Enhancing Li-Ion Battery Performance

Lithium-Ion Batteries

Lithium-ion batteries are a top choice for manufacturers to use as a power source for many everyday machines and devices, including mobile phones, laptop computers, and electric vehicles. Lithium-ion batteries are specifically preferred over other battery types due to having very high-energy densities, 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 anode to cathode to generate an electrical current. When being charged, lithium ions travel back through the electrolyte solution from cathode to 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 into and out of the electrode in a process known as intercalation.  A binder is used to hold the graphite particles together and give the mechanical strength they require to be used as an anode.  Historically, a combination of NMP and PVDF were used as the binder, however, carboxymethylcellulose (CMC) has become more popular because it is a much safer chemistry and more environmentally friendly.  While they typically compose a relatively small portion of the anodes formulation, the CMC binder used for production of lithium-ion battery anodes can have a significant impact on overall battery performance.

Optimizing Lithium-Ion Battery Performance with TEXTURECEL™ BA

TEXTURECEL™ BA are high purity sodium carboxymethylcellulose polymers that are designed specifically for use as binders in lithium-ion battery anodes.  The market standard CMC that is commonly used in anode manufacturing contains high levels of gel impurities.  These impurities have a detrimental effect on battery performance and can be observed by coating a 1% solution of CMC onto a glass substrate.

As we can see from the images above TEXTURECEL™ BA is produced to contain far fewer gel impurities than the market standard CMC.  To demonstrate the dramatic impact gel content has on battery performance,  anode coatings were prepared using both market standard CMC and TEXTURECEL™ BA grades and then coated onto copper to create anodes for pouch cells.  The formulation used for the anode coating is listed in the table below:
 

The electrodes were allowed to dry in a vaccum oven at 130°C overnight.  Pouch cells were then assembled utilizing the anodes that were 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 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.
 

During rapid charging and discharging the overall capacity of a battery is reduced.  Minimizing this decline in discharge capacity at high C-rates is critical for producing batteries that perform better in fast charging/discharging scenarios. The testing data above shows that the cells produced using TEXTURECEL™ BA exhibit a significantly smaller reduction in discharge capacity at high C-rates than the cells produced with the market standard CMC. On average an increase of 20% in discharge capacity was observed at 3C to 5C when gel impurities were minimized in the CMC binder.

Aging Study

To evaluate the effects of the CMC binder on the longevity of the cells, the discharge capacity of the cells was tested over ~800 discharge / recharge cycles.  The data for this testing is below.
 

The mostly parallel curves above suggests that all of the cells were aging / losing capacity at the same rate.  However, all of the cells that were produced using TEXTURECEL™ BA had a much higher capacity after 100 cycles and remained 10-15% higher in capacity than the market standard cells throughout 800 cycles.

Summary & Conclusion

Carboxymethylcellulose is a very small portion of the battery weight (~0.1%), but it influences battery energy density by about 10%.  Many of the market standard carboxymethylcellulose polymers used in battery manufacturing have a high level of gel impurities that adversely impact battery performance.  TEXTURECEL™ BA grades are produced to contain low to no gel impurities and when used as a binder in anode coatings significantly improve battery capacity, battery life, and charging speed.  Commercially available grades of TEXTURECEL™ BA are listed below.  Contact us today to request your sample.