Enhancing Li-Ion Battery Performance

Lithium-Ion Batteries

Lithium-ion batteries are a convenient and reliable power source for many everyday machines and devices, including mobile phones, laptop computers, and electric vehicles. Lithium-ion batteries are preferred over other battery types because they have very high energy densities, a low tendency to self-discharge, and no memory effect, which is detrimental to battery capacity over time. Lithium-ion batteries utilize two electrodes: the cathode and anode. When discharged, lithium ions travel through an electrolyte solution from the anode to the cathode to generate an electrical current. When being charged, lithium ions travel back through the electrolyte solution from the cathode to the anode in the opposite direction of the discharging current. 

Anode Binder Technology Trends

Graphite is the most commonly used material in the anode of lithium-ion batteries due to its ability to easily allow lithium ions in and out of the electrode in a process known as intercalation. A binder is used to hold the graphite particles together and give them the mechanical strength they require to be used as an anode. Historically, a combination of NMP and PVDF was used as the binder; however, a mixture of water-based carboxymethyl cellulose (CMC) polymers has become more popular because it is a much safer chemistry and more environmentally friendly. While typically composing a relatively small portion of an anode's formulation, the CMC binder used to produce lithium-ion battery anodes can significantly impact overall battery performance. 

Optimizing Lithium-Ion Battery Performance with TEXTURECEL™ BA

TEXTURECEL™ BA is a cellulose-based binder and thickening agent that provides the necessary purity, viscosity, and chemical functional groups to improve battery performance drastically. In terms of chemical composition, it is a high-purity sodium carboxymethylcellulose polymer designed to exceed the market standard for CMC purity. Typically, ordinary CMC is used as a cellulose-based thickening agent for food personal care, and pharmaceutical applications. While it performs to tight viscosity specifications, it contains high levels of cellulose gel impurities that are unsuitable for use in high-performance applications, such as battery anodes. Ultimately, these impurities have a detrimental effect on battery performance and can be observed and quantified by coating a solution of CMC onto a glass substrate. 

As you can see from the images above, TEXTURECEL™ BA contains far fewer gel impurities than the market-standard carboxymethyl cellulose. To demonstrate the dramatic impact of high gel content on battery performance, anode coatings were prepared using market-standard CMC and TEXTURECEL™ BA, then coated onto copper to create anodes to make pouch cells. The chemical formulation used for the anode coating is listed in the table below.

The electrodes were allowed to dry overnight in a vacuum oven at 130°C. Pouch cells were then assembled utilizing the anodes manufactured with varying CMC binders and the following components.

The cells were then subjected to C-rate testing and a long-term aging study. 

C-Rate Testing

C-rate is a measurement of the current at which a battery is discharged or charged. The cells were tested for discharge capacity over 100 cycles at C-rates varying from C/20 to 5C. 
 

Typically, the overall capacity is reduced during rapid charging and discharging of batteries. Minimizing this capacity decline at high C-rates is critical for producing batteries that perform better in fast charging and discharging scenarios. The testing data above show that the cells produced using the TEXTURECEL™ BA grades exhibited a significantly smaller reduction in discharge capacity at high C-rates than the cells produced with the market-standard CMC with low purity. These results show that, on average, a 20% increase in discharge capacity can be gained from 3C to 5C when gel impurities are minimized in the CMC binder. 

Aging Study

To evaluate the effects of the TEXTURECEL™ BA and market-standard CMC binders on the longevity of the cells, the discharge capacity was tested over approximately 800 discharge and recharge cycles. The data for this testing are below. 
 
 

The mostly parallel curves above suggest that all cells lost capacity at the same rate. However, the cells produced using TEXTURECEL™ BA grades had a much higher capacity after aging through 100 cycles, remaining 10%–15% higher in discharge capacity than the market-standard CMC cells through 800 cycles. 

Summary & Conclusion

Carboxymethyl cellulose makes up a very small portion of the battery weight, typically around 0.1%, but it can influence battery energy density and performance by about 10%. Many market-standard carboxymethyl cellulose polymers used in battery manufacturing have a high level of gel impurities that adversely impact battery performance. TEXTURECEL™ BA grades are produced to contain very low gel impurities and significantly improve battery capacity, battery life, and charging speed when used as a binder in anode coatings. Commercially available grades of TEXTURECEL™ BA are listed below. 

 

ChemPoint is a distributor and technical resource for specialty chemicals. Contact us today to request your TEXTURECEL™ BA sample and work with a technical specialist to improve your lithium-ion batteries. 

Click Here To Request A TEXTURECEL™ BA Sample 
 

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