News Detail

22.08.2017

Digatron’s Guide to the (battery formation) Galaxy!

Advice on getting the best from your Li-ion batteries from the world’s battery formation expert – coming soon!

Aachen, Germany, 17 August 2017. Digatron Power Electronics, the global leader in battery test and formation equipment, is about to publish a new series of tips on battery formation. Week by week our experts advise you on how to optimise your battery performance. Follow us on LinkedIn and Twitter so you don’t miss out!

 

Li ion Formation introduction

Lithium ion batteries need to have minimum performance variation due to the number of cells connected in series parallel arrangements for most applications. Variation in performance can lead to cells being overcharged or over-discharged in service. The consequences of this variance can be catastrophic failure, including fire.

The performance of a Li ion cell is critically dependent upon getting the formation process right. There are two major factors: the wetting of the electrodes and separator by the electrolyte and the formation of a solid electrolyte interphase (SEI) layer on the electrode surfaces. This is a complex layer formed from reactions between the electrolyte, lithium compounds and the carbon electrode. This layer, which is only partially understood, consumes some of the lithium, which reduces the cell capacity and also increases its resistance. The characteristics of this layer determine the cycle life and ultimate performance of the battery. It is a critical aspect of the formation process and should be controlled within tight limits with minimum variation.

Whilst being essentially a barrier layer which prevents electrolyte penetration and increases internal resistance, its open structure allows Li+ ions to diffuse through the layer and into the carbon electrode during discharge reactions. The SEI layer is formed in the initial stages of the formation programme and is critically dependent upon temperature, voltage and current density. Also important is the condition cycling during formation, which both enhances cell performance and can be used to perform repeated capacity checks to measure the formation and cell conditioning progress.

Due to the large range of Li ion chemistries, the variations in cathode and electrolyte compositions, it is not possible to be prescriptive with absolute values of current, voltage, time and temperature. Nor is it possible to give precise test values to indicate performance efficiency. Instead, the general process requirements for uniform production will be shown and the general operating band for the parameters mentioned will be given.

The whole process of filling, soaking, formation, cycling and ageing can take up to two weeks. Some companies take even longer. The formation process is broadly divided into six sections:

  • Electrolyte filling
  • Soaking or wetting period
  • Initial formation
  • Condition cycling
  • Cycle testing and performance
  • Ageing

The tips we are going to publish are designed to promulgate current best practice and to achieve minimum variation in cell performance. However, due to the diversity of materials and the diversity of physical and chemical properties of similar chemistries between different companies, it is essential that these are viewed as guidelines. Individual companies must determine the optimum process variables for their chemistries and the properties of their materials. The more tightly controlled and accurate the equipment used to perform the processes the less variability there will be in the final product. This can reduce process time and costs as well reducing the high infant mortality rate and the number of cells which are de-rated to lower performance bands.

 

About Digatron Power Electronics

Digatron Power Electronics is the world leader in the design and manufacture of test and formation equipment for all kinds of electrical energy storage devices, including lithium-ion and lead-acid batteries, fuel cells, super caps and hybrid systems.

The Group’s teams of 200 dedicated employees deployed at four engineering, manufacturing and service facilities around the world, in Germany, USA, India and China, work closely with customers to help them realise their projects. Investment in innovation, an extensive network of strategic partnerships and joint ventures, the widest and most innovative product range on the market and an unrivalled reputation for quality and reliability have made Digatron into the only truly global player in this fast-moving market.

Digatron Power Electronics – the future of battery testing www.digatron.com

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Press contact:

Jill Ledger - Ledger and Woolf

Tel: +33663748444

Jill@ledgerandwoolf.com