Patent Application
20140178602
This invention relates to lithium ion battery cathodes, and more particularly to methods for making solid state lithium ion battery cathodes.
The current methods of producing all-solid-state lithium ion batteries are only suited for small-scale, low power cells and involve high-temperature vacuum techniques. Baseline LiNixMnyCozAl1−x-y-zO2 (NMCA) and CuS/Cu2ZnSn(S,Se)4 (CZSS) cathode nanoparticle films were deposited onto aluminum and stainless steel substrates using a streaming process for electroless electrochemical deposition (SPEED) developed by Planar Energy Devices Corporation (Orlando, Fla.). The Oak Ridge National Laboratory (ORNL) has additionally shown in prior work that advanced photonic processing can be used to anneal conventionally coated cathode metal oxide structures into the active crystalline phase. Planar Energy Devices has also demonstrated SPEED with solid electrolyte layers consisting of LiGaAlSPO4.
All-solid-state lithium ion batteries are important to automotive and stationary energy storage applications because they would eliminate the problems associated with the safety of the liquid electrolyte in conventional lithium ion batteries and allow for use of lithium metal anodes. However, all-solid-state batteries are currently produced using expensive, energy consuming vacuum methods suited for small electrode sizes. Solid-state transition metal oxide cathode and electrolyte layers currently require about 30-60 minutes at 700-800° C. vacuum processing conditions.
A method of making a cathode for a battery includes the steps of depositing a precursor cathode film having a first crystallinity profile. The precursor cathode film is annealed by irradiating the precursor cathode film with from 1 to 100 photonic pulses having a wavelength of from 200 nm to 1600 nm, a pulse duration of from 0.01 μs to 5000 μs and a pulse frequency of from 1 nHz to 100 Hz. The photonic pulses are continued until the precursor cathode film has recrystallized from the first crystallinity profile to a second crystallinity profile.
The first crystallinity profile can be an amorphous phase. The wavelength of the pulses can be from 200 nm to 1200 nm. The pulse duration can be from 50 μs to 5000 μs. The pulse frequency can be from 0.1 Hz to 100 Hz. The irradiating step can comprise from 1 to 50 pulses. The pulse frequency can be from 1 mHz to 10 Hz. The intensity of the pulses can be between 0.1 J/cm2 and 20 J/cm2.
The pulses can be applied in a programmed irradiation step with at least two different pulse durations. The pulses can be applied to the cathode material in at least one step with each step containing at least one pulse.
The method can further comprise a stabilization step comprising applying a pulse to the cathode material, the pulse selected to remove impurity contents. The impurity contents can comprise at least one selected from the group consisting of carbonates, sulphates, nitrates, water, and organic solvent residue. The cathode material in one aspect does not change phase from the first crystallinity profile to a second crystallinity profile.
The cathode material can have a thickness of from 0.1 to 100 μm. The cathode material can have a thickness of from 10 to 20 μm.
The pulse duration can be ramped upward in increments of between 50 and 500 μs during the irradiating step for cathode film heating. The pulse duration can be ramped downward in increments of between 50 and 500 μs after the primary irradiating step for cathode film cooling.
The cathode film can be at least one selected from the group consisting of LiNixMnyCozAl1−x-y-zO2 (NMCA), LiCoO2, LiNiO2, LiMn2O4, LiFePO4, LiMnPO4, LiFexMn1−xPO4, LiNixMnyCo1−x-yO2, and Cu2ZnSn(S,Se)4. The cathode film can comprises CuS/Cu2ZnSn(S,Se)4 (CZTS).
The cathode film can be subjected to a stabilization step prior to the irradiating step. The stabilization step can comprise heating the cathode film to between 200-400° C. for from 5 to 30 min. The stabilization step can be completed with photonic irradiation at low energy density of 0.1-5.0 J/cm2.
The precursor cathode film can be deposited by a deposition process selected from the group consisting of streaming process for electroless electrochemical deposition (SPEED), chemical vapor deposition, and physical vapor deposition.
At least one of the wavelength, pulse duration, and pulse intensity can be varied during the irradiating step according to a predetermined annealing protocol. The annealing step can comprise a first pre-crystallization annealing step and a full crystallization annealing step.
The photonic pulse can be created by a photonic pulse generator. The voltage of the photonic pulse generator can be from 220 to 270V for the pre-crystallization annealing step, and from 300V to 500V for the full crystallization annealing step. The total energy absorbed during each annealing step can be from 0.2 J/cm2 to 2000 J/cm2.
The battery can be a solid state battery. The battery can be a lithium ion battery.
The depositing step can comprise forming a substantially alkali-free first solution comprising at least one transition metal and at least two ligands; spraying the first solution onto the substrate while maintaining the substrate at a temperature between about 100 and 400° C. to form a first solid film containing the transition metal on the substrate; forming a second solution comprising at least one alkali metal, at least one transition metal, and at least two ligands; spraying the second solution onto the first solid film on the substrate while maintaining the substrate at a temperature between about 100 and 400° C. to form a second solid film containing the alkali metal and at least one transition metal; and heating to a temperature between about 300 and 1000° C. in a selected atmosphere to react the first and second films to form a homogeneous cathode film.
The photonic pulses can be laser pulses. The photonic pulses can alternatively be produced by a spread spectrum pulse generator. The method can further comprise the step of filtering the photonic pulses to permit the passage of only selected wavelengths. The photonic pulses can irradiate an area of the precursor cathode film greater than 1 cm2 in a single pulse.
There is shown in the drawings embodiments which are presently preferred, it being understood, however, that the invention can be embodied in other forms without departing from the spirit or essential attributes thereof.
A method of making a cathode for a battery includes the steps of depositing a precursor cathode film having a first crystallinity profile. The precursor cathode film is annealed by irradiating the precursor cathode film with from 1 to 100 photonic pulses having a wavelength of from 200 nm to 1600 nm, a pulse duration of from 0.01 μs and 5000 μs and a pulse frequency of from 1 nHz to 100 Hz. The photonic pulses are continued until the precursor cathode film has recrystallized from the first crystallinity profile before photonic treatment to a second crystallinity profile after photonic treatment.
The first crystallinity profile can be an amorphous phase. The first crystallinity profile can also be a mixed profile of amorphous regions and crystalline regions. In one aspect the first crystallinity profile comprises at least 10% amorphous regions, by volume. The second crystallinity profile should have no more than 50% amorphous regions and should be further characterized by X-ray diffraction to determine the extent of recrystallization from the first crystallinity profile. The second crystallinity profile can be at least 50%, 60%, 70%, 80%, or at least 90% more crystalline than the first crystallinity profile, as determined by XRD peak height and width analysis of the primary diffracting peaks of the cathode active material. For example, the second crystallinity profile can have a 50% greater peak height and/or a 50% lower full-width half-maximum distance for LiNixMnyCo1−x-yO2 at 2θ≈8.5° for Mo Kα radiation than does the first crystallinity profile. The cathode material in one aspect does not change phase from the first crystallinity profile to a second crystallinity profile.
The wavelength of the pulses can vary between the range of 200 nm and 1600 nm. The wavelength of the pulses in one aspect can vary between any low value and any high value within this range. The wavelength of the pulses can, for example, be from 200 nm to 1200 nm.
The pulse duration can vary between the range of 0.01 μs and 5000 μs. The pulse duration in one aspect can vary between any low value and any high value within this range. The pulse duration can, for example, be from 50 μs to 5000 μs.
The pulse frequency can vary between the range of from 1 nHz to 100 Hz. The pulse frequency in one aspect can vary between any low value and any high value within this range. The pulse frequency can, for example, be from 0.1 Hz to 100 Hz. The pulse frequency can be from 1 mHz to 10 Hz.
The intensity of the pulses can vary. The intensity of the pulses can be between 0.1 J/cm2 and 20 J/cm2. The intensity of the pulses in one aspect can vary between any low value and any high value within this range.
The irradiating step can comprise any number of pulses within the range of 1 to 100. The number of pulses in one aspect can vary between any low value and any high value within this range. The number of pulses can, for example, be from 1 to 50 pulses.
The pulses can be applied in a programmed irradiation step with at least two different pulse durations. The pulses can be applied to the cathode material in at least one step with each step containing at least one pulse.
The method can further comprise a stabilization step that heats the cathode material to remove impurity contents. The cathode film can be subjected to the stabilization step prior to the irradiating step. The stabilization step can comprise heating the cathode film to between 200-400° C. for from 5 to 30 min. The stabilization step can be completed with photonic irradiation at low energy density of 0.1-5.0 J/cm2. The impurity contents can comprise at least one selected from the group consisting of carbonates, sulphates, nitrates, water, and organic solvent residue.
The thickness of the cathode material can vary. The cathode material in one aspect can have a thickness of from 0.1 to 100 μm. The cathode material in another aspect can have a thickness of from 10 to 20 μm.
The pulse duration can be ramped upward in increments of between 50 and 500 μs during the irradiating step for cathode film heating. The pulse duration can be ramped downward in increments of between 50 and 500 μs after the primary irradiating step for cathode film cooling. Other ramping protocols are possible.
The cathode film can be at least one selected from the group consisting of LiNixMnyCozAl1−x-y-zO2 (NMCA), LiCoO2, LiNiO2, LiMn2O4, LiFePO4, LiMnPO4, LiFexMn1−xPO4, LiNixMnyCo1−x-yO2, Li1+xNiyMnzCo1−x-y-zO2, and Cu2ZnSn(S,Se)4. The cathode film can comprise CuS/Cu2ZnSn(S,Se)4 (CZTS).
The precursor cathode film can be deposited by a deposition process selected from the group consisting of streaming process for electroless electrochemical deposition (SPEED), chemical vapor deposition, and physical vapor deposition. The SPEED process is described in Oladeji U.S. Pat. No. 7,776,705 (Aug. 17, 2010) and Oladeji US Pub 2012/0137508 (Jun. 7, 2012), the disclosures of which are incorporated fully by reference.
The depositing step can comprise forming a substantially alkali-free first solution comprising at least one transition metal and at least two ligands; spraying the first solution onto the substrate while maintaining the substrate at a temperature between about 100 and 400° C. to form a first solid film containing the transition metal on the substrate; forming a second solution comprising at least one alkali metal, at least one transition metal, and at least two ligands; spraying the second solution onto the first solid film on the substrate while maintaining the substrate at a temperature between about 100 and 400° C. to form a second solid film containing the alkali metal and at least one transition metal; and heating to a temperature between about 300 and 1000° C. in a selected atmosphere to react the first and second films to form a homogeneous cathode film.
At least one of the wavelength, pulse duration, and pulse intensity can be varied during the irradiating step according to a predetermined annealing protocol. The annealing step can comprise a first pre-crystallization annealing step and a full crystallization annealing step. The annealing step can be preceded by a pre-heating, or stabilization, step, wherein the sample is heated to generate the first crystalline phase (conversion from purely amorphous precursor precipitates) and remove excess physisorbed solvents (such as water from the atmosphere). The stabilization step may be done in one or two parts: it may be thermally heated in an oven or on a hot-plate only, it may be done with pulse thermal processing at low energy and power, or both. The pre-heating or stabilization step heats the cathode surface to lower temperatures than the first pre-crystallization annealing step or the full crystallization annealing step, in one aspect between about 300-400° C. The advantage of using pulse thermal processing is that the chemisorbed water may also be removed from the cathode surface.
The first pre-crystallization annealing is conducted at higher energy and power than the stabilization step to minimize any stress buildup or stress induced cracks or defects in the thin film layer. The energy of the pre-crystallization annealing step can be between 0.1 J/cm2 and 10 J/cm2. The power of the first pre-crystallization step can be between 0.5 kW/cm2 and 5 kW/cm2. The full crystallization annealing is conducted at still higher energy and power to densify the thin film microstructure and induce the desired crystalline phase (full recrystallization) for high performance battery development. The energy of the full-crystallization annealing step can be between 1 J/cm2 and 20 J/cm2. The power of the first full-crystallization step can be between 1 kW/cm2 and 20 kW/cm2.
The photonic pulse can be created by a photonic pulse generator. The voltage of the photonic pulse generator can be from 220 to 270V for the pre-crystallization annealing step, and from 300V to 500V for the full crystallization annealing step. The total energy absorbed during each annealing step can be from 0.2 J/cm2 to 2000 J/cm2. The total energy absorbed during each annealing step can range from any low value to any high value within this range.
The battery can be a solid state battery. The battery can be a lithium ion battery. The application can be automotive, grid storage, consumer electronics, energy harvesting, low-power sensors, smart cards, or any other application requiring chemical energy storage. The size of these lithium ion cells may be from 1 μAh to 100 Ah and may operate between 2.0 V to 5.0 V.
Different photonic pulse generators can be utilized. A suitable photonic pulse generator will be capable of generating the desired characteristics of the photonic pulses, which can be any value between from 1 to 100 photonic pulses, having a wavelength of from 200 nm to 1600 nm, a pulse duration of from 0.01 μs to 5000 μs, a pulse frequency of from 1 nHz to 100 Hz, and a pulse intensity of between 0.1 J/cm2 and 20 J/cm2.
Different materials will respond advantageously to different pulse characteristics. Some materials will respond preferentially to UV (approximately 200-400 nm), some will respond best to pulses in the visible spectrum (approximately 400-700 nm), while other materials will respond to pulses in the infrared (IR) portion of the spectrum (approximately 700-1600 nm). NMCA, for example, responds best to blue light and far UV. The photonic pulse generator can be a laser with a relative narrow photonic pulse spectrum. In another aspect, the pulse generator can be a spread spectrum photonic pulse generator. A spread spectrum photonic pulse generator as used herein means a photonic pulse generator that is capable of generating single photonic pulses comprised of wavelengths separated by at least 100 nm. For example, a photonic pulse centered at 800 nm would include wavelengths of less than 750 nm and also wavelengths of more than 850 nm, as well as wavelengths between 750-800 nm. One such spread spectrum photonic pulse generator is a plasma arc lamp.
An advantage of a spread spectrum pulse source is that filtering methods can be utilized to deliver to the material preferential wavelengths while filtering out unwanted wavelengths from the spectrum of wavelengths that are produced by the pulse generator. Such filtering can be accomplished with known equipment and without the need to change the more expensive pulse generator itself. Also, spread spectrum sources such as plasma arc lamps are capable of delivering pulses to a much wider area than is possible with a laser. For example, a plasma arc pulse generator can deliver a single pulse to cover an area or spot size of greater than at least 1 cm2, 10 cm2, or 1 m2 without redirecting the photonic pulse source.
A suitable photonic pulse generator is the PulseForge 3300 (Novacentrix, Austin Tex.) with capability of 170-750V set point (10 W/cm2 and 0.21 J/cm2 to 49 kW/cm2 and 2.47 J/cm2 output). Another suitable pulse generator is the plasma arc lamp manufactured by Vortek Industries Ltd (Vancouver, Canada) with capability of up to 1000 A set point, peak power density of 20 kW/cm2, and a wide range of thermal processing time (0.001 s to 30 s) (Vortek-300 kW and Vortek-750 kW).
A number of examples were prepared. Table 1 shows the initial NMCA samples annealed with the PulseForge 3300 using the continuous web mode with constant pulse frequency. The slower the web speed, the higher the number of pulses the samples were exposed to. These initial samples were used to establish the extent of recrystallization that could be achieved with a different number of pulses at maximum power. Table 2 shows the initial NMCA sample annealing conditions used for the Vortek plasma arc lamp. Several different current set points were used up to the maximum level of 1000 A to establish the extent of recrystallization that could be achieved at different energy intensities. Table 3 shows annealing conditions for NMCA samples processed at low energy intensity using the Vortek plasma arc lamp.
Table 4 shows energy and power density annealing conditions for a scan of the full range of PulseForge 3300 voltage set points for NMCA samples, and Table 5 shows a refined set of annealing conditions for NMCA samples between 220-305 V. The latter table was used for subsequent development of the first programmed set point protocols with the PulseForge 3300, which consisted of a single voltage plateau at lower energy and power conditions.
Table 6 shows the annealing conditions used for the Vortek plasma arc lamp for low power and energy NMCA sample processing where a hot-plate preheating (stabilization) step was implemented during the annealing step. This preheating step was found to be particularly necessary for removing adsorbed water inside the pores of the NMCA films.
Table 7 shows annealing conditions for the PulseForge 3300, which were used for NMCA sample damage threshold experiments (to determine how high the voltage set point and energy intensity exposure could be). Table 8 shows the annealing conditions used to verify the effectiveness of long pulse durations using the PulseForge 3300 and for further development of the first generation of programmed annealing protocols. These samples were compared to baseline samples 114 and 121 processed with the Vortek plasma arc lamp at 1000 A and 800 A, respectively. Tables 9-11 show the first, second, and third generations, respectively, of PulseForge 3300 programmed annealing protocols for NMCA samples using single voltage plateaus and long pulse durations. The major variables in these protocols were the voltage set point and number of pulses. Table 12 shows the programmed annealing conditions for the PulseForge 3300 where gradual sample heating (using pulse thermal processing) and gradual cooling (after pulse thermal processing at the maximum voltage plateau) was implemented. This advancement was used to prevent thermal shock and film cracking before and after the high energy exposure at the maximum voltage set point where NMCA recrystallization occurs. Table 13 shows the annealing conditions for the PulseForge 3300 where programmed protocols (implementing the advancements described in Tables 9-12) were used with even higher numbers of pulses at maximum voltage and duration. Finally, Table 14 shows the incorporation of all findings described in Tables 9-13 plus the addition of multiple voltage plateaus, i.e. the addition of set points where the voltage is increased for the previous plateau for a specified number of pulses at maximum duration.
The invention replaces physical vapor deposition (PVD) and high-temperature furnace annealing with room-temperature atomized spray deposition and photon-based pulse thermal processing (annealing). The processing of the invention involves minutes of room-temperature deposition and <1 min of photon exposure.
Adsorbed water can cause spallation of the NMCA films during annealing. A pre-heating stabilization step for 5-30 min at 200-400° C. can be implemented. The heat source can be left on during annealing step. Spallation was alleviated.
The following photonic processing protocols were utilized for cathode recrystallization (“single plateau” protocol):
Samples decrease in Li2CO3 and increase in Li(NixMnyCozAl1−x-y-z)O2 (NMCA) peak height with photonic processing according to the invention. Samples 122 and 123 show the best recrystallization.
The microstructure and electrical performance of the cathode material and the battery strongly depends on the PTP processing conditions. The key PTP process variables for low thermal budget annealing of the thin films are as follows: applied voltage, pulse duration, and number of pulses. In addition, the PTP system allows the creation of a sequence of pulses with varying amplitude and duration to control the thermal profile for the development of high quality thin films. The impact of the PTP processing conditions on the microstructure of thin films was analyzed by x-ray diffraction technique.
These samples were assembled into batteries and tested as indicated below:
D=7.14 mm; Area=0.4 cm2
Current: The current was set at 0.133
mA based on the electrode solid
loading to match the c-rate from the
cells tested at Planar Energy.
Half cells with samples 198-200 and 204-205 were assembled and tested with the same procedure and protocol as those in [00071] except that the area of electrode was 0.9 cm2 instead of 0.4 cm2 and the current was set at 30 μA.
FIG. 13 is a plot of discharge capacity (μAh/cm2) vs. cycles at 0.30 between 3.0 and 4.8 V for several samples. The samples tested were 198, 199, 200, 204, 205, 209 and 214. Samples 209 and 214 exhibited negligible capacity. Significant improvement was observed in samples 198, 199 and 204.
The chemical composition uniformity was preserved after annealing. In the examples identified below the samples were treated with pulses from a Vortek plasma arc lamp. The nominal composition of “15% Ni” sample is Li(Ni0.15Mn0.75CO0.05Al0.05)O2. The Ni:Mn:Co:Al surface ratio was found to be 5:13:1:1, which is slightly Ni rich and Mn deficient. The surface Li:Ni, Li:Mn, Li:Co, and Li:Al ratios were 4:1, 1.4:1, 18:1, and 18:1, respectively. The Li:O ratio was about 1:3 including surface adsorbed O.
Summary table of XPS compositional uniformity
This invention can be embodied in other forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be had to the following claims rather than the foregoing specification as indicating the scope of the invention.
This invention was made with government support under contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in this invention.
