Prediction: If for a given battery, rechargeable or otherwise, Lithium-Ion or otherwise, energy is drained via a pulsed DC (alternating) frequency (think LC coil) rather than direct DC, and if this frequency is switched at regular intervals (let's say at least once a second) -- then the battery should drain slower at a given current level -- than via direct DC (at the same current level) alone...
Reason: Everything in the universe, including metals, including metal oxides, resonate at given (asymmetric, in the case of two or more different substances) frequencies. Electricity is what naturally seeks the balance between those things. But if you disrupt/interrupt the way Nature flows her electricity and keep doing this quickly, over a long period of time, you'll preserve (for a longer period) the asymmetry that allows the electricity to exist in the first place!
I'll bet a 5% longer lifetime out of any battery could be realized -- by "switching it up" -- the frequency (using Pulsed DC) at which the device is drained, that is!
Depending on the application and how far you want to discharge them, Li-ion batteries generally can transfer more charge when drained with DC. Each battery chemistry has different impedance curves.
Higher impedance means more voltage drop will occur across the internal impedance of the cell while trying to pull current. For an equivalent average power, pulses will have to be higher current than a constant DC.
If you pulse the battery, and it is at a low state of charge where the impedance is high, the battery voltage will effectively "droop" and your system may brown out. This means you have to shut down before you've been able to fully discharge.
So pulsed power delivery does not necessarily improve efficiency.
>Depending on the application and how far you want to discharge them, Li-ion batteries generally can transfer more charge when drained with DC
This might very well be true -- but let's hold off on stating things exactly this way, until we've reviewed some fundamentals...
First off, we have a series of different things that "flow" (for lack of a better term) through a wire, when a circuit (in this case, with a battery as the power source) is shorted/closed/"has an electrical load put on it, etc.
First is voltage. Voltage is near-instantaneous. Next is Current. Current is near-instantaneous too -- but it is or should be slower than Voltage. Next is Magnetism, the magnetic field created by the flow of Current. Again, very fast, but should be slower than Current (the Magnetic field is still forming around the conductor in the instant of time that the conductor reaches maximum current -- in fact, it could be argued that Nature is trying to balance the "flow" of Current one way, with the "flow" of a Magnetic field the other...
Next is Heat. Now, heat may not flow at all, if the current carrying capacity of the conductor in question is not overloaded. But if it is, then heat will flow next. Heat is the last fast / most slowest thing that flows down a conductor, if it flows at all.
But the main point is, all of these various different phenomena associated with Electricity -- all flow at different rates of speed (if only by an instant!), that is, one lags behind the other...
Now, the idea that you're going to get more current out of a Li-ion battery when "drained with DC" (Is there any other way to drain it? Pulsed DC is still DC, albeit with a virtual on/off switch that is switched on/off many times per second -- up to millions of times... the cycle time of that being the frequency that I allude to...) is well, dependent on a lot of factors, for example, the battery's impedance, which you allude to next:
>Each battery chemistry has different impedance curves.
Exactly!
But what do you learn in Electrical Engineering 101?
That you the maximum power transfer in a circuit -- when the impedance between the sender and the receiver -- is perfectly matched!
(Because well, otherwise, fundamentally, impedance = "a type of" resistance (if not exactly matched!))
But, there's even more to all of this in batteries!
That's because there is not one circuit in a battery (the circuit between the + and - terminals of the battery!) -- but actually between the interface of the different metals and electrolytes!
That "second circuit" -- is usually not considered as a circuit, because it's sort of hidden, it's sort of not used (and how would you as the user of a battery access it and modify it anyway? It's deeply embedded in the design and construction of the battery! Without the ability to unravel the battery, and sandwich some other material in it, and roll it back up again, it's a circuit that in general, we (the user of the battery!) cannot touch; cannot modify!
In fact, one might go as far as comparing the outside, modifyable circuit between the battery's terminals as the "far field", and the inside, generally speaking non-modifyable circuit (between the battery's different metals eletrolytes) as the "near field":
But you see, it's not just the impedance of the battery!
It's the impedance of the battery's "near field" -- as compared to it's "far field" (the usual circuit between its terminals!)... which brings us to your statement:
>Higher impedance means more voltage drop will occur across the internal impedance of the cell while trying to pull current.
Absolutely correct!
But let's add an extra statement to that sentence for conciseness:
>Higher impedance means more voltage drop will occur across the internal impedance of the cell while trying to pull current, IF AND ONLY IF THE IMPEDANCE IS MISMATCHED -- WHICH IT WILL BE IN MOST CIRCUITS!
So, you're right... but I prefer that you be "extra extra right, extra extra concise" -- hence my teensy weensy, relatively insignificant addition to your statement! <g>
>So pulsed power delivery does not necessarily improve efficiency.
Again, absolutely correct for most cases!
Here's the other thing...
You see, most people in the world today -- assume that power/amperage/current -- is energy, that is, if you have it, then you've got power, and if it's not there, then you don't, and that when a battery loses power, that the power/amperage/current -- goes down because "the battery is losing energy"...
But you see, what if it was the other way around?
What if what we're calling energy (aka, power/amperage/current) -- is actually caused by the temporary destruction (again, for lack of a better term) -- of a higher symmetry? That the power/current/amperage -- while it flows, is really just the Universe "repairing" (aka "balancing") that broken symmetry?
In other words, as that broken symmetry gets more and more "fixed"/"balanced" (for lack of a better term) -- that current/power/what we're calling "energy" -- becomes less and less?
Now, I couldn't prove that to anybody -- at least without some very sensitive tools -- but you see, what exists as low-frequency (or no-frequency, DC) "power" at one level -- should exist as super-high-frequency, super-high-voltage, yet super-low amperage/"power" -- as a battery gets progressively "drained".
In other words, nature seeks equilibrium, and equilibrium exists as super-high-frequency, super-high-voltage, at ridiculously low amperages (aka "no power" -- unless you can rectify it -- which becomes increasingly harder to do the higher the frequency).
In the case of choosing a pulsed DC drain for an arbitrary battery, we're simply allowing part of the voltage/current/magnetic field/and possibly heat -- to dissipate and reset, that is, give the chemical reaction that is driving the whole thing a break, if only for an instant in time -- by turning the circuit on and off (maybe think of it like antilock brakes?) -- in hopes of preserving that chemical reaction a bit longer...
Do it wrong (which will probably be the case 99% of the time) -- and no, there's no efficiency improvement...
But do it right, and maybe someone could prevent a teeny bit of electrical loss from a battery, rechargeable or otherwise, Li-ion or otherwise...
Now, perhaps I'm wrong about any/all of the above...
But, I'd argue that it is a rich, very rich, super-rich area -- for more experiments by researchers...
Prediction: If for a given battery, rechargeable or otherwise, Lithium-Ion or otherwise, energy is drained via a pulsed DC (alternating) frequency (think LC coil) rather than direct DC, and if this frequency is switched at regular intervals (let's say at least once a second) -- then the battery should drain slower at a given current level -- than via direct DC (at the same current level) alone...
Reason: Everything in the universe, including metals, including metal oxides, resonate at given (asymmetric, in the case of two or more different substances) frequencies. Electricity is what naturally seeks the balance between those things. But if you disrupt/interrupt the way Nature flows her electricity and keep doing this quickly, over a long period of time, you'll preserve (for a longer period) the asymmetry that allows the electricity to exist in the first place!
I'll bet a 5% longer lifetime out of any battery could be realized -- by "switching it up" -- the frequency (using Pulsed DC) at which the device is drained, that is!