Written by Maria Beck
Whether in smartphones, laptops, wireless headsets or fitness trackers – rechargeable lithium-ion-batteries have been used for years for the storage of energy. The diverse range of applications are possible because of the different cell chemistries. They affect the energy density, robustness and lifetime of the battery. The energy storage systems from VARTA are also using this technology. Find out why we choose the lithium-ion-technology for our batteries.
First we should explain how they function. Lithium-ion-batteries consist of two electrodes; the anode and cathode, which are separated by a separator material. To enable a current flow between the electrodes an electrolyte is needed. The anode is the minus pole and usually consists of graphite. The cathode is the plus pole and normally consists of a metal oxide. Energy storage systems usually consist of Lithium-Iron-Phosphate (LiFePO4) or a Lithium-Nickel-Manganese-Cobalt-Combination (Li-NMC-Batteries). While charging the battery the positively charged lithium-ions migrate from the cathode to the anode. The electrons are supplied by the external circuit e.g. from the solar system. While discharging the battery, lithium-ions migrate back through the electrolyte to the cathode. The electrons also flow to the cathode but through the external circuit. These processes enable the storage and discharge of energy.
Our first models, VARTA one L and XL, are equipped with a LiFePO4-battery. This type of battery is especially safe and long-lasting. But a significant disadvantage is the energy density. To get the same capacity as Li-NMC-batteries more battery cells are needed which also results in a higher price.
Meanwhile the size and weight isn’t only important for smartphones, headsets and wearables. Many households can only provide a small space for an energy storage system and prefer compact devices.
Li-NMC-batteries meet this requirement because of their higher energy density which is why we’re using them for our VARTA element and VARTA pulse models. They are the perfect combination of high energy density, high safety requirements and lower costs. The VARTA pulse is especially recognized for its high performance, small size and moderate price. Compared to other manufactures of compact devices, the VARTA pulse requires for the same capacity up to 40 % less space.
Obviously the safety of our energy storage systems is important for us. In order to ensure a safe operation, some basic safety rules must be fulfilled. For example, there is a so-called operating window for each battery technology. To protect the battery from fire or irreversible chemical reactions, the battery cell has to operate within certain limits. That’s why we equip every battery with a battery management system (BMS). It controls important parameters such as the voltage, power and temperature and deactivates the battery in the unlikely event of a malfunction.
Besides the safety, the lifetime of our storage systems is also a major concern for us. For a continuously excellent performance of the battery cell, a temperature of approximately 25°C would be ideal, but should be at least between +5°C and 30°C. The so-called discharge depth is also a critical factor. This term describes how much of the maximum available energy is taken from the battery cell. We were able to find the optimal settings through a series of complex measurements to ensure a long-lasting product. In daily operation the BMS ensures that the operating parameters are always met.
Our energy storage systems meet all the mentioned requirements. However, which system is the best for you depends on your individual needs. For the calculation of a suitable energy storage system, please use our calculation tool or call us: +49 9081 240 86 44.
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