NOVELTY - An electrochemical thermodynamic measurement system (100) comprises a device (110) to measure open circuit voltages of electrochemical cell (115) as function of time; a composition controller (120) electrically connected to the cell; a temperature controller (130) in thermal contact with the cell; and an open circuit voltage analyzer (140). The analyzer receives the open circuit voltage measurements from device; and identifies open circuit voltages for thermochemically stabilized conditions of the cell, for selected cell temperature and composition combinations established by controllers.    USE - For thermodynamically evaluating an electrochemical cell having electrodes, such as fuel cell, photovoltaic cell, primary and secondary batteries e.g. lithium ion battery, electrochemical double layer capacitor and electrochemical double layer supercapacitor; for predicting capacity, specific energy, power, cycle life, cell voltage, stability or discharge current of the electrochemical cell; for assessing the composition, morphology, phase or physical state of the electrodes of electrochemical cell; for identifying surface defects, bulk defects or crystal structure defects in the electrodes; for identifying a phase transition in the electrodes; and for characterizing the electrochemical cell or a component of the electrochemical cell by determining changes in entropy, enthalpy or free energy for reactions at the electrodes (claimed); useful for thermodynamically evaluating an electrochemical cell including primary and secondary batteries such as lithium ion batteries, zinc-carbon batteries, zinc-manganese oxide alkaline batteries, lithium ion polymer batteries, lithium batteries, nickel cadmium batteries, nickel-metal hydride batteries, lead acid batteries and nickel hydrogen batteries; useful for thermodynamically evaluating electrochemical system such as gas electrodes, electrochemical sensors, catalysis materials, corrosion systems, electro-deposition systems and electrosynthesis systems; and useful for thermodynamic evaluating and analyzing of electrodes (e.g. carbon electrodes, nanostructure metal oxide electrodes and nano-phosphate electrodes), and electrode material including intercalating electrode materials.    ADVANTAGE - The measurement system accurately characterizes thermodynamic and materials properties of electrodes and electrochemical energy storage and conversion systems; simultaneously collects a suite of measurements characterizing several interconnected electrochemical and thermodynamic parameters relating to the electrode reaction state of advancement, voltage and temperature; provides enhanced sensitive characterization of the composition, phase and materials properties important for design and performance of electrodes in electrochemical systems; provides enhanced sensitivity combined with measurement conditions that reflect thermodynamically stabilized electrode conditions; provides very accurate measurement of thermodynamic parameters including state functions such as the Gibbs free energy, enthalpy and entropy of electrode or electrochemical cell reactions, that enable prediction of important performance attributes (e.g. energy, power density, current rate and the cycle life of an electrochemical cell) of electrode materials and electrochemical systems; and enables measurement of thermodynamic state functions with an accuracy that enables identification of major or small phase transformations, which may be difficult to detect via conventional means such as x-ray diffractometry or simple open-circuit cell potential measurements.    DETAILED DESCRIPTION - An electrochemical thermodynamic measurement system (100) comprises a device (110) for measuring open circuit voltages of an electrochemical cell (115) as a function of time; a composition controller (120) electrically connected to the electrochemical cell; a temperature controller (130) in thermal contact with the electrochemical cell; and an open circuit voltage analyzer (140). The composition controller establishes several, selected electrochemical cell compositions. The temperature controller establishes several, selected electrochemical cell temperatures for each of the selected cell compositions, to establish several selected electrochemical cell temperature and composition combinations. The open circuit voltage analyzer receives the open circuit voltage measurements from the device; and identifies open circuit voltages for thermochemically stabilized conditions of the electrochemical cell for the selected electrochemical cell temperature and composition combinations. The open circuit voltage analyzer is a processor, which executes an algorithm to calculate observed rates of change in open circuit voltage per unit time for the selected electrochemical cell temperature and composition combination using the open circuit voltage measurements. The device measures the open circuit voltages of the electrochemical cell with an accuracy within 1 mV. The temperature controller establishes selected electrochemical cell temperatures with an accuracy of greater than or equal to0.1degreesK.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic diagram of an electrochemical thermodynamic measurement system.    electrochemical thermodynamic measurement system (100)    device for measuring open circuit voltages (110)    electrochemical cell (115)    composition controller (120)    temperature controller (130)    open circuit voltage analyzer. (140)