On-vehicle algorithms to determine if lithium plating has occurred

A method of charging a lithium-ion battery cell which comprises (i) a first electrode formed of a porous layer of particles of graphite, the first electrode functioning as a negatively-charged anode during discharge of the battery cell, at least a portion of the particles of graphite being characterized by the presence of LiC6 when the battery cell is in a charged state, the graphite particles being depleted of LiC6 as the battery cell is being discharged, (ii) a second electrode physically separated from the first electrode and being formed of an electrode material electrochemically compatible with the graphite particles, the second electrode functioning as a cathode during discharge of the battery cell and (iii) an electrolyte solution comprising mobile lithium ions, the electrolyte solution being in contact with both electrodes, the charging method comprising:

• applying a predetermined direct current charging-potential for a predetermined period of time between the first and second electrodes so as to direct lithium ions in the electrolyte solution into contact with the graphite particles of the first electrode for the purpose of reacting lithium ions with electrons on the graphite particles and forming LiC6 in the graphite particles;
• terminating the charging current and placing the lithium-ion battery cell in an open-circuit state;
• measuring, over a first predetermined period of time (t, in seconds) of the open-circuit state, at least one of (i) the open-circuit cell voltage (Vcell) and (ii) the voltage of the negative electrode vs. a lithium metal reference electrode (Vneg) to obtain a voltage curve vs. time for Vcell or Vneg;
• determining a cubic polynomial fit of the open-circuit voltage data with time values during the time period, with the square root of the sum of the squared difference between the fit polynomial and the data, normalized by the number of data points, set equal to the standard deviation in the voltage measurement process, allowing for the appropriate selection of the window size of data to be included for a windowed polynomial regression or the smoothing parameter in a smoothing spline regression;
• preparing a derivative curve of the cubic polynomial fit for dVcell/dt or dVneg/dt;
• examining the derivative data collected over the specified time period to determine whether the data presents a smooth curve or a curve with a local maximum or minimum, the smooth curve indicating the absence of lithium plating, a curve with a local maximum or minimum indicating the presence of lithium plating;
• and, thereafter,
• using the derivative data in determining the specified voltage potential or the total charging current for a subsequent of the graphite anode material.

A method of monitoring the intercalation of a metal into particles of graphite or of graphite and silicon in the anode of a battery cell during charging of the battery cell, the metal being one selected from the group consisting of lithium, magnesium, and sodium, the battery cell also comprising a cathode, separated from the anode, and a metal ion-containing electrolyte in contact with the graphite or graphite-silicon particles of the anode and with the cathode, the charging of the battery cell being accomplished by the application of (i) a specified voltage potential applied to the anode and cathode and (ii) a specified total charging current, carrying metal ions to the graphite or graphite-silicon particles for the purpose of incorporating the metal into the graphite or graphite silicon particles, the purpose of the monitoring method being to detect the unwanted plating of the metal on the anode particles, the monitoring method comprising:

• maintaining the battery cell in an open-circuit state for a specified time period following the charging of the battery cell;
• and during the time period,
• measuring the open-circuit cell voltage (Vcell) at predetermined periods of time;
• determining a cubic polynomial fit of the open-circuit voltage data with time values during the time period;
• determining the derivative of the cubic polynomial fit of the open-circuit cell voltage with time (dVcell/dt, mV/s);
• examining the derivative data collected over the specified time period to determine whether the data presents a smooth curve or a curve with a local maximum or minimum, the smooth curve indicating the absence of metal plating, a curve with a local maximum or minimum indicating the presence of metal plating;
• and, thereafter,
• using the derivative data in determining the specified voltage potential or the total charging current for a subsequent intercalation of the metal into the graphite or graphite-silicon particles of anode material.