WO2009088009A1 - 半導体被覆正極活物質およびそれを用いたリチウム二次電池 - Google Patents
半導体被覆正極活物質およびそれを用いたリチウム二次電池 Download PDFInfo
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- WO2009088009A1 WO2009088009A1 PCT/JP2009/050068 JP2009050068W WO2009088009A1 WO 2009088009 A1 WO2009088009 A1 WO 2009088009A1 JP 2009050068 W JP2009050068 W JP 2009050068W WO 2009088009 A1 WO2009088009 A1 WO 2009088009A1
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- positive electrode
- active material
- electrode active
- coating layer
- type semiconductor
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49108—Electric battery cell making
- Y10T29/49115—Electric battery cell making including coating or impregnating
Definitions
- the present invention relates to a lithium secondary battery, in particular, a positive electrode active material used for forming a lithium secondary battery having improved cycle characteristics and improved output.
- lithium secondary batteries have been put into practical use because of their high energy density as the power source used for these equipment. It is becoming popular.
- the development of electric vehicles has been urgently caused by environmental problems and resource problems, and lithium secondary batteries have been studied as power sources for electric vehicles.
- a high-capacity lithium secondary battery using metallic lithium as a negative electrode or the like has attracted attention as a secondary battery exhibiting a high energy density, but has not yet been put into practical use. That is, the surface of the metal lithium foil is not flat and there is a portion where the electric field concentrates, and this causes lithium metal to grow in a dendrite shape due to repeated charge and discharge, causing an internal short circuit between the negative electrode and the positive electrode, resulting in a decrease in cycle characteristics. There was a problem.
- Patent Document 1 In order to improve the durability and cycle characteristics of such a lithium secondary battery, for example, in Patent Document 1, at least the positive electrode surface on the surface facing the negative electrode can transmit an ion involved in the battery reaction, a semiconductor
- a secondary battery characterized by being coated with one or more layers of a thin film selected from an insulator and a semiconductor is disclosed. This is because the surface of the positive electrode is covered with a thin film of an insulator or semiconductor that can transmit ions involved in the battery reaction without electron conduction, so that when the dendrite occurs in the negative electrode, the negative electrode inside the battery and the positive electrode are short-circuited. Is to improve cycle characteristics.
- Patent Document 1 since Patent Document 1 is covered with a thin film having no electron conduction, there is a problem that the output characteristics of the lithium secondary battery deteriorate due to difficulty in the movement of electrons.
- the present invention has been made in view of the above problems, and has as its main object to provide a positive electrode active material used for forming a lithium secondary battery with improved cycle characteristics and improved output. To do.
- a positive electrode active material an n-type semiconductor coating layer coated on the surface of the positive electrode active material, and a p-type semiconductor coating layer coated on the surface of the n-type semiconductor coating layer And a pn junction semiconductor coating layer comprising: a semiconductor-covered positive electrode active material.
- the present invention by having the pn junction semiconductor coating layer, it is possible to suppress the deterioration due to the reaction between the positive electrode active material and the electrolyte solution and improve the cycle characteristics. Furthermore, electrons can move from the positive electrode active material side to the electrolyte solution side in the pn junction semiconductor coating layer, and output characteristics can be improved.
- the pn junction semiconductor coating layer is partially coated on the surface of the positive electrode active material.
- the pn junction semiconductor coating layer is not coated on the surface of the positive electrode active material, it is possible to move lithium ions and electrons in the uncoated portion, thereby further improving output characteristics. be able to. That is, it is because it can be set as the semiconductor covering positive electrode active material excellent in balance with cycling characteristics and output characteristics.
- the present invention also provides a lithium secondary battery using the semiconductor-covered positive electrode active material.
- the lithium secondary battery having improved cycle characteristics and improved output characteristics can be obtained.
- a secondary battery can be obtained.
- a method for producing a semiconductor-covered positive electrode active material is provided.
- a pn junction can be formed between the n-type semiconductor coating layer and the p-type semiconductor coating layer by performing the semiconductor-covered positive electrode active material forming step.
- a charging reaction having a very high potential as described above it is difficult to transfer electrons from the electrolytic solution passing through the pn junction semiconductor coating layer to the positive electrode active material, so that the electrolytic solution at the time of the charging reaction, etc. Deterioration can be suppressed.
- the time of the discharge reaction having a low potential as described above the deterioration during the discharge reaction is suppressed, and the movement of electrons from the positive electrode active material passing through the pn junction semiconductor coating layer to the electrolytic solution is facilitated. Even in the portion where the surface of the positive electrode active material is coated, the electron conductivity during the discharge reaction is improved and the output can be improved. Therefore, a semiconductor-covered positive electrode active material with improved cycle characteristics and improved output can be obtained.
- the semiconductor-coated positive electrode active material, the lithium secondary battery, and the method for producing the semiconductor-coated positive electrode active material of the present invention are described in detail below.
- the semiconductor-covered positive electrode active material of the present invention is a pn comprising a positive electrode active material, an n-type semiconductor coating layer coated on the surface of the positive electrode active material, and a p-type semiconductor coating layer coated on the surface of the n-type semiconductor coating layer. And a bonding semiconductor covering layer.
- the deterioration by a positive electrode active material and electrolyte solution contacting and reacting can be suppressed. That is, in a positive electrode active material having lithium, during the charging reaction, lithium ions are usually desorbed from the positive electrode active material to the electrolytic solution, and electrons move from the electrolytic solution to the positive electrode active material. Since the electric potential at the time of the charging reaction is very high, deterioration such as decomposition of the electrolyte occurs.
- it has the said pn junction semiconductor coating layer, and an electron cannot move from a p-type semiconductor coating layer to an n-type semiconductor coating layer in the said pn junction semiconductor coating layer.
- the pn junction semiconductor coating layer is provided, and in the pn junction semiconductor coating layer, electrons can move from the n-type semiconductor coating layer to the p-type semiconductor coating layer. For this reason, the electron transfer from the positive electrode active material passing through the pn junction semiconductor coating layer during the discharge reaction to the electrolyte solution is facilitated, and the electron conduction during the discharge reaction is performed even in the portion where the surface of the positive electrode active material is coated. It is possible to improve the output and improve the output. In addition, since the electric potential at the time of the discharge reaction is low, deterioration such as decomposition of the electrolytic solution hardly occurs.
- FIG. 1 is a schematic cross-sectional view schematically showing an example of the semiconductor-covered positive electrode active material of the present invention.
- a semiconductor-covered positive electrode active material 1 shown in FIG. 1 includes a positive electrode active material 2, an n-type semiconductor coating layer 3 coated on the surface of the positive electrode active material 2, and p coated on the surface of the n-type semiconductor coating layer 3. And a pn junction semiconductor coating layer 5 made of a type semiconductor coating layer 4.
- the semiconductor-covered positive electrode active material has a portion where the n-type semiconductor coating layer is not coated on the surface of the positive electrode active material, and a p-type semiconductor coating layer is formed on the surface of the positive electrode active material in such a portion. May be.
- the semiconductor-coated positive electrode active material of the present invention will be described for each configuration.
- the pn junction semiconductor coating layer used in the present invention is characterized in that the surface of the positive electrode active material 2 is coated as illustrated in FIG. 1 described above.
- electrons (e ⁇ ) normally move from the p-type semiconductor coating layer 4 to the n-type semiconductor coating layer 3 (in the direction of the arrow in FIG. 2A). To move to).
- the movement of the electrons (e ⁇ ) from the positive electrode active material 2 passing through the pn junction semiconductor coating layer 5 during the discharge reaction to the electrolyte (not shown) is facilitated, and the positive electrode active Even in the portion where the surface of the substance 2 is coated, the electron conductivity during the discharge reaction is improved and the output can be improved.
- the n-type semiconductor material used for the n-type semiconductor coating layer has characteristics as an n-type semiconductor, and forms a pn junction semiconductor coating layer as described above to reduce the deterioration of the electrolyte during charging reaction. It is not particularly limited as long as it can be suppressed and can further improve the output by improving the electron conductivity during the discharge reaction.
- Examples of the n-type semiconductor material include Si (silicon) doped with P (phosphorus), Si (silicon) doped with As (arsenic), Si (silicon) doped with Sb (antimony), and the like. Among these, Si (silicon) doped with P (phosphorus) is preferable. This is because the load on the environment is low.
- the p-type semiconductor material used for the p-type semiconductor coating layer has characteristics as a p-type semiconductor, and forms a pn junction semiconductor coating layer as described above to reduce the electrolyte and the like during the charging reaction. It is not particularly limited as long as it can be suppressed and can further improve the output by improving the electron conductivity during the discharge reaction.
- Examples of the p-type semiconductor material include Si (silicon) doped with B (boron), Si (silicon) doped with Al (aluminum), Si (silicon) doped with Ga (gallium), and the like. Among these, Si (silicon) doped with B (boron) is preferable.
- the coating amount of the pn junction semiconductor coating layer coated on the surface of the positive electrode active material is such that a semiconductor-coated positive electrode active material with improved cycle characteristics and improved output characteristics can be obtained as described above.
- the coating amount of the n-type semiconductor material capable of obtaining a semiconductor-covered positive electrode active material excellent in balance between such cycle characteristics and output characteristics includes the average particle diameter of the positive electrode active material and the addition amount of the n-type semiconductor material.
- the amount of the positive electrode active material is not particularly limited as long as the amount can be partially coated on the surface of the positive electrode active material.
- the mass percentage of the addition amount of the n-type semiconductor material with respect to the addition amount of the positive electrode active material is specifically 20 mass% or less, particularly in the range of 0.1 to 10 mass%, particularly in the range of 1 to 6 mass%. It is preferable.
- the coating amount of the p-type semiconductor material capable of obtaining a semiconductor-covered positive electrode active material excellent in balance between such cycle characteristics and output characteristics includes the average particle diameter of the positive electrode active material, the n-type semiconductor material The amount varies depending on the amount of addition, etc., and the amount of the semiconductor-covered positive electrode active material coated on the surface of the n-type semiconductor coating layer and excellent in balance between cycle characteristics and output characteristics can be obtained. It is not limited.
- the mass percentage of the addition amount of the p-type semiconductor material to the addition amount of the n-type semiconductor material is, for example, 100 mass% or less, preferably in the range of 10 to 80 mass%, particularly preferably in the range of 20 to 70 mass%.
- the positive electrode active material used in the present invention will be described. As illustrated in FIG. 1, the positive electrode active material 2 used in the present invention is characterized in that the surface of the positive electrode active material 2 is covered with the pn junction semiconductor coating layer 5.
- the positive electrode active material is not particularly limited as long as it is a positive electrode active material capable of occluding and releasing lithium ions.
- examples thereof include metal oxides containing Li, metal phosphides containing Li and oxygen, metal borides containing Li and oxygen, and the like.
- a metal oxide containing Li is preferable.
- the general formula Li x MO y (M in the formula is mainly composed of a transition metal and includes at least one of Co, Mn, Ni, V, and Fe.
- the shape of the positive electrode active material is not particularly limited as long as it is a shape capable of covering the pn junction semiconductor coating layer, but is usually in the form of fine particles.
- the shape of the fine particles is preferably, for example, spherical or elliptical.
- the average particle diameter when the positive electrode active material is fine particles is preferably in the range of 10 nm to 10 ⁇ m, for example.
- the shape and average particle diameter of the positive electrode active material may be values measured based on image analysis using an electron microscope.
- the method for producing a semiconductor-covered positive electrode active material of the present invention is particularly limited as long as it is a method capable of obtaining the desired semiconductor-covered positive electrode active material with improved cycle characteristics and improved output characteristics. It is not a thing.
- the method etc. which are described in "C. the manufacturing method of a semiconductor covering positive electrode active material” mentioned later can be mentioned.
- the lithium secondary battery of the present invention is characterized by having the semiconductor-coated positive electrode active material described in “A. Semiconductor-covered positive electrode active material” above.
- FIG. 3 is a schematic cross-sectional view schematically showing an example of the power generating element for a lithium secondary battery used in the present invention.
- the power generating element for a lithium secondary battery shown in FIG. 3 includes a positive electrode body 8 composed of a positive electrode current collector 6 and a positive electrode layer 7 containing the semiconductor-covered positive electrode active material (not shown), and a negative electrode current collector.
- a negative electrode body 11 comprising a body 9 and a negative electrode layer 10 containing a negative electrode active material (not shown), a separator 12 disposed between the positive electrode body 8 and the negative electrode body 11, a positive electrode layer 7, A negative electrode layer 10 and an electrolyte (not shown) containing a lithium salt filled in the separator 12.
- a lithium secondary battery can be obtained by inserting the power generating element for a lithium secondary battery into a battery case or the like and sealing the periphery thereof.
- the lithium secondary battery of the present invention will be described for each configuration.
- Positive electrode body The positive electrode body used in the present invention will be described.
- the positive electrode body used in the present invention comprises at least a positive electrode current collector, a positive electrode layer containing the semiconductor-covered positive electrode active material, and an electrolyte.
- the semiconductor-covered positive electrode active material is the same as that described in “A. Semiconductor-covered positive electrode active material”, and description thereof is omitted here.
- the positive electrode layer usually contains a conductive material and a binder.
- the conductive material include carbon black and acetylene black.
- the binder is not particularly limited as long as it is used for a general lithium secondary battery, and specifically, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE). And fluorine resins such as ethylenetetrafluoroethylene (ETFE).
- the positive current collector is a current collector for the positive electrode layer.
- the material of the positive electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include aluminum, SUS, nickel, iron and titanium. Among them, aluminum and SUS are preferable.
- the positive electrode current collector may be a dense metal current collector or a porous metal current collector.
- the negative electrode body used in the present invention comprises at least a negative electrode current collector, a negative electrode layer containing a negative electrode active material, and an electrolyte.
- the negative electrode active material is not particularly limited as long as it can occlude and release lithium ions.
- the negative electrode layer may contain a conductive material and a binder as necessary.
- the conductive material and the binder the same materials as those for the positive electrode layer can be used.
- the negative electrode current collector is a current collector for the negative electrode layer.
- the material for the negative electrode current collector is not particularly limited as long as it has electrical conductivity, and examples thereof include copper, stainless steel, nickel, and the like, among which copper is preferable.
- the negative electrode current collector may be a dense metal current collector or a porous metal current collector.
- the separator used in the present invention is arrange
- resin such as polyethylene (PE), polypropylene (PP), polyester, a cellulose, and polyamide
- the separator may have a single layer structure or a multilayer structure. Examples of the separator having a multilayer structure include a separator having a two-layer structure of PE / PP and a separator having a three-layer structure of PP / PE / PP. Furthermore, in the present invention, the separator may be a nonwoven fabric such as a porous membrane, a resin nonwoven fabric, or a glass fiber nonwoven fabric.
- Electrolyte In the present invention, the positive electrode layer, the negative electrode layer, and the separator described above usually have an electrolyte containing a lithium salt.
- the electrolyte may be in a liquid form or in a gel form, and can be appropriately selected according to the type of the desired battery. This is because the lithium ion conductivity becomes better.
- the electrolyte is liquid, a non-aqueous electrolyte is preferable. This is because the lithium ion conductivity becomes better.
- the non-aqueous electrolyte usually has a lithium salt and a non-aqueous solvent.
- the lithium salt is not particularly limited as long as it is a lithium salt used in a general lithium secondary battery.
- the non-aqueous solvent is not particularly limited as long as it can dissolve the lithium salt, and examples thereof include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and 1,2-dimethoxy.
- these non-aqueous solvents may be used alone or in combination of two or more.
- room temperature molten salt can also be used as said non-aqueous electrolyte.
- the lithium secondary battery of the present invention is usually produced by inserting a power generation element for a lithium secondary battery as illustrated in FIG. 3 into a battery case and sealing the periphery thereof.
- a battery case generally, a metal case is used, for example, a stainless steel case.
- the shape of the battery case used in the present invention is not particularly limited as long as it can accommodate the separator, the positive electrode layer, the negative electrode layer, and the like described above. , Coin type, laminate type and the like.
- the method for producing a lithium secondary battery of the present invention is not particularly limited as long as desired cycle characteristics can be improved and the lithium secondary battery with improved output characteristics can be obtained.
- a method similar to a commonly used method can be used. For example, a slurry having the semiconductor-covered positive electrode active material is applied on a metal foil to form a positive electrode layer to obtain a positive electrode body. Next, the slurry which has a negative electrode active material is apply
- the separator sandwiched between the positive electrode body and the negative electrode body is inserted into a battery case or the like to obtain a battery.
- the method etc. which obtain the desired lithium secondary battery mentioned above can be mentioned.
- the use of the lithium secondary battery of the present invention is not particularly limited, but can be used as, for example, a lithium secondary battery for automobiles.
- the method for producing a semiconductor-covered positive electrode active material according to the present invention includes an n-type semiconductor coating layer forming step of obtaining a n-type semiconductor coating layer by coating the surface of a positive electrode active material with an n-type semiconductor material; A pn junction semiconductor coating layer precursor forming step of forming a p type semiconductor coating layer by coating with a p type semiconductor material and obtaining a pn junction semiconductor coating layer precursor, and heat-treating the pn junction semiconductor coating layer precursor a semiconductor-covered positive electrode active material forming step of forming a pn junction semiconductor cover layer and obtaining a semiconductor-covered positive electrode active material.
- the n-type semiconductor coating layer and the p-type semiconductor coating layer are formed.
- a pn junction can be formed between the two.
- lithium ions are usually desorbed from the positive electrode active material to the electrolytic solution, and electrons move from the electrolytic solution to the positive electrode active material. Since the potential at the time of the charging reaction is very high, degradation such as decomposition of the electrolyte occurs.
- the pn junction semiconductor coating layer having the pn junction obtained by the present invention electrons are p-type. It cannot move from the semiconductor coating layer to the n-type semiconductor coating layer. For this reason, it is difficult to transfer electrons from the electrolytic solution passing through the pn junction semiconductor coating layer during the charging reaction to the positive electrode active material, and deterioration of the electrolytic solution during the charging reaction can be suppressed. On the other hand, in the pn junction semiconductor coating layer having the pn junction obtained by the present invention, electrons can move from the n-type semiconductor coating layer to the p-type semiconductor coating layer.
- a positive electrode active material having lithium In a positive electrode active material having lithium, electrons normally move from the positive electrode active material to the electrolyte solution during the discharge reaction, and lithium ions are inserted from the electrolyte solution into the positive electrode active material, but the potential during the discharge reaction is low. Therefore, degradation such as decomposition of the electrolytic solution is unlikely to occur. For this reason, the deterioration at the time of the discharge reaction is suppressed, and the movement of the electrons from the positive electrode active material passing through the pn junction semiconductor coating layer to the electrolytic solution is facilitated, so that the surface of the positive electrode active material is coated. In addition, the electron conductivity during the discharge reaction is improved, and the output can be improved. Therefore, a semiconductor-covered positive electrode active material with improved cycle characteristics and improved output can be obtained.
- a semiconductor-covered positive electrode active material can be obtained through the following steps. For example, first, in the n-type semiconductor coating layer forming step, the positive electrode active material and the n-type semiconductor material are mixed on the positive electrode active material surface by mechanically applying physical force using a ball mill or the like. A semiconductor material is deposited to form an n-type semiconductor coating layer.
- a pn junction semiconductor coating layer precursor forming step is performed.
- a positive electrode active material hereinafter simply referred to as an n-type semiconductor-covered positive electrode
- a p-type semiconductor material may be mixed on the surface of the n-type semiconductor-covered positive electrode active material by mechanically applying a physical force using a ball mill or the like.
- a semiconductor-covered positive electrode active material forming step is performed.
- a positive electrode active material (hereinafter simply referred to as a precursor) formed on the surface of the pn-type semiconductor cover layer precursor obtained in the pn junction semiconductor cover layer precursor forming step.
- a pn junction is formed between the n-type semiconductor coating layer and the p-type semiconductor coating layer by heat treatment in an inert atmosphere by placing in a firing furnace.
- a semiconductor-covered positive electrode active material can be obtained.
- a pn junction semiconductor coating layer precursor forming step of forming a p type semiconductor coating layer by coating the surface of the layer with a p type semiconductor material and obtaining a pn junction semiconductor coating layer precursor, and heat treating the pn junction semiconductor coating layer precursor If it is a manufacturing method which has a semiconductor covering positive electrode active material formation process which forms a pn junction semiconductor coating layer and obtains a semiconductor covering positive electrode active material by doing, it will not be limited in particular, and has other processes May be. Hereinafter, each process in the manufacturing method of the semiconductor covering positive electrode active material of this invention is demonstrated in detail.
- the n-type semiconductor coating layer forming step in the present invention is a step of obtaining the n-type semiconductor coating layer by coating the surface of the positive electrode active material with an n-type semiconductor material.
- an n-type semiconductor coating layer can be formed on the surface of the positive electrode active material.
- the n-type semiconductor coating layer can be formed by adhering to the surface of the positive electrode active material.
- it will not specifically limit if it is a shape, For example, spherical shape, elliptical spherical shape etc. can be mentioned.
- the average particle diameter of such an n-type semiconductor material is not particularly limited as long as it can improve cycle characteristics and output when an n-type semiconductor coating layer is formed. .
- the n-type semiconductor coating layer may be excessively formed, and sufficient electronic conductivity may not be obtained, and the output may not be improved.
- the average particle size of the n-type semiconductor material can be a value measured based on image analysis using an electron microscope.
- the n-type semiconductor coating layer is formed by coating the surface of the positive electrode active material with an n-type semiconductor material, as long as the n-type semiconductor coating layer can be formed on the surface of the positive electrode active material.
- the method of making it adhere by the mechanical physical force using a ball mill, a mortar, etc. can be mentioned.
- the ball mill When the ball mill is used, for example, a predetermined ball, the positive electrode active material, and the n-type semiconductor material are added to a predetermined pot, and the ball mill is performed at a predetermined rotation speed and a predetermined time.
- Such ball mill conditions are not particularly limited as long as the surface of the positive electrode active material can be coated with a desired amount of the n-type semiconductor material as described above.
- examples of the material used for the pot include silicon nitride, zirconia, alumina, and stainless steel.
- silicon nitride is preferable. This is because it is difficult to scrape and contamination by impurities due to scraping is suppressed.
- examples of the material used for the ball include silicon nitride, zirconia, alumina, and stainless steel. Among these, silicon nitride is preferable. This is because it is difficult to scrape and contamination by impurities due to scraping is suppressed.
- the rotation speed is preferably in the range of 50 to 500 rpm, and more preferably in the range of 100 to 300 rpm.
- the ball milling time is, for example, preferably in the range of 1 to 50 hours, and more preferably in the range of 1 to 20 hours. If the time for ball milling is too short, the coating amount of the n-type semiconductor material may be insufficient. On the other hand, if the time for ball milling is too long, the active material may break and deteriorate.
- the pn junction semiconductor coating layer precursor forming step in the present invention is a step of coating the surface of the n-type semiconductor coating layer with a p-type semiconductor material to form a p-type semiconductor coating layer to obtain a pn junction semiconductor coating layer precursor. It is.
- a pn junction semiconductor coating layer precursor is obtained in which a p-type semiconductor material is deposited on the surface of the n-type semiconductor coating layer to form a p-type semiconductor coating layer on the n-type semiconductor coating layer.
- a type semiconductor covering layer may be formed.
- a p-type semiconductor coating layer is formed on the surface of the n-type semiconductor coating layer.
- the shape is not particularly limited as long as it can be formed, and examples thereof include a spherical shape and an elliptical spherical shape.
- the average particle diameter of such a p-type semiconductor material is not particularly limited as long as the desired p-type semiconductor coating layer can be obtained.
- the p-type semiconductor coating layer is preferably in the range of 1 nm to 10 ⁇ m, more preferably in the range of 1 nm to 1 ⁇ m, particularly in the range of 10 nm to 1 ⁇ m. If it is smaller than the above range, it is difficult to form the p-type semiconductor coating layer, and it may be difficult to obtain a desired pn junction semiconductor coating layer described later. On the other hand, if it is larger than the above range, the p-type semiconductor coating layer may be formed excessively, etc., so that sufficient electron conductivity cannot be obtained and the output cannot be improved.
- the average particle diameter of the p-type semiconductor material a value measured based on image analysis using an electron microscope can be used.
- the surface of the n-type semiconductor coating layer is formed by coating the surface of the n-type semiconductor coating layer with a p-type semiconductor material to obtain a pn junction semiconductor coating layer precursor.
- the method is not particularly limited as long as the p-type semiconductor coating layer can be formed.
- the specific method is the same as that described in the above-mentioned “C. Manufacturing method of semiconductor-covered positive electrode active material 1. n-type semiconductor cover layer forming step”, and thus the description thereof is omitted here.
- a method for obtaining a pn junction semiconductor coating layer precursor for example, when a ball mill is used, specifically, a predetermined ball, the n-type semiconductor-covered positive electrode active material, and the p-type semiconductor material are placed in a predetermined pot.
- the ball mill is performed at a predetermined rotation speed and for a predetermined time.
- Such a ball mill condition is not particularly limited as long as the surface of the n-type semiconductor coating layer can be coated with a desired amount of the p-type semiconductor material as described above.
- the material used for the pot and the material used for the ball are those described in the above-mentioned “C. Manufacturing method of semiconductor-covered positive electrode active material 1. n-type semiconductor coating layer forming step”. Since it is the same thing, description here is abbreviate
- the rotation speed is preferably in the range of 50 to 500 rpm, and more preferably in the range of 100 to 300 rpm.
- the ball milling time is, for example, preferably in the range of 1 to 50 hours, and more preferably in the range of 1 to 20 hours. If the time for ball milling is too short, the coating amount of the p-type semiconductor material may be insufficient. On the other hand, if the time for ball milling is too long, the active material may break and deteriorate.
- the semiconductor-covered positive electrode active material forming step in the present invention is a step of obtaining a semiconductor-covered positive electrode active material by forming a pn-junction semiconductor cover layer by heat-treating the pn junction semiconductor cover layer precursor.
- the semiconductor-covered positive electrode active material having a pn junction formed between the n-type semiconductor coating layer and the p-type semiconductor coating layer to improve desired cycle characteristics and output is improved.
- a method of forming a pn junction semiconductor coating layer by heat-treating the pn junction semiconductor coating layer precursor and obtaining a semiconductor-covered positive electrode active material a method capable of forming the pn junction semiconductor coating layer If it is, it will not specifically limit.
- a positive electrode active material having the above pn junction semiconductor coating layer precursor hereinafter sometimes simply referred to as a precursor positive electrode active material
- a precursor positive electrode active material is fired at a predetermined temperature, time, and atmosphere.
- the predetermined temperature at the time of heat treatment includes the type of the positive electrode active material, the type of the n-type semiconductor material in the pn junction semiconductor coating layer, and the type of the p-type semiconductor material in the pn junction semiconductor coating layer.
- the temperature varies depending on the type and the like, and is not particularly limited as long as it is a temperature at which the positive electrode active material is not deteriorated and a pn junction can be formed and the pn junction semiconductor coating layer can be formed. .
- it is preferably in the range of 200 to 1500 ° C., more preferably in the range of 400 to 1000 ° C., particularly in the range of 600 to 900 ° C.
- the positive electrode active material is LiCoO 2 , Si (silicon) powder doped with P (phosphorus) as the n-type semiconductor material in the pn junction semiconductor coating layer, and Si (silicon) doped with B (boron) as the p-type semiconductor material
- silicon powder When silicon) powder is used, it is usually in the range of 200 to 800 ° C.
- the atmosphere during the heat treatment is that a pn junction is formed between the n-type semiconductor coating layer and the p-type semiconductor coating layer to improve desired cycle characteristics and improve output.
- the atmosphere is not particularly limited as long as the semiconductor-covered positive electrode active material can be obtained.
- the inert atmosphere include N 2 gas and Ar gas.
- the semiconductor-covered positive electrode active material obtained from this step is the same as that described in “A. Semiconductor-covered positive electrode active material” described above, description thereof is omitted here.
- the present invention is not limited to the above embodiment.
- the above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
- Example (Semiconductor-coated positive electrode active material production) To 9.5 g of the positive electrode active material lithium cobalt oxide (LiCoO 2 ), 0.3 g of n-type-Si powder doped with P was added and mixed by ball milling to obtain an n-type-Si semiconductor-coated lithium cobalt oxide. As ball mill conditions, silicon nitride was used as the pot material, and silicon nitride was used as the ball material, and the rotational speed was 300 r. p. m for 3 hours.
- silicon nitride silicon nitride was used as the pot material
- silicon nitride was used as the ball material
- the rotational speed was 300 r. p. m for 3 hours.
- 0.2 g of p-type-Si powder doped with B is added to 9.8 g of n-type-Si semiconductor-coated lithium cobalt oxide and mixed with a ball mill to form p-type on the n-type-Si semiconductor coated layer.
- the precursor positive electrode active material in which the Si semiconductor coating layer was formed was obtained.
- silicon nitride was used as the pot material, and silicon nitride was used as the ball material, and the rotational speed was 300 r. p. m for 3 hours.
- the precursor positive electrode active material was heat treated at 800 ° C. in an inert atmosphere (argon) to obtain a semiconductor-coated lithium cobalt oxide having a pn junction formed thereon.
- a graphite powder as a negative electrode active material was added to water in which polyvinylidene fluoride (PVDF) as a binder was dispersed, and kneaded until mixed uniformly to prepare a slurry for a negative electrode layer.
- PVDF polyvinylidene fluoride
- the negative electrode layer was prepared by applying one side of the slurry for the negative electrode layer onto the Cu current collector and then drying.
- a coin-type battery was fabricated using the positive electrode body, the negative electrode body, and a PP porous separator as the separator.
- the electrolyte is a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) mixed at a volume ratio of 3: 7, and lithium hexafluorophosphate (LiPF 6 ) as a supporting salt dissolved at a concentration of 1 mol / L. Was used.
- a coin-type battery was obtained in the same manner as in the example except that n-type-Si semiconductor-coated lithium cobaltate was used in place of the semiconductor-coated lithium cobaltate having a pn junction formed as the positive electrode active material. It was.
- the capacity retention ratio was 76% in Comparative Example 1, 78% in Comparative Example 2, 80% in Comparative Example 3, and 82% in Example, and Comparative Example 1 and Comparative Example 2 were compared.
- the capacity retention rate was slightly lower than in Example 3.
- the Example showed the value superior to Comparative Example 1, Comparative Example 2, and Comparative Example 3, and showed the best capacity retention rate.
- the discharge capacity was 45 mAh / g in Comparative Example 1, 42 mAh / g in Comparative Example 2, 31 mAh / g in Comparative Example 3, and 46 mAh / g in Example, and Comparative Examples 1, Comparative Example 2 and Examples were compared. Compared to Example 3, the discharge capacity was better. Further, the example had the most excellent discharge capacity.
- Comparative Example 1 and Comparative Example 2 the surface of the positive electrode active material was coated with the n-type semiconductor coating layer or the p-type semiconductor coating layer, so that the positive electrode active material and the electrolyte solution contacted and reacted. It was possible to suppress deterioration due to the performance, and a good capacity retention rate was shown. Furthermore, electrons can move in the n-type semiconductor coating layer or the p-type semiconductor coating layer, and the output characteristics can be improved, and a good discharge capacity was exhibited. In addition, in the embodiment, by having the pn junction semiconductor coating layer, electrons cannot move from the p-type semiconductor coating layer to the n-type semiconductor coating layer in the pn junction semiconductor coating layer.
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Abstract
Description
一方、上述したように電位が低い放電反応時には、放電反応時の上記劣化は抑制され、かつ上記pn接合半導体被覆層中を通過する正極活物質から電解液への電子の移動を容易にして、正極活物質表面が被覆された部分においても放電反応時の電子伝導性が向上して出力を向上させることができるのである。
従って、サイクル特性を向上させ、かつ出力を向上させた半導体被覆正極活物質を得ることができる。
2 … 正極活物質
3 … n型半導体被覆層
4 … p型半導体被覆層
5 … pn接合半導体被覆層
6 … 正極集電体
7 … 正極層
8 … 正極電極体
9 … 負極集電体
10 … 負極層
11 … 負極電極体
12 … セパレータ
まず、本発明の半導体被覆正極活物質について説明する。本発明の半導体被覆正極活物質は、正極活物質と、上記正極活物質表面に被覆されたn型半導体被覆層、および上記n型半導体被覆層表面に被覆されたp型半導体被覆層からなるpn接合半導体被覆層とを有することを特徴とするものである。
また、上記pn接合半導体被覆層を有することにより、上記pn接合半導体被覆層中を電子が正極活物質側から電解液側へ移動することが可能となり、出力特性を向上することができる。すなわち、リチウムを有する正極活物質においては、放電反応時には、通常、正極活物質から電解質液へ電子が移動し、電解質液から正極活物質へリチウムイオンの挿入が起こる。本発明においては、上記pn接合半導体被覆層を有しており、上記pn接合半導体被覆層中においては、電子はn型半導体被覆層からp型半導体被覆層へ移動することが可能となる。このため、放電反応時の上記pn接合半導体被覆層中を通過する正極活物質から電解液への電子の移動を容易にして、正極活物質表面が被覆された部分においても放電反応時の電子伝導性を向上して出力を向上させることができるのである。
なお、上記放電反応時の電位は低いために、電解液の分解等の劣化は起こりにくい。
図1は、本発明の半導体被覆正極活物質の一例を模式的に示す概略断面図である。図1に示される半導体被覆正極活物質1は、正極活物質2と、上記正極活物質2表面に被覆されたn型半導体被覆層3、および上記n型半導体被覆層3表面に被覆されたp型半導体被覆層4からなるpn接合半導体被覆層5とを有するものである。
なお、上記半導体被覆正極活物質においては、上記正極活物質表面に上記n型半導体被覆層が被覆されていない部分があって、このような部分において正極活物質表面にp型半導体被覆層が形成されていても良い。
以下、本発明の半導体被覆正極活物質について、構成ごとに説明する。
まず、本発明に用いられるpn接合半導体被覆層について説明する。本発明に用いられるpn接合半導体被覆層は、上述した図1で例示したように、正極活物質2表面に被覆されていることを特徴とするものである。
本発明においては、図2(a)で模式的に例示するように、正極活物質2表面に被覆されたn型半導体被覆層3、および上記n型半導体被覆層3表面に被覆されたp型半導体被覆層4からなる上記pn接合半導体被覆層5中において、電子(e-)は、通常p型半導体被覆層4からn型半導体被覆層3へは移動(図2(a)中の矢印方向への移動)することができない。このため、上述したように、充電反応時の上記pn接合半導体被覆層5中を通過する電解液(図示せず)から正極活物質2への電子(e-)の移動を困難にして、充電反応時の電解液等の劣化を抑制することができる。
さらに、図2(b)で模式的に例示するように、正極活物質2表面に被覆されたn型半導体被覆層3、および上記n型半導体被覆層3表面に被覆されたp型半導体被覆層4からなる上記pn接合半導体被覆層5中において、電子(e-)は、n型半導体被覆層3からp型半導体被覆層4へ移動(図2(b)中の矢印方向への移動)することが可能となる。このため、上述したように放電反応時の上記pn接合半導体被覆層5中を通過する正極活物質2から電解液(図示せず)への電子(e-)の移動を容易にして、正極活物質2表面が被覆された部分においても放電反応時の電子伝導性が向上して出力を向上させることができる。
上記n型半導体材料としては、例えば、P(リン)をドープしたSi(シリコン)、As(ヒ素)をドープしたSi(シリコン)、Sb(アンチモン)をドープしたSi(シリコン)等を挙げることができ、中でも、P(リン)をドープしたSi(シリコン)が好ましい。環境への負荷が低いからである。
上記p型半導体材料としては、例えば、B(ホウ素)をドープしたSi(シリコン)、Al(アルミニウム)をドープしたSi(シリコン)、Ga(ガリウム)をドープしたSi(シリコン)等を挙げることができ、中でも、B(ホウ素)をドープしたSi(シリコン)が好ましい。
例えば、n型半導体材料の添加量の正極活物質の添加量に対する質量百分率が、具体的には20mass%以下、中でも0.1~10mass%の範囲内、特に1~6mass%の範囲内であることが好ましい。
例えば、p型半導体材料添加量のn型半導体材料の添加量に対する質量百分率としては、例えば100mass%以下、中でも10~80mass%の範囲内、特に20~70mass%の範囲内であることが好ましい。上記範囲内であれば、少なくとも上記n型半導体被覆層表面上にp型半導体被覆層が被覆された、図1に例示されるような所望のpn接合半導体被覆層形状を効果的に得ることができるからである。
次に、本発明に用いられる正極活物質について説明する。図1に例示するように、本発明に用いられる正極活物質2は、上記正極活物質2表面が、上記pn接合半導体被覆層5により被覆されていることを特徴とするものである。
(製造方法)
本発明の半導体被覆正極活物質の製造方法としては、サイクル特性を向上させ、かつ出力特性を向上させた、所望の上記半導体被覆正極活物質を得ることができる方法であれば、特に限定されるものではない。例えば、後述する「C.半導体被覆正極活物質の製造方法」に記載される方法等を挙げることができる。
本発明の半導体被覆正極活物質の用途としては、特に限定されるものではないが、例えば、リチウム二次電池に用いられる正極活物質等として用いることができる。中でも自動車用のリチウム二次電池に用いられる正極活物質として用いることが好ましい。
次に、本発明のリチウム二次電池について説明する。本発明のリチウム二次電池は、上記の「A.半導体被覆正極活物質」に記載した半導体被覆正極活物質を有することを特徴とするものである。
以下、このような本発明のリチウム二次電池について、構成ごとに説明する。
本発明に用いられる正極電極体について説明する。本発明に用いられる正極電極体は、少なくとも正極集電体と、上記半導体被覆正極活物質を含有する正極層と電解質とからなるものである。
次に、本発明に用いられる負極電極体について説明する。本発明に用いられる負極電極体は、少なくとも負極集電体と、負極活物質を含有する負極層と電解質とからなるものである。
次に、本発明に用いられるセパレータについて説明する。本発明に用いられるセパレータは、正極層および負極層の間に配置され、後述する電解質を保持する機能を有するものである。
上記セパレータの材料としては、特に限定されるものではないが、例えばポリエチレン(PE)、ポリプロピレン(PP)、ポリエステル、セルロースおよびポリアミド等の樹脂を挙げることができ、中でもポリプロピレンが好ましい。また、上記セパレータは、単層構造であっても良く、複層構造であってもよい。複層構造のセパレータとしては、例えばPE/PPの2層構造のセパレータ、PP/PE/PPの3層構造のセパレータ等を挙げることができる。さらに、本発明においては、上記セパレータが、多孔膜、樹脂不織布、ガラス繊維不織布等の不織布等であっても良い。
本発明においては、上述した正極層、負極層、およびセパレータ内に、通常、リチウム塩を含有する電解質を有する。
上記電解質は、具体的には、液状であっても良く、ゲル状であっても良く、所望の電池の種類に応じて適宜選択することができるが、中でも液状が好ましい。リチウムイオン伝導性が、より良好となるからである。
上記電解質が液状の場合は、非水電解液が好ましい。リチウムイオン伝導性が、より良好となるからである。上記非水電解液は、通常、リチウム塩および非水溶媒を有する。上記リチウム塩としては、一般的なリチウム二次電池に用いられるリチウム塩であれば特に限定されるものではないが、例えばLiPF6、LiBF4、LiN(CF3SO2)2、LiCF3SO3、LiC4F9SO3、LiC(CF3SO2)3およびLiClO4等を挙げることができる。一方、上記非水溶媒としては、上記リチウム塩を溶解できるものであれば特に限定されるものではないが、例えばプロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、エチルメチルカーボネート、1,2-ジメトキシエタン、1,2-ジエトキシエタン、アセトニトリル、プロピオニトリル、テトラヒドロフラン、2-メチルテトラヒドロフラン、ジオキサン、1,3-ジオキソラン、ニトロメタン、N,N-ジメチルホルムアミド、ジメチルスルホキシド、スルホラン、γ-ブチロラクトン等が挙げられる。本発明においては、これらの非水溶媒を一種のみ用いても良く、二種以上を混合して用いても良い。また、上記非水電解液として、常温溶融塩を用いることもできる。
また、本発明のリチウム二次電池は、通常、図3で例示されるようなリチウム二次電池用発電素子を電池ケースに挿入し、その周囲を封口して作製される。上記電池ケースとしては、一般的には、金属製のものが用いられ、例えばステンレス製のもの等が挙げられる。また、本発明に用いられる電池ケースの形状としては、上述したセパレータ、正極層、負極層等を収納できるものであれば特に限定されるものではないが、具体的には、円筒型、角型、コイン型、ラミネート型等を挙げることができる。
その後、所定のセパレータを上記正極層と上記負極層とにより挟持するように上記正極電極体と上記負極電極体とを上記セパレータ上に設置する。さらに、上記正極層、上記負極層、および上記セパレータに所定の電解質を充填した後、上記セパレータが上記正極電極体と上記負極電極体とにより挟持させたものを電池ケース等に挿入して電池とすることにより、上述した所望のリチウム二次電池を得る方法等を挙げることができる。
次に、本発明の半導体被覆正極活物質の製造方法について、以下詳細に説明する。
本発明の半導体被覆正極活物質の製造方法は、正極活物質表面をn型半導体材料により被覆してn型半導体被覆層を得るn型半導体被覆層形成工程と、上記n型半導体被覆層表面をp型半導体材料により被覆してp型半導体被覆層を形成し、pn接合半導体被覆層前駆体を得るpn接合半導体被覆層前駆体形成工程と、上記pn接合半導体被覆層前駆体を熱処理することによりpn接合半導体被覆層を形成し、半導体被覆正極活物質を得る半導体被覆正極活物質形成工程と、を有することを特徴とするものである。
一方、本発明により得られる上記pn接合を有するpn接合半導体被覆層においては、電子はn型半導体被覆層からp型半導体被覆層へ移動することが可能となる。リチウムを有する正極活物質においては、放電反応時には、通常、正極活物質から電解質液へ電子が移動し、電解質液から正極活物質へリチウムイオンの挿入が起こるが、上記放電反応時の電位は低いために、電解液の分解等の劣化は起こりにくい。このため、放電反応時の上記劣化は抑制され、かつ上記pn接合半導体被覆層中を通過する正極活物質から電解液への電子の移動を容易にして、正極活物質表面が被覆された部分においても放電反応時の電子伝導性が向上して出力を向上させることができるのである。
従って、サイクル特性を向上させ、かつ出力を向上させた半導体被覆正極活物質を得ることができる。
例えば、まず、n型半導体被覆層形成工程によって、正極活物質とn型半導体材料とを、ボールミル等を用いて機械的に物理力をかけながら混合するなどして、正極活物質表面にn型半導体材料を付着させてn型半導体被覆層を形成する。
以下、本発明の半導体被覆正極活物質の製造方法における各工程について詳細に説明する。
まず、本発明におけるn型半導体被覆層形成工程について説明する。本発明におけるn型半導体被覆層形成工程とは、正極活物質表面をn型半導体材料により被覆してn型半導体被覆層を得る工程である。
また、上記ボールに用いられる材料としては、例えば、窒化ケイ素、ジルコニア、アルミナ、ステンレス等を挙げることができ、中でも、窒化ケイ素が好ましい。削れにくく、削れることによる不純物混入が抑制されるためである。
上記ボールミルする時間としては、例えば、1~50時間の範囲内、中でも、1~20時間の範囲内であることが好ましい。ボールミルする時間が短すぎると、n型半導体材料の被覆量が不十分なものとなるおそれがある。一方、ボールミルする時間が長すぎると活物質が割れるなどして劣化するおそれがあるからである。
次に、本発明におけるpn接合半導体被覆層前駆体形成工程について説明する。本発明におけるpn接合半導体被覆層前駆体形成工程とは、上記n型半導体被覆層表面をp型半導体材料により被覆してp型半導体被覆層を形成し、pn接合半導体被覆層前駆体を得る工程である。
なお、上記pn接合半導体被覆層前駆体においては、上記n型半導体被覆正極活物質表面に、n型半導体被覆層が被覆されていない部分があって、このような部分において正極活物質表面にp型半導体被覆層が形成されていても良い。
上記ボールミルする時間としては、例えば、1~50時間の範囲内、中でも、1~20時間の範囲内であることが好ましい。ボールミルする時間が短すぎると、p型半導体材料の被覆量が不十分なものとなるおそれがある。一方、ボールミルする時間が長すぎると活物質が割れるなどして劣化するおそれがあるからである。
次に、本発明における半導体被覆正極活物質形成工程について説明する。本発明における半導体被覆正極活物質形成工程とは、上記pn接合半導体被覆層前駆体を熱処理することによりpn接合半導体被覆層を形成し、半導体被覆正極活物質を得る工程である。
上記正極活物質がLiCoO2であり、上記pn接合半導体被覆層中のn型半導体材料としてP(リン)をドープしたSi(シリコン)粉末、p型半導体材料としてB(ホウ素)をドープしたSi(シリコン)粉末を用いた場合には、通常200~800℃の範囲内である。
(半導体被覆正極活物質作製)
正極活物質コバルト酸リチウム(LiCoO2)9.5gに、Pをドープしたn型-Si粉末0.3gを添加し、ボールミル混合して、n型-Si半導体被覆コバルト酸リチウムを得た。ボールミル条件としては、ポット材料として窒化ケイ素、およびボール材料として窒化ケイ素を用い、回転数300r.p.mで3時間行った。
次に、n型-Si半導体被覆コバルト酸リチウム9.8gに、Bをドープしたp型-Si粉末0.2gを添加し、ボールミル混合して、n型-Si半導体被覆層上にp型-Si半導体被覆層を形成した前駆体正極活物質を得た。ボールミル条件としては、ポット材料として窒化ケイ素、およびボール材料として窒化ケイ素を用い、回転数300r.p.mで3時間行った。
その後、前駆体正極活物質を不活性雰囲気(アルゴン)中で800℃の熱処理を行い、pn接合を形成させた半導体被覆コバルト酸リチウムを得た。
結着材であるポリビニリデンフロライド(PVDF)を溶解させた溶剤n-メチルピロリドン溶液中に、(半導体被覆正極活物質作製)で得られたpn接合を形成させた半導体被覆コバルト酸リチウム粉末9.0gと導電化材であるカーボンブラック1.0gを添加し、均一に混合するまで混錬し正極層用スラリーを作製した。
正極層用スラリーをAl集電体上に片面塗布し、その後乾燥することで正極電極体を作製した。
結着材であるポリビニリデンフロライド(PVDF)を分散させた水中に、負極活物質であるグラファイト粉末を添加し、均一に混合するまで混錬し負極層用スラリーを作製した。
負極層用スラリーをCu集電体上に片面塗布し、その後乾燥することで負極電極体を作製した。
上記正極電極体、上記負極電極体、およびセパレータとしてPP製多孔質セパレータを用いて、コインタイプの電池を作製した。電解液は、EC(エチレンカーボネート)、DMC(ジメチルカーボネート)を体積比率で3:7で混合したものに、支持塩として六フッ化リン酸リチウム(LiPF6)を濃度1mol/L溶解させたものを用いた。
(半導体被覆正極活物質作製)
正極活物質LiCoO29.5gに、Pをドープしたn型-Si粉末0.5gを添加し、ボールミル混合して、n型-Si半導体被覆コバルト酸リチウムを得た。ボールミル条件としては、ポット材料として窒化ケイ素、およびボール材料として窒化ケイ素を用い、回転数300r.p.mで6時間行った。
半導体被覆正極活物質作製時に、Pをドープしたn型-Si粉末0.5gを添加する代わりに、Bをドープしたp型-Si粉末0.5gを添加した以外は、比較例1と同様にして、コインタイプの電池を作製した。
[比較例3]
半導体被覆正極活物質作製時に、Pをドープしたn型-Si粉末を添加する代わりに、Si粉末を添加した以外は、比較例1と同様にして、コインタイプの電池を作製した。
(容量維持率測定および放電容量測定)
実施例、比較例1、比較例2および比較例3で得られたコインタイプの電池を用いて、容量維持率および放電容量について試験を行った。容量維持率は、4.2Vまで充電、2.9Vまで放電ともに1Cで100サイクル繰り返し、容量維持率を測定した。また、放電容量は、4.2Vまで充電を1Cで行った後、2.9Vまで10Cで放電を行い、放電容量を測定した。得られた結果を表1に示す。
また、放電容量は比較例1では45mAh/g、比較例2では42mAh/g、比較例3では31mAh/g、実施例では46mAh/gとなり、比較例1、比較例2、および実施例は比較例3に比べて良好な放電容量を示した。また、実施例が最も放電容量に優れたものであった。
また、実施例においては、pn接合半導体被覆層を有することにより、pn接合半導体被覆層中においては、電子はp型半導体被覆層からn型半導体被覆層へは移動することができない。このため、充電反応時のpn接合半導体被覆層中を通過する電解液から正極活物質への電子の移動を困難にして、充電反応時の電解液等の劣化を抑制することを可能とし、最も良好な容量維持率を示した。さらに、実施例においては、pn接合半導体被覆層を有することにより、pn接合半導体被覆層中においては、電子はn型半導体被覆層からp型半導体被覆層へ移動することが可能となる。このため、放電反応時のpn接合半導体被覆層中を通過する正極活物質から電解液への電子の移動を容易にして、正極活物質表面が被覆された部分においても放電反応時の電子伝導性が向上して出力を向上させることを可能とし、最も良好な放電容量を示した。
Claims (4)
- 正極活物質と、前記正極活物質表面に被覆されたn型半導体被覆層、および前記n型半導体被覆層表面に被覆されたp型半導体被覆層からなるpn接合半導体被覆層とを有することを特徴とする半導体被覆正極活物質。
- 前記pn接合半導体被覆層が前記正極活物質表面に部分的に被覆されていることを特徴とする請求の範囲第1項に記載の半導体被覆正極活物質。
- 請求の範囲第1項または第2項に記載の半導体被覆正極活物質を用いたことを特徴とするリチウム二次電池。
- 正極活物質表面をn型半導体材料により被覆してn型半導体被覆層を得るn型半導体被覆層形成工程と、前記n型半導体被覆層表面をp型半導体材料により被覆してp型半導体被覆層を形成し、pn接合半導体被覆層前駆体を得るpn接合半導体被覆層前駆体形成工程と、前記pn接合半導体被覆層前駆体を熱処理することによりpn接合半導体被覆層を形成し、半導体被覆正極活物質を得る半導体被覆正極活物質形成工程と、を有することを特徴とする半導体被覆正極活物質の製造方法。
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KR101287106B1 (ko) * | 2011-03-02 | 2013-07-17 | 삼성에스디아이 주식회사 | 리튬 이차 전지용 양극 활물질, 이의 제조 방법 및 이를 포함하는 리튬 이차 전지 |
US9111861B2 (en) * | 2012-02-06 | 2015-08-18 | Taiwan Semiconductor Manufacturing Company, Ltd. | Method of fabricating a semiconductor structure with ion-implanted conductive layer |
US10170746B2 (en) * | 2012-10-17 | 2019-01-01 | Infineon Technologies Ag | Battery electrode, battery, and method for manufacturing a battery electrode |
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US8603672B2 (en) | 2013-12-10 |
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US20110111291A1 (en) | 2011-05-12 |
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