Smart cell management system for future batteries

Today’s battery management systems (BMSs) are based on a master/slave architecture, voltage/current measurements and passive balancing. Battery packs are complex systems where electrochemical reactions happen at cell level and determine the pack performance, ageing and safety.

Such BMSs present some issues:

1. Voltage and current do not relate accurately to the inner electrochemical reactions of Li-ion cells;
2. They cannot track the aging evolution of each single cell (i.e. SoH);
3. They cannot estimate the inner temperature of each single cell;
4. They do not implement operation margins to ensure an adequate level of safety reducing the battery's performance;
5. There is a limited degree of freedom in controlling each cell according to its state;
6. passive balancing fails to balance cells that have aged differently, reducing the pack lifetime (pack limited by its weakest cell);
7. They do not trace/store the state of battery cells, hindering reuse and recycling.

 

We have developed a hardware/software solution for Battery Management Systems (BMS) based on the smart-cell concept: the battery cell (hardware) plus its dedicated controlling electronics (software). The solution provide several advantages:

1. Accurate state estimation with EIS and dedicated battery models. Validated RMSE <5% in wide range of SoCs (5/95%) and temperatures (-10/40°C);
2. Novel active balancing method able to correct up to 50% SoC imbalance (without dissipation) and keep cells' SoHs uniform.
3. Battery lifetime extended by more than 20% thanks to a combination of sensing (EIS) and acting (switching) capabilities.
4. Increased safety, thanks to combination of sensing (EIS) and acting (switching) capabilities.
5. Savings on the diagnostic assessment for second-life repurposing. 

Our BMS solution is based on a fully-decentralised architecture, with these features:

• Distributed intelligence: each battery cell is equipped with its own cell management system (CMS);
• Electrochemical Impedance Spectroscopy (EIS) at cell level without external equipment;
• Capability to switch each single cell in/out to modulate the usage of each cell;
• Physically-based models to estimate battery states (SoC, SoH, etc.).
• Wireless communication to reduce wiring
• Cell traceability to store relevant information at cell-level.