JP2011071114A - Positive active material for lithium ion battery and lithium ion battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion battery charging and discharging by using Li<SB>2</SB>NiPO<SB>4</SB>F as a positive active material, and also to provide an electrochemical measuring method for examining electrochemical behavior such as charge-discharge characteristics of Li<SB>2</SB>NiPO<SB>4</SB>F. <P>SOLUTION: The positive active material for the lithium ion battery is a material in which part of M of Li<SB>2-x</SB>MPO<SB>4</SB>F (M is Co or Ni; and x=2 to 0) is replaced by one or two or more kinds selected from the group comprising Mg, Al, Ti, V, Mn, Fe, Cu, Zn, Zr, Nb, and Mo, which are different from M. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a positive electrode active material for a lithium ion battery and a lithium ion battery using the same, and in particular, improves the discharge potential and improves the energy density of the battery by improving the positive electrode active material.

Conventionally, oxide-based positive electrode active materials such as LiCoO ₂ and LiNiO _{2 that} can serve as intercalation hosts for lithium ions have been used as positive electrode active materials for lithium ion batteries. However, the charge and discharge in these oxide-based positive electrode active materials use the trivalent / tetravalent redox reaction of the central metals Co and Ni, so that Co and Ni are chemically unstable during charging. There was a problem that it was in a tetravalent state and was extremely inferior in thermal stability.

As positive electrode active materials for solving this problem, positive electrode active materials have also been developed for phosphates having an olivine type crystal structure such as LiCoPO ₄ and LiFePO ₄ . This positive electrode active material has improved thermal stability by using a divalent / trivalent redox reaction instead of a trivalent / tetravalent redox reaction of Co or Ni, and further, around the central metal. Since a phosphate group which is a polyanion of a heteroelement having a high electronegativity is arranged, the discharge potential is increased and the energy density is higher than that of the oxide-based positive electrode active material.

Further, in order to further improve the energy density of the phosphate having an olivine type crystal structure such as LiCoPO ₄ or LiFePO _4, a part of oxygen of the phosphate polyanion PO _{4 has} a higher electronegativity than oxygen. An olivine fluoride positive electrode active material such as Li ₂ CoPO ₄ F or Li ₂ NiPO ₄ F substituted with fluorine to further increase the discharge potential has been proposed (Patent Document 1).

JP 2003-229126 A

However, although Li ₂ CoPO ₄ F described in Patent Document 1 has a high discharge potential, there is a problem in that the positive electrode potential rapidly decreases in the middle when discharged at a constant current, and the amount of charge and discharge is small. .

  This invention is made | formed in view of the said conventional situation, and makes it the subject which should be solved to provide an olivine fluoride type | system | group positive electrode active material with a high discharge voltage and a large amount of charge / discharge electricity.

In order to further improve the charge / discharge capacity of Li ₂ CoPO ₄ F and Li ₂ NiPO ₄ F, the present inventors have conducted intensive studies on adding other metal elements as dopants. As a result, it has been found that addition of Mg, Al, Ti, V, Mn, Fe, Cu, Zn, Zr, Nb and Mo as dopants is effective, and the present invention has been completed.

That is, the positive electrode active material for a lithium ion battery of the present invention is Li _{2 -x} MPO ₄ F (wherein M represents either Co or Ni, and x = 2 to 0). It is characterized by being substituted by one or more selected from the group consisting of different Mg, Al, Ti, V, Mn, Fe, Cu, Zn, Zr, Nb and Mo.

  The dopant is preferably one or more selected from the group consisting of Mg, Al, Ti, V, Mn, Fe, Cu, Zn, Zr, Nb and Mo, and among them, Mg, Ti, Mn, Zn and One or more selected from the group consisting of Nb are preferred. Moreover, there is no restriction | limiting in particular about the addition amount of the element to dope, and what is necessary is just to determine suitably according to the property etc. of the target positive electrode active material, Usually, 0.001-50% by a stoichiometric ratio, Desirably It is about 0.1 to 20%, more preferably about 1 to 10%.

  By using the positive electrode active material for a lithium ion battery of the present invention, a positive electrode for a lithium ion battery having a large charge / discharge capacity can be obtained.

  Moreover, it can be set as a lithium ion battery with a large charging / discharging capacity | capacitance by using the positive electrode active material for lithium ion batteries of this invention.

Is an XRD chart of the _Li 2 NiPO ₄ F was used to prepare the positive electrode active for a lithium-ion battery of Example. It is a graph which shows the relationship between the amount of discharge electricity and positive electrode potential in the constant current discharge of the electrode using the positive electrode active material for lithium ion batteries of Example 1 and Comparative Example 1. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 2. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 3. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 4. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 5. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 6. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 7. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 8. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 9. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 10. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 11. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 12. It is a graph which shows the measurement result of the cyclic voltammogram measurement (1) of the electrode using the positive electrode active material for lithium ion batteries of Example 13. It is a graph which shows the measurement result of cyclic voltammogram measurement (2) in SB: EC: DMC = 50: 10: 40 (volume ratio). It is a graph which shows the measurement result of cyclic voltammogram measurement (2) in SB: EC: DMC = 10: 10: 80 (volume ratio). It is a graph which shows the measurement result of cyclic voltammogram measurement (2) in SB: EC: DMC = 10: 5: 85 (volume ratio). It is the charging / discharging characteristic of the electrode using the positive electrode active material for lithium ion batteries of Example 11.

Hereinafter, embodiments embodying the present invention will be described in detail.
Example 1
In Example 1, a positive electrode active material having the following chemical composition was prepared.
Li ₂ Co _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F
That is, first, lithium acetate hydrate (LiCH ₃ COO · 2H ₂ O), cobalt acetate (Co (CH ₃ COO) · 4H ₂ O), niobium (V) ethoxide (Nb (OC ₂ H ₅ ) ₅ ), Magnesium nitrate, manganese nitrate, titanium isopropoxide (Ti (i-OC ₃ H ₇ ) ₄ ), and ammonium dihydrogen phosphate (NH ₄ H ₂ PO 4) Li source, Co source, Nb source, Mg The sources, Mn source, Ti source and PO ₄ source were weighed so that the stoichiometric ratio was 1: 0.97: 0.01: 0.01: 0.005: 0.005: 1, and then mixed well using an agate mortar. The mixture was calcined at 500 ° C. for 12 hours in the atmosphere, and then pulverized and mixed again, followed by firing at 780 ° C. for 48 hours. The calcined product thus obtained was added with an equal amount of lithium fluoride (LiF) in a stoichiometric ratio, placed in a platinum crucible, and then baked at 780 ° C. for 72 hours in a quartz vacuum sealed tube. Li ₂ Co _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F as an active material was obtained. The XRD pattern of this positive electrode active material is shown in FIG.

<Preparation of positive electrode for lithium ion battery>
Li ₂ Co _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F obtained as described above and carbon (glassy carbon pulverized product) were mixed in an agate mortar, and further polytetrafluoroethylene (PTFE) powder Were added and mixed, and a disk-shaped pellet was formed by press molding. These mixing ratios were set to Li ₂ Co _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F: carbon: PTFE = 60: 35: 5 (weight ratio). The pellet was sandwiched between two Pt meshes and hot pressed by a hot press method (press condition: 140 ° C., 2 minutes, 500 kg / cm ² ) to obtain a positive electrode for a lithium ion battery.

<Preparation of negative electrode for lithium ion battery>
A lithium thin plate punched out into the same shape as the positive electrode for a lithium ion battery was used as a negative electrode for a lithium ion battery.

<Assembly of lithium-ion battery>
For the assembly of the lithium ion battery, a SUS coin cell 2032 type (made of SUS316L) was used. The positive electrode, the separator, and the negative electrode were sequentially stacked, immersed in the electrolyte, and then caulked and sealed to form a lithium ion battery. . The separator was made of polypropylene-based special paper that is ion-permeable and highly insulating. In addition, the electrolytic solution was LiBF ₄ dissolved in a mixed organic solvent of sebacononitrile: ethylene carbonate (EC): dimethyl carbonate (DMC) = 50 :: 25: 25 to a concentration of 1 mol / L.

(Comparative Example 1)
In Comparative Example 1, a positive electrode active material having the following chemical composition was prepared.
Li ₂ CoPO ₄ F
That is, lithium acetate hydrate (LiCH ₃ COO · 2H ₂ O) as a raw material for the positive electrode active material
), Cobalt acetate (Co (CH ₃ COO) · 4H ₂ O), lithium dihydrogen phosphate (NH ₄ H ₂ PO 4) Li source, Co source, PO ₄ source in a 1: 1: 1 stoichiometric ratio. And mixed well using an agate mortar (Nb source, Mg source, Mn source and Ti source as dopants were not used). About the subsequent process, it carried out similarly to Example 1, produced the positive electrode active material, and assembled the lithium ion battery.

-Evaluation of charge / discharge characteristics-
Regarding the lithium ion batteries of Example 1 and Comparative Example 1 obtained as described above, charge / discharge characteristics at a constant current were measured. That is, the lithium ion batteries of Example 1 and Comparative Example 1 were discharged at a discharge rate of 0.01 C, and the relationship between the amount of discharge electricity and the positive electrode potential was determined. As a result, as shown in FIG. 2, in Example 1, the discharge potential was not significantly reduced to 123 mAh / g, whereas in Comparative Example 1, the discharge charge was from about 82 mAh / g to the positive electrode. The decrease in potential became significant. From this result, the lithium ion battery of Example 1 has a voltage that is significantly higher than the lithium ion battery of Comparative Example 1 by about 1.5 times the amount of discharge electricity due to the influence of doped Nb, Mn, Mg, and Ti elements. It was found that the energy density was increased without causing a decrease.

(Example 2)
In Example 2, a positive electrode active material having the following chemical composition was prepared.
Li ₂ Ni _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F
That is, first, lithium acetate hydrate (LiCH ₃ COO · 2H ₂ O), nickel acetate hydrate (Ni (CH ₃ COO) ₂ · 4H ₂ O), niobium (V) ethoxide (Nb (OC ₂ H ₅ ) ₅ ), magnesium nitrate, manganese nitrate, titanium isopropoxide (Ti (i-OC ₃ H ₇ ) ₄ ), Li source of ammonium dihydrogen phosphate (NH ₄ H2PO4), Ni source, Nb source, Mg source, Mn source, Ti source, PO ₄ source are weighed so that the stoichiometric ratio is 1: 0.97: 0.01: 0.01: 0.005: 0.005: 1, and then mixed well using an agate mortar To do. The mixture was calcined at 500 ° C. for 12 hours in the atmosphere, and then pulverized and mixed again, followed by firing at 780 ° C. for 48 hours. The calcined product thus obtained was added with an equal amount of lithium fluoride (LiF) in a stoichiometric ratio, placed in a platinum crucible, and then baked at 710 ° C. for 72 hours in a quartz vacuum sealed tube. Li ₂ Ni _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F was obtained as an active material.

<Preparation of positive electrode for lithium ion battery>
Li ₂ Ni _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F obtained as described above is placed in an agate mortar, and an Au plate (thickness 0.5 mm) is placed thereon, and further Li ₂ Ni is placed thereon. _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F is sprinkled and then pressed strongly with a pestle to press the Li ₂ Ni _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F and Au plate into a lithium ion battery A positive electrode was obtained.

(Example 3)
In Example 3, a positive electrode active material having the following chemical composition was prepared.
Li ₂ Ni _0.99 Zn _0.01 PO ₄ F
That is, lithium acetate hydrate (LiCH ₃ COO · 2H ₂ O), nickel acetate hydrate (Ni (CH ₃ COO) ₂ · 4H ₂ O), and zinc carbonate (ZnCO ₃ ) Then, the lithium source of ammonium dihydrogen phosphate (NH ₄ H ₂ PO 4), Ni source, Zn source, and PO ₄ source are weighed so that the stoichiometric ratio is 1: 0.99: 0.01: 1, and an agate mortar is used. And mixed well. About the subsequent process, it carried out similarly to Example 2, and produced the positive electrode active material, and produced the positive electrode for lithium ion batteries.

Example 4
In Example 4, a positive electrode active material having the following chemical composition was prepared.
Li ₂ Ni _0.99 Mg _0.01 PO ₄ F
That is, lithium acetate hydrate (LiCH ₃ COO 2H ₂ O), nickel acetate hydrate (Ni (CH ₃ COO) ₂ 4H ₂ O), magnesium nitrate, ammonium dihydrogen phosphate (NH ₄ H2 PO4 Li source), Ni source, Mg source, PO ₄ source, a stoichiometric ratio of 1: 0.99: 0.01 to prepare a 1. About others, it carried out similarly to Example 2, the positive electrode active material was produced, and the positive electrode for lithium ion batteries was produced.

(Examples 5 to 8)
In Examples 5 to 8, positive electrode active materials were prepared by doping Nb, Ti, Mn, and Mg in the following proportions with respect to Li ₂ NiPO ₄ F.
Example 5 Li ₂ Ni _0.95 Nb _0.03 Ti _0.01 Mn _0.005 Mg _0.005 PO ₄ F
Example 6 Li ₂ Ni _0.9.95 Nb _0.01 Ti _0.03 Mn _0.005 Mg _0.005 PO ₄ F
Example 7 Li ₂ Ni _0.955 Nb _0.01 Ti _0.01 Mn _0.02 Mg _0.005 PO ₄ F
Example 8 Li ₂ Ni _0.955 Nb _0.01 Ti _0.01 Mn _0.005 Mg _0.02 PO ₄ F
In other words, lithium acetate hydrate (LiCH ₃ COO 2H ₂ O), nickel acetate hydrate (Ni (CH ₃ COO) ₂ 4H ₂ O), niobium (V) ethoxide ( Nb (OC ₂ H ₅ ) ₅ ), titanium isopropoxide (Ti (i-OC ₃ H ₇ ) ₄ ), manganese nitrate, magnesium nitrate, and ammonium dihydrogen phosphate (NH ₄ H2PO4) Li source, Ni source, Nb source, Ti source, Mn source, Mg source and PO ₄ source were weighed so as to have the above stoichiometric ratio, and mixed well using an agate mortar. About the subsequent process, it carried out similarly to Example 2, the positive electrode active material was produced, and the positive electrode for lithium ion batteries was produced.

Example 9
In Example 9, a positive electrode active material having the following chemical composition was prepared.
Li ₂ Ni _0.99 Ti _0.01 PO ₄ F
That is, lithium acetate hydrate (LiCH ₃ COO · 2H ₂ O), nickel acetate hydrate (Ni (CH ₃ COO) ₂ · 4H ₂ O), and titanium isopropoxide (Ti Li source, Ni source, Nb source, Ti source and PO ₄ source composed of (i-OC ₃ H ₇ ) ₄ ) and ammonium dihydrogen phosphate (NH ₄ H ₂ PO 4) have a stoichiometric ratio of 2: 0.99. : Weighed to 0.01: 1 and mixed well using an agate mortar. About the subsequent process, it carried out similarly to Example 2, the positive electrode active material was produced, and the positive electrode for lithium ion batteries was produced.

(Example 10)
In Example 10, a positive electrode active material having the following chemical composition was prepared.
Li ₂ Ni _0.99 Nb _0.01 PO ₄ F
In other words, lithium acetate hydrate (LiCH ₃ COO 2H ₂ O), nickel acetate hydrate (Ni (CH ₃ COO) ₂ 4H ₂ O), niobium (V) ethoxide ( Li, Ni source, Nb source, Ti source, Mn source, Mg source and PO ₄ source consisting of Nb (OC ₂ H ₅ ) ₅ ) and ammonium dihydrogen phosphate (NH ₄ H ₂ PO 4) are stoichiometric. The mixture was weighed so that the ratio was 1: 0.99: 0.01: 1 and mixed well using an agate mortar. About the subsequent process, it carried out similarly to Example 2, the positive electrode active material was produced, and the positive electrode for lithium ion batteries was produced.

(Example 11)
In Example 11, a positive electrode active material having the following chemical composition was prepared.
Li ₂ Ni _0.98 Co _0.02 PO ₄ F
That is, lithium acetate hydrate (LiCH ₃ COO · 2H ₂ O), nickel acetate hydrate (Ni (CH ₃ COO) ₂ · 4H ₂ O), and cobalt acetate hydrate ( and _{Ni (CH 3 COO) 2 ·} 4H 2 O), Li source consisting ammonium dihydrogen phosphate (NH ₄ H2PO4), Ni source, Co source, and PO ₄ sources in stoichiometric ratio 1: 0.98 : Weighed to 0.02: 1 and mixed well using an agate mortar. About the subsequent process, it carried out similarly to Example 2, the positive electrode active material was produced, and the positive electrode for lithium ion batteries was produced.

(Example 12)
In Example 12, a positive electrode active material having the following chemical composition was prepared.
Li ₂ Co _0.75 Ni _0.24 Mg _0.01 PO ₄ F
That is, lithium acetate hydrate (LiCH ₃ COO · 2H ₂ O), cobalt acetate hydrate (Co (CH ₃ COO) ₂ · 4H ₂ O), and nickel acetate hydrate ( Li source, Ni source, Co source, Mg source and PO ₄ source consisting of Ni (CH ₃ COO) ₂ · 4H ₂ O), magnesium nitrate, and ammonium dihydrogen phosphate (NH ₄ H ₂ PO 4) They were weighed so that the theoretical ratio was 1: 0.98: 0.02: 1 and mixed well using an agate mortar. About the subsequent process, it carried out similarly to Example 2, the positive electrode active material was produced, and the positive electrode for lithium ion batteries was produced.

(Example 13)
In Example 13, a positive electrode active material having the following chemical composition was prepared.
Li ₂ Co _0.50 Ni _0.49 Mg _0.01 PO ₄ F
That is, lithium acetate hydrate (LiCH ₃ COO · 2H ₂ O), cobalt acetate hydrate (Co (CH ₃ COO) ₂ · 4H ₂ O), and nickel acetate hydrate ( Li source, Ni source, Co source, Mg source and PO ₄ source consisting of Ni (CH ₃ COO) ₂ · 4H ₂ O), magnesium nitrate, and ammonium dihydrogen phosphate (NH ₄ H ₂ PO 4) They were weighed so that the theoretical ratio was 1: 0.98: 0.02: 1 and mixed well using an agate mortar. About the subsequent process, it carried out similarly to Example 2, the positive electrode active material was produced, and the positive electrode for lithium ion batteries was produced.

-Evaluation-
<Cyclic voltammogram measurement (1)>
In cyclic voltammogram measurement (1), cyclic voltammogram measurement was performed on the positive electrodes for lithium ion batteries of Examples 2 to 13 prepared as described above under the following conditions.
The electrolytic solution used was a solution of LiBF ₄ dissolved in a mixed organic solvent of sebacononitrile: ethylene carbonate (EC): dimethyl carbonate (DMC) = 50: 25: 25 to a concentration of 1 mol / L. The positive electrode for the lithium ion battery of the example was immersed in the electrolyte in the glass cell, Li metal was used as the counter electrode and the reference electrode, respectively, and the potential sweep rate was 100 mV / second (however, in Examples 7 to 13, 10 mV / second) ) And a potential sweep was performed in the range of 3.0 to 6.0 V (3.0 to 5.5 V in Examples 5 to 13) with respect to the reference electrode.

As a result, in the positive electrode for a lithium ion battery using Li ₂ Ni _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F of Example 2 as the positive electrode active material, the Li / Li ⁺ reference electrode was formed as shown in FIG. On the other hand, a clear redox peak based on the redox of Li ₂ Ni _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F was observed in the vicinity of 5V. A small oxidation current peak appearing at a position of 5 V appeared only in the first sweep, and almost disappeared after the second sweep. This oxidation current peak is considered to be a peak due to Au because an oxidation current peak appears at the same position for the Au electrode.
Further, lithium using a positive electrode for a lithium ion battery using the _{Li 2 Ni 0.99 Zn 0.01 PO 4} F of Example 3 as the positive electrode active material, and _{Li 2 Ni 0.99 Mg 0.01 PO 4} F of Example 4 as the positive electrode active material Also in the positive electrode for ion batteries, as shown in FIGS. 4 and 5, as in Example 2, a clear redox peak based on the redox of the positive electrode active material was observed in the vicinity of 5 V.

Moreover, also in the positive electrode for lithium ion batteries using the positive electrode active material of Examples 5-13, as shown in FIGS. 6-14, it is clear based on oxidation reduction in the vicinity of 5.3V with respect to a Li / Li ⁺ reference electrode. A good redox peak was observed. From the above results, the positive electrode active materials of Examples 5 to 13 show a smooth oxidation-reduction reaction at around 5.3 V as in Examples 1 to 4, and the overvoltage is not so large, and excellent charge / discharge characteristics. It was shown to show.

From the above results, the positive electrode active material in which a part of Ni in Li ₂ NiPO ₄ F is substituted by one or more selected from the group consisting of Mg, Ti, Mn, Co and Nb is smooth. Since charging / discharging is possible and the potential at the time of discharge is high, it has been found that the battery has an unprecedented high voltage.

<Cyclic voltammogram measurement (2)>
In cyclic voltammogram measurement (2), for the positive electrode for a lithium ion battery using Li ₂ Ni _0.97 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F of Example 2 as a positive electrode active material, sebacononitrile (SB) and ethylene carbonate ( EC) and dimethyl carbonate (DMC) were measured in the following three ratios. Other measurement conditions are the same as those in the cyclic voltammogram measurement (1), and the description thereof is omitted.
Mixing ratio (volume ratio)
SB: EC: DMC = 50: 10: 40
SB: EC: DMC = 10: 10: 80
SB: EC: DMC = 10: 5: 85

The results of cyclic voltammogram measurement (2) are shown in FIGS. 15 to 17 and FIG. 3, the mixing ratio (volume ratio) of sebacononitrile: ethylene carbonate (EC): dimethyl carbonate (DMC) was 50:10:40, 50:10:40, 10: 5: 85 and 50: Even if it was changed to 25:25, the cyclic voltammogram did not change so much, and an oxidation-reduction current was observed at almost the same potential. As a result, Li ₂ Ni _0.98 Nb _0.01 Mg _0.01 Mn _0.005 Ti _0.005 PO ₄ F can be charged and discharged smoothly and has a high potential during discharge, at least within the range of these mixing ratios. It turned out that it becomes a high voltage battery which is not in the past.

-Evaluation of charge / discharge characteristics-
About the lithium ion battery using the positive electrode active material of Example 11, the discharge characteristic in a constant current was measured. That is, the positive electrode for the lithium ion battery of Example 11 was charged with a constant current of 39 μA to 5.5 V with respect to the reference electrode, and discharged with a constant current of 19.5 μA to 3 V with respect to the reference electrode. It was. As a result, as shown in FIG. 18, it was confirmed that the discharge potential was 4.8 to 5.3 V and the plate was a high voltage positive electrode having a plateau. The average discharge potential is estimated to be about 5V.

(Examples 14 to 23)
In Examples 14 to 23, a positive electrode active material in which Nb, Ti, Mn, and Mg were doped in the following ratio with respect to Li ₂ CoPO ₄ F was prepared.
That is, lithium acetate hydrate (LiCH ₃ COO · 2H ₂ O), cobalt acetate hydrate (Co (CH ₃ COO) ₂ · 4H ₂ O), niobium (V) ethoxide ( Nb (OC ₂ H ₅ ) ₅ ), titanium isopropoxide (Ti (i-OC ₃ H ₇ ) ₄ ), manganese nitrate, magnesium nitrate, and ammonium dihydrogen phosphate (NH ₄ H2PO4) Li source, Ni source, Nb source, Ti source, Mn source, Mg source and PO ₄ source were weighed so as to have the following stoichiometric ratio, and mixed well using an agate mortar. About the subsequent process, it carried out similarly to Example 2, the positive electrode active material was produced, and the positive electrode for lithium ion batteries was produced.
Example _{14 Li 2 Co 0.99 Mg 0.01 PO} 4 F
Example 15 Li ₂ Co _0.98 Mg _0.02 PO ₄ F
Example 16 Li ₂ Co _0.99 Zn _0.01 PO ₄ F
Example 17 Li ₂ Co _0.99 Ti _0.01 PO ₄ F
Example _{18 Li 2 Co 0.99 Mn 0.01 PO} 4 F
Example _{19 Li 2 Co 0.98 Mn 0.02 PO} 4 F
Example _{20 Li 2 Co 0.96 Nb 0.02 Mg} 0.01 Mn 0.005 Ti 0.005 PO 4 F
Example _{21 Li 2 Co 0.96 Nb 0.01 Mg} 0.02 Mn 0.005 Ti 0.005 PO 4 F
Example _{22 Li 2 Co 0.955 Nb 0.01 Mg} 0.01 Mn 0.01 Ti 0.005 PO 4 F
Example _{23 Li 2 Co 0.955 Nb 0.01 Mg} 0.01 Mn 0.01 Ti 0.005 PO 4 F

-Evaluation of charge / discharge characteristics-
About the lithium ion battery of Examples 14-23 obtained as mentioned above, it discharged with the discharge rate of 0.01 C, and calculated | required the relationship between the amount of discharge electricity, and positive electrode potential. The results for Examples 14 to 23 are shown in Table 1 together with the results of Comparative Example 1 and Example 1.

  As shown in Table 1, in Examples 14 to 23, the amount of discharged electricity exceeds 100 mAh / g, whereas in Comparative Example 1, the amount of discharged electricity is as small as 82 mAh / g, and the positive electrode potential decreases significantly. It was. From this result, compared with the lithium ion battery of Comparative Example 1, the lithium ion batteries of Examples 14 to 23 have an increased discharge electricity amount due to the influence of doped Nb, Mn, Mg, and Ti elements, and the energy density is high. I found out that

  The positive electrode active material for a lithium ion battery of the present invention is applied to a lithium ion battery. Here, the lithium ion battery includes an electrolytic solution, a positive electrode, a negative electrode, a separator, and a case.

(Electrolyte)
The electrolytic solution contains a Li salt (electrolyte) and an organic solvent.
As the Li salt, a general Li salt for a Li ion battery can be used. For example, LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiTFSI (lithium bis (trifluoromethanesulfonyl) imide), LiTFS (lithium trifluoromethanesulfonate), LiBETI (lithium bis ( Pentafluoroethanesulfonyl) imide) or two or more thereof can be used.
Since the positive electrode active material of the present invention has a high oxidation-reduction potential, it is preferable to use LiPF ₆ and / or LiBF ₄ . In the case of using a LiTFSI and LiTFS and LiBETI, it is preferable to add LiPF ₆ or LiBF _4.

  In the case of organic solvents that are commonly used in ordinary lithium ion batteries, cyclic carbonates, cyclic carboxylates, and chain carbonates, alone or in combination, change the organic solvent at a high potential during charging. Therefore, it is not preferable. For this reason, it is preferable to use a nitrile compound as an organic solvent. Here, as the nitrile compound, a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of a chain saturated hydrocarbon compound, a chain ether in which a nitrile group is bonded to at least one terminal of a chain ether compound. Mention may be made of at least one nitrile compound among nitrile compounds and cyanoacetic acid esters.

Examples of the chain saturated hydrocarbon dinitrile compound in which nitrile groups are bonded to both ends of the chain saturated hydrocarbon compound include succinonitrile NC (CH ₂ ) ₂ CN, glutaronitrile NC (CH ₂ ) ₃ CN, adiponitrile In addition to linear dinitrile compounds such as NC (CH ₂ ) ₄ CN, sebaconitrile NC (CH ₂ ) ₈ CN, dodecanedinitrile NC (CH ₂ ) ₁₀ CN, 2-methylglutaronitrile NCCH (CH ₃ ) _CH 2 _CH 2 CN may have a branched as such. These chain saturated hydrocarbon dinitrile compounds are not particularly limited in carbon number, but are preferably 20 or less. More preferably, it is 7-12.

Examples of the chain ether nitrile compound in which a nitrile group is bonded to at least one end of the chain ether compound include oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN and 3-methoxypropionitrile CH _{3. -O-CH} 2 CH 2 CN, and the like. These chain ether nitrile compounds are not particularly limited in carbon number, but are preferably 20 or less.
Examples of the cyanoacetate include methyl cyanoacetate, ethyl cyanoacetate, propyl cyanoacetate, and butyl cyanoacetate. These cyanoacetic acid esters are not particularly limited in carbon number, but are preferably 20 or less.

These nitrile compounds have the effect of expanding the potential window particularly in the positive direction in the electrolytic solution.
A dinitrile compound is preferable from the viewpoint of the action of expanding the potential window. Of these, the use of sebacononitrile is more preferable.
However, since a nitrile compound has high viscosity, it is preferable to use together with the above-mentioned chain carbonate ester, cyclic carbonate ester, and / or cyclic carboxylic acid ester. More preferably, a nitrile compound, a chain carbonate ester and a cyclic carbonate ester are used in combination. Dimethyl carbonate can be employed as the chain carbonate, and ethylene carbonate can be employed as the cyclic carbonate.
In this case, the blending ratio of the nitrile compound in the whole organic solvent is preferably 1 to 90% by volume. More preferably, it is 5-70 volume%, More preferably, it is 10-50 volume%.

  The concentration of the Li salt is 0.1 mol / L or more, preferably 1 mol / L or more, and is lower than the saturated state. For example, if the concentration of Li salt is less than 0.1 mol / L, ion conduction by Li ions becomes extremely small, and the electric resistance of the electrolytic solution becomes extremely high, which is not preferable. On the other hand, exceeding the saturation state is not preferable because the dissolved Li salt precipitates due to environmental changes such as temperature.

(Positive electrode)
The positive electrode includes a positive electrode active material and a current collector.
(Positive electrode active material)
The positive electrode active material refers to “a material in which lithium is inserted / extracted in the crystal structure at a higher potential than the negative electrode, and oxidation / reduction is performed accordingly”.
In the present invention, as the positive electrode active material, Li _{2 -x} MPO ₄ F (wherein M represents either Co or Ni, and 0 ≦ x ≦ 2), part of M is different from M, Mg, Al, Those substituted by one or more selected from the group consisting of Ti, V, Mn, Fe, Cu, Zn, Zr, Nb and Mo are used.
When M is Ni, the positive electrode active material itself and / or its surface film has low conductivity, so that it may not function as the positive electrode of a lithium ion battery if it is simply supported on the current collector. . Such a positive electrode active material can be physically driven into a conductive thin film such as gold with a hammer or the like to form a positive electrode of a battery. As a physical implantation method, an aerosol deposition, an aerosol deposition, or the like in which the positive electrode active material powder is directly blown onto a metal plate in a solid state like sandblast can be employed.

(Current collector for positive electrode)
The positive electrode current collector is a conductive substrate carrying a positive electrode active material.
The molding material for the current collector of the positive electrode is required to be stable during charging. In particular, when using a phosphate-based and olivine fluoride-based positive electrode active material having an olivine-type crystal structure with a high redox potential, it is preferable to use a material excellent in corrosion resistance.
For example, when LiPF ₆ or LiBF ₄ is used as the electrolyte, SUS304, SUS316, SUS316L, Ni, Al, Ti, or the like can be used. However, it may be selected as appropriate in consideration of the operating potential of the positive electrode active material to be used. preferable. For example, when LiPF ₆ is used as the electrolyte, it can be used even at 6 V with respect to the Li / Li ⁺ electrode. However, when LiBF ₄ is used as the electrolyte, SUS304 is 5.8 V or less with respect to the Li / Li ⁺ electrode. It can be used only when charge / discharge is possible. Further, when LiTFSI is used as the electrolyte, it is preferable that LiPF ₆ coexists in order to form a corrosion-resistant film on the surface of the positive electrode current collector. LiBETI and LiTFS are the same as in LiTFSI.
In addition, a conductive metal material such as Al coated with conductive DLC (diamond-like carbon) by a well-known method can be used as a current collector. When the electrolyte is a lithium salt such as LiBF ₄ or LiPF ₆ that easily forms a fluoride film, a thick fluoride film is formed on the aluminum and the corrosion resistance is improved, but the electronic conductivity is lowered, and consequently The increase in output accompanying the increase in ohmic overvoltage is impeded. If the conductive metal material such as Al is coated with the conductive DLC, the fluoride film is generated only in a very small area of the defective portion of the conductive DLC. For this reason, even if the voltage is increased, the decrease in electron conductivity is negligible, and it is possible to prevent the decrease in output due to the increased voltage, which is a concern.
Here, the conductive diamond-like carbon is carbon having an amorphous structure in which both diamond bonds (SP ₃ hybrid orbital bonds between carbons) and graphite bonds (SP ₂ hybrid orbital bonds between carbons) are mixed. Among them, the one whose conductivity is 1000 Ωcm or less. However, in addition to the amorphous structure, those having a phase composed of a crystal structure partially composed of a graphite structure (that is, a hexagonal crystal structure composed of SP ₂ hybrid orbital bonds) and thereby exhibiting conductivity are also included. . Diamond-like carbon having properties intermediate between graphite and diamond adjusts the conductivity by adjusting the ratio of SP ₂ hybrid orbital bonds and SP ₃ hybrid orbital bonds of the carbon atoms constituting diamond-like carbon during film formation. be able to.
Of course, you may coat | cover the said corrosion-resistant electroconductive metal material with electroconductive DLC.
The shape and structure of the current collector can be arbitrarily designed according to the structure of the positive electrode active material and the battery.

(Pretreatment of positive electrode)
The positive electrode for a lithium ion battery performs an immersion treatment step of immersing the positive electrode in a pretreatment electrolytic solution in which a lithium salt is dissolved in an organic solvent containing 1% by volume or more of a nitrile compound before being incorporated in the lithium ion battery, Further, a positive voltage processing step for applying a positive voltage to the electrode is performed. The electrode thus pretreated has a wide potential window even when used in an electrolyte solution containing no nitrile compound or in a lithium ion battery using an electrolyte solution with a small amount of nitrile compound added. It becomes difficult to disassemble (see Japanese Patent Application No. 2009-180007). The reason why the electrode has such a wide potential window is presumed to be that a corrosion-resistant film containing nitrogen as a component is formed on the electrode.

(Negative electrode)
The negative electrode includes a negative electrode active material and a current collector.
(Negative electrode active material)
The negative electrode active material refers to “a material in which lithium is inserted / extracted in the crystal structure at a lower potential than the positive electrode, and oxidation / reduction is performed accordingly”.
Examples of the negative electrode active material include various carbon materials such as artificial graphite, natural graphite, and hard carbon, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), H ₂ Ti ₁₂ O ₂₅ , H ₂ Ti ₆ O ₁₃ , Fe ₂ O ₃ etc. are mentioned. Moreover, the composite material which mixed these suitably can also be mentioned. Further, there are Si fine particles and Si thin films, and fine particles and thin films in which these Si are Si-based alloys such as Si—Ni, Si—Cu, Si—Nb, Si—Zn, Si—Sn, and the like. Further, SiO oxide, Si-SiO ₂ composite, Si-SiO ₂ - can be given complex, etc., such as carbon.

(Current collector for negative electrode)
The current collector for the negative electrode can be formed of a general-purpose conductive metal material such as Cu, Al, Ni, Ti, SUS304, SUS316, or the like.
However, when a nitrile compound is used for the electrolytic solution (including combined use with other organic solvents), it is necessary to select appropriately according to the Li salt in the electrolytic solution. That is, when LiPF ₆ or LiBF ₄ is used as the electrolyte, SUS304, 316, 316L, Ni, Al, and Ti can be used. However, it is necessary to select appropriately according to the operating potential of the negative electrode active material to be used. In the case of using carbon or Si as the negative electrode active material, when LiBF ₄ is used as the electrolyte, a current collector made of Al, Ni, Ti, SUS304, SUS316, or the like other than Cu can be used. In the case where lithium titanate or a Fe ₂ O ₃ based compound is used as the negative electrode active material, all of the above materials containing Cu are applicable. On the other hand, when LiPF _{6 is} used as the electrolyte, Al, Ni and Ti are preferable, and SUS316, SUS316L and Cu are not preferable. In addition, when LiTFSI, LiBETI, or LiTFS is used as the electrolyte, any of Ni, Ti, Al, Cu, SUS304, 316, and 316L can be used.

(Electroconductive member for positive electrode)
Some positive electrode active materials have low electrical conductivity. Therefore, it is preferable to provide a sufficient electron conduction path between the positive electrode active material and the current collector by interposing a conductive electron conduction member.
Here, the form of the electron conducting member is not particularly limited as long as an electron conducting path can be formed between the positive electrode active material and the current collector. For example, carbon black such as acetylene black, graphite powder, diamond-like carbon, glassy Conductive powder (conductive aid) such as carbon can be used. Diamond-like carbon and glassy carbon have a much wider potential window than carbon black and graphite, and are excellent in corrosion resistance when a high potential is applied, and therefore can be suitably used. Moreover, it is also preferable that metal fine particles are supported on these conductive assistants. Examples of the metal fine particles include Pt, Au, Ni and the like. These may be used alone or an alloy thereof.
As the electron conductive material, a conductive film (such as a DLC film) covering the positive electrode active material or a conductive thin film (such as a gold thin film) in which the positive electrode active material is embedded can be used.
In particular, since the Li ₂ NiPO ₄ F-based positive electrode active material has low conductivity of its own and / or its surface coating, it functions as a positive electrode of a lithium ion battery if it is simply supported on a current collector. May not. In order to evaluate the performance of the Li ₂ NiPO ₄ F-based positive electrode active material, it can be physically driven into a conductive plate such as gold with a hammer or the like to form the positive electrode of the battery.
Here, the Li ₂ NiPO ₄ F-based positive electrode active material refers to Li ₂ NiPO ₄ F and a material appropriately doped with dopant.

(Electroconductive member for negative electrode)
The thing similar to the electron conductive member for positive electrodes can be used.

(Separator)
The separator is immersed in the electrolytic solution, separates the positive electrode and the negative electrode, prevents a short circuit therebetween, and allows the passage of Li ions.
Examples of such separators include porous films made of polyolefin resins such as polyethylene and polypropylene.

(Case)
The case is formed of a material having corrosion resistance against the electrolytic solution. The shape can be arbitrarily designed according to the intended use of the battery.
When LiPF ₆ or LiBF ₄ is used as the electrolyte, a case made of SUS304, 316, 316L, Ni, Al, Ti can be used. However, there are cases where it is necessary to select appropriately depending on the operating potential of the positive electrode and negative electrode active material to be used.
When the case also serves as a current collector or is electrically coupled to the current collector, the case is formed of the same or the same material as the current collector forming material of each electrode.

  The present invention is not limited to the description of the embodiment of the invention. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

Claims (2)

Mg, Al, Ti, V, Mn, Fe, Ni in which M of Li _{2 -x} MPO ₄ F (wherein M represents either Co or Ni, x = 2 to 0) is different from M , Cu, Zn, Zr, Nb and Mo are substituted with one or more selected from the group consisting of Mo and a positive electrode active material for a lithium ion battery.   The lithium ion battery using the positive electrode active material for lithium ion batteries of Claim 1.

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