JP2008091328A - Lithium secondary cell and its manufacturing method - Google Patents
Lithium secondary cell and its manufacturing method Download PDFInfo
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Abstract
Description
本発明は、固体電解質を含み、高容量で優れた充放電特性のリチウム二次電池に関するものである。 The present invention relates to a lithium secondary battery including a solid electrolyte and having a high capacity and excellent charge / discharge characteristics.
負極（以下負極層とも言う）にリチウム（Ｌｉ）系金属を使ったリチウム二次電池は、有機電解液を使ったものと固体電解質を使ったものがある。中でも金属Ｌｉを使ったものは、単位体積当たりの放電容量が大きく究極の電池とされている。しかしながら、前者で負極に金属Ｌｉを用いると、充放電を繰り返す内に、これが電解液と反応して針状結晶となり、それがセパレータを突き破り正極（以下正極層とも言う）に達して短絡を起こす可能性がある。このため、炭素とＬｉ金属箔の積層された複合材料、ウッドメタルとの複合化等々、それを抑える工夫がなされて来た。さらに電解質に有機電解液を使うため、リフロー半田実装時の温度に耐えられない場合が多く、耐熱性に課題がある。一方後者は、リフロー半田実装程度の温度での耐熱性には問題は無いが、Ｌｉによる短絡防止については、例えば、特開２００４−１７９１５８号公報（特許文献１）および特開２００４−１２７７４３号公報（特許文献２）に提案されているように、Ｌｉ金属やその粒子が炭素系材料中に埋設された複合材料などを負極材料として用いて来た。 Lithium secondary batteries using a lithium (Li) -based metal for the negative electrode (hereinafter also referred to as negative electrode layer) include those using an organic electrolyte and those using a solid electrolyte. Among them, the one using metal Li has a large discharge capacity per unit volume and is regarded as an ultimate battery. However, when metal Li is used for the negative electrode in the former, while it is repeatedly charged and discharged, it reacts with the electrolyte to form needle-like crystals that break through the separator and reach the positive electrode (hereinafter also referred to as the positive electrode layer), causing a short circuit. there is a possibility. For this reason, contrivances have been made to suppress this, such as composite materials in which carbon and Li metal foil are laminated, and composites with wood metal. Furthermore, since an organic electrolyte is used as the electrolyte, it often cannot withstand the temperature during reflow solder mounting, and there is a problem with heat resistance. On the other hand, the latter has no problem in heat resistance at a temperature comparable to that of reflow soldering. However, for prevention of short circuit by Li, for example, Japanese Patent Application Laid-Open No. 2004-179158 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2004-127743. As proposed in (Patent Document 2), Li metal or a composite material in which particles thereof are embedded in a carbon-based material has been used as a negative electrode material.
例えば、コバルト酸リチウム（ＬｉＣｏＯ２）などの遷移金属元素を含む正極層（以下電池要素１とも言う）、Ｌｉを含む負極層（以下電池要素３とも言う）との間に固体電解質層（以下電池要素２とも言う）が積層された基本構成のリチウム二次電池は、これらの要素を気相から析出させる手段（以下気相合成法とも言う）と、粉末から成型する手段（以下粉末法とも言う）によって作られて来た。なお固体電解質層の材料としては、上記特許文献２やＪｏｕｒｎａｌ ｏｆ Ｎｏｎ−Ｃｒｙｓｔａｌｌｉｎｅ Ｓｏｌｉｄｓ、１２３（１９９０年）ｐｐ．３２８−３３８（非特許文献１）に紹介されているように、主に燐（Ｐ）および硫黄（Ｓ）を含むＬｉ化合物やこれらにさらに酸素（Ｏ）が含まれるもの、さらには上記特許文献１に紹介されているように、ニオブ（Ｎｂ）、タンタル（Ｔａ）および酸素（Ｏ）が含まれるＬｉ化合物などが、知られている。 For example, a solid electrolyte layer (hereinafter referred to as battery) between a positive electrode layer (hereinafter also referred to as battery element 1) containing a transition metal element such as lithium cobaltate (LiCoO 2 ) and a negative electrode layer (hereinafter also referred to as battery element 3) containing Li. A lithium secondary battery having a basic structure in which element 2 is also stacked is a means for depositing these elements from the gas phase (hereinafter also referred to as a gas phase synthesis method) and a means for molding from a powder (hereinafter also referred to as a powder method). ). In addition, as a material of a solid electrolyte layer, the said patent document 2 and Journal of Non-Crystalline Solids, 123 (1990) pp.1. As introduced in 328-338 (Non-patent Document 1), Li compounds mainly containing phosphorus (P) and sulfur (S), those further containing oxygen (O), and the above-mentioned patent documents As introduced in 1, a Li compound containing niobium (Nb), tantalum (Ta) and oxygen (O) is known.
粉末法の場合、原料となる粉末は、主に溶融体の急冷凝固による手段（以下急冷法とも言う）または粉体をボールミルなどで混合反応させるメカニカルミリング法（以下ＭＡ法とも言う）によって製造されて来た。これらの粉末は、ガラス質および／または結晶質であり、ディスク状、塊状またはフレーク状の形態のものである。前者は、例えば、上記非特許文献１や特開平４−２３１３４６号公報（特許文献３）などに、後者は、例えば、特許第３２３３３４５号公報（特許文献４）、特開２００４−２６５６８５号公報（特許文献５）などに紹介されている。 In the case of the powder method, the raw material powder is produced mainly by means of rapid solidification of the melt (hereinafter also referred to as a rapid cooling method) or a mechanical milling method (hereinafter also referred to as an MA method) in which the powder is mixed and reacted with a ball mill or the like. I came. These powders are glassy and / or crystalline and are in the form of discs, lumps or flakes. The former is, for example, Non-Patent Document 1 and Japanese Patent Laid-Open No. 4-231346 (Patent Document 3), and the latter is, for example, Japanese Patent No. 3323345 (Patent Document 4), Japanese Patent Laid-Open No. 2004-265585 ( Patent Document 5) and the like.
粉末原料を使ったリチウム二次電池の電池要素が積層された複合体（以下電池要素複合体とも言う）の製造方法については、例えば、Ｊｏｕｒｎａｌ ｏｆ Ｊａｐａｎｅｓｅ Ｓｏｃ．Ｐｏｗｄｅｒ Ｍｅｔｔａｌｌｕｒｇｙ，Ｖｏｌ．５１，Ｎｏ．２，ｐｐ９１−９７（非特許文献２）の９２頁右コラムに、３００ＭＰａの圧力で直径１０ｍｍのものを加圧成型する手段が、また例えば、特許第３４５３０９９号公報（特許文献６）には粉末状の負極活物質、正極活物質および固体電解質を３７００ｋｇ／ｃｍ２（３６ｋＰａ）にてプレス成形して一体化する手段が、それぞれ紹介されている。さらに米国特許４，４７７，５４５号公報（特許文献７）は、硫化物系固体電解質とリチウム金属負極を９０〜１００℃にて１０，０００〜１００，０００ｐｓｉ（約６９〜６９０ＭＰａ）の圧力で熱間成形する手段を紹介している。さらに特公平５−４８５８２号公報（特許文献８）、特開２００４−２０６９４２号公報（特許文献９）および特開昭５９−１５１７７０号公報（特許文献１０）には、硫化物系固体電解質を用いた電池要素複合体の成型手段が開示されている。その成型は、いずれも室温で行われ、開示された成型圧力の例は、順に８００００ｐｓｉ（約５５０ＭＰａ）、４ｔｏｎ／ｃｍ２（約３９２ＭＰａ）および５ｔｏｎ／ｃｍ２（約４９０ＭＰａ）である。 For a method for producing a composite in which battery elements of a lithium secondary battery using a powder raw material are laminated (hereinafter also referred to as a battery element composite), see, for example, Journal of Japan Soc. Powder Metallurgy, Vol. 51, no. 2, pp91-97 (Non-patent Document 2), page 92, right column, means for pressure-molding a 10 mm diameter member at a pressure of 300 MPa, for example, Japanese Patent No. 3453099 (Patent Document 6) is a powder. Means for press-molding and integrating the negative electrode active material, the positive electrode active material, and the solid electrolyte at 3700 kg / cm 2 (36 kPa) have been introduced. Further, US Pat. No. 4,477,545 (Patent Document 7) discloses that a sulfide-based solid electrolyte and a lithium metal negative electrode are heated at a pressure of 10,000 to 100,000 psi (about 69 to 690 MPa) at 90 to 100 ° C. Introduces the means of inter-molding. Further, Japanese Patent Publication No. 5-48582 (Patent Document 8), Japanese Patent Application Laid-Open No. 2004-206942 (Patent Document 9) and Japanese Patent Application Laid-Open No. 59-151770 (Patent Document 10) use a sulfide-based solid electrolyte. A battery element composite molding means has been disclosed. Its molding are all carried out at room temperature, of the disclosed molded pressure is sequentially 80,000 psi (about 550MPa), 4ton / cm 2 (about 392 MPa) and 5 ton / cm 2 (about 490 MPa).
以上従来の粉末法で得られた電池要素の成型密度は明確ではないが、電池駆動される際の電流密度は、いずれも数１０μＡ／ｃｍ２から数１００μＡ／ｃｍ２程度であり、１ｍＡ／ｃｍ２以下であると記載されており、有機電解液を使用した通常のリチウムイオン二次電池での３〜１０ｍＡ／ｃｍ２と比較してかなり低い値となっている。 Although the molding density of the battery element obtained by the conventional powder method is not clear, the current density when the battery is driven is about several tens μA / cm 2 to several hundreds μA / cm 2 , and is 1 mA / cm 2. It is described as being 2 or less, and is considerably lower than 3 to 10 mA / cm 2 in a normal lithium ion secondary battery using an organic electrolyte.
また、有機電解液を使用したリチウムイオン二次電池では、電流密度向上の為、正極活物質表面にＬｉ４Ｔｉ５Ｏ１２等の固体電解質膜を形成する技術が開発されている（非特許文献３）。さらに、全固体電池系に於いても、正極活物質表面に電流密度向上の為、正極活物質表面にＬｉ４Ｔｉ５Ｏ１２等の固体電解質膜を形成する技術が開発されている（非特許文献４）。
以上紹介した従来の粉末法で作られた電池要素複合体では、成型された電池要素の界面での電気的な接触抵抗（以下単に接触抵抗とも言う）が大きいため、高い電流密度が得られない。その原因は、電池成型体中の構成粒子同士が点接触状態になっており、Ｌｉイオンが流れるに十分な接触面積が確保されていないことにある。このため、例えば、上記非特許文献２の電池要素複合体の電池特性評価は、充放電が加圧下で行われている。しかし、この手段は、大がかりな加圧手段が必要であり実用的ではない。 In the battery element composite made by the conventional powder method introduced above, the electrical contact resistance (hereinafter also simply referred to as contact resistance) at the interface of the molded battery element is large, so a high current density cannot be obtained. . The cause is that the constituent particles in the battery molded body are in a point contact state, and a contact area sufficient for the flow of Li ions is not ensured. For this reason, for example, the battery characteristic evaluation of the battery element composite according to Non-Patent Document 2 is performed under charge and discharge under pressure. However, this means requires a large-scale pressurizing means and is not practical.
一方、気相合成法で薄膜が積層された電池要素複合体の二次電池では、それぞれの電池要素が緻密であり、要素界面の密着度が高いため、接触抵抗は大幅に改善される。しかしながら、正極層が１０〜数１０μｍと薄いため、単位面積当たりの容量密度は、せいぜい数μＡｈ／ｃｍ２程度である。したがって、容量密度を、少なくとも１ｍＡｈ／ｃｍ２にするためには、正極活物質の厚みを大幅に大きくする必要がある。 On the other hand, in a secondary battery of a battery element composite in which thin films are laminated by a vapor phase synthesis method, each battery element is dense and the contact degree of the element interface is high, so that the contact resistance is greatly improved. However, since the positive electrode layer is as thin as 10 to several tens of μm, the capacity density per unit area is about several μAh / cm 2 at most. Therefore, in order to make the capacity density at least 1 mAh / cm 2 , it is necessary to greatly increase the thickness of the positive electrode active material.
固体電解質を使用したリチウム二次電池の容量密度を上げるためには、粉末法および気相合成法のいずれの手段を採る場合にも、単位面積当たりの正極活物質の量を大幅に増やす必要があり、正極活物質と正極集電体との間は勿論のこと、正極層、固体電解質層および負極層の各電池要素間の電気的な接触も十分に確保する必要がある。 In order to increase the capacity density of a lithium secondary battery using a solid electrolyte, it is necessary to significantly increase the amount of the positive electrode active material per unit area, regardless of whether the powder method or the vapor phase synthesis method is used. In addition to the positive electrode active material and the positive electrode current collector, it is necessary to ensure sufficient electrical contact between the battery elements of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer.
本発明は、遷移金属元素を含む正極層、固体電解質層、およびリチウムを含む負極層とを有するリチウム二次電池に関し、その正極層および固体電解質層の見掛密度の理論密度に対する割合が９５％以上であるリチウム二次電池である。さらにその一例として、本発明には固体電解質がリチウム（Ｌｉ）と燐（Ｐ）と硫黄（Ｓ）を主成分とするリチウムイオン伝導性固体電解質であるものも含まれる。 The present invention relates to a lithium secondary battery having a positive electrode layer containing a transition metal element, a solid electrolyte layer, and a negative electrode layer containing lithium, and the ratio of the apparent density of the positive electrode layer and the solid electrolyte layer to the theoretical density is 95%. This is the lithium secondary battery. Further, as an example, the present invention includes one in which the solid electrolyte is a lithium ion conductive solid electrolyte containing lithium (Li), phosphorus (P), and sulfur (S) as main components.
上記した本発明の二次電池は、例えば、遷移金属元素を含む正極層が、室温以上２５０℃以下の温度条件下、７５０〜２０００ＭＰａの圧力にて加圧成型される工程１、固体電解質層が、同正極層上に形成される工程２、同固体電解質層上にリチウムを含む負極層が形成される工程３とを含む方法で作られる。また、この場合、工程２では、固体電解質層が、工程１と同じ温度および加圧条件の下で正極層上に加圧成型されても良い。勿論工程１にて正極層と固体電解質層の双方が、同時に成型一体化されても良い。また工程２において固体電解質層が、正極上に気相合成法によって形成されても良い。 In the secondary battery of the present invention described above, for example, the positive electrode layer containing a transition metal element is pressure-molded at a pressure of 750 to 2000 MPa under a temperature condition of room temperature to 250 ° C., and the solid electrolyte layer is Step 2 formed on the positive electrode layer, and Step 3 of forming a negative electrode layer containing lithium on the solid electrolyte layer. In this case, in Step 2, the solid electrolyte layer may be pressure-molded on the positive electrode layer under the same temperature and pressure conditions as in Step 1. Of course, both the positive electrode layer and the solid electrolyte layer may be simultaneously molded and integrated in step 1. In step 2, the solid electrolyte layer may be formed on the positive electrode by a gas phase synthesis method.
本発明によれば、有機電解液を含有しているリチウムイオン二次電池に匹敵する実用的な電流密度で、充放電特性に優れた固体電解質層を含むリチウム二次電池が提供できる。 According to the present invention, it is possible to provide a lithium secondary battery including a solid electrolyte layer excellent in charge / discharge characteristics at a practical current density comparable to that of a lithium ion secondary battery containing an organic electrolyte.
本発明の電池の正極層は、元素周期律表の遷移金属元素を含む材料で構成される。正極層の材料の好適な例としては、コバルト酸リチウム（化学式ＬｉＣｏＯ２）、マンガン酸リチウム（化学式ＬｉＭｎ２Ｏ４）、リチウムリン酸鉄（化学式ＬｉＦｅＰＯ４）が挙げられる。また負極層のそれは、炭素（Ｃ）、リチウム（Ｌｉ）に加えて、アルミニウム（Ａｌ）、シリコン（Ｓｉ）、スズ（Ｓｎ）、及びこれらとリチウムとの合金が挙げられる。 The positive electrode layer of the battery of the present invention is made of a material containing a transition metal element in the periodic table. Preferable examples of the material of the positive electrode layer include lithium cobalt oxide (chemical formula LiCoO 2 ), lithium manganate (chemical formula LiMn 2 O 4 ), and lithium iron phosphate (chemical formula LiFePO 4 ). Examples of the negative electrode layer include carbon (C) and lithium (Li), as well as aluminum (Al), silicon (Si), tin (Sn), and alloys of these with lithium.
本発明の二次電池の正極層および固体電解質層の材料は、その見掛密度の理論密度に対する割合（以下理論密度比とも言う）が９５％以上、好ましくは９８％以上のもので構成されている。これによって、正極層と負極層の各々の粒子が、ともに固体電解質層との界面で同層の粒子と直接面接触した状態になり、界面で固体電解質層と有効に接触する正極活物質の単位面積当たりの量を大幅に増やすことができる。その結果有機電解液を用いるリチウム二次電池に匹敵する実用的な電流密度と充放電特性に優れた固体電解質層を含むリチウム二次電池が、提供できる。 The material of the positive electrode layer and the solid electrolyte layer of the secondary battery according to the present invention is configured such that the ratio of the apparent density to the theoretical density (hereinafter also referred to as the theoretical density ratio) is 95% or more, preferably 98% or more. Yes. As a result, each particle of the positive electrode layer and the negative electrode layer is in direct contact with the particles of the same layer at the interface with the solid electrolyte layer, and the unit of the positive electrode active material that effectively contacts the solid electrolyte layer at the interface. The amount per area can be greatly increased. As a result, a lithium secondary battery including a solid electrolyte layer excellent in practical current density and charge / discharge characteristics comparable to a lithium secondary battery using an organic electrolyte can be provided.
なお本発明での理論密度比は、それぞれの電池要素素材の理論密度に対する見掛密度の割合（％）で定義する。なお本発明の電池要素を構成する複合素材の理論密度ρｔは、構成する化学成分ｎの理論密度ρｎにその成分のその電池要素に占める体積割合ｖｎ（％）を乗じた値ρｎｖｎの総和Σρｎｖｎとし、複合素材の見掛密度ρａは、同素材の質量ｗをその外寸から算出された体積ｖで割った値ｗ／ｖとする。したがって、理論密度比は、ｗ／（ｖ・Σρｎｖｎ）［％］で表わす。 The theoretical density ratio in the present invention is defined by the ratio (%) of the apparent density to the theoretical density of each battery element material. The theoretical density ρ t of the composite material constituting the battery element of the present invention is a value ρ n obtained by multiplying the theoretical density ρ n of the constituent chemical component n by the volume ratio v n (%) of the component in the battery element. v is the total sum Σρ n v n of n, apparent density [rho a composite material, a value w / v defined by the volume v calculated mass w of the same material from the outer dimensions. Therefore, the theoretical density ratio is represented by w / (v · Σρ n v n ) [%].
本発明の電池の正極層と固体電解質層の理論密度比を、ともに９５％以上にする理由は、９５％未満になると、上述のようにこれら電池要素内および要素間でのリチウムイオン伝導率が低下し、実用レベルの電流密度（１ｍＡ／ｃｍ２以上）にて、容量密度が実用レベル（１ｍＡｈ／ｃｍ２）以上の電池が得られないからである。なお正極活物質と正極集電体との界面での電気的な接触を十分に確保することは、当然である。 The reason why both the theoretical density ratios of the positive electrode layer and the solid electrolyte layer of the battery of the present invention are 95% or more is that the lithium ion conductivity in and between these battery elements is as described above when the ratio is less than 95%. This is because a battery having a practical density (1 mAh / cm 2 ) or more cannot be obtained at a practical level of current density (1 mA / cm 2 or more). In addition, it is natural to ensure sufficient electrical contact at the interface between the positive electrode active material and the positive electrode current collector.
以上の条件が満たされた場合の本発明の電池の例として、充電時の電圧が４．２Ｖであり、放電時の電圧が３Ｖで電流値が３ｍＡ／ｃｍ２の場合の放電容量の維持率が、９５％以上のものがある。なお以上の充電時の電圧、放電時の電圧と電流の条件設定レベルは、リチウム二次電池では通常のものである。前記した各文献掲載のものも含め、従来のリチウム二次電池では、同じ条件下での放電容量の維持率は、高々２５％までである。 As an example of the battery of the present invention when the above conditions are satisfied, the discharge capacity retention rate when the voltage during charging is 4.2 V, the voltage during discharging is 3 V, and the current value is 3 mA / cm 2. However, there are 95% or more. Note that the above condition setting levels for the voltage during charging and the voltage and current during discharging are normal for lithium secondary batteries. In conventional lithium secondary batteries, including those described in the above-mentioned documents, the discharge capacity maintenance rate under the same conditions is at most 25%.
以下本発明の二次電池の製法の代表例を説明する。なおこの例は、少なくとも正極層の出発原料が粉末の場合である。前述のように、本発明の二次電池は、例えば、遷移金属元素を含む正極層が、室温以上２５０℃以下の温度条件下、７５０〜２０００ＭＰａの圧力にて加圧成型される工程１、固体電解質層が、正極上に形成される工程２、および同固体電解質層上にリチウムを含む負極層が形成される工程３とを含む方法で得られる。なおこの場合、工程２では、固体電解質層が、工程１と同じ温度および加圧条件の下で正極層上に加圧成型されても良く、正極層と固体電解質層の双方が、同時に成型一体化されても良い。また固体電解質層が、正極上に気相合成法によって形成されても良い。さらに工程３では負極層が固体電解質層の上に圧着または気相合成法で形成されても良いし、正極層、固体電解質層とともに負極層の原料を同時に、または段階的に積層して圧力を調整した粉末成型によって形成されても良い。 Hereinafter, representative examples of the method for producing the secondary battery of the present invention will be described. In this example, at least the starting material of the positive electrode layer is a powder. As described above, the secondary battery of the present invention includes, for example, step 1 in which a positive electrode layer containing a transition metal element is pressure-molded at a pressure of 750 to 2000 MPa under a temperature condition of room temperature to 250 ° C. The electrolyte layer is obtained by a method including Step 2 in which the positive electrode layer is formed on the positive electrode and Step 3 in which a negative electrode layer containing lithium is formed on the solid electrolyte layer. In this case, in step 2, the solid electrolyte layer may be pressure-molded on the positive electrode layer under the same temperature and pressure conditions as in step 1, and both the positive electrode layer and the solid electrolyte layer are molded integrally at the same time. It may be made. The solid electrolyte layer may be formed on the positive electrode by a vapor phase synthesis method. Further, in step 3, the negative electrode layer may be formed on the solid electrolyte layer by pressure bonding or vapor phase synthesis, or the negative electrode layer raw material may be laminated simultaneously or stepwise together with the positive electrode layer and the solid electrolyte layer to increase the pressure. It may be formed by adjusted powder molding.
工程１で用いる正極層の原料粉末は、元素周期律表の遷移金属元素を含むものであれば良いが、通常は、固体電解質、導電助剤、および活物質の混合物である。例えば、前述のようにコバルト酸リチウム（化学式ＬｉＣｏＯ２）系やスピネル型結晶構造のマンガン酸リチウム（化学式ＬｉＭｎ２Ｏ４）系のリチウムの複合酸化物などが挙げられる。この場合の固体電解質粉末には、例えば、（１）高温で溶融させた後室温付近まで急冷された（ｍｅｌｔ−ｑｕｅｎｃｈ、メルトクエンチまたは急冷法）ガラス状の粉末、（２）メカニカルミリング（ｍｅｃｈａｎｉｃａｌ ｍｉｌｌｉｎｇ）されたガラス状の粉末、（３）これらのガラス状粉末が熱処理されて全体または一部が再結晶化した粉末（以下再結晶粉末と言う）、さらには（４）以上の形態の粉末の混合物および（５）以上の形態の粉末の複合化物などが、挙げられる。これらの固体電解質粉末のリチウムイオン伝導率は、１×１０−４Ｓ／ｃｍ以上が望ましく、１×１０−３Ｓ／ｃｍ以上がより望ましい。添加される導電助剤には、ケッチェンブラック、アセチレンブラック、気相成長法で作られた炭素繊維、黒鉛などの炭素材料、およびニッケル（Ｎｉ）、銅（Ｃｕ）、ステンレススチール（ＳＵＳ）などの金属粉末がある。 The raw material powder for the positive electrode layer used in step 1 may be any material that contains a transition metal element in the periodic table of elements, but is usually a mixture of a solid electrolyte, a conductive additive, and an active material. For example, as described above, lithium cobalt oxide (chemical formula LiCoO 2 ) -based or spinel-type lithium manganate (chemical formula LiMn 2 O 4 ) -based lithium complex oxide may be used. Examples of the solid electrolyte powder in this case include (1) glassy powder that has been melted at high temperature and then rapidly cooled to near room temperature (melt-quench, melt quench or quenching method), and (2) mechanical milling. ) Glass-like powders, (3) powders obtained by heat-treating these glass-like powders in whole or in part (hereinafter referred to as re-crystallized powders), and (4) powders of the above form Examples thereof include a mixture and a composite of (5) the above-mentioned powder. The lithium ion conductivity of these solid electrolyte powders is preferably 1 × 10 −4 S / cm or more, and more preferably 1 × 10 −3 S / cm or more. Examples of conductive additives to be added include ketjen black, acetylene black, carbon fibers made by vapor deposition, carbon materials such as graphite, nickel (Ni), copper (Cu), stainless steel (SUS), etc. There are metal powders.
正極層の活物質粒子の表面に、酸化物層がコーティングされても良い。酸化物層はリチウムイオン伝導特性を有している事が必要となる。イオウ（Ｓ）を含有する固体電解質は、ＬｉＣｏＯ２等の酸化物系正極活物質と反応しやすく、混合の仕方によっては、界面にＬｉイオン伝導特性に乏しい反応層を形成する事がある。特に、加熱した場合には、Ｓ含有固体電解質と酸化物系正極活物質との反応はより促進される。リチウムイオン伝導性酸化物層を正極活物質粒子上の一部に形成する事により、Ｓ含有固体電解質との界面に形成する反応層の生成を抑制する事ができる。 An oxide layer may be coated on the surface of the active material particles of the positive electrode layer. The oxide layer needs to have lithium ion conductivity. The solid electrolyte containing sulfur (S) easily reacts with an oxide-based positive electrode active material such as LiCoO 2 , and depending on the way of mixing, a reaction layer having poor Li ion conductivity may be formed at the interface. In particular, when heated, the reaction between the S-containing solid electrolyte and the oxide-based positive electrode active material is further promoted. By forming the lithium ion conductive oxide layer on a part of the positive electrode active material particles, generation of a reaction layer formed at the interface with the S-containing solid electrolyte can be suppressed.
リチウムイオン伝導性酸化物層の厚みは１ｎｍ（ナノメーター）以上あれば良い。また、厚みの上限は、そのリチウムイオン伝導性酸化物層のイオン伝導度により影響されるが、１００ｎｍ以下である必要がある。１００ｎｍを超える場合には、リチウムイオン伝導性酸化物層のイオン伝導特性の影響を受けて、抵抗値は上昇して高抵抗化する。 The thickness of the lithium ion conductive oxide layer may be 1 nm (nanometer) or more. Moreover, although the upper limit of thickness is influenced by the ionic conductivity of the lithium ion conductive oxide layer, it needs to be 100 nm or less. When the thickness exceeds 100 nm, the resistance value increases and the resistance is increased under the influence of the ion conduction characteristics of the lithium ion conductive oxide layer.
正極活物質粒子上の被覆率は、全表面積の１０％以上、９０％以下であることが望ましい。１０％未満では被覆効果は限定的となり、９０％を超える場合には集電がとれなくなり、電池特性が低下する。 The coverage on the positive electrode active material particles is desirably 10% or more and 90% or less of the total surface area. If it is less than 10%, the covering effect is limited, and if it exceeds 90%, current cannot be collected and the battery characteristics deteriorate.
リチウムイオン伝導性酸化物の材質としては、Ｌｉ２Ｏ−ＳｉＯ２、Ｌｉ２Ｏ−Ｂ２Ｏ３、Ｌｉ２Ｏ−Ｐ２Ｏ５、Ｌｉ２Ｏ−ＴｉＯ２、Ｌｉ２Ｏ−Ｎｂ２Ｏ５、Ｌｉ２Ｏ−Ａｌ２Ｏ３、Ｌｉ２Ｏ−Ｇａ２Ｏ３、Ｌｉ２Ｏ−Ｂｉ２Ｏ３、Ｌｉ２Ｏ−Ｌａ２Ｏ３の非晶質化合物、及びこれらの複合化合物が上げられる。形成方法は、ゾルゲル法、水溶液法等の湿式法、及びスパッタ法、ＭＯＣＶＤ法等の気相法がある。 As a material of the lithium ion conductive oxide, Li 2 O—SiO 2 , Li 2 O—B 2 O 3 , Li 2 O—P 2 O 5 , Li 2 O—TiO 2 , Li 2 O—Nb 2 O 5 , an amorphous compound of Li 2 O—Al 2 O 3 , Li 2 O—Ga 2 O 3 , Li 2 O—Bi 2 O 3 , Li 2 O—La 2 O 3 , and a composite compound thereof It is done. As a forming method, there are a wet method such as a sol-gel method and an aqueous solution method, and a vapor phase method such as a sputtering method and an MOCVD method.
正極層は、例えば、上記のような手段で得られた各原料粉末をボールミルなどにより十分混合された後、加圧成型することにより作られる。なお混合後の粉末は、成型までの取り扱いをし易くするため、さらには成型時の圧縮性を高めるため、その嵩（単位質量当たりの充填体積）は、小さくしておくのが望ましい。このため混合後に造粒などが行われても良い。ただし、その場合、純度の確保など、電池要素の素材としての機能を損なわない範囲内で適正な手段を採るのが望ましい。 The positive electrode layer is produced, for example, by mixing each raw material powder obtained by the above means with a ball mill or the like and then performing pressure molding. In addition, in order to make the powder after mixing easy to handle until molding, and further to improve the compressibility at the time of molding, it is desirable to reduce the volume (filling volume per unit mass). For this reason, granulation etc. may be performed after mixing. However, in that case, it is desirable to take appropriate measures within a range that does not impair the function of the battery element, such as ensuring purity.
工程１の加圧成型は、室温以上２５０℃以下の温度条件下、７５０〜２０００ＭＰａの範囲の圧力で行う。なお加熱および加圧の手段は、９５％以上の理論密度比が確保できるとともに、正極層の実用機能に悪影響を及ぼさない範囲であれば、如何なる手段であっても良い。例えば、加圧手段が通常の型内粉末成形法であれば、型に適当な面状ヒータなどの熱源を介在させるか、または加温された区域内で行うなど、様々な実施形態の適用が可能である。加圧時の温度を室温以上２５０℃以下にするのは、室温（２０℃）未満では固体電解質の塑性変形が不十分であり、２５０℃を越えると固体電解質の変質もしくは結晶性の変化が起き、イオン伝導特性が低下する場合があるからである。成型によって原料中の各構成成分の粉末の粒子、特に固体電解質粉末の粒子が十分塑性変形するため、加圧解除後も粒子同士の密着した状態が維持される。圧力は、７５０〜２０００ＭＰａの範囲にする。望ましくは９００ＭＰａ以上である。７５０ＭＰａ未満では加圧解除後に粒子同士の密着状態が維持されず、９５％以上の理論密度比のものが安定して得られない。一方素材によっては、各電池要素間の接触界面を増加させる視点で圧力に上限の無い場合もあるが、通常２０００ＭＰａを超えると、圧力上昇による嵩密度の上昇効果が小さくなることや成型容器の材質が高価になるとともに耐用寿命が短くなることから、実用的ではない。 The pressure molding in step 1 is performed at a pressure in the range of 750 to 2000 MPa under a temperature condition of room temperature to 250 ° C. The heating and pressurizing means may be any means as long as the theoretical density ratio of 95% or more can be secured and the practical function of the positive electrode layer is not adversely affected. For example, if the pressurizing means is a normal in-mold powder molding method, various embodiments can be applied, such as by interposing a heat source such as a sheet heater suitable for the mold or in a heated area. Is possible. The reason why the temperature at the time of pressurization is room temperature or higher and 250 ° C. or lower is that the plastic deformation of the solid electrolyte is insufficient if it is lower than room temperature (20 ° C.), and if it exceeds 250 ° C., the solid electrolyte is altered or the crystallinity is changed. This is because the ion conduction characteristics may be deteriorated. Since the powder particles of each constituent component in the raw material, particularly the solid electrolyte powder particles, are sufficiently plastically deformed by molding, the state in which the particles are in close contact with each other is maintained even after the pressure is released. The pressure is in the range of 750 to 2000 MPa. Desirably, it is 900 MPa or more. When the pressure is less than 750 MPa, the adhesion state between the particles is not maintained after the pressure is released, and a particle having a theoretical density ratio of 95% or more cannot be stably obtained. On the other hand, depending on the material, there may be no upper limit to the pressure from the viewpoint of increasing the contact interface between the battery elements. However, when the pressure exceeds 2000 MPa, the effect of increasing the bulk density due to the pressure increase is reduced, and the material of the molded container Is not practical because it is expensive and has a short useful life.
工程２で用いる固体電解質層の原料粉末は、例えば、前述の工程１の説明で触れたような（１）ないし（５）の手段で調製された各種の化学組成ものが用いられる。なお成型後の固体電解質層のリチウムイオン伝導率は、少なくとも１×１０−４Ｓ／ｃｍは必要である。またその電子伝導率は、１×１０−９Ｓ／ｃｍ以下が望ましい。電子伝導率がこれ以上になると、正負両極間にリーク電流が発生し、両極間が短絡し易くなるからである。以上のことを適宜配慮しつつ、作製しようとする電池の仕様によって、原料粉末の種類やその調製手段などを選ぶ必要がある。このような視点と本発明の前記した課題を考慮すれば、例えば、リチウム（Ｌｉ）、燐（Ｐ）、硫黄（Ｓ）を含むものが望ましい。さらにはＬｉ金属を主成分とする負極層に対し化学的な安定性を確保するため、これらの成分に加え、例えば、酸素（Ｏ）を含むものがより望ましい。なお複数の素材成分の混合物（複合素材）を用いる場合は、上述の正極層に用いる粉末の説明で触れたような手段で混合する。また粒子の形状、大きさとその分布の調整、成型時の粉末の流れを良くするための顆粒化や嵩の調整などが必要であれば行う。 As the raw material powder for the solid electrolyte layer used in Step 2, for example, various chemical compositions prepared by the means (1) to (5) as mentioned in the description of Step 1 above are used. The lithium ion conductivity of the solid electrolyte layer after molding needs to be at least 1 × 10 −4 S / cm. The electronic conductivity is preferably 1 × 10 −9 S / cm or less. This is because if the electron conductivity exceeds this value, a leakage current is generated between the positive and negative electrodes, and the electrodes are easily short-circuited. While taking the above into consideration, it is necessary to select the type of raw material powder, its preparation means, etc. according to the specifications of the battery to be manufactured. In view of such a viewpoint and the above-described problem of the present invention, for example, those containing lithium (Li), phosphorus (P), and sulfur (S) are desirable. Furthermore, in order to ensure chemical stability with respect to the negative electrode layer mainly composed of Li metal, it is more desirable to include, for example, oxygen (O) in addition to these components. In addition, when using the mixture (composite material) of a several raw material component, it mixes by the means as mentioned in the description of the powder used for the above-mentioned positive electrode layer. If necessary, adjustment of the shape, size and distribution of the particles, granulation to improve the flow of the powder during molding, and adjustment of the bulk are performed.
以上のようにして調製された原料粉末を用いて加圧成型された正極層の上に、固体電解質の原料粉末を充填して加圧成型する。成型の温度ならびに加圧条件の選定については、既に工程１の説明で述べた内容に準ずる。なお固体電解質層は、成型された正極層の上に気相合成法によって形成されても良い。気相合成法としては、蒸着法、イオンプレーティング法、スパッタ法、レーザアブレーション法などがある。 The solid electrolyte raw material powder is filled on the positive electrode layer pressure-molded using the raw material powder prepared as described above, and pressure-molded. The selection of the molding temperature and the pressurizing condition conforms to the contents already described in the description of the step 1. The solid electrolyte layer may be formed on the molded positive electrode layer by a gas phase synthesis method. Examples of the vapor phase synthesis method include a vapor deposition method, an ion plating method, a sputtering method, and a laser ablation method.
工程３では、以上の手段で得られた固体電解質層の上に負極層を形成する。負極層の素材には、通常Ｌｉ金属を主成分とする合金が使われる。これらの合金は、柔らかいため、固体電解質層との高い密着性が確保されるとともに、さらに充放電時に固体電解質層との境で負極層の面方向の膨張や収縮が殆ど無い。このため、安定した界面が形成される。負極層の形態は、圧延された箔、蒸着された層などいくつかの選択肢がある。形成手段は、その所望の形態に応じて選ぶ。例えば、箔状であれば固体電解質層の上に圧着しても良い。また例えば、Ａｌ、Ｓｒ、Ｍｇ、Ｃａを含む金属箔の圧着された層または蒸着された層が、固体電解質層の上に予め形成されておれば、電池充電時のＬｉが供給された時に、これらの成分と自動的に合金化させる手段も採れる。なお負極層の厚みは、充放電時のその厚み方向の膨張や収縮で集電できなくなることさえ回避できれば、限定されない。 In step 3, a negative electrode layer is formed on the solid electrolyte layer obtained by the above means. For the material of the negative electrode layer, an alloy mainly containing Li metal is usually used. Since these alloys are soft, high adhesion to the solid electrolyte layer is ensured, and further, there is almost no expansion or contraction in the surface direction of the negative electrode layer at the boundary with the solid electrolyte layer during charge / discharge. For this reason, a stable interface is formed. There are several options for the form of the negative electrode layer, such as a rolled foil and a deposited layer. The forming means is selected according to the desired form. For example, if it is foil-like, it may be pressure-bonded on the solid electrolyte layer. Also, for example, if a pressure-bonded layer or a vapor-deposited layer of metal foil containing Al, Sr, Mg, Ca is formed in advance on the solid electrolyte layer, when Li is supplied during battery charging, A means for automatically alloying with these components can also be adopted. The thickness of the negative electrode layer is not limited as long as it can be prevented that current can no longer be collected due to expansion or contraction in the thickness direction during charge / discharge.
なお正極層、固体電解質層および負極層の三層を積層成型する場合、工程１において、正極層と固体電解質層の原料粉末を積層充填するか、負極層の原料となる素材をさらにその上に載せた状態で、同時に加圧成型して一体化する手段を採っても良い。 In addition, when three layers of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer are formed by lamination, in Step 1, the raw material powder of the positive electrode layer and the solid electrolyte layer is stacked and filled, or a material that is a raw material of the negative electrode layer is further formed thereon It is also possible to adopt a means for simultaneously pressing and integrating in the mounted state.
以上本発明の二次電池の製造方法の一例を説明してきた。この例は、少なくとも正極層が、粉末成型で形成される場合であるが、正極層の厚みが十分取れ、正極層と固体電解質層の理論密度比が９５％以上となる手段であれば、以上述べた手段にこだわること無く如何なる手段でも構わない。例えば、原料は塊状であっても良く、これと粉末との複合材料であっても良い。また例えば、成型手段は、静水圧成形、圧延など、所望の実用機能を満たせる手段であれば良い。以下実施例により本発明を説明するが、本発明は、これに制約されない。 In the above, an example of the manufacturing method of the secondary battery of this invention has been demonstrated. This example is a case where at least the positive electrode layer is formed by powder molding, but if the thickness of the positive electrode layer is sufficient and the theoretical density ratio between the positive electrode layer and the solid electrolyte layer is 95% or more, Any means can be used without sticking to the means described. For example, the raw material may be a lump or a composite material of this and a powder. For example, the molding means may be any means that can satisfy a desired practical function such as isostatic pressing or rolling. Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.
表１に記載の正極（電池要素１）ならびに固体電解質（電池要素２）の材質からなるＡないしＧの各種組み合わせの素材を用い、同表に記載の各種条件にて両電池要素が積層された複合体を成型し、得られた各成型体試料の固体電解質層の上に、蒸着法にてＡｌを５原子％含み厚みが１μmのＬｉ合金膜を形成した。次いでこの電池要素複合体の試料をコイン型電池用の容器に組み込み、かしめて電池試料にした。これらの電池試料を４．２Ｖで充電した後、放電電圧３Ｖにて電流値を０．３８ｍＡ（電流密度でほぼ３ｍＡ／ｃｍ２に相当）ないし１ｍＡ（電流密度でほぼ７．９ｍＡ／ｃｍ２に相当）の間で振って電池の放電特性を評価し、特に代表的な電流値０．７６ｍＡ（電流密度でほぼ６ｍＡ／ｃｍ２に相当）の時の容量維持率（理論的に算出された放電容量に対する同実測値の比率）を確認した。その結果を表１に示す。 Both battery elements were laminated under various conditions described in the table using materials of various combinations of A to G made of materials of the positive electrode (battery element 1) and the solid electrolyte (battery element 2) described in Table 1. The composite was molded, and an Li alloy film containing 5 atomic% of Al and having a thickness of 1 μm was formed on the solid electrolyte layer of each obtained molded body sample by vapor deposition. Next, the battery element composite sample was assembled into a coin-type battery container and caulked into a battery sample. After charging these battery samples at 4.2 V, the discharge by the voltage 3V current value 0.38mA in to 1 mA (current density no (equivalent to approximately 3mA / cm 2 in current density) approximately 7.9mA / cm 2 The discharge characteristics of the battery were evaluated by shaking the power supply capacity, and the capacity retention ratio (theoretical calculated discharge) at a typical current value of 0.76 mA (corresponding to a current density of approximately 6 mA / cm 2 ). The ratio of the measured value to the capacity) was confirmed. The results are shown in Table 1.
表１の横軸を以下説明する。「正極層」の欄の材質は、用意した正極活物質と固体電解質を変えたＡないしＣの３種類の組み合わせを示す。それぞれの組み合わせ内容は、表２の通りである。成型条件は、これらの混合物を型に充填して加圧した際の温度ならびに圧力である。また理論密度比は、得られた正極成型体の質量および体積から前述の計算式で計算された値である。「固体電解質層」の欄の材質は、用意した固体電解質で、符号は種類を示す。ＤないしＧの組成や形態については表３に示す。なお表３のＦおよびＧの粉末の平均粒径は、フレーク状粒子の最大径の平均値である。成型条件と理論密度比の欄の表示ルールは、上記した正極の場合と同じである。「電池放電特性」の欄は、上述の電池評価の際の４．２Ｖで充電後の放電特性の評価結果であり、放電電圧が３Ｖで設定電流値が０．７６ｍＡの時の容量維持率を示す。 The horizontal axis of Table 1 will be described below. The material in the column of “positive electrode layer” indicates three combinations of A to C in which the prepared positive electrode active material and solid electrolyte are changed. The contents of each combination are as shown in Table 2. The molding conditions are the temperature and pressure when these mixtures are filled in a mold and pressed. The theoretical density ratio is a value calculated by the above formula from the mass and volume of the obtained molded positive electrode. The material in the column of “Solid electrolyte layer” is a prepared solid electrolyte, and the symbol indicates the type. Table 3 shows the composition and form of D to G. The average particle size of the F and G powders in Table 3 is the average value of the maximum diameters of the flaky particles. The display rules in the columns of molding conditions and theoretical density ratio are the same as in the case of the positive electrode described above. The “Battery Discharge Characteristics” column shows the evaluation results of the discharge characteristics after charging at 4.2 V in the battery evaluation described above, and the capacity maintenance rate when the discharge voltage is 3 V and the set current value is 0.76 mA. Show.
露点が−９０℃のＡｒガスが充填されているグローブボックス内で、表２に記載の組み合わせと量比にて各正極活物質、固体電解質およびアセチレンブラック粉末をアルミナ製遊星型ボールミルに入れて、それぞれ１時間攪拌混合した。その混合粉末を加熱源を組み込んだ直径４ｍｍの超硬製の型に入れて、別途表３に記載の成分構成および製法で調製された各固体電解質原料との組み合わせによって、表１のように加圧条件を変え、油圧プレス機により表１に記載の厚みの成型体を、それぞれ３０個ずつ作製した。各層の型内への粉末の充填量は、予めそれぞれの成型条件に合わせ確認し、表に記載された厚みになるように調整した。なお個々の理論密度比（％）については、５個の試片を抜き取り、それぞれの成型体の質量と体積を確認し、各素材構成から試算した理論密度を使って算定した。表１の値は、その算術平均値である。さらにこの固体電解質層の上に、上述のように負極層を蒸着して電池要素１ないし３からなる電池複合体の試料を作製した。次いで各複合体試料を、電池ケースに組み入れてかしめ、コイン型電池試料とした。なお蒸着による層の形成手順は、以下の通りである。先ず試料４の正極層はスパッタリング法によって、同試料の固体電解質層は蒸着法によって、さらに試料２６ないし２８の固体電解質層は蒸着法によって、それぞれ形成した。 In a glove box filled with Ar gas having a dew point of −90 ° C., put each positive electrode active material, solid electrolyte and acetylene black powder in a planetary ball mill made of alumina in the combinations and quantitative ratios shown in Table 2, Each was stirred and mixed for 1 hour. The mixed powder is put into a 4 mm diameter cemented carbide mold in which a heating source is incorporated, and added as shown in Table 1 in combination with each of the solid electrolyte raw materials separately prepared by the component constitution and manufacturing method shown in Table 3. The pressure conditions were changed, and 30 molded bodies each having the thickness shown in Table 1 were produced using a hydraulic press. The filling amount of the powder into the mold of each layer was confirmed in advance according to each molding condition, and adjusted to the thickness described in the table. In addition, about each theoretical density ratio (%), five test pieces were extracted, the mass and volume of each molded object were confirmed, and it calculated using the theoretical density calculated from each raw material structure. The values in Table 1 are the arithmetic average values. Further, a negative electrode layer was vapor-deposited on the solid electrolyte layer as described above to prepare a battery composite sample comprising battery elements 1 to 3. Next, each composite sample was assembled into a battery case and caulked to obtain a coin-type battery sample. In addition, the formation procedure of the layer by vapor deposition is as follows. First, the positive electrode layer of Sample 4 was formed by sputtering, the solid electrolyte layer of the same sample was formed by vapor deposition, and the solid electrolyte layers of Samples 26 to 28 were formed by vapor deposition.
作製したコイン型電池試料は、４．２Ｖで充電した後、放電電圧３Ｖにて電流値が０．７６ｍＡｈの場合の容量維持率を確認した。なお試料１と同じ正極層と固体電解質層からなる成型体の上に箔状の金属からなる同じ化学組成の負極層を載せて成型した場合にも、試料１と同じ特性レベルの二次電池の得られることが分かった。また表１には記載しないが、試料番号１５の電池試料では、４．２Ｖで充電後、放電電圧３Ｖ、電流値０．３８ｍＡで放電させたところ、放電容量は０．３５ｍＡであり、理論的に算出された放電容量（理論値）０．３６ｍＡの９７％であった。 The produced coin-type battery sample was charged at 4.2 V, and then the capacity retention rate was confirmed when the current value was 0.76 mAh at a discharge voltage of 3 V. Even when a negative electrode layer having the same chemical composition made of a foil-like metal is placed on a molded body made of the same positive electrode layer and solid electrolyte layer as that of Sample 1, the secondary battery having the same characteristic level as Sample 1 is formed. It turns out that it is obtained. Although not shown in Table 1, the battery sample of Sample No. 15 was charged at 4.2 V and then discharged at a discharge voltage of 3 V and a current value of 0.38 mA. The discharge capacity was 0.35 mA, which is theoretical. It was 97% of the discharge capacity (theoretical value) calculated to 0.36 mA.
なお固体電解質層の化学組成にて、燐（Ｐ）に代えて硼素（Ｂ）、硫黄（Ｓ）の一部を酸素（Ｏ）や窒素（Ｎ）で置き換えた素材を使った場合にも、本発明の手段にて正極層と固体電解質層をより一層緻密にかつより一層密着一体化させることによって、より一層高い電流密度と放電容量維持率のリチウム二次電池の得られることが分かった。 In the case of using a material in which a part of boron (B) and sulfur (S) is replaced with oxygen (O) or nitrogen (N) instead of phosphorus (P) in the chemical composition of the solid electrolyte layer, It has been found that a lithium secondary battery having a higher current density and discharge capacity retention rate can be obtained by integrating the positive electrode layer and the solid electrolyte layer more densely and more closely by the means of the present invention.
正極活物質の表面にリチウムイオン伝導性酸化物層を形成した。正極活物質にはＬｉＣｏＯ２を使用し、リチウムイオン伝導性酸化物層としては、Ｌｉ２Ｏ−ＳｉＯ２系非晶質を使用した。リチウムイオン伝導性酸化物は次のようにして形成した。Ｌｉ金属をエタノール中に溶解させた液中に、テトラエチルオルソシリケート液を混合してコーティング液を作製した。このコーティング液中にＬｉＣｏＯ２粉末を浸漬、混合後、溶媒のエタノールを蒸発させて除去し、さらに４００℃にて加熱処理して、ＬｉＣｏＯ２粒子表面にＬｉ２Ｏ−ＳｉＯ２系非晶質膜を形成した。形成された非晶質膜の膜厚は重量増加量より１０ｎｍであった。 A lithium ion conductive oxide layer was formed on the surface of the positive electrode active material. LiCoO 2 was used as the positive electrode active material, and Li 2 O—SiO 2 -based amorphous was used as the lithium ion conductive oxide layer. The lithium ion conductive oxide was formed as follows. A coating solution was prepared by mixing a tetraethylorthosilicate solution in a solution in which Li metal was dissolved in ethanol. After immersing and mixing LiCoO 2 powder in this coating solution, the solvent ethanol is removed by evaporation, and heat treatment is performed at 400 ° C. to form a Li 2 O—SiO 2 amorphous film on the surface of LiCoO 2 particles. Formed. The film thickness of the formed amorphous film was 10 nm from the increase in weight.
Ｌｉ２Ｏ−ＳｉＯ２系非晶質膜を形成したＬｉＣｏＯ２活物質を使用して、活物質重量７０重量％、硫化物系固体電解質重量３０重量％の混合比で混合し、正極活物質層を形成した。その他は実施例１と同様の方法にて全固体電池を作製した。 Using a LiCoO 2 active material in which a Li 2 O—SiO 2 amorphous film is formed, mixing is performed at a mixing ratio of 70% by weight of active material and 30% by weight of sulfide solid electrolyte, and a positive electrode active material layer Formed. Other than that, an all-solid battery was produced in the same manner as in Example 1.
その電池性能は、電流密度をさらに２倍の１．５ｍＡにしてもほぼ同程度の充放電容量が確保された。 Regarding the battery performance, even when the current density was further doubled to 1.5 mA, approximately the same charge / discharge capacity was secured.
本発明の固体電解質層を含むリチウム二次電池は、優れた充放電特性と有機電解液を含有しているリチウムイオン二次電池に匹敵する電流密度とを有する。このため、本発明によって固体電解質層を含む従来のもの以上に有用なリチウム二次電池の提供が可能になる。 The lithium secondary battery including the solid electrolyte layer of the present invention has excellent charge / discharge characteristics and a current density comparable to a lithium ion secondary battery containing an organic electrolyte. For this reason, according to the present invention, it is possible to provide a lithium secondary battery more useful than the conventional one including the solid electrolyte layer.
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