JP2015144104A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which has, as a positive electrode active material, a Mn-containing olivine based material including Mn as an essential constituent, and is arranged so that the capacity deterioration can be suppressed.SOLUTION: A nonaqueous electrolyte secondary battery comprises: a positive electrode; a negative electrode; a separator; and a nonaqueous electrolyte. The positive electrode has: a positive electrode active material including Mn and having an olivine structure; and a coating film formed the surface of the positive electrode active material and originating from a diisocyanate compound. It has been found that as to a nonaqueous electrolyte secondary battery having a Mn-containing olivine based material as a positive electrode active material, Mn elution can be suppressed by reacting a diisocyanate compound with the Mn-containing olivine based material. The reaction of a diisocyanate compound can be finally realized by adding it to a nonaqueous electrolyte used in a nonaqueous electrolyte secondary battery as it is, which can be also realized by independently reacting a diisocyanate compound with the positive electrode active material.

Description

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

The capacity of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery largely depends on the type of positive electrode active material that electrochemically desorbs and inserts metal ions such as lithium ions. As the positive electrode active material, an inorganic powder of an oxide such as LiCoO ₂ or LiMn ₂ O ₄ is used.

The positive electrode active material differs in capacity, battery voltage, input / output characteristics, safety, etc. depending on the type. Therefore, the current situation is that the positive electrode active material is properly used depending on the use of the battery. Among them, a positive electrode active material having a polyanion structure containing XO ₄ tetrahedron (X = P, As, Si, Mo, etc.) in the crystal structure is known to have a stable structure, A non-aqueous electrolyte secondary battery using an olivine-based material having an olivine structure such as LiFePO ₄ having one of polyanion structures has been reported.

Here, since the positive electrode potential of the positive electrode active material is determined by the transition metal used theoretically, LiMnPO ₄ in which Fe in LiFePO ₄ is substituted with Mn is a candidate for increasing the potential.

JP 2007-242411 A JP 2012-182131 A

  The present inventors have conducted various studies on Mn-containing olivine-based materials containing Mn as an essential component and having an olivine structure. As a result, it was found that the Mn-containing olivine-based material can suppress battery capacity deterioration by suppressing elution of Mn.

  The present invention has been completed in view of the above circumstances, and provides a non-aqueous electrolyte secondary battery capable of suppressing capacity deterioration of a non-aqueous electrolyte secondary battery having an olivine-based material essential for Mn as a positive electrode active material. Is a problem to be solved.

  As a result of intensive studies on a non-aqueous electrolyte secondary battery having a Mn-containing olivine-based material as a positive electrode active material, the present inventors can suppress elution of Mn by reacting the positive active material with a diisocyanate compound. I found. Patent Documents 1 and 2 disclose that a diisocyanate compound is added, but a diisocyanate compound is added for the purpose of forming a film on the negative electrode surface, and a Mn-containing olivine-based material is adopted as a positive electrode active material. Thus, it is not assumed that a film is formed on the surface.

The reaction of the diisocyanate compound can also be realized by adding it to a non-aqueous electrolyte solution that is finally used as it is in a non-aqueous electrolyte secondary battery, or by reacting the diisocyanate compound independently with respect to the positive electrode active material. realizable. The present invention has completed the following inventions (a) and (b) based on the above findings. The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte.
(A) The positive electrode in the non-aqueous electrolyte secondary battery of the present invention has a positive electrode active material having an olivine structure containing Mn, and a film derived from a diisocyanate compound formed on the surface of the positive electrode active material.
(B) The positive electrode in the nonaqueous electrolyte secondary battery of the present invention has a positive electrode active material having an olivine structure containing Mn, and is brought into contact with the nonaqueous electrolyte containing a diisocyanate compound. It can be manufactured.

  In the olivine-based material of the positive electrode active material of the present invention disclosed in (a) and (b) described above, OH groups often remain on the surface of particles during the synthesis process. Therefore, when the diisocyanate compound is brought into contact, it reacts with the olivine-based material quickly to form a film on the surface. Since the diisocyanate compound has a reactive isocyanate group in one molecule, the surface of the olivine-based material can be cross-linked, and Mn elution from the surface of the olivine-based material is suppressed.

The non-aqueous electrolyte secondary battery of (b) described above can have the components described in (c) below.
(C) The diisocyanate compound is added in an amount of 0.1% to 3.0% based on the mass of the whole nonaqueous electrolytic solution. By making the content of the diisocyanate compound within this range, elution of Mn can be sufficiently suppressed, and the internal resistance due to the film of the diisocyanate compound can be suppressed low.

The non-aqueous electrolyte secondary batteries of (a) to (c) described above can have any one or more of the components described in the following (d) to (h).
(D) The positive electrode active material has a specific surface area of 10 m ² / g or more. A positive electrode active material with a large specific surface area can improve battery performance and also increase the elution of Mn. Therefore, by forming a film with a diisocyanate compound, the Mn elution is suppressed while keeping the battery performance high, thereby suppressing the deterioration of the battery capacity. Effectively possible.
(E) The diisocyanate compound is represented by the general formula (1): OCN-R-NCO (where R is an aliphatic hydrocarbon chain having 1 to 8 carbon atoms. Part of hydrogen may be substituted with an arbitrary substituent. ).
(F) The non-aqueous electrolyte is composed of one or more first additives selected from the compounds described in the following general formula (2) and the compounds described in the following general formulas (3) to (6). One or two or more selected second additives are contained, or a film derived from the first additive and the second additive is formed on at least one of the positive and negative electrodes. When the coating derived from the general formula (2) is formed, the internal resistance can be suppressed even if a highly durable coating is formed thereon. The compounds of the general formulas (3) to (6) are compounds that can form a highly durable film.

General formula (6): Li [P (C ₂ O ₄ ) K ₄ ]
(In Formula (2), X is an aliphatic hydrocarbon chain having 2 to 4 carbon atoms, and one or more arbitrary hydrogens may be substituted with any substituent. Formulas (5) and (6) In the formula, K is a group 17 element or a hydrogen atom selected independently of each other.)
(G) The positive active material is _{Li x Mn y M 1-y} XO 4 (M; Co, Ni, Fe, Cu, Cr, Mg, Ca, Zn, one or more selected from Ti, X; P, As, One or more selected from Si and Mo, 0 ≦ x <1.0, 0 <y ≦ 1.0).
(H) The negative electrode contains graphite and carboxymethylcellulose.

It is sectional drawing of a coin-type battery. It is the graph which showed the relationship between the capacity | capacitance maintenance factor and resistance in an Example.

  Hereinafter, the nonaqueous electrolyte secondary battery according to the embodiment of the present invention will be described in detail. In this specification, the “non-aqueous electrolyte secondary battery” is a battery that employs a non-aqueous electrolyte as an electrolyte, uses lithium ions, sodium ions, etc. as electrolyte ions, and accompanies exchange of electrolyte ions between the positive and negative electrodes. A secondary battery in which charge and discharge are realized by movement of electric charge. Secondary batteries generally referred to as lithium ion batteries (or lithium ion secondary batteries), lithium polymer batteries, lithium-air batteries, lithium-sulfur batteries, and the like can be included in the nonaqueous electrolyte secondary batteries in this specification. . Further, in this specification, the “active material” refers to a substance (compound) involved in power storage on the positive electrode side or the negative electrode side. That is, it refers to a substance that is involved in the storage and release of electrons during battery charge / discharge.

In addition, the nonaqueous electrolyte secondary battery in this invention is not limited to what was shown to the following embodiment, In the range which does not change the summary, it can change suitably and can implement. In the following embodiments, a battery using lithium ions is described. However, since the feature of the present invention is a positive electrode active material having an olivine-based material containing Mn, other ions (such as sodium ions) are used. The present invention can also be applied to the positive electrode active material.
[Lithium secondary battery]
A lithium secondary battery as a nonaqueous electrolyte secondary battery has a positive electrode, a negative electrode, a separator interposed between positive and negative electrodes, a nonaqueous electrolyte as a nonaqueous electrolyte, a case, and other necessary members.

A coin-type battery will be described below with reference to FIG. 1 as an example of the configuration. As shown in FIG. 1, a coin-type battery 10 includes a positive electrode 1, a negative electrode 2, a non-aqueous electrolyte 3, a separator 7 interposed between positive and negative electrodes, and a case (a positive electrode case 4 and a negative electrode case 5). ) In the positive electrode 1, a composite material layer is formed on the positive electrode current collector 1 a, and in the negative electrode 2, a composite material layer is formed on the positive electrode current collector 2 a. The positive electrode case 4 and the negative electrode case 5 serve as a positive electrode terminal and a negative electrode terminal. A gasket 6 made of polypropylene is interposed between the positive electrode case 4 and the negative electrode case 5, thereby ensuring sealing and insulation between the positive electrode case 4 and the negative electrode case 5.
(Positive electrode)
The positive electrode is obtained by suspending and mixing a positive electrode active material capable of reversibly occluding and desorbing lithium ions and a positive electrode mixture composed of a conductive material and a binder in an appropriate solvent to form a slurry. It can be produced by applying to one side or both sides and drying.

The positive electrode active material has a Mn-containing olivine-based material having an olivine structure containing Mn. Mn-containing olivine-based material _{Li x Mn y M 1-y} XO 4 (M; Co, Ni, Fe, Cu, Cr, Mg, Ca, Zn, one or more selected from Ti, X; P, As, Si, One or more types selected from Mo, 0 ≦ x <1.0, 0 <y ≦ 1.0) can be exemplified. In particular _{Li α Fe x Mn 1-x} PO 4 (0 <α ≦ 1,0 ≦ x <1) can be exemplified. The Mn-containing olivine-based material may be combined with carbon.

  Moreover, the film (shell) made of carbon may have a core-shell structure in which the Mn-containing olivine-based material (core) is formed. The mass ratio between the core part and the shell part in the case of having a core-shell structure is not particularly limited. For example, the core portion: shell portion can be in a range of about 99: 1 to about 90:10 by mass ratio. The shell portion has carbon. Carbon includes a carbon material that is a simple substance of carbon, and is desirably the carbon material itself.

The particle size of the positive electrode active material is not particularly limited, but it is preferable that the primary particles have a volume average particle size of 30 nm to 200 nm and the secondary particles have a volume average particle size of about 0.5 μm to 40 μm. The specific surface area of the positive electrode active material is desirably 10 m ² / g or more.

  The positive electrode of this embodiment employs at least one of the following configurations (A) or (B). (A) A film derived from a diisocyanate compound is formed on the surface of the positive electrode active material. (B) The positive electrode is brought into contact with the diisocyanate compound.

  It is estimated that both (A) and (B) form a chemical bond by reacting an isocyanate group with an OH group present on the surface of the positive electrode active material. In particular, in (B), it is presumed that a film of a diisocyanate compound is formed on the surface of the whole positive electrode.

  The coating film derived from the diisocyanate compound is obtained by bringing the positive electrode active material into contact with a solution in which the diisocyanate compound is dissolved in some solvent, the liquid diisocyanate compound itself, or the vaporized diisocyanate compound in a gas state by a method that is not particularly limited. Can be manufactured. Moreover, reaction can also be advanced when a battery is manufactured by dissolving the diisocyanate compound in the nonaqueous electrolyte solution mentioned later.

  When the diisocyanate compound is contained in the non-aqueous electrolyte, the lower limit is about 0.1%, about 0.5%, and the upper limit is about 3.0%, about 1.5% based on the total mass of the non-aqueous electrolyte. Each can be combined arbitrarily. By containing the diisocyanate compound at the lower limit or more, a film capable of sufficiently protecting the positive electrode active material can be formed. Moreover, by making it contain below this upper limit, it is possible to prevent the diisocyanate compound from reacting with other constituents other than the positive electrode active material, thereby preventing unexpected effects. Needless to say, an amount of diisocyanate compound larger than this upper limit can be added if the action on other components other than the positive electrode active material is acceptable or desirable.

  It does not specifically limit as a diisocyanate compound. The compound of the above-mentioned general formula (1) can be illustrated. The compound of the general formula (1) includes hexamethylene diisocyanate having 6 carbon atoms in R, cyclohexanediyl diisocyanate, phenylene diisocyanate, heptane diyl diisocyanate having 7 carbon atoms in R, methylcyclohexylene diisocyanate, toluene diisocyanate, carbon number in R. And m-xylylene diisocyanate having 8 and cyclohexanediyl bismethylene diisocyanate. Hydrogen in the R portion of these compounds can be substituted with a substituent such as halogen.

The Mn-containing olivine-based material can be synthesized by a method such as a hydrothermal method, a wet solid phase method, or a coprecipitation method. In general, the synthesis is performed by mixing raw materials having elements corresponding to the composition of the Mn-containing olivine material to be synthesized. In the case of Li _x Mn _y M _1-y XO ₄ described above, the Li source, Mn source, M source, and X source are mixed at an appropriate ratio (for example, the same as the composition ratio) to perform the synthesis reaction. When carbon is compounded, a carbon source is also mixed. Examples of the raw materials include salts (sulfates, etc.) and oxides containing elements constituting the Mn-containing olivine material. The carbon source is a compound that is carbonized by firing, and is, for example, a polymer compound (soluble cellulose such as carboxymethyl cellulose (CMC) or synthetic polymer such as polyvinyl alcohol (PVA)).

  A shell part can be arrange | positioned on the surface of a core part by baking with a carbon source after forming a core part. Examples of the carbon source include polysaccharides such as CMC and synthetic polymers such as PVA. Firing is performed in an inert atmosphere so that carbon contained in the carbon source is not oxidized, or in a reducing atmosphere (hydrogen or the like). The firing temperature is not particularly limited, but it is desirable to perform the firing in a range of about 500 ° C to 800 ° C.

In addition to the Mn-containing olivine-based material described above as the positive electrode active material, the positive electrode may further be mixed with a commonly used positive electrode active material as necessary. For example, various oxides, sulfides, lithium-containing oxides, conductive polymers, and the like can be used. For example, MnO ₂ , TiS ₂ , TiS ₃ , MoS ₃ , FeS ₂ , Li _1-x MnO ₂ , Li _1-x Mn ₂ O ₄ , Li _1-x CoO ₂ , Li _1-x NiO ₂ , LiV ₂ O ₃ , V ₂ O ₅ , polyaniline, polyparaphenylene, polyphenylene sulfide, polyphenylene oxide, polythiophene, polypyrrole, derivatives thereof, and stable radical compounds. In addition, x in these positive electrode active materials shows the number of 0-1. A material obtained by adding or substituting a transition metal such as Li, Mg, Al, or Co, Ti, Nb, or Cr may be used. Moreover, not only these lithium-metal composite oxides are used alone, but also a plurality of them can be mixed and used. Among these, the lithium-metal composite oxide is preferably at least one of a lithium manganese-containing composite oxide having a layered structure or a spinel structure, a lithium nickel-containing composite oxide, and a lithium cobalt-containing composite oxide.

  The conductive material is not particularly limited as long as it is usually used for a lithium secondary battery, and is mixed as necessary. For example, a carbon material, a metal powder, a conductive polymer, or the like can be used. From the viewpoint of conductivity and stability, it is preferable to use a carbon material such as acetylene black, ketjen black, or carbon black.

  The binder is not particularly limited as long as it is usually used for a lithium secondary battery. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluororesin copolymer (tetrafluoroethylene / hexafluoropropylene copolymer, etc.), styrene butadiene rubber (SBR), acrylic rubber, fluorine Rubber, polyvinyl alcohol (PVA), styrene / maleic acid resin, polyacrylate, carboxymethyl cellulose (CMC) and the like can be used.

  When manufacturing the positive electrode, an organic solvent that normally dissolves the binder is used as a solvent for dispersing the positive electrode active material and the like. For example, N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, water and the like can be mentioned. However, it is not limited to these. In some cases, the active material is slurried with PTFE or the like by adding a dispersant, a thickener or the like to water.

  The current collector is not particularly limited as long as it is normally used for a lithium secondary battery. For example, a member mainly composed of a metal having good conductivity such as copper, aluminum, nickel, titanium, and stainless steel can be used. The shape of the current collector is not particularly limited because it may vary depending on the shape of the battery constructed using the obtained electrode, and is not limited to a rod shape, plate shape, foil shape, net shape, punching metal shape, expanded metal shape, etc. Can be used.

For the positive electrode, one or more first additives selected from the compounds described in the general formula (2) described above and 1 selected from the compounds described in the general formulas (3) to (6) described above. Alternatively, it is desirable that a film derived from two or more second additives is formed. This coating is preferably formed outside the coating derived from the diisocyanate compound. As the compound of the general formula (2), X is —CH ₂ CH ₂ —, —CH═CH—, —CH ₂ CH ₂ CH ₂ —, —CH ₂ CH ₂ CH ₂ CH ₂ —, —CH ₂ CH═CH _{-, - CH 2 CH 2 CH} = CH -, - CH = CHCH = CH -, - CH 2 CHCH 3 -, - CH = C (CH 3) - , etc. are exemplified. Any number of these atoms can be substituted. For example, a compound substituted with a halogen such as F can be exemplified. Examples of K in the general formulas (3), (5) and (6) include hydrogen, fluorine, chlorine, bromine and iodine.
(Negative electrode)
The negative electrode is obtained by suspending and mixing a negative electrode active material capable of reversibly occluding and desorbing lithium ions and a negative electrode mixture containing a conductive material and a binder mixed as necessary in a suitable solvent. This can be prepared by applying to one or both sides of the current collector and drying.

  The negative electrode active material is composed of a carbon material. As the carbon material, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), graphite (graphite) and the like can be used, and graphite is particularly preferable. For graphite, natural graphite, artificial graphite, graphitized mesocarbon microbeads, pitch-based, polyacrylonitrile-based, mesophase pitch-based, and vapor-phase-grown graphitized carbon fibers should also be used. Can do. These may be used alone or in combination of two or more.

  The carbon material of the negative electrode active material is desirably surface-modified graphite whose surface is modified. By modifying the surface of the carbon material, the surface of the carbon material is easily wetted with the electrolytic solution, and a good SEI film can be generated. Therefore, high temperature cycle characteristics and energy density are improved. The method for modifying the surface of the carbon material that is the negative electrode active material is not particularly limited, such as fluorine treatment, acid treatment, alkali treatment, and plasma treatment.

  The solvent in which the conductive material, the binder, the negative electrode active material, and the like are dispersed, and the current collector can be appropriately selected from those exemplified for the positive electrode. By adopting graphite as the negative electrode active material and CMC as the binder, a film capable of improving the durability of the battery can be formed on the surface of the negative electrode by incorporating a diisocyanate compound in the non-aqueous electrolyte.

For the negative electrode, 1 or 2 or more first additives selected from the compounds described in the general formula (2) and 1 selected from the compounds described in the general formulas (3) to (6). Alternatively, it is desirable that a film derived from two or more second additives is formed. This coating is preferably formed outside the coating derived from the diisocyanate compound.
(Nonaqueous electrolyte)
As the non-aqueous electrolyte, a solution in which an electrolyte is dissolved in a generally used non-aqueous solvent can be used, and there is no particular limitation. For example, a cyclic carbonate such as ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC) and a chain carbonate such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC). A mixed solvent or a mixed solvent of a cyclic carbonate and an ether solvent such as 1,2-dimethoxyethane or 1,2-diethoxyethane can be used.

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

  The above-mentioned diisocyanate compound can be contained in the non-aqueous electrolyte. A preferable range of the addition amount is as described above.

The non-aqueous electrolyte is selected from one or more first additives selected from the compounds described in the general formula (2) and the compounds described in the general formulas (3) to (6). 1 or 2 or more second additives to be contained. These first and second additives can form a film on the surface of at least one of the positive and negative electrodes by the progress of charge and discharge after battery formation. Since the first and second additives have different potentials for forming a film, the composition of the formed film changes in the thickness direction.
(Separator)
The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film may be used. The size of the separator is preferably larger than that of the positive electrode and the negative electrode in order to ensure insulation between the positive electrode and the negative electrode.

The lithium secondary battery of the present invention comprises other elements as needed in addition to the above elements. The lithium secondary battery of the present invention is not particularly limited in its shape, and can be used as a battery having various shapes such as a coin shape, a cylindrical shape, and a square shape. Further, the case of the lithium secondary battery of the present invention is not limited, and can be used as various types of batteries such as a metal or resin case that can retain its outer shape, a soft case such as a laminate pack, and the like. .
(conditioning)
Such a lithium secondary battery is activated and conditioned by performing initial charging. The initial charging condition is not particularly limited except for the condition described in the column of the lithium secondary battery. Charging can be performed until the potential difference between the positive and negative electrodes reaches an upper limit potential (for example, 4.1 V or more) that is appropriately determined depending on the type of the active material, the electrolytic solution, and the like. For charging, a general charging method such as constant current charging, constant voltage charging, or constant current-constant voltage charging can be employed. And even if it does not complete | finish an initial stage charge once, it can also add discharge operation and it can also repeat twice or more. When the initial charging is performed twice or more, a lithium source can be added into the positive electrode every charging operation. In order to remove the gas (derived from the lithium source) present in the battery after the initial charging, the inside and outside of the battery can be communicated, or the initial charging can be performed in a state before the battery is sealed. . It is desirable to perform charging before sealing, or to perform communication in a low-humidity atmosphere when communicating inside and outside the battery after charging.

Hereinafter, the nonaqueous electrolyte secondary battery of the present invention will be described in detail based on examples. However, the following examples are for the purpose of illustrating the present invention and do not limit the scope of the present invention.
[Manufacture of non-aqueous electrolyte secondary batteries]
-Non-aqueous electrolyte LiPF ₆ was added as an electrolyte to a solvent mixed in a mass ratio of EC: DMC: EMC = 3: 3: 4 to produce a non-aqueous electrolyte that was a 1.0 M LiPF ₆ solution. As an additive, the compounds shown in Table 1 were added in the amounts shown in Table 1. This addition amount is a value expressed as a percentage based on the whole non-aqueous electrolyte.

Here, Compound 1 is m-xylylene diisocyanate, and Compound 2 is hexamethylene diisocyanate. VC is a compound in which X in the general formula (2) is —CH═CH—, FEC is a compound in which X in the general formula (2) is —CH ₂ CHF—, LiFOB is K in the general formula (3). A compound in which both are fluorine, LiBOB is a compound of the general formula (4), and LiPFO is a compound in which K in the general formula (5) is fluorine. Here, additive A corresponds to the diisocyanate compound, additive B corresponds to the first additive, and additive C corresponds to the second additive.
-Positive electrode 80 parts by mass of LiMnPO ₄ (specific surface area 20 m ² / g) as a Mn-containing olivine-based material as a positive electrode active material, 10 parts by mass of acetylene black as a conductive material, and polyvinylidene fluoride as a binder ( 10 parts by mass of PVDF) was dispersed in water to form a slurry. This slurry was applied to the surface of an aluminum positive electrode current collector (thickness 0.05 mm) to form a positive electrode active material layer. After drying, it was press-molded to obtain a positive electrode plate. The active material layer on the current collector was 0.3 mg / mm ² and the density was 2.0 g / cm ³ . This positive electrode plate was cut into a predetermined size to produce a sheet-like positive electrode in which a positive electrode active material layer was formed on a positive electrode current collector.
-Negative electrode 98 parts by mass of graphite as a negative electrode active material and 1 part by mass of CMC and SBR as binders were dispersed in water to form a slurry. This slurry was applied to the surface of a copper negative electrode current collector (thickness 0.05 mm) to form a negative electrode active material layer. After drying, it was press-molded to obtain a negative electrode plate. The active material layer on the current collector was 0.2 mg / mm ² and the density was 1.5 g / cm ³ . This negative electrode plate was cut into a predetermined size to produce a sheet-like negative electrode in which a negative electrode active material layer was formed on a negative electrode current collector.
-Assembly The prepared positive and negative electrodes were laminated through a polyethylene porous membrane as a separator and sealed in a laminate container together with the non-aqueous electrolyte described above to obtain test batteries for each test example. In addition, about the test battery of Test Example 9, the binder was changed from CMC and SBR, and PVdF was manufactured at 2 parts by mass.

  The test batteries of each test example were conditioned by charging and discharging at 1/10 C and 2 to 4.5 V three times.

  Thereafter, the capacity and the internal resistance were measured after 500 cycles of charging and discharging under conditions of CC-CV (up to 4V) during charging, CC (up to 2V) during discharging, and 2C during CC. The results are shown in Table 1 and FIG. The battery capacity and internal resistance are shown as relative values calculated with the value after 500 cycles of the battery of Test Example 1 as 100.

  As is clear from Table 1, from the comparison between Test Example 1 and Test Example 10 in which additive A is not added, the effect of additive A is that the capacity retention rate can be improved and the resistance can be increased. I understood. Further, in Test Examples 2 to 9 in which the additive A was added, in comparison with Test Example 10 in which the additive A was not added, the effect of improving the capacity retention rate was recognized. Therefore, it has been clarified that the capacity retention rate is improved by adding the additive A.

  Next, when the results of Test Examples 6 to 8 in which only the amount of the additive A was changed were examined, it was found that the capacity retention ratio increased and the resistance increased according to the amount of additive A added. Therefore, it was suggested that there is an appropriate range for the amount of additive A (diisocyanate compound) to be added depending on the performance of the nonaqueous electrolyte secondary battery that is desired to be finally produced.

  Comparing the results of Test Examples 6 to 8 with Test Example 10 in which additive A was not added, additive A showed excellent values for both capacity retention and resistance even when 0.2% was added. I understood that. Further, if the resistance value may be kept at about Test Example 10, the capacity retention rate could be drastically improved to 99 when 1% of Additive A was added as in Test Example 6.

  From a comparison between Test Example 1 and Test Example 2 to which LiBOB was added, it was found that by adding LiBOB as additive C, the degree of improvement in capacity retention rate was slightly reduced, but the resistance could be reduced.

  From the results of Test Examples 3 to 5 in which the type of the additive C was changed, it was suggested that there are desirable types of the additive C depending on the values required for the capacity retention ratio and the resistance value.

  From a comparison between Test Example 1 and Test Example 9 in which the negative electrode binder was changed to PVdF, it was found that by using PVdF as the binder, the capacity retention rate was reduced, but the resistance could be reduced.

1: Positive electrode 1a: Positive electrode current collector 1b: Positive electrode active material 2: Negative electrode 2a: Negative electrode current collector 2b: Negative electrode active material 3: Electrolytic solution 4: Positive electrode case 5: Negative electrode case 6: Gasket 7: Separator 10: Coin type battery

Claims (8)

A positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte;
The non-aqueous electrolyte secondary battery, wherein the positive electrode has a positive electrode active material having an olivine structure containing Mn and a coating film derived from a diisocyanate compound formed on the surface of the positive electrode active material. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte,
The said positive electrode has a positive electrode active material with the olivine structure containing Mn, The non-aqueous electrolyte secondary battery which can be manufactured by making it contact in the state which contained the diisocyanate compound in the said non-aqueous electrolyte.   The non-aqueous electrolyte secondary battery according to claim 2, wherein the diisocyanate compound is added in an amount of 0.1% to 3.0% based on the mass of the entire non-aqueous electrolyte. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material has a specific surface area of 10 m ² / g or more.   The diisocyanate compound is represented by the general formula (1): OCN-R-NCO (where R is an aliphatic hydrocarbon chain having 1 to 8 carbon atoms. Hydrogen may be partially substituted with an arbitrary substituent). The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4. The non-aqueous electrolyte is selected from one or more first additives selected from the compounds described in the following general formula (2) and the compounds described in the following general formulas (3) to (6). The 1st or 2 or more 2nd additive is contained, The film derived from the said 1st additive and the said 2nd additive is formed in at least one of the said positive and negative electrodes of Claims 1-5 The nonaqueous electrolyte secondary battery according to any one of the above.

General formula (6): Li [P (C ₂ O ₄ ) K ₄ ]
(In Formula (2), X is an aliphatic hydrocarbon chain having 2 to 4 carbon atoms, and one or more arbitrary hydrogens may be substituted with any substituent. Formulas (5) and (6) In the formula, K is a group 17 element or a hydrogen atom selected independently of each other.) The positive active material is _{Li x Mn y M 1-y} XO 4 (M; Co, Ni, Fe, Cu, Cr, Mg, Ca, Zn, one or more selected from Ti, X; P, As, Si, Mo The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein at least one selected from the group consisting of 0 ≦ x <1.0 and 0 <y ≦ 1.0.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode contains graphite and carboxymethyl cellulose.

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