KR100686805B1 - Lithium rechargeable battery - Google Patents

Abstract

In a lithium secondary battery having an electrode assembly having two electrodes and a separator, and an electrolyte, and a case for receiving and sealing the electrode assembly and the electrolyte, one of the two electrodes is a titanium oxide as an active material component for storing and releasing lithium or lithium ions. A lithium secondary battery is disclosed, comprising a ceramic material as a filler. In the present invention, the electrode containing titanium oxide may act as a cathode during discharge, and titanium oxide having a spinel structure is preferable as the titanium oxide. The active material may further include silicon oxide in addition to titanium oxide.

According to the present invention, it is possible to implement a high capacity battery by increasing the amount of available lithium per unit mass and to obtain a lithium secondary battery having high cycle life characteristics.

Description

Lithium secondary battery {Lithium rechargeable battery}

1 is an exploded perspective view showing the overall configuration of a lithium secondary battery according to an embodiment of the present invention;

2 is a partial cross-sectional view showing a state in which a separator is interposed between two electrode active materials according to an embodiment of the present invention;

3 is a conceptual diagram showing the particle configuration of the filler of the separator according to an embodiment of the present invention.

* Explanation of symbols for the main parts of the drawings

10: can 15: bead

13a and 13b: insulating plate 20: electrode assembly

25: separator 21, 23: electrode

27,29: electrode tab 30: gasket

40: vent 50: CID (current interrupt device)

60: positive thermal coefficient (PTC)

70: cap up 80: cap assembly

211 and 231: active material layer 213 and 233: current collector

251: filler 255: binder

The present invention relates to a lithium secondary battery, and more particularly to a separator of a lithium secondary battery electrode assembly.

Secondary batteries are rechargeable and have a high possibility of being small and large in capacity. Recently, as demand for portable electronic devices such as camcorders, portable computers, and mobile phones is increasing, research and development on secondary batteries has been made with the power of these portable electronic devices. Representative examples of the recent development and use include nickel-hydrogen (Ni-MH) batteries, lithium (Li) ion batteries, and lithium ion (Li-ion) polymer batteries.

Lithium, which is widely used as a material for secondary batteries, is a material suitable for producing a battery having a large electric capacity per unit mass due to a small atomic weight of the element itself. On the other hand, since lithium reacts violently with moisture, a non-aqueous electrolyte is used in a lithium battery. In this case, since it is not affected by the electrolysis voltage of water, the lithium-based battery has an advantage of generating an electromotive force of about 3 to 4 volts.

Lithium secondary batteries usually have two electrodes and a separator that prevents short-circuits between them, and are stacked in a case together with a non-aqueous electrolyte and placed in a case together with a nonaqueous electrolyte. Has

The nonaqueous electrolyte used in the lithium ion secondary battery is largely a liquid electrolyte and a solid electrolyte. The liquid electrolyte is obtained by dissociating lithium salt into an organic solvent. As the organic solvent, ethylene carbonate, propylene carbonate or other alkyl group-containing carbonates or similar organic compounds can be used.

The solid electrolyte is a material having a property that the solid itself passes ions such as lithium ions while a voltage is applied, and may be divided into an organic system made of a polymer material and an inorganic system made of a crystalline or amorphous inorganic material. The solid electrolyte may be itself a ionic conductivity, but is usually not a conductor, and thus may serve as a separator.

On the other hand, the separator is to prevent the short circuit of the two electrodes in the battery, and should have a structure that can pass ions in the state with the electrolyte or by itself. Therefore, the separator becomes a factor to limit the movement of lithium ions between the two electrodes. Except in the case where the fully solid electrolyte also serves as the separator, if the separator present between the two electrodes does not have sufficient permeability and wettability to the electrolyte, the restriction of the movement of lithium ions between the two electrodes by the separator is likewise This is an important problem in discharge.

Therefore, in the characteristics of the separator related to the performance of the battery, it means the area of the empty space portion at any cross section of the separator together with the ion conductivity of the separator (polymer separator, etc.), heat resistance, heat deformation resistance, chemical resistance, mechanical strength, and the like. Porosity, wettability by the electrolyte, and the like are major indicators.

Meanwhile, the separator of the lithium secondary battery using the liquid electrolyte also serves as a safety device that prevents the battery from overheating. The polyolefin-based microporous membrane, which is a conventional material of the separator, becomes soft and partially melted when it reaches a certain temperature due to an abnormal battery. Therefore, the micro-pores of the microporous membrane serving as the connection passage of the electrolyte solution and the passage of lithium ions are shut down. The movement of lithium ions is stopped, and the flow of internal and external currents of the battery stops, so that the temperature rise of the battery due to the current also stops.

However, if the temperature of the battery suddenly rises for some reason, for example, due to external heat transfer or the like, despite the fine pore closure of the separator, the temperature rise of the battery may continue for a certain time, resulting in breakage of the separator. That is, when the separator is partially melted and the two poles of the battery directly touch at that portion, causing an internal short circuit, and the separator is retracted, and the two poles of the battery may abut and short at that position. This short-circuit poses a more serious risk.

In addition, according to the tendency of increasing the capacity of the battery, a large amount of current can flow in the secondary battery in a short time. In this case, once the abnormal current flows in the secondary battery, even if the micropores are closed, the melting of the separator is continued due to the heat generated, rather than the temperature of the battery being immediately lowered by the current blocking, and the internal short circuit caused by the breakage of the separator is prevented. The probability of occurrence is increasing.

In such a situation, the interruption of the current by the opening of the separator is also important, but the problem that the separator melts or shrinks when the battery is overheated becomes more important. That is, it is desired to stably prevent the internal short circuit between the electrodes even at a relatively high temperature of 200 degrees Celsius or more.

In addition, according to the tendency of high capacity in lithium secondary batteries, there is a continuous demand for the development of active materials capable of increasing the amount of lithium available for charging and discharging per unit volume or unit mass of an electrode active material and increasing the discharge potential difference between two electrodes. There is also a demand for development of an electrode material capable of improving characteristics.

An object of the present invention is to provide a lithium secondary battery having a configuration that can reduce the problems of the conventional lithium secondary battery described above.

An object of the present invention is to provide a lithium secondary battery having a separator film resistant to deformation and damage even at a high temperature of 200 ° C or higher.

An object of the present invention is to provide a lithium secondary battery having a negative electrode active material capable of increasing battery capacity and having excellent life cycle characteristics compared to conventional carbon-based negative electrodes.

In the lithium secondary battery of the present invention for achieving the above object is a lithium secondary battery having an electrode assembly and an electrolyte having two electrodes and a separator, a case for receiving and sealing the electrode assembly and the electrolyte,

One of the two electrodes includes titanium oxide as an active material component that absorbs and releases lithium or lithium ions, and the separator is characterized by using a ceramic material as a filler.

In the present invention, the electrode containing titanium oxide may act as a cathode during discharge, and titanium oxide having a spinel structure is preferable as the titanium oxide. The active material may further include silicon oxide in addition to titanium oxide.

In the present invention, the titanium oxide may be used Ti ₅ O ₁₂ , the silicon oxide may be used SiO ₂ . For example, Li ₃ Ti ₅ O ₁₂ , Li ₄ Ti ₅ O ₁₂ , LiSiO ₂ , or the like may be used as the active material including these. Of course, this example does not exclude other substances having different bonding ratios of the constituent elements.

In the present invention, as the active material of the electrode acting as a positive electrode during discharge, lithium cobalt, lithium nickelate, lithium manganate having a spinel structure, and the like, which are conventionally used as a standard reduction potential difference of 4 volts or more, may be used.

In the present invention, the separator may be a ceramic separator in which particles of materials such as silicon oxide, zirconium oxide, titanium oxide, and alumina are bonded with a binder having a mass of about 5% of the total weight. Non-organic solid electrolyte particles may be used alone or in combination with other nonconductive ceramic materials to enhance ion conductivity with the material particles that make up the ceramic separator.

In addition, in the ceramic separator, the ceramic material particles may be secondary particles formed by partially sintering primary particles by pulverization and pulverizing the sintered mass again to form a plurality of primary particles fused to each other on the surface. In this case, the secondary particles may be connected to each other through a small amount of binder in a portion in the form of a bridge to form a separator film.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is an exploded perspective view showing the overall configuration of a lithium secondary battery according to an embodiment of the present invention;

2 is a partial cross-sectional view showing a state in which a separator is interposed between two electrode active materials according to an embodiment of the present invention;

3 is a conceptual diagram showing the particle configuration of the filler of the separator according to an embodiment of the present invention.

According to the present invention, in order to form a secondary battery as shown in FIG. 1, two electrodes 21 and 23 coated with an active material on a current collector are first formed. The electrode tabs 27 and 29 are bonded to the current collector non-coating region where the active material is not coated. When the separator 25 is opened so that a short circuit is not formed between the two electrodes 21 and 23, the jelly roll electrode assembly 20 is formed by winding the layer structure of the electrode and the separator with a winder. The electrode assembly 20 is inserted into the can 10 having an opening in a container shape, and the opening is coupled to and sealed with the cap assembly 80 with the gasket 30 interposed therebetween. Before the electrode assembly is inserted into the can, the lower insulating plate 13b is first joined to the lower insulating plate 13b, and after the electrode assembly 20 is inserted, one electrode tab 29 is inserted into the can 10. The process of connecting to and the process of inject | pouring electrolyte solution are performed. The phase insulator plate 13a is installed above the electrode assembly 20, and the other one of the electrode tabs (signed by reference numeral 27) is welded to the cap assembly 80 before closing the opening.

In an embodiment of the present invention, a method of forming an electrode assembly 20 of a lithium secondary battery may include forming two electrodes 21 and 23 by applying a slurry including a binder resin and an electrode active material to a current collector. Forming a separator film on the electrode surface such that the separator film 25 is present on at least one of the electrode surfaces of the two electrodes to be opposed to each other in the state of the electrode, and the two electrodes 21 and 23 are formed in the state in which the separator film 25 is formed. And forming an electrode assembly 20 including the same.

At this time, in order for the separator film to exist on at least one of the electrode faces of the two electrodes that will be opposed to each other, for example, in a jelly roll type electrode assembly formed by stacking and winding two electrodes, the separator film may be disposed on the outer surface of each of the two electrodes. The method of formation can be taken. Alternatively, the separator 25 may be formed on the inner surface of each of the two electrodes, or the separator 25 may be formed on both surfaces of the inner and outer active material layers 231 formed on both sides of the current collector 233 of one of the two electrodes. In order to integrally form a separator film on both electrode surfaces of one electrode, the electrode may be dipped into a separator membrane liquid containing solid electrolyte particles that are ion conductive and dried.

In another embodiment, a separator 25 separate from the electrode may be formed and interposed between the two electrodes. In order to prevent a short circuit between two electrodes in the step of forming a jelly roll by laminating and winding electrodes, a winding process is performed in a state in which two separators 25 are laminated so as to be interposed between two electrodes.

In the present invention, in any of the above cases, the ceramic separator 25 is interposed between the active material layers 211 and 231 of the two electrodes.

In the present invention, the formation of the electrode for the secondary battery, most of the process except for the material side can be made by a conventional electrode forming method. That is, as the current collectors 213 and 233, an active material slurry containing a binder and an active material powder is applied to at least one surface of a metal foil made of copper or aluminum or a metal mesh.

Typically, the current collector is composed of a foil of 10 to 15 micrometers thick in the electrode forming the cathode during discharge. Both surfaces are coated with an active material slurry. In this case, unlike the carbon-based materials such as graphite and activated carbon, the active material slurry is mixed with a binder and a solvent such as polyvinylidene fluoride (PVDF) in a state in which the titanium oxide and silicon oxide particles are mixed and a conductive assistant such as carbon is added. It is made by mixing.

When used as a negative electrode active material in a lithium secondary battery, a spinel structured titanium oxide can also use a low potential discharge characteristic to realize a positive electrode having a suitable active material and a wide battery of operating voltage, thereby increasing the battery capacity. .

The standard reduction potential difference of titanium oxide with respect to lithium is 0 to 1 volt, the standard reduction potential difference of silicon oxide is also 0 to 1 volt, and the potential value at the time of discharge according to the specific oxygen ratio of titanium oxide and silicon oxide and the mixing ratio of the two materials. The size and shape of the change can vary.

The formation of titanium oxide and silicon oxide may be performed in various ways, and depending on the formation conditions, the number of oxygen bonded to unit atoms may vary, and the standard reduction potential may vary.

For example, in the case of silicon oxide, the chemical composition of lithium-containing silicon oxide, in particular the ratio of the number of oxygen atoms to the number of silicon atoms, has a significant effect on the electrochemical absorption, release performance, ie charge and discharge performance, of lithium ions in the non-aqueous electrolyte. It is known to drive crazy. As the silicon oxide, SiO ₂ is most common, which is well known in the form of quartz crystal, amorphous silica (glass) and the like. In the case of lithium LixSiOy (x ≧ 0, 2>y> 0) containing silicon oxide or a compound thereof and having a small ratio of oxygen water as compared to SiO ₂ , the electrochemical absorption, emission amount of lithium ions in the non-aqueous electrolyte, ie The charging and discharging characteristics are significantly increased.

In addition, since the low oxygen-containing silicon oxide has a small relative potential difference with respect to the metal lithium and a large charge and discharge capacity in the base region with a relative potential of 1 V or less, the low oxygen-containing silicon oxide has a relative potential of 2 V or more such as the metal oxide and the metal chalcogenide. When used in conjunction with the positive electrode of a battery using an active material having an electrode potential of about 3 V-4 V or more, such as V ₂ O ₃ , MnO ₂ , LixCoO ₂ , LixNiO ₂ , LixMn ₂ O ₄ A secondary battery having high voltage, high energy density, and good charge and discharge characteristics can be provided.

In particular, a negative electrode using a negative electrode active material made of silicon oxide or lithium-containing silicate, and a composition formula of LiaMbLcO ₂ (wherein M is a transition metal and L is at least one semimetal material selected from boron and silicon, a, b, c Is in a range satisfying 0 <a <1.15, 0.85 <b + c <1.3 and 0 <c) and uses a positive electrode using a positive electrode active material made of a composite oxide having a layered structure containing lithium. It is known that a secondary battery having high energy density, high charging and discharging characteristics, small performance degradation due to overcharging or overdischarging, and long life cycle can be manufactured.

Low-oxygen silicon oxide SiOy is specifically an oxide such as SiO _1.5 (Si ₂ O ₃ ), SiO _1.2 (Si ₃ O ₄ ), SiO and SiO _0.5 (Si ₂ O), with any composition of y greater than 0 and less than 2 It can be used having an oxide. In addition, SiOy is a method of mixing SiO ₂ and Si at a predetermined molar ratio and then heating in a non-oxidizing atmosphere or in a vacuum state, a method of heating SiO 2 in a reducing gas such as H 2 and reducing it to a predetermined amount, and SiO 2 in a predetermined amount of carbon. Or a method of mixing with a metal or the like and heating to reduce a predetermined amount, a method of mixing Si with an oxygen gas or an oxide to oxidize to a predetermined amount, a heating reaction or plasma decomposition of a mixed gas of a silicon compound gas such as SiH 4 and O 2 gas It can form using the CVD method, plasma CVD method, etc. which make it react.

In addition, binding of lithium ions to titanium oxide or silicon oxide through an electrochemical reaction may be performed in the battery after battery assembly, or may be performed inside or outside the battery during the battery manufacturing process. For example, one of each of these oxides, or a mixture thereof, a conductive agent, or a binder, may be cast in a predetermined form to be used as one electrode (working electrode) and metal lithium or lithium-containing metal may be used as another electrode (counter electrode). These two electrodes come in contact with the lithium ion conductive non-aqueous electrolyte to form an electrochemical cell, and current flows so that the working electrode acts as an anode. Reactions occur in the cell, causing lithium ions to enter these oxides and bond electrochemically. The working electrode is used as a negative electrode in another cell as it is or as a negative electrode active material for forming a secondary battery of a non-aqueous electrolyte through processing.

On the other hand, the aluminum current collector in the electrode forming the anode during discharge is usually made of a mesh of 20 micrometers thick. The surface of the active material slurry is coated with an active material powder containing a lithium such as lithium cobalt acid, lithium permanganate, lithium nickelate, conductive assistant, and a binder.

An appropriate amount of a solvent such as acetone for dissolving the binder is used to form the active material slurry, and after the coating is performed, the solvent is removed through a baking process or the like.

After coating the active material slurry, pressure is applied to the electrode plate through a roller, and the thickness of the evenly applied active material coating is about 100 micrometers. The process using a roller may be performed after integrally forming the separator film of this invention on the whole surface including the active material layer of an electrode.

On the other hand, in one embodiment of the present invention, the separator film is not formed as a separate component from the electrode, and the separator component liquid or the precursor liquid of the separator membrane is applied to the surface covered with the active material layer of at least one electrode, and then the solvent component is removed from the separator membrane liquid. Or a precursor is cured.

At this time, in order to form a separator film, a binder material, a solvent, and a filler powder are first stirred, and a slurry or a liquid mixture is formed. The filler is formed by mixing solid electrolyte particles and powder of a non-electrolytic ceramic material. LiCl-Li ₂ OP ₂ O ₅ , LiTi ₂ (PO ₄ ) ₃ -AlPO ₄ , Li ₃ N single crystal, LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SB ₂ S ₃ , LiI-Li ₂ S-SiS ₄ , P ₂ O ₅ -SiO ₂ -Li ₂ O, P ₂ O ₅ -TiO ₂ -Li ₂ O, P ₂ O ₅ -Al ₂ O ₃ -Li2O, Li ₂ S-GeS ₂ -P ₂ S ₅ , La 0.55 Li 0.35 TiO ₃ , or the like can be used. As the non-electrolyte, that is, the ion non-conductive material, ceramic materials such as alumina (aluminum oxide), silica (silicon oxide), zirconia (zirconium oxide), titania (titanium oxide), and the like may be used. The ion nonconductive material is a relative concept, and it is also possible to have a constant ion conductivity although lower than the solid electrolyte.

Since the filler may be brittle when winding the electrode assembly only by sintering a small particle powder, the mixed powder of the solid electrolyte particles and the non-electrolyte ceramic material powder is mixed with a binder and a mass ratio of about 95: 5, and an appropriate amount of solvent is added. To form a separator film liquid.

The mixed powder once forms primary particles such as solid electrolyte particles and non-electrolyte ceramic material, and in this state is sintered to partially melt the particle surface and then roughly crushed again to form secondary particles in which at least three primary particles are clustered together. Can be made in such a way. When the shape of the primary particles has a scaly structure, the secondary particles may have a laminated phase structure. It is preferable that the primary particle or individual particle is 0.01-0.3 micrometers, and the scale-shaped individual flake which forms a layered particle group is 100 nm-1 micrometer in width.

Since the amount of the binder is smaller than that of the filler in the state where the solvent is removed and the separator is formed, the particles are separated from the particles in the secondary particles or in the mixture of the secondary particles and the primary particles, rather than being coated with the binder as a whole. In the form of a bridge (bridge). This configuration has a higher ion conductivity than the case where the binder material has a low ion conductivity and the binder material covers the filler particles as a whole.

That is, when the binder binds the secondary particles while covering the entire surface of the individual secondary particles, when the ion conductivity of the binder is small, ion conduction through the inside of the secondary particles may not be performed smoothly. Therefore, in order to increase the ion conductivity of the separator 25 irrespective of the ion conductivity of the binder 255 as illustrated in FIG. 3, the binder 255 exists only on a part of the surface of the particle 251 to connect the secondary particles. It is preferable to bind the secondary particles in the form of a bridge. For this purpose, the binder 255 is preferably used in a small amount in the slurry for forming the separator 25. When the ratio of the filler material particle 251 and the binder 255 in the separator film of the present invention is 98: 2 to 85:15 by mass, the filler may be completely covered by the binder. That is, the problem that the binder covers the filler material and the ion conductivity through the filler material, in particular, the solid electrolyte, can be avoided.

As a method of forming the separator film on the electrode surface, a method of front printing, a spraying method, a dipping, or the like may be used for the electrode surface.

In the present invention, for example, a zirconium oxide powder and a high ion conductivity sulfide-based amorphous LiI-Li ₂ SB ₂ S ₃ are mixed in half, 96w%, and acrylic rubber 4w% mainly composed of methacrylate material. Were mixed and diluted with a solvent so that the viscosity was 3000 cps to form a slurry. The slurry is coated on the electrode surface by a printing method. The solvent is removed by passing the electrode through a dryer at 120 ° C., and a separator film can be obtained on the electrode surface.

When two or more particles are present, when the sintering temperature of one particle is low, the particles of the material having the low sintering temperature in the binary particles act as a binder, thereby lowering the process temperature of the entire sintering molding.

In the separator film formed through the above-mentioned process, the gap between the secondary particles and the gap between the primary particles in the secondary particles may be filled with an electrolyte, and lithium ions may move between the two electrodes through the electrolyte. . In addition, lithium ions can also move between the two electrodes through the solid electrolyte itself. The ions can be synergistically increased throughout the cell through the electrolyte filling the voids and the solid electrolyte in the filler.

In some embodiments, a liquid electrolyte may not be used at all. In the separator membrane, ion conduction may be performed at a portion where the solid electrolyte particles come into contact with each other. Such ion conduction paths may be formed in a plurality of manners, and a binder material or a nonionic conducting particle may be interposed in the middle of the ion path. Even in this case, ion transfer may occur within the cell through other passes. However, when the electrolyte forms a state in which the separator film is impregnated even in the pores even in the form of a gel, the path of ion conductance may be more diversified, and the ion conductivity in the electrolyte is higher than the ion conduction through the solid electrolyte. This can be much higher.

When using a liquid electrolyte, it is preferable that a separator film has high porosity. In order to obtain a porosity of 50% or more, it is preferable that the proportion of the binder is 20% or less, and it is important that the binder itself does not expand. In particular, it is important that the expansion or swellability by the electrolyte is low. As a binder that satisfies these conditions, there is an acrylic rubber binder having excellent binding ability to other materials and low expansion ratio.

On the other hand, it is necessary to disperse the binder evenly in order to reduce the amount of the binder. Since this work is of high difficulty, it is difficult to obtain a stable film having a high porosity in the past. However, when a partially sintered solid electrolyte-containing ceramic material as the filler is used as the filler, and an acrylic rubber binder is used, the binder can be easily dispersed and a film having a large porosity can be obtained with a small amount of binder.

The two electrodes are stacked and wound in a state where the separator film is formed on at least one surface of the two electrodes. Since the separator film itself on the surface of the electrode is formed integrally with the electrode to serve as a separator, it is not necessary to interpose a separate separator film between the electrodes. However, for the shutdown function of the conventional separator, an insulating film made of a polyolefin resin other than the separator film of the present invention may exist. In such a case, the separator film of the present invention and these polyolefin resin insulating films together act as separators in the secondary battery. In this case, in order to prevent the polyolefin resin insulating film from lowering the ion conductivity to the level of a conventional separator, the polyolefin resin insulating film is formed to be thinner than half of the conventional one.

As in the embodiment of the present invention, the method of forming a separator by forming a separator film integrally with the electrode has several advantages over the conventional method of forming a separator separate from the electrode.

That is, when the separator is formed separately as in the related art, when the two electrodes and the separator are laminated or wound up after lamination to form an electrode assembly, the separator may be misaligned and a short circuit may occur between the two electrodes. . However, when the separator is formed with the electrode to cover the electrode surface, there is no need to sandwich the separator between the electrodes, and the problem due to misalignment is also eliminated.

In the case where the separator is formed separately from the electrode, the separator in the battery may cause a contraction action when the battery is overheated, thereby causing a short circuit between the electrodes. However, once the separator is formed by binding to the electrode, even if the battery is overheated, the binding force can reduce the probability that the separator receives heat and contracts or causes a short circuit. In addition, compared to the case of forming a separate separator, the separator bound to the electrode can lower the probability of damage such as tearing of the separator during the battery production process.

In the present invention, when the filler of the separator film is a ceramic material, whether the solid electrolyte is amorphous or crystalline, it is a kind of ceramic material, which is used in alumina, zirconium dioxide, silica, etc. It plays a role in preventing deformation causing short-circuit between electrodes such as deformation and melting. In addition, these materials have the advantage of improving the preservation and retention of the separator film as a whole, and the partially sintered stave structure can increase the porosity.

The electrode assembly is then inserted into a canned container or the like and sealed with a cap assembly. Typically the electrolyte is injected into the electrolyte inlet of the cap assembly, after which the inlet is sealed. At this time, the separator membrane of the electrode assembly of the present invention has a high porosity and can increase the electrolyte injection rate by two or more times as compared to a separator made of a conventional polyolefin-based material.

Meanwhile, in the present invention, the method of forming the grape stalk-shaped secondary sintered compact particles will be described in more detail. The method of making the sintered compact includes various chemical methods such as melting and recrystallization using chemicals, And physical methods such as applying pressure. One of the easy methods is a method of raising the temperature of the material by heating to near the melting temperature of the particle material and necking. The melt rate in some molten state is then determined to be low in density, so that the characteristic shape of the present invention remains unbroken during the material stirring process when making a paste with a binder, a solvent, and the like.

When using zirconium oxide as a filler, the individual particle which forms the particle group or secondary particle of this invention is 0.01-0.3um, and the scale-shaped individual flake which forms a layered particle group is 100-100 nm in width preferably. Do. This particle size can be confirmed by observing a scanning electron microscope (SEM) photograph after forming a material having good properties.

In the present invention, the ceramic material constituting the separator layer preferably has a thermal expansion rate of 0.2% or less at 200 ° C and a thermal expansion rate of 0.1 to 0.4% at 400 ° C. Ceramic materials having a thermal expansion rate higher than the thermal expansion rate have a problem of deforming the shape of the battery itself due to an increase in pressure inside the battery.

The use of a material in which the particles are in some sintered state causes the agglomerated particles to be irregularly present in one another, making it difficult to fill the space regularly as in crystals. In other words, it is difficult for the filler made of these ceramic materials to be densely packed in the space constituting the separator. In addition, it is possible to prevent the resin from filling in the spaces between the particles by lowering the proportion of the resin. In this way, the public rate of the separator can be increased. The thermal conductivity of the ceramic material of the present invention is preferably about 10 W / (m × K) in a wide temperature range of 500 ° C. or more and 1000 ° C. or less.

In the present invention, the binder is mainly composed of a polymer resin, and the polymer resin is preferably made of a polymer of acrylate or methacrylate or a copolymer thereof that can withstand heat of 200 ° C. or higher.

According to the present invention, even when a high temperature is generated due to a battery failure by using a ceramic separator, it is possible to effectively prevent a short circuit between two electrodes to increase the safety of the battery.

The secondary battery according to the present invention uses a composite oxide LiaMb LcO ₂ having a layer structure of silicon and / or boron as a positive electrode active material and at least one of titanium oxide and lithium titanate as a negative electrode active material, and selectively uses silicon oxide, lithium silicate, or the like. In this case, a high voltage operation of about 4V is possible. In addition, the energy density is higher, and the negative electrode active material can reduce structural deformation and side reactions when entering and exiting lithium, compared to conventional carbon materials, and thus has excellent charge and discharge characteristics, less deterioration due to excessive charge and discharge, and long cycle life. .

Claims (13)

An electrode assembly and electrolyte having two electrodes and a separator, In the lithium secondary battery having a case for receiving and sealing the electrode assembly and the electrolyte, Among the two electrodes, the negative electrode is made of titanium oxide as an active material component that absorbs and releases lithium or lithium ions. The separator includes a ceramic material filler and a binder, and the ceramic material includes secondary particles formed by partially sintering primary particles, and the binder of the separator is located in a portion of the secondary particles in a bridge form. Lithium secondary battery, characterized in that for bonding between the secondary particles. delete The method of claim 1, The titanium oxide has a spinel structure, characterized in that the lithium secondary battery. The method of claim 3, wherein A lithium secondary battery using Ti ₅ O ₁₂ as the titanium oxide. The method of claim 1, Lithium secondary battery, characterized in that further comprises silicon oxide as the active material component. The method of claim 5, wherein The silicon oxide is a lithium secondary battery, characterized in that using less oxygen than silicon compared to SiO ₂ or SiO ₂ . The method of claim 1, Lithium metal oxide is used as an active material of the other electrode of the two electrodes, the combination of at least one of cobalt, nickel, manganese is used as the metal. The method of claim 1, Among the two electrodes, the active material of the other electrode is a composition formula of LiaMbLcO ₂ (wherein M is a transition metal, L is at least one semimetal material selected from boron and silicon, and a, b, and c are 0 <a <1.15, 0.85 < A material that satisfies the conditions of b + c &lt; 1.3 and 0 &lt; c) is used. The method of claim 1, The ceramic material comprises at least one of silicon oxide, zirconium oxide, titanium oxide, aluminum oxide. The method according to claim 1 or 9, The separator is a lithium secondary battery, characterized in that it comprises an inorganic (non organic) solid electrolyte particles. delete The method according to claim 1 or 9, The binder of the separator is a lithium secondary battery, characterized in that one of the acrylate, methacrylate, polymers, copolymers thereof. The method according to claim 1 or 9, The separator is a lithium secondary battery, characterized in that formed integrally on the surface of at least one of the two electrodes.

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