DE102018213267A1 - Secondary electrochemical energy store and method for producing the same - Google Patents

Abstract

Secondary electrochemical energy storage device, comprising a dimensionally stable housing, the gas carbon dioxide being present as the filling gas within the housing.

Description

The invention relates to a secondary electrochemical energy store, comprising a dimensionally stable housing, and a method for producing a secondary electrochemical energy store.

According to the prior art, lithium-ion batteries (LiB), for example, as representatives of secondary electrochemical energy stores, are assembled with a dimensionally stable housing in a drying room and sealed under dry air. Thus there is dry air inside the housing of the LiB produced. LiB in this document can also be understood to mean lithium-ion cells.

It is an object of the invention to provide an improved secondary electrochemical energy store, comprising a dimensionally stable housing, and an improved method for producing a secondary electrochemical energy store.

This object is achieved by a secondary electrochemical energy store with a dimensionally stable housing according to claim 1 and by a method for producing a secondary electrochemical energy store according to claim 5. Advantageous embodiments and developments of the invention result from the dependent claims.

According to the invention, the gas carbon dioxide (CO ₂ ) is located as the filling gas within the dimensionally stable housing.

In the context of this document, a dimensionally stable housing is understood to mean a preferably metallic housing that is solid and not flexible in comparison to, for example, foiled LiB, so-called pouch batteries. Such a solid housing is used in particular for prismatic LiB. Although such housings are solid compared to Pouch-LiBen's film packaging, a prismatic LiB can also "breathe", i.e. the housing of the LiB can bulge out or in under pressure. Such a housing usually consists of aluminum. However, it is not intended as intended, i.e. not non-destructively possible, for example, to bend such a LiB along several axes in total. In the sense of this application, this refers to the feature that a prismatic LiB is not flexible.

The term filling gas is intended to describe the predominant component of the gaseous fraction within the housing. In other words, the gas atmosphere within the battery housing is predominantly, preferably more than 50%, formed by CO ₂ . It is based on the time before the LiB is put into operation. Ideally, the CO _{2 is} consumed very slowly, optionally completely, during the service life. Due to the necessity of the SEI (see following paragraphs), a large part of the CO _{2 is} consumed in the first cycle when the SEI is formed. Instead, less electrolyte is consumed in the formation of the SEI. It should be noted that gaseous electrolyte decomposition products can be formed by side reactions in the LiB, in particular during the formation of the SEI, but also during the lifetime, so that the percentage of CO ₂ in the LiB can vary widely. For this reason, the fill level specification of more than 50% relates to the time before commissioning if the SEI has not yet been formed.

In the example of the LiB, a material layer is deposited on the active material of the negative electrode in the first cycles, which shields the negative active material in the subsequent cycles (eg graphite or metallic lithium) from direct contact with the electrolyte. Due to the very strong negative electrochemical potential of the negative active material, the electrolyte would decompose in the long run through reduction, which applies universally to electrochemical energy stores with a strongly negative electrochemical potential of the negative active material. The protective layer passivating these parasitic side reactions is called the “solid electrolyte interface” (SEI). The formation of the SEI, which takes place predominantly during the first cycles of the LiB, is supported by the filling gas CO ₂ . This is because the CO _{2 is} reduced by the strong negative potential of the active material and typical components of an SEI such as Li ₂ CO _{3 are} formed. Even with SEI already formed, carbon dioxide can increase the durability and longevity of the SEI during cycle operation, since the SEI is subject to slow decomposition and is rebuilt by the CO ₂ and thereby stabilized. This prevents the LiB from losing capacity.

According to a preferred embodiment of the invention, the dimensionally stable housing is designed in a cylindrical shape or in a prismatic shape.

It is also advantageous if the secondary electrochemical energy store is a lithium-ion battery with a liquid or solid electrolyte. The minimum concentration of the filling gas CO ₂ should be 50% by weight. This ensures a sufficient fill gas reserve until the end of the LiB's service life.

• - a) Bereitstellung eines formstabilen Gehäuses, umfassend einen Gehäusebehälter und einen Gehäusedeckel,
• - b) Assemblierung von Energiespeicherkomponenten in den Gehäusebehälter,
• - c) Einbringen des Gases Kohlenstoffdioxid in den Gehäusebehälter und
• - d) Verschließen des Gehäusebehälters mit dem Gehäusedeckel,

wobei die Schritte b), c) und d) in einer der Reihenfolgen b), c), d) oder c), b), d) oder b), d) c) erfolgen können. Diese Schritte umfassen nicht alle nach dem Stand der Technik notwendigen weiteren Schritte zur Herstellung eines sekundären elektrochemischen Energiespeichers, sondern stellen auf die Schritte ab, auf die es zur Ausführung der Erfindung ankommt. So kann etwa die Befüllung mit Elektrolyt als geeigneter Zwischenschritt in den wiedergegebenen Schrittreihenfolgen erfolgen. A method for producing a secondary electrochemical energy store is also specified, with the steps,

• a) provision of a dimensionally stable housing, comprising a housing container and a housing cover,
• - b) assembly of energy storage components in the housing container,
• - c) introducing the gas carbon dioxide into the housing container and
• - d) closing the housing container with the housing cover,

wherein steps b), c) and d) can take place in one of the orders b), c), d) or c), b), d) or b), d) c). These steps do not include all the further steps required to produce a secondary electrochemical energy store, which are necessary according to the prior art, but instead focus on the steps which are important for carrying out the invention. For example, filling with electrolyte can take place as a suitable intermediate step in the sequence of steps shown.

In the order b), c), d), a cell coil comprising the anode, the cathode and the separator is inserted into the housing container, electrolyte is added, if it is a liquid electrolyte, then the housing container is filled with CO ₂ and, before the filling gas escapes below the minimum concentration, including a concentration reserve for the SEI formation, the housing container is welded to the housing cover. After a modification of this sequence, the filling with electrolyte and CO ₂ can take place in one work step, whereby the CO _{2 can} also be bound to the electrolyte, so that only one filling system is required for filling the electrolyte and CO ₂ .

In the order c), b), d), the housing container is flooded with the filling gas, then the anode, the cathode and the separator are inserted into the housing container, electrolyte is added if it is a liquid electrolyte, and, before the filling gas escapes below the minimum concentration including a concentration reserve for the SEI formation, the housing container is welded to the housing cover.

In the order b), d), c), the anode, the cathode and the separator are inserted into the housing container, electrolyte is filled in, if it is a liquid electrolyte, the housing container is welded to the housing cover and finally the filling gas up to and including the minimum concentration a concentration reserve for the SEI formation. A reclosable filling hole in the housing container or in the housing cover can be used for injection. According to a variant of this sequence b), d), c) the anode, the cathode and the separator are pushed into the housing container, then the housing container is welded to the housing cover and finally the electrolyte and finally the filling gas CO ₂ to the minimum concentration under vacuum including a concentration reserve for the SEI formation. After the injection, the filling hole is welded shut. Filling with CO ₂ replaces the step of flooding with dry air, ie a mixture of oxygen and nitrogen, which is frequently used according to the prior art.

• Insbesondere von LiB ist es bekannt, dass auf das Aktivmaterial der negativen Elektrode eine Materialschicht abgeschieden wird, die das negative Aktivmaterial (z.B. Graphit oder metallisches Lithium) vor einem direkten Kontakt mit dem Elektrolyten abschirmt. Aufgrund des recht starken negativen elektrochemischen Potentials des negativen Aktivmaterials würde sich der Elektrolyt auf Dauer durch Reduktion zersetzen. Die diese parasitären Nebenreaktionen passivierende Schutzschicht ist die SEI. Die genaue chemische Zusammensetzung und die Dicke der Schicht hängt von mehreren Parametern ab, insbesondere von der Wahl des Elektrolyten. Ohne Beschränkung der Allgemeinheit sind beispielhafte Komponenten einer SEI die Verbindungen LiF, Li₂O und Li₂CO₃.

The invention is based on the considerations set out below:

• From LiB in particular, it is known that a material layer is deposited on the active material of the negative electrode, which shields the negative active material (for example graphite or metallic lithium) from direct contact with the electrolyte. Due to the very strong negative electrochemical potential of the negative active material, the electrolyte would decompose in the long run through reduction. The protective layer that passivates these parasitic side reactions is the SEI. The exact chemical composition and the thickness of the layer depend on several parameters, in particular on the choice of the electrolyte. Without limiting the generality, exemplary components of an SEI are the compounds LiF, Li ₂ O and Li ₂ CO ₃ .

The idea is to introduce CO ₂ into the LiB as a filling gas. The formation of the SEI, which takes place predominantly during the first cycles of the LiB, is supported by CO ₂ . This is because the CO _{2 is} reduced by the strongly negative potential of the active material and typical components of an SEI such as Li ₂ CO _{3 are} formed. The CO ₂ in the LiB can thus also be understood as an SEI-forming additive. Even with SEI already formed, carbon dioxide can increase the durability and longevity of the SEI during cycle operation, since the SEI is subject to slow decomposition. This results in the reduction of the electrolyte, which in turn leads to an irreversible loss of cyclable lithium. This is equivalent to a loss of capacity at the LiB. If CO _{2 is} reduced instead of the electrolyte, this does not immediately prevent the loss of cyclizable lithium, but leads to a more stable SEI, which decomposes less quickly, so that less loss of cyclizable lithium occurs as a result. Furthermore, the reduction of the CO ₂ instead of the electrolyte, which is essential for the Li-ion transport, prevents a slower lithium-ion transport or, in extreme cases, a drying out of the cell.

The CO ₂ in the LiB as the filling gas thus has the effect that the decomposition rate of the SEI slows down, the electrolyte consumption is reduced, and the SEI is stabilized with slow consumption of the CO ₂ , which has a significantly positive effect on the life of the LiB. In addition, CO ₂ displaces the gases oxygen and nitrogen, which are the main components of dry air, which are used as a working atmosphere in the production of LiB according to the prior art, from the LiB. The latter can react with metallic lithium and lithiated graphite, which is also synonymous with a loss of capacity.

The production of LiB with CO ₂ as filling gas differs from the production of ordinary LiB. Typically, LiB are assembled in a drying room and sealed in dry air. This means that there is dry air inside the LiB housing at the end of the manufacturing process. Before the process step of welding a LiB housing part to a cover, the LiB is filled with CO ₂ according to the invention. Alternatively, this can also be done after welding by means of an injection through a closable filling opening.

Another alternative production variant is that the assembly or the filling with electrolyte takes place simultaneously with the filling with CO _{2 in} order to combine process steps. It is also conceivable to saturate the electrolyte with CO ₂ and in this way to apply the CO ₂ with the filling with electrolyte into the LiB.

Filling the LiB with CO ₂ does not require any serious changes to the other components of the LiB. The integration of CO ₂ filling into existing processes is also relatively straightforward. Only so-called pouch cells are not accessible to the manufacturing process according to the invention, since pouch cells are to be built as empty as possible. In contrast, prismatic and cylindrical cells are suitable for filling with CO2.

A preferred exemplary embodiment of the invention is described below with reference to the accompanying drawings. This results in further details, preferred embodiments and developments of the invention. In detail shows schematically 1 Process for producing a secondary electrochemical energy store with the filling gas CO ₂

It shows 1 the process steps for producing a secondary electrochemical energy store with the filling gas CO ₂ using the example of a LiB. First, an aluminum case is provided. Energy storage components, namely the anode, the cathode and the separator, are then assembled in the housing container. The housing container is then welded to the housing with a housing cover. The housing is then filled with liquid electrolyte via a filling hole. In a further step, the filling gas CO _{2 is introduced} into the housing container by flooding. In a final step, the filling hole is welded.

Claims (5)

Secondary electrochemical energy store, comprising a dimensionally stable housing, characterized in that - within the dimensionally stable housing, the gas carbon dioxide is present as the filling gas. Secondary electrochemical energy storage after Claim 1 , characterized in that - the dimensionally stable housing is designed in a cylindrical shape or in a prismatic shape. Secondary electrochemical energy store according to one of the preceding claims, characterized in that - the secondary electrochemical energy store is a lithium-ion battery. Secondary electrochemical energy store according to one of the preceding claims, characterized in that - the concentration of the filling gas carbon dioxide is at least 50% by weight. Method for producing a secondary electrochemical energy store, comprising the steps a) provision of a dimensionally stable housing, comprising a housing container and a housing cover, - b) assembly of energy storage components in the housing container, - c) introducing the gas carbon dioxide into the housing container and - d) closing the housing container with the housing cover, steps b), c) and d) in one of the orders b), c), d) or c), b), d) or b), d) c) can be done.

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