KR20070066942A - Lithium secondary battery and method for preparing the same - Google Patents

Abstract

Provided is a lithium secondary battery, which has a low irreversible capacity during the first charge and discharges and does not lead to dendrite formation, the decomposition of an electrolyte solution, and the dissolution of a negative electrode current collector. The lithium secondary battery(1) comprises: a positive electrode(11) containing a positive active material capable of intercalating and deintercalating lithium; a negative electrode(12) containing a negative active material capable of intercalating and deintercalating lithium; and a non-aqueous electrolyte. The negative electrode(12) includes a lithium-containing metal compound which is insoluble in water and is able to deintercalate lithium at least upon discharge.

Description

Lithium secondary battery, and manufacturing method therefor {LITHIUM SECONDARY BATTERY AND METHOD FOR PREPARING THE SAME}

1 is a schematic cross-sectional view of a lithium secondary battery according to an embodiment of the present invention.

Figure 2a is a schematic diagram showing a negative electrode active material of a lithium secondary battery according to an embodiment of the present invention.

Figure 2b is a schematic cross-sectional view showing a negative electrode active material of a lithium secondary battery according to an embodiment of the present invention.

[Industrial use]

The present invention relates to a lithium secondary battery, and a method for manufacturing the same, more particularly, less irreversible capacity generated by the first charging and discharging, dendrites are generated, the electrolyte is decomposed, or the negative electrode current collector may be dissolved. The present invention relates to a lithium secondary battery and a method of manufacturing the same.

[Prior art]

BACKGROUND ART A lithium secondary battery using a material capable of reversibly intercalating and deintercalating lithium ions as an electrode active material has been put to practical use. As a positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), and the like are used, for example. Moreover, the carbon material is generally used for the negative electrode active material of a lithium secondary battery. As a specific example of a carbon material, graphite, amorphous carbon, low crystalline carbon, etc. are mentioned.

The positive electrode active material contains lithium, and this lithium travels between the positive electrode and the negative electrode in the form of lithium ions upon charge and discharge, and is reversibly intercalated and deintercalated with the positive electrode active material or the negative electrode active material.

Here, carbon materials such as graphite, amorphous carbon, or low crystalline carbon have a large charge and discharge capacity, and also have an irreversible capacity. The irreversible capacity is a capacity of lithium ions intercalated in the carbon material, which is not deintercalated in the captured state in the carbon material during the second and subsequent discharge processes and which does not contribute to the battery reaction. In particular, the irreversible capacity of the carbon material at the time of first charge reaches about 5%-about 10% of the charge / discharge capacity of the whole battery.

If part of the lithium ions supplied from the positive electrode active material to the negative electrode active material by the first charge cannot be recovered by subsequent discharge, even if a carbon material possessing a large charge / discharge capacity is used, for example, the irreversible If the capacity is large, the amount of lithium ions contributing to the second and subsequent charge / discharge reactions is small, and a high capacity lithium secondary battery cannot be obtained. In addition, generation of such an irreversible capacity | capacitance is a phenomenon which is not limited to a carbon material but is similarly generated also in Si type material, Sn type material, Al type material, etc.

On the other hand, in the second and subsequent charge and discharge reactions, the irreversible capacity of the carbon material is extremely small, and there is no fear that the amount of lithium ions that contributes to the charge and discharge reaction is greatly reduced. Therefore, as a countermeasure to increase the capacity of the lithium secondary battery, countermeasures such as improving the carbon material to reduce the irreversible capacity itself at the time of the first charge, or charging lithium inside the battery in advance corresponding to the irreversible capacity, etc. This is under consideration.

In particular, as a countermeasure for the latter, a lithium secondary battery in which metal lithium for an irreversible capacity is included in a negative electrode electrode in advance, and this metal lithium is used as an active material at the first discharge, thereby replenishing lithium for an irreversible capacity is provided. It is proposed.

In addition, a lithium secondary battery in which a lithium-containing composite nitride is contained in a negative electrode along with a carbon material instead of metallic lithium is also proposed (Japanese Patent Laid-Open No. 2002-117836).

However, in a lithium secondary battery in which metal lithium for an irreversible capacity is included in a negative electrode electrode in advance, it is difficult to predict the irreversible capacity. Thus, a design in which a slight excess amount of metallic lithium is included in the negative electrode active material in comparison with the irreversible capacity in advance is made. In the lithium secondary battery designed as described above, metallic lithium may remain in the negative electrode after the first discharge.

On the surface of this remaining metallic lithium, lithium ions may be precipitated at the next charge. Since the precipitated form of lithium ions is generally precipitated in the form of a dendrite, this dendrite lithium may penetrate the separator and cause a short between the anode and the anode.

In Japanese Patent Laid-Open No. 2002-117836, the lithium-containing composite nitride has a property of reacting with water to decompose. Therefore, when manufacturing the negative electrode electrode containing this lithium containing composite nitride, it is necessary to make the atmosphere at the time of manufacture into a dry atmosphere, and there exists a problem that production cost increases accordingly.

Further, in Fig. 2 of Japanese Patent Laid-Open No. 2002-117836, a charge / discharge curve of a lithium secondary battery having a positive electrode as LiCoO ₂ and a negative electrode as a carbon material and a lithium-containing composite nitride is disclosed. It is shown that the discharge reaction of the lithium-containing composite nitride occurs in the voltage range of 2.5 to 3V. However, the above charging and discharging curves are obtained only by adjusting the charging and discharging current and the final voltage at the time of charging and discharging, and no method of adjusting the discharge capacity with respect to the first charging capacity is considered. For this reason, when lithium-containing composite nitride is excessively added with respect to the irreversible capacity at the time of the first charge / discharge, a so-called overdischarge state continues for a long time, and there exists a problem of decomposition | disassembly of electrolyte solution or melt | dissolution of an anode collector.

An object of the present invention is to provide a lithium secondary battery having a low irreversible capacity generated by the first charge and discharge, no dendrites, no electrolyte decomposition, or no negative electrode current collector.

Still another object of the present invention is to provide a manufacturing method for manufacturing the lithium secondary battery.

In order to achieve the above object, the present invention is a positive electrode containing a positive electrode active material capable of intercalating and deintercalating lithium, a negative electrode containing a negative electrode active material capable of intercalating and deintercalating lithium And a nonaqueous electrolyte, wherein the negative electrode is inert to water and provides a lithium secondary battery comprising at least a lithium-containing metal compound capable of deintercalating lithium at discharge.

The lithium-containing metal compound preferably has a potential of 1.0 to 4.0 V for intercalating and deintercalating lithium when metal lithium is used as a counter electrode.

The lithium-containing metal compound preferably contains an element selected from the group consisting of Li and S, P, O, Cl, Se, F, Br, I, and combinations thereof.

The lithium-containing metal compound is selected from the group consisting of Ni, Co, Cu, Zn, Ga, Ge, Si, Al, Fe, V, Mn, Ti, Mo, Cr, Nb, Pt, and combinations thereof. It is preferable to further include.

In addition, the lithium-containing metal compound is preferably an olivine-based lithium-containing metal compound.

The lithium-containing metal compound preferably includes Li ₃ T ₂ (PO ₄ ) ₃ (wherein T is selected from the group consisting of Fe, V, and combinations thereof).

The lithium-containing metal compound preferably comprises a Li ₂ CuO _2.

The negative active material is C; Si; Sn; Al; Si alloys; Sn alloy; Al alloy; A metal compound containing an element selected from the group consisting of C, Si, Sn, Al, and combinations thereof; And combinations thereof.

The present invention also provides a positive electrode comprising a positive electrode active material, a negative electrode active material capable of intercalating and deintercalating lithium, and a lithium-containing metal that is inert to water and capable of deintercalating lithium at least at discharge. Preparing a negative electrode including a compound and a nonaqueous electrolyte, and interposing the nonaqueous electrolyte between the positive electrode and the negative electrode to form a base battery, and the base battery until the voltage of the base battery reaches the end-of-charge voltage Charging the battery; It provides a method for manufacturing a lithium secondary battery comprising the step of discharging the primary battery until the discharge capacity is the same as the charge capacity at the time of charging.

In the manufacturing method of the said lithium secondary battery, it is preferable to perform a 1st discharge until the potential of the said negative electrode turns into 1.0-4.0V when metal lithium is made into a counter electrode.

EMBODIMENT OF THE INVENTION Hereinafter, one Example of this invention is described in detail.

A lithium secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the components are housed in a battery case having various shapes such as a cylindrical shape, a square shape, a coin shape, and a sheet shape. It is constructed. Moreover, when a nonaqueous electrolyte consists of a nonaqueous electrolyte, a separator is interposed between the positive electrode and the negative electrode. The separator can be interposed between the positive electrode and the negative electrode even when the nonaqueous electrolyte is a solid electrolyte.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

1 is a schematic cross-sectional view of a rechargeable lithium battery according to one embodiment of the present invention.

Referring to FIG. 1, a lithium secondary battery according to an exemplary embodiment of the present invention is described. The lithium secondary battery 1 includes a positive electrode 11, a negative electrode 12, and a space between the positive electrode 11 and the negative electrode 12. The electrode assembly 14 including the existing separator 13 is placed in the case 15, and then the electrolyte is injected into the upper portion of the case 15 and sealed with the cap plate 16 and the gasket 17. .

(anode)

Examples of the positive electrode include a positive electrode material containing a positive electrode active material, a conductive agent, and a binder; And a positive electrode current collector bonded to the positive electrode mixture can be used. In addition, a pellet-like or sheet-like electrode formed by forming the cathode mixture in a disc shape can be used.

The positive electrode active material is made of a material capable of intercalating and deintercalating lithium. Examples of such a material include a compound containing Li, an oxide, a sulfide, and the like. The positive electrode active material preferably includes one selected from the group consisting of Mn, Co, Ni, Fe, Al, and a combination thereof. As the cathode active material is preferably used as the _{LiMn 2 O 4, LiCoO 2,} LiNiO 2, LiFeO 2, LiNi 1/3 Co 1/3 Mn 1/3 O 2, LiNi 0 .8 Co 0 .2 O 2 , etc. Do. As said binder, polyfluoro vinylidene, polytetrafluoro ethylene, etc. are preferable. It is preferable to use carbon, such as carbon black, Ketjen black, and graphite, as said electrically conductive agent. As the positive electrode current collector, it is preferable to use a metal foil or a metal net made of aluminum, stainless steel, or the like.

(cathode)

The negative electrode may include a negative electrode mixture including a negative electrode active material and a lithium-containing metal compound, a conductive agent, and a binder according to the present invention; And a negative electrode current collector bonded to the negative electrode mixture. Moreover, the pellet type or sheet type electrode which formed said negative electrode mixture in disk shape can also be used.

The negative electrode active material is made of a material capable of intercalating and deintercalating lithium, for example, C; Si; Sn; Al; Si alloys; Sn alloy; Al alloy; A metal compound containing an element selected from the group consisting of C, Si, Sn, Al, and combinations thereof; And it is preferable to include those selected from the group consisting of a combination thereof. Specific examples of the negative electrode active material include carbon materials such as graphite, amorphous carbon, low crystalline carbon, Si powder, tin oxide, and the like.

The lithium-containing metal compound preferably contains an element selected from Li, S, P, O, Cl, Se, F, Br, I, and combinations thereof. In addition, the lithium-containing metal compound is selected from the group consisting of Ni, Co, Cu, Zn, Ga, Ge, Si, Al, Fe, V, Mn, Ti, Mo, Cr, Nb, Pt, and combinations thereof. It may further include an element.

As the lithium-containing metal compound, an olivine-based lithium-containing metal compound can be preferably used, and as the olivine-based compound, in particular, Li ₃ T ₂ (PO ₄ ) ₃ (wherein the element T is Fe, V, and these It is selected from the group consisting of a combination). The Li ₃ T ₂ (PO ₄ ) ₃ may also intercalate and deintercalate lithium in the second and subsequent charge and discharge processes.

Li ₂ CuO ₂ can also be suitably used as a lithium-containing metal compound. The Li ₂ CuO ₂ deintercalates lithium during the first discharging process, but the crystal structure is changed during the second and subsequent charge and discharge, and thus lithium cannot be intercalated and deintercalated.

The lithium-containing metal compound can deintercalate lithium at least at the first discharge. The Li ₃ T ₂ (PO ₄ ) ₃ , and Li ₂ CuO ₂ may deintercalate about 1 mole of lithium per mole of the compound. The lithium-containing metal compound preferably has a potential of 1.0 to 4.0 V for intercalating and deintercalating lithium when metal lithium is used as a counter electrode. The potential range is equal to the battery voltage of 0 V to 1 V in the case of a battery using LiMn ₂ O ₄ , LiCoO ₂ , or the like as the positive electrode active material.

The lithium-containing metal compound is added to compensate for the irreversible capacity, and the amount of the lithium-containing metal compound is preferably equal to the irreversible capacity. It is preferable that the amount corresponds to a capacity of about 5% to 15% of the theoretical capacity of the substance. Specifically, when the negative electrode active material is a carbon material, it is preferable to add it in the range of 5% by mass to 10% by mass per mass of the carbon material. Moreover, when a negative electrode active material is Si powder, it is preferable to add in the range of 7 mass%-15 mass% per mass of Si powder. In the case of the polyphase alloy powder described below, the negative electrode active material is preferably added in the range of 7% by mass to 15% by mass per mass of the polyphase alloy powder.

It is preferable to determine the addition amount of the negative electrode active material per battery in relation to the theoretical capacity of the positive electrode active material, and specifically, the addition amount of the negative electrode active material is adjusted so that the theoretical capacity of the negative electrode active material is larger than the theoretical capacity of the positive electrode active material. The excess of the theoretical capacity of the negative electrode active material relative to the theoretical capacity of the positive electrode active material corresponds to the storage amount of lithium ions to be supplemented by the lithium-containing metal compound. Accordingly, in the second and subsequent charge and discharge processes, excess lithium ions are prevented from being precipitated as metallic lithium on the surface of the negative electrode.

The binder of the negative electrode may be either organic or inorganic, but any agent may be used as long as it is dispersed or dissolved in a solvent together with the negative electrode active material and the lithium-containing metal compound and the solvent is removed to bind the negative electrode active material. have. Moreover, after mixing with a negative electrode active material, what can solidify formation, such as pressurization, and bind | conclude a negative electrode active material can also be used.

As such a binder, it is preferable to use vinyl resin, cellulose resin, phenol resin, thermoplastic resin, thermosetting resin, and the like. Resin such as polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, styrene butadiene rubber is preferably used. It is more preferable to use. In addition to the negative electrode active material and the binder, carbon black, graphite powder, carbon fiber, metal powder, metal fiber, or the like may be added as the conductive agent. As the negative electrode current collector, it is preferable to use a metal foil or a metal net made of copper.

As for the said negative electrode active material, it is more preferable to use the polyphase alloy powder demonstrated below especially. The multiphase alloy powder is a powder that necessarily includes a Si phase and a SiM phase and includes either or both of an X phase and a SiX phase. In the multiphase alloy powder, the Si phase content on the particle surface is preferably less than the Si phase content in the particles. The schematic diagram of the one particle which comprises a multiphase alloy powder is shown in FIG. 2A, and the cross-sectional schematic diagram of the one particle shown in FIG. 2A is shown in FIG. As shown in FIGS. 2A and 2B, the polyphase alloy powder particles 211 constituting the negative electrode active material contain a Si phase 212, a SiM phase 213, and an X phase or a SiX phase 214.

Si phase 212 exists more in particle inside than a particle surface. The Si phase 212 forms an LiSi _x phase by alloying with lithium at the time of charging, and deintercalates lithium to become the Si phase 212 at the time of discharge. Since the content of the Si phase 212 on the particle surface is less than the content of the Si phase 212 in the particles, decomposition reaction of the electrolyte solution by the Si phase 212 on the particle surface is suppressed.

The SiM phase 213 does not react with lithium during charge and discharge, and maintains the shape of the particles 211 to suppress expansion and contraction of the particles 211 itself. The element M constituting the SiM phase 213 is a metal element that is not alloyed with lithium and is selected from the group consisting of Ni, Co, As, B, Cr, Cu, Fe, Mg, Mn, Y, and combinations thereof. Element. In particular, it is preferable to use Ni as the element M. In this case, the composition of the SiM phase 213 becomes a Si ₂ Ni phase.

In addition, the X phase 214 imparts electrical conductivity to the multiphase alloy powder, thereby reducing the specific resistance of the negative electrode active material itself. The element X constituting the X phase 214 is a metal element having a specific resistance of 3 Ω · m or less, and is an element selected from the group consisting of Ag, Cu, Au, and a combination thereof.

Since it does not form an alloy especially with lithium, it is preferable to use Cu which has an expansion suppression effect. Since Ag hardly forms an alloy with Si, by selecting a metal which does not form an alloy with Ag as element M, Ag can be present as a single phase and the conductivity of the particles can be improved.

On the other hand, Cu forms an alloy with Si and has a smaller resistance than Si, and therefore Cu is an element possessing both the properties of element M and element X. Therefore, in the present invention, Cu can be selected for both the element M and the element X, but Cu is not selected at the same time as the element M and the element X.

A SiX phase may be deposited instead of the X phase 214 or together with the X phase 214. SiX phase, like X phase 214, imparts electrical conductivity to the multiphase alloy powder, thereby reducing the resistivity of the negative electrode active material itself.

The crystal forms of the Si phase 212, the SiM phase 213, the X phase 214, and the SiX phase are determined by the quench rate, alloy composition, and the presence or absence of heat treatment after quenching. In the negative electrode active material according to an embodiment of the present invention, each phase may be a crystalline phase, an amorphous phase may be good, and a crystalline phase and an amorphous phase may be mixed. In addition to the Si phase, SiM phase, X phase, and SiX phase, other alloy phases may be included.

Since Si is an element which forms a Si single phase, a SiM phase, and a SiX phase, the capacity | capacitance of Si can be obtained by selecting a composition ratio so that a Si single phase may still be produced even if it forms SiM phase and SiX phase judged from the state diagram of an alloy. However, when the amount of Si increases excessively, many Si phases precipitate, and the expansion and shrinkage amount of the whole negative electrode active material becomes large at the time of charge and discharge, and it is unpreferable because the negative electrode active material is micronized and the cycling characteristics fall. It is preferable that the composition ratio of Si in a negative electrode active material is 30 mass%-70 mass% specifically ,.

Since element M is an element which forms SiM phase with Si, it is preferable to add so that the whole quantity may form an alloy with Si. When the amount of M exceeds the amount capable of forming an alloy with Si, all of Si forms an alloy, which causes a large decrease in capacity.

Moreover, when there is little M amount, SiM phase will become small, the expansion suppression effect of Si phase will decrease, cycling characteristics will fall, and it is unpreferable. Moreover, a plurality of M phases may exist like other elements, M1 phase, M2 phase, and M3 phase. Although the composition ratio of M cannot be specifically limited because the solid solution limit with Si differs from element, it is preferable that it is a composition ratio which makes a Si phase exist even if alloying is formed to the solid solution limit of Si and M. Element M does not form an alloy with lithium and therefore does not have an irreversible capacity. In addition, the element M is preferably insoluble in the alkaline solution.

In addition, when the composition ratio of X increases, the specific resistance is decreased, but the Si phase is relatively decreased, and the charge / discharge capacity is lowered. On the other hand, when the composition ratio of X is small, the specific resistance of the negative electrode active material becomes high and the charge / discharge efficiency falls. For this reason, it is preferable that the composition ratio of X in a negative electrode active material is the range of 1 mass%-30 mass%. In addition, the element X is preferably insoluble in the alkaline solution.

It is preferable that the average particle diameter of a polyphase alloy powder is 5 micrometers-30 micrometers. In general, an alloy powder containing Si has a higher resistance than graphite powder which is conventionally used as a negative electrode material of a lithium secondary battery, and therefore, it is preferable to use a conductive agent. However, when the average particle diameter is 5 μm or less, it is better than the particle size of the conductive agent. Since the average particle diameter of a polyphase alloy powder may become small, it becomes difficult to obtain the effect of a electrically conductive agent, and battery characteristics, such as a capacity | capacitance and a cycle characteristic, fall, and are unpreferable. When the average particle diameter exceeds 30 µm, the packing density of the negative electrode active material in the lithium secondary battery is lowered, which is not preferable.

As shown in Figs. 2A and 2B, a plurality of fine pores 215 are formed on the particle surface of the multiphase alloy powder. The fine pores 215 are formed by impregnating the alkaline solution immediately after quenching the molten alloy, and are traces generated by the elution of the Si phase exposed to the particle surface immediately after quenching. As such, since Si is not exposed to the particle surface, the reaction with the electrolyte solution is suppressed during charging, and the micropores 215 are formed to increase the specific surface area of the multiphase alloy powder, thereby increasing the contact area with the electrolyte solution. The discharge efficiency is improved.

The average diameter of the micropores 215 is preferably 10nm to 5μm. In addition, the depth of the micropores 215 is preferably 10nm to 1μm. In addition, the specific surface area of the multiphase alloy powder is preferably 0.2 m ² / g to 5 m ² / g.

The negative electrode active material can be manufactured by the following method.

The method for producing the negative electrode active material comprises a step of obtaining a quenched alloy powder containing Si, an element M, and an element X, and a step of impregnating the obtained quenched alloy powder in an alkaline solution. Hereinafter, each process is demonstrated one by one.

First, in the process of manufacturing a quenching alloy powder, quenching alloy powder is quenched by quenching the molten alloy containing Si, element M, and element X. The molten alloy contains the above-mentioned elements M, X, and Si. The alloy molten metal can be obtained by simultaneously dissolving a single substance or an alloy of the above elements by, for example, a high frequency induction heating method.

It is preferable that the content rate of Si in the said molten alloy is 30 mass%-70 mass%. If the content of Si in the molten alloy is out of the above range, it is not preferable because the Si content is too small to precipitate the Si phase, or the amount of Si is excessively large to produce a negative electrode active material that is easy to expand and contract.

It is preferable to use the gas atomizing method, the water atomizing method, the roll quenching method, or the like as a method of rapidly cooling the molten alloy. In the gas atomizing method and the water atomizing method, a powdery quenching alloy is obtained, and in the roll quenching method, a thin band-shaped quenching alloy is obtained. Thin strip quenched alloys can be ground to powder. The average particle diameter of the quench alloy powder thus obtained becomes the average particle diameter of the multiphase alloy powder to be finally obtained. Therefore, when obtaining a quenching alloy powder, it is necessary to adjust the average particle diameter to the range of 5 micrometers or more and 30 micrometers or less.

The quench alloy powder obtained from the molten alloy is a quench alloy in which the entire structure is in an amorphous phase, or a quench alloy in which a part is in an amorphous phase and the remainder is crystalline particles, or a quench alloy in which the entire structure is in a crystalline phase. In the quenching alloy powder, a SiX phase and a SiM phase are necessarily included, and either or both phases of the X phase and the SiX phase may be included. In addition, the Si phase, SiM phase, X phase, and SiX phase are in a state in which alloy phases are uniformly mixed.

In addition, in the case of quenching, the quenching speed is preferably 100 K / sec or more. If the quenching rate is less than 100 K / sec, there is a fear that the phases of the Si phase, the SiM phase, the X phase, and the SiX phase may not be uniformly precipitated in the alloy structure, and the size of the crystals of each phase becomes too large, resulting in a uniform expansion inhibiting effect It is not preferable because it becomes difficult to obtain the effect of imparting electrical conductivity.

Next, in the step of impregnating the quench alloy with the alkaline solution, the Si phase precipitated on the particle surface of the quench alloy powder is eluted and removed. Specifically, the quench alloy powder is impregnated with an alkaline solution, followed by washing and drying. The impregnation is preferably performed while stirring at room temperature slowly for about 30 minutes to 5 hours. Moreover, it is preferable to use sodium hydroxide and potassium hydroxide aqueous solution as an alkaline solution, and it is preferable that concentration is 1-5N.

The impregnation conditions described herein are only one example, and in practice, the impregnation conditions can be determined by confirming that only the Si phase precipitated on the particle surface is eluted and removed. Excessive impregnation treatment is not preferable because not only the surface but also the Si phase inside the particles are eluted and removed, and the charge / discharge capacity of the negative electrode active material is lowered. Moreover, when eluting to the Si phase inside a particle | grain, since the intensity | strength of the particle itself falls, it is not preferable. Insufficient impregnation treatment is not preferable because the Si phase remains on the surface of the particles, causing decomposition reaction of the electrolyte solution.

Specifically, after removing the Si phase, it is preferable to perform impregnation with an alkaline solution until the specific surface area of the powder becomes 1.2 times or more of the specific surface area of the quench alloy powder before removing the Si phase. By performing the impregnation treatment until the specific surface area becomes 1.2 times or more of the original, part or all of Si on the surface can be removed, and the reaction with the electrolyte solution can be suppressed.

After removing the Si phase, it is preferable to perform an impregnation treatment with an alkaline solution so that the specific surface area of the powder is at least 50 times the specific surface area of the quench alloy powder before removing the Si phase. Thereby, dissolution of Si more than necessary can be prevented, and reduction of battery capacity can be prevented.

By performing the above impregnation treatment, the Si phase precipitated on the particle surface of the quench alloy powder is eluted and the SiM phase and the X phase or SiX phase remain on the particle surface. Further, micropores are formed in the portion from which the Si phase is removed. In addition, since the Si phase on the particle surface is removed, the amount of the Si phase on the particle surface becomes smaller than the amount of the Si phase on the inside of the particle.

In addition, the element M and the element X are insoluble with respect to the alkaline solution, and since the SiM phase and the SiX phase are also insoluble in the alkali solution, the Si phase is eluted first.

According to the above production method, by quenching the molten alloy containing the element M, element X and Si, the SiX phase and SiM phase are necessarily included, and the phase selected from the group consisting of X phase, SiX phase, and combinations thereof It is possible to easily form a quenching alloy powder containing. By immersing the obtained quenching alloy powder in an alkaline solution to remove the Si phase on the particle surface, the amount of Si phase on the particle surface becomes smaller than the amount of Si phase on the inside of the particle. The negative electrode active material thus obtained can improve the cycle characteristics by suppressing the decomposition reaction of the electrolyte solution and simultaneously reducing the amount of expansion and shrinkage of the particles themselves.

In addition, according to the above production method, a multiphase alloy powder containing a phase selected from the group consisting of an SiX phase and a SiM phase and an X phase, a SiX phase, and a combination thereof can be easily produced. In particular, according to the gas atomization method or the water atomization method, since the spherical powder is obtained, the packing density of the negative electrode active material can be increased, and the energy density of the negative electrode active material can be increased.

(Nonaqueous electrolyte)

As the nonaqueous electrolyte, it is preferable to use a nonaqueous electrolyte in which a lithium salt is dissolved in an aprotic solvent.

As an aprotic solvent, propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetra hydrofuran, 2-methyl tetra hydrofuran, γ-butyrolactone, dioxolane, 4-methyl dioxolane, N , N-dimethylformamide, dimethyl acetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxy ethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methylethyl carbonate, diethyl carbonate, methyl Preferred are aprotic solvents selected from the group consisting of propyl carbonate, methylisopropyl carbonate, ethylbutyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, diethylene glycol, dimethyl ether, and combinations thereof, Especially propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and aprotic solvents selected from the group consisting of combinations thereof, and in the group consisting of dimethyl carbonate (DMC), methylethyl carbonate (MEC), diethyl carbonate (DEC), and combinations thereof More preferably, the aprotic solvent selected is necessarily included.

Lithium salts include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x +1} SO ₂ ) (C _y F _{2y +1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, and combinations thereof Preferably, it is more preferable to include LiPF ₆ especially.

Instead of the non-aqueous electrolyte, a polymer electrolyte such as a polymer obtained by mixing any one of the lithium salts with a polymer such as polyethylene oxide (PEO) and polyvinyl alcohol (PVA) or impregnated with an organic electrolyte solution into a polymer having high swellability may be used. have.

(Separator)

As a material of a separator, the microporous membrane which consists of polyolefin resins, such as polypropylene and polyethylene, is preferable.

(Method for producing lithium secondary battery)

Hereinafter, in one Example of this invention, the manufacturing method of a lithium secondary battery is demonstrated.

First, a binder for positive electrode (for example, polyfluoro vinylidene) is dissolved in a solvent (for example, N-methyl pyrrolidone), and a positive electrode active material and a conductive agent are added to this solution to prepare a slurry. This slurry is applied to a positive electrode current collector, dried, cut into appropriate sizes, and a positive electrode is produced.

A negative electrode binder (e.g., polyfluorovinylidene) is dissolved in a solvent (e.g., N-methyl pyrrolidone), and a negative electrode active material and a lithium-containing metal compound and a conductive agent are optionally added to the solution. It is added to prepare a slurry, the slurry is applied to a negative electrode current collector, dried, and cut to a suitable size to prepare a negative electrode.

A base cell is manufactured by forming an electrode group through a separator between the obtained positive electrode and negative electrode, storing the electrode group in a cylindrical battery container, for example, injecting an electrolyte solution and then sealing the inlet of the battery container. do.

In the case of using a solid electrolyte, an electrode group is formed between a positive electrode and a negative electrode through a solid electrolyte and a separator, if necessary, and the electrode group is stored in, for example, a cylindrical battery container and the inlet of the battery container is opened. It seals and manufactures a basic battery.

Next, the manufactured base battery is charged at 0.05C to 0.2C until the end voltage of charging is 4.1V to 4.3V, followed by constant current charging for 10 hours to 2.5 hours, and the first charging is performed. . Subsequently, the primary cell is discharged (first discharge) at 0.1C to 0.2C until the discharge capacity becomes the same as the charge capacity at the time of the first charge.

According to the first charge, lithium included in the positive electrode active material is intercalated with the negative electrode active material. At this point, the battery voltage is about 4.1V to 4.3V. Then, when the first discharge is performed, most of the lithium intercalated to the negative electrode active material is intercalated to the positive electrode active material, but some remain in the negative electrode active material. The capacity equivalent to the remaining lithium is an irreversible capacity. The battery voltage at the time of lithium deintercalation from the negative electrode active material varies depending on the combination of the positive electrode active material and the negative electrode active material, but is about 2.7 V. The discharge capacity at this point is lower than the charging capacity because there is an irreversible capacity.

In order to make the discharge capacity equal to the charge capacity, it is necessary to continue the discharge. When discharge continues, when the battery voltage is about 1V to 0V (the negative electrode potential when the metal lithium is counter electrode is in the range of 3.0V to 4.0V), lithium is deintercalated with the lithium-containing metal compound. To start. Since the lithium-containing metal compound is added to the extent that the irreversible capacity can be compensated, lithium corresponding to the capacity of the irreversible capacity is deintercalated into the lithium-containing metal compound until the discharge capacity is about the same as the charging capacity. By discharging when the discharge capacity reaches the charge capacity, the same amount of lithium that has moved to the cathode side during the first charge is returned to the anode side.

As described above, a lithium secondary battery in which the irreversible capacity of the negative electrode active material is supplemented by lithium contained in the lithium-containing metal compound can be produced.

When charging and discharging the manufactured lithium secondary battery, it is preferable to perform charging and discharging with a charge end voltage of about 4.1V to 4.3V and a discharge end voltage of 2.7V.

As described above, according to the lithium secondary battery of one embodiment according to the present invention, since the lithium-containing metal compound is added to the negative electrode, the irreversible capacity generated by the first charge / discharge is discharged from the lithium-containing metal compound at the time of discharge. It can replenish with lithium to deintercalate, and can charge and discharge capacity of a lithium secondary battery. In addition, since the lithium-containing metal compound is inert to water, handling at the time of manufacture is easy.

In addition, the potential for intercalating and deintercalating lithium of a lithium-containing metal compound is 3.0 V to 4.0 V or less when the metal lithium is a counter electrode, and the potential range is LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ In a battery using the light (hereinafter, referred to as LiCoO ₂ or the like), it is the same as the battery voltage of 0V to 1V. In a battery using LiCoO ₂ or the like as the positive electrode active material, the normal discharge termination voltage is about 2.7V and does not discharge to about 1V.

Therefore, in the lithium secondary battery according to the embodiment of the present invention, only during the first discharge process, the discharge end voltage is set to 0V to 1V to deintercalate lithium from the lithium-containing metal compound, and the second discharge Thereafter, the discharge end voltage can be, for example, 2.7 V, so that overdischarge can be avoided, and decomposition and dissolution of the negative electrode current collector in the electrolyte can be avoided.

In addition, according to the method for manufacturing a lithium secondary battery according to an embodiment of the present invention, the base battery is charged until the battery voltage reaches a predetermined end voltage of charging, and then only the capacity equal to the charging capacity at the time of charging is obtained. Since the base battery is discharged, lithium is deintercalated from the lithium-containing metal compound as well as the negative electrode active material at the time of discharge, and the irreversible capacity generated during the first charge is deintercalated from the lithium-containing metal compound. The lithium secondary battery can be supplemented with lithium, and has a high charge / discharge capacity. In addition, by making the charge capacity and the discharge capacity the same, there is no risk of intercalating an excessive amount of lithium as compared with the charge capacity of the positive electrode active material, and overcharge can be prevented.

In addition, when the potential of the negative electrode is the counter electrode, the first discharge is performed until the discharge termination voltage is reached, whereby lithium deintercalates from the lithium-containing metal compound only in the first discharge process. Therefore, overdischarge can be avoided by this, and decomposition and dissolution of a negative electrode current collector in an electrolyte solution can be avoided.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited by the following examples.

(Example 1)

Polyvinylidene fluoride was dissolved in N-methyl pyrrolidone to make a solution at a concentration of 50%, and LiCoO ₂ and carbon black were added to the solution to make a slurry. The slurry was applied to Al foil, dried, and cut to an appropriate size to prepare a positive electrode. The theoretical capacity (charge / discharge capacity) of the positive electrode was 140 mAh / g.

Further, polyvinylidene fluoride was dissolved in N-methyl pyrrolidone to make a solution having a concentration of 50%, and graphite and Li ₃ V ₂ (PO ₄ ) ₃ were added to the solution to form a slurry. The slurry was applied to Cu foil, dried, and cut to an appropriate size to prepare a negative electrode.

The addition amount of Li ₃ V ₂ (PO ₄ ) ₃ was 10 mass% per mass of graphite. Moreover, the theoretical capacity (charge / discharge capacity) of the negative electrode was 330 mAh / g, and the electric capacity of Li ₃ V ₂ (PO ₄ ) ₃ was 120 mAh / g.

An electrode group was formed through a polypropylene separator between the prepared positive and negative electrodes, and the electrode group was accommodated in a coin-type battery container. Then, the electrolyte solution obtained by dissolving 1.3 M LiPF ₆ in a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a ratio of EC: DMC = 30: 70 capacity ratio is injected, and the inlet of the battery container is poured. By sealing, the basic battery of Example 1 was manufactured.

(Example 2)

A basic battery of Example 2 was manufactured in the same manner as in Example 1 except that Li ₂ CuO ₂ was added in place of Li ₃ V ₂ (PO ₄ ) ₃ . On the other hand, the amount of Li ₂ CuO ₂ added was 10 mass% per mass of graphite, the theoretical capacity (charge and discharge capacity) of the negative electrode was 330 mAh / g, and the electric capacity of Li ₂ CuO ₂ was 110 mAh / g. The theoretical capacity (charge / discharge capacity) of the positive electrode was 140 mAh / g.

(Comparative Example 1)

A basic battery of Comparative Example 1 was prepared in the same manner as in Example 1 except that Li ₃ V ₂ (PO ₄ ) ₃ was not added. On the other hand, the theoretical capacity (charge / discharge capacity) of the negative electrode was 330 mAh / g, and the theoretical capacity (charge / discharge capacity) of the positive electrode was 140 mAh / g.

The primary batteries of Examples 1, 2 and Comparative Example 1 were subjected to constant current charging until the end-of-charge voltage was 4.2V at 0.2C, and then constant voltage charging for 2.5 hours. Was carried out.

Subsequently, the base batteries of Examples 1 and 2 were discharged at 0.1 C (first discharge) until the discharge capacity was the same as the charge capacity at the time of the first charge. The discharge end voltage at this time was about 0V (about 4.0V in the case where the counter electrode was Li).

On the other hand, about the basic battery of the comparative example 1, discharge (first discharge) was performed at 0.1 C until voltage became 2.75V.

Thereafter, charging and discharging were repeated four times for the basic batteries of Examples 1, 2 and Comparative Example 1 under the same conditions. The charging conditions were constant current charging until charging end voltage 4.2V was 0.5 C, and the constant voltage charge was performed for 1 hour after that, discharge conditions were 0.5C, and the discharge end voltage was 2.75V.

For each basic battery, charge and discharge efficiency (nth discharge capacity / nth charge capacity x 100 (%)) was obtained for each charge and discharge cycle. The results are shown in Table 1.

Anode active material Lithium-containing metal compounds Charge and discharge efficiency (%) 1 cycle 2 cycles 3 cycles 4 cycles 5 cycles Example 1 black smoke Li ₃ V ₂ (PO ₄ ) ₃ 100 99 99.2 99.3 99.6 Example 2 black smoke Li ₂ CuO ₂ 100 98.9 99.1 99.3 99.4 Comparative Example 1 black smoke - 91.3 98.5 99.2 99.4 99.6

As shown in Table 1, in Examples 1 and 2, the charge and discharge efficiency of one cycle is 100%, and the charge and discharge efficiency of about 99% is maintained even after two cycles.

On the other hand, in Comparative Example 1, the charge and discharge efficiency of one cycle was 91.3%, which was lower than that of Examples 1 and 2. This is considered to be because part of lithium was trapped in the negative electrode active material as an irreversible capacity. The charge and discharge efficiency after two cycles of Comparative Example 1 does not appear to be significantly different from Examples 1 and 2, but when comparing the actual charge and discharge capacity, reflecting the difference of the first charge and discharge efficiency, the charge of Comparative Example 1 It can be seen that the discharge capacity is reduced by about 10% with respect to Examples 1 and 2.

According to the lithium secondary battery of the present invention, since the lithium-containing metal compound which is inert to water and capable of deintercalation of lithium at the time of discharge is added to the negative electrode, the irreversible capacity generated by the first charge / discharge is reduced to lithium. The containing metal compound can be replenished by lithium deintercalated at the time of discharge, and the charge / discharge capacity of a lithium secondary battery can be raised.

In addition, since the lithium-containing metal compound is inert to water, handling at the time of manufacture is easy.

The potential for intercalating and deintercalating lithium of a lithium-containing metal compound is in the range of 1.0 V or more and 4.0 V or less when the metal lithium is the counter electrode, and the potential range is LiCoO ₂ , LiNiO in the positive electrode active material. ₂ , a battery using LiMn ₂ O ₄ (hereinafter referred to as LiCoO ₂ and the like) corresponds to a battery voltage of 0V to 1V. In a battery using LiCoO ₂ or the like as the positive electrode active material, the normal discharge termination voltage is about 2.7V and does not discharge to about 1V. Therefore, in the lithium secondary battery with a lithium-containing metal compound according to the present invention, only during the first discharge process, the discharge end voltage is set to 0V to 1V to deintercalate lithium in the lithium-containing metal compound, After the first discharge, the discharge end voltage is preferably set to 2.7V. As a result, overdischarge can be prevented and decomposition of the electrolyte solution and dissolution of the negative electrode current collector can be completely prevented.

In addition, according to the method for producing a lithium secondary battery of the present invention, a lithium-containing metal compound is added to a negative electrode to form a base battery, and the base battery is charged until the battery voltage reaches a predetermined end-of-charge voltage. Since the base battery is discharged only at the same capacity as the charging capacity at the time of charging, at the time of discharge, lithium is deintercalated not only in the negative electrode active material but also in the lithium-containing metal compound, and thus irreversible generated during the first charging. The capacity can be supplemented by lithium of this lithium-containing metal compound, whereby a lithium secondary battery having a high charge and discharge capacity can be produced. Moreover, there is no possibility of intercalating excess lithium with respect to the charge capacity of a positive electrode active material, and overcharge can be prevented.

In addition, since the first discharge is performed until the potential of the negative electrode becomes the discharge end voltage when the metal lithium is made counter electrode, lithium is discharged from the lithium-containing metal compound only in the first discharge process, thereby overdischarging. Can be avoided and decomposition or dissolution of the negative electrode current collector in the electrolyte can be prevented.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (17)

A positive electrode containing a positive electrode active material capable of intercalating and deintercalating lithium; A negative electrode containing a negative electrode active material capable of intercalating and deintercalating lithium; And Includes nonaqueous electrolyte, The negative electrode is a lithium secondary battery which is inert to water and contains at least a lithium-containing metal compound capable of deintercalating lithium during discharge. The method of claim 1, The lithium-containing metal compound is a lithium secondary battery having a potential of 1.0 to 4.0V intercalation and deintercalation of lithium when the metal lithium as a counter electrode. The method of claim 1, The lithium-containing metal compound is Li; And S, P, O, Cl, Se, F, Br, I, and a lithium secondary battery comprising an element selected from the group consisting of a combination thereof. The method of claim 3, The lithium-containing metal compound is selected from the group consisting of Ni, Co, Cu, Zn, Ga, Ge, Si, Al, Fe, V, Mn, Ti, Mo, Cr, Nb, Pt, and combinations thereof. A lithium secondary battery that further comprises. The method of claim 1, The lithium-containing metal compound is an olivine-based lithium-containing metal compound lithium secondary battery. The method of claim 1, The lithium-containing metal compound is Li ₃ T ₂ (PO ₄ ) ₃ (wherein the element T is selected from the group consisting of Fe, V, and combinations thereof). The method of claim 1, The lithium-containing metal compound is Li ₂ CuO ₂ It is a lithium secondary battery. The method of claim 1, The negative active material is C; Si; Sn; Al; Si alloys; Sn alloy; Al alloy; A metal compound containing an element selected from the group consisting of C, Si, Sn, Al, and combinations thereof; And a combination thereof. The method of claim 1, Content of the lithium-containing metal compound is a lithium secondary battery that corresponds to a capacity of 5 to 15% of the theoretical capacity of the negative electrode active material. The method of claim 1, The negative electrode active material is a lithium secondary battery (M is Ni, Co, As, B, Cr, which is a multi-phase alloy powder necessarily containing a Si phase and a SiM phase, including any one or both of the X or SiX phase) Element selected from the group consisting of Cu, Fe, Mg, Mn, Y, and combinations thereof, and X is an element selected from the group consisting of Ag, Cu, Au, and combinations thereof). Preparing a positive electrode including a positive electrode active material, a negative electrode active material and a negative electrode containing a lithium-containing metal compound which is inert to water and capable of at least deintercalating lithium at discharge; Constructing a basic battery by interposing the nonaqueous electrolyte between the positive electrode and the negative electrode; Charging the base battery until the voltage of the base battery reaches a charge end voltage; And And discharging the primary battery until the discharge capacity becomes the same as the charge capacity at the time of charging. The method of claim 11, The first discharge is performed until the potential of the negative electrode is 1.0 to 4.0V when the metal lithium is the counter electrode. The method of claim 11, The lithium-containing metal compound is Li; And S, P, O, Cl, Se, F, Br, I, and a method for producing a lithium secondary battery comprising an element selected from the group consisting of a combination thereof. The method of claim 13, The lithium-containing metal compound is selected from the group consisting of Ni, Co, Cu, Zn, Ga, Ge, Si, Al, Fe, V, Mn, Ti, Mo, Cr, Nb, Pt, and combinations thereof. The method of manufacturing a lithium secondary battery further comprising. The method of claim 11, The lithium-containing metal compound is an olivine-based lithium-containing metal compound manufacturing method of a lithium secondary battery. The method of claim 11, The lithium-containing metal compound is Li ₃ T ₂ (PO ₄ ) ₃ (However, the element T is selected from the group consisting of Fe, V, and combinations thereof). The method of claim 11, The lithium-containing metal compound is Li ₂ CuO ₂ Method for producing a lithium secondary battery.

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