WO2017221678A1 - Positive electrode active material for lithium ion batteries and lithium ion battery using same - Google Patents

Abstract

The purpose of the present invention is to provide: a positive electrode active material having high capacity; and a lithium ion battery which uses this positive electrode active material. A positive electrode active material which is represented by LiCo_xNi_yMn_zM_1-x-y-zO₂ (wherein x is 0.3-1; y is 0-1; z is 0-0.4; and M represents one or more elements selected from among boron (B), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), titanium (Ti), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), silver (Ag), barium (Ba), tungsten (W), iridium (Ir), tin (Sn), lead (Pb) and antimony (Sb), and which has an Ni2p3/2 peak within the range of from 852.8 eV (inclusive) to 854 eV (exclusive) as determined by XPS analysis.

Description

Cathode active material for lithium ion battery and lithium ion battery using the same

The present invention relates to a positive electrode active material for a lithium ion battery and a lithium ion battery using the same.

From the viewpoints of environmental protection and energy saving, hybrid vehicles using an engine and a motor as a power source have been developed and commercialized. In the future, fuel cell hybrid vehicles that use fuel cells instead of engines are also actively developed.
A secondary battery capable of repeatedly charging and discharging electricity as an energy source of this hybrid vehicle is an essential technology. Among them, the lithium ion battery is a battery having a high operating voltage and a high energy density that easily obtains a high output, and is becoming increasingly important as a power source for a hybrid vehicle in the future. In applications of hybrid vehicles to electric vehicles, batteries with high capacity and high output are regarded as important. Battery design that realizes this item is important.

In Patent Document 1, a coating layer containing at least nickel (Ni) and / or manganese (Mn) is provided on the surface of a composite oxide particle containing lithium (Li) and cobalt (Co), and the surface of the coating layer A technology that achieves both a high discharge capacity and a capacity maintenance rate by adjusting the state to a specific state is disclosed.

JP 2010-135207 A

When the Li ion diffusion path in the electrode is shortened by reducing the thickness of the electrode, the resistance decreases, resulting in higher output. However, when the electrode is thinned, the capacity is reduced. For this reason, it is necessary to increase the capacity of the active material.

There is a possibility that this point can be improved by adjusting the surface state of the positive electrode active material as in Patent Document 1. However, when a thin electrode as described above is used, a higher capacity is required.

An object of the present invention is to provide a high capacity positive electrode active material and a lithium ion battery using the same.

The features of the present invention are, for example, as follows.

LiCo _x Ni _y Mn _z M _1-xyz O ₂ (x is 0.3 to 1, y is 0 to 1, z is 0 to 0.4, M is boron (B), magnesium (Mg) , Aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), titanium (Ti), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo) , Silver (Ag), barium (Ba), tungsten (W), iridium (Ir), tin (Sn), lead (Pb) and antimony (Sb). A positive electrode active material having a peak of Ni2p3 / 2 analyzed by XPS of 852.8 eV or more and less than 854 eV.

According to the present invention, a high-capacity positive electrode active material and a lithium ion battery using the same can be provided.

It is a figure which shows the structure of the cylindrical battery which concerns on embodiment of this invention. It is the figure of the active material in which the surface modification layer was formed by the surface modification process It is a figure which shows the structural example of the electrode body which comprises a battery. It is a figure which shows a mode that an electrode body is inserted | pinched between sheets. It is a figure which shows a mode that the sheet | seat was heat-welded. It is a figure which shows a mode that the sheet | seat was heat-welded. It is a figure which shows a XPS surface analysis result.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible.

FIG. 1 is a diagram schematically showing the internal structure of a battery according to an embodiment of the present invention. A battery 1 according to an embodiment of the present invention shown in FIG. 1 includes a positive electrode 10, a separator 11, a negative electrode 12, a battery container (that is, a battery can) 13, a positive electrode current collecting tab 14, a negative electrode current collecting tab 15, an inner lid 16, It comprises an internal pressure release valve 17, a gasket 18, a positive temperature coefficient (PTC) resistance element 19, a battery lid 20, and an axis 21. The battery lid 20 is an integrated part composed of the inner lid 16, the internal pressure release valve 17, the gasket 18, and the PTC resistance element 19. A positive electrode 10, a separator 11, and a negative electrode 12 are wound around the shaft center 21.

The separator 11 is inserted between the positive electrode 10 and the negative electrode 12 to produce an electrode group wound around the axis 21. As the axis 21, any known one can be used as long as it can support the positive electrode 10, the separator 11, and the negative electrode 12. In addition to the cylindrical shape shown in FIG. 1, the electrode group has various shapes such as a laminate of strip electrodes, or a positive electrode 10 and a negative electrode 12 wound in an arbitrary shape such as a flat shape. Can do. The shape of the battery case 13 may be selected from shapes such as a cylindrical shape, a flat oval shape, a flat oval shape, and a square shape according to the shape of the electrode group.

The material of the battery container 13 is selected from materials that are corrosion resistant to non-aqueous electrolytes, such as aluminum, stainless steel, and nickel-plated steel. Further, when the battery container 13 is electrically connected to the positive electrode 10 or the negative electrode 12, the material is not deteriorated due to corrosion of the battery container 13 or alloying with lithium ions in the portion in contact with the nonaqueous electrolyte. Thus, the material of the battery container 13 is selected.

The electrode group is housed in the battery container 13, the negative electrode current collecting tab 15 is connected to the inner wall of the battery container 13, and the positive electrode current collecting tab 14 is connected to the bottom surface of the battery lid 20. The electrolyte is injected into the battery container interior 13 before the battery is sealed. As a method for injecting the electrolyte, there are a method of adding directly to the electrode group in a state where the battery cover 20 is released, or a method of adding from an injection port installed in the battery cover 20.

Thereafter, the battery lid 20 is brought into close contact with the battery container 13 to seal the entire battery. If there is an electrolyte inlet, seal it as well. As a method for sealing the battery, there are known techniques such as welding and caulking.

<Positive electrode>
The positive electrode 10 includes a positive electrode mixture and a positive electrode current collector, and a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder is applied to a positive electrode current collector such as an aluminum foil. What is formed can be used.

As the positive electrode active material, a composition formula positive electrode active material LiCo _x Ni _y Mn _z M _1-xyz O ₂ (x is 0.3 to 1, y is 0 to 1, z is 0 to 0.4, M is boron (B), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), titanium (Ti), chromium (Cr), iron (Fe), copper (Cu ), Zinc (Zn), molybdenum (Mo), silver (Ag), barium (Ba), tungsten (W), iridium (Ir), tin (Sn), lead (Pb) and antimony (Sb) Lithium composite oxide represented by (a kind of element or more) can be used. The capacity can be increased by increasing the Ni ratio, the output at low temperature can be improved by increasing Co, and the material cost can be suppressed by increasing Mn. Further, the additive element as M is effective in stabilizing the cycle characteristics.

The valence of a part of Ni existing on the surface of the positive electrode active material is usually divalent, but it is preferable to modify the surface so as to be less than divalent. That is, it is preferable to use an active material having a peak of Ni2p3 / 2 by analysis of 852.8 eV or more and less than 854 eV in XPS. In addition, as another index indicating that there is a large amount of Ni less than 2 valences, the intensity at 853 eV in XPS analysis is greater than the intensity at 855 eV. When the intensity at 853 eV is greater than the intensity at 855 eV, less than 2 valences It shows that there is more Ni than divalent Ni.

It is considered that the number of sites where Li can come and go increases as a result of the low valence of Ni, resulting in an increase in capacity.

Considering the places where lithium ions come and go, it is desirable that the layer in which Ni of less than 2 valence is generated has a depth of less than 100 to 150 nm from the surface of the positive electrode active material.

<Surface modification method of positive electrode active material>
As a surface modification method, for example, a method in which the positive electrode active material is baked at 900 to 1000 ° C. for 30 to 60 minutes in a reducing gas atmosphere such as carbon oxide gas or hydrogen gas can be used. Regarding the hydrogen gas, it is sufficient that a small amount of hydrogen gas is contained in the argon gas, and the hydrogen gas concentration is preferably in the range of 3-5 wt% of the whole.

As another method, for example, a method in which a positive electrode active material is put into a solution obtained by dissolving a reducing agent in a solvent and stirred can be used. The reducing agent has an electrochemically lower redox potential than Ni divalent ions. For example, the reducing agent is hypophosphite H ₂ PO ₂ ⁻ , phosphite HPO ₃ , hydrogenated by dissociation. Boron compounds BH ₄ ⁻ , hydrazine N ₂ H ₅ ⁺ , dithionate S ₂ O ₆ ²⁻ , sulfite SO ₃ ^2−, etc., such as NaH ₂ PO ₂ , Na ₂ HPO ₃ , NaBH ₄ , LiBH ₄ , BH ₃ , NaHSO ₃ , N ₂ H ₄ , Na ₂ SO ₃ , Na ₂ O ₄ S ₂ can be used.

The cathode active material having the surface modified layer 101 as shown in FIG. 2 can be obtained by modifying the surface of the cathode active material by these methods. The surface modified layer 101 is a layer in which Ni having a valence less than 2 is present.

Examples of the conductive agent to be added to the positive electrode mixture include carbon materials such as carbon black, graphite, carbon fiber, and metal carbide, which may be used alone or in combination.

The binder may be any material as long as the material constituting the positive electrode and the current collector for the positive electrode are brought into close contact with each other. For example, a homopolymer or copolymer such as vinylidene fluoride, tetrafluoroethylene, acrylonitrile, ethylene oxide, Examples thereof include styrene-butadiene rubber.

<Negative electrode>
As the negative electrode 12, a negative electrode mixture in which a negative electrode current collector is applied can be used. As the positive electrode mixture, one having a negative electrode active material and a conductive material can be used. As the negative electrode active material particles, a carbon material such as graphite or a material that occludes lithium by forming an alloy with lithium, or a mixture of a carbon material and an alloy thereof may be used. For example, Si (silicon), Sn (tin), Al (aluminum), Mg (magnesium), P (phosphorus), Sb (lead), or the like is used as a material that occludes lithium by forming an alloy with lithium. Can do. In addition, it is preferable to use a material that forms a compound with lithium, such as Fe ₂ O ₃ (iron oxide (III)) and NiO (nickel oxide (II)). These active materials have a large volume change accompanying lithium occlusion as compared with graphite, but have a large lithium occlusion amount and can increase the capacity of the lithium ion secondary battery. In particular, Si has a theoretical capacity density of about 4200 mAh / g, which is the largest among these. Therefore, it is preferable to use Si or a Si compound as the negative electrode active material.

The Si compound is not particularly limited as long as it can occlude and release lithium ions. For example, oxides such as SiO _x (silicon oxide) and SiN _x (silicon nitride), nitrides, SiNi Transition metal compounds such as _x can be used.

Examples of the conductive agent include carbon materials such as carbon black, graphite, carbon fiber, and metal carbide, which may be used alone or in combination.

The binder resin (binder) is not particularly limited. For example, polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, polyalginic acid, polyacrylic acid, carboxymethylcellulose, and the like are used. Can do. An active material that forms an alloy with lithium, such as a Si-based active material, expands and contracts when Li is inserted into and desorbed from the active material. At that time, the binding between the active materials or the binding between the active material and the current collector is lost, and the capacity is deteriorated. In order to prevent capacity deterioration, it is desirable to use a binder having a high strength. In order to improve the strength of polyimide and polyamideimide, it is necessary to perform heat treatment in a vacuum, and the strength of the binder can be changed depending on the temperature of the heat treatment.

<Electrolyte>
A non-aqueous solvent containing a compound containing lithium ions as the electrolyte can be used as the electrolyte. Examples of the non-aqueous solvent used in the electrolytic solution include ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) from the viewpoint of low temperature characteristics and film formation on the negative electrode, and vinylene carbonate. Additives such as (VC) may be added.

The lithium salt used in the electrolytic solution is not particularly limited, but for inorganic lithium salts, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiI, LiCl, LiBr, etc., and for organic lithium salts, LiB [OCOCF ₃ ] ₄ , LiB [OCOCF ₂ CF ₃ ] ₄ , LiPF ₄ (CF ₃ ) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) _2, or the like can be used. In particular, LiPF ₆ is a suitable material in terms of quality stability, and is often used in consumer batteries. LiB [OCOCF ₃ ] ₄ is effective because it has good dissociation and solubility and exhibits high conductivity at a low concentration.

(Comparative Example 1)
Next, the present embodiment will be described more specifically with reference to comparative examples and examples.

<Positive electrode>
LiCo _0.2 Ni _0.5 Mn _0.3 O ₂ as a positive electrode active material, acetylene black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are 93: 4: 3 in weight ratio. N-methylpyrrolidone (NMP) was mixed as a solvent. Then, this mixture was mixed with N-methylpyrrolidone (NMP; solvent) to prepare a positive electrode mixture slurry. And this positive mix slurry was apply | coated to 15-micrometer-thick aluminum foil, and it dried in air | atmosphere. The positive electrode obtained by drying was molded by a roll press to produce a positive electrode.

<Negative electrode>
Water was mixed as a solvent so that graphite and a conductive material, and CMC and SBR as a binder were in a weight ratio of 98: 1: 1. Then, this mixture was mixed with water (a negative electrode mixture slurry was prepared. Then, this negative electrode mixture slurry was applied to a copper foil having a thickness of 10 μm and dried in a vacuum. The negative electrode obtained by drying was applied. The negative electrode was produced by molding with a roll press.

<Separator>
As the separator, a separator having a total thickness of 20 μm in which polypropylene, polyethylene, and polypropylene were laminated in three layers was used. The positive electrode was sandwiched between two separators, and three sides were thermally welded to form a bag. This separator was used.

<Electrolyte>
As an electrolytic solution, lithium hexafluoroethylene was added to an organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 2: 2 so as to be 1.0 mol / L. What dissolved the phosphate (LiPF6) was used.

<Production of lithium ion secondary battery>
A rocking chair type lithium ion secondary battery was manufactured using the positive electrode, the negative electrode, the electrolytic solution, and the separator. A positive electrode 201 and a negative electrode 202 housed in a bag-like separator 203 were inserted and laminated to obtain a laminate. Then, in this laminate, the positive electrode terminal 5 and the negative electrode terminal 206 were connected to the portions of the positive electrode 201 and the negative electrode 202 exposed to the outside (current collector foil exposed portions) by ultrasonic welding, respectively, and FIG. The electrode body 204 shown was obtained. Next, as shown in FIG. 4, the electrode body 204 is disposed between the two heat-weldable sheets 207, and parts other than the electrolyte injection portion of the sheet 207 are heat-welded, so that FIG. The electrode placement container 209 shown was obtained.

Then, the electrolyte solution was injected into the electrode-arranged container 209. The battery 211 shown in FIG. 6 was produced by thermally welding the opening after injecting the electrolytic solution. Then, an electrolyte impregnation time of 8 hours was provided after sealing, and then a battery 211 subjected to the following test was charged and discharged in a voltage range of 4.2 V to 2.5 V for 3 cycles at a current value of 0.2 A. Completed.

<Battery capacity evaluation method>
The battery was charged at a constant current of 0.5 A to 4.2 V, and after 30 minutes of operation stop, it was discharged to 0.5 V at 0.5 A. The capacity ratio was calculated by setting Comparative Example 2 to 100. The measurement results are shown in Table 1.

<Internal resistance evaluation>
In the discharge DCR evaluation, the battery is charged to 3.7 V at a constant current of 0.5 A, discharged at 1 A for 10 s, charged again to 3.7 V at a constant current, discharged at 2 A for 10 s, and charged again to 3.7 V. The battery was discharged at 3 A for 10 s. The DCR of the battery was evaluated from the IV characteristics at this time. The measurement results are shown in Table 1.

<XPS evaluation>
The positive electrode active material before electrode preparation was subjected to surface analysis by X-ray photoelectron spectroscopy. The spectrum of Ni2p / 3 is shown in FIG.

Example 1
In Comparative Example 1, the surface modification layer 101 was provided on the positive electrode active material. Otherwise, the battery was produced and evaluated in the same manner as in Comparative Example 1.

<Surface modification process>
LiCo _0.2 Ni _0.5 Mn _0.3 O ₂ was used as the positive electrode active material. This positive electrode active material was put into an electric furnace, and this active material was fired at 1000 ° C. for 60 minutes in a reducing gas atmosphere. As the reducing gas, an Ar gas containing 3 wt% hydrogen was used. Next, the electric furnace was returned to room temperature, and the positive electrode active material was taken out of the electric furnace.

<Positive electrode production process>
N-methylpyrrolidone so that the weight ratio of the positive electrode active material surface-modified in the surface modification step, acetylene black as the conductive material, and polyvinylidene fluoride (PVdF) as the binder is 93: 4: 3 (NMP) was mixed as a solvent. Then, this mixture was mixed with N-methylpyrrolidone (NMP; solvent) to prepare a positive electrode mixture slurry. And this positive mix slurry was apply | coated to 15-micrometer-thick aluminum foil, and it dried in air | atmosphere. The positive electrode obtained by drying was molded by a roll press to produce a positive electrode.

(Example 2)
In Example 1, a battery was produced and evaluated in the same manner except that a surface modification step different from that in Example 1 was used.

<Surface modification process>
After firing LiCo _0.2 Ni _0.5 Mn _0.3 O ₂ as a positive electrode active material in an electric furnace, this positive electrode active material was placed in a 0.1 wt% aqueous solution of a borohydride compound (NaBH ₄ ), and 40 ° C. And stirred for about 1 hour. Calcination can be carried out, for example, at 950 ° C. for 10-20 hours.

<Electrode process>
N-methylpyrrolidone so that the weight ratio of the positive electrode active material surface-modified in the surface modification step, acetylene black as the conductive material, and polyvinylidene fluoride (PVdF) as the binder is 93: 4: 3 (NMP) was mixed as a solvent. Then, this mixture was mixed with N-methylpyrrolidone (NMP; solvent) to prepare a positive electrode mixture slurry. And this positive mix slurry was apply | coated to 15-micrometer-thick aluminum foil, and it dried in air | atmosphere. The positive electrode obtained by drying was molded by a roll press to produce a positive electrode.

Table 1 shows the results of the comparative example and Examples 1 and 2. The capacity and the internal resistance are shown as values when the result of Comparative Example 1 is 100 (%). The capacity of Example 1 increased by 5% compared to the comparative example, and the capacity of Example 2 increased by 4%. The internal resistance was the same in Examples 1 and 2 and the comparative example.

FIG. 7 shows the Ni2p3 / 2 peak in the XPS measurement of the positive electrode. The comparative example has a peak near 855 eV, but Examples 1 and 2 have a peak around 853 eV and have a peak less than divalent.

In the comparative example, the intensity at 853 eV is smaller than the intensity at 855 eV, while in Examples 1 and 2, the intensity at 853 eV is larger than the intensity at 855 eV.

FIG. 1: Battery 1, positive electrode 10, separator 11, negative electrode 12, battery container (battery can) 13, positive electrode current collector tab 14, negative electrode current collector tab 15, inner lid 16, internal pressure release valve 17, gasket 18, positive temperature Coefficient resistance element 19, battery cover 20, axis 21
FIG. 2: Active material 100 having a surface modified layer, surface modified layer 101, and active material 102
3 to FIG. 6: battery 211, positive electrode 201, negative electrode 202, separator 203, electrode body 204, positive electrode terminal 205, negative electrode terminal 206, sheet 207, heat welded portion 208

Claims (5)

1. LiCo _x Ni _y Mn _z M _1-xyz O ₂ (x is 0.3 to 1, y is 0 to 1, z is 0 to 0.4, M is boron (B), magnesium (Mg) , Aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), titanium (Ti), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo) , Silver (Ag), barium (Ba), tungsten (W), iridium (Ir), tin (Sn), lead (Pb) and antimony (Sb). A positive electrode active material having a peak of Ni2p3 / 2 analyzed by XPS of 852.8 eV or more and less than 854 eV.
2. LiCo _x Ni _y Mn _z M _1-xyz O ₂ (x is 0.3 to 1, y is 0 to 1, z is 0 to 0.4, M is boron (B), magnesium (Mg) , Aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), titanium (Ti), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo) , Silver (Ag), barium (Ba), tungsten (W), iridium (Ir), tin (Sn), lead (Pb) and antimony (Sb). A positive electrode active material whose intensity at 853 eV in XPS analysis is larger than that at 855 eV.
3. In claim 1 or claim 2,
   The positive electrode active material is a positive electrode active material having a surface modification layer in a range of less than 100 to 150 nm from the surface.
4. It has a positive electrode mixture and a negative electrode mixture,
   The positive electrode mixture has a positive electrode active material,
   The said positive electrode active material is a lithium ion secondary battery which is a positive electrode active material shown in Claim 3.
5. A step of firing the positive electrode active material in a reducing atmosphere or stirring in a reducing solution;
   The reducing atmosphere is an atmosphere mainly composed of CO or hydrogen,
   The reducing solution includes hypophosphite (H ₂ PO ₂ ⁻ ), phosphite (HPO ₃ ), borohydride compound (BH ₄ ⁻ ), hydrazine (N ₂ H ₅ ⁺ ), dithionate (S ₂ O ₆ ²⁻ ) or a sulfite (SO ₃ ²⁻ ) -containing positive electrode active material production method.

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