JP4763169B2

JP4763169B2 - Method for producing metallic lithium

Info

Publication number: JP4763169B2
Application number: JP2001237841A
Authority: JP
Inventors: 佳治高田
Original assignee: Santoku Corp
Current assignee: Santoku Corp
Priority date: 2001-08-06
Filing date: 2001-08-06
Publication date: 2011-08-31
Anticipated expiration: 2021-08-06
Also published as: JP2003049291A

Description

【０００１】
【発明の属する技術分野】
本発明は、塩素ガスの発生の要因となる塩化リチウムを使用せずに、金属リチウムの単体を高純度で製造することができる炭酸リチウムを用いた金属リチウムの製造方法に関する。
【０００２】
【従来の技術】
従来から、金属リチウムの製造方法として、溶融塩電解法が知られている。この方法は、リチウム原料に塩化リチウムを用い、更に浴の融点を下げるために塩化カリウムを加えた電解浴を、黒鉛陽極及び鉄陰極を用いて電解し、鉄陰極上に金属リチウムを析出させる方法である。しかし、このような塩化物を用いた電解法では、いくつかの実用上の問題がある。
このような実用上の問題としては、例えば、電解原料である塩化リチウムが強い潮解性を示すので、その保管、移送、取り扱いの際に完全に湿分を遮断する必要があり、このような作業が煩雑であり、加えてコストが非常に高くつくという問題、陽極より有毒な塩素ガスが発生するため、この塩素を回収し、無害化処理を行う設備の導入が必要であり、また塩素ガスは、鉄、ステンレス等の一般に用いる耐熱鋼に対し、腐食性を有するため、その設備部材として高価な特殊部材が必要であって、塩素ガスの無害化処理等に多大な費用を要するという問題、更に、溶融塩電解浴に使用している塩化リチウム及び塩化カリウムの理論分解電圧の差が０．１Ｖ程度しかなく、電圧制御が難しく、陰極に生成する金属リチウムへのカリウム混入が生じ易いなど、高純度の金属リチウムの製造が困難であるという問題が主に挙げられる。
【０００３】
そこで、このような塩化リチウムを用いた溶融塩電解法の問題点を解決するために、以下の炭酸リチウムを用いた溶融塩電解法が提案されている。
特開平5−279886号公報には、電解浴として塩化リチウムを用い、アノード室に炭酸リチウムを投入し、炭素電極と酸化反応させて炭酸ガスとリチウムイオンとを生成させ、そのリチウムイオンをカソード室に移動させ、そのカソード室内で還元、貯留した溶融アルミニウムと合金化してリチウムを回収する方法が開示されている。
また、特開平3−140492号公報には、組成が炭酸リチウム５９〜７２重量％、フッ化リチウム９〜１３重量％、フッ化カリウム１９〜２８重量％、フッ化ナトリウム1〜１０重量％の電解浴を用い、陰極にアルミニウム、陽極に炭素の消耗電極を用い、Al−Li合金を製造する方法が提案されている。
上記特開平5−279886号公報に記載の方法では、電解浴として塩化リチウムを用いるが、電解原料として炭酸リチウムを用いているので、塩素の発生を極力抑えることができる。しかし、塩素の発生を完全に無くすことはできず、上記問題解決が充分であるとは言えない。また上記それぞれの方法では、いずれも電解原料として炭酸リチウムを用いて、Al−Li合金を製造することはできるが、活性な金属である金属リチウム単体を高純度で製造することが充分であるとは言えない。
【０００４】
【発明が解決しようとしている課題】
従って、本発明の目的は、塩素ガスの発生を全く伴なわずに、活性な金属である金属リチウム単体を高純度で容易に製造することができる金属リチウムの製造方法を提供することにある。
【０００５】
【課題を解決するための手段】
すなわち本発明によれば、陰極電解室及び陽極電解室を有する浴用隔壁により区画された電解室と、各電解室に設けた陽極及び陰極とを備え、前記浴用隔壁の少なくとも一部が通電及びリチウムイオンの移動を可能にする多孔質材料で形成された電解装置を用意し、実質的に炭酸リチウム及びフッ化物からのみなり、該炭酸リチウムの含有割合が０．１〜３０質量％である陽極電解浴と、実質的にフッ化物からのみなる陰極電解浴とを前記電解装置のそれぞれの電解室に入れ、陰極電流密度２〜５００Ａ／ｃｍ²、電解温度６００〜１０００℃の電解条件で電解還元することを特徴とする金属リチウムの製造方法が提供される。
【０００６】
【発明の実施の形態】
以下本発明を更に詳細に説明する。
本発明の製造方法では、まず、陰極電解室及び陽極電解室を有する浴用隔壁により区画された電解室と、各電解室に設けた陽極及び陰極とを備える電解装置を用意する。この電解装置について図１を参照して以下に詳細に説明するが、本発明に用いる電解装置はこれに限定されない。
【０００７】
図１は、本発明に用いる電解装置の一実施態様を示す電解装置１０の概略図である。電解装置１０は、浴用隔壁１２により区画された陽極電解室１１ａ及び陰極電解室１１ｂを有する電解室１１と、各電解室(１１ａ、１１ｂ)に設けられた陽極１３及び陰極１４を備える。なお、図中において、陽極電解室１１ａは後述する陽極電解浴を、並びに陰極電解室１１ｂは後述する陰極電解浴を入れた状態(灰色部分)を表す。また、電解室１１は、電解炉外筒１５によって包囲されている。
【０００８】
浴用隔壁１２は、陽極電解浴と陰極電解浴とが接触し、電解により陰極に生成する金属リチウムに炭酸リチウムが接触して酸化するのを防止するため等に作用する。後述する電解原料としての炭酸リチウムは、溶融金属に対して強い酸化力を示すため、金属リチウムが生成する陰極電解浴に存在すると、金属リチウムが陰極で生成すると同時に酸化され、電解効率を著しく減少させる。この反応を抑止するためには、炭酸リチウムを陽極近辺に隔離する必要があるため、陰極電解浴と陽極電解浴とを浴用隔壁１２により区画する必要がある。
この浴用隔壁１２は、通電及びリチウムイオンの移動を可能にする多孔質材料で少なくともその一部が構成される必要があり、上記作用を得るために、当然ながら炭酸リチウムの移動を抑制する必要がある。このような多孔質材料としては、好ましくはZrO₂製、Al₂O₃製の多孔質材料等が挙げられ、特に、浴用隔壁が全てこのような多孔質材料で形成されていることが望ましい。
前記多孔質材料の空孔率は、上記作用を示すように１〜５０％の範囲、特に５〜４０％が好ましい。前記空孔率が５０％を超えると、陽極電解室１１ａから陰極電解室１１ｂへ炭酸リチウムの移動が生じ、電解効率が低下する恐れがあるので好ましくない。一方、前記空孔率が１％未満では直流電流の通電が困難になるので好ましくない。
【０００９】
前記陽極１３は、消耗電極であるので、浴に溶け出す傾向にあり、溶け出した陽極材料は金属リチウムと合金を生成する恐れが生じる。このため、目的とする金属リチウムの収率を高くするために陽極１３には炭素を用いることが好ましい。炭素を用いることにより、消耗した炭素が二酸化炭素ガスとなり雰囲気中へと抜け、生成した金属リチウムとの反応を抑制することができる。
一方、前記陰極１４は、金属リチウムを高収率で得るために、金属リチウムとの反応性がほとんどない鉄の使用が好ましく、特に、純鉄の使用が望ましい。
陰極１４の周りには、生成する金属リチウムを集積させるためのマグネシア筒１４ａ等を図示するように設けることができる。
【００１０】
本発明の製造方法では、上記電解室１１の陽極電解室１１ａに陽極電解浴を、陰極電解室１１ｂに陰極電解浴をそれぞれ入れる。
前記陽極電解浴は、実質的に炭酸リチウム及びフッ化物からのみなり、前記陰極電解浴は、実質的にフッ化物からのみなる。ここで、実質的にとは、不純物や本願発明の作用に影響を及ぼさない微量の他の成分を含んでいてもよい意であり、影響を及ぼす塩化リチウム等を全く含まない意である。
【００１１】
陽極電解浴に用いる炭酸リチウムは、電解原料として作用し、その含有割合は、陽極電解浴全量に対して０．１〜３０質量％、好ましくは０．５〜２５質量％、さらに好ましくは1〜１０質量％の範囲である。炭酸リチウムの含有割合が３０質量％を超えると、陽極電解浴から陰極電解浴への炭酸リチウムの移動が発生する恐れがあり、０．１質量％未満では、陽極効果が発生し易くなる。該炭酸リチウムは、電解の進行に合わせて、陽極電解浴に補給することができ、この補給により電解を連続的に行うことができる。
【００１２】
陽極電解浴及び陰極電解浴に用いるフッ化物としては、アルカリ金属元素、アルカリ土類金属元素等のフッ化物又はこれらの混合物等が挙げられる。これらフッ化物の大部分の理論分解電圧は、後述する電解温度において、炭酸リチウムの理論分解電圧約２Ｖ以下と大きく異なる５Ｖ以上であるので、後述する電解により炭酸リチウムのみを容易に電解することができる。
仮に、陰極電解浴や陽極電解浴に塩化リチウムが含有される場合、塩化リチウムの理論分解電圧は約３．５Ｖ以下であるので、炭酸リチウムだけでなく、一部塩化リチウムの電解も生じる可能性が高く、有毒ガスの塩素が発生する恐れがある。
このようなフッ化物としては、上記理論分解電圧を示すフッ化物であることが好ましく、特に、フッ化リチウム、フッ化カリウム及びフッ化ナトリウムからなる群より選択される１種又は２種以上を含むことが望ましい。
【００１３】
前記フッ化物として、電解浴の融点降下、電解効率の向上を得るために、フッ化バリウムを含有させることもできる。該フッ化物バリウムの含有割合は、各電解浴それぞれの全量に対して、通常０．１〜４０質量％、特に５〜３５質量％、更には５〜１５質量％が好ましい。
【００１４】
本発明の製造方法では、次いで、電解還元を行ない、所望の金属リチウムを製造する。
電解条件としては、陰極電流密度２〜５００Ａ/ｃｍ²、好ましくは２〜２０Ａ/ｃｍ²の範囲、電解温度６００〜１０００℃、好ましくは８００〜１０００℃、特に好ましくは８００〜９５０℃の範囲が挙げられる。
陰極電流密度が２Ａ/ｃｍ²未満では、金属リチウムの析出が生じない。また、５００Ａ/ｃｍ²を超えると陰極部での発熱量が多く、電解浴の温度管理が困難となる。
一方、電解温度が１０００℃を超える場合には、溶融塩電解浴の温度維持に多大なコストを要し、経済的でなく、６００℃未満では、電解浴が凝固し、直流電流の通電ができない。
【００１５】
本発明の製造方法においては、図１に示す電解室１１と、各電解浴の液上面とにより区切られた電解室１１内の上方部分の雰囲気を、乾燥アルゴン雰囲気等の乾燥不活性ガス雰囲気とすることが好ましい。このように雰囲気を制御することにより、電解時に陰極に生成した金属リチウムが、前記電解室１１内の上方部分の大気に含有される水分、窒素ガス、二酸化炭素ガス等、並びに電解時に陽極で発生した二酸化炭素ガス又は一酸化炭素ガスと接触し反応することを抑制することができ、電解効率を下げる要因を排除することができる。
このような雰囲気の制御は、上述の大気及び陽極で発生する二酸化炭素ガス、一酸化炭素ガスを置換するに十分な流量の乾燥不活性ガスを電解室１１内に流すことにより行なうことができる。
【００１６】
また、本発明の製造方法においては、図１に示す電解室１１と、各電解浴の液上面とにより区切られた電解室１１内の上方部分の雰囲気を、陽極室雰囲気及び陰極室雰囲気に区画する雰囲気区画用隔壁１６を図示するように電解室１１内に設けることができる。
前記雰囲気区画用隔壁１６を設けることにより、電解開始前に陰極室雰囲気及び陽極室雰囲気を上述の雰囲気制御のために乾燥不活性ガス雰囲気とすれば、電解中は、陰極室雰囲気のみを乾燥不活性ガス雰囲気に制御すれば上述のような効果を得ることができる。陽極では、二酸化炭素ガスや一酸化炭素ガスが発生し、陽極室雰囲気は二酸化炭素ガス、一酸化炭素ガス雰囲気となるが、これを乾燥不活性ガス雰囲気とするような制御は必要なく、単に大気が流入しないようにすればよい。一方、陰極室雰囲気の制御は、陰極からのガスの発生がほとんどないので、制御が容易であり経済的に行うことができる。
前記雰囲気区画用隔壁１６の材質は、電解浴との反応性がなく、二酸化炭素ガス及び一酸化炭素ガスを透過しないものが好ましい。例えば、鉄、ステンレス、緻密に焼結させたZrO₂、Al₂O₃等が挙げられる。
【００１７】
【実施例】
以下、実施例及び比較例により本発明を更に詳細に説明するが本発明はこれらに限定されるものではない。
実施例１
図１に示す電解装置を用意した。なお、電解室１１として鉄製の電解室を、陽極１３にカーボンを、陰極１４に鉄を用いた。また、浴用隔壁１２として空孔率４０％のZrO₂製のるつぼを、雰囲気区画用隔壁１６としては鉄製の隔壁を用いた。
陽極電解浴として、炭酸リチウム３質量％、フッ化リチウム８９質量％及びフッ化バリウム８質量％からなる電解浴を用い、陰極電解浴として、フッ化リチウム９２質量％及びフッ化バリウム８質量％からなる電解浴を用いた。
電解開始前に、隔壁１６により区画された陽極室雰囲気及び陰極室雰囲気の双方を乾燥アルゴン雰囲気とし、電解中は陰極室雰囲気のみを乾燥アルゴン雰囲気とし、電解温度９００℃、陰極電流密度３Ａ／ｃｍ²の電解条件で溶融塩電解を行った。その結果、有毒な塩素ガスの発生は無く、純度９９質量％の金属リチウムが収率９５％で得られた。電解浴の組成、電解条件、結果等を表１に示す。
【００１８】
実施例２〜５、比較例１〜８
表１に示す電解浴の組成及び電解条件とし、浴用隔壁１２の空孔率を表１に示すものに代えた以外は、実施例１と同様に電解を行ない、塩素ガスの発生、並びに純度９９質量％の金属リチウムの収率を測定した。結果を表１に示す。
【００１９】
実施例６
隔壁１６を用いなかった以外は、実施例１と同様に電解を行ない、塩素ガスの発生、並びに純度９９質量％の金属リチウムの収率を測定した。結果を表１に示す。
【００２０】
【表１】

【００２１】
【発明の効果】
本発明の製造方法では、陰極電解室及び陽極電解室を有する浴用隔壁により区画された電解室等を有する特定の電解装置を用意し、特定の陽極電解浴及び特定の陰極電解浴を電解室に入れ、特定電解条件で電解を行なうので、有毒な塩素ガスを発生させることなく、高純度の金属リチウムを得ることができる。
【図面の簡単な説明】
【図１】本発明に用いる電解装置の一実施態様を示す概略図である。
【符号の説明】
１０：電解装置
１１：電解室
１１ａ：陽極電解室
１１ｂ：陰極電解室
１２：浴用隔壁
１３：陽極
１４：陰極
１４ａ：マグネシア筒
１５：電解炉外筒
１６：雰囲気区画用隔壁[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing metallic lithium using lithium carbonate capable of producing a single metallic lithium with a high purity without using lithium chloride which causes generation of chlorine gas.
[0002]
[Prior art]
Conventionally, a molten salt electrolysis method is known as a method for producing metallic lithium. In this method, lithium chloride is used as a lithium raw material, and an electrolytic bath with potassium chloride added to lower the melting point of the bath is electrolyzed using a graphite anode and an iron cathode, and metallic lithium is deposited on the iron cathode. It is. However, there are some practical problems in the electrolytic method using such a chloride.
As such a practical problem, for example, since lithium chloride, which is an electrolytic raw material, exhibits strong deliquescence, it is necessary to completely block moisture during storage, transfer, and handling. In addition, there is a problem that the cost is very high, and toxic chlorine gas is generated from the anode. Therefore, it is necessary to introduce equipment for recovering this chlorine and detoxifying it. In addition, the heat-resistant steel generally used, such as iron and stainless steel, has a corrosive property, so that an expensive special member is necessary as its equipment member, and a problem that a great deal of cost is required for detoxification treatment of chlorine gas, etc. The difference in the theoretical decomposition voltage between lithium chloride and potassium chloride used in the molten salt electrolytic bath is only about 0.1 V, voltage control is difficult, and potassium contamination occurs in the lithium metal produced at the cathode. Inado, a problem that the production of high-purity metallic lithium is difficult and the like mainly.
[0003]
Therefore, in order to solve such problems of the molten salt electrolysis method using lithium chloride, the following molten salt electrolysis method using lithium carbonate has been proposed.
In JP-A-5-279886, lithium chloride is used as an electrolytic bath, lithium carbonate is introduced into an anode chamber, and an oxidation reaction is performed with a carbon electrode to generate carbon dioxide gas and lithium ions. A method of recovering lithium by alloying with molten aluminum reduced and stored in the cathode chamber is disclosed.
Japanese Patent Laid-Open No. 3-140492 discloses an electrolysis having a composition of 59 to 72% by weight of lithium carbonate, 9 to 13% by weight of lithium fluoride, 19 to 28% by weight of potassium fluoride, and 1 to 10% by weight of sodium fluoride. There has been proposed a method for producing an Al-Li alloy using a bath, using a consumable electrode of aluminum as a cathode and carbon as an anode.
In the method described in JP-A-5-279886, lithium chloride is used as an electrolytic bath. However, since lithium carbonate is used as an electrolytic raw material, generation of chlorine can be suppressed as much as possible. However, the generation of chlorine cannot be completely eliminated, and it cannot be said that the above problem is sufficiently solved. In each of the above methods, it is possible to produce an Al-Li alloy using lithium carbonate as an electrolytic raw material, but it is sufficient to produce a single metal lithium as an active metal with high purity. I can't say that.
[0004]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for producing metallic lithium, which can easily produce metallic lithium alone, which is an active metal, with high purity without generating any chlorine gas.
[0005]
[Means for Solving the Problems]
That is, according to the present invention, an electrolytic chamber partitioned by a bath partition having a cathode electrolysis chamber and an anode electrolysis chamber, and an anode and a cathode provided in each electrolysis chamber, and at least a part of the bath partition is energized and lithium Anode electrolysis comprising an electrolytic device formed of a porous material capable of ion migration, substantially consisting of lithium carbonate and fluoride, and a content ratio of the lithium carbonate being 0.1 to 30% by mass A bath and a cathode electrolytic bath substantially made of fluoride are placed in the respective electrolysis chambers of the electrolysis apparatus, and electrolytic reduction is performed under electrolysis conditions of a cathode current density of ^{2 to} 500 A / cm ² and an electrolysis temperature of 600 to 1000 ° C. A method for producing metallic lithium is provided.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
In the production method of the present invention, first, an electrolysis apparatus including an electrolysis chamber partitioned by a partition wall for a bath having a cathode electrolysis chamber and an anode electrolysis chamber, and an anode and a cathode provided in each electrolysis chamber is prepared. Although this electrolysis apparatus is demonstrated in detail below with reference to FIG. 1, the electrolysis apparatus used for this invention is not limited to this.
[0007]
FIG. 1 is a schematic view of an electrolysis apparatus 10 showing an embodiment of the electrolysis apparatus used in the present invention. The electrolysis apparatus 10 includes an electrolysis chamber 11 having an anode electrolysis chamber 11a and a cathode electrolysis chamber 11b divided by a bath partition wall 12, and an anode 13 and a cathode 14 provided in each electrolysis chamber (11a, 11b). In the drawing, the anodic electrolysis chamber 11a represents an anodic electrolysis bath described later, and the cathodic electrolysis chamber 11b represents a state (gray portion) in which a cathodic electrolysis bath described later is placed. The electrolysis chamber 11 is surrounded by an electrolysis furnace outer cylinder 15.
[0008]
The bath partition 12 acts to prevent the anodic electrolytic bath and the cathodic electrolytic bath from contacting each other and preventing the lithium carbonate from contacting and oxidizing the metallic lithium produced at the cathode by electrolysis. Lithium carbonate as an electrolytic raw material, which will be described later, exhibits a strong oxidizing power against molten metal, so if it exists in a cathode electrolytic bath where metallic lithium is generated, metallic lithium is oxidized at the same time as it is generated at the cathode, and the electrolytic efficiency is significantly reduced. Let In order to suppress this reaction, since it is necessary to isolate lithium carbonate in the vicinity of the anode, it is necessary to partition the cathode electrolytic bath and the anode electrolytic bath by the partition wall 12 for bath.
This bath partition wall 12 must be at least partly composed of a porous material that enables energization and movement of lithium ions, and of course, it is necessary to suppress the movement of lithium carbonate in order to obtain the above-described action. is there. Examples of such a porous material include ZrO ₂ and Al ₂ O ₃ porous materials, and it is particularly desirable that the bath partition walls are all formed of such a porous material.
The porosity of the porous material is preferably in the range of 1 to 50%, particularly 5 to 40% so as to exhibit the above action. If the porosity exceeds 50%, lithium carbonate moves from the anode electrolysis chamber 11a to the cathode electrolysis chamber 11b, which is not preferable because the electrolysis efficiency may be lowered. On the other hand, if the porosity is less than 1%, it is difficult to apply a direct current, which is not preferable.
[0009]
Since the anode 13 is a consumable electrode, it tends to melt into the bath, and the dissolved anode material may generate an alloy with lithium metal. For this reason, it is preferable to use carbon for the anode 13 in order to increase the yield of the target metallic lithium. By using carbon, exhausted carbon becomes carbon dioxide gas and escapes into the atmosphere, and the reaction with the generated lithium metal can be suppressed.
On the other hand, in order to obtain metallic lithium in a high yield, the cathode 14 is preferably made of iron having little reactivity with metallic lithium, and particularly preferably pure iron.
Around the cathode 14, a magnesia cylinder 14 a for accumulating the generated metal lithium can be provided as shown.
[0010]
In the production method of the present invention, an anodic electrolytic bath is placed in the anodic electrolysis chamber 11a of the electrolysis chamber 11, and a cathodic electrolysis bath is placed in the cathodic electrolysis chamber 11b.
The anodic electrolytic bath consists essentially of lithium carbonate and fluoride, and the cathodic electrolytic bath consists essentially of fluoride. Here, the term “substantially” means that it may contain impurities and a trace amount of other components that do not affect the action of the present invention, and means that it does not contain any influential lithium chloride or the like.
[0011]
Lithium carbonate used for the anode electrolytic bath acts as an electrolytic raw material, and the content thereof is 0.1 to 30% by mass, preferably 0.5 to 25% by mass, more preferably 1 to 2%, based on the total amount of the anode electrolytic bath. The range is 10% by mass. If the content of lithium carbonate exceeds 30% by mass, lithium carbonate may move from the anode electrolytic bath to the cathode electrolytic bath. If the content is less than 0.1% by mass, the anode effect tends to occur. The lithium carbonate can be replenished to the anode electrolytic bath as electrolysis proceeds, and electrolysis can be continuously performed by this replenishment.
[0012]
Examples of the fluoride used in the anode electrolytic bath and the cathode electrolytic bath include fluorides such as alkali metal elements and alkaline earth metal elements, or mixtures thereof. The theoretical decomposition voltage of most of these fluorides is 5 V or more, which is greatly different from the theoretical decomposition voltage of lithium carbonate of about 2 V or less at the later-described electrolysis temperature, so that only lithium carbonate can be easily electrolyzed by the later-described electrolysis. it can.
If lithium chloride is contained in the cathode electrolytic bath or anodic electrolytic bath, the theoretical decomposition voltage of lithium chloride is about 3.5 V or less, so that not only lithium carbonate but also some lithium chloride may be electrolyzed. And toxic gas chlorine may be generated.
Such a fluoride is preferably a fluoride exhibiting the above theoretical decomposition voltage, and particularly includes one or more selected from the group consisting of lithium fluoride, potassium fluoride and sodium fluoride. It is desirable.
[0013]
The fluoride may contain barium fluoride in order to obtain a melting point drop of the electrolytic bath and an improvement in electrolysis efficiency. The content of the fluoride barium is usually 0.1 to 40% by mass, particularly 5 to 35% by mass, and more preferably 5 to 15% by mass with respect to the total amount of each electrolytic bath.
[0014]
In the production method of the present invention, electrolytic reduction is then performed to produce desired metallic lithium.
As electrolysis conditions, the cathode current density is ^{2 to} 500 A / cm ² , preferably ² to 20 A / cm ² , the electrolysis temperature is 600 to 1000 ° C., preferably 800 to 1000 ° C., particularly preferably 800 to 950 ° C. Can be mentioned.
When the cathode current density is less than 2 A / cm ² , metallic lithium does not precipitate. On the other hand, if it exceeds 500 A / cm ² , the amount of heat generated at the cathode part is large, and the temperature control of the electrolytic bath becomes difficult.
On the other hand, when the electrolysis temperature exceeds 1000 ° C., it takes a great deal of cost to maintain the temperature of the molten salt electrolysis bath, which is not economical. When the electrolysis temperature is less than 600 ° C., the electrolysis bath is solidified and direct current cannot be applied. .
[0015]
In the production method of the present invention, the atmosphere in the upper part of the electrolysis chamber 11 partitioned by the electrolysis chamber 11 shown in FIG. 1 and the liquid upper surface of each electrolysis bath is a dry inert gas atmosphere such as a dry argon atmosphere. It is preferable to do. By controlling the atmosphere in this manner, metallic lithium generated at the cathode during electrolysis is generated at the anode during electrolysis, such as moisture, nitrogen gas, carbon dioxide gas, etc. contained in the atmosphere in the upper part of the electrolysis chamber 11. The carbon dioxide gas or carbon monoxide gas contacted and reacted can be suppressed, and the factor of reducing the electrolysis efficiency can be eliminated.
Such control of the atmosphere can be performed by flowing a dry inert gas at a flow rate sufficient to replace the carbon dioxide gas and carbon monoxide gas generated in the atmosphere and the anode described above into the electrolytic chamber 11.
[0016]
In the manufacturing method of the present invention, the atmosphere in the upper part of the electrolysis chamber 11 divided by the electrolysis chamber 11 shown in FIG. 1 and the upper surface of each electrolytic bath is partitioned into an anode chamber atmosphere and a cathode chamber atmosphere. The partition 16 for the atmosphere partition to be formed can be provided in the electrolysis chamber 11 as illustrated.
By providing the partition wall 16 for the atmosphere partition, if the cathode chamber atmosphere and the anode chamber atmosphere are set to a dry inert gas atmosphere for the above-mentioned atmosphere control before the start of electrolysis, only the cathode chamber atmosphere is not dried during electrolysis. The effects as described above can be obtained by controlling the active gas atmosphere. At the anode, carbon dioxide gas and carbon monoxide gas are generated, and the atmosphere in the anode chamber becomes carbon dioxide gas and carbon monoxide gas atmosphere. Should be prevented from flowing in. On the other hand, the control of the cathode chamber atmosphere is easy and economical because there is almost no gas generation from the cathode.
The atmosphere partition wall 16 is preferably made of a material that is not reactive with the electrolytic bath and does not transmit carbon dioxide gas and carbon monoxide gas. For example, iron, stainless steel, densely sintered ZrO ₂ , Al ₂ O _{3 and the} like can be mentioned.
[0017]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these.
Example 1
The electrolyzer shown in FIG. 1 was prepared. An electrolytic chamber made of iron was used as the electrolytic chamber 11, carbon was used for the anode 13, and iron was used for the cathode 14. Further, a ZrO ₂ crucible having a porosity of 40% was used as the bath partition 12, and an iron partition was used as the atmosphere partition partition 16.
An electrolytic bath composed of 3% by mass of lithium carbonate, 89% by mass of lithium fluoride and 8% by mass of barium fluoride was used as the anode electrolytic bath, and 92% by mass of lithium fluoride and 8% by mass of barium fluoride were used as the cathode electrolytic bath. An electrolytic bath was used.
Before starting electrolysis, both the anode chamber atmosphere and the cathode chamber atmosphere partitioned by the partition wall 16 are set to a dry argon atmosphere, and only the cathode chamber atmosphere is set to a dry argon atmosphere during electrolysis. The electrolysis temperature is 900 ° C. and the cathode current density is 3 A / cm. Molten salt electrolysis was performed under the electrolysis conditions of ² . As a result, no toxic chlorine gas was generated, and metallic lithium having a purity of 99% by mass was obtained with a yield of 95%. Table 1 shows the composition of the electrolytic bath, electrolytic conditions, results, and the like.
[0018]
Examples 2-5, Comparative Examples 1-8
Electrolysis was carried out in the same manner as in Example 1 except that the composition and electrolytic conditions of the electrolytic bath shown in Table 1 were used, and the porosity of the partition wall 12 for bath was changed to that shown in Table 1, generation of chlorine gas, and purity 99 The yield of mass% metallic lithium was measured. The results are shown in Table 1.
[0019]
Example 6
Electrolysis was performed in the same manner as in Example 1 except that the partition wall 16 was not used, and the generation of chlorine gas and the yield of 99% by mass of metallic lithium were measured. The results are shown in Table 1.
[0020]
[Table 1]

[0021]
【The invention's effect】
In the production method of the present invention, a specific electrolyzer having an electrolysis chamber or the like partitioned by a partition wall for a bath having a cathode electrolysis chamber and an anode electrolysis chamber is prepared, and the specific anode electrolysis bath and the specific cathode electrolysis bath are provided in the electrolysis chamber. In addition, since electrolysis is performed under specific electrolysis conditions, high-purity metallic lithium can be obtained without generating toxic chlorine gas.
[Brief description of the drawings]
FIG. 1 is a schematic view showing one embodiment of an electrolysis apparatus used in the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10: Electrolytic apparatus 11: Electrolytic chamber 11a: Anode electrolytic chamber 11b: Cathodic electrolytic chamber 12: Bath partition 13: Anode 14: Cathode 14a: Magnesia cylinder 15: Electrolytic furnace outer cylinder 16: Atmosphere partition partition

Claims

An electrolysis chamber partitioned by a bath partition having a cathode electrolysis chamber and an anode electrolysis chamber, and an anode and a cathode provided in each electrolysis chamber, wherein at least a part of the bath partition enables energization and movement of lithium ions Prepare an electrolyzer made of porous material,
An anodic electrolytic bath that is substantially composed of lithium carbonate and fluoride, and the content ratio of the lithium carbonate is 0.1 to 30% by mass, and a cathodic electrolytic bath that is substantially composed only of fluoride. Put in each electrolysis chamber,
A method for producing metallic lithium, characterized by performing electrolytic reduction under electrolysis conditions of a cathode current density of ^{2 to} 500 A / cm ² and an electrolysis temperature of 600 to 1000 ° C.

The production method according to claim 1, wherein the fluorides of the anode electrolytic bath and the cathode electrolytic bath contain at least one selected from the group consisting of lithium fluoride, potassium fluoride, and sodium fluoride.

The manufacturing method of Claim 1 or 2 with which the fluoride of an anode electrolytic bath and a cathode electrolytic bath contains barium fluoride.

The manufacturing method according to any one of claims 1 to 3, wherein a porosity of the porous material forming the partition wall for bath is 1 to 50%.

The manufacturing method according to claim 1, wherein the anode is carbon and the cathode is iron.

6. The electrolysis apparatus according to claim 1, further comprising an atmosphere partition wall that divides an atmosphere of a space defined by an electrolysis chamber and a liquid upper surface of each electrolytic bath into an anode chamber atmosphere and a cathode chamber atmosphere. Manufacturing method.

The manufacturing method according to claim 6, wherein the cathode chamber atmosphere is controlled to a dry inert gas atmosphere during electrolytic reduction.