Application

Metallized polymer films as current collectors represent interesting opportunities to increase both gravimetric and volumetric energy density while improving battery safety aspects and saving scarce resources compared to previously used metal films.

• Thin and lightweight current collectors to increase volumetric and gravimetric energy density
• Replacement of metal foils by metallized polymer foils

Development Parameters

• Film thickness (base substrate) < 8 µm
• Metal thickness > 1 µm
• Total thickness < 10 µm

Technology

• Roll-to-roll process for film widths > 400 mm and strip lengths > 100 m
• Double side coating with Al or Cu by means of
  • electron beam evaporation
  • cathode sputtering (magnetron sputtering)

Advantages

• Weight, thickness
• Increasing the intrinsic safety of battery cells
  

Application

Pure silicon anodes in lithium-ion cells potentially enable a dramatic increase in volumetric energy density. Porous nodular structures are required to enable high cell cycle stability.

• Growth of silicon in nodular structures to incorporate free spaces in the layer to compensate for volume expansion

Development Parameters

• Silicon area loading, e. g.: 1 ... 4 mgSi/cm² per film side. (corresponds to a geometric film thickness of approx. 5 ... 15 μm)
• Deposition rate
• Porosity

Technology

• Roll-to-roll process for film widths > 400 mm
• Coating by magnetron sputtering
• Electron beam process in preparation

Advantages

• High charge capacity of porous silicon layers
• Good cycle stability
• Roll-to-roll process

Application

Porous layers with adapted properties are required, for example, in microelectronics for sensors, actuators and other functional layers with low dielectric constants. In chemistry, porous layers are used for catalysts or for filtration. Due to the large internal surface area of porous materials, the focus is on energy conversion applications such as super capacitors or innovative anodes for lithium-ion batteries. Silicon is a promising material for this purpose, among others. However, a porous Si matrix is needed to compensate for mechanical stresses and volume expansion occurring during the charging process.

Development Parameters

• Materials used
• Porosity and morphology
• Technology transfer for roll-to-roll processes

Technology

• Co-evaporation of silicon and zinc
• Mixing of the two elements in the vapor phase and deposition of compound layers on metal substrates
• Subsequent annealing treatment in vacuum for re-evaporation of zinc and structure formation

Advantages

• High coating rate (up to 100 nm/s demonstrated)
• Creation of a porous structure in the silicon that provides space for its expansion in the charging process and minimizes capacity loss
• Process can be adapted and optimized to specific battery requirements
• Reuse of zinc in the process possible in the long term
• Initial charge capacity of the layers over 3,000 mAh/gSi
• Comparatively good cycle stability

Motivation

Usually, lithium layers are produced in the form of thin films by rolling processes, which also necessitate the use of lubricants. By thermal vapor deposition in a vacuum, lithium layers can be produced without contaminating additives in a thickness of 1 – 20 micrometers. This allows very pure and, above all, thin metallic lithium layers to be produced in a reproducible manner.  

State of Research

• Fabrication of pure lithium thin films on metal substrates
• Optimization of layer thickness and layer morphology
• Development of suitable passivation layers
• Pre-lithiation of anodes

Technology

• PVD of pure metallic lithium layers by thermal evaporation at deposition rates > 100 nm/s and > 1 µm m/min, respectively
• Deposition of Li compound layers by co-evaporation from separate crucibles for the production of  pre-lithiated layers
• Deposition of protective coatings by PVD

Advantages

• High degree of freedom for adjusting the optimum anode thickness
• Highest degree of purity
• Adaptation of the optimum layer morphology in layer growth direction possible
• High flexibility in layer composition

Application

The use of small-scale Si particles as anode material is an alternative way to minimize the stresses that occur during cycling. A carbon coating on the particle surface also supports the electronic conductivity, stabilizes the silicon and prevents the loss of lithium and electrolyte through continued SEI formation. Fraunhofer FEP is pursuing the approach of coating the Si particle surface with carbon in the arcPECVD process with a high deposition rate.

Development Parameters

• Coating rate (≥ 35 nm/s on flat substrates already demonstrated)
• Powder delivery set up in vacuum
• Variation of coating thickness possible by manipulation of exposure time and particle distribution

Technology

• Precursors (e. g. C₂H₂) are converted into compact carbon coatings by exposure to an intense hollow cathode plasma
• The powder is conveyed through the plasma‘s action zone by a special conveying mechanism and then collected again
  

Advantages

• All-sided coating of particles with high throughputs
• High degrees of freedom with regard to the size distribution of the particles
• Flexibility of the coating material by using different precursors
  

• Interfaces
• Solid-state electrolyte coatings
• Separators
• Deposition of active materials on metal foils
• Post-Lithium Technologies