Positive electrode active material for non-aqueous electrolyte energy storage elements, positive electrode for non-aqueous electrolyte energy storage elements, non-aqueous electrolyte energy storage elements, energy storage units and energy storage devices

Abstract

The positive electrode active material for nonaqueous electrolyte power storage elements according to one aspect of the present invention comprises: a lithium transition metal compound having a polyanion structure and given by the general formula LiMPO4 (M is at least one element selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3, and a lithium transition metal composite oxide having an α-NaFeO2 crystalline structure and given by the general formula Li1+αMe1-αO2 (0 < α and Me is transition metal element comprising Ni and Mn or Ni, Mn, and Co). The molar ratio of Mn to transition metal (Me) in the lithium transition metal composite oxide is 0.4 ≤ Mn / Me ≤ 0.6.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a non-aqueous electrolyte storage element, a positive electrode for a non-aqueous electrolyte storage element, a non-aqueous electrolyte storage element, a power storage unit, and a power storage device.

Background Art

[0002] In recent years, as a positive electrode active material used in non-aqueous electrolyte storage elements such as non-aqueous electrolyte secondary batteries, transition metal compounds having a polyanion structure have attracted attention. Since this transition metal compound having a polyanion structure forms a polyanion structure by oxygen covalently bonding with an element other than the transition metal, it does not release oxygen even at a relatively high temperature, and it is known that using it as a positive electrode active material enhances the safety of the storage element. An invention in which a transition metal compound having a polyanion structure is mixed with a lithium-excess type lithium transition metal composite oxide to form a positive electrode active material is known (see Patent Document 1).

[0003] Patent Document 1 states that "a dual-active Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 / LiFePO4 nano-insertion cathode material was obtained via a combustion synthesis route. Each of the stoichiometric masses of the acetates Li(COOCH3)2·2H2O, Mn(COOCH3)2·4H2O, Ni(COOCH3)2·4H2O, and Co(COOCH3)2·4H2O was dissolved in deionized water to form a solution. Citric acid (C6H8O7) was added to the solution as a fuel, and the pH of the solution was adjusted to 2 by adding citric acid. Then, LiFePO4 powder was added to the solution at a molar ratio of about 1:0.05 of Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2:LiFePO4. LiFePO4 provides oxygen atoms having a stronger bond than the bond of Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2." (Paragraph

[0047] ).

[0004] Furthermore, the invention of using a transition metal compound having a polyanionic structure mixed with a LiMeO2-type lithium transition metal composite oxide ("NCM" or "NMC") (where Me is a transition metal containing Ni, Co, and Mn) to form a positive electrode active material is well known (see, for example, Patent Documents 2 to 4).

[0005] Patent Document 2 states, "Layered lithium-nickel-manganese-cobalt composite oxide (NMC) and olivine-type lithium iron phosphate (LFP), which are positive electrode active materials, were mixed in a predetermined weight ratio of active materials (NMC / LFP). To this mixture of positive electrode active materials, flake-shaped graphite (average particle size: 20 μm) as a conductive material and polyvinylidene fluoride as a binder were sequentially added and mixed to obtain a mixture of positive electrode materials." (Paragraph

[0141] )

[0006] Patent Document 3 states: "<Example 1>...To the obtained carbon-coated LiFePO4 (compound A), PVDF was added in a mass ratio of LiFePO4:carbon coating:binding agent (PVDF) of 88:2:10, and the mixture was uniformly ground and kneaded in a bead mill using NMP as a dispersion medium to obtain a slurry-like cathode composite material with a solid content (NV) of 40% by mass.To this cathode composite material, LiNi with an average particle size of 1 μm 1 / 3 Mn 1 / 3 Co 1 / 3 O2 (compound B) was added so that the mass ratio of compound A to B was 90:10, and it was mixed well. (Paragraph

[0049] ) "LiNi with an average particle size of 10 μm 1 / 3 Mn 1 / 3 Co 1 / 3 A battery according to Example 5 was obtained in the same manner as in Example 1, except that O2 was used. (Paragraph

[0052] ) "LiNi with an average particle size of 10 μm 1 / 3 Mn 1 / 3 Co 1 / 3 A battery according to Example 7 was obtained in the same manner as in Example 3, except that O2 was used. "LiNi with an average particle size of 10 μm 1 / 3 Mn 1 / 3 Co 1 / 3 The text states, "A battery according to Example 8 was obtained in the same manner as in Example 4, except that O2 was used." (Paragraph

[0053] )

[0007] Patent Document 4 describes "Positive electrode active materials LiFePO4 (LFP) and LiNi produced in manufacturing examples 1 and 3." 0.6 Co 0.2 Mn 0.2 The text states, "Pellets were produced by mixing O2 (hereinafter referred to as "NCM") powder in a certain proportion and then applying pressure." (paragraph

[0077] ) [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Special Publication No. 2020-527832 [Patent Document 2] Patent No. 6065901 [Patent Document 3] Patent No. 5081886 [Patent Document 4] Patent No. 6236197 [Overview of the project] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a non-aqueous electrolyte energy storage element, energy storage unit, and energy storage device that have high output performance at low SOC (State of Charge) after charge-discharge cycles. [Means for solving the problem]

[0010] The positive electrode active material for a non-aqueous electrolyte energy storage element according to one aspect of the present invention is a lithium transition metal compound having a polyanionic structure and represented by the general formula LiMPO4 (where M is one or more elements selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3, and having an α-NaFeO2 type crystal structure and represented by the general formula Li 1+α Me 1-αThe present invention provides a lithium transition metal composite oxide represented by O2 (0 < α, where Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co), wherein the lithium transition metal composite oxide has a molar ratio of Mn to the transition metal (Me) of 0.4 ≤ Mn / Me ≤ 0.6. Another aspect of the present invention relates to a positive electrode for a non-aqueous electrolyte energy storage element, which contains the positive electrode active material. A non-aqueous electrolyte energy storage element according to yet another aspect of the present invention comprises the positive electrode. A further aspect of the present invention relates to a power storage unit comprising a plurality of non-aqueous electrolyte power storage elements connected in series. A further aspect of the present invention relates to a power storage device comprising a plurality of the power storage units connected together. [Effects of the Invention]

[0011] By using a positive electrode active material for a non-aqueous electrolyte energy storage element according to one aspect of the present invention as the positive electrode, it is possible to provide a non-aqueous electrolyte energy storage element, energy storage unit, and energy storage device that have high output performance at low SOC after charge-discharge cycles. [Brief explanation of the drawing]

[0012] [Figure 1A] Figure 1A is a schematic diagram showing the change in positive electrode potential with respect to the amount of charge (Q) in a non-aqueous electrolyte secondary battery using only LiFePO4 (LFP) as the positive electrode active material. [Figure 1B] Figure 1B is a schematic diagram showing the change in positive electrode potential with respect to the amount of charge (Q) in a non-aqueous electrolyte secondary battery using a mixture of LiFePO4 (LFP) and Li,Ni,Co,Mn composite oxide (NCM) as the positive electrode active material. [Figure 2] Figure 2 is a perspective view showing one embodiment of a non-aqueous electrolyte energy storage element. [Figure 3] Figure 3 is a schematic diagram showing one embodiment of an energy storage device configured by assembling multiple non-aqueous electrolyte energy storage elements. [Modes for carrying out the invention]

[0013] First, an overview of the positive electrode active material for non-aqueous electrolyte energy storage elements, positive electrode for non-aqueous electrolyte energy storage elements, non-aqueous electrolyte energy storage elements, energy storage units, and energy storage devices disclosed herein will be described.

[0014] The positive electrode active material for a non-aqueous electrolyte energy storage element according to one aspect of the present invention is a lithium transition metal compound having a polyanionic structure and represented by the general formula LiMPO4 (where M is one or more elements selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3, and having an α-NaFeO2 type crystal structure and represented by the general formula Li 1+α Me 1-α The present invention provides a lithium transition metal composite oxide represented by O2 (0 < α, where Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co), wherein the lithium transition metal composite oxide has a molar ratio of Mn to the transition metal (Me) of 0.4 ≤ Mn / Me ≤ 0.6.

[0015] This positive electrode active material makes it possible to provide a positive electrode for a non-aqueous electrolyte energy storage element and a non-aqueous electrolyte energy storage element that have high output performance at low SOC after charge-discharge cycles. By using a positive electrode active material that mixes a LiMeO2 (where Me is a transition metal element containing Ni, Co, and Mn) type lithium transition metal composite oxide (NCM) with a lithium transition metal compound having a polyanionic structure (e.g., LiFePO4:LFP) (see Patent Documents 2 to 4), a 3.5V (vs. Li / Li) voltage can be achieved. + ) Above 3.7V (vs. Li / Li + In the following positive electrode potential range, capacitance derived from NCM is exhibited, the potential change with respect to the amount of charge shows a gradient, and the rapid potential rise seen when only lithium transition metal compounds with a polyanionic structure are used as the positive electrode active material can be suppressed (see Figures 1A and 1B). However, when such a positive electrode active material is used, the NCM is mainly used at low SOC during normal operation of the non-aqueous electrolyte energy storage element, and as the charge-discharge cycle progresses, resistance is likely to increase due to cracking of the NCM particles. Therefore, the inventors have developed a material with an α-NaFeO2 type crystal structure that exhibits capacity in a potential range similar to that of NCM and has the general formula Li 1+α Me1-α We investigated mixing a lithium transition metal composite oxide represented by O2 (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co, 0.4≦Mn / Me≦0.6) with a lithium transition metal compound having a polyanionic structure such as LFP and represented by the general formula LiMPO4 (M is one or more elements selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3, and found that this can suppress the increase in resistance due to cracking of the lithium transition metal composite oxide particles and improve output performance at low SOC after charge-discharge cycles.

[0016] A positive electrode having the aforementioned polyanionic structure and a lithium transition metal compound represented by the general formula LiMPO4 (where M is one or more elements selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3 as the positive electrode active material has a positive electrode potential of 3.7V (vs.Li / Li + When charging is performed to the point of 3.2V (vs.Li / Li), + ) Above 3.4V (vs. Li / Li + Within the positive electrode potential range of less than ), a region where the potential change is relatively flat with respect to the amount of charge may be observed.

[0017] If this lithium transition metal compound having a polyanionic structure is used, and combined with the lithium transition metal composite oxide to form a positive electrode active material, then 3.5V(vs.Li / Li) + ) Above 3.7V (vs. Li / Li + The capacity derived from the lithium transition metal composite oxide can be effectively expressed within the following positive electrode potential range.

[0018] According to this lithium transition metal compound having a polyanionic structure, a positive electrode using this compound as the positive electrode active material has a positive electrode potential of 3.7V (vs.Li / Li + When charging is performed to the point of 3.2V (vs.Li / Li), + ) Above 3.4V (vs. Li / Li + Within the positive electrode potential range of less than ), a region can be observed where the potential change is relatively flat with respect to the amount of charge.

[0019] The lithium transition metal composite oxide may have a molar ratio of Li to the transition metal (Me), (1+α) / (1-α), of 1.1 ≤ (1+α) / (1-α), or (1+α) / (1-α) ≤ 1.3.

[0020] Using this lithium transition metal composite oxide, 3.5V(vs.Li / Li + ) Above 3.7V (vs. Li / Li + In the positive electrode potential range below ) the capacity derived from the lithium transition metal composite oxide can be effectively expressed, and cracking of the lithium transition metal composite oxide particles as the charge-discharge cycle progresses is suppressed. In particular, even when used for a long period of time in a high-temperature environment and some degree of degradation has occurred, the output performance at low SOC is improved.

[0021] The proportion of the lithium transition metal composite oxide in the positive electrode active material may be 20% by mass or less.

[0022] This positive electrode active material has a high proportion of lithium transition metal compounds with a polyanionic structure, which can be used to improve thermal stability.

[0023] A positive electrode for a non-aqueous electrolyte energy storage element according to another aspect of the present invention contains the positive electrode active material, and a non-aqueous electrolyte energy storage element according to yet another aspect of the present invention comprises the positive electrode.

[0024] The positive electrode of the aforementioned non-aqueous electrolyte energy storage element has a positive electrode potential of 3.7V (vs.Li / Li + When charging is performed to the point of 3.2V (vs.Li / Li), + ) Above 3.7V (vs. Li / Li + Within the positive electrode potential range below, a region where the potential change is relatively flat with respect to the amount of charge may be observed.

[0025] According to this non-aqueous electrolyte energy storage element, 3.5V (vs. Li / Li + ) Above 3.7V (vs. Li / Li +Within the positive electrode potential range below, the capacitance derived from the lithium transition metal composite oxide is effectively expressed, and the rapid voltage rise observed when using only lithium transition metal compounds having a polyanionic structure as the positive electrode active material can be suppressed.

[0026] The aforementioned non-aqueous electrolyte energy storage element has a maximum potential of 3.7V (vs.Li / Li) at the positive electrode when fully charged (SOC 100%). + It may be used at a voltage below )

[0027] A further aspect of the present invention relates to a power storage unit comprising a plurality of non-aqueous electrolyte power storage elements connected in series.

[0028] This energy storage unit suppresses a rapid voltage increase at the end of charging and also suppresses voltage variations among multiple non-aqueous electrolyte energy storage elements.

[0029] A further aspect of the present invention relates to a power storage device comprising a plurality of the power storage units connected together.

[0030] This energy storage device suppresses a rapid voltage increase at the end of charging and also suppresses voltage variations among multiple non-aqueous electrolyte energy storage elements and energy storage units.

[0031] This document describes in detail the configuration of a non-aqueous electrolyte energy storage element, the configuration of an energy storage unit, the configuration of an energy storage device, a method for manufacturing a non-aqueous electrolyte energy storage element, and other embodiments according to one embodiment of the present invention (hereinafter referred to as "this embodiment"). Note that the names of the components (each element) used in each embodiment may differ from the names of the components (each element) used in the background art.

[0032] <Configuration of a non-aqueous electrolyte energy storage element> The non-aqueous electrolyte energy storage element according to this embodiment (hereinafter also simply referred to as "energy storage element") comprises an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with a separator in between, or a wound type in which the positive electrode and negative electrode are wound in a stacked state with a separator in between. The non-aqueous electrolyte exists contained within the positive electrode, negative electrode, and separator. As an example of a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0033] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer disposed directly on the positive electrode substrate or via an intermediate layer.

[0034] The positive electrode substrate is conductive. Whether or not it is conductive is determined by the volume resistivity measured in accordance with JIS-H-0505 (1975), which is 10 7 The determination is made using Ω·cm as the threshold. The positive electrode substrate material can be a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoint of high potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

[0035] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per unit volume of the secondary battery.

[0036] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

[0037] The positive electrode active material layer contains the positive electrode active material. The positive electrode active material layer may optionally contain conductive agents, binders, thickeners, fillers, and other optional components.

[0038] In this embodiment, the positive electrode active material includes a lithium transition metal compound having a polyanionic structure and represented by the general formula LiMPO4 (where M is one or more elements selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3. Examples of lithium transition metal compounds having a polyanionic structure and represented by the general formula LiMPO4 (where M is one or more elements selected from Fe, Mn, Ni, and Co) include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., where M in the above general formula is specifically one element selected from Fe, Mn, Ni, and Co, and LiFePO4 where M is two or more elements. x Mn 1-x PO4(0 <x<1)、LiFe y M 1-y Examples include PO4 (where M is one or more transition metal elements selected from Mn, Ni, and Co, and 0.5 ≤ y < 1).

[0039] Lithium transition metal compounds having a polyanionic structure and represented by the general formula LiMPO4 (where M is one or more elements selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3 may be carbon-coated. It is preferable to produce carbon-coated lithium transition metal compounds having a polyanionic structure by mixing raw materials for a transition metal compound containing Fe, Mn, Ni, Co, V, etc., with a carbon raw material such as Li phosphate (e.g., LiH2PO4) and sucrose powder, and then firing the mixture. By controlling the type of carbon raw material, the amount of carbon raw material mixed, the firing temperature, and the firing time during the firing process, the ratio of the increase in BET specific surface area due to the carbon coating of the polyanionic lithium transition metal compound to the BET specific surface area of ​​the positive electrode mixture can be set to 12% or more and 30% or less. For example, when producing LiFePO4, it is preferable to set the firing temperature to 650°C to 700°C and the firing time to 2 to 12 hours.

[0040] In this embodiment, the positive electrode active material is a lithium transition metal compound having a polyanionic structure and represented by the general formula LiMPO4 (where M is one or more elements selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3, along with a material having an α-NaFeO2 type crystal structure and represented by the general formula Li 1+α Me 1-α It contains lithium transition metal composite oxides represented as O2 (0 < α, Me is a transition metal element containing Ni and Mn, or Ni, Mn and Co, 0.4 ≤ Mn / Me ≤ 0.6). When this lithium transition metal composite oxide is mixed with a lithium transition metal compound having a polyanionic structure, 3.5V(vs.Li / Li + ) Above 3.7V (vs. Li / Li + In the positive electrode potential range below this, the capacity derived from the lithium transition metal composite oxide is exhibited, and the cracking of the lithium transition metal composite oxide particles as the charge-discharge cycle progresses is suppressed. Having the aforementioned α-NaFeO2 type crystal structure and general formula Li 1+α Me 1-αLithium transition metal composite oxides represented by O2 (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co, 0.4≦Mn / Me≦0.6) preferably have X-ray diffraction patterns using CuKα rays that can be attributed to a crystal structure model of space group R3-m, with the full width at half maximum F(104) of diffraction peaks attributed to the (104) plane (diffraction peaks at 2θ=44°±1°) being in the range of 0.15° to 0.35°, and the full width at half maximum F(003) of diffraction peaks attributed to the (003) plane (diffraction peaks at 2θ=18.6°±1°) being in the range of 0.15° to 0.40°.

[0041] In this embodiment, other positive electrode active materials other than the lithium transition metal compound having a polyanionic structure and the lithium transition metal composite oxide may be included, to the extent that they do not impair the output performance at low SOC after charge-discharge cycles of the non-aqueous electrolyte energy storage element, which is a problem of positive electrode active materials for non-aqueous electrolyte energy storage elements according to one aspect of the present invention. Other positive electrode active materials include, for example, lithium transition metal compounds having a polyanionic structure other than the lithium transition metal compounds mentioned above, lithium transition metal composite oxides having an α-NaFeO2 type crystal structure other than the lithium transition metal composite oxides mentioned above, lithium transition metal composite oxides having a spinel type crystal structure, chalcogen compounds, sulfur, etc. Examples of lithium transition metal compounds having a polyanionic structure other than the lithium transition metal compounds include Li2MnSiO4 and Li2CoPO4F. Examples of lithium transition metal composite oxides having an α-NaFeO2 type crystal structure other than the lithium transition metal composite oxides include Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0 <x<0.5、0.6<(1-γ))、LiNi γ Mn (1-γ)O2((1-γ)≦0.5), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0 <x<0.5、0<γ、0.6<β、0.6<γ+β<1)、LiNi γ Mn β Co (1-γ-β) ]O2(0<γ, 0<β≦0.5), Li[Li x Ni γ Co β Al (1-x-γ-β) Examples include ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). As a lithium transition metal composite oxide having a spinel-type crystal structure, Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples include O4. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Some atoms or polyanions in these materials may be substituted with atoms or anions of other elements. The surfaces of these materials may be coated with other materials.

[0042] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material above the lower limit makes it easier to manufacture or handle the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite material of the positive electrode active material and other materials is used, the average particle size of the composite material is used as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering method on a dilution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013), becomes 50%.

[0043] To obtain powder with a predetermined particle size, grinders and classifiers are used. Examples of grinding methods include using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter-jet mills, swirling airflow jet mills, or sieves. Wet grinding, which involves the coexistence of water or organic solvents such as hexane, can also be used during grinding. For classification, sieves and wind classifiers are used as needed, both dry and wet.

[0044] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0045] The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent can take the form of powder or fiber. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. These materials may also be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coating properties, and acetylene black is particularly preferred.

[0046] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the secondary battery can be increased.

[0047] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0048] The binder content in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the active material can be stably maintained.

[0049] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium or the like, this functional group may be deactivated beforehand by methylation or the like.

[0050] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

[0051] The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0052] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from, for example, the configurations exemplified in the positive electrode.

[0053] The negative electrode substrate is electrically conductive. Suitable materials for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, as well as carbonaceous materials. Among these, copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials, with foil being preferred from a cost perspective. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0054] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the secondary battery.

[0055] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains conductive agents, binders, thickeners, fillers, and other optional components. These optional components can be selected from the materials exemplified above for the positive electrode.

[0056] The negative electrode active material layer may contain, as components other than the negative electrode active material, conductive agent, binder, thickening agent, and filler, typical non-metal elements such as B, N, P, F, Cl, Br, I, etc., typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc., and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc.

[0057] As the negative electrode active material, it can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium-ion secondary battery, usually, a material capable of occluding and releasing lithium ions is used. Examples of the negative electrode active material include metallic Li; metals or semi-metals such as Si, Sn, etc.; metal oxides or semi-metal oxides such as Si oxide, Ti oxide, Sn oxide, etc.; Li4Ti5O 12 、LiTiO 2、 titanium-containing oxides such as TiNb2O7; polyphosphoric acid compounds; silicon carbide; carbon materials such as graphite (graphite), non-graphitic carbon (easily graphitizable carbon or difficult-to-graphitize carbon), etc. Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used.

[0058] "Graphite" refers to a carbon material with an average lattice plane spacing (d 002 ) of the (002) plane determined by X-ray diffraction method of 0.33 nm or more and less than 0.34 nm before charge-discharge or in the discharged state. Examples of graphite include natural graphite and artificial graphite. From the perspective of obtaining a material with stable physical properties, artificial graphite is preferred.

[0059] "Non-graphitic carbon" refers to a carbon material with an average lattice plane spacing (d 002 ) of the (002) plane determined by X-ray diffraction method of 0.34 nm or more and 0.42 nm or less before charge-discharge or in the discharged state. Examples of non-graphitic carbon include difficult-to-graphitize carbon and easily graphitizable carbon. Examples of non-graphitic carbon include, for example, resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, alcohol-derived materials, etc.

[0060] Here, "discharge state" refers to a state in which sufficient lithium ions that can be absorbed and released during charging and discharging are released from the carbon material, which is the negative electrode active material. For example, in a half-cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode, this is the state in which the open-circuit voltage is 0.7V or higher.

[0061] "Non-graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength between 0.36 nm and 0.42 nm.

[0062] "Easily graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.34 nm or more and less than 0.36 nm.

[0063] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, between 1 nm and 100 μm. If the negative electrode active material is a carbon material, titanium-containing oxide, or polyphosphate compound, its average particle size may be between 1 μm and 100 μm. If the negative electrode active material is Si, Sn, Si oxide, or Sn oxide, its average particle size may be between 1 nm and 1 μm. Setting the average particle size of the negative electrode active material above the lower limit makes it easier to manufacture or handle. Setting the average particle size of the negative electrode active material below the upper limit improves the electronic conductivity of the negative electrode active material layer. To obtain powder with a predetermined particle size, a pulverizer or classifier is used. The pulverizing method and powder grading method can be selected from, for example, the methods exemplified above for the positive electrode. If the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of foil.

[0064] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer.

[0065] (Separator) The separator can be appropriately selected from known separators. Examples of separators include a separator consisting only of a base layer, or a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer. Examples of the base layer shape of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. As for the material of the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative degradation resistance. A composite material of these resins may also be used as the base layer of the separator.

[0066] The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C. Inorganic compounds are examples of materials with a mass loss of less than the specified amount. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. These inorganic compounds may be used individually or in combination, or two or more may be used as a mixture. Among these inorganic compounds, silicon dioxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for energy storage elements.

[0067] The porosity of the separator is preferably 80 volume% or less from the viewpoint of strength, and preferably 20 volume% or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and means the measurement value obtained using a mercury porosimeter.

[0068] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. Using a polymer gel has the effect of suppressing leakage. A polymer gel may also be used in combination with a porous resin film or nonwoven fabric as described above as a separator.

[0069] (Non-aqueous electrolytes) As the non-aqueous electrolyte, it can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0070] As the non-aqueous solvent, it can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.

[0071] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Among these, EC is preferred.

[0072] Examples of linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. Among these, EMC is preferred.

[0073] It is preferable to use a cyclic carbonate or a linear carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a linear carbonate in combination. Using a cyclic carbonate can promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. Using a linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using a cyclic carbonate and a linear carbonate in combination, the volume ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

[0074] The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred.

[0075] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2; lithium oxalate salts such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); and lithium salts having halogenated hydrocarbon groups such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0076] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at 20°C and 1 atm. 32.5 mol / dm or less is preferable, and 0.3 mol / dm 3 or more is more preferable, and 2.0 mol / dm 3 or less is even more preferable, and 0.5 mol / dm 3 or more is still more preferable, and 1.7 mol / dm 3 or less is particularly preferable, and 0.7 mol / dm 3 or more is especially preferable, and 1.5 mol / dm 3 or less. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased. 3

[0077] ​Non-aqueous electrolytes may contain additives in addition to the non-aqueous solvent and electrolyte salt. Examples of additives include halogenated carbonate esters such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate) difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halogenated compounds of the aforementioned aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, and ethyl vinylene carbonate. - Bonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1) Examples include 3,2-dioxathiolane, 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propensultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butensultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakithtrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used individually or in combination of two or more.

[0078] The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total mass of the non-aqueous electrolyte, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By setting the additive content within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

[0079] For the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte and a solid electrolyte may be used in combination.

[0080] The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, and calcium, and is solid at room temperature (e.g., 15°C to 25°C). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0081] Examples of sulfide solid electrolytes in lithium-ion secondary batteries include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 These are some examples.

[0082] The shape of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like. Figure 2 shows a non-aqueous electrolyte energy storage element 1 as an example of a rectangular battery. Note that the figure is a transparent view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound around a separator is housed in a rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51.

[0083] <Configuration of energy storage unit and energy storage device> The energy storage unit according to this embodiment is formed by connecting a plurality of non-aqueous electrolyte energy storage elements of this embodiment in series. This energy storage unit suppresses a rapid voltage rise at the end of charging and suppresses the occurrence of voltage variations among the plurality of non-aqueous electrolyte energy storage elements. The energy storage unit of this embodiment can be installed in power supplies for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power storage power supplies. In this case, it is sufficient that the technology of the present invention is applied to at least two of the non-aqueous electrolyte energy storage elements included in the energy storage unit. Preferably, the energy storage unit is formed by connecting four non-aqueous electrolyte energy storage elements in series. The energy storage device according to this embodiment is formed by connecting a plurality of energy storage units according to this embodiment. This energy storage device suppresses a rapid voltage rise at the end of charging and suppresses the occurrence of voltage variations among the plurality of non-aqueous electrolyte energy storage elements and energy storage units. In this case, it is sufficient that the technology of the present invention is applied to at least two of the energy storage units included in the energy storage device. Figure 3 shows an example of an energy storage device 30 which is formed by further assembling energy storage units 20, each of which is an assembly of two or more electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may include a busbar (not shown) for electrically connecting two or more non-aqueous electrolyte energy storage elements 1, a busbar (not shown) for electrically connecting two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage elements.

[0084] <Method for manufacturing a non-aqueous electrolyte energy storage element> The method for manufacturing the non-aqueous electrolyte energy storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and housing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by stacking or winding the positive electrode and the negative electrode via a separator.

[0085] The method for housing the non-aqueous electrolyte in a container can be appropriately selected from known methods. For example, when using a non-aqueous electrolyte solution, the non-aqueous electrolyte solution can be injected through an inlet formed in the container, and then the inlet can be sealed.

[0086] <Other Embodiments> Furthermore, the positive electrode active material for non-aqueous electrolyte energy storage elements, the positive electrode for non-aqueous electrolyte energy storage elements, the non-aqueous electrolyte energy storage elements, the energy storage unit, and the energy storage device of the present invention are not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0087] In the above embodiment, the case in which the non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery) was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors.

[0088] In the above embodiment, an electrode body in which a positive electrode and a negative electrode are stacked with a separator in between has been described, but the electrode body does not need to have a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of either the positive electrode or the negative electrode. [Examples]

[0089] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0090] In the following examples and comparative examples, a non-aqueous electrolyte secondary battery was fabricated as the non-aqueous electrolyte energy storage element, and its output performance at low SOC after charge-discharge cycles was evaluated.

[0091] [Example 1] (Preparation of Cathode Active Material) (Preparation of LiFePO4) First, while dropping an aqueous solution of FeSO4 of 1 mol / dm 3 into a reaction vessel containing ion-exchanged water at a constant rate, an aqueous solution of NaOH of 4 mol / dm 3 and an aqueous solution of NH3 of 0.5 mol / dm 3 and an aqueous solution of NH2NH2 of 0.5 mol / dm 3 were dropped so that the pH during that time was maintained at a constant value of 10.0 ± 0.1, and a Fe(OH)2 precursor was prepared. Next, the prepared Fe(OH)2 precursor was taken out from the reaction vessel and solid-phase mixed with LiH2PO4 and sucrose powder. Then, by firing at a firing temperature of 650 °C for 5 hours in a nitrogen atmosphere, LiFePO4 (LFP) having a carbon-coated polyanion structure was prepared.

[0092] (Preparation of Lithium Transition Metal Composite Oxide) First, while dropping an aqueous solution of a mixture composed of NiSO4, CoSO4, and MnSO4 of 1 mol / dm 3 (the molar ratio of Ni / Co / Mn is 34 / 20 / 46, and the concentration of SO4 ions is 1 mol / dm 3 ), an aqueous solution of a mixture composed of NiSO4, CoSO4, and MnSO4) into a reaction vessel containing ion-exchanged water at a constant rate, an aqueous solution of NaOH of 4 mol / dm 3 and an aqueous solution of NH3 of 0.5 mol / dm 3 and an aqueous solution of NH2NH2 of 0.5 mol / dm 3 were dropped so that the pH during that time was maintained at a constant value of 11.0 ± 0.1, and a hydroxide precursor in which Ni, Co, and Mn were dispersed in one particle was prepared. Next, this precursor was taken out from the reaction vessel and solid-phase mixed with LiOH·H2O so that the Li / Me ratio was 1.2 in molar ratio. Then, by firing at a firing temperature of 900 °C in an air atmosphere, the lithium transition metal composite oxide Li 1.09 (Ni 0.34 Co 0.20 Mn 0.46 ) 0.91O2 was produced. Powder X-ray diffraction measurements were performed on the aforementioned lithium transition metal composite oxide using an X-ray diffractometer (Rigaku, model: MiniFlex II) to confirm that it possesses an α-NaFeO2 type crystal structure.

[0093] (Fabrication of the positive electrode) LiFePO4 and lithium transition metal composite oxide Li, which have the above polyanion structure, are used as positive electrode active materials. 1.09 Ni 0.31 Co 0.18 Mn 0.42 A mixture of O2 in a mass ratio of 9:1 was used, N-methylpyrrolidone (NMP) was used as the dispersion medium, acetylene black as the conductive agent, and PVDF as the binder. The above positive electrode active material, conductive agent, binder, and dispersion medium were mixed. At that time, the solid content mass ratio of the mixed active material:conductive agent:binder was 90:5:5. An appropriate amount of dispersion medium was added to these mixtures to adjust the viscosity and prepare a positive electrode active material mixture paste. Next, the above positive electrode active material mixture paste was applied to both sides of the aluminum foil, which was the positive electrode substrate, leaving uncoated areas (areas where the positive electrode active material layer was not formed), dried at 120°C, and roll-pressed to form a positive electrode active material layer on the positive electrode substrate. The amount of positive electrode active material mixture paste applied was 10 mg / cm² in solid content. 2 This is how the positive electrode according to Example 1 was fabricated.

[0094] (Fabrication of the negative electrode) Graphite was used as the negative electrode active material, SBR as the binder, and CMC as the thickener. The negative electrode active material, binder, thickener, and water as the dispersion medium were mixed. At that time, the solid content mass ratio of the active material:binder:thickener was 97:2:1. An appropriate amount of water was added to these mixtures to adjust the viscosity and prepare a negative electrode mixture paste. This negative electrode mixture paste was applied to both sides of a copper foil, which was the negative electrode substrate, leaving uncoated areas (areas where the negative electrode active material layer was not formed), dried, and roll-pressed to create a negative electrode active material layer on the negative electrode substrate. In this way, a negative electrode was prepared.

[0095] (Preparation of non-aqueous electrolytes) A mixed solvent of EC and EMC in a volume ratio of 3:7 is mixed with 1 mol / dm³ of LiPF6. 3 A non-aqueous electrolyte was prepared by dissolving it at the specified concentration.

[0096] (Fabrication of non-aqueous electrolyte secondary batteries) An electrode body was fabricated by laminating the positive electrode and the negative electrode via a separator consisting of a polyethylene microporous membrane substrate and a heat-resistant layer formed on the polyethylene microporous membrane substrate. The heat-resistant layer was positioned on the surface facing the positive electrode. This electrode body was housed in a rectangular aluminum container, and positive and negative electrode terminals were attached. After injecting the non-aqueous electrolyte into the rectangular container, it was sealed to fabricate the non-aqueous electrolyte secondary battery according to Example 1.

[0097] (Measurement of "capacity from 3.5V to 3.7V") For the non-aqueous electrolyte secondary batteries prepared as described above, the battery capacity exhibited in the voltage range of 3.5V to 3.7V (referred to as "capacity from 3.5V to 3.7V") was measured using the following method. Under 25°C conditions, constant current charging was performed with a charging current of 0.1C until the battery voltage reached 3.7V. Subsequently, constant voltage charging was performed while maintaining 3.7V until the current was reduced to 0.05C. In this charging process, the charging capacity obtained within the voltage range from 3.5V to 3.7V was defined as the "capacity from 3.5V to 3.7V".

[0098] (Measurement of "low SOC output at 25°C after cycling") The output performance of the non-aqueous electrolyte secondary battery fabricated as described above at low SOC after charge-discharge cycles (indicated as "Post-cycle 25°C Low SOC Output") was measured using the following method. Under a 60°C environment, the battery was charged with a constant current of 1.0C until it reached 3.7V, and then charged with a constant voltage at 3.7V. The charging was terminated when the charging current reached 0.05C. After a 10-minute rest period following charging, the battery was discharged with a constant current of 1.0C until the battery voltage reached 2.0V, followed by another 10-minute rest period. This constituted one cycle, and 100 charge-discharge cycles were performed. Subsequently, the battery was moved to a 25°C environment, and constant current charging was performed from the discharged state with a charging current of 0.1C until the SOC reached 25%. After that, the battery was discharged for 10 seconds with a discharge current of 0.1C under a 25°C environment, followed by a 10-minute rest period, and then supplemental charging for 10 seconds with a charging current of 0.1C. Similarly, discharge and recharge were performed with currents of 0.3C and 0.5C, and the output was calculated from the battery voltage 10 seconds after the start of discharge at each discharge current, and this was defined as "Post-cycle 25°C Low SOC output".

[0099] [Examples 2, 3, and 5] In the process of preparing the hydroxide precursor, the molar ratio of Ni / Co / Mn in the aqueous solution of the mixture was changed to 35 / 7 / 58, and this hydroxide precursor was solid-phase mixed with LiOH·H2O so that the Li / Me ratio was 1.5. Except for this, the process was the same as in Example 1, and the lithium transition metal composite oxide Li of Example 2 was prepared. 1.20 (Ni 0.35 Co 0.07 Mn 0.58 ) 0.80 O2 was produced. In the process of preparing the hydroxide precursor, the molar ratio of Ni / Co / Mn in the aqueous solution of the mixture was changed to 45 / 15 / 40, and this hydroxide precursor was solid-phase mixed with LiOH·H2O so that the Li / Me ratio was approximately 1.3 in molar ratio. Except for these changes, the lithium transition metal composite oxide Li of Example 3 was prepared in the same manner as in Example 1. 1.12 (Ni 0.45 Co 0.15 Mn 0.40 ) 0.88 O2 was produced. In the process of preparing the hydroxide precursor, the molar ratio of Ni / Co / Mn in the aqueous solution of the mixture was changed to 30 / 5 / 65, and this hydroxide precursor was solid-phase mixed with LiOH·H2O so that the Li / Me ratio was approximately 1.7 in molar proportions. Otherwise, the process was the same as in Example 1, to produce the lithium transition metal composite oxide Li related to Comparative Example 5. 1.25 (Ni 0.30 Co 0.05 Mn 0.65 ) 0.75 O2 was produced. The lithium transition metal composite oxide described above was also confirmed to have an α-NaFeO2 type crystal structure, similar to that in Example 1. As a lithium transition metal composite oxide to be mixed with LiFePO4, the Li prepared as described above was used. 1.20 (Ni 0.35 Co 0.07 Mn 0.58 ) 0.80 O2, Li 1.12 (Ni 0.45 Co 0.15 Mn 0.40 ) 0.88 O2, Li 1.25 (Ni 0.30 Co 0.05 Mn 0.65 ) 0.75 Except for using O2, the positive electrodes according to Example 2, Example 3, and Comparative Example 5 were prepared in the same manner as in Example 1, and a non-aqueous electrolyte secondary battery equipped with these positive electrodes was constructed.

[0100] [Comparative Example 1 to Comparative Example 4] LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1Except for using O2 (NCM811), the positive electrodes according to Comparative Examples 1 to 4 were prepared in the same manner as in Example 1, and a non-aqueous electrolyte secondary battery equipped with these positive electrodes was constructed.

[0101] For the non-aqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 5, the "capacity from 3.5V to 3.7V" and the "low SOC output at 25°C after cycling" were determined using the method described above, and the results, along with the composition of the positive electrode active material, are shown in Table 1.

[0102] [Table 1]

[0103] Table 1 shows lithium transition metal compounds (LiFePO4) having a polyanionic structure, and Li 1+α Me 1-α Examples 1 to 3 of the non-aqueous electrolyte secondary batteries, which use a cathode active material containing a lithium transition metal composite oxide represented as O2 (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co, 0.4≦Mn / Me≦0.6), show that they exhibit a "capacity from 3.5V to 3.7V" and a large "low SOC output at 25°C after cycling". In contrast, the non-aqueous electrolyte secondary batteries of Comparative Examples 1 to 4, which used positive electrode active materials containing LiFePO4 and NCM, had a large "capacity from 3.5V to 3.7V," but a small "low SOC output at 25°C after cycling." On the other hand, LiFePO4 has the general formula Li 1+α Me 1-α The non-aqueous electrolyte secondary battery in Comparative Example 5, which used a lithium transition metal composite oxide as the positive electrode active material, is represented as O2 (0<α, where Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co), but in which the molar ratio of Mn to the transition metal (Me) exceeds 0.6, showed a smaller "capacity from 3.5V to 3.7V", a smaller effect in suppressing the rapid voltage rise caused by using LiFePO4 as the positive electrode active material, and a sufficiently large "low SOC output at 25°C after cycling". Therefore, in this embodiment, lithium transition metal compounds having a polyanionic structure and represented by the general formula LiMPO4 (where M is one or more elements selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3, and lithium transition metal compounds having an α-NaFeO2 type crystal structure and represented by the general formula Li 1+α Me 1-α By using a positive electrode active material containing a lithium transition metal composite oxide represented as O2 (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn and Co, 0.4≦Mn / Me≦0.6) as the positive electrode, it can be said that a non-aqueous electrolyte energy storage element with high output performance at low SOC after charge-discharge cycles can be obtained. [Industrial applicability]

[0104] By using a positive electrode active material according to one aspect of the present invention, it is possible to provide a non-aqueous electrolyte energy storage element that has high output performance at low SOC after charge-discharge cycles. Therefore, this non-aqueous electrolyte energy storage element is useful as a non-aqueous electrolyte energy storage element for hybrid vehicles, plug-in hybrid vehicles, and electric vehicles. [Explanation of Symbols]

[0105] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage units 30 Energy storage devices

Claims

1. A lithium transition metal compound having a polyanion structure and represented by the general formula LiMPO ４ (M is one or more elements selected from Fe, Mn, Ni and Co) or Li ３ V ２ (PO ４ ) ３ , and a lithium transition metal composite oxide having an α-NaFeO ２ -type crystal structure and represented by the general formula Li １＋α Me １－α O ２ (0 < α, Me is a transition metal element containing Ni and Mn, or Ni, Mn and Co), wherein the lithium transition metal composite oxide has a molar ratio of Mn to Me of 0.4 ≦ Mn / Me ≦ 0.6 and a molar ratio of Li to Me of (1 + α) / (1 - α) of 1.1 ≦ (1 + α) / (1 - α) ≦ 1.3, and is a positive electrode active material for a non-aqueous electrolyte storage element.

2. The positive electrode, in which the lithium transition metal compound is the positive electrode active material, has a positive electrode potential of 3.7 V (vs. Li / Li ＋ When charging is performed to the point of 3.2V (vs. Li / Li ＋ ) or more 3.4V (vs.Li / Li ＋ The positive electrode active material for a non-aqueous electrolyte energy storage element according to claim 1, wherein a region is observed within the positive electrode potential range of less than ) in which the potential change with respect to the amount of charge is relatively flat.

3. The positive electrode active material for a non-aqueous electrolyte energy storage element according to claim 1 or 2, wherein the proportion of the lithium transition metal composite oxide in the positive electrode active material is 20% by mass or less.

4. A positive electrode for a non-aqueous electrolyte energy storage element containing the positive electrode active material described in any one of claims 1 to 3.

5. A non-aqueous electrolyte energy storage element comprising the positive electrode described in claim 4.

6. The positive electrode has a positive electrode potential of 3.7V (vs. Li / Li ＋ When charging is performed to the point of 3.2V (vs. Li / Li ＋ ) or more 3.7V (vs.Li / Li ＋ The non-aqueous electrolyte energy storage element according to claim 5, wherein a region is observed within the following positive electrode potential range in which the potential change is relatively flat with respect to the amount of charge.

7. The maximum potential that can be reached at the positive electrode in a fully charged state (SOC 100%) is 3.7V (vs. Li / Li ＋ A non-aqueous electrolyte energy storage element according to claim 6, used for voltages below the specified voltage.

8. A power storage unit comprising a plurality of non-aqueous electrolyte energy storage elements according to any one of claims 5 to 7 connected in series.

9. An energy storage device comprising a plurality of energy storage units as described in claim 8, connected together.

Images