JP4897223B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

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

In recent years, a nonaqueous electrolyte secondary battery represented by a lithium ion secondary battery has attracted attention as a battery having a high energy density. This non-aqueous electrolyte secondary battery is a battery using a metal oxide as the positive electrode active material and a carbon-based material as the negative electrode active material, and its demand is rapidly expanding due to its high voltage and high energy density. is doing. In particular, a battery using LiCoO ₂ as a positive electrode active material is frequently used because of its high battery voltage, high energy density, and excellent cycle characteristics.

A non-aqueous electrolyte secondary battery using LiCoO ₂ as a positive electrode active material is theoretically charged with about 4.8 V on the basis of metallic lithium, so that all LiCoO ₂ Li is released, and the theoretical capacity is about It reaches up to 274 mAh / g. However, when the charging potential is increased to increase the capacity, the heavy load characteristic and the cycle characteristic are remarkably deteriorated, and the safety is lowered.

For this reason, in the conventional non-aqueous electrolyte secondary battery using LiCoO ₂ as the positive electrode active material, the maximum potential of the positive electrode during charging is limited to about 4.3 V with respect to metallic lithium, and LiCoO ₂ discharge in the battery The capacity has been limited to 140 mAh / g or less.

Therefore, in order to prevent deterioration of heavy load characteristics under high voltage of a non-aqueous electrolyte secondary battery using LiCoO ₂ as a positive electrode active material, a part of Co in LiCoO ₂ is replaced with a group IIIB element. It has been proposed to use a positive electrode active material in which the atomic ratio of substituent atoms to Co on the surface of the positive electrode active material particles is 1.5 times or more the average atomic ratio of substituent atoms to Co in the entire positive electrode active material particles (See Patent Document 1).
JP 2002-75356 A

  Currently, non-aqueous electrolyte secondary batteries are used in mobile devices such as mobile phones and personal digital assistants (PDAs), and with higher capacities, improved cycle characteristics and storage characteristics, as well as higher safety. It is requested.

  However, in the non-aqueous electrolyte secondary battery described in Patent Document 1, although the capacity is increased by high voltage charging and the heavy load characteristics are improved, the cycle characteristics, the storage characteristics, and the high safety are sufficiently improved. I have not been told.

  The present invention solves the above problems, and provides a non-aqueous electrolyte secondary battery that is further excellent in cycle characteristics, storage characteristics, and high safety while realizing high capacity by high voltage charging.

The non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has a composition formula Li _{(1 + δ)} as a positive electrode active material. A first oxide having a composition represented by Mn _x Ni _y Co _(1-xy) O ₂ , wherein δ, x, and y are −0.15 <δ <0.15, 0.1, respectively. <X ≦ 0.5, 0.5 <x + y < 1.0 is satisfied, the positive electrode has a composition represented by a composition formula Li ₂ MO ₃ , and M is Zr, Nb, Mo , W, Al, Si, Ga, seen second oxide further contains representative of at least one element selected from the group consisting of Ge and Sn, wherein the positive electrode, the second and the first oxide The second oxide is contained in an amount of 0.1% by mass to 10% by mass with respect to the total mass with the oxide .

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having a high capacity and excellent safety, and excellent cycle characteristics and storage characteristics even under a high voltage.

An example of the nonaqueous electrolyte secondary battery of the present invention is a lithium ion secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The positive electrode includes, as a positive electrode active material, a first oxide having a composition represented by a composition formula Li _{(1 + δ)} Mn _x Ni _y Co _(1-xy) O ₂ , , X, and y satisfy the relationships −0.15 <δ <0.15, 0.1 <x ≦ 0.5, and 0.5 <x + y ≦ 1.0, respectively. Furthermore, the positive electrode includes a second oxide containing at least one element selected from the group consisting of Ti, Zr, Nb, Mo, W, Al, Si, Ga, Ge, and Sn.

By using the first oxide represented by the above composition formula as the positive electrode active material, both high capacity and high safety of the battery can be realized. That is, even if almost all Li is moved from the positive electrode active material to the negative electrode side by high voltage charging for high capacity, the positive electrode can be stably maintained and heat generation of the positive electrode can be suppressed. Thereby, both high capacity and high safety of the battery can be achieved. In addition, since the first oxide is composed of a Li-containing composite oxide having a layered structure containing Mn and Ni, the stability of the positive electrode during charging while having a capacity equivalent to that of LiCoO ₂ that has been used conventionally. Therefore, it is possible to achieve both high capacity and high safety.

  In the composition formula of the first oxide, it is preferable that −0.03 ≦ y−x ≦ 0.03 because the safety of the battery can be further improved, and it is more preferable that x = y.

  Further, when the positive electrode contains the second oxide, it is possible to realize both improvement in cycle characteristics and storage characteristics in addition to increase in capacity and safety of the battery. This is because the presence of the second oxide containing the electrochemically stable element around or on the surface of the first oxide further improves the stability of the positive electrode during high voltage charging, and the battery It is considered that the cycle characteristics and the storage characteristics are improved in addition to the high safety.

  The at least one element selected from the group consisting of Ti, Zr, Nb, Mo, W, Al, Si, Ga, Ge, and Sn constituting the second oxide is all of the second oxide. As a constituent element, it is not necessary to exist separately from the first oxide, and a part thereof may be dissolved in the first oxide.

  Moreover, it is preferable that the said positive electrode contains 0.1 to 10 mass% of 2nd oxides with respect to the total mass of a 1st oxide and a 2nd oxide. This is because, within this range, the cycle characteristics and storage characteristics of the battery can be reliably improved, and a decrease in battery capacity can be suppressed.

The second oxide is represented by, for example, a composition formula Li ₂ MO ₃ . However, M represents at least one element selected from the group consisting of Ti, Zr, Nb, Mo, W, Al, Si, Ga, Ge, and Sn. The second oxide represented by the above composition formula is stable without being involved in charge and discharge, and the presence of the second oxide in the positive electrode improves the stability of the positive electrode during high-voltage charging. In addition to the high safety of the battery, it is considered that the cycle characteristics and the storage characteristics are improved.

  The first oxide and the second oxide may be present in the positive electrode in a physically mixed state, but the second oxide is fixed to the surface of the first oxide. The positive electrode active material particles may be formed as a unit. Examples of the form of the positive electrode active material particles include spherical particles, rod-like particles, plate-like particles, and fibrous particles.

The average particle diameter and specific surface area of the positive electrode active material particles are preferably 5 μm or more and 25 μm or less and 0.2 m ² / g or more and 0.6 m ² / g or less, respectively. This is because within this range, higher capacity and higher safety, and cycle characteristics and storage characteristics can be further improved.

Although the manufacturing method of the positive electrode active material (1st oxide) containing the said 2nd oxide is not specifically limited, For example, it can manufacture as follows. First, a first oxide having a composition represented by the composition formula Li _{(1 + δ)} Mn _x Ni _y Co _(1-xy) O ₂ , a hydroxide, carbonate, oxide, etc. of the element M , Lithium hydroxide, carbonate, etc. are mixed. Thereafter, the mixture is fired at a predetermined synthesis temperature in an oxidizing atmosphere to obtain a positive electrode active material containing the second oxide. This calcination can be performed in an oxygen atmosphere with an oxygen partial pressure of 0.19 to 1 atm, a synthesis temperature of 600 to 1000 ° C., and a synthesis time of 6 to 48 hours.

  Further, the positive electrode active material containing the second oxide can be produced simultaneously with the synthesis of the first oxide. That is, first, an aqueous solution in which sulfates, nitrates, and the like of manganese, nickel, and cobalt are dissolved in a predetermined ratio is added to an alkali hydroxide aqueous solution to cause reaction, and a coprecipitated hydroxide of manganese, nickel, and cobalt is added. obtain. Next, after thoroughly washing and drying, add lithium hydroxide, carbonate, etc., and hydroxide, carbonate, oxide, etc. of element M to the coprecipitated hydroxide and Mix. Thereafter, the mixture is fired at a predetermined synthesis temperature in an oxidizing atmosphere to obtain a positive electrode active material containing the second oxide. This calcination can be performed in an oxygen atmosphere with an oxygen partial pressure of 0.19 to 1 atm, a synthesis temperature of 600 to 1000 ° C., and a synthesis time of 6 to 48 hours.

  Presence of the first oxide and the second oxide in the positive electrode active material containing the second oxide can be confirmed by analyzing the positive electrode active material by X-ray diffraction.

  It is preferable that the positive electrode further includes a conductive additive and a binder. This is because the electron conductivity and strength of the positive electrode are improved. In this case, the positive electrode includes 94% by mass or more of the first oxide and the second oxide with respect to the total mass of the first oxide, the second oxide, the conductive additive, and the binder. It is preferable to contain 99% by mass or less, 0.5% by mass or more and 3% by mass or less of a conductive additive, and 0.5% by mass or more and 3% by mass or less of a binder. If it is within this range, it is possible to reduce the contents of the conductive additive and the binder that are not directly involved in the electrode reaction, so that the capacity of the electrode can be increased.

As the conductive additive for the positive electrode, any inorganic or organic material can be used as long as it is chemically stable in the battery. For example, graphite such as natural graphite and artificial graphite, acetylene black, ketjen black (trade name), carbon black such as channel black, furnace black, lamp black and thermal black, conductive fibers such as carbon fiber and metal fiber, aluminum Examples include metal powders such as powder, conductive whiskers made of carbon fluoride, zinc oxide, potassium titanate, etc., conductive metal oxides such as titanium oxide, or organic conductive materials such as polyphenylene derivatives. Or it can be used as a mixture. Among these, carbon black is particularly preferable. Since carbon black has a small average particle size of 0.01 μm to 1 μm, it can be filled in the gaps between the positive electrode active material particles, and a space that is not originally involved in the battery capacity can be used, so without reducing the amount of the positive electrode active material particles This is because electron conductivity can be imparted. The effect of this carbon black is remarkably exhibited when the average particle diameter and specific surface area of the positive electrode active material particles are 5 μm or more and 25 μm or less and 0.2 m ² / g or more and 0.6 m ² / g or less, respectively. The

As the positive electrode binder, any thermoplastic resin or thermosetting resin can be used as long as it is chemically stable in the battery. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrif Oroechiren copolymer (ECTFE), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer, ethylene - acrylic acid copolymer or its Na ⁺ Ionic cross-linked product, ethylene-methacrylic acid copolymer or its Na ⁺ ion cross-linked product, ethylene-methyl acrylate copolymer or its Na ⁺ ion cross-linked product, ethylene-methyl methacrylate copolymer or its Na ⁺ ion cross-linked product These can be used, and these can be used alone or in combination. Among these, PVDF and PTFE are particularly preferable. This is because the binding force can be exerted in a small amount.

  The positive electrode is formed, for example, by forming a positive electrode mixture obtained by appropriately adding a conductive additive or a binder to a positive electrode active material containing a second oxide and applying it to a current collector. Is used. The thickness of the positive electrode mixture layer applied to the current collector is usually 20 μm to 100 μm.

  The material for the current collector of the positive electrode is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed battery. For example, in addition to aluminum or aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of aluminum, aluminum alloy, or stainless steel can be used. . Among these, aluminum or an aluminum alloy is particularly preferable. This is because they are lightweight and have high electron conductivity. As the current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like made of the above material is used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, they are 1 micrometer-500 micrometers.

  Examples of the negative electrode active material for the negative electrode include graphite, pyrolytic carbons, cokes, glassy carbons, sintered bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, lithium such as Si and Sn. And a metal that can be alloyed or an alloy thereof.

  As the negative electrode, for example, a negative electrode mixture in which a binder or the like is appropriately added to a negative electrode active material is applied to a current collector and formed into a band-shaped molded body. The thickness of the negative electrode mixture layer applied to the current collector is usually 20 μm to 100 μm. In addition, although it is not necessary to add a conductive support agent to a negative electrode, you may add.

  As the conductive auxiliary for the negative electrode, any inorganic or organic material can be used as long as it is chemically stable in the battery. For example, graphite such as natural graphite and artificial graphite, acetylene black, ketjen black (trade name), carbon black such as channel black, furnace black, lamp black and thermal black, conductive fibers such as carbon fiber and metal fiber, copper Metal powders such as powder, nickel powder, conductive whiskers made of carbon fluoride, zinc oxide, potassium titanate, etc., conductive metal oxides such as titanium oxide, or organic conductive materials such as polyphenylene derivatives, etc. These can be used alone or in combination.

  The negative electrode preferably includes 90% to 99% by mass of the negative electrode active material and 1% to 10% by mass of the binder with respect to the total mass of the negative electrode active material and the binder. This is because, within this range, the content of the binder that does not directly participate in the electrode reaction is small, so that the capacity of the electrode can be increased.

As the binder for the negative electrode, the same binders as those used for the positive electrode described above can be used. Among them, styrene butadiene rubber, polyvinylidene fluoride, ethylene-acrylic acid copolymer or Na ⁺ ion thereof is particularly preferable. Cross-linked product, ethylene-methacrylic acid copolymer or its Na ⁺ ion cross-linked product, ethylene-methyl acrylate copolymer or its Na ⁺ ion cross-linked product, ethylene-methyl methacrylate copolymer or its Na ⁺ ion cross-linked product preferable.

  The material for the current collector of the negative electrode is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed battery. For example, in addition to copper or copper alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of copper, copper alloy, or stainless steel can be used. . Among these, copper or a copper alloy is particularly preferable. This is because they are not alloyed with lithium and have high electron conductivity. Other conditions for the current collector are the same as those for the positive electrode current collector described above.

  The non-aqueous electrolyte includes a solvent and an electrolyte salt. Examples of the solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone, 1, 2 -Dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, Sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether, 1,3-propane sultone, etc. One protic organic solvent, or a mixture of two or more kinds mixed solvent can be used. In these, the mixed solvent of EC, MEC, and DEC is preferable, and it is especially preferable that this mixed solvent contains 15 volume% or more and 80 volume% or less of DEC with respect to the whole volume of a mixed solvent. This is because within this range, the stability of the solvent during high-voltage charging is improved while maintaining low temperature characteristics and cycle characteristics.

As the electrolyte salt, a salt of a fluorine-containing compound such as lithium perchlorate, organic boron lithium salt, trifluoromethanesulfonate, imide salt, or the like is preferably used. Specific examples of the electrolyte salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (Rf ₃ OSO ₂ ) ₂ , Rf represents a fluoroalkyl group. ] Etc. are used alone or in admixture of two or more. In particular, LiPF ₆ and LiBF ₄ are desirable because of their good charge / discharge characteristics. This is because these fluorine-containing organolithium salts are highly anionic and easily ion-separated, so that they are easily dissolved in the solvent. The concentration of the electrolyte salt in the solvent is not particularly limited, but is usually 0.5 mol / L or more and 1.7 mol / L or less.

  The material and shape of the separator are not particularly limited, and those having insulating properties, high ion permeability, low electrical resistance, and high liquid retention are preferable. Usually, a separator having a thickness of 10 μm to 300 μm and a porosity of 30 to 80% is used. In addition, the pore diameter of the separator is preferably in a range in which the active material, the conductive auxiliary agent, the binder, and the like detached from the electrode do not permeate, for example, 0.01 μm to 1 μm is preferable.

  It is preferable that the separator has a shutdown function in which the separator is softened or melted according to heat generated by an internal short circuit (100 to 140 ° C.) so that the pores of the separator are closed and current is cut off. This is because the safety of the battery can be further improved. Specifically, for example, a microporous film made of polyolefin such as polyethylene, polypropylene, or polymethylpentene, a nonwoven fabric, or the like is preferably used as a separator because a shutdown function can be provided. Further, by using a separator having a multilayer structure constituted by laminating a plurality of microporous films and nonwoven fabrics of the above materials or by laminating a plurality of microporous films or non-woven fabrics, in a high temperature environment. The reliability when used can be further increased.

  Next, the nonaqueous electrolyte secondary battery of the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view showing an example of the nonaqueous electrolyte secondary battery of the present invention, and FIG. 2 is a cross-sectional view taken along the line II of FIG. In the following description, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte are the same as those described in the above embodiment, and thus detailed description thereof is omitted.

  In FIG. 1, the nonaqueous electrolyte secondary battery 1 includes a rectangular battery case 2 and a cover plate 3. The battery case 2 is made of a metal such as an aluminum alloy and serves as a battery exterior material. The battery case 2 also serves as a positive electrode terminal. The cover plate 3 is also formed of a metal such as an aluminum alloy and seals the opening of the battery case 2. The lid 3 is provided with a terminal 5 made of a metal such as stainless steel via an insulating packing 4 made of a resin such as polypropylene.

  In FIG. 2, the nonaqueous electrolyte secondary battery 1 includes a positive electrode 6, a negative electrode 7, and a separator 8. The positive electrode 6 and the negative electrode 7 are spirally wound via a separator 8 and then pressed so as to be flattened to form an electrode winding body 9 having a flat winding structure in a battery case 2 together with a nonaqueous electrolyte. It is stored. However, in FIG. 2, in order to avoid complication, the metal foil, the non-aqueous electrolyte, and the like used as the current collector used for manufacturing the positive electrode 6 and the negative electrode 7 are not illustrated. Further, the inner peripheral side portion of the electrode winding body 9 is not cross-sectional.

  Further, an insulator 10 formed of a resin sheet such as PTFE is disposed at the bottom of the battery case 2, and a positive electrode lead body 11 connected to one end of each of the positive electrode 6 and the negative electrode 7 from the electrode winding body 9 and The negative electrode lead body 12 is drawn out. The positive electrode lead body 11 and the negative electrode lead body 12 are made of a metal such as nickel. A lead plate 14 made of metal such as stainless steel is attached to the terminal 5 via an insulator 13 made of resin such as polypropylene.

  The cover plate 3 is inserted into the opening of the battery case 2, and the opening of the battery case 2 is sealed and the inside of the battery is sealed by welding the joint of both.

  In FIG. 2, by directly welding the positive electrode lead body 11 to the lid plate 3, the battery case 2 and the lid plate 3 function as positive electrode terminals, and the negative electrode lead body 12 is welded to the lead plate 14. By connecting the negative electrode lead body 12 and the terminal 5 through 14, the terminal 5 functions as a negative electrode terminal. However, depending on the material of the battery case 2, the sign may be reversed. .

  As the battery case 2, a metal square case is used, but a metal cylindrical case or a laminate case made of a laminate film can also be used.

  Although the manufacturing method of the said nonaqueous electrolyte secondary battery 1 is not specifically limited, it charges after accommodating the positive electrode 6, the negative electrode 7, the separator 8, and the nonaqueous electrolyte in the battery case 2, and before sealing a battery completely. It is preferable to carry out. This is because gas generated at the beginning of charging and residual moisture in the battery can be removed outside the battery.

  Next, based on an Example, this invention is demonstrated more concretely. However, the present invention is not limited to the following examples.

  A nonaqueous electrolyte secondary battery having the same structure as that shown in FIGS. 1 and 2 was produced as follows.

<Preparation of positive electrode>
First, a positive electrode active material (first oxide) containing a second oxide was produced as follows. In the reaction vessel, 2% by mass of ammonia water whose pH was adjusted to about 12 by adding sodium hydroxide was prepared, and while stirring vigorously, 1.02 mol / L of manganese sulfate and 1.02 mol of nickel sulfate were added thereto. / L and cobalt sulfate 0.96 mol / L mixed aqueous solution at a rate of 46 mL / min and 25% by mass of aqueous ammonia at a rate of 3.3 mL / min were respectively added dropwise using a metering pump, and Mn and A coprecipitated hydroxide of Ni and Co was produced. At this time, the temperature of the reaction solution was maintained at 50 ° C., and a 3.2 mol / L sodium hydroxide aqueous solution was simultaneously added dropwise so that the pH of the reaction solution was maintained at about 12. Further, during the reaction, nitrogen gas was purged at a rate of 1 L / min so that the atmosphere of the reaction solution became an inert atmosphere.

The obtained product was washed with water, filtered and dried to obtain a hydroxide containing Mn, Ni and Co in an atomic ratio of 0.34: 0.34: 0.32. 1 mol of LiOH · H ₂ O was mixed with 1 mol of this hydroxide, and the mixture was dispersed with ethanol to form a slurry, and then mixed with a planetary ball mill for 40 minutes. Next, this mixture is put in an alumina crucible, heated to 800 ° C. in an air stream of 1 L / min, kept at that temperature for 2 hours for preheating, and further heated to 1000 ° C. for 12 hours. The first composite oxide was synthesized by firing. To 1 mol of the first composite oxide, 0.05 mol of zirconium hydroxide and 0.05 mol of LiOH.H ₂ O were mixed, and the mixture was mixed for 40 minutes with a planetary ball mill. Next, the mixture is put in an alumina crucible, heated to 800 ° C. in an air stream of 1 L / min, kept at that temperature for 2 hours, preheated, further heated to 1000 ° C. and fired for 12 hours Thus, a composite oxide containing zirconium was synthesized. The composite oxide containing zirconium was pulverized in a mortar and stored in a desiccator as a positive electrode active material of this example.

Next, the positive electrode active material of this example was analyzed by X-ray diffraction. FIG. 3 shows the X-ray diffraction pattern of the positive electrode active material of this example and the X-ray diffraction pattern of Li _0.99 Mn _0.34 Ni _0.34 Co _0.32 O ₂ . FIG. 4 is an enlarged view of part A in FIG. 3, and a characteristic peak of Li ₂ ZrO ₃ is indicated by ●. FIG. 3 shows that the positive electrode active material of this example mainly includes an oxide (first oxide) represented by the composition formula Li _0.99 Mn _0.34 Ni _0.34 Co _0.32 O ₂ . FIG. 4 also shows that the positive electrode active material of this example includes an oxide (second oxide) represented by the composition formula Li ₂ ZrO ₃ .

Then, when the average particle diameter and BET specific surface area of the positive electrode active material of a present Example were measured, they were 10 micrometers and 0.25 m < ² > / g, respectively. The average particle size was measured with a laser scattering type particle size distribution measuring device, and the BET specific surface area was measured with a one-point type BET measuring device utilizing N ₂ gas adsorption.

  Further, 0.2 g of the positive electrode active material of this example was put in a 100 mL container, and 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added to the container in this order and heated to dissolve the positive electrode active material. After cooling this, it was further diluted 25 times with water, and the composition of the positive electrode active material was measured by inductively coupled high-frequency plasma spectroscopic analysis (ICP spectroscopic analysis). From the result of the ICP spectroscopic analysis and the result of the X-ray diffraction analysis, the positive electrode active material of the present example is the second oxide with respect to the total mass of the first oxide and the second oxide. It was found that 5 mass% was contained.

  Next, 96 parts by mass of the positive electrode active material is mixed with 1 part by mass of artificial graphite having an average particle diameter of 2 μm and acetylene black (AB) having an average particle diameter of 0.05 μm as a conductive auxiliary agent. As a binder, 2 parts by mass of PVDF was dissolved in N-methylpyrrolidone and added to obtain a positive electrode mixture slurry. That is, the positive electrode active material is 96% by mass, the artificial graphite is 1% by mass, AB is 1% by mass, and the binder is 2% by mass with respect to the total mass of the positive electrode active material, the conductive additive and the binder. It was a ratio.

Subsequently, this positive electrode mixture slurry was applied to both sides of an aluminum foil having a thickness of 15 μm, and then vacuum drying was performed at 120 ° C. for 12 hours. Thereafter, a nickel lead body was welded to produce a strip-like positive electrode. The electrode density of this positive electrode was 3.35 g / cm ³ .

<Production of negative electrode>
Water was added to 97.5 parts by mass of natural graphite having an average particle diameter of 10 μm as a negative electrode active material, 1.5 parts by mass of styrene butadiene rubber as a binder, and 1 part by mass of carboxymethyl cellulose as a thickener. It mixed and it was set as the negative mix slurry. This negative electrode mixture slurry was applied to both sides of a 10 μm thick copper foil, and then vacuum dried at 120 ° C. for 12 hours. Thereafter, a lead body made of nickel was welded to produce a strip-shaped negative electrode. The electrode density of this negative electrode was 1.65 g / cm ³ .

<Preparation of non-aqueous electrolyte>
As the non-aqueous electrolyte, a solution in which 1 mol / L of LiPF ₆ was dissolved in a mixed solvent having a volume ratio of 1: 1: 1 between EC, MEC, and DEC was prepared.

<Battery assembly>
The belt-like positive electrode is stacked on the belt-like negative electrode via a microporous polyethylene separator (porosity: 41%) having a thickness of 18 μm, wound in a spiral shape, and then pressed so as to be flat. Thus, an electrode winding body having a flat winding structure was formed, and the electrode winding body was fixed with an insulating tape made of polypropylene. Next, the electrode winding body is inserted into a rectangular battery case made of aluminum alloy having an outer dimension of 4.0 mm in thickness, 34 mm in width, and 50 mm in height, and the lead body is welded. The plate was welded to the open end of the battery case. Thereafter, the non-aqueous electrolyte was injected from an inlet provided in the lid plate and allowed to stand for 1 hour.

  As described above, the nonaqueous electrolyte secondary battery of this example was produced. In addition, the design electric capacity of the nonaqueous electrolyte secondary battery of the present example was set to 1000 mAh.

To 1 mol of the first composite oxide containing Mn, Ni, and Co synthesized in the same manner as in Example 1 at an atomic ratio of 0.34: 0.34: 0.32, 0.03 mol of titanium hydroxide, A positive electrode active material of this example was obtained in the same manner as in Example 1 except that 0.03 mol of LiOH.H ₂ O was mixed.

Next, as a result of analyzing the positive electrode active material of this example by X-ray diffraction in the same manner as in Example 1, the positive electrode active material of this example is represented by the composition formula Li _0.99 Mn _0.34 Ni _0.34 Co _0.32 O _2. It was found that an oxide (second oxide) represented by the composition formula Li ₂ TiO ₃ was further included.

Subsequently, when the average particle diameter and the BET specific surface area of the positive electrode active material of this example were measured in the same manner as in Example 1, they were 10 μm and 0.25 m ² / g, respectively.

  Further, the composition of the positive electrode active material of this example was measured by ICP spectroscopic analysis in the same manner as in Example 1. From the result of the ICP spectroscopic analysis and the result of the X-ray diffraction analysis, the positive electrode active material of the present example is the second oxide with respect to the total mass of the first oxide and the second oxide. It was found that 4 mass% was contained.

Next, a nonaqueous electrolyte secondary battery of this example was produced in the same manner as in Example 1 except that the above positive electrode active material was used. The electrode density of the positive electrode of this example was 3.35 g / cm ³ .

To 1 mol of the first composite oxide containing Mn, Ni, and Co synthesized in the same manner as in Example 1 in an atomic ratio of 0.34: 0.34: 0.32, 0.03 mol of germanium hydroxide, A positive electrode active material of this example was obtained in the same manner as in Example 1 except that 0.03 mol of LiOH.H ₂ O was mixed.

Next, as a result of analyzing the positive electrode active material of this example by X-ray diffraction in the same manner as in Example 1, the positive electrode active material of this example is represented by the composition formula Li _0.99 Mn _0.34 Ni _0.34 Co _0.32 O _2. It was found that an oxide (second oxide) represented by the composition formula Li ₂ GeO ₃ was further included.

Subsequently, when the average particle diameter and the BET specific surface area of the positive electrode active material of this example were measured in the same manner as in Example 1, they were 10 μm and 0.25 m ² / g, respectively.

  Further, the composition of the positive electrode active material of this example was measured by ICP spectroscopic analysis in the same manner as in Example 1. From the result of the ICP spectroscopic analysis and the result of the X-ray diffraction analysis, the positive electrode active material of the present example is the second oxide with respect to the total mass of the first oxide and the second oxide. It was found that 5 mass% was contained.

Next, a nonaqueous electrolyte secondary battery of this example was produced in the same manner as in Example 1 except that the above positive electrode active material was used. The electrode density of the positive electrode of this example was 3.35 g / cm ³ .

To 1 mol of the first composite oxide containing Mn, Ni and Co synthesized in the same manner as in Example 1 in an atomic ratio of 0.34: 0.34: 0.32, 0.03 mol of tin hydroxide, A positive electrode active material of this example was obtained in the same manner as in Example 1 except that 0.03 mol of LiOH.H ₂ O was mixed.

Next, as a result of analyzing the positive electrode active material of this example by X-ray diffraction in the same manner as in Example 1, the positive electrode active material of this example is represented by the composition formula Li _0.99 Mn _0.34 Ni _0.34 Co _0.32 O _2. It was found that an oxide (second oxide) represented by the composition formula Li ₂ SnO ₃ was further included.

Subsequently, when the average particle diameter and the BET specific surface area of the positive electrode active material of this example were measured in the same manner as in Example 1, they were 10 μm and 0.25 m ² / g, respectively.

  Further, the composition of the positive electrode active material of this example was measured by ICP spectroscopic analysis in the same manner as in Example 1. From the result of the ICP spectroscopic analysis and the result of the X-ray diffraction analysis, the positive electrode active material of the present example is the second oxide with respect to the total mass of the first oxide and the second oxide. It was found that 6 mass% was contained.

Next, a nonaqueous electrolyte secondary battery of this example was produced in the same manner as in Example 1 except that the above positive electrode active material was used. The electrode density of the positive electrode of this example was 3.35 g / cm ³ .

  In the reaction vessel, 2% by mass of ammonia water having a pH adjusted to about 12 by adding sodium hydroxide was prepared, and while stirring this strongly, manganese sulfate 1.18 mol / L, nickel sulfate 1.18 mol / L and a mixed aqueous solution containing 0.64 mol / L of cobalt sulfate were added dropwise at a rate of 46 mL / min and 25% by mass of ammonia water at a rate of 3.3 mL / min using a metering pump. A coprecipitated hydroxide of Ni and Co was produced. At this time, the temperature of the reaction solution was maintained at 50 ° C., and a 3.2 mol / L sodium hydroxide aqueous solution was simultaneously added dropwise so that the pH of the reaction solution was maintained at about 12. Further, during the reaction, nitrogen gas was purged at a rate of 1 L / min so that the atmosphere of the reaction solution became an inert atmosphere.

The obtained product was washed with water, filtered and dried to obtain a hydroxide containing Mn, Ni and Co in an atomic ratio of 0.39: 0.39: 0.22. Using this hydroxide, a first composite oxide was synthesized in the same manner as in Example 1. A positive electrode active material was obtained in the same manner as in Example 1 except that 1 mol of the first composite oxide was mixed with 0.03 mol of zirconium hydroxide and 0.03 mol of LiOH.H ₂ O.

Next, the positive electrode active material of this example was analyzed by X-ray diffraction in the same manner as in Example 1. As a result, the positive electrode active material of this example was represented by the composition formula Li _1.02 Mn _0.39 Ni _0.39 Co _0.22 O _2. It was found that an oxide (second oxide) represented by a composition formula Li ₂ ZrO ₃ was further included.

Subsequently, when the average particle diameter and the BET specific surface area of the positive electrode active material of this example were measured in the same manner as in Example 1, they were 10 μm and 0.25 m ² / g, respectively.

  Further, the composition of the positive electrode active material of this example was measured by ICP spectroscopic analysis in the same manner as in Example 1. From the result of the ICP spectroscopic analysis and the result of the X-ray diffraction analysis, the positive electrode active material of the present example is the second oxide with respect to the total mass of the first oxide and the second oxide. It was found that 5 mass% was contained.

Next, a nonaqueous electrolyte secondary battery of this example was produced in the same manner as in Example 1 except that the above positive electrode active material was used. The electrode density of the positive electrode of this example was 3.30 g / cm ³ .

To 1 mol of the first composite oxide containing Mn, Ni, and Co synthesized in the same manner as in Example 5 in an atomic ratio of 0.39: 0.39: 0.22, 0.03 mol of titanium hydroxide, A positive electrode active material was obtained in the same manner as in Example 1 except that 0.03 mol of LiOH.H ₂ O was mixed.

Next, the positive electrode active material of this example was analyzed by X-ray diffraction in the same manner as in Example 1. As a result, the positive electrode active material of this example was represented by the composition formula Li _1.02 Mn _0.39 Ni _0.39 Co _0.22 O _2. It was found that an oxide (second oxide) represented by the composition formula Li ₂ TiO ₃ was further included.

Subsequently, when the average particle diameter and the BET specific surface area of the positive electrode active material of this example were measured in the same manner as in Example 1, they were 10 μm and 0.25 m ² / g, respectively.

  Further, the composition of the positive electrode active material of this example was measured by ICP spectroscopic analysis in the same manner as in Example 1. From the result of the ICP spectroscopic analysis and the result of the X-ray diffraction analysis, the positive electrode active material of the present example is the second oxide with respect to the total mass of the first oxide and the second oxide. It was found that 4 mass% was contained.

Next, a nonaqueous electrolyte secondary battery of this example was produced in the same manner as in Example 1 except that the above positive electrode active material was used. The electrode density of the positive electrode of this example was 3.30 g / cm ³ .

(Comparative Example 1)
In the reaction vessel, 2% by mass of ammonia water whose pH was adjusted to about 12 by adding sodium hydroxide was prepared, and while stirring vigorously, 1.03 mol / L manganese sulfate and 1.03 mol nickel sulfate were added thereto. / L and cobalt sulfate 0.97 mol / L mixed aqueous solution at a rate of 46 mL / min, and 25% by mass of aqueous ammonia at a rate of 3.3 mL / min. A coprecipitated hydroxide of Ni and Co was produced. At this time, the temperature of the reaction solution was maintained at 50 ° C., and a 3.2 mol / L sodium hydroxide aqueous solution was simultaneously added dropwise so that the pH of the reaction solution was maintained at about 12. Further, during the reaction, nitrogen gas was purged at a rate of 1 L / min so that the atmosphere of the reaction solution became an inert atmosphere.

The obtained product was washed with water, filtered and dried to obtain a hydroxide containing Mn, Ni and Co in an atomic ratio of 0.34: 0.34: 0.32. 1 mol of LiOH · H ₂ O was mixed with 1 mol of this hydroxide, and the mixture was dispersed in ethanol to form a slurry, followed by mixing with a planetary ball mill for 40 minutes and drying at room temperature. Next, the mixture is put in an alumina crucible, heated to 800 ° C. in an air stream of 1 L / min, kept at that temperature for 2 hours, preheated, further heated to 1000 ° C. and fired for 12 hours Thus, a composite oxide was synthesized. The synthesized composite oxide was pulverized in a mortar and stored in a desiccator as a positive electrode active material of this comparative example.

Further, when the composition of this positive electrode active material was measured by ICP spectroscopic analysis in the same manner as in Example 1, it was found to be Li _0.99 Mn _0.34 Ni _0.34 Co _0.32 O ₂ .

Next, a nonaqueous electrolyte secondary battery of this comparative example was produced in the same manner as in Example 1 except that the positive electrode active material was used. The electrode density of the positive electrode of this comparative example was 3.35 g / cm ³ .

(Comparative Example 2)
A nonaqueous electrolyte secondary battery of this comparative example was produced in the same manner as in Example 1 except that LiCoO ₂ was used as the positive electrode active material. The electrode density of the positive electrode of this comparative example was 3.55 g / cm ³ .

<Capacity test>
Each battery of Examples 1 to 6 and Comparative Examples 1 and 2 was charged at a constant current at 20 ° C. until it reached 4.4 V at 0.2 A, and then at a constant voltage of 4.4 V until the current value reached 0.02 A. Charged. Then, it discharged to 3.0V at 0.2A at 20 degreeC, and measured the discharge capacity.

<Overcharge test>
Each battery after the capacity test was charged to 1.0 V at 12 A and then charged at a constant voltage of 12 V. When the surface temperature of the battery exceeded 130 ° C., it was determined as “bad”. The number of samples of the test battery was 3, and if any of these batteries was defective, it was judged as “failed”, and if there were no bad batteries, it was judged as “passed”, and the overcharge characteristics were evaluated. .

<Cycle test>
The batteries of Examples 1 to 6 and Comparative Examples 1 and 2 that were newly produced were charged at a constant current of 1.0 A and 4.4 V at 20 ° C., and then the current value was 0.1 A. A constant voltage charge was performed at 4 V, and then a charge / discharge cycle of discharging to 3.0 V at 1.0 A at 20 ° C. was repeated 300 times, and the discharge capacity at the first cycle and the discharge capacity at the 300th cycle were measured.

  Next, using the discharge capacity at the first cycle and the discharge capacity at the 300th cycle, the capacity retention rate was calculated by the following formula to evaluate the cycle characteristics.

(Equation 1)
Capacity retention rate (%) = (discharge capacity at 300th cycle / discharge capacity at the first cycle) × 100
<Storage characteristics test>
The batteries of Examples 1 to 6 and Comparative Examples 1 and 2 that were newly produced were charged at a constant current of 0.2 A at 20 ° C. until reaching 4.4 V, and then until the current value reached 0.02 A. Constant voltage charging was performed at 4V. Then, it discharged to 3.0V at 0.2A at 20 degreeC, and measured the discharge capacity. Next, after charging in the same manner as described above, it was stored in a thermostatic bath at 60 ° C. for 20 days. The battery after storage was naturally cooled to 20 ° C., and then each battery was discharged to 3.0 V at 0.2 A at 20 ° C., and the discharge capacity after storage was measured. Subsequently, using the discharge capacity before storage and the discharge capacity after storage, the capacity recovery rate was calculated by the following formula, and the storage characteristics were evaluated.

(Equation 2)
Capacity recovery rate (%) = (discharge capacity after storage / discharge capacity before storage) × 100
The results are shown in Table 1.

From Table 1, the main component is a first oxide having a composition represented by Li _{(1 + δ)} Mn _x Ni _y Co _(1-xy) O ₂ , and Ti, Zr, Nb, Mo, W, Al In Examples 1 to 6 using the positive electrode active material further including a second oxide containing at least one element selected from the group consisting of Si, Ga, Ge, and Sn, high capacity and high safety It can be seen that a nonaqueous electrolyte secondary battery excellent in cycle characteristics and storage characteristics even under high voltage can be provided. On the other hand, in Comparative Example 1 not including the second oxide, the cycle characteristics and the storage characteristics were deteriorated.

  This is because the positive electrode active material in the vicinity of the positive electrode surface is exposed to the highest potential, so that the reaction with the electrolytic solution (liquid electrolyte) and the collapse of the crystal structure easily proceed, and the collapsed portion reacts with the electrolytic solution. Therefore, a stable second oxide that does not participate in charge / discharge is distributed around or on the surface of the positive electrode active material in Examples 1 to 6, and the positive electrode active material is disposed on the surface of the positive electrode. By making it exist, the stability of the positive electrode active material under a high voltage is improved, and the reaction with the electrolyte and the collapse of the crystal structure are less likely to occur. It is considered that the storage characteristics have been improved. On the other hand, in Comparative Example 1, it is considered that the cycle characteristics and the storage characteristics are deteriorated for the opposite reason.

Moreover, in the comparative example ₂ which used LiCoO2 for the positive electrode active material, it turns out that an overcharge test fails and there exists a problem in safety. It can also be seen that in Comparative Example 2, the cycle characteristics were also significantly reduced. From this, it is considered that it is difficult to use a LiCoO ₂ -based positive electrode active material in a battery currently used for high voltage charging.

  Using the positive electrode active material of Example 2 as a reference, Example 1 using a positive electrode active material in which the average particle size and BET specific surface area were changed as shown in Table 2 by changing the firing temperature, firing time, and pulverization conditions. A nonaqueous electrolyte secondary battery was produced in the same manner as described above. Subsequently, a capacity test, an overcharge test, a cycle test, and a storage characteristic test were performed using each battery in the same manner as described above. The results are shown in Table 3. Table 2 also shows the electrode density of the positive electrode of each battery.

Table 2 and Table 3, the average particle size and specific surface area of the positive electrode active material, 5 [mu] m or more 25μm or less, it can be seen that the improved battery characteristics when below 0.2 m ² / g or more 0.6 m ² / g.

  Based on the composition of the positive electrode of Example 1, the composition of the positive electrode was changed as shown in Table 4, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1. Subsequently, a capacity test, an overcharge test, a cycle test, and a storage characteristic test were performed using each battery in the same manner as described above. The results are shown in Table 5. However, in Example 13, ketjen black (KB) having an average particle size of 0.02 μm was used in place of acetylene black (AB). Table 4 also shows the electrode density of the positive electrode of each battery.

  From Tables 4 and 5, in the composition of the positive electrode, the conductive additive is 0.5% by mass or more and 3% by mass or less with respect to the total mass of the positive electrode active material, the conductive auxiliary agent, and the binder. It can be seen that the battery characteristics are improved when the content is 0.5 mass% or more and 3 mass% or less.

  As described above, the present invention can provide a non-aqueous electrolyte secondary battery having a high capacity and excellent safety, and excellent cycle characteristics and storage characteristics even under a high voltage.

It is an external appearance perspective view which shows an example of the nonaqueous electrolyte secondary battery of this invention. It is sectional drawing of the II line | wire of FIG. Is a diagram showing a positive electrode active X-ray diffraction pattern of the material and _{Li 0.99 Mn 0.34 Ni 0.34 Co 0.32} O 2 of X-ray diffraction pattern of Example 1. It is an enlarged view of the A section of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Battery case 3 Cover plate 4 Insulation packing 5 Terminal 6 Positive electrode 7 Negative electrode 8 Separator 9 Electrode winding body 10 Insulator 11 Positive electrode lead body 12 Negative electrode lead body 13 Insulator 14 Lead plate

Claims (9)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode includes, as a positive electrode active material, a first oxide having a composition represented by a composition formula Li _{(1 + δ)} Mn _x Ni _y Co _(1-xy) O ₂ ;
Δ, x, and y satisfy the relations −0.15 <δ <0.15, 0.1 <x ≦ 0.5, 0.5 <x + y < 1.0, respectively.
The positive electrode has a composition represented by a composition formula Li ₂ MO ₃ , and the M is at least one selected from the group consisting of Zr, Nb, Mo, W, Al, Si, Ga, Ge, and Sn. further look at including a second oxide, which represents an element,
The positive electrode includes the second oxide in an amount of 0.1% by mass to 10% by mass with respect to the total mass of the first oxide and the second oxide. Electrolyte secondary battery. _2. The nonaqueous electrolyte secondary battery according to claim 1 , wherein x + y ≦ 0.78 in the composition formula Li _{(1 + δ)} Mn _x Ni _y Co _(1-xy) O ₂ . It said second oxide is a non-aqueous electrolyte secondary battery according to claim 1 or 2 is fixed to a surface of the first oxide to form a positive electrode active material particles. The positive active mean particle size and specific surface area of the material particles, 5 [mu] m or more 25μm or less, the non-aqueous electrolyte secondary battery according to claim 3 or less 0.2 m ² / g or more 0.6 m ² / g. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode further includes a conductive additive and a binder . The positive electrode includes the first oxide and the second oxide with respect to a total mass of the first oxide, the second oxide, the conductive additive, and the binder. The non-conducting material according to claim 5 , comprising 94% by mass or more and 99% by mass or less, containing 0.5% by mass or more and 3% by mass or less of the conductive additive, and containing 0.5% by mass or more and 3% by mass or less of the binder. Water electrolyte secondary battery. The conductive additive is a non-aqueous electrolyte secondary battery according to claim 5 or 6 carbon black. The binder is a non-aqueous electrolyte secondary battery according to claim 5 or 6 comprising a polyvinylidene fluoride or polytetrafluoroethylene.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte includes a solvent and an electrolyte salt, and the solvent includes 15% by volume to 80% by volume of diethyl carbonate with respect to the total capacity of the solvent. .

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