1. Cells (the Energy Core)
- Individual lithium-ion cells are connected in series and/or parallel to reach needed voltage and capacity.
- Cell formats include cylindrical (e.g., 18650, 21700), prismatic (rectangular), and pouch (flexible laminate)—each offering unique energy density, safety, and manufacturing trade-offs.
2. Battery Management System (BMS)
The BMS is the intelligent “brain” and safety unit of the pack:
- Monitors cell voltages, temperatures, current, SoC (state of charge), and SoH (state of health).
- Prevents overcharge, over-discharge, short circuits, and thermal hazards.
- Balances cell voltages via passive or active balancing methods.
- Interfaces with other systems through communication protocols (CAN, LIN, SOC).
- Controls contactors and thermal systems for safe operation.
3. Passive and Structural Components
- Bus bars, nickel strips, and high-current connectors to pack and deliver power.
- Housing, cooling plates, thermal interface materials, and vibration dampers.
- Fuses, contactors, thermal sensors, insulation barriers, and structural enclosures for mechanical support and safety.
⚙️ How It Works
- Charging: Lithium ions move from the cathode to the anode; current flows through external circuitry.
- Discharging: Ions return to the cathode, and electrons flow to power a device.
- Balancing: The BMS equalizes voltage among cells to prevent imbalance.
- Safety triggers: The BMS enforces cutoff thresholds (e.g. 2.5 V low‑cell, 4.2 V high‑cell for NMC) and shuts down if conditions deviate.
🚗 Why They Matter
- High Energy Density: ~260–270 Wh/kg vs. 50–100 Wh/kg for lead-acid types.
- Lightweight & Compact: Enables long-range EVs and portable applications.
- Fast Charging: Enables rapid and repeated recharging.
- Longevity: Hundreds to thousands of charge cycles, depending on chemistry and usage.
- Application Versatility: Used in mobile devices, EVs, drones, grid-tied storage, industrial tools, and medical systems.
📌 Common Chemistry Types in Packs
LiFePO₄ (LFP): Less energy-dense but safer, longer-lasting, and cheaper—now ~41% of the EV pack market by capacity
NMC (Nickel‑Manganese‑Cobalt Oxides): High energy density (~3.6–3.7 V nominal per cell), common in EVs like Kia, Hyundai, and Tesla.
