Most microcontrollers have sleep modes, usually multiple (light sleep, deep sleep). This is especially useful when the target device is battery powered. Sleep modes can also reduce interference from other systems or from the own subsystems of the device, and can also increase the lifetime of the MCU.
Lithium batteries are most commonly used in embedded systems, electric and hybrid vehicles, and other battery-powered devices. There are countless types in terms of chemistry, such as LiNMC and LiFePO4, which refer to the cathode material. OCV (Open Circuit Voltage), DOD (Depth of Discharge), SOC (State of Charge), and SOH (State of Health) are all different terms used to describe battery properties and the condition of cells.
It has high energy density, which is important for smaller devices where space and weight are limited. Due to cobalt, it has negative environmental impacts and is also expensive. The voltage of NMC cells rises rapidly at the start of charging, then slows down as the SOC increases. Charging and discharging are well controllable, and it performs well even after thousands of charging cycles.
It has a lower energy density than an NMC cell, so it requires a larger volume and mass for the same capacity, reducing battery life in weight-dependent applications. On the other hand, it is significantly safer, less prone to overheating. It has better long-term stability and a longer service life for the same use. The challenge lies in the flatness of the charge-discharge curve, as it is difficult to determine DOD or SOC by voltage alone.
Sodium-ion batteries work in a similar way to lithium-ion batteries. Their advantage is that sodium is widely available, inexpensive, and environmentally friendly. The energy density of current SIB cells is lower than that of NMC and LFP cells, but they offer great low-temperature performance and reasonable life cycle. Because of the novelty of the technology, their price is high, but a substantially reduced cost is expected in the coming years compared to lithium-ion batteries.
The purpose of the Battery Management System is to ensure optimal battery operation. It provides protection against overheating, overcharging, and deep discharge. It protects batteries by individual cell voltage, current consumption, and temperature monitoring. A good BMS also maintains the same voltage across cells, as voltage differences between cells reduce battery performance and service life.
All batteries degrade with use. Degradation can be illustrated by examining electric vehicles. In cold weather, the range of an EV typically decreases as battery efficiency drops, internal resistance increases, and the SOC window narrows. Moreover, temperature control systems also require more energy. This effect is actually not degradation, only a temporary state. The main causes of permanent damage are overheating, overcharging, over-discharging, but also simple charge-discharge cycles. These can cause a gradual increase in the internal resistance of the cells, a permanent narrowing of the SOC window, and a reduction in capacity. Degradation also amplifies the effects of cold weather, as the winter range of an EV with a significantly degraded battery can be half that of summer, even though the cold only caused a 20-30% reduction when the battery was at 100% SOH. Interestingly, degradation is usually a gradually slowing process.