JP4639634B2 - Positive electrode active material for lithium secondary battery and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery using the same, and in particular, a lithium secondary battery comprising a composite oxide having a spinel structure that charges and discharges at a potential of 4.5 V or higher with respect to Li. The present invention relates to a lithium secondary battery which is a positive electrode active material for a secondary battery and has improved reliability.

Lithium secondary batteries have the feature of being small and have a large capacity, and are widely used as power sources for mobile phones, notebook computers and the like. The lithium secondary battery described here is a battery that operates by the presence of a positive electrode active material capable of occluding and releasing lithium in each of the positive electrode and the negative electrode, and movement of lithium ions in the electrolyte. In addition to materials that occlude and release lithium ions, such as carbon materials, the active material includes metal materials that form an alloy with Li, such as Li and Al. Currently, LiCoO ₂ (lithium cobaltate) is mainly used as the positive electrode active material of the lithium secondary battery, but the safety of the charged state is not always sufficient, and the price of the Co raw material is high. The search for a new positive electrode active material to replace is energetically advanced. In recent years, lithium manganate using an inexpensive Mn raw material has been promoted. However, since lithium manganate has a lower energy density than lithium cobaltate, methods for increasing the energy density have been further studied.

There are several possible methods for increasing the energy density of a lithium secondary battery. Among them, increasing the operating potential of the battery is an effective means. In a lithium secondary battery using conventional lithium cobaltate and lithium manganate as a positive electrode active material, the operating potential is 4 V class (average operating potential = 3.6 to 3.8 V: lithium potential). This is because the expression potential is defined by the redox reaction of Co ions or Mn ions (Co ³⁺ ← → Co ⁴⁺ or Mn ³⁺ ← → Mn ⁴⁺ ).

On the other hand, for example, it is known that an operating potential of 5 V class can be realized by using a compound having a spinel structure in which Mn of lithium manganate is substituted with Ni or the like as a positive electrode active material. Specifically, it is known that a potential plateau is exhibited in a region of 4.5 V or more by using a compound having a spinel structure such as LiNi _0.5 Mn _1.5 O ₄ (see Patent Document 1). In a compound having such a spinel structure, Mn exists in a tetravalent state, and the operating potential is defined by the oxidation and reduction of Ni ²⁺ ← → Ni ⁴⁺ instead of the oxidation reduction of Mn ³⁺ ← → Mn ^4+. The Rukoto. In this case, in order to make maximum use of the oxidation / reduction of Ni ²⁺ ← → Ni ⁴⁺ , x = 0.5 is most preferable when LiNi _x Mn _2−x O ₄ is used. If it is the range of 0.4 or more and 0.6 or less, a high energy density will be obtained. When x = 0.5, a reaction such as Li [Ni ²⁺ _0.5 Mn ⁴⁺ _1.5 ] O ₄ ← → Li ⁺ + [Ni ⁴⁺ _0.5 Mn ⁴⁺ _1.5 ] O ₄ occurs.

Similarly, Li [CoMn] O ₄ , Li [FeMn] O ₄ , Li [CrMn] O ₄ , Li [Cu _x Mn _2−x ] O _{4, and the} like also have a potential of 4.5 V or higher with respect to Li metal. It is known to charge and discharge at In the case of Co, Fe, and Cr, the operating potential is defined by redox of M ³⁺ ← → M ⁴⁺ (M is Co, Fe or Cr) instead of redox of Mn ³⁺ ← → Mn ^4+. The Rukoto. The charge / discharge potentials in the case of Co, Fe, and Cr are about 5.1V, about 5.0V, and about 4.9V, respectively. In these cases, theoretically, in the composition of LiM ³⁺ Mn ⁴⁺ O ₄ , redox of M ³⁺ ← → M ⁴⁺ (M is Co, Fe or Cr) is used to the maximum extent, High energy density can be obtained. In this case, a reaction such as Li [M ³⁺ Mn ⁴⁺ ] O ₄ ← → Li ⁺ + [M ⁴⁺ Mn ⁴⁺ ] O ₄ occurs. In the case of LiM _x Mn _{2 -x} O ₄ , x = 1.0 is most preferable, but when x is in the range of 0.9 to 1.1, high capacity is obtained at a potential of 4.5 V or more. Will be obtained. Although the theoretical capacity is about 150 mAh / g, in reality, since it is difficult to produce a spinel structure, the discharge capacity of 4.5 V or more is only about 100 mAh / g. In the case of Cu, the operating potential is defined by redox of Cu ²⁺ ← → Cu ³⁺ instead of redox of Mn ³⁺ ← → Mn ⁴⁺ . The charge / discharge potential is approximately 4.9V. In this case, for example, in LiCu _0.5 Mn _1.5 O ₄ , all Cu is divalent and all Mn is tetravalent. However, due to Li insertion / extraction, Li [Cu ²⁺ _0.5 Mn ⁴⁺ _1.5 ] O ₄ ← → 0.5Li + Li _0.5 [Cu ³⁺ _0.5 Mn ⁴⁺ _1.5 ] O ₄ , half of the spinel. Only desorption of moles of Li can be performed. For this reason, high capacity is not obtained in the case where Cu is substituted. On the other hand, as another composition, for example, a composition Li [Ni _0.5x M _(1-x) Mn _{1.5x + in which} Li [Ni _0.5 Mn _1.5 ] O ₄ and LiMMnO ₄ (M is Co, Fe or Cr) are dissolved. _{In (1-x)} ] O ₄ (M is Co, Fe or Cr), the valence changes to Mn, and both the valence change of Ni and the valence change of Co, Fe or Cr are possible. For this reason, a positive electrode active material having a high capacity of 100 mAh / g or more can be obtained in a discharge region of 4.5 V or more. Thus, in LiM _x Mn _2-x O ₄ (M: Ni, Co, Cr, Fe, or Cu, 0.4 <x <1.1), a high capacity can be obtained at 4.5 V or more. It becomes.

On the other hand, considering the reliability of the battery, at present, the deterioration of the electrolyte solution is significant at a potential of 4.9 V or higher, so that it was replaced with Co, Cr, Fe, or Cu that is charged / discharged at a potential of 4.9 V or higher. In LiM _x Mn _2−x O ₄ (0.4 <x <1.1), it is difficult at present to maintain sufficient battery reliability. In the case where only Ni is substituted, the charge / discharge region is in the range of 4.5 V or more and 4.9 V or less. Therefore, considering reliability and the like, only Ni is optimal. From this point of view, at present, we are preferred to use LiNi _x Mn _2-x O ₄ and (0.4 <x <0.6) as a positive electrode active material.

There are several possible techniques for improving the reliability of the battery. Among them, as a method for improving the characteristics by improving the positive electrode active material, introduction of other elements into the positive electrode active material is conceivable. Patent Document 2 discloses Li [M _x Mn _1.5-xz Z _z ] O ₄ (0. 0) in which Mn of LiM _x Mn _2-x O ₄ (0.4 <x <1.1) is substituted with Ti or Si. 4 <x <1.1, 0 ≦ z <0.5, and Z is Si or Ti). Charge / discharge voltage equivalent to LiM _x Mn _2−x O ₄ (0.4 <x <1.1) It is shown that a high capacity can be obtained. When this equation is rewritten, Li [M1 _m M2 _2-m ] O ₄ (wherein M1 is at least one of transition metals selected from Ni, Cr, Fe, Co and Cu, 1.1>m> 0) .4, M2 can be written as: at least one of Mn, Ti and Si). The ratio of Ti and Si in M2 is preferably 0% or more and 20% or less. If it is large, the capacity may decrease. Considering the reliability of the battery and the like, when M1 is Ni and 0.4 <m <0.6, the charge / discharge region is in the range of 4.5 V to 4.9 V, which is preferable. Other, Patent Document 3, a Mn of _{LiM x Mn 2-x O 4} (0.4 <x <1.1), Cr, Fe, B, the positive electrode active material is shown substituted with Cu. However, these positive electrode active materials have not always had sufficient reliability during high-temperature operation.
JP-A-9-147867 JP 2003-197194 A JP 2002-063900 A

These positive electrode active materials are charged and discharged at a high potential of 4.5 V or higher with respect to lithium. However, when stored in a high temperature environment such as 50 ° C. or higher in a charged state, the structure of the positive electrode active material There is a problem that the element is eluted in the electrolyte solution and the capacity of the positive electrode active material is reduced. Thus, a battery using a positive electrode active material that operates at a high potential has a problem with reliability. As a result of investigation, in LiNi _x Mn _2-x O ₄ (0.4 <x <0.6), elution of Ni is more problematic than elution of Mn when stored at a high temperature in a charged state. I understood that. In _{LiNi x Mn 2-x O 4} (0.4 <x <0.6), for charging and discharging at 4.5V or more potential by valence change of Ni is done, the elution of Ni charge and discharge capacity Has a major impact on the decline of The elution of Ni is considered to be because Ni diffuses in the spinel structure and is released from the surface in the charged state. For the above reasons, it is considered necessary to have a method for blocking the diffusion of Ni in the crystal.

  An object of the present invention is to provide a lithium secondary battery having high energy density and high reliability during high-temperature operation even when a positive electrode active material that is charged and discharged at a potential of 4.5 V or higher is used. And

  In the present invention, in a positive electrode active material composed of a composite oxide having a spinel structure that can be charged / discharged at a high potential of 4.5 V or higher with respect to lithium, decomposition of the electrolytic solution at high temperature and electrolysis of elements constituting the positive electrode active material It is intended to suppress elution into the liquid and suppress deterioration of the battery.

Examples of the positive electrode active material having a spinel structure that can be charged and discharged at a potential of 4.5 V or more include Li [Ni _0.5 Mn _1.5 ] O ₄ and Li [Ni _0.5 Mn _1.5-x Ti _x ] O ₄ (0 <x <0 .5), a positive electrode active material called a 5V class spinel such as Li [CoMn] O ₄ , Li [CrMn] O ₄ , Li [FeMn] O _4, and the like. The present invention achieves the object by further forming a positive electrode active material comprising a composite oxide having a spinel structure containing Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta and W. is there.

That is, the present invention provides the following general formula (I)
Li _a1 [M1 _m1 Mn _2-m1-z1 Z1 _z1 ] O ₄ (I)
(Wherein, M1 is at least one of transition metals selected from Ni, Cr, Fe, Co and Cu, and Z1 is Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta and W At least one of the metals selected from: 0 ≦ a1 ≦ 1, 0.4 <m1 <1.1, 0 <z1 < 0.2 )
A positive electrode active material for a lithium secondary battery, comprising a composite oxide having a spinel structure represented by

The present invention also provides the following general formula (II)
Li _a2 [M2 _m2 Mn _2-m2-z2-x Z2 _z2 X _x ] O ₄ (II)
(Wherein M2 is at least one of transition metals selected from Ni, Cr, Fe, Co and Cu, and Z2 is Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta and W X is at least one element selected from Li, B, Na, Al, Mg, Si and Ti, 0 ≦ a2 ≦ 1, 0.4 <m2 < 1.1, 0 <z2 < 0.2 , 0 <x ≦ 0.3 )
A positive electrode active material for a lithium secondary battery, comprising a composite oxide having a spinel structure represented by

  Moreover, this invention is a lithium secondary battery using said positive electrode active material for lithium secondary batteries.

  The first effect can provide a highly reliable lithium secondary battery.

  The second effect is that a high energy density lithium secondary battery can be provided. For this reason, the lithium secondary battery reduced in size and weight can be provided.

  Embodiments of the present invention will be described below.

  The lithium secondary battery of the present invention is mainly composed of a positive electrode having a lithium-containing metal composite oxide as a positive electrode active material and a negative electrode having a negative electrode active material capable of occluding and releasing lithium, and is electrically connected between the positive electrode and the negative electrode. The positive electrode and the negative electrode are immersed in a lithium ion conductive electrolyte solution, and these are sealed in a battery case. When a voltage is applied to the positive electrode and the negative electrode, lithium ions are released from the positive electrode active material, and the lithium ions are occluded in the negative electrode active material, resulting in a charged state. In addition, by causing electrical contact between the positive electrode and the negative electrode outside the battery, lithium ions are released from the negative electrode active material, and lithium ions are occluded in the positive electrode active material, which is opposite to that during charging.

In the first embodiment of the present invention, as a positive electrode active material for a lithium secondary battery, the following general formula (I)
Li _a1 [M1 _m1 Mn _2-m1-z1 Z1 _z1 ] O ₄ (I)
(Wherein, M1 is at least one of transition metals selected from Ni, Cr, Fe, Co and Cu, and Z1 is Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta and W At least one of the metals selected from: 0 ≦ a1 ≦ 1, 0.4 <m1 <1.1, 0 <z1 < 0.2 )
A composite oxide characterized by having a spinel structure represented by By using this composite oxide as a lithium secondary battery using a positive electrode active material for a lithium secondary battery, a lithium secondary battery with high energy density and high reliability even at high temperature operation can be obtained.

  M1 in the general formula (I) is at least one of transition metals selected from Ni, Cr, Fe, Co, and Cu. M1 is preferably Ni. When M1 is Ni, the charge / discharge potential range is 4.5 V or more and 4.9 V or less, whereas when Co, Fe, Cr, or Cu is included, the charge / discharge potential range is 4.8 V or more and 5. Since it becomes 2V or less, when Co, Fe, Cr or Cu is used, decomposition of the electrolytic solution may be a problem, and long-term reliability may be lowered.

  Z1 in the general formula (I) is at least one of metals selected from Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta, and W. By containing such Z1 element, elution of the constituent elements of the positive electrode active material can be reduced and the reliability of the battery can be improved. Z1 is preferably any one of Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta, and W.

  The range of a1 in the general formula (I) is 0 ≦ a1 ≦ 1. Generally, a1 at the time of preparing the positive electrode active material is 1, Li is desorbed from the positive electrode active material with charge, and a1 becomes less than 1, and is fully charged at a potential of 5 V or higher with respect to Li. In the state, a1 becomes 0. Li is occluded by the discharge, and a1 becomes 1 when discharged to a potential of about 3 V with respect to Li. By such Li insertion / extraction, a1 changes in the range of 0 to 1, and operates as an active material of the battery.

  The range of m1 in the general formula (I) is 0.4 <m1 <1.1. It is preferable that 0.4 <m1 <0.6. In particular, when M1 is Ni, a high capacity of 120 mAh / g or more can be obtained, so this range is preferable.

The range of z1 in the general formula (I) is 0 <z1 < 0.2 . 0 . It is good preferable is 002 ≦ z1 ≦ 0.1. If the amount is too small, the effect of improving the characteristic deterioration at high temperature tends to be small, and if the amount is too large, the accumulated energy density of the positive electrode active material may be lowered.

  In the general formula (I), 0.4 <m1 + z1 <2. That is, it contains at least Mn element.

In the second embodiment of the present invention, as the positive electrode active material for a lithium secondary battery, the following general formula (II)
Li _a2 [M2 _m2 Mn _2-m2-z2-x Z2 _z2 X _x ] O ₄ (II)
(Wherein M2 is at least one of transition metals selected from Ni, Cr, Fe, Co and Cu, and Z2 is Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta and W X is at least one element selected from Li, B, Na, Al, Mg, Si and Ti, 0 ≦ a2 ≦ 1, 0.4 <m2 < 1.1, 0 <z2 < 0.2 , 0 <x ≦ 0.3 )
A composite oxide characterized by having a spinel structure represented by By using this composite oxide as a lithium secondary battery using a positive electrode active material for a lithium secondary battery, a lithium secondary battery with high energy density and high reliability even at high temperature operation can be obtained.

  M2 in the general formula (II) is at least one of transition metals selected from Ni, Cr, Fe, Co, and Cu. M2 is preferably Ni. When M2 is Ni, the charge / discharge potential range is 4.5 V or more and 4.9 V or less, whereas when Co, Fe, Cr, or Cu is included, the charge / discharge potential range is 4.8 V or more and 5. Since it becomes 2V or less, when Co, Fe, Cr or Cu is used, decomposition of the electrolytic solution may be a problem, and long-term reliability may be lowered.

  Z2 in the general formula (II) is at least one of metals selected from Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta, and W. By containing such Z2 element, elution of the constituent elements of the positive electrode active material can be reduced and the reliability of the battery can be improved. Z2 is preferably any one of Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta, and W.

  X in the general formula (II) is at least one element selected from Li, B, Na, Al, Mg, Si and Ti. By introducing the X element, the capacity can be increased while maintaining the high temperature storage characteristics.

  The range of a2 in the general formula (II) is 0 ≦ a2 ≦ 1. In general, a2 at the time of preparing the positive electrode active material is 1, Li is desorbed from the positive electrode active material with charge and becomes less than 1, and is fully charged at a potential of 5 V or higher with respect to Li. In the state, a is 0. Li is occluded by the discharge, and a2 becomes 1 when discharged to a potential of about 3 V with respect to Li. Due to such insertion and removal of Li, a2 changes in the range of 0 to 1, and operates as an active material of the battery.

  The range of m2 in the general formula (II) is 0.4 <m2 <1.1. It is preferable that 0.4 <m2 <0.6. In particular, when M2 is Ni, a high capacity of 120 mAh / g or more can be obtained, so this range is preferable.

The range of z2 in the general formula (II) is 0 <z2 < 0.2 . 0 . It is good preferable is 002 ≦ z2 ≦ 0.1. If the amount is too small, the effect of improving the characteristic deterioration at high temperature tends to be small, and if the amount is too large, the accumulated energy density of the positive electrode active material may be lowered.

Range of x in the general formula (II), Ru 0 <x ≦ 0.3 der. If the amount is too large, the accumulated energy density of the positive electrode active material may be reduced.

  In the general formula (II), 0.4 <m2 + z2 + x <2. That is, it contains at least Mn element.

  Next, a method for producing a positive electrode active material for a lithium secondary battery will be described.

As a raw material for producing the positive electrode active material, a raw material corresponding to the element contained in the target positive electrode active material is used. As the Li raw material, lithium salts such as Li ₂ CO ₃ and LiOH, Li ₂ O, Li ₂ SO _{4 and the} like can be used. Lithium salts such as Li ₂ CO ₃ and LiOH are preferred. Such a lithium salt has high reactivity with the transition metal raw material, and the CO ₃ group and OH group volatilize in the form of CO ₂ and H ₂ O during firing, and do not adversely affect the positive electrode active material. Examples of the raw materials for other elements include the following compounds.
Mn raw material: Various manganese oxides such as electrolytic manganese dioxide (EMD) / Mn ₂ O ₃ , Mn ₃ O ₄ , CMD, MnCO ₃ , MnSO _{4, and the} like.
Ni raw _{materials: NiO, Ni (OH) 2} , NiSO 4, Ni (NO 3) 2 , etc..
Ti raw material: Ti oxide such as Ti ₂ O ₃ and TiO ₂ , Ti carbonate, Ti hydroxide, Ti sulfate, Ti nitrate, and the like.
Cr raw material: Cr oxide such as Cr ₂ O ₃ , Cr carbonate, Cr hydroxide, Cr sulfate, Cr nitrate, etc.
Co raw material: Co oxide such as Co ₂ O ₃ , Co carbonate, Co hydroxide, Co sulfate, Co nitrate, etc.
Cu raw material: Cu oxide such as CuO, Cu carbonate, Cu hydroxide, Cu sulfate, Cu nitrate, and the like.
Fe raw materials: oxides such as Fe ₂ O ₃ and Fe ₃ O ₄ , Fe (OH) ₂ , FeCO ₃ , FeNO _{3 and the} like.
Si raw material: SiO, SiO ₂ or the like.
Sr raw material: oxide such as SrO, SrCO ₃ , Sr (NO ₃ ) ₂ , SrSO _{4 and the} like.
Y raw material: oxides such as Y ₂ O ₃ , Y ₂ (SO ₄ ) _{3 and the} like.
Zr raw material: oxide such as ZrO ₂ .
Ru raw material: oxide such as RuO ₂ .
Rh raw material: oxide such as Rh ₂ O ₃ .
Pd raw material: oxide such as PdO.
Ba raw material: oxide such as BaO, BaCO ₃ , Ba (NO ₃ ) ₂ , BaSO _{4 and the} like.
Hf raw material: oxide such as HfO ₂ .
Ta raw material: oxide such as Ta ₂ O ₅
W raw material: oxide such as WO ₃
B raw materials: oxides such as B ₂ O ₃ .
Al raw material: hydroxides such as Al (OH) _{3 in} addition to oxides such as Al ₂ O ₃ .
Mg raw material: In addition to oxides such as MgO, hydroxides such as Mg (OH) ₂ .
Na raw material: Oxides such as Na ₂ O, hydroxides such as NaOH, carbonates such as Na ₂ CO ₃ and the like.

  These raw materials are weighed and mixed so as to have a desired composition ratio. The mixing is performed by pulverizing and mixing with a ball mill or the like. A positive electrode active material can be obtained by baking the mixed powder at a temperature of 500 ° C. to 1200 ° C. in air or oxygen. The firing temperature is preferably a high temperature for diffusing each element. However, if the firing temperature is too high, oxygen deficiency occurs, resulting in a crystal structure other than the spinel structure, and the battery characteristics are adversely affected. For this reason, it is desirable that the temperature is about 500 ° C. to 900 ° C. in the final firing process.

  Each positive electrode active material raw material may hardly cause element diffusion at the time of firing, and an oxide of each element may remain as a different phase after the raw material firing. For this reason, it is possible to use, as a raw material, a mixture in which each elemental raw material is dissolved and mixed in an aqueous solution and then precipitated in the form of hydroxide, sulfate, carbonate, nitrate or the like. It is also possible to use a mixed composite oxide obtained by firing such a mixture. When such a mixture is used as a raw material, each element is well diffused at the atomic level, and it becomes easy to produce a crystal with few different phases.

The specific surface area of the obtained composite oxide is preferably 0.01 m ² / g or more and 3 m ² / g or less, more preferably 0.1 m ² / g or more and 1 m ² / g or less. If the specific surface area is too large, a large amount of binder is required, which may be disadvantageous in terms of the capacity density of the positive electrode. On the other hand, if the specific surface area is too small, ionic conduction between the electrolytic solution and the positive electrode active material may decrease. The center particle size of the composite oxide is preferably 0.1 μm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less. If it is too large, uneven portions such as irregularities may occur during the formation of the positive electrode active material layer. If it is too small, the binding property of the formed positive electrode active material layer may deteriorate.

  The positive electrode active material thus prepared is mixed with a conductivity-imparting material, and formed into a film shape on a current collector with a binder, whereby a positive electrode active material layer can be obtained. Examples of the conductivity-imparting material include carbon materials such as acetylene black, carbon black, graphite, or fibrous carbon, metal substances such as Al, and conductive oxide powders. As the binder, polyvinylidene fluoride or the like is used. As the current collector, a metal thin film mainly composed of Al or the like can be used.

  Preferably, the addition amount of the conductivity-imparting material is about 0.5 to 20% by mass (relative to the total amount of the positive electrode active material, the conductivity-imparting material and the binder), and the addition amount of the binder is 0.5 to It is about 10% by mass (relative to the total amount of the positive electrode active material, the conductivity-imparting material, and the binder). If the ratio of the conductivity-imparting material and / or the binder is too small, the electron conductivity may be inferior or electrode peeling may occur. If the ratio of the conductive material and / or the binder is too large, the capacity per battery mass tends to be small. The proportion of the positive electrode active material is preferably 70 to 99% by mass (relative to the total amount of the positive electrode active material, the conductivity-imparting material and the binder). More preferably, it is 88-97 mass% (with respect to the total amount of a positive electrode active material, a conductive provision material, and a binder). If the proportion of the positive electrode active material is too small, it may be disadvantageous in terms of battery energy density. If the proportion of the positive electrode active material is too large, the proportion per mass of the conductivity-imparting material and the binder is low, which is disadvantageous in that it tends to be inferior in electronic conductivity or easily peeled off from the electrode.

  Examples of the electrolyte solvent in the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Chain carbonates such as diethyl carbonate (DEC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, Chain ethers such as 2-ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetami Dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl -2-Oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, fluorinated carboxylate, etc. Can be used. Moreover, you may use what added the polymer etc. and solidified the electrolyte solution solvent in the gel form. Among these, it is suitable to use a mixture of a cyclic carbonate and a chain carbonate from the viewpoint of stability at a high voltage and the viscosity of the solvent.

In these electrolyte solutions, lithium salts are dissolved as electrolyte solution supporting salts. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO _{2) 2, LiN (C 2} F 5 SO 2) 2, lower aliphatic carboxylic acids, lithium carboxylate, chloroborane lithium, lithium tetraphenylborate, LiBr, LiI, LiSCN, such as LiCl and the like. The electrolyte concentration is preferably 0.2 mol / l to 3 mol / l, and more preferably 0.5 mol / l to 1.5 mol / l. If the concentration is too high, density and viscosity increase. If the concentration is too low, the electrical conductivity may decrease.

  As the negative electrode active material, a material capable of occluding and releasing lithium is used, and a carbon material such as graphite or amorphous carbon, Li metal, Si, Sn, Al, SiO, SnO, or the like can be used alone or in combination. .

  A negative electrode active material is mixed with a conductivity-imparting material, and a negative electrode is formed on the current collector by a binder. Examples of the conductivity-imparting material include acetylene black, carbon black, graphite, carbon materials such as fibrous carbon, and conductive oxide powder. As the binder, polyvinylidene fluoride or the like can be used. As the current collector, a metal thin film mainly composed of Cu or the like can be used.

  The lithium secondary battery according to the present invention includes a negative electrode and a positive electrode laminated in a dry air or inert gas atmosphere via a separator, or wound in a battery can, A battery can be manufactured by sealing with a flexible film made of a laminate with a metal foil.

  The present invention is not limited in battery shape, and can take the form of a positive electrode and a negative electrode facing each other with a separator in between, a wound type, a laminated type, etc. A cell or a cylindrical cell can be used. FIG. 1 shows a cross-sectional view of a coin-type lithium ion secondary battery. The structure is such that the positive electrode current collector 3, the positive electrode active material layer 1, the separator 5, the negative electrode active material layer 2, and the negative electrode current collector 4 are laminated in this order. The can 6 and the negative electrode outer layer can 7 are sealed.

[Experimental Example 1]
A coin-type lithium ion secondary battery having the configuration shown in FIG. 1 was produced. Specifically, samples 1 to 10 having the compositions shown below were prepared, and batteries using these as positive electrode active materials were prepared and evaluated. The sample 1 is a comparative example of the present invention, and the samples 2 to 10 are examples of the present invention. The evaluation results are shown in Table 1.

Li [Ni _0.5 Mn _1.5 ] O ₄ (Sample 1)
Li [Ni _0.5 Mn _1.48 Sr _0.02 ] O ₄ (Sample 2)
Li [Ni _0.5 Mn _1.48 Y _0.02 ] O ₄ (Sample 3)
Li [Ni _0.5 Mn _1.48 Zr _0.02 ] O ₄ (Sample 4)
Li [Ni _0.5 Mn _1.48 Ru _0.02 ] O ₄ (Sample 5)
Li [Ni _0.5 Mn _1.48 Pd _0.02 ] O ₄ (Sample 6)
Li [Ni _0.5 Mn _1.48 Ba _0.02 ] O ₄ (Sample 7)
Li [Ni _0.5 Mn _1.48 Hf _0.02 ] O ₄ (Sample 8)
Li [Ni _0.5 Mn _1.48 Ta _0.02 ] O ₄ (Sample 9)
Li [Ni _0.5 Mn _1.48 W _0.02 ] O ₄ (Sample 10)
(Positive electrode active material preparation conditions)
As raw materials, Li ₂ CO ₃ , MnO ₂ , NiO, SrO, Y ₂ O ₃ , ZrO ₂ , RuO ₂ , PdO, BaO, HfO ₂ , Ta ₂ O ₅ , and WO ₃ are made to have a target metal composition ratio. Weighed and pulverized and mixed. The mixed powder was fired in oxygen at 900 ° C. for 3 days, pulverized and mixed again, and fired in oxygen at 650 ° C. for 24 hours. The crystal structures of these samples were evaluated by X-ray diffraction. FIG. 3 shows an X-ray diffraction pattern of Sample 1. Since all the observed peaks coincided with the peaks due to the spinel structure, it was confirmed that the crystal had a substantially single-phase spinel structure. Similarly, it was confirmed that each sample had a substantially single-phase spinel structure. The specific surface areas were all about 0.5 m ² / g, and the center particle diameters were all about 12 μm.

(Positive electrode fabrication conditions)
The obtained positive electrode active material and carbon black as a conductivity-imparting material were mixed and dispersed in N-methylpyrrolidone (NMP) in which polyvinylidene fluoride (PVDF) as a binder was dissolved to form a slurry. The mass ratio of the positive electrode active material, the conductivity-imparting material, and the binder was 94/3/3. The slurry was applied on an Al current collector having a thickness of 25 μm. Then, it was dried in vacuum for 12 hours. Thereafter, a positive electrode having the positive electrode active material layer 1 formed on the positive electrode current collector 3 was obtained by cutting into a circle having a diameter of 12 mm and press-molding at a pressure of 3 t / cm ² .

(Evaluation 1)
(Preparation of negative electrode)
A negative electrode sheet was prepared by applying a mixture of graphite: PVdF = 90: 10 (mass%) and dispersing in NMP on a copper foil having a thickness of 20 μm. Then, the negative electrode in which the negative electrode active material layer 2 was formed on the negative electrode current collector 4 was obtained by cutting into a circle having a diameter of 13 mm.

(Production of battery)
The electrolyte used was a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) at 40:60 (vol.%) As the electrolyte solvent, LiPF ₆ was used as the electrolyte support salt, and the support salt concentration was Was 1 mol / l.

  The positive electrode and the negative electrode were placed facing each other with no separator in between and placed in a coin cell, filled with an electrolyte solution and sealed to produce a battery. A polypropylene film was used as the separator.

(Battery evaluation: Recovery capacity ratio)
The battery characteristics of the battery produced as described above were evaluated. The discharge capacity of the battery was about 2 mAh. First, the battery was charged and discharged, and the measured discharge capacity was defined as “discharge capacity before storage”. In this charging / discharging, charging was performed at a current of 2 mA with an upper limit voltage of 4.8 V, and after reaching 4.8 V, charging was performed at a constant voltage. The total charging time was 150 minutes. Discharging was performed at a constant current of 2 mA and the lower limit voltage was 2.5V. Thereafter, the battery was charged again and stored in a high-temperature bath at 60 ° C. for 2 weeks. Thereafter, discharging was performed, and the discharging capacity when charging / discharging was performed again under the same conditions described above was defined as “recovery capacity after storage”. A ratio of “recovery capacity after storage” to “discharge capacity before storage” is expressed as “recovery capacity ratio”.

(Evaluation 2)
(Preparation of negative electrode)
As the negative electrode, a Li metal foil in which Li metal was formed on a Cu current collector was used. This was cut into a circle having a diameter of 13 mm to obtain a negative electrode in which the negative electrode active material layer 2 (Li metal) was formed on the negative electrode current collector 4.

(Production of battery)
The electrolyte used was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at 30:70 (vol.%) As the electrolyte solvent, LiPF ₆ was used as the electrolyte support salt, and the support salt concentration was Was 1 mol / l.

  The positive electrode and the negative electrode were placed facing each other with no separator in between and placed in a coin cell, filled with an electrolyte solution and sealed to produce a battery. A polypropylene film was used as the separator.

(Battery evaluation: discharge capacity)
The battery characteristics of the battery produced as described above were evaluated. The discharge capacity of the battery was about 2 mAh. Subsequently, charging / discharging with a constant current of 0.1 mA was performed. In addition, as a voltage range of charging / discharging, the lower limit voltage was 3V and the upper limit voltage was 4.9V. The discharge capacity at this time was measured.

ここで、試料１を正極活物質として用いた電池の放電曲線を図２に示す。図２に示すように、４．５Ｖから４．９Ｖの範囲で１２０ｍＡｈ／ｇ以上の高電圧の範囲で高い放電容量があり、高い蓄積エネルギーであることが確認された。また、表２から明らかなように、Ｓｒ、Ｙ、Ｚｒ、Ｒｕ、Ｒｈ、Ｐｄ、Ｂａ、Ｈｆ、Ｔａ、およびＷのうちの少なくとも１種を正極活物質中に含むことによって、保存後の回復容量率が増加することが確認された。したがって、これらの元素によって４．５Ｖ以上の電位を有する正極活物質の信頼性を向上させることが可能である。以上の結果は、選択された元素を含有した正極活物質は、リチウムに対して４．５Ｖ以上の電位においても、Ｎｉ、Ｍｎなどのスピネル主要構成元素の電解液への溶出を抑制する効果があったものと考えられる。放電容量は、他元素の導入によって減少するものの、１３０ｍＡｈ／ｇ以上が保たれており、十分に高い容量である。放電容量の低下よりも、回復容量率の増加の効果の方が大きいと考えられる。

Here, the discharge curve of the battery using Sample 1 as the positive electrode active material is shown in FIG. As shown in FIG. 2, it was confirmed that there was a high discharge capacity and a high stored energy in the high voltage range of 120 mAh / g or higher in the range of 4.5 V to 4.9 V. Further, as apparent from Table 2, the positive electrode active material contains at least one of Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta, and W to recover after storage. It was confirmed that the capacity rate increased. Therefore, the reliability of a positive electrode active material having a potential of 4.5 V or more can be improved by these elements. The above results show that the positive electrode active material containing the selected element has an effect of suppressing elution of spinel main constituent elements such as Ni and Mn into the electrolytic solution even at a potential of 4.5 V or more with respect to lithium. It is thought that there was. Although the discharge capacity decreases with the introduction of other elements, it is maintained at 130 mAh / g or more, and is a sufficiently high capacity. The effect of increasing the recovery capacity rate is considered to be greater than the decrease in discharge capacity.

[Experimental example 2]
Samples 11 to 16 having the following composition were produced under the same conditions as in Experimental Example 1, batteries using these as positive electrode active materials were produced in the same manner as in Experimental Example 1, and evaluated in the same manner as in Experimental Example 1. . Note that the samples 11 to 16 are all examples of the present invention. For comparison, the evaluation results are shown in Table 2 together with the results of Sample 1.

Li [Ni _0.5 Mn _1.498 W _0.002 ] O ₄ (Sample 11)
Li [Ni _0.5 Mn _1.49 W _0.01 ] O ₄ (Sample 12)
Li [Ni _0.5 Mn _1.49 W _0.02 ] O ₄ (Sample 13)
Li [Ni _0.5 Mn _1.45 W _0.05 ] O ₄ (Sample 14)
Li [Ni _0.5 Mn _1.4 W _0.1 ] O ₄ (Sample 15)
Li [Ni _0.5 Mn _1.3 W _0.2 ] O ₄ (Sample 16)
It was confirmed that the crystal structures of these samples were almost single-phase spinel structures. The specific surface areas were all about 0.5 m ² / g, and the center particle diameters were all about 12 μm.

表２の結果から、一般式（Ｉ）で表される組成式におけるｚ１の値は大きすぎると容量が低下する場合がある。ｚ１が０．１よりも大きい場合には１２０ｍＡｈ／ｇ以下となる。一方、回復容量率についてはｚ１＝０．２の場合でもｚ１＝０よりも高い傾向であることがわかった。このような結果から、ｚ１は０より大きく、０．２以下であることが好ましく、０．００２以上０．１以下であることがさらに好ましい。Ｗの代わりに、Ｓｒ、Ｙ、Ｚｒ、Ｒｕ、Ｒｈ、Ｐｄ、Ｂａ、Ｈｆ、およびＴａ用いた場合も、同様の傾向であることを確認した。

From the results in Table 2 , when the value of z1 in the composition formula represented by the general formula (I) is too large, the capacity may decrease. When z1 is larger than 0.1, it becomes 120 mAh / g or less. On the other hand, the recovery capacity ratio was found to be higher than z1 = 0 even when z1 = 0.2. From such results, z1 is greater than 0 and preferably 0.2 or less, and more preferably 0.002 or more and 0.1 or less. The same tendency was confirmed when Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, and Ta were used instead of W.

[Experimental Example 3]
Samples 17 to 24 having the following composition were produced under the same conditions as in Experimental Example 1, batteries using these as positive electrode active materials were produced in the same manner as in Experimental Example 1, and evaluated in the same manner as in Experimental Example 1. . All samples 17 to 24 are examples of the present invention. As a comparison, the evaluation results are shown in Table 3 together with the results of Sample 10.

Li [Ni _0.5 Mn _1.46 W _0.02 Li _0.02 ] O ₄ (Sample 17)
Li [Ni _0.5 Mn _1.46 W _0.02 B _0.02 ] O ₄ (Sample 18)
Li [Ni _0.5 Mn _1.46 W _0.02 Na _0.02 ] O ₄ (Sample 19)
Li [Ni _0.5 Mn _1.46 W _0.02 Al _0.02 ] O ₄ (Sample 20)
Li [Ni _0.5 Mn _1.46 W _0.02 Mg _0.02 ] O ₄ (Sample 21)
Li [Ni _0.5 Mn _1.43 W _0.02 Si _0.05 ] O ₄ (Sample 22)
Li [Ni _0.5 Mn _1.43 W _0.02 Ti _0.05 ] O ₄ (Sample 23)
Li [Ni _0.5 Mn _1.18 W _0.02 Ti _0.3 ] O ₄ (Sample 24)
As raw material was used _{B 2 O 3, Na 2 O} , MgO, Al 2 O 3, SiO, as required TiO _2. It was confirmed that the crystal structures of these samples were almost single-phase spinel structures. The specific surface areas were all about 0.5 m ² / g, and the center particle diameters were all about 12 μm.

以上のような結果から、Ｌｉ、Ｂ、Ｎａ、Ａｌ、Ｍｇ、ＳｉおよびＴｉをさらに導入することによっても、同様に、保存後の回復容量率は高く、高い容量となる正極活物質となる。一般式（ＩＩ）において、Ｚ２がＳｒ、Ｙ、Ｚｒ、Ｒｕ、Ｒｈ、Ｐｄ、Ｂａ、ＨｆおよびＴａにおいても、同様の傾向であることを確認した。一般式（ＩＩ）におけるｘの範囲は、０より大きいことが好ましく、さらに、０＜ｘ≦０．３であることがさらに好ましい。

From the above results, even when Li, B, Na, Al, Mg, Si, and Ti are further introduced, similarly, the recovery capacity ratio after storage is high, and a positive electrode active material having a high capacity is obtained. In the general formula (II), it was confirmed that Z2 had the same tendency in Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf and Ta. The range of x in the general formula (II) is preferably larger than 0, and more preferably 0 <x ≦ 0.3.

  Examples of utilization of the present invention include batteries used in mobile phones, notebook computers, automobiles, uninterruptible power supplies, and portable music equipment.

It is sectional drawing of the coin-type lithium ion secondary battery which concerns on this invention. It is a figure which shows the discharge curve of the battery which used the sample 1 in the Example as a positive electrode active material. It is a figure which shows the X-ray-diffraction pattern of the sample 1 in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode collector 4 Negative electrode collector 5 Separator 6 Positive electrode outer can 7 Negative electrode outer can 8 Insulation packing part

Claims (27)

The following general formula (I)
Li _a1 [M1 _m1 Mn _2-m1-z1 Z1 _z1 ] O ₄ (I)
(Wherein, M1 is at least one of transition metals selected from Ni, Cr, Fe, Co and Cu, and Z1 is Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta and W At least one of the metals selected from: 0 ≦ a1 ≦ 1, 0.4 <m1 <1.1, 0 <z1 < 0.2 )
A positive electrode active material for a lithium secondary battery, comprising a composite oxide having a spinel structure represented by:   The positive electrode active material for a lithium secondary battery according to claim 1, wherein M1 is Ni and 0.4 <m1 <0.6. 0.002 <positive active material according to claim 1 or 2, characterized in that the z1 ≦ 0.1. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3 , wherein Z1 is Sr. Said Z1 is Y, The positive electrode active material for lithium secondary batteries in any one of Claims 1-3 characterized by the above-mentioned. Said Z1 is Zr, The positive electrode active material for lithium secondary batteries in any one of Claims 1-3 characterized by the above-mentioned. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3 , wherein Z1 is Ru. Said Z1 is Rh, The positive electrode active material for lithium secondary batteries in any one of Claims 1-3 characterized by the above-mentioned. Said Z1 is Pd, The positive electrode active material for lithium secondary batteries in any one of Claims 1-3 characterized by the above-mentioned. Said Z1 is Ba, The positive electrode active material for lithium secondary batteries in any one of Claims 1-3 characterized by the above-mentioned. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3 , wherein Z1 is Hf. Said Z1 is Ta, The positive electrode active material for lithium secondary batteries in any one of Claims 1-3 characterized by the above-mentioned. Said Z1 is W, The positive electrode active material for lithium secondary batteries in any one of Claims 1-3 characterized by the above-mentioned. The following general formula (II)
Li _a2 [M2 _m2 Mn _2-m2-z2-x Z2 _z2 X _x ] O ₄ (II)
(Wherein M2 is at least one of transition metals selected from Ni, Cr, Fe, Co and Cu, and Z2 is Sr, Y, Zr, Ru, Rh, Pd, Ba, Hf, Ta and W X is at least one element selected from Li, B, Na, Al, Mg, Si and Ti, 0 ≦ a2 ≦ 1, 0.4 <m2 < 1.1, 0 <z2 < 0.2 , 0 <x ≦ 0.3 )
A positive electrode active material for a lithium secondary battery, comprising a composite oxide having a spinel structure represented by: The positive electrode active material for a lithium secondary battery according to claim 14 , wherein the M2 is Ni and 0.4 <m2 <0.6. The positive electrode active material for a lithium secondary battery according to claim 14 , wherein 0.002 <z2 ≦ 0.1. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein Z2 is Sr. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein Z2 is Y. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein the Z2 is Zr. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein Z2 is Ru. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein Z2 is Rh. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein Z2 is Pd. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein Z2 is Ba. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein Z2 is Hf. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein Z2 is Ta. The positive electrode active material for a lithium secondary battery according to any one of claims 14 to 16 , wherein Z2 is W. Lithium secondary battery using a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 26.

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