WO2016103591A1 - 非水電解質二次電池用正極活物質及び非水電解質二次電池 - Google Patents
非水電解質二次電池用正極活物質及び非水電解質二次電池 Download PDFInfo
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- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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Definitions
- the present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a technique for a non-aqueous electrolyte secondary battery.
- non-aqueous electrolyte secondary batteries have been required to have a high capacity that enables long-term use and an improvement in output characteristics that enables repeated charging and discharging of a large current in a relatively short time. It has been.
- Patent Document 1 discloses a reaction between a positive electrode active material and an electrolytic solution even when the charging voltage is increased by causing a group 3 element of the periodic table to be present on the surface of base material particles as a positive electrode active material. It has been suggested that deterioration of charge storage characteristics can be suppressed.
- NaF is contained in the battery can (added to the positive electrode, the negative electrode, and the electrolytic solution) to suppress cycle deterioration due to a reaction between HF and the positive electrode active material, and cycle characteristics (capacity maintenance). It is suggested that the rate is improved.
- DCR Direct Current Resistance
- the objective of this invention is providing the nonaqueous electrolyte secondary battery provided with the positive electrode active material for nonaqueous electrolyte secondary batteries which can suppress the raise of DCR after a charging / discharging cycle, and the said positive electrode active material. is there.
- the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention includes a secondary particle in which primary particles of a lithium-containing transition metal oxide are aggregated, a secondary particle in which primary particles of a rare earth compound are aggregated, and an alkali metal fluoride.
- the secondary particles of the rare earth compound are attached to the recesses formed between adjacent primary particles on the surface of the secondary particles of the lithium-containing transition metal oxide, and the rare earth compound
- the secondary particles are attached to both the primary particles adjacent to each other in the recess, and the alkali metal fluoride particles are attached to the surface of the lithium-containing transition metal oxide secondary particles.
- the positive electrode active material according to the present invention can suppress an increase in DCR after a charge / discharge cycle.
- FIG. 2 is a schematic cross-sectional view taken along line AA in FIG. It is the schematic cross section which expanded a part of positive electrode active material particle and this positive electrode active material particle of this embodiment.
- 4 is a partial schematic cross-sectional view of positive electrode active material particles of Comparative Example 2.
- FIG. It is a partial schematic cross section of the positive electrode active material particles obtained in the reference example.
- FIG. 1 is a cross-sectional view showing a nonaqueous electrolyte secondary battery which is an example of the present embodiment.
- FIG. 2 is a schematic cross-sectional view along the line AA in FIG.
- the nonaqueous electrolyte secondary battery 11 includes a positive electrode 1, a negative electrode 2, and a nonaqueous electrolyte secondary battery separator 3 interposed between the positive electrode 1 and the negative electrode 2 (hereinafter, Simply “separator 3”) and a non-aqueous electrolyte (not shown).
- the positive electrode 1 and the negative electrode 2 are wound around a separator 3 and constitute a flat electrode group together with the separator 3.
- the nonaqueous electrolyte secondary battery 11 includes a positive electrode current collecting tab 4, a negative electrode current collecting tab 5, and an aluminum laminate outer package 6 having a closed portion 7 whose peripheral edges are heat-sealed.
- the flat electrode group and the nonaqueous electrolyte are accommodated in the aluminum laminate outer package 6.
- the positive electrode 1 is connected to the positive electrode current collection tab 4, the negative electrode 2 is connected to the negative electrode current collection tab 5, and it has a structure which can be charged / discharged as a secondary battery.
- the shape of the battery may be, for example, a cylindrical battery, a square battery, a coin battery, or the like.
- the positive electrode 1 includes a positive electrode current collector such as a metal foil and a positive electrode active material layer formed on the positive electrode current collector.
- a positive electrode current collector a metal foil that is stable in the potential range of the positive electrode such as aluminum, a film in which the metal is disposed on the surface layer, or the like can be used.
- the positive electrode active material layer preferably includes a positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter may be referred to as a positive electrode active material), and additionally includes a conductive material and a binder.
- FIG. 3 is an enlarged schematic cross-sectional view of the positive electrode active material particles of the present embodiment and a part of the positive electrode active material particles.
- the positive electrode active material particles include lithium-containing transition metal oxide secondary particles 21 formed by aggregation of lithium-containing transition metal oxide primary particles 20 and rare-earth compound primary particles 24 aggregated.
- the secondary particles 25 of the rare earth compound and the alkali metal fluoride particles 22 are formed.
- the secondary particles 25 of the rare earth compound are concave portions formed between the primary particles 20 and the primary particles 20 of the adjacent lithium-containing transition metal oxide on the surface of the secondary particles 21 of the lithium-containing transition metal oxide.
- the secondary particles 25 of the rare earth compound adhering to 23 are attached to both the primary particles 20 and the primary particles 20 of the lithium-containing transition metal oxide adjacent to each other in the recess 23.
- the alkali metal fluoride particles 22 are attached to the surfaces of the lithium-containing transition metal oxide secondary particles 21.
- the alkali metal fluoride particles 22 may be in the form of primary particles or secondary particles.
- the secondary particles 25 of the rare earth compound are attached to both of the primary particles 20 of the lithium-containing transition metal oxide that are adjacent to each other in the recess 23.
- the primary particles 20 of the adjacent lithium-containing transition metal oxide in the recesses 23 formed between the primary particles 20 of the adjacent lithium-containing transition metal on the surface of the secondary particle 21 of the lithium-containing transition metal oxide.
- the secondary particles 25 of the rare earth compound are attached to both surfaces.
- the secondary particles 25 of the rare earth compound adhering to both of the primary particles 20 of the lithium-containing transition metal oxide adjacent to each other in the recesses 23 are adjacent in the charge / discharge cycle.
- Surface modification of the primary particles 20 of the lithium-containing transition metal oxide that are in contact with each other is suppressed, and cracking from the primary particle interface in the recesses 23 is suppressed.
- the secondary particles 25 of the rare earth compound are considered to have an effect of fixing (adhering) the primary particles 20 of the adjacent lithium-containing transition metal oxide to each other, the positive electrode active material in the charge / discharge cycle However, even if it repeats expansion and contraction, cracks from the primary particle interface in the recess 23 are suppressed.
- a lithium ion permeable film is formed on the surface of the secondary particles 25 of the lithium transition metal oxide by the rare earth compound adhering to the lithium-containing transition metal oxide.
- Alkali metal derived from alkali metal fluoride and fluorine adhering to the surface of the secondary particle 21 of the transition metal oxide are contained. And by this Li ion permeable film, decomposition
- the rare earth compound used in this embodiment is preferably at least one compound selected from rare earth hydroxides, oxyhydroxides, oxides, carbonic acid compounds, phosphoric acid compounds and fluorine compounds. Among these, in particular, at least one compound selected from rare earth hydroxides and oxyhydroxides is preferable. When these rare earth compounds are used, for example, the effect of suppressing surface alteration that occurs at the primary particle interface is obtained. More effective.
- the rare earth element constituting the rare earth compound is at least one selected from scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.
- neodymium, samarium, and erbium are particularly preferable.
- the neodymium, samarium, and erbium compounds exhibit a greater effect of suppressing surface alteration that occurs, for example, at the primary particle interface than other rare earth compounds.
- rare earth compounds include neodymium hydroxide, neodymium oxyhydroxide, samarium hydroxide, samarium oxyhydroxide, erbium hydroxide, erbium oxyhydroxide, and other hydroxides and oxyhydroxides, as well as neodymium phosphate.
- the average particle diameter of the primary particles of the rare earth compound is preferably 5 nm or more and 100 nm or less, and more preferably 5 nm or more and 80 nm or less.
- the average particle size of the secondary particles of the rare earth compound is preferably 100 nm or more and 400 nm or less, and more preferably 150 nm or more and 300 nm or less. If the average particle size exceeds 400 nm, the particle size of the secondary particles of the rare earth compound becomes too large, and the number of recesses of the lithium-containing transition metal oxide to which the secondary particles of the rare earth compound adhere may decrease. .
- the average particle size is less than 100 nm, the area where the secondary particles of the rare earth compound contact between the primary particles of the lithium-containing transition metal oxide is reduced, so the primary particles of the adjacent lithium-containing transition metal oxide are adjacent to each other.
- the effect of fixing (adhering) is reduced, and the effect of suppressing cracks from the primary particle interface of the secondary particle surface may be reduced.
- the ratio (attachment amount) of the rare earth compound is preferably 0.005% by mass or more and 0.5% by mass or less, in terms of rare earth element, with respect to the total mass of the lithium-containing transition metal oxide, and 0.05% by mass or more and 0.0. More preferably, it is 3 mass% or less.
- the ratio is less than 0.005% by mass, the amount of the rare earth compound adhering to the recesses formed between the primary particles of the lithium-containing transition metal oxide is reduced. It may not be possible.
- the ratio exceeds 0.5% by mass, not only the primary particles of the lithium-containing transition metal oxide, but also the secondary particle surface of the lithium-containing transition metal oxide is excessively covered. The characteristics may deteriorate.
- the alkali metal fluoride is not particularly limited as long as it is a compound containing lithium, sodium, potassium, rubidium, cesium, alkali metal and fluorine, but the production cost, secondary lithium-containing transition metal oxide is not limited. From the viewpoint of adhesion to particles, lithium fluoride, sodium fluoride, potassium fluoride, and the like are preferable.
- the proportion of the alkali metal fluoride is preferably 0.005% by mass or more and 1.0% by mass or less, particularly 0.01% by mass or more, 0% in terms of fluorine element with respect to the total mass of the lithium-containing transition metal oxide. More preferably, it is 5 mass% or less.
- the alkali metal fluoride is less than 0.005% by mass in terms of fluorine element, the effect of suppressing the decomposition of the nonaqueous electrolyte may not be sufficiently obtained.
- a specific capacity may fall.
- the average particle size of the alkali metal fluoride is preferably 1 nm or more and 500 nm or less, and more preferably 2 nm or more and 100 nm. If the average particle size is less than 1 nm, it may be difficult to control the surface treatment. If the average particle size exceeds 500 nm, the alkali metal fluoride is non-uniform on the surface of the positive electrode active material, and the effect of fluorine is sufficiently obtained. There is a case where a part that cannot be generated occurs.
- the average particle size of primary particles of the lithium-containing transition metal oxide is preferably 100 nm or more and 5 ⁇ m or less, and more preferably 300 nm or more and 2 ⁇ m or less.
- the average particle size is less than 100 nm, the primary particle interface including the inside of the secondary particles is too much, and the primary particles may be easily cracked due to expansion and contraction of the positive electrode active material in the charge / discharge cycle.
- the average particle diameter exceeds 5 ⁇ m, the amount of the primary particle interface including the inside of the secondary particles becomes too small, and the output at a low temperature may be reduced.
- the average particle size of the secondary particles of the lithium-containing transition metal oxide is preferably 2 ⁇ m or more and 40 ⁇ m or less, and more preferably 4 ⁇ m or more and 20 ⁇ m or less.
- the secondary particles of the lithium-containing transition metal oxide are formed by bonding (aggregation) of the primary particles of the lithium-containing transition metal oxide, so the primary particles of the lithium-containing transition metal oxide are lithium-containing transition metal oxides. It is not larger than the secondary particles of the object.
- the average particle size was determined by observing the surface and cross section of the active material particles with a scanning electron microscope (SEM) and measuring the particle size of several tens of particles, for example.
- SEM scanning electron microscope
- the average particle diameter of the primary particles of the rare earth compound and the alkali metal fluoride is a size along the surface of the active material, and is not in the thickness direction.
- the lithium-containing transition metal oxide not only can the positive electrode capacity be increased, but also the proportion of Ni in the lithium-containing transition metal oxide from the viewpoint that a proton exchange reaction at the primary particle interface described later is more likely to occur.
- the nickel ratio is preferably 80% or more when the molar amount of the entire metal excluding Li in the lithium-containing transition metal oxide is 1.
- lithium-containing nickel-manganese composite oxide, lithium-containing nickel-cobalt-manganese composite oxide, lithium-containing nickel-cobalt composite oxide, lithium-containing nickel-cobalt aluminum composite oxide, etc. are used as the lithium-containing transition metal oxide.
- the lithium-containing nickel cobalt aluminum composite oxide the molar ratio of nickel, cobalt and aluminum is 8: 1: 1, 82: 15: 3, 85: 12: 3, 87: 10: 3, 88: 9: 3. 88: 10: 2, 89: 8: 3, 90: 7: 3, 91: 6: 3, 91: 7: 2, 92: 5: 3, 94: 3: 3, etc. Can do. These may be used alone or in combination.
- the ratio of trivalent Ni increases, so that proton exchange reaction between water and lithium in the lithium-containing transition metal oxide occurs in water.
- LiOH is likely to occur, and a large amount of LiOH produced by the proton exchange reaction appears on the secondary particle surface from the inside of the primary particle interface of the lithium-containing transition metal oxide.
- the alkali (OH ⁇ ) concentration between the primary particles of the lithium-containing transition metal oxide adjacent to the secondary particle surface of the lithium-containing transition metal oxide becomes higher than the surroundings.
- the primary particles of the rare earth compound are aggregated so as to be attracted to the alkali of the recesses formed between the primary particles, and are easily adhered while forming secondary particles.
- the lithium-containing transition metal composite oxide having a Ni ratio of less than 80% the ratio of trivalent Ni is small and the proton exchange reaction is less likely to occur.
- the concentration is almost the same as the surroundings. For this reason, even if the primary particles of the precipitated rare earth compound are combined to form secondary particles, the primary particles of the lithium-containing transition metal oxide that are likely to collide when adhered to the surface of the lithium-containing transition metal oxide. It becomes easy to adhere to the convex part.
- a particularly preferable composition is such that the proportion of cobalt in the lithium-containing transition metal oxide is 7 with respect to the total molar amount of metal elements excluding lithium from the viewpoint of increasing the capacity of the battery. It is preferably at most mol%, more preferably at most 5 mol%.
- the proportion of cobalt in the lithium-containing transition metal oxide is 7 with respect to the total molar amount of metal elements excluding lithium from the viewpoint of increasing the capacity of the battery. It is preferably at most mol%, more preferably at most 5 mol%.
- the lithium-containing transition metal oxide may further contain other additive elements.
- additive elements include boron (B), magnesium (Mg), aluminum (Al), titanium (Ti), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), and niobium (Nb). ), Molybdenum (Mo), tantalum (Ta), tungsten (W), zirconium (Zr), tin (Sn), sodium (Na), potassium (K), barium (Ba), strontium (Sr), calcium (Ca) ), Bismuth (Bi), germanium (Ge), and the like.
- Lithium-containing transition metal oxide is an alkaline component that adheres to the surface of the lithium-containing transition metal oxide by washing the lithium-containing transition metal oxide with water or the like from the viewpoint of obtaining a battery having excellent high-temperature storage characteristics. Is preferably removed.
- Examples of the method of attaching the rare earth compound to the secondary particle surface of the lithium-containing transition metal oxide include a method of adding an aqueous solution in which the rare earth compound is dissolved in a suspension containing the lithium-containing transition metal oxide.
- the suspension In attaching the rare earth compound to the secondary particle surface of the lithium-containing transition metal oxide, while adding the aqueous solution in which the compound containing the rare earth element is dissolved to the suspension, the suspension has a pH of 11.5 or more, preferably It is desirable to adjust to a pH range of 12 or higher. This is because the rare earth compound particles tend to be unevenly distributed and adhered to the surfaces of the secondary particles of the lithium-containing transition metal oxide by treatment under these conditions.
- the pH of the suspension is 6 or more and 10 or less, the rare earth compound particles tend to be uniformly attached to the entire surface of the secondary particles of the lithium-containing transition metal oxide, and the primary particle interface on the surface of the secondary particles. In some cases, cracking of the active material due to surface alteration that occurs in the case cannot be sufficiently suppressed.
- pH becomes less than 6 at least one part of a lithium containing transition metal oxide may melt
- the pH of the suspension is adjusted to 14 or less, preferably 13 or less.
- the pH is higher than 14, not only the primary particles of the rare earth compound become too large, but excessive alkali remains inside the particles of the lithium-containing transition metal oxide, so that gelation is likely to occur during slurry preparation, Excess gas may be generated during storage.
- aqueous solution in which a rare earth compound is dissolved When an aqueous solution in which a rare earth compound is dissolved is added to a suspension containing a lithium-containing transition metal oxide, if the aqueous solution is simply used, it will precipitate as a rare earth hydroxide, and if carbon dioxide is sufficiently dissolved Precipitate as a rare earth carbonate compound.
- phosphate ions When phosphate ions are sufficiently added to the suspension, the rare earth compound can be deposited on the surface of the lithium-containing transition metal oxide particles as a rare earth phosphate compound.
- the lithium-containing transition metal oxide particles on which the rare earth compound is deposited are preferably heat-treated.
- the heat treatment temperature is preferably 80 ° C. or higher and 500 ° C. or lower, and more preferably 80 ° C. or higher and 400 ° C. or lower. If the temperature is lower than 80 ° C, it may take excessive time to sufficiently dry the positive electrode active material obtained by the heat treatment. If the temperature exceeds 500 ° C, a part of the rare earth compound adhering to the surface may be a lithium-containing transition. In some cases, the metal oxide particles diffuse into the particles, and the effect of suppressing surface alteration that occurs at the primary particle interface of the lithium-containing transition metal oxide may be reduced. On the other hand, when the heat treatment temperature is 400 ° C.
- rare earth elements hardly diffuse inside the particles of the lithium-containing transition metal composite oxide and adhere firmly to the primary particle interface.
- the effect of suppressing surface alteration that occurs at the primary particle interface and the adhesion effect between these primary particles are increased.
- rare earth hydroxide When rare earth hydroxide is adhered to the primary particle interface, most of the hydroxide changes to oxyhydroxide at about 200 ° C. to about 300 ° C., and further at about 450 ° C. to about 500 ° C. Usually changes to oxide. For this reason, when heat-treated at 400 ° C. or lower, rare earth hydroxides and oxyhydroxides having a large effect of suppressing surface alteration can be selectively disposed at the primary particle interface of the lithium-containing transition metal oxide. Therefore, the increase in DCR after the charge / discharge cycle can be further suppressed.
- the heat treatment of the lithium-containing transition metal oxide with the rare earth compound attached to the surface is preferably performed under vacuum.
- the water content of the suspension used to deposit the rare earth compound penetrates into the lithium-containing transition metal oxide particles, but at the primary particle interface on the secondary particle surface of the lithium-containing transition metal oxide. If secondary particles of a rare earth compound adhere to the formed recess, it is difficult for moisture to escape from the inside during drying. Therefore, moisture may not be effectively removed unless heat treatment is performed under vacuum. As a result, the amount of moisture brought into the battery from the positive electrode active material increases, and the surface of the active material may be altered by the product generated by the reaction between the moisture and the nonaqueous electrolyte.
- an aqueous solution containing a rare earth compound a solution obtained by dissolving acetate, nitrate, sulfate, oxide or chloride in water or an organic solvent can be used. It is preferable to use one dissolved in water because of its high solubility.
- an aqueous solution in which a rare earth sulfate, chloride, or nitrate is obtained by dissolving it in an acid such as sulfuric acid, hydrochloric acid, nitric acid, or acetic acid may be used.
- the rare earth compound when attached to the secondary particle surface of the lithium-containing transition metal oxide using a dry mixing method of the lithium-containing transition metal oxide and the rare earth compound, the particles of the rare earth compound contain lithium. Since it randomly adheres to the secondary particle surface of the transition metal oxide, it is difficult to selectively adhere to the primary particle interface of the secondary particle surface. Further, when the dry mixing method is used, it is difficult to firmly attach the rare earth compound to the lithium-containing transition metal oxide, so that the effect of fixing (adhering) the primary particles cannot be sufficiently obtained. There is a case. Further, when a positive electrode mixture is prepared by mixing with a conductive agent or a binder, the rare earth compound may be easily removed from the lithium-containing transition metal oxide.
- Examples of the method of attaching the alkali metal fluoride to the secondary particle surface of the lithium-containing transition metal oxide include, for example, a method of adding an aqueous solution in which the alkali metal fluoride is dissolved in a suspension containing the lithium transition metal oxide, And a method of adding (spraying) an aqueous solution in which an alkali metal fluoride is dissolved while mixing lithium-containing transition metal oxide particles.
- a method of adding an aqueous solution in which an alkali metal fluoride is dissolved to a suspension containing a lithium transition metal oxide an aqueous solution in which an alkali metal fluoride is dissolved together with an aqueous solution in which the rare earth compound is dissolved is used.
- a rare earth is added to the suspension containing the lithium-containing transition metal oxide. It is desirable to add (spray) the aqueous solution in which the alkali metal fluoride is dissolved while mixing the particles of the lithium-containing transition metal oxide to which the rare earth compound is adhered by the method of adding the aqueous solution in which the compound is dissolved.
- the positive electrode active material is not limited to the case where the lithium-containing transition metal oxide particles of the present embodiment described above are used alone. It is also possible to mix the lithium-containing transition metal oxide of the present embodiment described above and another positive electrode active material.
- the other positive electrode active material is not particularly limited as long as it is a compound that can reversibly insert and desorb lithium ions. For example, cobalt that can insert and desorb lithium ions while maintaining a stable crystal structure. Those having a layered structure such as lithium oxide and nickel cobalt lithium manganate, those having a spinel structure such as lithium manganese oxide and lithium nickel manganese oxide, and those having an olivine structure can be used.
- the positive electrode active materials may be of the same particle diameter or of different particle diameters. Also good.
- the conductive material is used, for example, to increase the electrical conductivity of the positive electrode active material layer.
- Examples of the conductive material include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more.
- the binder is used, for example, to maintain a good contact state between the positive electrode active material and the conductive material and to enhance the binding property of the positive electrode active material and the like to the surface of the positive electrode current collector.
- the binder include fluorine-based polymers and rubber-based polymers.
- PTFE polytetrafluoroethylene
- PVdF polyvinylidene fluoride
- coalescence examples include coalescence. These may be used alone or in combination of two or more.
- the binder may be used in combination with a thickener such as carboxymethyl cellulose (CMC) or polyethylene oxide (PEO).
- the negative electrode 2 includes a negative electrode current collector such as a metal foil, and a negative electrode active material layer formed on the negative electrode current collector.
- a negative electrode current collector such as a metal foil, and a negative electrode active material layer formed on the negative electrode current collector.
- the negative electrode active material layer preferably contains a binder in addition to the negative electrode active material capable of inserting and extracting lithium ions.
- PTFE styrene-butadiene copolymer
- the binder may be used in combination with a thickener such as CMC.
- the negative electrode active material examples include a carbon material capable of inserting and extracting lithium, a metal capable of forming an alloy with lithium, or an alloy compound containing the metal.
- the carbon material natural graphite, non-graphitizable carbon, graphite such as artificial graphite, coke, etc. can be used, and examples of the alloy compound include those containing at least one metal capable of forming an alloy with lithium. It is done.
- silicon or tin is preferable as an element capable of forming an alloy with lithium, and silicon oxide, tin oxide, or the like in which these are combined with oxygen can also be used.
- what mixed the said carbon material and the compound of silicon or tin can be used.
- a negative electrode material having a higher charge / discharge potential than lithium carbon such as lithium titanate can be used.
- a porous sheet having ion permeability and insulating properties is used.
- the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric.
- polyolefin such as polyethylene and polypropylene is suitable.
- the non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.
- the electrolyte salt of the non-aqueous electrolyte include LiClO 4 , LiBF 4 , LiPF 6 , LiAlCl 4 , LiSbF 6 , LiSCN, LiN (FSO 2 ) 2 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiB 10 Cl 10, lower aliphatic lithium carboxylate, LiCl, LiBr, LiI , Chloroborane lithium, borates, imide salts and the like can be used.
- lithium salt other than fluorine-containing lithium salt [lithium salt containing one or more elements in P, B, O, S, N, Cl (for example, LiPO 2 F 2 etc.)] You may use what added.
- LiPF 6 is preferably used from the viewpoint of ion conductivity and electrochemical stability.
- One electrolyte salt may be used alone, or two or more electrolyte salts may be used in combination. These electrolyte salts are preferably contained at a ratio of 0.8 to 1.5 mol with respect to 1 L of the nonaqueous electrolyte.
- a lithium salt having an oxalato complex as an anion can also be used.
- LiBOB lithium-bisoxalate borate
- a cyclic carbonate, a chain carbonate, a cyclic carboxylic acid ester or the like is used.
- the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC).
- the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).
- Examples of the cyclic carboxylic acid ester include ⁇ -butyrolactone (GBL) and ⁇ -valerolactone (GVL).
- Examples of the chain carboxylic acid ester include methyl propionate (MP) fluoromethyl propionate (FMP).
- a non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.
- the volume ratio of the cyclic carbonate to the chain carbonate in the mixed solvent is preferably regulated in the range of 2: 8 to 5: 5.
- esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and ⁇ -butyrolactone; compounds containing sulfone groups such as propane sultone; 1,2-dimethoxyethane, 1,2- Compounds containing ethers such as diethoxyethane, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, 2-methyltetrahydrofuran; butyronitrile, valeronitrile, n-heptanenitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile , 1,2,3-propanetricarbonitrile, compounds containing nitriles such as 1,3,5-pentanetricarbonitrile; compounds containing amides such as dimethylformamide, etc. can be used together with the above-mentioned solvents, These
- a layer made of an inorganic filler that has been conventionally used may be disposed at the interface between the positive electrode 1 and the separator 3 or the interface between the negative electrode 2 and the separator 3.
- the filler it is possible to use an oxide or a phosphoric acid compound using titanium, aluminum, silicon, magnesium or the like alone or plurally, and a material whose surface is treated with a hydroxide or the like.
- Example 1 [Production of positive electrode] LiOH and nickel cobalt aluminum composite hydroxide represented by Ni 0.91 Co 0.06 Al 0.03 (OH) 2 obtained by coprecipitation were converted into an oxide at 500 ° C. The mixture was mixed in an Ishikawa type mortar so that the molar ratio with the whole metal (Ni 0.91 Co 0.06 Al 0.03 ) was 1.05: 1.0. Next, this mixture was heat-treated at 760 ° C. for 20 hours in an oxygen atmosphere and then pulverized to obtain Li 1.05 Ni 0.91 Co 0.06 Al 0.03 O having a uniform secondary particle size of about 15 ⁇ m. Lithium nickel cobalt aluminum composite oxide particles represented by 2 were obtained.
- the suspension was filtered, and the obtained powder was sprayed with an aqueous solution having a concentration of 0.6 mol / L obtained by dissolving sodium fluoride in pure water. Thereafter, it was dried in vacuum at 200 ° C. to prepare a positive electrode active material.
- Example 1 since the pH of the suspension was as high as 11.5 to 12.0, the primary particles of erbium hydroxide precipitated in the suspension were bonded (aggregated) to form secondary particles. it is conceivable that. Moreover, in Example 1, since the ratio of Ni is as high as 91% and the ratio of trivalent Ni is increased, proton exchange is performed between LiNiO 2 and H 2 O at the primary particle interface of the lithium-containing transition metal oxide. A large amount of LiOH generated by the proton exchange reaction comes out from the inside of the interface where the primary particles and the primary particles on the secondary particle surface of the lithium-containing transition metal oxide are adjacent to each other.
- the adhesion amount of the erbium compound was measured by inductively coupled plasma ionization (ICP) emission analysis, and found to be 0.15 mass% with respect to the lithium nickel cobalt aluminum composite oxide in terms of erbium element. Moreover, when the adhesion amount of alkali metal fluoride was measured with the ion chromatograph, it was 0.10 mass% with respect to lithium nickel cobalt aluminum complex oxide in conversion of a fluorine element.
- ICP inductively coupled plasma ionization
- the positive electrode active material particles, carbon black as a conductive agent, and N-methyl-2-pyrrolidone solution in which polyvinylidene fluoride is dissolved as a binder, positive electrode active material particles, a conductive agent, and a binder Were weighed to a mass ratio of 100: 1: 1 and kneaded using TK Hibismix (Primics) to prepare a positive electrode mixture slurry.
- the positive electrode mixture slurry is applied to both surfaces of a positive electrode current collector made of an aluminum foil, dried, and then rolled with a rolling roller, and a current collector tab made of aluminum is further attached.
- a positive electrode plate having a positive electrode mixture layer formed on both sides of the electric body was produced.
- the packing density of the positive electrode active material in this positive electrode was 3.60 g / cm 3 .
- LiPF 6 Lithium hexafluorophosphate
- EC ethylene carbonate
- MEC methyl ethyl carbonate
- DMC dimethyl carbonate
- VC vinylene carbonate
- Example 2 A battery was produced in the same manner as in Example 1 except that in the production of the positive electrode active material, an aqueous solution having a concentration of 0.14 mol / L obtained by dissolving sodium fluoride in pure water was sprayed.
- the adhesion amount of the erbium compound was 0.15 mass% with respect to the lithium nickel cobalt aluminum composite oxide in terms of erbium element.
- the adhesion amount of the alkali metal fluoride was 0.10% by mass with respect to the lithium nickel cobalt aluminum composite oxide in terms of fluorine element.
- ⁇ Comparative Example 1> A battery was produced in the same manner as in Experimental Example 1 except that in the production of the positive electrode active material, an aqueous solution obtained by dissolving sodium fluoride in pure water was not sprayed on the lithium-containing transition metal oxide.
- the adhesion amount of the erbium compound was 0.15 mass% with respect to the lithium nickel cobalt aluminum composite oxide in terms of erbium element.
- Example 2 A battery was fabricated in the same manner as in Example 2 except that the pH of the suspension was kept constant at 9 while the erbium sulfate aqueous solution was added to the suspension. In addition, in order to adjust (maintain) the pH of the suspension to 9, a 10% by mass aqueous sodium hydroxide solution was appropriately added.
- the primary particles of erbium hydroxide having an average particle diameter of 10 nm to 50 nm were not converted into secondary particles, but the entire surface of the secondary particles of the lithium-containing transition metal oxide. It was confirmed that the particles were uniformly dispersed and adhered to the (projections and recesses). Further, it was confirmed that the alkali metal fluoride having an average particle size of 10 to 30 nm was adhered to the surfaces (convex portions and concave portions) of the secondary particles of the lithium-containing transition metal oxide.
- the adhesion amount of the erbium compound was 0.15% by mass with respect to the lithium nickel cobalt aluminum composite oxide in terms of erbium element. Moreover, the adhesion amount of the alkali metal fluoride was 0.10% by mass with respect to the lithium nickel cobalt aluminum composite oxide in terms of fluorine element.
- ⁇ Comparative example 4> In the production of the positive electrode active material, a battery was produced in the same manner as in Comparative Example 2 except that the erbium sulfate aqueous solution was not added and erbium hydroxide was not attached to the secondary particle surface of the lithium-containing transition metal oxide. did.
- the adhesion amount of the alkali metal fluoride was 0.10% by mass with respect to the lithium nickel cobalt aluminum composite oxide in terms of fluorine element.
- Table 1 shows DCRs after 100 cycles of the batteries of Examples 1 and 2 and Comparative Examples 1 to 5.
- the positive electrode active materials of the batteries of Examples 1 and 2 were adhered to both of the primary particles 20 of the lithium-containing transition metal oxide in which the secondary particles 25 of the rare earth compound were adjacent in the recesses 23. Yes.
- the surface alteration of the primary particles 20 of the adjacent lithium-containing transition metal oxide and cracking from the primary particle interface can be suppressed.
- the secondary particles 25 of the rare earth compound also have an effect of fixing (adhering) the primary particles 20 of the adjacent lithium-containing transition metal oxide, cracks are formed in the recesses 23 from the primary particle interface. It can be suppressed from occurring.
- the positive electrode active materials of the batteries of Examples 1 and 2 are of good quality on the entire surface of the secondary particles 21 of the lithium-containing transition metal oxide due to the rare earth compound on the surfaces of the secondary particles 21 of the lithium-containing transition metal oxide.
- a coating is produced.
- this coating film contains alkali metal and fluorine derived from alkali metal fluoride. And this Li ion permeable film suppresses decomposition of the electrolyte during the charge / discharge cycle.
- the positive electrode active material used in the battery of Comparative Example 1 is the same as the battery of Example 1 because the secondary particles of the rare earth compound are attached to both primary particles of the lithium-containing transition metal oxide that are adjacent to each other in the recesses. Furthermore, surface modification and cracking of the primary particles of the adjacent lithium-containing transition metal oxide are suppressed during the charge / discharge cycle.
- the positive electrode active material used in the battery of Comparative Example 1 since the alkali metal fluoride is not attached to the particle surface, the high-quality coating film formed on the entire surface of the secondary particle of the lithium-containing transition metal oxide Does not contain alkali metal and fluorine derived from alkali metal fluoride. For this reason, compared with the batteries of Examples 1 and 2, the decomposition reaction of the electrolytic solution during the charge / discharge cycle cannot be suppressed.
- FIG. 4 is a partial schematic cross-sectional view of the positive electrode active material particles of Comparative Example 2.
- the positive electrode active material used in the battery of Comparative Example 2 has a surface of the secondary particles 21 of the lithium-containing transition metal oxide without the primary particles 24 of the rare earth compound forming secondary particles. It adheres uniformly throughout. That is, in the battery of Comparative Example 2, since the secondary particles of the rare earth compound do not adhere to the recesses 23 on the surface of the secondary particles 21 of the lithium-containing transition metal oxide, the battery of Examples 1 and 2 is used. Compared with the positive electrode active material, the surface modification and cracking of the particle surface of the positive electrode active material cannot be suppressed.
- the positive electrode active material used in the battery of Comparative Example 2 has primary particles 24 of the rare earth compound and alkali metal fluoride particles 22 on the surface of the secondary particles 21 of the lithium-containing transition metal oxide.
- a good-quality film containing alkali metal and fluorine derived from alkali metal fluoride is generated on the entire surface of the secondary particles 21 of the lithium-containing transition metal oxide. For this reason, the decomposition reaction of the electrolytic solution during the charge / discharge cycle is suppressed.
- the positive electrode active material used in the battery of Comparative Example 3 is the same as the positive electrode active material of Comparative Example 2, but the primary particles of the rare earth compound do not form secondary particles, and the secondary particles of the lithium-containing transition metal oxide. It adheres uniformly to the entire surface. Furthermore, no alkali metal fluoride is attached to the surface of the lithium-containing transition metal oxide. Therefore, in the battery of Comparative Example 3, the surface modification and cracking on the particle surface of the positive electrode active material cannot be suppressed, and further, the decomposition reaction of the electrolyte solution during the charge / discharge cycle cannot be suppressed. Compared to the batteries of Examples 1 and 2, it is considered that the DCR after the charge / discharge cycle was increased due to, for example, an increase in the contact resistance between the particles and the interface resistance between the particles and the electrolyte.
- the positive electrode active material in which the secondary particles of the rare earth compound are attached to both of the primary particles of the lithium-containing transition metal oxide adjacent to each other in the recess (hereinafter, the secondary particles of the lithium-containing transition metal oxide
- the secondary particles of the lithium-containing transition metal oxide In the batteries of Examples 1 and 2 and the battery of Comparative Example 1 using the positive electrode active material that is agglomerated and adhered to the recesses of the first electrode, the primary particles of the rare earth compound form secondary particles.
- the DCR after 100 cycles is lower than 100 m ⁇ .
- the method of suppressing surface alteration and cracking on the particle surface of the positive electrode active material has a greater effect of suppressing the increase in DCR after the charge / discharge cycle than the method of suppressing decomposition of the electrolytic solution during the charge / discharge cycle. .
- the following reasons can be inferred for this point.
- the difference (100 m ⁇ ) in DCR after the charge / discharge cycle between the battery of Comparative Example 1 and the battery of Comparative Example 3 is, for example, after the charge / discharge cycle of the battery of Example 2 and the battery of Comparative Example 1. This is considered to be larger than the difference in DCR (55 m ⁇ ).
- the rare earth compound does not adhere to the secondary particles of the lithium-containing transition metal oxide, surface modification and cracking on the surface of the positive electrode active material cannot be suppressed. . Further, in the positive electrode active material used in the battery of Comparative Example 4, the alkali metal fluoride is adhered to the surface of the lithium-containing transition metal oxide, but the rare earth compound is not adhered. A thick film is not formed. For this reason, the decomposition suppression effect of the electrolyte solution during the charge / discharge cycle is not obtained.
- the decomposition of the electrolyte during the charge / discharge cycle cannot be suppressed, and the surface alteration and cracking of the positive electrode active material particles cannot be suppressed.
- the DCR after the charge / discharge cycle is increased due to, for example, an increase in the contact resistance between the particles and the interface resistance between the particles and the electrolyte.
- the battery of Comparative Example 5 since rare earth compounds and alkali metal fluorides are not attached to the lithium-containing transition metal oxide surface, surface modification and cracking of the positive electrode active material particles can be suppressed. Further, the effect of suppressing the decomposition of the electrolyte during the charge / discharge cycle is not obtained. Therefore, the battery of Comparative Example 5 has a higher DCR after the charge / discharge cycle, for example, because the contact resistance between the particles and the interfacial resistance between the particles and the electrolytic solution increase compared to the batteries of Examples 1 and 2. It is thought that it became.
- LiOH and nickel cobalt manganese composite hydroxide represented by Ni 0.35 Co 0.35 Mn 0.30 (OH) 2 obtained by coprecipitation were converted into an oxide at 500 ° C.
- the mixture was mixed in an Ishikawa type mortar so that the molar ratio of the entire metal (Ni 0.35 Co 0.35 Mn 0.30) was 1.05: 1.
- this mixture was pulverized after heat treatment at 1000 ° C. for 20 hours in an air atmosphere, so that Li 1.05 Ni 0.35 Co 0.35 Mn 0.30 O 2 having an average secondary particle size of about 15 ⁇ m.
- FIG. 5 is a partial schematic cross-sectional view of the positive electrode active material particles obtained in the reference example.
- the positive electrode active material obtained in the reference example has a secondary particle 25 of a rare earth compound formed by agglomeration of primary particles 24 of a rare earth compound, and a secondary particle of a lithium-containing transition metal oxide. 21 and adhered to the recesses 23 between the primary particles 20 of the lithium-containing transition metal oxide. However, it was confirmed that the secondary particles 25 of the rare earth compound adhering to the recesses 23 were attached only to one of the adjacent primary particles 20 of the lithium-containing transition metal oxide.
- the adhesion amount of the erbium compound was measured by the inductively coupled plasma ionization (ICP) emission analysis method, it was 0.15 mass% with respect to lithium nickel cobalt manganese complex oxide in terms of erbium element.
- the proportion of Ni is as low as 35% and the proportion of trivalent Ni is reduced, LiOH generated by the proton exchange reaction passes through the interface of the primary particles 20 of the lithium-containing transition metal oxide, It is considered that the reaction that appeared on the surface of the secondary particles 21 of the lithium-containing transition metal oxide hardly occurred.
- the pH of the suspension was as high as 11.5 to 12.0, and primary particles of erbium hydroxide precipitated in the suspension were bonded (aggregated) to form secondary particles.
- the secondary particles of erbium hydroxide adhere to the surface of the lithium-containing transition metal oxide, they almost adhere to the convex portions 26 on the surface of the secondary particles 21 of the lithium-containing transition metal oxide that easily collide. it is conceivable that.
- some of the secondary particles of erbium hydroxide may adhere to the recess 23.
- the secondary particles of erbium hydroxide are the primary lithium-containing transition metal oxide adjacent to each other in the recess 23. It adheres to only one of the particles 20.
- Example 3 A battery was produced in the same manner as in Example 2 except that a samarium sulfate solution was used instead of the erbium sulfate aqueous solution in the production of the positive electrode active material.
- the adhesion amount of the samarium compound was 0.13 mass% with respect to the lithium nickel cobalt aluminum composite oxide in terms of samarium element.
- Example 4 A battery was produced in the same manner as in Example 2 except that a neodymium sulfate solution was used instead of the erbium sulfate aqueous solution in the production of the positive electrode active material.
- the adhesion amount of the neodymium compound was 0.13 mass% with respect to the lithium nickel cobalt aluminum composite oxide in terms of neodymium elements.
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Abstract
Description
正極1は、例えば金属箔等の正極集電体と、正極集電体上に形成された正極活物質層とで構成される。正極集電体には、アルミニウムなどの正極の電位範囲で安定な金属の箔、当該金属を表層に配置したフィルム等を用いることができる。正極活物質層は、非水電解質二次電池用正極活物質(以下、正極活物質と呼ぶ場合がある)を含み、その他に、導電材及び結着材を含むことが好適である。
負極2は、例えば金属箔等の負極集電体と、負極集電体上に形成された負極活物質層とを備える。負極集電体には、銅などの負極の電位範囲で安定な金属の箔、銅などの負極の電位範囲で安定な金属を表層に配置したフィルム等を用いることができる。負極活物質層は、リチウムイオンを吸蔵・脱離可能な負極活物質の他に、結着剤を含むことが好適である。結着剤としては、正極の場合と同様にPTFE等を用いることもできるが、スチレン-ブタジエン共重合体(SBR)又はこの変性体等を用いることが好ましい。結着剤は、CMC等の増粘剤と併用されてもよい。
セパレータ3には、イオン透過性及び絶縁性を有する多孔性シートが用いられる。多孔性シートの具体例としては、微多孔薄膜、織布、不織布等が挙げられる。セパレータの材質としては、ポリエチレン、ポリプロピレン等のポリオレフィンが好適である。
非水電解質は、非水溶媒と、非水溶媒に溶解した電解質塩とを含む。非水電解質の電解質塩としては、例えばLiClO4、LiBF4、LiPF6、LiAlCl4、LiSbF6、LiSCN、LiN(FSO2)2、LiN(CF3SO2)2、LiN(C2F5SO2)2、LiN(CF3SO2)(C4F9SO2)、LiCF3SO3、LiCF3CO2、LiAsF6、LiB10Cl10、低級脂肪族カルボン酸リチウム、LiCl、LiBr、LiI、クロロボランリチウム、ホウ酸塩類、イミド塩類などを用いることができる。さらに、フッ素含有リチウム塩に、フッ素含有リチウム塩以外のリチウム塩〔P、B、O、S、N、Clの中の一種類以上の元素を含むリチウム塩(例えば、LiPO2F2等)〕を加えたものを用いても良い。この中でも、イオン伝導性と電気化学的安定性の観点から、LiPF6を用いることが好ましい。電解質塩は、1種を単独で用いてもよく、2種以上を組み合わせて用いてもよい。これら電解質塩は、非水電解質1Lに対し0.8~1.5molの割合で含まれていることが好ましい。また、オキサラト錯体をアニオンとするリチウム塩を用いることもできる。例として、LiBOB〔リチウム-ビスオキサレートボレート〕、Li[B(C2O4)F2]、Li[P(C2O4)F4]、Li[P(C2O4)2F2]が挙げられる。中でも特に負極で安定な被膜を形成させるLiBOBを用いることが好ましい。
[正極の作製]
LiOHと、共沈により得られたNi0.91Co0.06Al0.03(OH)2で表されるニッケルコバルトアルミニウム複合水酸化物を500℃で酸化物にしたものを、Liと遷移金属全体(Ni0.91Co0.06Al0.03)とのモル比が1.05:1.0となるように、石川式らいかい乳鉢にて混合した。次に、この混合物を酸素雰囲気中にて760℃で20時間熱処理後、粉砕することにより、均二次粒径が約15μmのLi1.05Ni0.91Co0.06Al0.03O2で表されるリチウムニッケルコバルトアルミニウム複合酸化物の粒子を得た。
ビウム塩水溶液を複数回にわけて加えた。懸濁液に硫酸エルビウム塩水溶液を加えている間の懸濁液のpHは11.5~12.0であった。懸濁液を濾過し、得られた粉末にフッ化ナトリウムを純水に溶解させて得られた0.6 mol/Lの濃度の水溶液を噴霧し、
その後真空中200℃で乾燥して正極活物質を作製した。
負極活物質としての人造黒鉛と、分散剤としてのCMC(カルボキシメチルセルロースナトリウム)と、結着剤としてのSBR(スチレン-ブタジエンゴム)とを、100:1:1の質量比で水溶液中において混合し、負極合剤スラリーを調製した。次に、この負極合剤スラリーを銅箔からなる負極集電体の両面に均一に塗布した後、乾燥させ、圧延ローラーにより圧延し、さらにニッケル製の集電タブを取り付けた。これにより、負極集電体の両面に負極合剤層が形成された負極極板を作製した。なお、この負極における負極活物質の充填密度は1.50g/cm3であった。
エチレンカーボネート(EC)と、メチルエチルカーボネート(MEC)と、ジメチルカーボネート(DMC)とを、2:2:6の体積比で混合した混合溶媒に対して、六フッ化リン酸リチウム(LiPF6)を1.3モル/リットルの濃度になるように溶解した。さらに、ビニレンカーボネート(VC)を上記混合溶媒に対して2.0質量%溶解させた非水電解液を調製した。
このようにして得た正極および負極を、これら両極間にセパレータを配置して渦巻き状に巻回した後、巻き芯を引き抜いて渦巻状の電極体を作製した。次に、この渦巻状の電極体を押し潰して、扁平型の電極体を得た。この後、この偏平型の電極体と上記非水電解液とを、アルミニウムラミネート製の外装体内に挿入し、電池を作製した。尚、当該電池のサイズは、厚み3.6mm×幅35mm×長さ62mmであった。また、当該非水電解質二次電池を4.20Vまで充電し、3.0Vまで放電したときの放電容量は950mAhであった。
正極活物質の作製において、フッ化ナトリウムを純水に溶解させて得られた0.14 mol/Lの濃度の水溶液を噴霧したこと以外は、実施例1と同様にして電池を作製した。エルビウム化合物の付着量は、エルビウム元素換算で、リチウムニッケルコバルトアルミニウム複合酸化物に対して0.15質量%であった。また、アルカリ金属フッ化物の付着量は、フッ素元素換算で、リチウムニッケルコバルトアルミニウム複合酸化物に対して0.10質量%であった。
正極活物質の作製において、フッ化ナトリウムを純水に溶解させて得られた水溶液をリチウム含有遷移金属酸化物に噴霧しなかったこと以外は、実験例1と同様にして電池を作製した。エルビウム化合物の付着量は、エルビウム元素換算で、リチウムニッケルコバルトアルミニウム複合酸化物に対して0.15質量%であった。
懸濁液に硫酸エルビウム塩水溶液を加えている間の懸濁液のpHを9で一定に保持したこと以外は、上記実施例2と同様にして電池を作製した。なお、上記懸濁液のpHを9に調整(保持)するために、10質量%の水酸化ナトリウム水溶液を適宜加えた。
正極活物質の作製において、フッ化ナトリウムを純水に溶解させて得られた水溶液をリチウム含有遷移金属酸化物に噴霧しなかったこと以外は、比較例2と同様にして電池を作製した。エルビウム化合物の付着量は、エルビウム元素換算で、リチウムニッケルコバルトアルミニウム複合酸化物に対して0.15質量%であった。
正極活物質の作製において、硫酸エルビウム塩水溶液を加えず、リチウム含有遷移金属酸化物の二次粒子表面に水酸化エルビウムを付着させなかったこと以外は、上記比較例2と同様にして電池を作製した。アルカリ金属フッ化物の付着量は、フッ素元素換算で、リチウムニッケルコバルトアルミニウム複合酸化物に対して0.10質量%であった。
正極活物質の作製において、硫酸エルビウム塩水溶液を加えず、また、フッ化ナトリウムを純水に溶解させて得られた水溶液を噴霧しなかったこと以外は、実施例1と同様にして電池を作製した。
上述のようにして作製した実施例1~2及び比較例1~5の電池について、下記条件での充放電を1サイクルとして、この充放電サイクルを100回繰り返し行った後、下記条件で100サイクル後のDCRを測定した。
・充電条件
475mAの電流で電池電圧が4.2V(正極電位はリチウム基準で4.3V)となるまで定電流充電を行い、電池電圧が4.2Vに達した後は、4.2Vの定電圧で電流値が30mAとなるまで定電圧充電を行った。
・放電条件
950mAの定電流で電池電圧が3.0Vとなるまで定電流放電を行った。
・休止条件
上記充電と放電の間の休止間隔は10分間とした。
上記100サイクル後の電池をSOC100%まで475mAの電流で充電した後、SOCが100%に到達した電池電圧で電流値が30mAとなるまで定電圧充電を行った。充電終了後120分間休止した時点のOCVを測定し、475mAで10秒間放電を行い放電10秒後の電圧を測定し、下記式(1)により100サイクル後のDCR(SOC100%)を測定した。
DCR(Ω)=(120分休止後のOCV(V) - 放電10秒後の電圧(V))/(放電10秒後の電流値(A))・・・(1)
LiOHと、共沈により得られたNi0.35Co0.35Mn0。30(OH)2で表されるニッケルコバルトマンガン複合水酸化物を500℃で酸化物にしたものを、Liと遷移金属全体(Ni0.35Co0.35Mn0。30)とのモル比が1.05:1になるように、石川式らいかい乳鉢にて混合した。次に、この混合物を空気雰囲気中にて1000℃で20時間熱処理後に粉砕することにより、平均二次粒径が約15μmのLi1.05Ni0.35Co0.35Mn0.30O2で表されるリチウムニッケルコバルトマンガン複合酸化物を得た。
正極活物質の作製において、硫酸エルビウム塩水溶液の代わりに、硫酸サマリウム溶液を用いたこと以外は、実施例2と同様にして電池を作製した。サマリウム化合物の付着量は、サマリウム元素換算で、リチウムニッケルコバルトアルミニウム複合酸化物に対して0.13質量%であった。
正極活物質の作製において、硫酸エルビウム塩水溶液の代わりに、硫酸ネオジム溶液を用いた以外は、実施例2と同様にして電池を作製した。ネオジム化合物の付着量は、ネオジム元素換算で、リチウムニッケルコバルトアルミニウム複合酸化物に対して0.13質量%であった。
Claims (5)
- リチウム含有遷移金属酸化物の一次粒子が凝集した二次粒子と、希土類化合物の一次粒子が凝集した二次粒子と、アルカリ金属フッ化物の粒子と、を含み、
前記希土類化合物の二次粒子は、前記リチウム含有遷移金属酸化物の二次粒子の表面において、隣接する一次粒子間に形成された凹部に付着し、且つ、前記希土類化合物の二次粒子は、前記凹部において隣接し合う前記一次粒子の両方に付着しており、
前記アルカリ金属フッ化物の粒子は、前記リチウム含有遷移金属酸化物の二次粒子の表面に付着している、非水電解質二次電池用正極活物質。 - 前記希土類化合物を構成する希土類元素が、ネオジム、サマリウム及びエルビウムから選ばれる少なくとも1種の元素である、請求項1に記載の非水電解質二次電池用正極活物質。
- 前記希土類化合物が、水酸化物及びオキシ水酸化物から選ばれる少なくとも1種の化合物である、請求項1又は2に記載の非水電解質二次電池用正極活物質。
- 前記リチウム含有遷移金属酸化物に占めるニッケルの割合が、リチウムを除く金属元素の総モル量に対して80モル%以上である、請求項1~3のいずれか1項に記載の非水電解質二次電池用正極活物質。
- 請求項1~4のいずれか1項に記載の非水電解質二次電池用正極活物質を含む正極を備える、非水電解質二次電池。
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