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Lithium Ion technology

Introduction

A lithium ion battery cell is based on a technology where lithium ions are the charge ‘carrier’ and can move back and forth from the cathode (positive current collector) to the anode (negative current collector). Cathode and anode are electrically isolated from each other with a separator. An electrochemical cell consists of two currents. One external electric current, and one internal ionic current. The separator is designed to allow for an ionic current, but not an electric current.

Therefore a separator is used which has the double function to isolate and to allow the ions to pass through.

When charging the battery the ions move from the cathode (positive) to the anode (negative). When discharging the ions move back to the cathode.

This process can be repeated a number of times during the life of the battery cell which is called the cycle life of a battery

Different technologies with different characteristics

There are many different rechargeable battery technologies, and amongst them various lithium ion battery technologies are available on the market, which all have their specific characteristics. Each of them is most suitable for certain applications; it is the application that determines the best suitable battery technology.

For example: an application where a lot of pulse power is needed like an electric bus that has to start moving, requires a battery that is able to deliver a high discharge for a short time.

On the other hand when we store solar energy during the day for use at night, we need a battery technology that can hold a lot of energy and discharge it gradually over several hours.

Comparison rechargeable battery technologies



Lithium Ion
Lead acidNickel CadmiumNickel Metal HydrideGraphite/NMCTitanate Oxide
Energy Density40 Wh/kg45-60 Wh/kg80 Wh/kg120-200 Wh/kg70-80 Wh/kg
Cycles200-3001000-1500300-500500-300015000-20000
Charge power★★★★★★★★★★★★★★
Discharge power★★★★★★★★★★★★★★★★★★★★★★★★★
Energy efficiency★★★★★★★★★★★★★★★★
Nominal cell voltage2.0 V1.2 V1.2 V3.6 V2.3 V

Leclanché developed and manufactures both Lithium Graphite/NMC and Lithium Titanate Oxide (LTO) technologies.

Lithium Titanate (LTO) cells excel in applications requiring fast charge capability and very long calendar and cycle life time. (see graph showing symmetric cycling at 4D/4C).

Safety is paramount

Each battery cell is built out of 4 main components:

  1. An anode , which is the negative electrode
  2. A cathode, which is the positive electrode
  3. A separator which allows for ions, to move from one electrode to the other, but electrically insulates both electrodes from each other.
  4. An electrolyte, which serves as a medium for ion transport.
Image of ceramics separator
Image of ceramics separator

The performance and the safety of a cell are dependent on all these four components and the various combinations that can be used in a cell. There are many different anode materials, graphite and Lithium Titanate Oxide being the most used. Several cathode materials are available, the most commonly used are materials such as Nickel Manganese Cobalt (NMC), Nickel Cobalt Aluminium (NCA) and Lithium Iron Phosphate (LFP). Between the cathode and the anode is a separator, which serves as an electric insulator and an ionic permeable layer. It also serves as a safety layer preventing direct contact between the electrodes, as this would lead to an internal short circuit. The use of ceramic material in the separator further enhances the safety features of the separator and increases its thermal stability.

Layered build-up of lithium ion cell
Layered build-up of lithium ion cell

Here lies a major challenge because the separator cannot be thick yet it has to be safe and avoid a thermal runaway when the integrity of the cell is jeopardized.

Leclanché developed a unique technology for this, a separator which consists of both polymer and ceramics. The characteristics of this separator are such that it allows the ions to travel back and forth and the ceramics ensure the separator maintains its role even under extreme conditions. The ceramic also increases the electrolytes dispersion within the separator and improves the thermal properties of the battery.

High quality manufacturing yields high performance cells

One of the most important factors for the performance of a battery cell is the way the cell is produced. The production of a cell consists of several steps bringing it from raw material all the way to an assembled, activated cell that is ready for operation.

Leclanché is unique in using a water based production process for the electrodes which eliminates the need to use polluting solvents and therefore we have a more sustainable production process.

Leclanché, in its factory in Germany, has a fully automated production line where both Lithium Titanate Oxide and Lithium Graphite/NMC cells are produced. The production starts with the processing of the powders through coating on the anode and the cathode. Next the cathodes and anodes are assembled in a roll to roll process together with the ceramic separator. All these layers are laminated to assure optimal integrity of the cell and ensure maximum performance over its life.

Once all these layers are stacked, a tab is welded onto the cathodes and anodes and next they are inserted into a pouch. After adding the electrolyte, the pouches are sealed and formed during which they are charged for the first time in their life.

After the formation the cells undergo a final quality check and they are ready to go into the application.