Optimizing Battery Quality is Fundamental: The Five Biggest Issues Affecting Li-ion Battery Quality

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The Five Biggest Issues Affecting Li-ion Battery Quality 

Introduction 

Optimizing battery quality is critical for ensuring reliability, safety, and performance in various applications. Despite advancements in battery technology, achieving high-quality batteries remains a complex task fraught with challenges. This article outlines the key issues that are a thorn in every battery manufacturer’s backside and some basic recommendations for keeping your battery quality high and your stress level low 😉 

As an encore to this post, we’ll dive deep into each of these issues and propose actionable solutions to help you mitigate risk and optimize quality. Stay tuned! 

What are the Top 5 issues affecting lithium-ion battery quality? 

Moisture: wetter is not better 

 

1. 1. Gas generation – the most common salt in liquid electrolytes is lithium hexafluorophosphate (LiPF₆). In the presence of water, LiPF₆ forms hydrofluoric acid (HF) via the reaction: LiPF₆ + H₂O → LiF + 2HF + POF₃. 

HF further reacts with intercalated lithium in the anode to form hydrogen gas via: 

2HF + 2Li → 2LiF + H₂. Gas blocks Li⁺ ion diffusion and causes cells to bloat (pouch cells are especially susceptible), reducing effective cell capacity. 

 

2. 2. Electrode degradation – HF attacks electrode active materials and current collectors, resulting in an accelerated self-discharge rate. 

 

3. 3. SEI degradation – HF attacks the Solid Electrolyte Interphase (SEI) passivation layer, depleting its protective compounds. In addition to generating gas, the presence of water in a cell can lead to ongoing SEI thickening, which increases resistance as the SEI continues to thicken. 

 

 

Particle Contamination: everything has a place and everything in its place 

 

1. 1. Internal short circuits – foreign debris particles on the cathode can oxidize and dissolve in the electrolyte, eventually migrating to the anode where they will reduce and form dendrites during charging. Over time, dendrites will travel through the separator and cause a short circuit. Debris can also result in shorts by directly piercing the separator. 

 

2. 2. Isolation reduction – foreign particles can reduce the separator’s dielectric properties, resulting in a decreased hipot yield and an increased self-discharge rate. 

 

3. 3. Performance degradation – foreign particles can reduce the performance and cycle life of a battery by contributing to gas generation, electrolyte/electrode degradation, SEI disruption, and increased internal resistance. 

 

 

Unopposed Cathode: it takes two to tango  

 

1. 1. Electrode alignment – a cell stack or jerry roll made with cathode overhanging any opposing anode risks lithium plating, which reduces overall capacity, generates gas, and increases the chance of internal short circuits from dendrite formation. Electrode alignment is critical to not only ensure proper anode / cathode alignment, but to also reduce the shorting potential from separator misalignment. 

 

2. 2. Electrode manufacturing – ensure the electrode slurry is homogenously mixed, electrodes are free of pinholes and gaps in the film, and that both sides of the electrode’s coated area are properly aligned. 

 

3. 3. Cell design – design the cell so the anode plates are slightly larger in width and length than the cathode plates to increase the cell’s manufacturability. The outer layers of a cell should always be anode. 

 

 

Electrode Quality: garbage in, garbage out 

 

1. 1. Adhesion & cohesion – electrode coating that bonds poorly to the current collector (adhesion) or to itself (cohesion) contributes to resistance and decreased cycle life. 

 

2. 2. Porosity – calendering to the incorrect thickness will result in nonoptimal porosity, affecting ionic transport and electrolyte uptake. 

 

3. 3. Coat weight – the areal mass of the electrode film ensures that the negative to positive (N:P) ratio is as designed, ensuring there are enough anode intercalation sites for all of the available Li⁺ in the system. 

 

4. 4. Anode spring back – improper calendaring, poorly dispersed electrode, or binder with improper molecular weight and crystallinity can encourage swelling of the anode during formation and operation, generating gas as newly exposed graphite particles contact electrolyte and reducing cell capacity. Capacity reduces further as active material particles disconnect from the conductive network. 

 

 

Welding: a battery company is a welding company 

 

1. 1. Ensuring both the internal welds of a cell and the assembly welds of the battery module or pack are robust helps reduce the risk of faults, voltage loss, resistance increase, cycle life reduction, short circuits, and thermal runaway. 

 

 

Joe’s Recommendations for High Battery Quality and Low Stress 

 

1. 1. Water contamination: ensure that the dry room is truly and consistently dry (‒30°C max dew point, preferably lower) and that all residual moisture is driven off the electrodes and cell components before electrolyte filling. 

 

2. 2. Particulate matter contamination: employ vacuum brushing to both sides of every electrode as they are punched. Maintain battery dry rooms also as ISO Class 6-8 clean rooms. 

 

3. 3. Unopposed cathode: understand the tolerances and tolerance stacking of the electrode dimensions coupled with the accuracy of your stacking or winding equipment. 

 

4. 4. Electrode quality: tune micro- and macroscopic defects out of the electrodes through slurry mixing and coating optimization. 

 

5. 5. Welding: employ periodic destructive (tensile test) and frequent nondestructive tests (microohm meter; IR camera; X-ray methods) to ensure weld success and robustness inside and outside of cells. 

 

6. 6. Leave it to the experts! We work with dozens of companies to develop bespoke high-quality batteries for many different applications. Whether you’re starting from scratch or you’re optimizing your batteries or the manufacturing process, we love hard problems! Let’s talk and see what we can do for you. 

Conclusion 

The complexities and challenges involved in optimizing battery quality underscore the importance of consulting with a battery expert before moving out of the lab and into production. Professional expertise can provide invaluable insights and solutions, reducing the risk of failure and ensuring that your batteries meet the highest standards of performance, safety, and reliability. Engaging with battery specialists can help save time, eliminate pain points, fast track optimization, reduce costs, and enhance the overall quality and success of your battery-powered products. 

About Treetown Tech 

Treetown Tech provides deep knowledge and execution in cell chemistries, cell products, battery pack design, development, prototyping, production, and battery management systems (BMS). Our battery expertise and services are complemented by Treetown Tech’s extensive product development and engineering capabilities including software, electronics, and mechanical system design, located in a state-of-the-art facility in Ann Arbor, Michigan. You can learn more about our battery engineering solutions here and the rest of our capabilities here. 

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