5. Battery based ESS Energy storage technologies E. Garayalde, Hybrid Energy Storage Systems via Power Electronic Converters 14.10.21 Mondragon Unibertsitatea 2 Basic nomenclature Cell Definition: the smallest individual electrochemical unit, which delivers a certain voltage depending on the chemistry • There are primary (single use) and secondary (rechargeable) cells • A cell is different from a battery Battery and battery pack Definition: made up from groups of cells Cell 14.10.21 Battery Mondragon Unibertsitatea 3 Basic nomenclature Instantaneous capacityq t Definition: instantaneous quantity of charge represented in Ampere-hours (Ah) Calculation: integration of the current over time (positive current means charging) q t i t dt Rated capacity Q nom Definition: quantity of charge that the battery is rated to hold, represented in Ampere-hours (Ah). Value provided by the manufacturer for certain temperature and current conditions 14.10.21 Mondragon Unibertsitatea 4 Basic nomenclature State of charge (SoC) Definition: instantaneous charge with respect to maximum cell capacity (%) 𝑆𝑂𝐶[%] = 1 𝑄0 + 3600 𝑡 𝐼(𝑡) dt 0 𝑄𝑁 𝑥 100 State of health (SoH) Definition: degradation with respect to initial nominal capacity (Qnom0) in percentage. In electromobility applications an 80% of the initial rated capacity is usually considered as the end of life (EoL) of a battery. 𝑄𝑛𝑜𝑚1 𝑆𝑂𝐻[%] = 𝑥 100 𝑄𝑛𝑜𝑚0 14.10.21 Mondragon Unibertsitatea 5 Basic nomenclature C-rate Definition: measurement of the current relative to the cell capacity Calculation: for a 20 Ah cell, 1C current means 20 A, whereas C/10 means 2 A The cell should be able to deliver 1C current for 1 h, and C/10 for 10 h Rated voltage Vnom Definition: nominal voltage of the cell, usually measured at 50% of state of charge. For nickel-based cells 1.2 V, for lithium-based cells 3 V Cell voltage v t Definition: instantaneous terminal voltage of the cell 14.10.21 Mondragon Unibertsitatea 6 Basic nomenclature Energy Definition: this is the storage capacity of a cell in electrochemical form (Wh or kWh) Calculation: the total storage capacity is approximately its nominal voltage multiplied by its rated capacity p t v t i t Instantaneous Power Definition: energy release rate in a certain instant 14.10.21 Mondragon Unibertsitatea 7 Basic nomenclature 14.10.21 Concept Unit Description q t Ah Instantaneous charge Q nom Ah Rated charge SoC % State of charge SoH % State of health C-rate - Current rate v t V Instantaneous cell voltage Vnom V Rated cell voltage Enom Wh Cell energy p t W Instantaneous cell power Mondragon Unibertsitatea 8 Basic nomenclature Interconnection of batteries Series connection If a single cell has 3 V and 20 Ah, how much voltage, capacity and energy has the following battery pack? Parallel connection If a single cell has 3 V and 20 Ah, how much voltage, capacity and energy has the following battery pack? 14.10.21 Mondragon Unibertsitatea 9 Basic nomenclature Energy density and specific energy Definition: maximum amount of stored energy per unit weight (specific energy in Wh/kg) or volume (energy density in Wh/l) http://mocha-java.uccs.edu/ECE5710/index.html 14.10.21 Mondragon Unibertsitatea 10 Basic nomenclature Power density Definition: energy release rate per unit of weight (W/kg) I. Aizpuru, Energy efficiency improvement of Li-ion battery packs via balancing techniques 14.10.21 Mondragon Unibertsitatea 11 Energy storage technologies E. Garayalde, Hybrid Energy Storage Systems via Power Electronic Converters 14.10.21 Mondragon Unibertsitatea 12 Batteries – More concepts End of charging voltage: maximum cell voltage during charging End of discharging voltage: minimum voltage during discharging Open circuit voltage (OCV): voltage of a single cell when no current is flowing through it Internal resistance (mΩ): sum of the ionic and electric resistance of the cell components. Example of a LiFePO4 datasheet 14.10.21 Mondragon Unibertsitatea 13 Electrochemical ESS What is a cell? 14.10.21 Mondragon Unibertsitatea 14 Cell meaning Cells are the building blocks of batteries. A cell is a closed power source, in which energy is stored chemically. Johnson Matthey Battery Systems, “Our Guide to Batteries,” 2015. 14.10.21 Mondragon Unibertsitatea 15 Electrochemical ESS How does a cell work? 14.10.21 Mondragon Unibertsitatea 16 Cell working principle The chemical energy of the cell contained in its active materials can be converted directly into electric energy by means of electrochemical oxidation-reduction (redox) reactions Johnson Matthey Battery Systems, “Our Guide to Batteries,” 2015. 14.10.21 Mondragon Unibertsitatea 17 Cell working principle Redox (reduction/oxidation) reaction During discharge, the negative electrode, named the anode, gives up electrons (oxidation is loss of electrons) and the positive electrode, named the cathode, accepts electrons (reduction is gain of electrons) During charge it is the opposite process http://mocha-java.uccs.edu/ECE5710/index.html 14.10.21 Mondragon Unibertsitatea 18 Cell working principle Redox (reduction/oxidation) reaction The electrolyte provides the medium for the internal ion charge transfer between the electrodes. The electrolyte and separator must be electronic insulators to avoid self discharge and short circuits. http://mocha-java.uccs.edu/ECE5710/index.html 14.10.21 Mondragon Unibertsitatea 19 Degradation Cycle life: Cell ageing due to the number of cycles done. o Working temperature. High temperatures age the cell but also low temperatures, best temperature around 20ºC. o Depth of discharge (DOD). High DODs age the cell. o Current rate. High rates age the cell. o Overdischarge and overcharge the cell can also age the cell. Calendar life: Degradation processes even if the cell or battery is not cycled. o Storage temperature, around 8-10ºC. o SOC for the storage, better a SOC of 40% to store batteries. 14.10.21 Mondragon Unibertsitatea 20 Lead-based cells Lead-acid (Pb) cells – Composition Positive electrode: the cathode is usually made from lead-dioxide Negative electrode: the anode is usually made from metallic lead Electrolyte: usually made from water and sulphuric acid https://www.off-grid-europe.com/info/lead-acid-battery/ 14.10.21 Mondragon Unibertsitatea 22 Lead-acid cells – Operation Principles Discharge The anode gives up electrons and is oxidised, and the cathode is reduced Charge The anode is reduced and the cathode oxidised, giving up electrons https://www.off-grid-europe.com/info/lead-acid-battery/ 14.10.21 Mondragon Unibertsitatea 23 Lead-acid cells – Operation Principles https://www.youtube.com/watch?v=rhIRD5YVNbs 14.10.21 Mondragon Unibertsitatea 24 Lead-acid cells Low cost technology, wide variety of sizes and designs Cell components easily recycled Wide operating temperatures and high power outputs Good high-rate performance Good low- and high-temperature performance SoC can be easily estimated 14.10.21 Mondragon Unibertsitatea 25 Lead-acid cells Heavy metal element → toxic and hazardous for the environment if not properly disposed Low performance High volume and weight → low energy density Long charging times Need for careful maintenance 14.10.21 Mondragon Unibertsitatea 26 Lead-acid (Pb) cells – Applications It can be used for stationary applications where the battery is normally fully charged and is used for a few number of operations. o Telecommunications. o Emergency lights. o UPS systems. o Security systems for different purposes. (Elevator) But it can be used for cycling, for instance a solar application where the battery is charged during the day and discharged during the night. The normal use of the battery is to keep it fully charged if possible and use the accumulated energy when required. 14.10.21 Mondragon Unibertsitatea 27 Nickel-based cells Nickel cells – Composition Cathode: usually made from nickel hydroxide Anode: cadmium (Cd) or a metal hydride (MH) to form NiCd or NiMH cells, respectively Electrolyte: usually an alkaline material 14.10.21 https://chem.libretexts.org/LibreTexts/Howard_University Mondragon Unibertsitatea 29 Nickel Cadmium (NiCd) cells Long cycle life Good low-temperature and high-rate performance Rapid recharge capability Memory effect Cadmium is highly toxic → banned for most applications 14.10.21 Mondragon Unibertsitatea 30 Nickel Metal Hydride (NiMH) cells Higher energy density than NiCd Good low-temperature performance Rapid recharge capability Lower high-rate performance than NiCd Higher cost anodes 14.10.21 Mondragon Unibertsitatea 31 Nickel Metal Hydride (NiMH) cells https://youtu.be/-yfPpIZYEjI 14.10.21 Mondragon Unibertsitatea 32 Lithium-based cells Li-ion cells – Composition Positive electrode: the cathode can be made from different materials (gives the name to the cell technology, e.g. LiFePO4) Negative electrode: the anode is usually made from a carbon/graphite material Separator: microporous layer responsible for avoiding a shortcut between electrodes 14.10.21 Mondragon Unibertsitatea Johnson Matthey Battery Systems, “Our Guide to Batteries,” 2015. 34 Li-ion cells – Composition Electrolyte: ionically conducting but electrically insulating charge transfer material Current collectors: materials attached to the electrodes that are able to conduct the current. Positive collector is normally made from aluminium and negative from copper Johnson Matthey Battery Systems, “Our Guide to Batteries,” 2015. 14.10.21 Mondragon Unibertsitatea 35 Li-ion cells – Operation principles Discharge The anode gives up electrons and is oxidised, and the cathode is reduced Charge The anode is reduced and the cathode oxidised, giving up electrons https://www.youtube.com/watch?v=4NqWSZQeyV4 (Interesting video about batteries, minute 23, explanation about li-ion chemical reactions) 14.10.21 Mondragon Unibertsitatea 36 Li-ion cells – Composition During the charge and discharge, lithium ions are transferred via the electrolyte from the anode to the cathode or vice versa. This is called the intercalation process Solid-state cells are the new trend A ceramic electrolyte is used instead of a liquid one to provide greater stability and safety while keeping a good performance Johnson Matthey Battery Systems, “Our Guide to Batteries,” 2015. 14.10.21 Mondragon Unibertsitatea 37 Cells – Composition https://www.youtube.com/watch?v=kqR7MihP5k4 14.10.21 Mondragon Unibertsitatea 38 Lithium-ion cell types Cathode materials 14.10.21 Mondragon Unibertsitatea 39 Lithium-ion cell types 14.10.21 Mondragon Unibertsitatea 40 Electrochemical ESS How are cells constructed? 14.10.21 Mondragon Unibertsitatea 41 Cells – How are cells constructed https://www.youtube.com/watch?v=6vBH6zlrXuM 14.10.21 Mondragon Unibertsitatea 42 Cell types Prismatic cells High energy density Can be packed more efficiently Relative high mechanical strength Volume efficient geometry More challenging to manufacture Johnson Matthey Battery Systems, “Our Guide to Batteries,” 2015. 14.10.21 Mondragon Unibertsitatea 43 Cell types Cylindrical cells Low price for standard shapes, they are produced in very high quantities High energy density High mechanical stability Preferred for high volume production of small-sized cells Inefficient use of space, but cavities can be used for cooling purposes 14.10.21 Mondragon Unibertsitatea Johnson Matthey Battery Systems, “Our Guide to Batteries,” 2015. 44 Cell types Pouch cells Most efficient use of available space No metal container → less weight → higher energy density Thin design Relatively easy and cheap manufacturing Low mechanical strength → protective case is used often 14.10.21 Mondragon Unibertsitatea Johnson Matthey Battery Systems, “Our Guide to Batteries,” 2015. 45 Electrochemical ESS How are battery packs assembled? 14.10.21 Mondragon Unibertsitatea 46 Battery pack construction 1 https://youtu.be/5L9hOVG_0RQ 14.10.21 Mondragon Unibertsitatea 47 Battery pack construction 2 https://www.youtube.com/watch?v=iiJsKza5CF4 Mondragon assembly machine for building battery packs 14.10.21 Mondragon Unibertsitatea https://www.youtube.com/watch?v=0XGqxu9DBcU&t=10s 48 Electrochemical ESS Which chemistry should we choose? 14.10.21 Mondragon Unibertsitatea 49 Comparison of cell chemistries Johnson Matthey Battery Systems, “Our Guide to Batteries,” 2015. 14.10.21 Mondragon Unibertsitatea 50 Electrochemical ESS Is this technology used for many applications? 14.10.21 Mondragon Unibertsitatea 51 Electrochemical ESS - Applications https://www.batteryuniversity.eu 14.10.21 Mondragon Unibertsitatea 52 Electrochemical ESS - Companies https://www.batteryuniversity.eu 14.10.21 Mondragon Unibertsitatea 53 Electrochemical ESS What about safety? 14.10.21 Mondragon Unibertsitatea 54 Electrochemical ESS – Safety – Li-ion 1.Undervoltage: Copper dissolves into the electrolyte. 2.Overvoltage: Formation of lithium dendrites. 3.Undertemperature: damage, short circuit platting. Cathode and lithium 4.Overtemperature: Loss of capacity, contacts between anode and electrolyte, decomposition, release gases, fire, thermal runaway. 14.10.21 Mondragon Unibertsitatea 55 Electrochemical ESS – Safety – Li-ion Degradation due to lithium platting Performance reduction Cycle life degradation due to high temperature Optimal temperature range High temperature risk Irreversible Irreversible -10ºC 14.10.21 20ºC 40ºC Mondragon Unibertsitatea 60ºC 56 Electrochemical ESS – Safety – Li-ion Nail penetration tests https://www.youtube.com/watch?v=QvUjIWEVRnY https://www.youtube.com/watch?v=jnXYDRifTBA Water and lithium, very bad combination!!! Do not fight with your batteries, they will win 14.10.21 https://www.youtube.com/watch?v=CUgbmCSmSNY https://www.youtube.com/watch?v=buNm9Xyabxg Mondragon Unibertsitatea 57 Electrochemical ESS – Charge and discharge Is there any fixed process for charging and discharging batteries? 14.10.21 Mondragon Unibertsitatea 58 Charging process – CC + CV Although there are different charging profiles, the most common profile to charge a li-ion cell is the CC+CV charge, constant current and constant voltage charge. There are battery chargers for li-ion batteries depending on their voltage and nominal capacity. In our labs, typically lab power supplies are used. (How to configure a power supply to charge a battery, look at the datasheet of a cell) 14.10.21 Mondragon Unibertsitatea 59 Discharging process It is mandatory to cut the discharge current when the voltage of the cell reaches a certain value, the end voltage, end of discharging voltage…. If not the cell can be damaged irreversibly or even can fail. Depending on the current discharged and the internal resistance, the amount of energy we can obtain is different. 14.10.21 Mondragon Unibertsitatea 60 Electrochemical ESS What about the batteries of the future? 14.10.21 Mondragon Unibertsitatea 61 Electrochemical ESS – Future trends 14.10.21 Mondragon Unibertsitatea 62 Eskerrik asko Muchas gracias Thank you Unai Iraola uiraola@mondragon.edu
