CA3219323A1 - Battery and electrolytes therefor - Google Patents

Abstract

A battery cell having an internal pressure, the battery cell including a first electrode, a second electrode, an electrolyte, a separator, and a conductive spacer having a rigid body and being coupled to the first electrode, the spacer being dimensioned to occupy an interior of the battery cell and increase the internal pressure of the battery cell for increasing a compression acting on the first electrode; the electrolyte for forming a solid-electrolyte interphase (SEI) in a battery cell having a lithium based chemistry, comprising: a carbonate based electrolyte, the carbonate based electrolyte for diluting a solute and a solvent having high solubility for lithium ions and film-additives; the solvent being selected for disassociating the film-additives and for forming a contact ion pair with an anion and the lithium ions.

Description

BATTERY AND ELECTROLYTES THEREFOR
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to United States Provisional Patent Application number US 63/191,003, filed May 20, 2021, the entire contents of which are hereby incorporated by reference.
FIELD

[0002] The present disclosure relates generally to batteries and electrolytes, including but not limited to lithium batteries, anode-free lithium batteries, and electrolytes therefor.
BACKGROUND

[0003] Energy storage is critical for utilizing renewable energy and eventually realizing a carbon-neutral society; high-performance energy storage devices could also enable advanced technology and improve human life quality. One example is Lithium (Li) metal batteries, which have provided profound success in powering electric vehicles and portable electronics. Lithium-ion batteries (LiBs) have dominated the market for electric vehicles and portable electronics due to their excellent cycle life and improved energy density compared with other known secondary batteries. Typical commercial LiBs consist of a Li metal oxide cathode, a polymer separator soaked with organic liquid electrolyte, and a graphite anode and possess a specific energy density of about 250 Wh/kg at the cell level.
Elemental Li has a theoretical capacity of 3860 rnAh/g that is ten times higher than that of graphite; a Li-metal battery could deliver a specific energy density as high as 500 Wh/kg, enabling applications such as electric aircraft. Emerging solid-state electrolytes (SSEs) are considered promising candidates for utilizing the Li metal anode. However, the critical current density of SSEs are still insufficient for applications that require a high cycling rate.

[0004] Nevertheless, the ever-growing demand for energy storage invokes progressive battery techniques possessing higher energy density and lower cost, especially with the advent of revolutionary new technologies such as 5G, wearable device, electric aircraft, etc. Li-metal batteries remain promising candidates for such next-generation energy storage devices due to their high energy density. However, Li-metal batteries employ a large amount of excess Li, resulting in a much lower energy density than their theoretical value. Recently, the concept of an "anode-free" Li battery has attracted wide attention, where the cathode stores all the active Li, and the Li anode is formed in-situ during charging. An anode-free Li-metal battery provides significantly higher energy density and lower cost compared with conventional Li-ion batteries. Nevertheless, the absence of a Li host at the anode side creates a tough challenge for an anode-free lithium battery to be reversibly cycled over several hundred cycles like Li-ion batteries.

[0005] Furthermore, electrolyte compositions profoundly impact electrochemical performance in Li-metal batteries. Lithium for example is highly reducing, and instantly reacts with electrolytes to form a solid-electrolyte interphase (SE) in Li-metal batteries. Due to Li's "infinite" volume change during deposition/stripping, inhomogeneity leads to breaks in the SEI and exposure of fresh Li, causing side reactions and loss of active material].
Further yet, Li dendrite usually grows upon cycling, which could penetrate the separator and entail safety concerns.

[0006] Accordingly, improvements in energy storage, including for batteries such as lithium batteries and electrolytes therefor, are desirable.
BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Embodiments will now be described by way of example only, with reference to the accompanying simplified, diagrammatic, not-to-scale drawings. Any dimensions provided in the drawings are provided only for illustrative purposes, and do not limit the scope as defined by the claims. In the drawings:

[0008] FIG. 1 is a diagram of a first battery cell (a) and a second battery cell (b) having a spacer according to an embodiment herein for increasing an internal pressure in the battery cell.

[0009] FIG. 2 illustrates a first plot (a) of Coulombic efficiency for a Li-Cu half cell according to each of the two battery cells illustrated in FIG.1; and, a second plot (b) of the corresponding voltage profiles for the two battery cells.

[0010] FIG. 3 illustrates four plots: a first plot (a) illustrating capacity retention and Coulombic efficiency of anode-free Li-metal batteries using NMC cathode (capacity ¨ 2 mAh/cm2), the electrolyte is 1M LiPF6 in EC/DEC, the cells were either charged at 0.2C and discharged at 1C or charged/discharged constantly at 0.3C, a second plot (b) illustrating Nyquist plots of the anode-free Li-metal batteries charged at 0.2C and discharged at 1C
before/after cycles, with/without an extra spacer; a third plot (c) illustrating voltage profiles of the cell without an extra spacer charged at 0.2C and discharged at 1C; and, a fourth plot (d) illustrating voltage profiles of the cell with an extra spacer charged at 0.2C and discharged at 1C.

[0011] FIG. 4 depicts two images of the microstructure of a deposited Li (2nd cycle after charging) including an inset of the corresponding copper current collector after cycling, the first image (a) illustrating an anode-free Cu-NMC cell without an extra spacer; and, the second image (b) illustrating a anode-free Cu-NMC cell with an extra spacer.

[0012] FIG. 5 is an FTIR spectrum plot of a 0-0 peak and its solvation shoulder in EC/DEC (1:1), 1M LiPF6 in EC/DEC, and 1m1 1M LiPF6 in EC/DEC mixed with lml G2.

[0013] FIG. 6 illustrates two plots: a first plot (a) illustrating 130 NMR spectra of EC/DEC (1:1), 1M LiPF6 in EC/DEC, and 1m1 1M LiPF6 in EC/DEC mixed with lml G2; and, a second plot (b) illustrating 13C NMR spectra of G2 and 1 ml 1M LiNO3 in G2 mixed with 1m1 EC/DEC.

[0014] FIG. 7 is an electrochemical impedance spectra (EIS) spectra plot of four different electrolytes.

[0015] FIG. 8 illustrates three plots: a first plot (a) illustrating Li cycling CE on Cu using CGHE, 1M LiPF6 EC/DEC (baseline), and 1m1 1M LiPF6 EC/DEC mixed + 0.3m1 G2 +
0.3g LiNO3 as electrolytes; a second plot (b) illustrating a voltage profile of Li cycling on Cu in CGHE in CGHE electrolyte at 1 mA cm-2, 2 mA cm-2, and 4 mA cnn-2; and a third plot (c) illustrating a voltage profile of Li stripping/plating in a symmetric cell using CGHE, 1M LiPF6 EC/DEC, and 1M LiNO3 in G2 as electrolytes.
[0018] FIG. 9 illustrates two plots: a first plot (a) illustrating capacity retention of Li1NCA
cells using CGHE and 1M LiPF6 EC/DEC as electrolytes cycled at 0.20 at -2100, the inset shows the digital photo of CGHE and 1M LiPF6 EC/DEC just taken out from a -21 C
environment, showing the partial crystallization of 1M LiPF6 EC/DEC; and a second plot (b) illustrating the corresponding voltage profile of the cells testing at -21 C.
[0017] FIG. 10 illustrates a plot of the capacity retention of the uncompressed cell using the baseline electrolyte, compressed cell using the baseline electrolyte, uncompressed cell using CGHE electrolyte, and compressed cell using CGHE
electrolyte.
DETAILED DESCRIPTION
[0018] For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the features illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications, and any further applications of the principles of the disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. It will be apparent to those skilled in the relevant art that some features that are not relevant to the present disclosure may not be shown in the drawings for the sake of clarity.

[0019] At the outset, for ease of reference, certain terms used in this application and their meaning as used in this context are set forth below. To the extent a term used herein is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent.
Further, the present systems and methods are not limited by the usage of the terms shown below, as all equivalents, synonyms, new developments and terms or processes that serve the same or a similar purpose are considered to be within the scope of the present disclosure.
[0020] In an aspect in accordance with the disclosure herein, is a battery cell having an internal pressure, the battery cell including a first electrode; a second electrode; an electrolyte; a separator, and a conductive spacer having a rigid body and being coupled to the first electrode, the spacer being dimensioned to occupy an interior of the battery cell and increase the internal pressure of the battery cell for increasing a compression acting on the first electrode.
[0021] In an embodiment of a battery cell in accordance with the disclosure herein, the battery cell further includes a spring coupled to the first electrode, the spring configured to modify the compression acting on the first electrode based on a spring constant of the spring.
[0022] In an embodiment of a battery cell in accordance with the disclosure herein, a thickness of the first electrode is increased to reduce the amount of unoccupied space in the battery cell, for increasing the compression acting on the first electrode.
[0023] In an embodiment of a battery cell in accordance with the disclosure herein, the spacer contacts the first electrode.
[0024] In an embodiment of a battery cell in accordance with the disclosure herein, the spacer comprises a plurality of spacers, each spacer of the plurality of spacers being directly coupled to the first electrode or the second electrode.
[0025] In an embodiment of a battery cell in accordance with the disclosure herein, the spacer comprises a first spacer and a second spacer, each of the first spacer and the second spacer being directly coupled to the first electrode or the second electrode.
[0026] In an embodiment of a battery cell in accordance with the disclosure herein, the first spacer contacts the first electrode.
[0027] In an embodiment of a battery cell in accordance with the disclosure herein, the first electrode is a cathode, and the second electrode is an anode.
[0028] In an embodiment of a battery cell in accordance with the disclosure herein, the anode is formed in-situ during a charging phase of the cathode.

[0029] In an embodiment of a battery cell of a battery cell in accordance with the disclosure herein, the battery cell further includes a current collector disposed at the anode.
[0030] In an embodiment of a battery cell in accordance with the disclosure herein, a size of the spacer is greater than or equal to a size of the current collector.
[0031] In an embodiment of a battery cell in accordance with the disclosure herein, the cathode is a Li-containing compounds.
[0032] In an embodiment of a battery cell in accordance with the disclosure herein, the spacer comprises a electrically conducting material.
[0033] In an embodiment of a battery cell in accordance with the disclosure herein, the spacer comprises stainless steel.
[0034] In an embodiment of a battery cell in accordance with the disclosure herein, the spacer has a circular profile.
[0035] In an aspect in accordance with the disclosure herein, is a battery including a plurality of battery cells in accordance with the disclosure herein.
[0036] In an aspect in accordance with the disclosure herein, is an electrolyte for forming a solid-electrolyte interphase (SEI) in a battery cell having lithium based chemistry, the electrolyte including a carbonate based electrolyte, the carbonate based electrolyte for diluting a solute and a solvent having high solubility for lithium ions and film-additives; the solvent being selected for disassociating the film-additives and for forming a contact ion pair with an anion and the lithium ions.
[0037] In an embodiment of an electrolyte in accordance with the disclosure herein, the solvent, solute, and the carbonate form a solvation structure when exposed to lithium, the solvation structure having a solvation shell comprising the solvent.
[0038] In an embodiment of an electrolyte in accordance with the disclosure herein, the carbonate based electrolyte comprises lithium hexafluorophosphate (LiPF6) and the anion disassociated by the solvent is a hexafluorophosphate anion.
[0039] In an embodiment of an electrolyte in accordance with the disclosure herein, the carbonate based electrolyte comprises the LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC).
[0040] In an embodiment of an electrolyte in accordance with the disclosure herein, the solvent is a glyme- based solvent.
[0041] In an embodiment of an electrolyte in accordance with the disclosure herein, the glyme-based solvent is diglyme (G2).
[0042] In an embodiment of an electrolyte in accordance with the disclosure herein, the solute is lithium nitrate (LiNO3).

[0043] In an embodiment of an electrolyte in accordance with the disclosure herein, the electrolyte includes LiPF6 in EC/DEC, LiNO3, and a glynne-based solvent, mixed at room temperature.
[0044] In an aspect in accordance with the disclosure herein, is a battery cell having a lithium based chemistry and an electrolyte in accordance with the disclosure herein, the battery cell including a cathode; an anode formed in situ during charging of the cathode; a separator, and a conductive spacer having a rigid body and being coupled to the cathode, the spacer being dimensioned to occupy an interior of the battery cell and increase the internal pressure of the battery cell for increasing a compression acting on the cathode.
[0045] In an aspect in accordance with the disclosure herein, is a battery comprising a plurality of battery cells having a lithium based chemistry and an electrolyte in accordance with the disclosure herein.
[0046] In accordance with the disclosure herein, one way to utilize Li-metal's full theoretical capacity would be the realization of an anode-free Li-metal battery. In such an embodiment, all the active Li-ions may initially store in the cathode materials. When charging the cell, Li-ions are extracted from the cathode and deposited on a current collector at the anode, such as a copper current collector; this process reverses during a subsequent discharge process. Apart from the improvement in specific energy density, other advantages of such an "anode-free" embodiment include lower costs, simpler manufacturing processes, and increases in the volumetric density. Preliminary calculations based on embodiments of the disclosure herein have demonstrated a 16-layer pouch anode free cell could deliver energy density of about ¨420 Wh/kg and ¨1230 Wh/L
compared to ¨290 Wh/kg and ¨750 Wh/L in a conventional graphite anode.
[0047] The absence of a Li host at the anode side creates challenges for an anode-free lithium battery to be reversibly cycled over several hundred cycles like Li-ion batteries.
For example, anode-free cell design may impose strict requirements on the Coulon-11)1c efficiency (CE); with a CE of 99%, the cell may retain less than 40% of the initial capacity after 50 cycles. Considering the CE is usually less than 90% for the first cycle, the capacity retention will worsen. Improvements in cell configurations and electrolytes, however, can address such limitations that may exist with such Li-metal batteries, anode free Li-metal batteries, or other batteries not based in lithium chemistry. Advantages of an anode-free Li-metal battery in accordance with the disclosure herein include higher energy density and lower cost compared with conventional Li-ion batteries. Other advantages include improving cell cycling life, lowering impedance, and Li deposition on the current collector.

[0048] Cell Configuration: for example, in accordance with the disclosure herein, modifying a battery cell to increase an internal pressure in the battery cell acts to compress the electrodes of the battery cell, providing improvements in charge and discharge cycle performance. For example, a normal anode-free coin cell's capacity may drop to zero within 20 cycles, while a battery cell having an increased internal pressure in accordance with the disclosure herein may retain 150 mAh g-1 at the 20th cycle, which is 87.3% of the first cycle discharge capacity. As demonstrated through electrochemical impedance spectroscopy (EIS), a compressed battery cell possesses lower bulk resistance and charge transfer resistance through the solid-electrolyte interphase (SEI). It also leads to homogeneous Li deposition free of dendrites.
[0049] FIG. 1 illustrates a first battery cell and a second battery cell in accordance with the disclosure herein. In particular, the second battery cell comprises an additional spacer coupled to an electrode, in particular to a cathode. The spacer is dimensioned to occupy an interior portion of the battery, for increasing an internal pressure of the battery cell. For example, a tightness of the fit between the spacer and surrounding components, such as between the spacer and an interior wall of the battery cell, a cathode, an anode, or other component in the cell, causes the spacer to exert a force that influences internal pressure within the battery cell. Consequently, as internal pressure in the battery cell increases, the cathode, and other battery cell components experience greater compression. The degree of pressure exerted by the spacer can be selected based on several factors that influence the fit of the spacer within the battery cell, including but not limited to, a thickness of the spacer, a density of the spacer, a rigidity of the spacer, and the material of the spacer.
Advantageously, by disposing an additional spacer within the battery cell, greater compression levels within the battery cell can be achieved without having to resort to using an apparatus external to the battery cell. In an embodiment, the battery cell is a coin cell or button cell. In an embodiment, the battery cell is a Li-metal battery cell. In an embodiment, the battery cell is anode-free lithium battery cell. Other components with the battery cell may also be modified to increase an internal pressure of the battery cell. For example, increasing a thickness of the cathode can similarly increase an internal pressure of the battery cell; or, by selecting a spring having a particular spring constant to exert a desired level of force within the battery cell.
[0050] In an embodiment disclosed herein is a battery cell comprising materials including LiNi03Mn0 iCo0102 (NMC811, referred to hereinafter as NMC); a cathode sheet having an active loading of 11.37 mg/cm2 ( 0.03 mg/cm2); 1M LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC 1:1 v/v); and lithium. The battery cell can be fabricated in an Ar-filled glovebox (Etelux). The anode-free Li-metal full cells (Cu-NMC) can be assembled in coin cells (CR2032) with the following configurations: upper case + spring + first spacer (0.9 mm) + Cu disc + separator + NMC disc (+ second spacer) +
lower case.
Similarly, the configuration for Li-Cu half cell is: upper case + spring +
first spacer + Cu disc + separator + Li disc (+ second spacer) + lower case. The diameter of Li and NMC discs was 10 mm and the Li is rolled to be 40-50 pm thick. The stainless steel spacer was 0.9 mm in thickness. The electrolyte amount used for each cell was 30 pL. The cells were pressed at 800 Psi with a hydraulic crimping machine. Such a battery cell was so fabricated by the named inventors to this application, and further subjected to cyclic tests and discussed below.
[0051]
The cyclic test (Cu-NMC full cell, Li-Cu half cell, and Li-Li symmetric cell) was carried out using a Neware BTS4000 testing station. The electrochemical impedance spectroscopy (EIS) was collected using a potentiostat (VersaSTAT 3, Princeton Applied Research) with a frequency range from 100 kHz to 1 Hz. Scanning electron microscopic (SEM) analysis of the deposited Li was conducted with Carl Zeiss supra 40. For the post-mortem analysis, deposited lithium samples were transferred to the SEM vacuum chamber while the air exposure was less than 5s.
[0052]
FIG. 1 illustrates the configuration of a typical anode-free Li-metal battery in a coin cell, including an NMC cathode disc and a Cu disc as the anode current collector, separated by a Celgard separator; and the configuration of the fabricated battery cell containing an extra spacer (0.9 mm-thick) or a spacer with different thickness or combination of more than one spacer, as described above. Regardless of the number of spacers in the cell (either one or more), the cells can be pressed by hydraulic crimping.
Each cell includes proper electrical contact and can be cycled without showing unstable charge or discharge behavior. Since all the other components in both cells are the same, most of the difference in thickness is attributed to the deformable spring.
With an extra spacer in the cell, the spring deforms more, creating a stronger force on the cell components. A similar effect can be achieved by tuning the thickness of different components, including spacer, active materials, current collector, and coin cell case or increasing the spring constant of the spring. Increasing the pressure generally improves cycling performance.
[0053]
As shown in the results illustrated in FIGS. 2-4, the increased internal pressure within the battery cell arising from a spacer as disclosed herein, increases the compression acting on the battery cell components, thereby providing performance improvements over a more conventional battery cell. To generate these results, 1 mAh/cm2 of Li was deposited on Cu at 1 mA/cm2, then stripped back until reaching 1V, and using a 1M LiPF6 in EC/DEC
(a baseline electrolyte for LiBs) in both half cell and full cell. FIG 2. plot (a) displays the Coulombic efficiency (CE), where the cell with an extra spacer can be cycled with a CE
between 80-90% for 80 cycles. In contrast, the CE of the reference cell, without an extra spacer, continuously decays until reaching zero after 70 cycles, which means no Li can be stripped back. Their corresponding voltage profiles of the 2h and 20th cycles are shown in FIG. 2, plot (b). The cell without an extra spacer delivers lower stripped capacity for each cycle and a significantly higher over-potential at the 2nd Li deposition. As made clear by the foregoing, the compactness, fit, and/or internal pressure with the battery cell impacts Li deposition/stripping. The Li used has a thickness of about 40 pm.
[0054] Further, anode-free Li-metal full cells have been assembled using NMC as the cathode and Cu foil as the current collector at the anode side. The Cu-NMC
cells with an areal capacity of 2 mAh/cm2 were cycled continually at 0.3C or with a slow charging (0.2C)/fast discharging (1C) protocol. FIG. 3 plot (a) displays the capacity retention and Coulombic efficiency (CE) of the cells either with or without an extra spacer, demonstrating dramatically different performances. Cells without an additional spacer experienced capacity declining to zero within 20 cycles. The initial CE is about 80% and undergoes a further drop after 15 cycles. In contrast, the cells with an extra spacer possess significantly higher CEs (higher than 90%). The cell charged at 0.2C and discharged at 1C
can still deliver a capacity of 29 mAh/g at the 50th cycle. The slow charging/fast discharging protocol leads to better performance than the 0.3C constant cycling. While charging, less concentration gradient results in a denser Li plating morphology; during discharging, Li tends to strip from the tips with a higher concentration gradient, which removes any dendritic structure.
[0055] Furthermore, EIS analysis was conducted with the cells charged at 0.2C and discharged at 1C. The Nyquist plots of the as-assembled cells and cycled cells are shown in FIG. 3, plot (b). The anode-free cell with an extra spacer possesses a slightly lower bulk resistance, presumably due to better contact between electrodes and the separator. Both cycled cells present one semicircle at the high-frequency end, attributable to Li-ion's migration through the solid-electrolyte-interphase (SEI). The cell without an additional spacer has higher impedance even though it was only cycled for 10 cycles. The higher resistance results from more pulverized Li and a thicker SEI indicating more Li lost during each cycle. The dead Li accumulates very fast in a cell without an additional spacer, which degrades the cell. The voltage profile for the cell without an extra spacer is shown in FIG.
3 plot (c). The first discharging capacity is 147 mAh/g, while It drops dramatically to 17 mAh/g for the 10th cycle. FIG. 3 plot (d) illustrates the charge/discharge profile of the cell with an additional spacer, indicating almost no capacity decay for the first 10th cycle (173 mAh/g for the first cycle and 178 mAh/g for the 10th cycle). The early cycling profile is almost identical with cells having excess Li at the anode side. The 20th cycle delivers 151 mAh/g, which is 87.3% of the first cycle capacity. The cell also shows less voltage polarization than the reference. Such cyclic performance could replace some primary batteries with applications in car keys, sensors, main circuit board, etc.
[0056] In order to examine Li deposition characteristics, two anode-free cells were cycled two times and charged to 4.4 V; then, they were disassembled for post-mortem analyses. FIG. 4 plot (a) presents the microstructure of the deposited Li for the cell without an extra spacer. It has inadequate Li coverage, where Li forms separate islands. Mossy structures can be found in some regions (highlighted in dashed rectangles).
Those dendritic Li reacts with electrolyte dramatically due to its high surface area. It could quickly lose contact with the current collector and become "dead" Li. By contrast, as illustrated in FIG.
4 plot (b), the cell comprising an extra spacer, Li homogeneously covers almost the entire Cu surface, and no dendrite can be observed. The insets for each of FIG. 4 plot (a) and (b) illustrate corresponding digital photos of the cycled Cu current collector.
Visual observation demonstrates that the cell without an extra spacer has an uneven distribution of Li. An additional spacer in the coin cell results in a higher compression level, which affects the deposited Li's morphology. It improves the cyclic performance from at least two aspects:
(1) the higher coverage of surface and homogeneous deposition reduces the cell internal resistance, and (2) the lower surface area of Li minimize the side reaction between Li and electrolyte, which preserves more active Li in each cycle.
[0057] Electrolyte composition: in an aspect disclosed herein is an electrolyte for improving electrochemical performance in batteries. In an embodiment, the electrolyte is a carbonate-glyme hybrid electrolyte (CGHE) compatible with both Li-metal anode and Ni-rich cathode. The electrolyte provides a unique solvation structure, in particular, diglyme (or other glyme-based solvents) solvates both Li-ions and film-forming additives, and carbonates dilute the mixture, enabling facile ion migration. Advantages realized by an electrolyte in accordance with the disclosure herein include, but are not limited to, improvements in an Li-metal battery cycled at 2C delivering a specific capacity of 99.2 mAh g-1 after 200th cycle, almost 4 times higher than a baseline electrolyte with the capacity retention of 27.0 mAh g-1. A hybrid electrolyte in accordance with the disclosure herein can support capacity retention of 73% at the 50th cycle for the cell with zero Li excess, wherein the cell with a baseline electrolyte drops to zero.
[0058] A hybrid electrolyte in accordance with the disclosure herein is suitable at least for Li-metal batteries with lean lithium excess or a completely anode-free configuration. The resulting hybrid electrolyte possesses a unique solvation structure, where diglyme (or other glyme-based solvents) dominates the primary solvation sheath of Li salt, and carbonate dilutes the mixture. The inorganic-rich SEI exhibits a remarkable passivating capability and fast ion transfer property, enabling an excellent Li cycling which has been demonstrated to achieve an efficiency of 97.66% for 100 cycles, inclusive of the initial SEI
formation cycles.
The hybrid electrolyte may also possess a lower melting point than a baseline electrolyte such as 1M LiPF6 EC/DEC (or other carbonate-based electrolytes), allowing for such battery cells to operate in more inclement temperatures. Embodiments of a battery cell in accordance with the disclosure herein may also implement both a hybrid electrolyte in accordance with the disclosure, and a battery cell configuration in accordance with the disclosure herein, for enhancing an internal pressure of the battery cell, thereby increasing a compression acting on the cell components.
[0059] Implementing metallic Li remains challenges because highly reducing Li reacts instantaneously with an electrolyte, forming a solid¨electrolyte interphase (SEI) that dictates much of a lithium-based batteries performance. Consequently, since the electrolyte components predominately determine the SEI properties, the electrolyte has a significant impact on lithium battery cell performance. Some known limitations with electrolytes include carbonate-based electrolyte which suffer from high reactivity against Li-metal while glyme-based electrolytes suffer from limited oxidation stability. In an aspect disclosed herein is a hybrid electrolyte comprising blending diglyme (G2) and lithium nitrate (LiNO3) with the commercial carbonate electrolyte (1M lithium hexafluorophosphate (LiPF6) in ethylene carbonate/diethyl carbonate (EC/DEC) (or other carbonate-based electrolytes)).
The hybrid electrolyte exhibits a unique solvation structure, wherein G2 dominates the primary solvation shell of the Li-ions. Furthermore, the G2 can completely disassociate hexafluorophosphate anions and form contact ion pairs (CIP) with lithium nitrate. As a result, the hybrid electrolyte leads to a robust inorganic-rich SEI while maintaining ionic conductivity and anodic stability. Advantageously, the hybrid electrolyte possesses better wettability with Li metal and a lower melting point. In addition to the above advantages, both LiNO3 and G2 are cost-effective and widely available, making the hybrid electrolyte disclosed herein particularly suitable for mass producing Li-metal batteries.
[0060] In an embodiment a hybrid electrolyte according to the disclosure herein includes diglyme (G2), ethylene carbonate (EC), diethyl carbonate (DEC) (or other carbonate-based electrolytes), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), and 1M LiPF6 in EC/DEC, lithium nitrate (LiNO3); and, LiNio8Mno15A100502 (hereinafter NCA) with an active material loading of 10.94 ring/crn2. In an embodiment, the carbonate-glyme hybrid electrolyte (CGHE) can be obtained by mixing 1 ml 1M
LiPFG in EC/DEC, 0.07g LiNO3, and 0.6 ml G2 at room temperature.

[0061] In an embodiment is a battery cell having a hybrid electrolyte as disclosed herein, the battery cell being a 2032-type coin cell, assembled in an Ar-filled glovebox. A
plurality of such cells were further evaluated. Coulombic efficiency (CE) of Li-metal was evaluated in Cup half cells using 20 pL of electrolyte. Li was deposited on the Cu foil at different current densities and capacities, then stripped back until reaching 1V. LilLi symmetric cells were fabricated using the same amount of Li on both sides of the cell separated by a Celgard separator, and electrochemical impedance spectroscopy (EIS) (from 100 kHz to 1 Hz), CV (from -0.2 V to 0.2 V, 1 mV/s), and stripping/plating measurements were conducted. The anode-free full cells (CuINCA) were assembled in the following configurations: upper case + spring + spacer (different thickness) +
Cu disc +
separator + cathode disc + lower case. For the LiINCA full cells, Li chips were rolled to reach a thickness of ¨40 pm used as the anode. The electrolyte amount added in the full cells (LiINCA and CuINCA) was 10 pL mAh-1. The cyclic test (LilCu half cells, LilLi symmetric cells, and LiINCA, CuINCA full cells) were carried out using a testing station. For the tests at -21 C, the cryogenic environment was created by mixing crushed ice and NaCI
at a weight ratio of 1:1. EIS measurements were performed using a potentiostat.
Furthermore, Fourier Transform Infrared (FTIR) spectral analysis was performed using Thermo-Nicolet Nexus 470 instrument. Raman spectra were recorded on a Witec alpha 300R Confocal Raman Microscope using a 532 nnn laser. 13C NMR spectra were recorded on a Bruker RDQ400 NMR (Avance III) at room temperature and the electrolyte samples were prepared by mixed with CDCI3. Scanning electron microscopy (SEM) analysis was conducted using a Carl Zeiss supra 40. The results of the FTIR and NMR further demonstrate the advantageous of the unique solvation structure developing using a hybrid electrolyte according to the disclosure herein.
[0062] FIG. 5 displays the FTIR spectra of EC/DEC (1:1), 1M
LiPF6 in EC/DEC, and the mixture of I nil 1M LiPF6 in EC/DEC and lml G2. The peak at 1262 cm-1 and 1302 cm -1 correspond to DEC's C-0 stretch and its solvation shoulder. For 1M LiPF6 in EC/DEC, the solvation peak appears at 1302 cm-1. However, with the addition of G2, the peak intensity diminishes, indicating Li + is no longer solvated by DEC. FIG. 6 plot (a) depicts the NMR
spectra of EC/DEC (1:1), 1M LiPF6 in EC/DEC, and the mixture of lml 1M LiPF6 in EC/DEC
and lml G2. Two peaks within the range of 158 ppm to 153 ppm are attributed to the carbonyl carbon in EC (left) and DEC (right), respectively. Both of the peaks shift substantially downfield for 1M LiPF6 in EC/DEC due to the coordination of EC/DEC with Li+
and their electron density moves towards Li, exhibiting less shielding effect on the nuclei of carbon and causing the resonance signal to shift to the higher field.
However, when lml G2 is introduced to lml 1M LiPF6 in EC/DEC, the two peaks shift back to their original location with pristine EC/DEC, suggesting the carbonate molecules no longer participate in the solvation of Lit In contrast, the resonance signal of G2 shifts from 57.6 ppm to 58.0 ppm as G2 coordinated with Lit As depicted in FIG. 6 plot (b), the peak associated with G2 shifts from 57.6 ppm to 58.4 ppm when LiNO3 is added into the blend of G2, EC, and DEC.
[0063] Although EC and DEC barely participate in the solvation of Li, they still affect the physical properties of the electrolyte, such as viscosity, which is in close connection with ionic conductivity. As shown in FIG. 7, 0.5M LiPFG in G2's ionic conductivity is measured to be 2.1x10-3 S cm-1, which is 4 times lower than CGHE (8.5x10-3 S
cm-1).
Therefore, EC and DEC are included to dilute the system and effectively enhance the ionic conductivity.
[0064] FIG. 8 plot (a) displays the Coulombic efficiency (CE) of different electrolytes in Li1Cu half cells testing at 1mA cm-2 with a capacity of 1mAh cm-2. The CE of the baseline electrolyte (1M LiPFG EC/DEC) continuously drops upon cycling from 94.6% at the 1st cycle to 66.1% at oo n nth cycle. In contrast, introducing 0.3m1 G2 and 0.03g LiNO3 to 1m1 1M LiPFG
EC/DEC results in an increase in CE averaged 93.87% for the first 40 cycles, demonstrating the effectiveness of LiNO3 and G2. CGHE (0.6m1 G2, 0.07g LiNO3 mixed with lml 1M LiPFG
EC/DEC) demonstrates even higher efficiency over 100 cycles with an average CE
of 97.66%, inclusive of the initial activation cycles. FIG. 8 plot (b) illustrates the voltage profile of Li metal deposition/stripping in CGHE at different current densities, and indicates that the Li cycling is highly stable at different current densities. The outstanding cycling stability of CGHE is further confirmed in a Li symmetric cell under a harsh testing condition of 4 mA
cm-2 and 2 mAh cm-2, as illustrated in FIG. 8, plot (c). The cell with CGHE
sustains steady cycling for more than 180 cycles with low polarization, while the baseline electrolyte and 1M LiNO3 in G2 exhibit much higher over-potential and voltage variation.
[0065] Advantageously, a hybrid electrolyte according to the disclosure herein can have a lower melting point comparatively to other baseline electrolytes. For example, a CGHE electrolyte has a lower melting point than the parent phase 1M LiPFG
EC/DEC as G2 has a melting point of -64 C, effectively impeding the crystallization of EC at low temperatures. As shown in the inset of FIG. 9, plot (a), 1M LiPF6 in EC/DEC
partially crystalized at -21 00, while CGHE remains a clear liquid. To demonstrate the practical application of the above advantage, the cyclic performance of the cells has been evaluated at lower temperature (-21 C) using LiINCA cells with 1M LiPFG EC/DEC and CGHE
cycled at 0.2C after 1 cycle of activation at room temperature. As shown in FIG. 5 plot (a), the CGHE cell delivers 167 mAh g-1 at the 1st cycle, and the capacity retains for 10 cycles without noticeable degradation. In comparison, the cell with the baseline electrolyte provides a lower specific capacity of 152 mAh g-1 at the 1st cycle; it decays to 124 mAh g-1 at the 10th cycle, likely as a result of the impeded ion transfer in the partially solidified electrolyte. Their 1st cycle voltage profile is shown in FIG. 9 plot (b). CGHE
cell exhibits considerably smaller voltage hysteresis in both charging and discharging, implying lower cell resistance.
[0066] Embodiments according to the disclosure herein include realizing improvements in energy density of Li-metal battery which can fully benefit from the high theoretical capacity of Li, based on no excess Li being utilized at the anode side. Such anode free embodiments also reduces fabrication costs and eliminate the difficulty of processing metallic Li. The results of testing such an anode-free Li metal battery (compressed and uncompressed) are shown in FIG. 10. The cells were assembled in coin cells with the following configurations: upper case + spring + spacer (different thickness) +
Cu disc + separator + cathode disc + lower case. The cell with a thick spacer is a compressed cell. FIG. 10 displays the cyclic performance of the anode-free Li-metal charged at 0.2C and discharged at 1C. The capacity of the uncompressed cell using baseline electrolyte drops to zero within 20 cycles. The compressed cell using the baseline electrolyte improves significantly from the uncompressed one. But it still undergoes tremendous capacity loss since the beginning of cycling, resulted from the severe side reaction between Li and electrolyte and the specific capacity drops to zero within 50 cycles.
In contrast, the compressed cell with CGHE electrolyte exhibits a specific capacity of 128 mAh g-1 at the 50th cycle with a good capacity retention of 73%. This performance is improved from the uncompressed cell using CGHE electrolyte. Here we use a thick spacer to increase the compression level [0067] Unless the context clearly requires otherwise, throughout the description and the "comprise", "comprising", and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to"; "connected", "coupled", or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof;
"herein", "above", "below", and words of similar import, when used to describe this specification, shall refer to this specification as a whole, and not to any particular portions of this specification; "or", in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list; the singular forms "a", "an", and "the"
also include the meaning of any appropriate plural forms.

[0068] Where a component is referred to above, unless otherwise indicated, reference to that component should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments.
[0069] Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure.
Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the full scope consistent with the claims. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.

Claims (26)

WHAT IS CLAIMED IS:

1. A battery cell having an internal pressure, comprising:
a first electrode;
a second electrode;
an electrolyte;
a separator, and a conductive spacer having a rigid body and being coupled to the first electrode, the spacer being dimensioned to occupy an interior of the battery cell and increase the internal pressure of the battery cell for increasing a compression acting on the first electrode.

2. The battery cell of claim 1, further comprising a spring coupled to the first electrode, the spring configured to modify the compression acting on the first electrode based on a spring constant of the spring.

3. The battery cell of claim 1 or claim 2, wherein a thickness of the first electrode is increased to reduce the amount of unoccupied space in the battery cell, for increasing the compression acting on the first electrode.

4. The battery cell of any one of claims 1 to 3, wherein the spacer contacts the first electrode.

5. The battery cell of any one of claims 1 to 3, wherein the spacer comprises a plurality of spacers, each spacer of the plurality of spacers being directly coupled to the first electrode or the second electrode.

6. The battery cell of any one of claims 1 to 3, wherein the spacer comprises a first spacer and a second spacer, each of the first spacer and the second spacer being directly coupled to the first electrode or the second electrode.

7. The battery cell of claim 6, wherein the first spacer contacts the first electrode.

8. The battery of any one of claims 1 to 7, wherein the first electrode is a cathode, and the second electrode is an anode.

9. The battery cell of claim 8, wherein the anode is formed in-situ during a charging phase of the cathode.

10. The battery cell of claim 8 or claim 9, further comprising a current collector disposed at the anode.

11. The battery cell of claim 10, wherein a size of the spacer is greater than or equal to a size of the current collector.

12. The battery cell of any one of claims 8 to 11, wherein the cathode is a Li-containing compounds.

13. The battery cell of any one of claims 1 to 12, wherein the spacer comprises a electrically conducting material.

14. The battery cell claim 13, wherein the spacer comprises stainless steel.

15. The battery cell of any one of claims 1 to 14, wherein the spacer has a circular profile.

16. A battery comprising a plurality of the battery cell according to any one of claims 1 to 15.

17. An electrolyte for forming a solid-electrolyte interphase (SEI) in a battery cell having lithium based chemistry, comprising:
a carbonate based electrolyte, the carbonate based electrolyte for diluting a solute and a solvent having high solubility for lithium ions and film-additives;
the solvent being selected for disassociating the film-additives and for forming a contact ion pair with an anion and the lithium ions.

18. The electrolyte of claim 17, wherein the solvent, solute, and the carbonate form a solvation structure when exposed to lithium, the solvation structure having a solvation shell comprising the solvent.

19. The electrolyte of claim 17 or claim 18, wherein the carbonate based electrolyte comprises lithium hexafluorophosphate (LiPF6) and the anion disassociated by the solvent is a hexafluorophosphate anion.

20. The electrolyte of claim 16, wherein the carbonate based electrolyte comprises the LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC).

21. The electrolyte of any one of claims 17 to 20, wherein the solvent is a glyme-based solvent.

22. The electrolyte of claim 21, wherein the glyme-based solvent is diglyme (G2).

23. The electrolyte of any one of claims 17 to 22, wherein the solute is lithium nitrate (LiNO3).

24. The electrolyte of claim 17 or claim 18 comprising LiPF6 in EC/DEC, LiNO3, and a glyme-based solvent, mixed at room temperature.

25. A battery cell having a lithium based chemistry and the electrolyte according to any one of claims 17 to 24, comprising:
a cathode;
an anode formed in situ during charging of the cathode;
a separator, and a conductive spacer having a rigid body and being coupled to the cathode, the spacer being dimensioned to occupy an interior of the battery cell and increase the internal pressure of the battery cell for increasing a compression acting on the cathode

26. A battery comprising a plurality of the battery cell according to claim 25.