JP2012160324A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery that has an interface layer which resists cracking, and can maintain a junction between a negative electrode layer and a solid electrolyte layer even if charging and discharging are repeated.SOLUTION: A nonaqueous electrolyte battery comprises a positive electrode layer 13, a negative electrode layer 14, and a solid electrolyte layer 15 intervening between the electrode layers. The battery comprises an interface layer 16 mainly composed of Si between the negative electrode layer 14 and the solid electrolyte layer 15. The interface layer 16 is formed by physical vapor deposition using Si as a vapor deposition material in an atmosphere of a mixed gas prepared by adding oxygen to an inert gas. The addition ratio of the oxygen in the mixed gas is less than 0.5 vol.%.

Description

  The present invention relates to a nonaqueous electrolyte battery having excellent charge / discharge cycle characteristics.

  Nonaqueous electrolyte batteries are used as power sources for relatively small electric devices such as portable devices. Typical examples of the nonaqueous electrolyte battery include a lithium battery and a lithium ion secondary battery (hereinafter sometimes simply referred to as a lithium ion battery) using a transfer reaction of Li ions between the positive and negative electrode bodies.

  This lithium ion battery is a battery that charges and discharges by exchanging lithium (Li) ions between a positive electrode layer and a negative electrode layer through an electrolyte layer. In recent years, research on an all-solid lithium secondary battery using an incombustible inorganic solid electrolyte instead of an organic electrolyte in an electrolyte layer has been performed (see, for example, Patent Document 1).

  Patent Document 1 proposes a battery in which a positive electrode layer, a negative electrode layer, and a solid electrolyte layer are formed by a vapor phase method (for example, a sputtering method or a vapor deposition method). This battery includes an interface layer between the negative electrode layer and the solid electrolyte layer. The interface layer has a function of occluding Li ions that have moved from the positive electrode layer through the solid electrolyte layer during battery charging and diffusing the ions into the negative electrode layer. This makes it difficult for Li to precipitate at the negative electrode layer / solid electrolyte layer interface during charging, and suppresses peeling between the negative electrode layer and the solid electrolyte layer. For example, Si can be used as the material of the interface layer.

JP 2009-277381 A

  However, in the conventional lithium ion battery, when the interface layer is formed on the solid electrolyte layer, a crack may reach from the interface layer to the solid electrolyte layer. This crack causes peeling between the negative electrode layer and the solid electrolyte layer, and causes a short circuit due to the progress of Li dendrite along the crack.

  The present invention has been made in view of the above circumstances, and one of its purposes is to have an interface layer that is difficult to crack, and maintain the bonding between the negative electrode layer and the solid electrolyte layer even after repeated charge and discharge. An object of the present invention is to provide a nonaqueous electrolyte battery that can be used.

  (1) The nonaqueous electrolyte battery of the present invention has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer interposed between these two layers. The battery includes an interface layer mainly composed of Si between the negative electrode layer and the solid electrolyte layer, and the interface layer is a mixed gas atmosphere in which oxygen is added to an inert gas, and Si is vapor-deposited. It is formed by physical vapor deposition. The oxygen addition ratio in the mixed gas is less than 0.5% by volume.

  The interface layer containing Si as a main component has a high ability (diffusion ability) to occlude Li ions that have moved from the positive electrode layer through the solid electrolyte layer during charging and diffuse Li ions into the negative electrode layer. Therefore, according to the configuration of the present invention, it is difficult for Li to precipitate at the negative electrode layer / solid electrolyte layer interface at the time of charging, and it is possible to prevent the interface between both layers from being widened and causing poor bonding.

  Further, the exact reason is unknown due to the addition of oxygen to the atmospheric gas during the formation of the interface layer, but cracks are unlikely to occur in the interface layer after film formation. When a crack occurs in the interface layer, the solid electrolyte layer adjacent to the interface layer usually cracks, and Li dendrite grows through the crack, which causes a short circuit between the positive and negative electrode layers. Therefore, if an interface layer without cracks can be formed with a high probability, it is possible to prevent the battery from functioning early due to the short circuit.

  Along with the suppression of such bonding failure and cracks, even when charging and discharging are repeated, the bonding between the negative electrode layer and the solid electrolyte layer is maintained well, and the battery capacity is unlikely to decrease. The content of Si in the interface layer is preferably 50% by mass or more, and more preferably 80% by mass or more.

  (2) As one form of the nonaqueous electrolyte battery of this invention, the form whose addition ratio of the said oxygen is 0.1 volume% or more is mentioned.

  According to this configuration, by further specifying the amount of oxygen added to the mixed gas at the time of forming the interface layer, it is possible to further easily form an interface layer without cracks.

As a form of non-aqueous electrolyte battery (3) The present invention, the solid electrolyte layer, and a form which is the sulfide-based solid electrolyte containing Li ₂ S and P ₂ S _5.

If it is the above sulfides, it can be set as the solid electrolyte layer which has high Li ion conductivity. As a result, the internal resistance of the nonaqueous electrolyte battery can be reduced. Examples of the sulfide-based solid electrolyte used for the solid electrolyte layer include Li ₂ S-P ₂ S ₅ system, Li ₂ S-SiS ₂ system, Li ₂ S-B ₂ S ₃ system, and further P ₂ O. ₅ or Li ₃ PO ₄ may be added. Among these, a sulfide-based solid electrolyte containing Li ₂ S and P ₂ S ₅ is preferable because it exhibits high Li ion conductivity.

  The nonaqueous electrolyte battery of the present invention includes a specific interface layer between the negative electrode layer and the solid electrolyte layer, so that peeling between the negative electrode layer and the solid electrolyte layer and cracking of the solid electrolyte layer accompanying repeated charge and discharge are provided. Can be prevented. As a result, even if charging / discharging is repeated, the battery capacity is unlikely to decrease and a nonaqueous electrolyte battery exhibiting excellent charge / discharge cycle characteristics can be obtained.

It is a schematic sectional drawing of the nonaqueous electrolyte battery which concerns on embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG.

≪Overall structure≫
This lithium battery 1 has a laminated structure in which a positive electrode layer 13, a solid electrolyte layer (SE layer) 15, an interface layer 16, a negative electrode layer 14, and a negative electrode current collector layer 12 are laminated in this order on a positive electrode current collector layer 11. have. One of the features of the battery 1 is that the main component of the interface layer 16 is Si, and the interface layer contains a predetermined amount of oxygen. Hereinafter, each configuration will be described in detail.

≪Each component≫
(Positive electrode current collector layer)
The positive electrode current collector layer 11 is a thin metal plate having a predetermined thickness, and also serves as a substrate for supporting each layer described later. As the positive electrode current collector layer 11, one selected from aluminum (Al), nickel (Ni), alloys thereof, and stainless steel can be suitably used. In addition, a positive electrode current collector layer may be formed by forming a metal film over an insulating substrate. The current collector layer 11 made of a metal film can be formed by a PVD method (physical vapor deposition method) or a CVD method (chemical vapor deposition method). Examples of the PVD method include a vacuum deposition method, a sputtering method, an ion plating method, and a laser ablation method. Examples of the CVD method include a thermal CVD method and a plasma CVD method.

(Positive electrode layer)
The positive electrode layer 13 is a layer containing an active material that absorbs and releases Li ions. As the positive electrode active material, an oxide of lithium and at least one element selected from Mn, Fe, Co, and Ni can be suitably used. For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiCo _0.5 Fe _0.5 O _{2 and the} like can be mentioned.

  The positive electrode layer 13 may further contain a conductive additive. As a conductive support agent, what consists of metal fibers, such as carbon black, such as acetylene black, natural graphite, thermal expansion graphite, carbon fiber, ruthenium oxide, titanium oxide, aluminum, and nickel, can be utilized, for example. In particular, carbon black is preferable because it can secure high conductivity in a small amount.

  As a method for forming the positive electrode layer 13 described above, a dry method such as a PVD method or a CVD method, or a wet method such as a coating method or a screen printing method can be used. If a wet method is used, a binder is included in the positive electrode layer so that the active materials are bound to each other, or the active material and a material other than the active material (electrolyte particles and conductive aid). Also good. As such a binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or the like can be used.

(Solid electrolyte layer)
The solid electrolyte layer (SE layer) 15 preferably has a Li ion conductivity (20 ° C.) of 10 ⁻⁵ S / cm or more and a Li ion transport number of 0.999 or more. In particular, the Li ion conductivity should be 10 ⁻⁴ S / cm or more and the Li ion transport number should be 0.9999 or more. The SE layer 15 preferably has an electronic conductivity of 10 ⁻⁸ S / cm or less. The material of the SE layer 15 is preferably composed of an oxide (eg, Li-PON), sulfide (eg, Li-PSO or Li-PS) amorphous film or polycrystalline film. In particular, Li-PS composed of Li ₂ S and P ₂ S ₅ has excellent Li ion conductivity. Therefore, when it is used for the SE layer 15, the performance of the battery can be improved.

  As a method for forming the SE layer 15, a solid phase method or a vapor deposition method can be used. Examples of the solid phase method include forming a raw material powder using a mechanical milling method and sintering the raw material powder. On the other hand, examples of the vapor deposition method include a PVD method and a CVD method. When the SE layer 15 is formed by the vapor deposition method, the thickness of the SE layer 15 can be made thinner than when the SE layer is formed by the solid phase method.

(Interface layer)
The interface layer 16 is a layer that plays a role of ensuring the bonding between the SE layer 15 and a negative electrode layer 14 described later. Si can be used as a main material of the interface layer 16. The Si content in the interface layer 16 is preferably 50% by mass or more, more preferably 80% by mass or more. More specifically, the interface layer 16 is substantially composed of Si and oxygen. As will be described later, the oxygen-containing interface layer 16 can be easily formed by adding a predetermined amount of oxygen to the atmosphere gas during the formation of the interface layer 16. The interface layer 16 containing oxygen can be used as a member of a lithium ion battery that is less prone to crack during film formation and has excellent discharge characteristics.

As a method for forming the interface layer 16, physical vapor deposition can be suitably used. For example, resistance heating, electron beam evaporation, sputtering, ion plating, PLD (pulse laser deposition) method, and the like can be used. These are usually techniques for forming a film by using a target as vapor deposition particles in a predetermined atmosphere and attaching the vapor deposition particles to a substrate. Here, a Si target is used, and the atmosphere during film formation is a mixed gas obtained by adding oxygen to an inert gas. Ar, N ₂ or the like can be used as the inert gas. The oxygen content in the mixed gas is less than 0.5% by volume. By using this oxygen addition amount, defects such as cracks, discoloration, and spot-like portions can be suppressed as compared with the interface layer formed in an atmosphere to which oxygen is not added, and the yield of the interface layer formation is reduced. Can be increased. The lower limit of the oxygen addition amount is about 0.1% by volume. By adding oxygen above the lower limit value to the atmospheric gas, the effect of suppressing cracks on the interface layer 16 can be easily obtained.

  The thickness of the interface layer 16 is preferably 50 nm or less. When the thickness of the interface layer 16 is more than 50 nm, the Li ion occlusion property of the interface layer itself is superior to the Li ion diffusing ability of the interface layer 16 to the negative electrode layer 14, and the volume change of the interface layer 16 is increased. There is a possibility that the junction at the negative electrode layer / solid electrolyte layer interface is destroyed. A preferred interface layer thickness is 20 nm or less. Further, if the thickness of the interface layer 16 is made too small, the effect of providing the interface layer 16 is low, and there is a possibility that the junction at the negative electrode layer / solid electrolyte layer interface is broken. Therefore, the thickness of the interface layer 16 is preferably more than 5 nm, more preferably 10 nm or more.

It is preferable to define Tb / Tn, which is a ratio between the thickness Tb of the interface layer 16 and the thickness Tn of the negative electrode layer 14 described below, as follows.
0.005 <Tb / Tn <0.5

  By setting Tb / Tn, which is the ratio between the thickness of the interface layer 16 and the thickness of the negative electrode layer 14, to 0.005 to 0.5, it is possible to sufficiently secure the bonding between the negative electrode layer 14 and the SE layer 15. In particular, Tb / Tn is preferably 0.01 to 0.4. When Tb / Tn is less than 0.005, the interface layer thickness Tb is relatively thin, so that it is difficult to maintain the bonding between the negative electrode layer 14 and the SE layer 15. On the other hand, if Tb / Tn is more than 0.5, the interface layer thickness Tb is relatively thick, so that the volume change of the interface layer 16 accompanying the charging / discharging of the battery is large, and the negative electrode layer 14 and the SE layer 15 It becomes difficult to maintain the bonding.

(Negative electrode layer)
The negative electrode layer 14 is composed of a layer containing an active material that absorbs and releases Li ions. Specifically, Li metal or Li alloy (for example, Li—Al, Li—Mn—Al, etc.) is used as the negative electrode layer 14. Since such a negative electrode layer 14 can provide the negative electrode layer 14 itself with a function as a current collector, the negative electrode current collector 12 described later can be omitted.

  The thickness Tn of the negative electrode layer 14 is preferably in the range of 0.1 μm to 10 μm. By having such negative electrode layer thickness Tn, it can be set as a lithium battery provided with the discharge capacity which can be used for various uses. A more preferable range of the thickness Tn of the negative electrode layer 14 is 0.5 μm to 2 μm.

  The negative electrode layer 14 is preferably formed using a vapor deposition method such as a PVD method or a CVD method. By using the vapor deposition method, the thickness of the negative electrode layer 14 can be reduced and contact with the SE layer 15 can be sufficiently ensured as compared with the case where the negative electrode layer 14 is formed with a metal foil.

(Negative electrode current collector layer)
The negative electrode current collector layer 12 is a metal film for supplying power to the negative electrode layer 14. As the negative electrode current collector layer 12, one selected from copper (Cu), nickel (Ni), iron (Fe), chromium (Cr), and alloys thereof can be suitably used. This negative electrode current collector layer 12 can also be formed by the PVD method or the CVD method as in the case of the positive electrode current collector layer 11. As described above, the negative electrode current collector layer 12 can be omitted.

(Other)
Although not shown in FIG. 1, an intermediate layer may be provided between the positive electrode layer 13 and the SE layer 15 to alleviate the deviation of Li ions near the interface between these two layers. When a sulfide-based solid electrolyte is used for the SE layer 15, Li ions are biased between the SE layer 15 and the positive electrode layer 13, and the internal resistance of the battery tends to increase. Therefore, it is preferable to provide an intermediate layer between the positive electrode layer 13 and the SE layer 15 to alleviate the deviation of Li ions near the interface between these two layers. As the material of the intermediate layer, Li conductive oxide, for example, LiNbO ₃ , LiTaO ₃ , Li ₄ Ti ₅ O ₁₂ , Li _X La _{(2-X) / 3} TiO ₃ (X = 0.1 to 0.5), Li _{7 + X} La ₃ Zr ₂ O _{12+ (X / 2)} (-5 ≦ X ≦ 3), Li _3.6 Si _0.6 P _0.4 O ₄ , Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , Li _1.8 Cr _0.8 Ti Examples include _1.2 (PO ₄ ) ₃ and Li _1.4 In _0.4 Ti _1.6 (PO ₄ ) ₃ , and these may be used alone or in combination of two or more.

  A battery sample usable for an all-solid lithium secondary battery as shown in FIG. 1 was prepared, and the interface layer was evaluated. This sample is a laminate in which the positive electrode current collector layer 11, the positive electrode layer 13, the intermediate layer, the SE layer 15, and the interface layer 16 are formed in this order.

<Battery Sample Preparation Procedure>
By depositing LiCoO ₂ using a PLD method on a stainless steel substrate (thickness 0.5 mm, diameter φ16 mm) to be the positive electrode current collector layer 11, the positive electrode layer 13 (thickness 5 μm, diameter φ16 mm) ) Was formed. Further, after the film formation, the base material on which the LiCoO ₂ positive electrode layer 13 was formed was annealed in the atmosphere at 500 ° C. for 3 hours.

Next, an intermediate layer (not shown) was formed on the positive electrode layer 13 by depositing LiNbO ₃ using the PLD method. The intermediate layer had a thickness of 0.02 μm and a diameter of 16 mm.

Next, an SE 2 layer (thickness 10 μm, diameter φ16 mm) was formed on the intermediate layer by depositing a Li ₂ S—P ₂ S ₅ based solid electrolyte using the PLD method.

  Next, an interface layer 16 (thickness 0.01 μm (10 nm), diameter φ10 mm) was formed on the SE layer 15 by sputtering. The interface layer 16 is formed using Si as a target and using an oxygen gas addition amount Ar gas shown in Table 1 as an atmospheric gas. For comparison, Sample No. 1 having the same configuration as the above sample was also prepared except that oxygen was not added. In this sample No. 1, the atmosphere gas at the time of film formation is Ar gas only, and oxygen is not added. If a negative electrode layer 14 (thickness 1 μm, diameter φ10 mm) is formed on the interface layer 16 of the battery sample by depositing Li using a vacuum deposition method, a lithium secondary battery can be configured.

  And the visual observation and microscopic observation were performed with respect to the obtained battery sample, and the surface state of the interface layer of each sample was evaluated. In the evaluation items in Table 1, “white discoloration” indicates that there was a part that was partly clouded by visual inspection, and “crack” indicates that a clear crack was observed on the surface of the interface layer. The “spot-like” indicates that a spot-like region is locally observed in the microscopic observation. A plurality of samples are manufactured, and the surface property of the interface layer 16 having the highest occurrence frequency is shown.

  As is clear from Table 1, abnormalities such as cracks were observed in both cases where oxygen was not added to the atmospheric gas during the formation of the interface layer and when oxygen was added in an amount of 0.5% by volume or more. In contrast, Sample No. 2 in which 0.1% by volume of oxygen was added to the atmospheric gas showed no abnormality. Therefore, when a battery is configured using this sample No. 2, it is considered that various problems associated with the occurrence of cracks in the interface layer 16 and the SE layer 15 can be solved.

  The embodiments of the present invention are not limited to those described above, and can be appropriately changed without departing from the gist of the present invention. For example, as a constituent element of the interface layer, C, Ge, Sn, Pb, or the like, which is a group 14 element of the periodic table other than Si, can be used. These Group 14 elements of the periodic table have the common property that they can occlude Li ions that have migrated from the positive electrode layer during battery charging and can be diffused into the negative electrode layer. It can be expected to perform the same function.

  The nonaqueous electrolyte battery of the present invention can be suitably used as a power source for portable devices and the like.

1 Lithium battery
11 Positive electrode current collector layer 12 Negative electrode current collector layer 13 Positive electrode layer 14 Negative electrode layer
15 Solid electrolyte layer (SE layer) 16 Interface layer

Claims (3)

A non-aqueous electrolyte battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer interposed between the two layers,
Between the negative electrode layer and the solid electrolyte layer, comprising an interface layer mainly composed of Si,
This interface layer is formed by physical vapor deposition using Si as a vapor deposition material in a mixed gas atmosphere in which oxygen is added to an inert gas,
A nonaqueous electrolyte battery characterized in that the proportion of oxygen added to the mixed gas is less than 0.5% by volume.   2. The nonaqueous electrolyte battery according to claim 1, wherein an addition ratio of the oxygen is 0.1% by volume or more. 3. The nonaqueous electrolyte battery according to claim 1, wherein the solid electrolyte layer is a sulfide-based solid electrolyte containing Li ₂ S and P ₂ S ₅ .

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