JP5610034B2 - Secondary battery and negative electrode for secondary battery - Google Patents

Description

  The present invention relates to a secondary battery and a negative electrode for a secondary battery.

  With the widespread use of mobile terminals such as mobile phones and laptop computers, the role of the battery serving as the power source has been regarded as important. These batteries are required to have a small size, light weight, high capacity, and performance that does not easily deteriorate even after repeated charge and discharge.

  From the viewpoint of high energy density and light weight, metallic lithium may be used for the negative electrode. In this case, acicular crystals (dendrites) are deposited on the lithium surface as the charge / discharge cycle progresses, or the dendrites are collected by current. The phenomenon of peeling from the body occurs. As a result, the dendrite penetrates the separator and causes a short circuit inside, resulting in a problem that the battery life is shortened and cycle characteristics are deteriorated.

  Therefore, carbon materials that do not have the above problems are used in practical batteries. A typical one of these is a graphite-based carbon material, but the amount of lithium ions that can be occluded by this material is limited by the amount that can be inserted between graphite layers, and its specific capacity is 372 mAh / It is difficult to make it g or more. Therefore, a method has been developed that uses an oxide that can occlude lithium ions and has a larger specific capacity than graphite.

  For example, Patent Document 1 proposes a method of effectively using lithium ion storage sites by adding and dispersing metal fine particles in molten oxide particles to increase electron conductivity.

  Patent Document 2 binds carbon particles carrying two or more kinds of metals including a metal that forms an alloy with lithium such as Ag and Sn and a metal that does not form an alloy with lithium such as Cu. There has been proposed a negative electrode in which an aggregate of the particles is formed by an agent and the aggregate is used as a negative electrode active material.

JP 2000-12036 A JP-A-10-334889

  However, it is difficult to obtain a sufficient capacity with the above prior art.

  For example, in the negative electrode having a structure in which a plurality of kinds of metals are supported on carbon particles as in the technique described in Patent Document 2, the initial discharge capacity is lower than the capacity expected from the used material and undergoes a charge / discharge cycle. And there was a significant decrease in capacity. Hereinafter, these points will be described.

  The decrease in the initial discharge capacity is considered to be due to the bonded portion of the particles being peeled and the electrode active material layer being damaged in the initial charge / discharge process. A material having a large amount of lithium occlusion such as Sn has a large charge / discharge capacity, but has a large volume change accompanying charge / discharge. Therefore, when a negative electrode is formed by binding carbon particles supporting such a material, a part of the binding portion between the particles is damaged in the first charge / discharge process, and the internal resistance is increased and the capacity is increased. A decrease is considered to occur.

  On the other hand, it is surmised that the decrease in capacity during the charge / discharge cycle is caused not only by the breakage of the interparticle binding part due to the volume change but also by the microscopic electric field nonuniformity generated in the negative electrode. The When mixing metal particles or the like into carbon particles, the distribution is usually non-uniform due to differences in powder characteristics. Since carbon particles and metal particles have different resistivities and specific capacities, microscopic non-uniformity in the electric field distribution occurs in the charge / discharge process. Therefore, since the volume change at the time of charge / discharge is localized, the structure of the negative electrode is destroyed and the capacity is reduced.

  Therefore, in view of the above-described problems of the prior art, the present invention provides a negative electrode for a secondary battery that has a high capacity and that suppresses an increase in resistance and a decrease in capacity even after a cycle, and a secondary battery using the same. For the purpose.

According to the present invention for solving the above problems, a negative electrode for a secondary battery capable of occluding and releasing lithium ions, comprising a metal that forms an alloy with lithium or a metal that does not form an alloy with lithium. Including a layer made of an alloy or a composite oxide, wherein the layer made of the alloy or the composite oxide is made of a Li—Co—N based amorphous compound or a Li—Ti—O based amorphous compound. A negative electrode for a secondary battery is provided.
According to the present invention, there is also provided a negative electrode for a secondary battery capable of occluding and releasing lithium ions , wherein the first lithium occluding layer is different from the charge / discharge potential of the first lithium occluding layer. There is provided a negative electrode for a secondary battery , wherein the first lithium storage layer is made of an Sn-Co alloy .

  According to the invention, in the negative electrode for a secondary battery, the metal forming an alloy with lithium is selected from the group consisting of Si, Ge, Sn, Al, Pb, Pd, Ag, In, and Cd. There is provided a negative electrode for a secondary battery comprising at least one metal.

  Furthermore, according to the present invention, in the negative electrode for a secondary battery, the metal that does not form an alloy with lithium is selected from the group consisting of Cu, Fe, B, Ni, Ti, Ta, W, Cr, and Co. There is provided a negative electrode for a secondary battery comprising at least one metal.

  According to the present invention, there is further provided a negative electrode for a secondary battery, wherein the negative electrode for a secondary battery includes a layer made of a lithium storage material.

  In addition, according to the present invention, there is provided the negative electrode for a secondary battery, wherein in the negative electrode for a secondary battery, the layer made of the lithium storage material is a layer containing carbon as a main component.

  According to the invention, in the negative electrode for a secondary battery, the layer made of the alloy or the composite oxide is a layer formed by a sputtering method, a CVD method, a vapor deposition method, or a plating method. A negative electrode for a secondary battery is provided.

  In addition, according to the present invention, there is provided a negative electrode for a secondary battery, wherein the layer made of the alloy or the composite oxide has an amorphous structure in the negative electrode for a secondary battery.

  According to the present invention, there is further provided a negative electrode for a secondary battery, wherein the negative electrode for a secondary battery further includes a lithium metal layer.

  Furthermore, according to the present invention, it is provided with the above-described negative electrode for a secondary battery, a positive electrode capable of inserting and extracting lithium ions, and an electrolyte disposed between the negative electrode and the positive electrode. A secondary battery is provided.

  The negative electrode according to the present invention includes a layer made of an alloy or a composite oxide made of an alloy containing a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium. This layer is different from the aggregate of particles bound by the binder as in the prior art, and includes a metal that forms an alloy with lithium or a metal that does not form an alloy with lithium. An alloy is formed in a film form. In the present invention, the metal that forms an alloy with lithium refers to a metal that forms a plateau at a potential of 0 to 2.5 V with respect to the lithium electrode when lithium is occluded / released. On the other hand, a metal that does not form an alloy with lithium means a metal that does not form a plateau at a potential of 0 to 2.5 V with respect to the lithium electrode when lithium is occluded / released.

  In the present invention, since the layer made of the alloy or the complex oxide is formed into a film shape, the following effects are obtained.

  First, since the bonding between the substances constituting the layer made of the alloy or the composite oxide can be strengthened, the layer structure is not easily broken due to the volume change caused by charging and discharging. As a result, an increase in internal resistance during the initial charge is suppressed, and a decrease in the initial discharge capacity can be suppressed. Further, even when a cycle is passed, since the action of suppressing the destruction of the alloy layer is maintained, it is possible to suppress an increase in resistance and a decrease in capacity inside the battery.

  Secondly, in the layer made of an alloy or composite oxide, the metal or lithium forming the alloy and lithium are distributed relatively uniformly, so that local stresses due to volume changes due to charge / discharge are suppressed. As a result, it is possible to suppress the breakdown of the structure of the negative electrode active material layer, and to suppress the increase in resistance and the decrease in capacity inside the battery even after a cycle.

  Moreover, since the layer which consists of an alloy or composite oxide containing the metal which forms an alloy with lithium or lithium, and the metal which does not form an alloy with lithium is employ | adopted, there exist the following effects.

  First, since a metal that does not form an alloy with lithium does not change in volume during charge and discharge, the volume change as a whole can be suppressed.

  Second, during discharge, the metal that does not form an alloy with lithium plays a role of a wedge that supports the structure of the negative electrode active material layer.

  In the present invention, these synergistic actions can effectively prevent the destruction of the structure of the layer made of an alloy or composite oxide. As a result, it is possible to suppress an increase in resistance and a decrease in capacity inside the battery even after a cycle.

  Furthermore, when a layer made of a lithium storage material, for example, a layer containing carbon as a main component is further provided, the charge / discharge potential of each layer constituting the negative electrode is different, so that charging / discharging is performed stepwise. As a result, the expansion and contraction of the negative electrode active material layer can be further suppressed.

  According to the present invention, it is possible to suppress destruction of the structure of the negative electrode by providing the negative electrode with an alloy layer made of a metal that forms an alloy with lithium or an alloy that includes lithium and a metal that does not form an alloy with lithium. it can. As a result, it is possible to provide a negative electrode for a secondary battery that has a high capacity and suppresses an increase in resistance and a decrease in capacity inside the battery even after a cycle, and a secondary battery using the same.

It is a negative electrode sectional view of a rechargeable battery which shows a first embodiment. It is a negative electrode sectional view of a rechargeable battery which shows a first embodiment. It is a schematic diagram of the battery using the negative electrode of the secondary battery which shows 1st embodiment. 6 is a cross-sectional view of a negative electrode of a secondary battery according to Comparative Example 1. FIG. It is negative electrode sectional drawing of the secondary battery which shows 2nd embodiment. It is a schematic diagram of the battery using the negative electrode of the secondary battery which shows 2nd embodiment. It is the graph which showed the cycle characteristic of Example 5,6,7 of this invention, and the cycle characteristic of the comparative example 1. FIG. It is negative electrode sectional drawing of the secondary battery which shows 3rd embodiment. It is a schematic diagram of the battery using the negative electrode of the secondary battery which shows 3rd embodiment. It is negative electrode sectional drawing of the secondary battery which shows 4th Embodiment. It is a schematic diagram of the battery using the negative electrode of the secondary battery which shows 4th Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described.

(First embodiment)
A first embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view of a negative electrode of a secondary battery showing a first embodiment of the present invention.

  The current collector 1a is an electrode that takes out current to the outside of the battery during charging and discharging, and takes in current into the battery from the outside. As the current collector 1a, various conductive metal foils can be used, and examples thereof include aluminum, copper, stainless steel, gold, tungsten, molybdenum, and titanium.

  The first active material layer 2a is a negative electrode member that occludes and releases Li during charge and discharge. The first active material layer 2a is composed of a lithium alloy, a lithium storage metal, a lithium storage alloy, a metal oxide, graphite, hard carbon, soft carbon, fullerene, carbon nanotube, or a mixture of these, or a plurality of these. Are illustrated. The thickness of the first active material layer 2a is preferably about 5 to 200 μm.

  The second active material layer 3a is a film capable of inserting and extracting Li, and is made of an alloy material or a composite oxide containing a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium. The second active material layer 3a may have a structure containing oxygen or the like, and the alloy may contain lithium. Here, Cu, Fe, B, Ni, Ti, Ta, W, Cr, Co, etc. are mentioned as a metal which does not form an alloy with lithium. Examples of the metal that forms an alloy with lithium include Si, Ge, Sn, Al, Pb, Pd, Ag, In, and Cd. Examples of the alloy material or composite oxide include Si—Cu alloy, Si—Fe alloy, Sn—Co alloy, Li—Ti—O oxide, and Na—Si—B—O oxide. Here, the ratio of the metal that forms an alloy with lithium or the metal that does not form an alloy with lithium can be set to, for example, 100: 1 to 1:10 (atomic ratio). The reason is that if the amount of metal that does not form an alloy with lithium is too small, the effect of the wedge is reduced and structural destruction proceeds by charge / discharge. In addition, if the amount of metal that does not form an alloy with lithium becomes too large, the proportion of lithium that can be occluded in the negative electrode becomes small, so that the superiority in specific capacity cannot be maintained.

  The second active material layer 3a can be produced, for example, by the following method. A method of melting and synthesizing a metal that forms an alloy with lithium or a metal that does not form an alloy with lithium, a method of producing by chemical reaction, a method of producing by mechanical milling, or a sintered product It can be obtained by a method of forming by vacuum film formation as a sputtering target or vapor deposition material. Further, a method of forming a film by a CVD method using a gas containing a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium, or a metal or lithium that forms an alloy with lithium or an alloy with lithium A method of forming a film using a plating technique from a solution containing a metal that does not form, or a metal that forms an alloy with lithium or is vaporized into an atomic or molecular state, or a metal that does not form an alloy with lithium. It can also be obtained by an ion plating method that is ionized and accelerated and deposited on a substrate having a negative high potential. Further, when the second active material layer 3a is produced by the above method, the amount of metal that does not form an alloy with lithium can be set to, for example, 5 to 35 atom%.

  The second active material layer 3a preferably has an amorphous structure. This is because it is possible to further suppress an increase in resistance and a decrease in capacity inside the battery even after a cycle. Here, the amorphous in the present invention means a material having a broad scattering band having an apex at 15 to 40 degrees in the 2θ value of the X-ray diffraction method using CuKα rays. The second active material layer 3a is desirably 0.1 μm to 30 μm.

  The negative electrode of the secondary battery shown in FIG. 1 is produced by the following procedure. First, the first active material layer 2a is deposited on the current collector 1a. Further, a second active material layer 3a made of a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium is formed on the first active material layer 2a by the above method, and a desired negative electrode is formed. obtain.

  In addition, as shown in FIG. 2, the structure which deposits the 1st active material layer 2a and the 2nd active material layer 3a on both surfaces of the electrical power collector 1a is also employable.

The positive electrode can be used in the lithium secondary battery of the present invention, LixMO ₂ (where M represents. At least one transition metal) complex oxide is, for _{example, LixCoO 2, LixNiO 2, LixMn} 2 O 4 , LixMnO ₃ , LixNiyC _1-y O _2, etc. are dispersed and kneaded with a conductive material such as carbon black and a binder such as polyvinylidene fluoride (PVDF) with a solvent such as N-methyl-2-pyrrolidone (NMP). What apply | coated the thing on base | substrates, such as aluminum foil, can be used.

  By using such a compound, a high electromotive force can be stably realized. Here, if M includes at least Ni, cycle characteristics and the like are further improved. x is preferably in a range where the valence of Mn is +3.9 or more. Further, in the above compound, if 0 <y, Mn is replaced with a lighter element, the discharge amount per weight is increased, and the capacity is increased.

  Further, the negative electrode of the lithium secondary battery of the present invention is laminated or laminated in the dry air or inert gas atmosphere through the positive electrode and a separator made of a polyolefin such as polypropylene or polyethylene, or a porous film such as a fluororesin. After being wound, the battery can be produced by being housed in a battery can or sealed with a flexible film made of a laminate of a synthetic resin and a metal foil.

  Moreover, as electrolyte solution, cyclic carbonates, such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl Linear carbonates such as carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2- Chain ethers such as ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethyl Formamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2- An aprotic organic solvent such as oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, etc. is used alone or in combination of two or more thereof. The lithium salt that dissolves in the solvent is dissolved. Examples of the lithium salt include LiPF6, LiAsF6, LiAlCl4, LiClO4, LiBF4, LiSbF6, LiCF3SO3, LiCF3CO2, Li (CF3SO2) 2, LiN (CF3SO2) 2, LiB10Cl10, lithium lower aliphatic carboxylate, lithium chloroborane, four Examples thereof include lithium phenylborate, LiBr, LiI, LiSCN, LiCl, and imides. Further, a polymer electrolyte may be used instead of the electrolytic solution.

  Next, the operation when the negative electrode of the secondary battery shown in FIG. 1 or FIG. 2 is incorporated in the battery will be described in detail with reference to FIG. FIG. 3 is a schematic view of a battery using the negative electrode according to the first embodiment of the present invention. In this embodiment, the second active material layer 3a corresponds to “a layer made of an alloy or composite oxide containing a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium”, and The one active material layer 2a corresponds to “a layer made of a lithium storage material”. During charging, the negative electrode receives lithium ions 6a from the positive electrode active material layer 5a facing each other with the separator 4a separating the negative electrode and the positive electrode interposed therebetween. For example, when a carbon-based material is used for the first active material layer 2a, since the second active material layer 3a has a higher discharge potential than the first active material layer 2a, the lithium ions 6a are first occluded in the second active material layer 3a. Is done. When lithium occlusion in the second active material layer 3a is completed, the lithium ions 6a then pass through the second active material layer 3a and are occluded in the first active material layer 2a. When the first active material layer 2a is filled with lithium, charging is completed. Further, at the time of discharge, lithium ions 6a stored in the first active material layer 2a having a low discharge potential are first released. Next, lithium ions 6a occluded in the second active material layer 3a are released. The released lithium ions 6a move to the positive electrode active material layer 5a through the electrolytic solution.

  At this time, since the second active material layer 3a is in the form of a film, the bonding between the constituent metals is strong, and the distribution of the constituent metals is uniform. Therefore, the structural destruction of the second active material layer 3a due to the volume change that occurs during charging and discharging is suppressed. Furthermore, since the second active material layer 3a contains a metal that does not form an alloy with lithium, volume change associated with charge / discharge can be suppressed. Further, a metal that does not form an alloy with lithium serves as a wedge that maintains the structure of the second active material layer 3a. The synergistic effect of the above action makes it possible to effectively prevent structural destruction such as pulverization even after charging and discharging. As a result, an increase in internal resistance during the initial charge is suppressed, and a good initial discharge capacity is obtained. Further, even when a cycle is passed, since the action of suppressing the destruction of the alloy layer is maintained, it is possible to suppress an increase in resistance and a decrease in capacity inside the battery.

  Furthermore, by adopting a multilayer structure composed of the first active material layer 2a and the second active material layer 3a having different charging / discharging potentials from the second active material layer 3a, charging / discharging is performed in stages. Expansion and contraction of the negative electrode active material layer due to discharge can be reduced. Moreover, it becomes possible to further suppress the expansion and contraction of the entire negative electrode active material layer by a synergistic effect of this action and the action by adopting the configuration of the second active material layer 3a.

Example 1
Example 1 of the first embodiment of the present invention will be described below.
The negative electrode of the secondary battery shown in FIG. 1 was produced by the following procedure. First, a copper foil having a thickness of 10 μm was used as the current collector 1a, and artificial graphite having a thickness of 100 μm was deposited on the current collector 1a as the first active material layer 2a. Thereafter, a Si—Cu alloy was formed as the second active material layer 3a by a 2 μm sputtering method to obtain a negative electrode. A lithium cobaltate mixture was used for the positive electrode active material, and an aluminum foil was used for the current collector. As the electrolytic solution, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in which LiPF ₆ was dissolved so as to have a concentration of 1 mol / L (mixing volume ratio: EC / DEC = 30/70) was used. A square secondary battery was assembled using the negative electrode, the positive electrode, and the electrolytic solution. The electrical characteristics of the prismatic secondary battery were evaluated with a charge / discharge tester. The current density of charge / discharge was 10 mA / cm ² . Regarding the cycle characteristic evaluation, the capacity maintained after 500 cycles was divided by the initial discharge capacity, and the evaluation was performed using a numerical value expressed as a percentage.

(Example 2)
In Example 2, a negative electrode was produced in the same manner as in Example 1, but natural graphite having a thickness of 70 μm was used for the first active material layer 2a, and a Si—Fe amorphous alloy was deposited by 1 μm for the second active material layer 3a. Formed with. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

(Example 3)
In Example 3, a negative electrode was produced in the same manner as in Example 1. However, hard carbon having a thickness of 90 μm was used for the first active material layer 2a, and amorphous WSi ₂ was formed by 1 μm CVD for the second active material layer 3a. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

Example 4
In Example 4, a negative electrode was produced in the same manner as in Example 1. However, Sn having a thickness of 5 μm was used for the first active material layer 2a, and a Si—Cu alloy was formed by a 2 μm CVD method for the second active material layer 3a. . Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

(Comparative Example 1)
The negative electrode of Comparative Example 1 was produced by the following procedure. By binding carbon particles carrying Si as a metal that forms an alloy with lithium and Cu as a metal that does not form an alloy with lithium onto a current collector 1a of a 10 μm copper foil as shown in FIG. An active material layer 7a was formed to obtain a negative electrode. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

  Table 1 shows the results of initial discharge capacity, initial charge / discharge efficiency, and cycle characteristic evaluation for the batteries of Examples 1 to 4 and Comparative Example 1. From these results, it was found that the initial discharge capacity was 1.2 times or more in Examples 1 to 4 as compared with Comparative Example 1. The reason is considered as follows. That is, in the case of the comparative example 1, the binding between particles on the negative electrode current collector is weakened due to expansion and contraction caused by charging and discharging. As a result, the internal resistance increases, charging of a sufficient capacity is hindered, and further complete discharge is not performed. On the other hand, in the case of Examples 1 to 4, since it has a uniform film structure that does not use a binder, an increase in internal resistance is unlikely to occur, and there is no inconvenience as in Comparative Example 1. It is considered that a higher initial discharge capacity than Comparative Example 1 can be obtained.

  Further, as shown in Table 1, in Comparative Example 1, the capacity faded after 150 cycles, whereas in Examples 1 to 4, 85% or more of the initial discharge capacity was maintained even after 500 cycles. There was found.

  The cause of capacity deterioration in Comparative Example 1 is that the structure of the negative electrode active material layer is caused by the bond between the particles on the negative electrode current collector being weakened by the volume change of the metal accompanying charging and discharging, and further by being broken. It is thought that destruction has occurred. Furthermore, since the distribution of the metal particles is non-uniform, it is considered that a local stress caused by a change in the volume of the metal generated during charge / discharge is also a cause of the structural destruction of the negative electrode active material layer.

  On the other hand, the reason why the cycle characteristics are good in Examples 1 to 4 is that the second active material layer 3a is a film-like alloy layer, and therefore the bonds between the metals constituting the second active material layer 3a are strong. Since the metal distribution is uniform, it is considered that the cause of capacity deterioration in Comparative Example 1 is eliminated. In addition, as the metal constituting the second active material layer 3a, a metal that forms an alloy with lithium or lithium, and a metal that does not form an alloy with lithium, and the first active material layer 2a and the second Since the two active material layers 3a are laminated to form a multilayer structure, the volume change of the negative electrode active material layer is effectively suppressed, which contributes to good cycle characteristics.

(Second embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 5 is a cross-sectional view of a negative electrode of a secondary battery showing a second embodiment of the present invention.

  The current collector 1b is an electrode that takes out a current from the outside of the battery during charging / discharging or takes in a current from the outside into the battery. As the current collector 1b, various conductive metal foils can be used, and examples thereof include aluminum, copper, stainless steel, gold, tungsten, molybdenum, and titanium.

  In this embodiment, the negative electrode active material layer 8b corresponds to “a layer made of an alloy or composite oxide containing a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium”. The same configuration as that of the second active material layer 3a in this embodiment can be adopted, and it can be manufactured by the same method. However, the negative electrode active material layer 8b is desirably 0.5 μm to 30 μm.

  In addition, a battery can be manufactured using the same positive electrode, separator, and electrolytic solution as in the first embodiment.

  Next, the operation when the negative electrode of the secondary battery shown in FIG. 5 is incorporated in the battery will be described in detail with reference to FIG. FIG. 6 is a schematic view of a battery produced using the negative electrode of the second embodiment of the present invention. During charging, the negative electrode receives lithium ions 6b from the positive electrode active material layer 5b facing each other with the separator 4b separating the negative electrode and the positive electrode interposed therebetween. The lithium ions 6b are occluded in the negative electrode active material layer 8b. When the negative electrode active material layer 8b is filled with lithium, charging is completed. In discharging, lithium ions 6b occluded during charging are released from the negative electrode active material layer 8b. The released lithium ions 6b move to the positive electrode active material layer 5b through the electrolytic solution.

  At this time, since the anode active material layer 8b is a film-like layer, the bonding between the constituent metals is strong, and the distribution of the constituent metals is uniform. Therefore, structural destruction of the negative electrode active material layer 8b due to the volume change that occurs during charge and discharge is suppressed. Furthermore, since the negative electrode active material layer 8b contains a metal that does not form an alloy with lithium, volume change associated with charge / discharge can be suppressed. In addition, a metal that does not form an alloy with lithium serves as a wedge that maintains the structure of the negative electrode active material layer 8b. The synergistic effect of the above action makes it possible to effectively prevent structural destruction such as pulverization even after charging and discharging. As a result, an increase in internal resistance during the initial charge is suppressed, and a good initial discharge capacity is obtained. Further, even when a cycle is passed, since the action of suppressing the destruction of the alloy layer is maintained, it is possible to suppress an increase in resistance and a decrease in capacity inside the battery.

(Example 5)
Example 5 of the second embodiment of the present invention will be described below.
The negative electrode of the secondary battery shown in FIG. 5 was produced by the following procedure. First, a copper foil having a thickness of 10 μm was used as the current collector 1b, and an Sn—Cu alloy was formed as a negative electrode active material layer 8b on the current collector 1b by a 10 μm vapor deposition method to obtain a negative electrode. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

(Example 6)
In Example 6, a negative electrode was produced in the same manner as in Example 5. However, the negative electrode active material layer 8b was formed of a Li—Co—N amorphous compound by a 10 μm sputtering method. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

(Example 7)
In Example 7, a negative electrode was produced in the same manner as in Example 5. However, the negative electrode active material layer 8b was formed of a Li—Ti—O based amorphous compound by a 10 μm sputtering method. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

  FIG. 7 shows the results of the cycle characteristics evaluation for the batteries of Examples 5 to 7 and Comparative Example 1. From this result, it was found that in Comparative Example 1, rapid fading occurred after 150 cycles and the capacity deteriorated, but in Examples 5-7, 85% or more of the initial discharge capacity was maintained even after 300 cycles. did. Also in the present embodiment, it was suggested that by adopting a uniform film structure that does not use a binder, an increase in internal resistance is suppressed, and destruction of the structure of the negative electrode active material layer is suppressed.

  Table 2 shows the initial discharge capacities of the batteries of Examples 5 to 7 and Comparative Example 1. From this result, it was found that the initial discharge capacity was 1.5 times or more in Examples 5 to 7 as compared with Comparative Example 1. From the viewpoint of discharge capacity, there is an advantage that a battery having a large initial discharge capacity can be obtained by adopting only a metal negative electrode active material layer having a large specific capacity without providing a carbon-based negative electrode active material layer having a small specific capacity. .

(Third embodiment)
Next, a third embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 8 is a cross-sectional view of the negative electrode of the secondary battery showing the third embodiment of the present invention.

  The current collector 1c is an electrode that takes out a current to the outside of the battery during charging / discharging or takes a current into the battery from the outside. As the current collector 1c, various conductive metal foils can be used, and examples thereof include aluminum, copper, stainless steel, gold, tungsten, molybdenum, and titanium.

  In this embodiment, the first lithium storage layer 9c corresponds to “a layer made of an alloy or composite oxide containing a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium,” and The structure is the same as that of the second active material layer 3a in the one embodiment, and it can be manufactured by the same method. However, the first lithium occlusion layer 9c is desirably 0.1 μm to 10 μm. The second lithium occlusion layer 10c corresponds to a “layer made of a lithium occlusion material” and has the same configuration as the first active material layer 2a in the first embodiment.

  The negative electrode of the secondary battery shown in FIG. 8 is produced by the following procedure. First, a first lithium occlusion layer 9c made of a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium is deposited on the current collector 1c by a sputtering method, a CVD method, an evaporation method, or the like. Further, a desired negative electrode is obtained by depositing the second lithium storage layer 10c on the first lithium storage layer 9c.

  In this embodiment also, a battery can be manufactured using the same positive electrode, separator, and electrolytic solution as in the first embodiment.

  Next, the operation when the negative electrode of the secondary battery shown in FIG. 8 is incorporated in the battery will be described in detail with reference to FIG. FIG. 9 is a schematic view of a battery produced using the negative electrode of the third embodiment of the present invention. During charging, the negative electrode receives lithium ions 6c from the positive electrode active material 5c facing each other with the separator 4c separating the negative electrode and the positive electrode through the electrolytic solution. For example, when a carbon-based material is used for the second lithium storage layer 10c, the first lithium storage layer 9c has a discharge potential higher than that of the second lithium storage layer 10c, so that the lithium ions 6c pass through the second lithium storage layer 10c. First, it is occluded in the first lithium occlusion layer 9c. When the lithium occlusion in the first lithium occlusion layer 9c is completed, the lithium ion 6c is occluded in the second lithium occlusion layer 10c, and when it is completed, the charging is completed. Further, during discharge, the lithium ions 6c stored in the second lithium storage layer 10c having a low discharge potential are first released. Next, lithium ions 6c occluded in the first lithium occlusion layer 9c are released. The lithium ions 6c released from the first lithium storage layer 9c pass through the second lithium storage layer 10c, and move to the positive electrode active material layer 5c through the separator 4c via the electrolytic solution.

  Since this first lithium occlusion layer 9c is a film-like layer, the bonding between the constituent metals is strong, and the distribution of the constituent metals is uniform. Therefore, the structural destruction of the first lithium storage layer 9c due to the volume change that occurs during charging and discharging is suppressed. Furthermore, since the 1st lithium occlusion layer 9c contains the metal which does not form an alloy with lithium, the volume change accompanying charging / discharging can be suppressed. In addition, a metal that does not form an alloy with lithium serves as a wedge that maintains the structure of the first lithium storage layer 9c. The synergistic effect of the above action makes it possible to effectively prevent structural destruction such as pulverization even after charging and discharging.

  Furthermore, by adopting a multilayer structure composed of the second lithium occlusion layer 10c and the first lithium occlusion layer 9c having different charge / discharge potentials from the first lithium occlusion layer 9c, charging and discharging are performed in stages. Expansion and contraction of the negative electrode active material layer due to discharge can be reduced. Moreover, it becomes possible to further suppress the expansion and contraction of the entire negative electrode active material layer by a synergistic effect of this action and the action by adopting the configuration of the first lithium storage layer 9c. As a result, an increase in internal resistance during the initial charge is suppressed, and a good initial discharge capacity is obtained. Further, even when a cycle is passed, since the action of suppressing the destruction of the alloy layer is maintained, it is possible to suppress an increase in resistance and a decrease in capacity inside the battery.

(Example 8)
Example 8 of the third embodiment of the present invention will be described below.
The negative electrode of the secondary battery shown in FIG. 8 was produced by the following procedure. First, a copper foil having a thickness of 8 μm was used as the current collector 1c, and an Sn—Ni alloy was formed as a first lithium storage layer 9c on the current collector 1c by a 30 μm plating method. Thereafter, 50 μm of natural graphite was deposited as the second lithium storage layer 10c to obtain a negative electrode. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

Example 9
In Example 9, a 18 μm thick copper foil was used as the current collector 1c, and a Sn—Co alloy was formed as the first lithium storage layer 9c by a 15 μm vapor deposition method. Thereafter, 50 μm of soft carbon was deposited thereon as the second lithium storage layer 10c to obtain a negative electrode. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

(Example 10)
In Example 10, a 15 μm thick copper foil was used as the current collector 1c, and an Sn—Ni amorphous alloy was formed as the first lithium storage layer 9c by a 30 μm vapor deposition method. Thereafter, 50 μm of natural graphite was deposited thereon as the second lithium storage layer 10c to obtain a negative electrode. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

  Table 3 shows the results of initial discharge capacity and cycle characteristics evaluation for the batteries of Examples 8 to 10. From this result, in Comparative Example 1, the capacity faded after rapid fading after 150 cycles, whereas in Examples 8-10, 82% or more of the initial discharge capacity was maintained even after 500 cycles. found. The present embodiment is different from the first embodiment in that a layer formed of a metal that forms an alloy with lithium or a metal that does not form an alloy with lithium is in direct contact with the current collector. However, as can be seen from the comparison between Table 1 and Table 3, in this embodiment as well, when the first embodiment is adopted, the increase in internal resistance is suppressed, and the expansion and contraction of the negative electrode active material layer due to charge and discharge is suppressed. It is thought that the effect which can effectively relieve is appearing.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described in detail with reference to the drawings. FIG. 10 is a cross-sectional view of the negative electrode of the secondary battery showing the fourth embodiment of the present invention.

  The current collector 1d is an electrode that takes out current to the outside of the battery during charging and discharging, and takes in current into the battery from the outside. As the current collector 1d, various conductive foils can be used, and examples thereof include aluminum, copper, stainless steel, gold, tungsten, molybdenum, and titanium.

  In this embodiment, the second active material layer 3d corresponds to “a layer made of an alloy or composite oxide containing a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium”, The structure is the same as that of the second active material layer 3a in the one embodiment, and it can be manufactured by the same method. The first active material layer 2d corresponds to a “layer made of a lithium storage material”, has the same configuration as the first active material layer 2a in the first embodiment, and can be manufactured by the same method. .

  The Li layer 11d is a layer made of Li metal and compensates for the irreversible capacity generated in the battery. The amount of compensation is preferably 80 to 120% with respect to the irreversible capacity of the battery. This is because if the amount is too small, it does not mean that the irreversible capacity is compensated, and if it is too large, Li metal may be deposited on the negative electrode surface.

  The negative electrode of the secondary battery shown in FIG. 10 is produced by the following procedure. First, the first active material layer 2d is deposited on the current collector 1d. Further, on the first active material layer 2d, a second active material layer 3d made of a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium is formed by sputtering, CVD, vapor deposition, or the like. To form. Further, a Li layer 11d is formed on the second active material layer 3d by vapor deposition to obtain a desired negative electrode.

  In this embodiment also, a battery can be manufactured using the same positive electrode, separator, and electrolytic solution as in the first embodiment.

  Next, the operation when the negative electrode of the secondary battery shown in FIG. 10 is incorporated in the battery will be described in detail with reference to FIG. FIG. 11 is a schematic view of a battery manufactured using the negative electrode according to the fourth embodiment of the present invention. During charging, the negative electrode receives lithium ions 6d from the positive electrode active material layer 5d facing each other with the separator 4d separating the negative electrode and the positive electrode through the electrolytic solution. For example, when a carbon-based material is used for the first active material layer 2d, since the second active material layer 3d has a higher discharge potential than the first active material layer 2d, the lithium ions 6d are first occluded in the second active material layer 3d. Is done. When the lithium occlusion in the second active material layer 3d is completed, the lithium ions 6d then pass through the second active material layer 3d and are occluded in the first active material layer 2d. When the first active material layer 2d is filled with lithium, charging is completed. During charging, the Li layer 11d diffuses into the negative electrode and is occluded in the first active material layer 2d or the second active material layer 3d. Further, at the time of discharge, lithium ions 6d stored in the first active material layer 2d having a low discharge potential are first released. Next, lithium ions 6d occluded in the second active material layer 3d are released. The released lithium ions 6d move to the positive electrode active material 5d through the electrolytic solution. Since the amount of Li corresponding to the Li layer 11d remains at the irreversible capacity site (positive and negative electrode surface, first active material layer 2d, second active material layer 3d, layer interface, battery wall surface, etc.) in the battery, the second active material layer It takes the form of disappearance from 3d or part of it remaining.

  At this time, since the second active material layer 3d is a film-like layer, the bonding between the constituent metals is strong, and the distribution of the constituent metals is uniform. Therefore, structural destruction of the second active material layer 3d due to the volume change that occurs during charging and discharging is suppressed. Furthermore, since the 2nd active material layer 3d contains the metal which does not form an alloy with lithium, the volume change accompanying charging / discharging can be suppressed. In addition, a metal that does not form an alloy with lithium serves as a wedge that maintains the structure of the second active material layer 3d. The synergistic effect of the above action makes it possible to effectively prevent structural destruction such as pulverization even after charging and discharging. As a result, an increase in internal resistance during the initial charge is suppressed, and a good initial discharge capacity is obtained. Further, even when a cycle is passed, since the action of suppressing the destruction of the alloy layer is maintained, it is possible to suppress an increase in resistance and a decrease in capacity inside the battery.

  Furthermore, by adopting a multilayer structure composed of the first active material layer 2d and the second active material layer 3d having different charge / discharge potentials from the second active material layer 3d, charging / discharging is performed in stages. Expansion and contraction of the negative electrode active material layer due to discharge can be reduced. Further, the synergistic effect of this action and the action by adopting the configuration of the second active material layer 3d described above can further suppress the expansion and contraction of the entire negative electrode active material layer.

(Example 11)
Next, Example 11 of the fourth embodiment of the present invention will be described.
The negative electrode of the secondary battery shown in FIG. 10 was produced by the following procedure. First, a copper foil having a thickness of 10 μm was used for the current collector 1d, and 100 μm of artificial graphite was deposited on the current collector 1d as the first active material layer 2d. Thereafter, a Si—Cu alloy was formed as the second active material layer 3d by a 2 μm sputtering method. Furthermore, 1 μm of Li film (corresponding to an irreversible capacity compensation amount of 80%) was formed as a Li layer 11d by a vapor deposition method to obtain a negative electrode. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

(Example 12)
In Example 12, a negative electrode was produced in the same manner as in Example 11. However, as the first active material layer 2d, natural graphite having a thickness of 70 μm was deposited, and as the second active material layer 3d, a Si—Fe alloy was deposited by 1 μm. Formed by the law. Further, as the Li layer 11d, a film of 1.5 μm (corresponding to an irreversible capacity filling amount of 100%) was formed by a vapor deposition method. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

(Example 13)
In Example 13, a negative electrode was produced in the same manner as in Example 11. However, as the first active material layer 2d, 90 μm thick hard carbon was deposited, and as the second active material layer 3d, amorphous WSi ₂ was deposited by a 1 μm CVD method. Formed. Further, as the Li layer 11d, a film of 2 μm (corresponding to an irreversible capacity filling amount of 100%) was formed by a vapor deposition method. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

(Example 14)
In Example 14, a negative electrode was produced in the same manner as in Example 11. However, Sn having a thickness of 5 μm was deposited as the first active material layer 2d, and a Si—Cu alloy was used as the second active material layer 3d by a 2 μm CVD method. Formed. Further, as the Li layer 11d, a film of 2 μm (corresponding to an irreversible capacity filling amount of 120%) was formed by a vapor deposition method. Other positive electrodes, separators, electrolytic solutions, evaluation methods, measurement conditions, and the like are the same as in Example 1.

  Table 4 shows the results of initial discharge capacity, initial charge / discharge efficiency, and cycle characteristics evaluation for the batteries of Examples 11 to 14 and Comparative Example 1. From these results, it was found that in Examples 11 to 14, the usable capacity increased by supplementing the irreversible capacity from the Li layer 11d, and as a result, high charge / discharge efficiency was obtained.

  In Comparative Example 1, it was found that capacity faded by rapid fading after 150 cycles, whereas Examples 11-14 maintained 85% or more of the initial discharge capacity even after 500 cycles. In Examples 11 to 14, as in the first and third embodiments, the increase in internal resistance is suppressed, and the expansion / contraction of the negative electrode active material layer due to charge / discharge due to charge / discharge is effectively mitigated. It is done.

1a, 1b, 1c, 1d Current collector 2a, 2d First active material layer 3a, 3d Second active material layer 4a, 4b, 4c, 4d Separator 5a, 5b, 5c, 5d Positive electrode active material layer 6a, 6b, 6c , 6d Lithium ion 7a Active material layer 8b Negative electrode active material layer 9c First lithium storage layer 10c Second lithium storage layer 11d Li layer

Claims (3)

A secondary battery negative electrode capable of inserting and extracting lithium ions,
A layer made of an alloy or a composite oxide containing a metal that forms an alloy with lithium or lithium and a metal that does not form an alloy with lithium,
The negative electrode for a secondary battery, wherein the layer made of the alloy or the composite oxide is made of a Li—Ti—O based amorphous compound. In the negative electrode for secondary battery of claim 1, wherein the alloy or layer of a composite oxide, a negative electrode for a secondary battery, characterized in that a layer thus formed sputtering.   A negative electrode for a secondary battery according to claim 1, a positive electrode capable of inserting and extracting lithium ions, and an electrolyte disposed between the negative electrode and the positive electrode. Secondary battery.

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