JP2018037380A - Positive electrode and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode arranged by use of both of a lithium metal composite oxide high in Ni composition ratio, and a compound of an olivine structure, which enables the achievement of both of superior battery characteristics and excellent thermal stability.SOLUTION: A positive electrode comprises a positive electrode active material layer including a lithium nickel composite oxide of a lamellar rock-salt structure, which is represented by LiNiCoMnDO(0.5≤b) and a lithium metal phosphate compound in which LiMPOof an olivine structure is coated with carbon. The lithium nickel composite oxide is smaller than the lithium metal phosphate compound in average particle diameter. Further, the lithium nickel composite oxide is larger than the lithium metal phosphate compound in volume resistance.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode and a lithium ion secondary battery including the positive electrode.

  It is known that various materials can be used as the positive electrode active material of the secondary battery, and lithium ion secondary batteries employing a plurality of materials as the positive electrode active material are also known.

For example, a lithium metal composite oxide having a layered rock salt structure such as LiCoO ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is a high-capacity positive electrode active material. It is known that there is. The compounds of olivine structure represented by LiFePO ₄ is known to be a positive electrode active material excellent in thermal stability. These positive electrode active materials may be used in combination in order to achieve both high capacity and thermal stability.

Specifically, Patent Document 1 discloses a lithium ion secondary battery using LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and carbon-coated LiFePO ₄ as a positive electrode active material. ing.

Special table 2010-517238

  As for the lithium ion secondary battery, a battery having both favorable battery characteristics and thermal stability is desired. A lithium ion secondary battery including a positive electrode in which a lithium metal composite oxide and a compound having an olivine structure are used has both a certain degree of battery characteristics and a certain degree of thermal stability.

  Here, this inventor aimed at providing a high capacity | capacitance lithium ion secondary battery. Of the transition metals that can be included in the layered rock salt structure lithium metal composite oxide, it is known that Ni has a high activity during the charge / discharge reaction. Therefore, a lithium metal composite oxide having a high Ni composition ratio is recognized as a high capacity positive electrode active material. However, simply using a lithium metal composite oxide having a high Ni composition ratio and a compound having an olivine structure does not always provide a lithium ion secondary battery having both excellent battery characteristics and excellent thermal stability. The present inventor has found out.

  The present invention has been made in view of such circumstances, and is a positive electrode using a combination of a lithium metal composite oxide having a high Ni composition ratio and a compound having an olivine structure, which has excellent battery characteristics and excellent thermal stability. It is an object to provide compatible items.

  As a result of intensive studies, a lithium ion secondary battery having a positive electrode in which both the average particle size and the volume resistance of the lithium metal composite oxide and the olivine structure compound are combined with the lithium metal composite oxide and the olivine structure compound The inventor has discovered that it affects properties and thermal stability. Based on this discovery, the present inventor has completed the present invention.

The positive electrode of the present _{invention, Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2,0.5 ≦ b, 0 ≦ c <0.5,0 ≦ d <0 of layered rock-salt structure .5, b + c + d + e = 1, 0 ≦ e <0.5, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La At least one element selected from Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, 1.7 ≦ f ≦ 3) and LiM _h PO ₄ having an olivine structure (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba) Lithium coated with carbon at least one element selected from Ti, Al, Si, B, Te and Mo, 0 <h <2) A positive electrode having a positive electrode active material layer containing a metal-free phosphate compound,
The average particle size of the lithium nickel composite oxide is smaller than the average particle size of the lithium metal phosphate compound,
And,
The volume resistance of the lithium nickel composite oxide is larger than the volume resistance of the lithium metal phosphate compound.

  The lithium ion secondary battery of the present invention provided with the positive electrode of the present invention achieves both excellent battery characteristics and excellent thermal stability.

  Below, the form for implementing this invention is demonstrated. Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y in the range. And a new numerical value range can be comprised by combining these arbitrarily including those upper limit values and lower limit values and numerical values listed in the embodiments. Furthermore, numerical values arbitrarily selected from any one of the numerical ranges described above can be used as the upper and lower numerical values of the new numerical range.

The positive electrode of the present _{invention, Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2,0.5 ≦ b, 0 ≦ c <0.5,0 ≦ d <0 of layered rock-salt structure .5, b + c + d + e = 1, 0 ≦ e <0.5, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La At least one element selected from Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, 1.7 ≦ f ≦ 3) and LiM _h PO ₄ having an olivine structure (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba) Lithium coated with carbon at least one element selected from Ti, Al, Si, B, Te and Mo, 0 <h <2) A positive electrode having a positive electrode active material layer containing a metal-free phosphate compound,
The lithium nickel composite oxide has an average particle size (hereinafter may be abbreviated as D _Ni ) smaller than the average particle size of the lithium metal phosphate compound (hereinafter may be abbreviated as D _P ).
And,
The volume resistivity of the lithium nickel composite oxide (hereinafter, may be abbreviated as R _Ni.) Is the volume resistivity of the lithium metal phosphate compound (hereinafter sometimes referred to as R _P.) Being greater than And

  The lithium nickel composite oxide in the positive electrode of the present invention has a high capacity because the nickel composition ratio b is 0.5 ≦ b.

  In the above general formula of the lithium nickel composite oxide, the values of b, c and d are not particularly limited as long as the above conditions are satisfied. 5 ≦ b ≦ 0.7, 0.5 ≦ b ≦ 0.6, 0.1 ≦ c ≦ 0.35, 0.2 ≦ c ≦ 0.35, 0.2 ≦ c ≦ 0.25 with respect to c 0.25 ≦ c ≦ 0.35, d ≦ 0.1 ≦ 0.35, 0.2 ≦ d ≦ 0.35, 0.2 ≦ d ≦ 0.25, 0.25 ≦ d ≦ Each of 0.35 can be exemplified as a suitable range.

  a, e, f may be any numerical value within the range defined by the general formula, and a is preferably within a range of 0.5 ≦ a ≦ 1.5, and a range of 0.7 ≦ a ≦ 1.3. The inside is more preferable, and the range of 0.9 ≦ a ≦ 1.2 is more preferable. For e and f, 0 ≦ e ≦ 0.2, 0 ≦ e ≦ 0.1, e = 0, 1.8 ≦ f ≦ 2.5, 1.9 ≦ f ≦ 2.2, and f = 2. It can be illustrated.

Specific examples of the layered rock salt structure lithium nickel composite oxide include LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.75 Co _0.1 Mn _0.15 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ LiNi _0.82 Co _0.15 Al _0.03 O ₂ and LiNiO ₂ .

Lithium metal phosphate compounds are olivine-structured LiM _h PO ₄ (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te and Mo. At least one element selected from the group 0 <h <2) is coated with carbon. As the lithium metal phosphate compound, a part of LiM _h PO ₄ may be coated with carbon, or the whole surface of LiM _h PO ₄ may be coated with carbon.

M in the LiM _h PO ₄ is preferably at least one element selected from Mn, Fe, Co, Ni, Mg, V, and Te, and h is 0.6 <h <1.1. Is preferred. The M is more preferably Mn and / or Fe, and more preferably h = 1. As LiM _h PO ₄ , those represented by LiMn _x Fe _y PO ₄ (x + y = 1, 0 <x <1, 0 <y <1) in which Mn and Fe coexist are more preferable. Examples of the range of x and y include 0.1 ≦ x ≦ 0.9, 0.1 ≦ y ≦ 0.9, 0.2 ≦ x ≦ 0.8, and 0.2 ≦ y ≦ 0.8.

Examples of LiM _h PO _4, for _{example, LiFePO 4, LiCoPO 4, LiNiPO} 4, LiMnPO 4, LiVPO 4, LiTePO 4, LiV 2/3 PO 4, LiFe 2/3 PO 4, LiMn 7/8 Fe 1 _{/ 8} PO ₄ , LiMn _0.67 Fe _0.33 PO ₄ .

In the positive electrode of the present invention, the average particle diameter of the lithium nickel composite oxide is smaller than the average particle diameter of the lithium metal phosphate compound, and the volume resistance of the lithium nickel composite oxide is greater than the volume resistance of the lithium metal phosphate compound. Is also big. In other words, the positive electrode of the present invention satisfies _D Ni _{<D P} and _R Ni> _{R P.}

  The average particle diameter of the lithium nickel composite oxide is preferably 100 μm or less, more preferably in the range of 0.1 to 50 μm, further preferably in the range of 1 to 20 μm, and particularly preferably in the range of 3 to 12 μm. If the thickness is less than 0.1 μm, there may be a problem that, when the electrode is manufactured, the adhesion to the current collector is easily impaired. If it exceeds 100 μm, problems such as affecting the size of the electrode and damaging the separator constituting the secondary battery may occur. In addition, the average particle diameter in this specification means the value of D50 when measured with a general laser diffraction type particle size distribution measuring apparatus.

  The average particle size of the lithium metal phosphate compound is preferably 100 μm or less, more preferably in the range of 1 to 50 μm, still more preferably in the range of 5 to 30 μm, and particularly preferably in the range of 12 to 21 μm.

  The volume resistance of the lithium nickel composite oxide is preferably 1500 Ω · cm or less, more preferably in the range of 10 to 1000 Ω · cm, and still more preferably in the range of 100 to 500 Ω · cm. The volume resistance of the lithium metal phosphate compound is preferably 500 Ω · cm or less, more preferably in the range of 1 to 100 Ω · cm, and still more preferably in the range of 5 to 50 Ω · cm. In addition, the value of the volume resistance in this invention means the measured value at the time of putting the sample 2g into the cylindrical tube of diameter 2cm and compressing with the load of 20 kN using the resistance measuring apparatus.

  In addition, it is publicly known that there are various volume resistances as the lithium nickel composite oxide, and the composition ratio of the transition metal in the lithium nickel composite oxide is changed and the sintering temperature at the time of manufacture is changed. It is also known that the volume resistance changes. For example, Table 2 of JP 2013-157109 A and Table 1 of JP 2013-025887 A specifically disclose lithium nickel composite oxides having various volume resistances.

  It is also known that lithium metal phosphate compounds have various volume resistances. For example, paragraphs 0043 and 0057 (Table 1) of JP 2014-179176 A, paragraph 0187 of JP 2014-029863 A, paragraph 0057 of JP 2012-204079 A, and the like have various volume resistances. Lithium metal phosphate compounds are specifically disclosed.

  In the positive electrode of the present invention, the mass ratio of the lithium nickel composite oxide and the lithium metal phosphate compound is preferably in the range of 65:35 to 85:15, and more preferably in the range of 65:35 to 80:20. 67:33 to 75:25 is more preferable.

  Specifically, the positive electrode of the present invention includes a current collector and a positive electrode active material layer formed on the surface of the current collector.

  The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel Examples of such a metal material can be given.

  When the potential of the positive electrode is 4 V or more on the basis of lithium, it is preferable to employ aluminum as the positive electrode current collector.

  Specifically, it is preferable to use a positive electrode current collector made of aluminum or an aluminum alloy. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or more is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is referred to as an aluminum alloy. Examples of the aluminum alloy include Al—Cu, Al—Mn, Al—Fe, Al—Si, Al—Mg, Al—Mg—Si, and Al—Zn—Mg.

  Specific examples of aluminum or aluminum alloy include A1000 series alloys (pure aluminum series) such as JIS A1085 and A1N30, A3000 series alloys (Al-Mn series) such as JIS A3003 and A3004, JIS A8079, A8021, etc. A8000-based alloy (Al-Fe-based).

  The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  The positive electrode active material layer includes a lithium nickel composite oxide and a lithium metal phosphate compound as a positive electrode active material, and may further include additives such as a conductive additive, a binder, and a dispersant.

  When the total amount of the positive electrode active material layer is 100% by mass, the amount of the positive electrode active material composed of the lithium nickel composite oxide and the lithium metal phosphate compound is preferably in a range of 50 to 99% by mass, The inside of the range of 60-98 mass% is more preferable, and the inside of the range of 70-97 mass% is especially preferable.

  The porosity of the positive electrode active material layer is preferably within a range of 20 to 30%, and more preferably within a range of 25 to 29%. When the porosity of the positive electrode active material layer is within a preferable range, the thermal stability of the lithium ion secondary battery of the present invention may be further improved.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent.

  The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, vapor grown carbon fiber (VGCF), and various metal particles, which are carbonaceous fine particles. Is done. Examples of the carbon black include acetylene black, ketjen black (registered trademark), furnace black, and channel black. These conductive assistants can be added to the positive electrode active material layer alone or in combination of two or more.

  The shape of the conductive auxiliary agent is not particularly limited, but it is preferable that the average particle diameter of the conductive auxiliary agent is small in view of its role. A preferable average particle size of the conductive auxiliary is 10 μm or less, and a more preferable average particle size is in the range of 0.01 to 1 μm.

  Although the compounding quantity of a conductive support agent is not specifically limited, If it dares to mention the compounding quantity of the conductive support agent in a positive electrode active material layer, the inside of the range of 0.5-10 mass% is good, and the inside of the range of 1-7 mass% is good. The range of 2 to 5% by mass is particularly preferable.

  The binder plays a role of connecting the positive electrode active material and the conductive additive to the surface of the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to. Moreover, you may employ | adopt the polymer which has a hydrophilic group as a binder. Examples of the hydrophilic group of the polymer having a hydrophilic group include a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group, and a phosphate group. Specific examples of the polymer having a hydrophilic group include polyacrylic acid, carboxymethylcellulose, polymethacrylic acid, and poly (p-styrenesulfonic acid).

  Although the compounding quantity of a binder is not specifically limited, If the compounding quantity of the binder in a positive electrode active material layer is dared, the inside of the range of 0.5-10 mass% is preferable, and the inside of the range of 1-7 mass% is preferable. More preferably, the range of 2 to 5% by mass is particularly preferable. If the blending amount of the binder is too small, the moldability of the positive electrode active material layer may be lowered. Moreover, when there are too many compounding quantities of a binder, since the quantity of the positive electrode active material in a positive electrode active material layer reduces relatively, it is unpreferable.

  Known additives can be employed as additives such as a dispersing agent other than the conductive assistant and the binder.

  In order to form the positive electrode active material layer on the surface of the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used. A positive electrode active material may be applied to the surface of the electric body. Specifically, an active material, a solvent, and if necessary, a binder and a conductive additive are mixed to form a slurry, and the slurry is applied to the surface of the current collector and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.

  From the gist of the present invention, as one step of the method for producing the positive electrode of the present invention, a step of confirming the average particle size of the lithium nickel composite oxide and the average particle size of the lithium metal phosphate compound, and the lithium nickel composite oxide It is preferable to include a step of confirming the volume resistance and the volume resistance of the lithium metal phosphate compound.

  The lithium ion secondary battery of the present invention includes the positive electrode of the present invention. The lithium ion secondary battery of this invention contains the positive electrode of this invention, a negative electrode, electrolyte solution, and a separator as needed as a specific battery component.

  The negative electrode has a current collector and a negative electrode active material layer formed on the surface of the current collector. The negative electrode active material layer contains a negative electrode active material, and may further contain additives such as a conductive additive, a binder, and a dispersant. What is necessary is just to employ | adopt what was demonstrated with the positive electrode as a collector and a conductive support agent. A well-known thing can be employ | adopted for a dispersing agent.

  Examples of the negative electrode active material include a carbon-based material capable of inserting and extracting lithium, an element that can be alloyed with lithium, a compound having an element that can be alloyed with lithium, a polymer material, and the like.

  Examples of the carbon-based material include non-graphitizable carbon, natural graphite, artificial graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature. Specific examples of the polymer material include polyacetylene and polypyrrole.

  Specifically, elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. , Ge, Sn, Pb, Sb, Bi can be exemplified, and Si or Sn is particularly preferable.

Specific examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , _{CaSi 2, CrSi 2, Cu 5} Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO or LiSnO. Moreover, tin compounds, such as a tin alloy (Cu-Sn alloy, Co-Sn alloy, etc.), can be illustrated as a compound which has an element which can be alloyed with lithium.

The above silicon oxide composed of SiO _v (0 <v ≦ 2) is obtained by heat-treating SiO, which is an amorphous silicon oxide obtained using silicon dioxide (SiO ₂ ) and simple silicon (Si) as raw materials. Can be obtained by disproportionation. The disproportionation reaction is a reaction in which SiO is decomposed into a Si phase and a SiO ₂ phase. In general, when oxygen is turned off, it is said that almost all SiO is disproportionated and separated into two phases at 800 ° C. or higher. Specifically, amorphous SiO ₂ is subjected to heat treatment at 800 to 1200 ° C. for 1 to 5 hours in an inert atmosphere such as in a vacuum or an inert gas. A silicon oxide containing two phases of a phase and a crystalline Si phase is obtained.

  The average particle diameter of the silicon oxide is preferably 4 μm or more. The average particle diameter is a median diameter and can be obtained based on a volume-based particle size distribution by a laser diffraction method. The average particle diameter of the silicon oxide is preferably 20 μm or less, and preferably 15 μm or less. If the average particle size is too small, there are many active points, so that generation of SEI (Solid Electrolyte Interphase) is large and cycle characteristics may be deteriorated. On the other hand, if the average particle diameter is too large, the conductivity of the silicon oxide is poor, so that the conductivity of the entire electrode becomes non-uniform, and the resistance may increase or the output may decrease.

Moreover, you may employ | adopt the silicon material as described in international publication 2014/080608 as a negative electrode active material. The silicon material has a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction. For example, the silicon material is subjected to a process of synthesizing a layered silicon compound containing polysilane as a main component by reacting CaSi ₂ with an acid, and further a process of heating the layered silicon compound at 300 ° C. or higher to desorb hydrogen. It is manufactured.

The production method of the silicon material is represented by the following ideal reaction formula when hydrogen chloride is used as the acid.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl ₂
Si ₆ H ₆ → 6Si + 3H ₂ ↑

However, in the upper reaction for synthesizing Si ₆ H ₆ which is polysilane, water is usually used as a reaction solvent from the viewpoint of removing by-products and impurities. Since Si ₆ H ₆ can react with water, in the step of synthesizing the layered silicon compound including the upper reaction, the layered silicon compound is hardly manufactured as containing only Si ₆ H ₆ , and the layered The silicon compound is represented by Si ₆ H _s (OH) _t X _u (X is an element or group derived from an acid anion, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6). Manufactured as a product. In the above chemical formula, inevitable impurities such as Ca that can remain are not taken into consideration. A silicon material obtained by heating the layered silicon compound also contains an element derived from an anion of oxygen or acid.

As described above, the silicon material has a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction. In order to efficiently store and release charge carriers such as lithium ions, the plate-like silicon body preferably has a thickness in the range of 10 nm to 100 nm, more preferably in the range of 20 nm to 50 nm. The length in the longitudinal direction of the plate-like silicon body is preferably within a range of 0.1 μm to 50 μm. The plate-like silicon body preferably has (length in the longitudinal direction) / (thickness) in the range of 2 to 1000. The laminated structure of the plate-like silicon body can be confirmed by observation with a scanning electron microscope or the like. This laminated structure is considered to be a remnant of the Si layer in the raw material CaSi ₂ .

  The silicon material preferably includes amorphous silicon and / or silicon crystallites. In particular, the above plate-like silicon body is preferably in a state where amorphous silicon is used as a matrix and silicon crystallites are scattered in the matrix. The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, still more preferably in the range of 1 nm to 50 nm, and particularly preferably in the range of 1 nm to 10 nm. The size of the silicon crystallite is calculated from the Scherrer equation using X-ray diffraction measurement on the silicon material and using the half-value width of the diffraction peak of the Si (111) plane of the obtained X-ray diffraction chart. .

  The abundance and size of the plate-like silicon body, amorphous silicon and silicon crystallite contained in the silicon material mainly depend on the heating temperature and the heating time. The heating temperature is preferably in the range of 350 ° C to 950 ° C, more preferably in the range of 400 ° C to 900 ° C.

  As the negative electrode active material, a Si-containing negative electrode active material containing silicon, such as silicon oxide or silicon material, is particularly preferable because of its high theoretical energy density. The Si-containing negative electrode active material may be coated with carbon. The Si-containing negative electrode active material coated with carbon is excellent in conductivity.

  The binder for the negative electrode includes polyvinylidene fluoride, polytetrafluoroethylene, fluorine-containing resins such as fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. What is necessary is just to employ | adopt well-known things, such as a styrene butadiene rubber.

  Moreover, you may employ | adopt the polymer which has a hydrophilic group as a binder. The lithium ion secondary battery of the present invention comprising a polymer having a hydrophilic group as a binder can maintain the capacity more suitably. Examples of the hydrophilic group of the polymer having a hydrophilic group include a phosphate group such as a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group, and a phosphate group. Among them, a polymer containing a carboxyl group in a molecule such as polyacrylic acid, carboxymethylcellulose, or polymethacrylic acid, or a polymer containing a sulfo group such as poly (p-styrenesulfonic acid) is preferable.

  A polymer containing many carboxyl groups and / or sulfo groups such as polyacrylic acid or a copolymer of acrylic acid and vinyl sulfonic acid becomes water-soluble. The polymer having a hydrophilic group is preferably a water-soluble polymer, and in terms of chemical structure, a polymer containing a plurality of carboxyl groups and / or sulfo groups in one molecule is preferable.

  The polymer containing a carboxyl group in the molecule can be produced by, for example, a method of polymerizing an acid monomer or a method of imparting a carboxyl group to the polymer. Acid monomers include acrylic acid, methacrylic acid, vinyl benzoic acid, crotonic acid, pentenoic acid, angelic acid, tiglic acid, etc., acid monomers having one carboxyl group in the molecule, itaconic acid, mesaconic acid, citraconic acid, fumaric acid , Maleic acid, 2-pentenedioic acid, methylene succinic acid, allyl malonic acid, isopropylidene succinic acid, 2,4-hexadiene diacid, acetylenedicarboxylic acid, etc., acid monomers having two or more carboxyl groups in the molecule Is done.

  A copolymer obtained by polymerizing two or more acid monomers selected from the above acid monomers may be used as a binder.

  Further, for example, a polymer containing an acid anhydride group formed by condensation of carboxyl groups of a copolymer of acrylic acid and itaconic acid, as described in JP 2013-065493 A, in the molecule It is also preferable to use as a binder. When the binder has a structure derived from a highly acidic monomer having two or more carboxyl groups in one molecule, it becomes easier for the binder to trap lithium ions etc. before the electrolyte decomposition reaction occurs during charging. It is considered. Furthermore, since the polymer has more carboxyl groups per monomer than polyacrylic acid or polymethacrylic acid, the acidity is increased, but since the predetermined amount of carboxyl groups is changed to acid anhydride groups, the acidity is increased. Is not too high. Therefore, a secondary battery including a negative electrode using the polymer as a binder has improved initial efficiency and improved input / output characteristics.

  A cross-linked polymer obtained by cross-linking a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid with a polyamine such as diamine disclosed in International Publication No. 2016/063882 may be used as a binder.

  Examples of the diamine used in the crosslinked polymer include alkylene diamines such as ethylene diamine, propylene diamine, and hexamethylene diamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, isophorone diamine, and bis (4-aminocyclohexyl) methane. Saturated carbocyclic diamine, m-phenylenediamine, p-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, bis (4-aminophenyl) sulfone, benzidine, o-tolidine, 2,4- Aromatic diamines such as tolylenediamine, 2,6-tolylenediamine, xylylenediamine, and naphthalenediamine are exemplified.

  Further, a mixture or a reaction product of a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid and polyamideimide may be used as a binder.

  Polyamideimide means a compound having two or more amide bonds and imide bonds in the molecule. Polyamideimide is produced by reacting an acid component that becomes a carbonyl moiety in an amide bond and an imide bond with a diamine component or diisocyanate component that becomes a nitrogen moiety in the amide bond and imide bond. In order to obtain a polyamideimide, it may be produced by the method, or a commercially available polyamideimide may be purchased.

  Acid components used for the production of polyamideimide include trimellitic acid, pyromellitic acid, biphenyltetracarboxylic acid, diphenylsulfonetetracarboxylic acid, benzophenonetetracarboxylic acid, diphenylethertetracarboxylic acid, oxalic acid, adipic acid, malonic acid, Sebacic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene), dicarboxypoly (styrene-butadiene), cyclohexane-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, Dicyclohexylmethane-4,4′-dicarboxylic acid, terephthalic acid, isophthalic acid, bis (carboxyphenyl) sulfone, bis (carboxyphenyl) ether, naphthalenedicarboxylic acid, and These anhydrides, acid halides, mention may be made of derivatives. As the acid component, the above compounds may be employed singly or in combination, but from the point of forming an imide bond, an acid component in which a carboxyl group is present on the carbon adjacent to the carbon to which the carboxyl group is bonded or Its equivalent is essential. As the acid component, trimellitic anhydride is preferable from the viewpoints of reactivity and heat resistance. In addition to trimellitic acid anhydride, pyromellitic acid anhydride, benzophenonetetracarboxylic acid anhydride, biphenyltetra, as part of the acid component in addition to trimellitic acid anhydride, from the viewpoint of tensile strength, tensile modulus, and electrolyte resistance of polyamideimide It is preferable to employ a carboxylic acid anhydride.

  What is necessary is just to employ | adopt the diamine used for the crosslinked polymer mentioned above as a diamine component used for manufacture of a polyamideimide. From the viewpoint of heat resistance and solubility, 4,4'-diaminodiphenylmethane, 2,4-tolylenediamine, o-tolidine, naphthalenediamine, and isophoronediamine are preferable. From the viewpoint of tensile strength and tensile modulus of polyamideimide, o-tolidine and naphthalenediamine are preferable.

  Examples of the diisocyanate component used for producing the polyamideimide include those obtained by replacing the amine of the diamine component with an isocyanate.

  The blending ratio of the binder in the negative electrode active material layer is preferably a mass ratio of negative electrode active material: binder = 1: 0.005 to 1: 0.3. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes. A known separator may be employed, such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, polyacrylonitrile or other synthetic resin, cellulose, amylose or other polysaccharide, fibroin. And porous materials, nonwoven fabrics, woven fabrics, and the like using one or more electrical insulating materials such as natural polymers such as keratin, lignin, and suberin, and ceramics. The separator may have a multilayer structure.

  The electrolytic solution includes a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.

  As the non-aqueous solvent, cyclic esters, chain esters, ethers and the like can be used. Examples of the cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. These nonaqueous solvents may be used alone or in combination with the electrolyte.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As the electrolytic solution, lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ and the like in a non-aqueous solvent such as ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and the like is from 0.5 mol / l to 1. A solution dissolved at a concentration of about 7 mol / l can be exemplified.

  A specific method for manufacturing the lithium ion secondary battery will be described. For example, a separator is sandwiched between a positive electrode and a negative electrode to form an electrode body. The electrode body may be any of a stacked type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a positive electrode, a separator and a negative electrode are stacked. After connecting the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like, an electrolyte is added to the electrode body to form a lithium ion secondary battery. Good.

  The lithium ion secondary battery can be mounted on a vehicle. Since a lithium ion secondary battery maintains a large charge / discharge capacity and has excellent cycle performance, a vehicle equipped with the lithium ion secondary battery is a high-performance vehicle.

  The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.

  Although the positive electrode and the lithium ion secondary battery of the present invention have been described above, the present invention is not limited to the above embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited by these Examples.

The lithium nickel composite oxide shown in Table 1 below and the lithium metal phosphate compound coated with carbon shown in Table 2 were prepared. In addition, the value of the volume resistance of Table 1 and Table 2 put the sample 2g in the cylindrical tube of diameter 2cm, and compressed it with the load of 20kN using the resistance measuring apparatus (brand name MCP-PD51) made from Mitsubishi Chemical Analytech. Measured value.

Example 1
As the positive electrode active material, No. 1 in Table 1 was obtained. No. 1 in Table 2 as 67 parts by mass of the lithium nickel composite oxide of No. 1 and the positive electrode active material. 27 parts by mass of 1 lithium metal phosphate compound, 3 parts by mass of acetylene black as a conductive assistant, 3 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone were mixed. A slurry was produced. An aluminum foil was prepared as a positive electrode current collector. The slurry was applied in a film form on the surface of the aluminum foil using a doctor blade. The aluminum foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone. Thereafter, the aluminum foil was pressed to obtain a bonded product. The obtained joined product was heated and dried with a drier to produce a positive electrode of Example 1 made of an aluminum foil on which a positive electrode active material layer was formed. The calculated porosity calculated from the volume of the positive electrode active material layer, the true density of each material, and the blending ratio of each material was 27%.

  32 parts by mass of SiO as a negative electrode active material, 50 parts by mass of graphite as a negative electrode active material, 8 parts by mass of acetylene black as a conductive additive, 10 parts by mass of polyamideimide as a binder, and an appropriate amount of N-methyl- 2-Pyrrolidone was mixed to produce a slurry. A copper foil was prepared as a negative electrode current collector. The slurry was applied in a film form on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone to produce a negative electrode on which a negative electrode active material layer was formed.

LiPF ₆ was added and dissolved in an organic solvent in which ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate were mixed at a volume ratio of 3: 3: 4 to produce an electrolytic solution containing LiPF ₆ at a concentration of 1 mol / L. .

  A polyolefin porous film was prepared as a separator. A separator was sandwiched between the positive electrode and the negative electrode of Example 1 to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then the electrolyte solution was poured into the bag-like laminated film. Thereafter, the remaining one side was sealed, whereby the four sides were hermetically sealed, and the lithium ion secondary battery of Example 1 in which the electrode plate group and the electrolyte solution were sealed was manufactured.

(Example 2)
As the positive electrode active material, No. 1 in Table 1 was obtained. No. 2 in Table 2 as 67 parts by mass of the lithium nickel composite oxide of No. 2 and the positive electrode active material. A positive electrode and a lithium ion secondary battery of Example 2 were produced in the same manner as in Example 1, except that 27 parts by mass of 1 lithium metal phosphate compound was used.

(Example 3)
As the positive electrode active material, No. 1 in Table 1 was obtained. No. 3 in Table 2 as 67 parts by mass of a lithium nickel composite oxide of No. 3 as a positive electrode active material. A positive electrode and a lithium ion secondary battery of Example 3 were produced in the same manner as in Example 1, except that 27 parts by mass of lithium metal phosphate compound 2 was used.

(Comparative Example 1)
As the positive electrode active material, No. 1 in Table 1 was obtained. No. 1 in Table 2 as 67 parts by mass of the lithium nickel composite oxide of No. 1 and the positive electrode active material. A positive electrode and a lithium ion secondary battery of Comparative Example 1 were produced in the same manner as in Example 1 except that 27 parts by mass of 3 lithium metal phosphate compounds were used.

(Comparative Example 2)
As the positive electrode active material, No. 1 in Table 1 was obtained. No. 3 in Table 2 as 67 parts by mass of a lithium nickel composite oxide of No. 3 as a positive electrode active material. A positive electrode and a lithium ion secondary battery of Comparative Example 2 were produced in the same manner as in Example 1 except that 27 parts by mass of the lithium metal phosphate compound of No. 4 was used.

(Comparative Example 3)
As the positive electrode active material, No. 1 in Table 1 was obtained. No. 3 in Table 2 as 67 parts by mass of a lithium nickel composite oxide of No. 3 as a positive electrode active material. A positive electrode and a lithium ion secondary battery of Comparative Example 3 were produced in the same manner as in Example 1, except that 27 parts by mass of lithium metal phosphate compound of 5 was used.

(Evaluation example 1)
For the lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3, a nail penetration test as a forced short circuit test was performed by the following method.

  The lithium ion secondary battery was charged at a constant voltage until stabilized at a potential of 4.5V. The lithium ion secondary battery after charging was placed on a restraint plate having a hole with a diameter of 20 mm. A restraint plate was placed on a press machine with a nail attached to the top. Until the nail penetrates the battery on the restraining plate and the tip of the nail is located inside the hole of the restraining plate, the nail is moved from the upper part to the lower part at 20 mm / sec. Moved at a speed of. The surface temperature of the battery after penetrating the nail was measured over time. The nail used had a diameter of 8 mm and a tip angle of 60 °, and the nail material was S45C defined by JIS G 4051.

  Table 3 shows the maximum temperature among the measured surface temperatures. In Table 3, the first row in the column of lithium nickel composite oxide describes the composition formula of the transition metal in the lithium nickel composite oxide, and the first row in the column of lithium metal phosphate compound contains lithium. The composition formula of the transition metal in the metal phosphate compound is described.

From Table _3, Comparative Example D Ni _{<D P} and _R Ni> The lithium ion secondary battery of Examples 1 to 3 satisfying the _{R P is,} satisfies D Ni> _{D P} and _R Ni> _{R P} 1 compared with the lithium ion secondary battery and D _{Ni <D P} and R _{Ni <lithium} ion secondary battery of Comparative example 2 which satisfies the R _P, it can be seen that markedly superior thermal stability. Moreover, from the comparison of Example 1 to Example 3, the positive electrode using the lithium metal phosphate compound in which Mn and Fe coexist as the transition metal is the positive electrode using the lithium metal phosphate compound in which only Fe is present as the transition metal. It can be said that it is excellent in thermal stability.

(Evaluation example 2)
The lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 adjusted to a voltage of 3.6 V were discharged at a constant current of 25 ° C. and 1 C rate for 10 seconds. From the voltage change amount and current value before and after the discharge, the direct current resistance at the time of discharge was calculated according to Ohm's law. The results are shown in Table 4.

From Table _{4, D} Ni <D _P and _R Ni> The lithium ion secondary battery of Examples 1 to 3 satisfying the _{R P is} a comparative example 1 which satisfies D Ni> _{D P} and _R Ni> _{R P} compared with the lithium ion secondary battery and D _Ni> D _P and R _Ni> lithium ion secondary battery of Comparative example 3 which satisfies R _P, the resistance is seen to be lower at the time of discharge.

From the results of Table 3 and Table 4, the positive electrode and a lithium ion secondary battery of the present invention which satisfies the D _{Ni <D P} and R _Ni> R _P can be said to achieve both suitable cell characteristics and thermal stability. On the other _hand, D Ni> _{D P} and _R Ni> _{R P, or,} D Ni _{<D P} and _R Ni <positive electrode and a lithium ion secondary battery satisfies any of the conditions of _{R P,} the battery characteristics or thermal stability It can be said that either of the battery characteristics and the thermal stability are difficult.

Claims (6)

_{Li a Ni b Co c Mn d} D e O f (0.2 ≦ a ≦ 2,0.5 ≦ b, 0 ≦ c <0.5,0 ≦ d <0.5 a layered rock salt structure, b + c + d + e = 1 , 0 ≦ e <0.5, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca At least one element selected from Ir, Hf, Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, 1.7 ≦ f ≦ 3) and LiM _h PO ₄ having an olivine structure (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si) Lithium metal phosphorylation in which at least one element selected from B, Te, Mo, 0 <h <2) is coated with carbon A positive electrode having a positive electrode active material layer containing a thing,
The average particle size of the lithium nickel composite oxide is smaller than the average particle size of the lithium metal phosphate compound,
And,
The positive electrode characterized in that the volume resistance of the lithium nickel composite oxide is larger than the volume resistance of the lithium metal phosphate compound. The positive electrode according to claim 1, wherein the LiM _h PO ₄ is represented by LiMn _x Fe _y PO ₄ (x + y = 1, 0 <x <1, 0 <y <1).   3. The positive electrode according to claim 1, wherein an average particle diameter of the lithium nickel composite oxide is in a range of 3 to 12 μm, and an average particle diameter of the lithium metal phosphate compound is in a range of 12 to 21 μm.   The volume resistance of the lithium nickel composite oxide is in the range of 100 to 500 Ω · cm, and the volume resistance of the lithium metal phosphate compound is in the range of 5 to 50 Ω · cm. The positive electrode according to item.   5. The positive electrode according to claim 1, wherein a mass ratio between the lithium nickel composite oxide and the lithium metal phosphate compound is in a range of 65:35 to 85:15. A lithium ion secondary battery comprising the positive electrode according to any one of claims 1 to 5 and a negative electrode comprising a Si-containing negative electrode active material.