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 used material in the anode formulation in a lithium-ion battery due to its ability to easily allow lithium ions to go into and out of the anode, in a process known as intercalation. A binder holds graphite particles together and provides the required mechanical strength and consistency for an anode.  The slurry formed from this graphite-binder mixture is then coated onto a metal surface. Historically, a combination of NMP and PVDF was used as binder materials. However, carboxymethylcellulose (CMC) has recently become more popular because it is a much safer, more environmentally friendly chemistry. While they typically comprise a relatively small portion of an anode formulation, the CMC binder used for producing lithium-ion battery anodes can significantly affect overall battery performance.

Optimizing Lithium-Ion Battery Performance with TEXTURECEL™ BA

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

    Market Standard CMC

    TEXTURECEL™ BA Grades

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

    IngredientAmount
    Graphite46.75 g
    2% CMC Solution30.44 g
    Water11.18 g
    SBR Latex1.01 g
    Conductive Carbon Black0.73 g

The anodes coated with this slurry were allowed to dry in a vacuum oven at 130°C overnight. Pouch cells were then assembled utilizing the anodes manufactured with several types of CMC binders, including market-standard CMC and TEXTURECEL™ BA. The following components were used to complete the pouch-cell battery.

    ComponentDetails
    CathodeLithium sheet plate, unilaterally coated with NMC 622
    SeparatorPolyolelfin nonwoven, coated with ceramics (Separion®)
    ElectrolyteLiPF6 EC/DMC

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

C-Rate Tests

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.

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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 test data above shows that the cells produced using TEXTURECEL™ BA exhibit a significantly smaller reduction in discharge capacity at high C-rates than those produced with an Asian market-standard CMC. On average, a 20% increase in performance from 3C to 5C can be expected. Therefore, TEXTURECEL™ BA can be used to create lithium-ion batteries that have much better charging speeds.

Aging Study

To evaluate the effects of the CMC binder on the longevity of battery cells, the discharge capacity of the cells was tested over 600 discharge and recharge cycles. The data for cycles 100 through 500 of this test is below.

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The mostly parallel curves above suggest that all the cells were aging and losing capacity at the same rate. However, all the cells produced using TEXTURECEL™ BA had a much higher capacity after 100 cycles. They even remained 10-15% higher in capacity than the Asian market-standard cells even after 800 cycles. This indicates that lithium-ion batteries made with TEXTURECEL™ BA can provide electronic devices with greater capacity for charge and discharge as device age increases.

Summary & Conclusion

When considering the overall composition of lithium-ion batteries, the CMC binder comprises a very small portion of the battery weight (~0.1%). However, depending on quality, the CMC binder can improve overall battery energy density by up to 10%. Particularly, up to 20% higher performance is achievable during fast-charging scenarios (i.e., C-rate tests at 5C). Additionally, up to 10-15% higher specific discharge capacity may be realized during battery aging cycles.

Many market-standard CMC binders used in lithium-ion battery anode coatings contain a high level of gel impurities that adversely impact battery performance. TEXTURECEL™ BA grades are produced to contain lower gel impurities. When used as a binder in coatings for anodes, it can provide significantly improved lithium-ion battery capacity and charging speed. Commercially available grades of TEXTURECEL™ BA are listed here. Contact us below to request your sample.

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