positive electrode 11 when the SOC of the secondary battery 1 is 0% is 18 to 28%, which is higher than that of each comparative example. A region where the SOC of the positive electrode 11 is 18% or more is a region where the resistance of the positive electrode 11 is low.

  From these SOC values of the positive electrode 11 at 0% SOC of the secondary battery 1, it can be confirmed that the secondary battery 1 of each example does not utilize the high resistance region of the positive electrode 11 at low SOC.

  As described above in detail, it was confirmed that the secondary battery 1 of each example was a lithium-ion secondary battery in which the deterioration of the battery characteristics in the low SOC region was suppressed.

1: Lithium ion secondary battery 11: Positive electrode 110: Positive electrode current collector 111: Positive electrode active material layer 12: Negative electrode 120: Negative electrode current collector 121: Negative electrode active material layer 13: Non-aqueous electrolyte 14: Separator 15: Battery case 2 , 3: Battery case 20: Laminated film 21: Flat plate part 22: Sealing part 23: Tank-like part 24: Sealant 25: Positive electrode terminal 26: Negative electrode terminal 31: Positive electrode case 32: Negative electrode case 33: Sealing material 34: Holding member

Claims (6)

Non-aqueous electrolyte secondary battery (1) comprising a positive electrode (11) and a negative electrode (12) using a material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte (13) having lithium ions as electrolyte ions. And
The positive electrode (11) is Li ₂ Ni _α M ¹ _β M ² _γ Mn _η O _4-ε (0.50<α≦1.33, 0≦β≦0.67, 0.33≦γ≦1. 1, 0 ≤ ε ≤ 1.00, 0 ≤ η ≤ 1.00, M ¹ : at least one selected from Co and Ga, M ² : at least one selected from Ge, Sn and Sb) Including metal oxides,
Positive electrode, the resistance at SOC 0%, has a relationship of resistance -SOC to be 2.0 times or more resistance at SOC 10%,
The lithium transition metal oxide has a local structure in which all of Ni, M ¹ , M ² and Mn are hexacoordinated,
The negative electrode (12) has an electric capacity (average OCP-0.10 [V]) and an average OCP+0.25 when the potential of the negative electrode at 50% SOC of the non-aqueous electrolyte secondary battery is the average OCP. [V]) is the difference between the electric capacity at (average OCP+0.25 [V]) and the electric capacity at the limit value at which OCP of the negative electrode is larger than the average electric capacity , which is the difference in electric capacity at [V]. A non-aqueous electrolyte secondary battery having a ratio value in the denominator of the section electric capacity of 0.05 or more. The negative electrode (12) has a carbon material containing non-graphitizable carbon or graphitizable carbon,
The non-aqueous electrolyte secondary battery according to claim 1, wherein the carbon material contains non-graphitizable carbon or graphitizable carbon at 5 mass% or more when the total mass of the carbon material is 100 mass %.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode (12) contains silicon or silicon oxide as a negative electrode active material.   The non-aqueous electrolyte secondary battery according to claim 3, wherein the negative electrode active material further contains a carbon material.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode (12) contains a lithium titanium composite oxide as a negative electrode active material. The non-aqueous electrolyte secondary battery according to claim 5, wherein the lithium-titanium composite oxide contains TiO ₂ (B) at 5 mass% or more when the total mass is 100 mass %.

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