In this paper, by introducing a layer of dense gel electrolyte at the LAGP solid electrolyte and the metal lithium interface, it prevents LAGP and metal lithium side reactions, efficiently conducting lithium ions and mitigation due to the stress of the lithium metal negative electrode volume, and achieves mixed solid state Stable operation of electrolyte lithium metal batteries at room temperature. Background introduction Lithium metal negative electrode is considered a key material for the next generation of high energy density lithium ion batteries. However, if the electrolyte widely used in the commercial lithium ion battery is directly applied to a lithium metal battery, it is possible to bring great safety hazards.
. Solid electrolytes have a greater potential in solving safety problems in solving metal lithium negative applications due to their high thermal stability and mechanical properties..
Nasicon solid electrolyte has been widely studied because they have a lower and easy control of sintering conditions, and in the air even in the air, it has been widely studied.. It is usually produced by chemical composition: Li (1 + x) Alm2-x (PO4) 3, when M is a GE or Ti element, such solid electrolyte is generally referred to as LAGP and LATP, these two types of solid electrolytes are The most research in the fast ion conductors, and usually think that both are very similar.
. In addition to the high electrode / electrolyte interface impedance problem, the starting point is in addition to the high electrode / electrolyte interface impedance problem, the LAGP fast ion conductive solid electrolyte also has a problem that is unstable with metal, that is, the problem of lithium metal reduction..
▲ Fig. 1 Important research contents and use mechanisms for different electrolyte systems, this paper introduces a dense gel electrolyte (3DGPE) in the interface of LAGP ceramic sheet and lithium metal negative electrode, thereby obtaining stable energy at room temperature. Under loop mix solid lithium metal battery.
The lithium metal battery uses a mixed solid electrolyte to match the phosphithium phosphate (LFP) positive electrode, metal lithium negative constitution. The LFP / LAGP / 3DGPE / LI battery exhibits excellent electrochemical properties at room temperature (at 1 C current density of 148 mAhg-1, which cycles at 0.3c current densities for 300 times, the capacity retention ratio is 91.
2%). The decomposition challenge of the circulating battery is characterized to compare the recession mechanism of different electrolyte systems, and prove the effectiveness of the strategy of introducing the interfacial crystal growth between the LAGP ceramic sheet and the lithium metal negative electrode Sex and necessity. Picture Analysis ▲ Fig.
2 (a) Raw LAGP powder and XRD of a sintered ceramic sheet; the original LAGP powder (B) and LAGP ceramic (CE) SEM map; (f) 3Dgpe film surface SEM Figure 2.a give LAGP powder and X-ray diffraction chart (XRD) of ceramic tablets for 12 hours of 850 ° C. Important diffraction peaks of powder and ceramic sheets and fast ionic conductor LiGe2 (PO4) 3 structure (PDF # 80-1924).
Figure 2. Bd is a scanning electron microscope (SEM) of LAGP powder and sheet, the original LAGP particle size is less than 1 μm, and after 12 hours of sintering 850 ° C, the size of the LAGP particles increase, a large amount of LAGP particles from nanoparticles Long is micron particles (Figure 2.C).
The growing particles are closely accumulated to form a dense structure, as shown in Figure 2. C-E. The casting method used can ensure that the thickness of the ceramic sheet is controlled within 150 μm, and the dense structure can improve the ion conductivity and mechanical strength of the ceramic sheet.
. As can be seen from the surface SEM diagram of 3DGPE, the surface of 3DGPE is more dense. This property facilitates the uniform deposition of lithium ions to inhibit dendritic growth, which is essential to construct a stable lithium metal battery.
. ▲ Fig. 3Li / LAGP / Li (a), Li / LE / LAGP / LE / Li (B) and Li / 3DGPE / LAGP / 3DGPE / Li (C) Symmetrical Battery EIS map under different shelving time is by using different solid states The electrolyte system assembles symmetrical lithium metal cells and tests its impedance changes, compared to interface stability of different solid-state electrolyte systems, impedance maps such as Figure 3.
As shown in Figure 3.a, and lithium direct contact assembly LI / LAGP / LI battery is approximately 8kΩ after placing an hour, the value is high, can be considered from two parts: high solid-adverse interface Impedance and mixing (electronic and ion) conduction (MCI) film, the impedance of Li / LAGP / LI batteries increases significantly as the shelving time after the battery pack is completed. Impedizing map of Li / LE / LAGP / LE / LI battery added to Liquid electrolyte, Figure 3.
B. Even if the battery has been placed 240 hours, the interface impedance continues to increase, indicating that the side reaction continues to occur..
Compared with the system of unsubmented liquid electrolytes, the total interface impedance of the Li / LE / LAGP / LE / LI battery is small, which can be explained to increase the contact of the liquid electrolyte to increase the contact of the LAGP ceramic and lithium metal, and at the interface The formed (solid electrolyte boundary layer) SEI and solid state liquid electrolyte interface layer (SLEI) film can prevent the side reaction to a certain extent, but the reaction cannot be completely inhibited.. Therefore, it can be considered that the SLEI film on LAGP is a mixed conductor film, similar to MCI, which may differ from LATP.
. When introducing 3dgpe to protect LAGP (Figure 3.C), the total interface impedance of Li / 3DGPE / LAGP / 3DGPE / LI battery is 160Ω, the total interface impedance of the value of the LI / LE / LAGP / LE / LI battery (140Ω ) Similar, explaining that the addition of 3DGPE does not cause hysteresis of charge delivery.
The total interface impedance of the Li / 3DGPE / LAGP / 3DGPE / LI battery gradually increased to 230 Ω and started stable after 168 hours, and the stable value illustrates that the 3DGPE can effectively prevent the side reaction and form a stable interface.. ▲ Figure 4.
(a) Li / LE / LAGP / LE / Li and Li / 3DGPE / LAGP / 3DGPE / Li symmetric battery deposition deprotection; (b) LFP / LAGP / LE / LI battery top 5 under 0.1c Circle charger; (c) LFP / LAGP / 3DGPE / LI battery magnification graph and (d) corresponding charge and discharge curve diagram; (e) loop performance chart at LFP / LAGP / 3DGPE / LI battery at 0.3C magnification.
Figure 4. A lithium deposition of Li / LE / LAGP / LE / Li and Li / 3DGPE / LAGP / 3DGPE / LI battery. These symmetrical batteries are charged and discharged at a constant current density of 0.
1MACM-2.. The overvoltage of the Li / LE / LAGP / LE / LI battery has been significantly added after a circulating 50 hours, which may be attributed to LAGP and the metal lithium.
. The lithium metal tends to form the deposition of the dendritic in the liquid electrolyte, and thus continuously growing the dendritic crystal and LAGP ceramic sheet during the circulation process, which causes a continuous side reaction..
In comparison, the symmetric battery under 3Dgpe protection has a small over-potential, which means that the interface of the battery is very stable, and can continue to maintain stable for 240 hours.. The significant difference in the two indicates the necessity of 3DGPE to hinder the interface layer of LAGP ceramic sheet and metal lithium while ensuring effective ion transmission.
. Lithium iron phosphate (LFP) is selected as the positive electrode and the lithium metal is selected as an negative electrode assembled the battery and tested its performance, as shown in Figure 4. B-E.
Figure 4.B is a charge and discharge curve for the top 5 laps in front of the LFP / LAGP / LE / LI battery. In the first circle cycle, the excessive power of the LFP / LAGP / LE / LI battery is smaller, about 60mV, which is higher than the discharge ratio, about 160 mAhg-1 at a current density of 0.
1c.. However, as the loop progresses, the polarization has increased in a few times, only after the five-loop cycle, the overpot force increased to more than 600mV, the specific capacity is also reduced to 150mAhg-1.
The recession of this battery performance is important because of the side reactions of LAGP and lithium metal, as discussed above. Therefore, the LAGP electrolyte cannot achieve stability performance of the mixed solid lithium metal battery by simply adding liquid electrolyte in the interface layer, which is different from LATP..
In comparison, even if the LFP / LAGP / 3DGPE / LI battery can exhibit excellent electrochemical properties even at an increased current density.. Figure 4.
C is the magnification performance test diagram of the LFP / LAGP / 3DGPE / LI battery, Figure 4.D is a charge and discharge curve corresponding to the corresponding current density..
From this we can see that the discharge ratio of the LFP / LAGP / 3DGPE / LI battery at 1C current density is as high as 148mAhg-1, and its corresponding polarization is also relatively small.. This shows that the introduction of 3DGPE can supply efficient ion transmission.
Figure 4. E is the cycle performance of the LFP / LAGP / 3DGPE / LI battery at a current density of 0.3 C, which is 91.
2% in the current density of the current density, that is, the capacity attenuation rate of each lap is 0.03%. Such performance is more excellent in comparing mixed solids batteries in the report at room temperature.
. The excellent performance of the hybrid solid battery illustrates that using 3DGPE for protecting LAGP is a very effective means. ▲ Figure 5.
(AD) LAGP ceramic piece Sem map (illustration is optical photo); (a) original LAGP map; Li / LAGP / LI battery (B), Li / LE / LAGP / LE / LI battery (C) And LI / 3DGPE / LAGP / 3DGPE / LI battery (D) after testing; (EF) lithium metal surface SEM; Li / LE / LAGP / LE / LI battery (E) and Li / 3DGPE / LAGP / 3DGPE / LI battery ( f). Figure 5.A-D SEM map for surface topography of different LAGP.
The surface of the original LAGP ceramic sheet is dense and relatively smooth, as shown in Figure 5.a. However, as shown in Figure 5.
B, when the LAGP ceramic sheet and metal lithium are directly in contact with a few lap electrochemical tests, irregular, increased particles (greater than 10 μm) appear on its surface, which can be considered LAGP is produced by metal lithium reducing. LAGP and metal lithium side effects cause new LAGP particles, so dense ceramic tablets will receive internal stress. From the perspective, the ceramic sheet has ruined, as shown in the illustration.
. The part of the black surface of the LAGP corresponds to the reduction product of LAGP. When the liquid electrolyte is added, as shown in Figure 5.
C, it is increased, but the particle size relatively small particles are widely dispersed in the LAGP surface, which can be construed as being related to the direct contact with lithium metal, due to the addition Liquid electrolyte, the degree of reaction is reduced. Since the liquid electrolyte results in the formation of the SLEI film, the side reaction is slowed down..
The illustration in Figure 5.C is an optical photograph of LAGP-LE-Li (corresponding to Li / LE / LAGP / LE / LI battery), indicating its reaction range relating to LAGP-Li (corresponding to Li / LAGP / LI) The battery is wider, which is due to the large-scale growth of the branch crystal in this case where the liquid electrolyte is added, and the degree of black in the ceramic sheet is low, and the degree of reaction is relatively low..
When the LAGP ceramic sheet and metal lithium are separated, as shown in Figure 5.D, the LAGP ceramic sheet can maintain a relatively smooth surface after cycle, and the surface of the original LAGP ceramic sheet is similar, illustrating LAGP and metal lithium. Sub-reactive.
Lithium metallographic surface topography after LAGP-LE and LAGP-3DGPE electrolyte system, as shown in Figure 5.E and F, it can be seen that there is a large difference. The surface of the lithium sheet circulating in the LAGP-LE electrolyte is a rough porous structure, and contains a large amount of dendrites, which can be attributed to the non-uniform deposition characteristics of lithium metal in conventional electrolyte.
. Continuously growing lithium delegation, contact with LAGP ceramic sheets, resulting in side reactions. In comparison, the surface of the lithium metal negative electrode circulating in the LAGP-3DGPE electrolyte is dense and smooth, and there is no obvious dendritic crystal.
After the 3DgPe is added, the lithium metal exhibits uniform deposition properties.. The negative electrode of the non-decystal lithium metal negative electrode in the LAGP-3DGPE electrolyte can not only reduce the possibility of the lithium metal negative electrode and the LAGP ceramic sheet, but also improve the safety of lithium metal electricity.
. ▲ Figure 6. Surface X – ray photoelectron energy spectrum X – ray photoelectron spectrum (XPS) of Different LAGP Ceramics (XPS) Tests the surface of the LAGP ceramic sheet of different electrolyte systems, so that more comprehensive surface chemical information can be obtained, as shown in Figure 6.
. The LAGP ceramic sheet after the circulation is a lithium metal symmetric battery assembled from the corresponding electrolyte system 10 hours after 10 hours of 0.1 mACM-2 current density, and DMC is used to wash away the lithium salt before testing.
. Regarding the GE3D spectrum in Figure 6.a, corresponding to the chemical change of GE element.
Regarding the original LAGP ceramic sheet, the existence of single peak and GE4 + in 32.5 EV. After a day in the liquid electrolyte, 30.
4 eV corresponds to the signal peak of F2S, which is due to the residual LiPF6 salt introduced by the liquid electrolyte (consistent with F1S in the figure).. Regarding LAGP-Le-Li, a new peak corresponding to GE0 is located at a lower combination of energy, which is the supply of GE4 + in LAGP and supplies evidence by lithium metal reduction.
. The low-cost GE has better electron conductivity, which may give a SLEI film to the LAGP surface to conduct electronics. The GE3D spectrum of LAGP-Li illustrates more GE to be restored, and therefore, the reduction reaction will be more severe when LAGP and metal lithium are directly in contact.
. When 3DGPE is added to the LAGP ceramic sheet and the metal lithium, as shown in the GE3D map of LAGP-3DGPE-Li, there is no peak corresponding to GE0, and 3DGPE can effectively protect the LAGP ceramic sheet..
It can be found in the Li1S spectrum of lagp-le-li and lagp-li. When LAGP is reduced by lithium, the signal intensity of the Li element has increased, and corresponding to the restore of the LAGP. Sample, the peak is almost different.
This peak can also give the degree of side reactance of LAGP to some extent.. In the F1S spectrum in the figure, the compound LIF / ALF3 corresponds to a new peak at 685.
2 eV in the peak corresponding to PF-6 at 687.5 EV, LAGP-LE-Li and LAGP-3DGPE-LI..
These products can be classified as the decomposition product of LiPF6 during cycle or LAGP and HF (also a decomposition product of LiPF6).. Regarding the C1S spectrum in the figure, the only significant difference is that the LAGP-LE-Li has a new peak corresponding to the OC = O group of carbonates at 289.
6EV. This group can usually be considered a carbonate electrolysis. The decomposition product of the liquid, that is, the composition of the SEI film, further confirmed the SLEI film formed on the surface of the LAGP.
. Since these organic decomposition products have electron insulation, it is possible to hinder the dramatic side effects of LAGP and metal lithium..
However, due to the partially electron conductivity, such SLEI films do not completely hinder the side react, and the continuous growth of lithium dendrides will continue to be carried out.. ▲ Figure 7.
Different electrolytes and lithium metal mutual use. (a) LAGP direct contact with the ceramic sheet and lithium metal; (b) Liquid electrolyte addition to the interface of LAGP and lithium metal; (c) 3DGPE separating LAGP ceramic sheet and metal lithium according to the foregoing experimental results, we summed up LAGP is schematically illustrated under different systems and metal lithium interlocking mechanisms, as shown in Figure 7. When the LAGP ceramic sheet and lithium metal negative are in direct contact, due to the solid-insulating interface, there is a point of contact between them, the area of the reaction is relatively.
Since the MCI layer is formed, lithium will continue to react with the LAGP, and the degree of reaction will increase with the contact time. The particles after the reaction will become black and expanded..
Due to large volume changes, the increased particles inside the lagp ceramic sheet will initiate ceramic rupture.. After adding liquid electrolytes at the interface, the LAGP ceramic sheet prevents direct contact with metal lithium to a certain extent.
. Moreover, due to the electron-insulating properties of the liquid electrolyte, the reduction reaction of lithium and LAGP is more difficult. Therefore, in the initial period, the side reaction is significantly slowed, and the introduction of the liquid electrolyte increases the contact of LAGP and lithium, so that the interface impedance is small.
. However, the lithium metal negative electrode tends to be uneven in conventional liquid electrolyte, and the lithium delegated crystal will continue to grow extensively..
Adding from the dendritic crystal sessions and LAGP ceramic sheets, resulting in the occurrence of side reactions. Due to the presence of liquid electrolytes, lithium may reduce liquid electrolyte while reducing LAGP. Therefore, the decomposition product of the liquid electrolyte can appear on the surface of the LAGP ceramic sheet, which can be referred to as a SLEI film, which corresponds to the results of XPS.
. Although the sub-reaction is slowed down due to partial electron insulation characteristics of the SLEI film, as the cycle is carried out, there is a growing and gradually rising lithium delegra, the range of reactions becomes larger..
Further, since the appearance of GE0 has better electron conductivity, so that SLEI on the surface of the LAGP does not have a complete electronic insulation property.. Therefore, regardless of whether the battery is loop, the impedance of such an electrolyte system continues to increase slowly.
. According to previous studies, 3DGPE can efficiently and uniformly conduct lithium ions, and it has a better mechanical properties and dense structures to inhibit the formation of dendrites..
3DGPE introduced at the interface not only prevents direct contact of LAGP ceramic sheet and metal lithium negative electrode, but also supplies efficient ion conductance, and inhibits dendritic crystal growth to suppress subsequent side reactions.. In addition, soft 3DGPE can be used as a buffer layer to release metal lithium negative electrode during the cycle process due to volume changes.
. 3DGPE This unique nature can ensure the stability performance of lithium metal batteries during long cycle. Summary and Overlook this work successfully proposed an effective method that enables LAGP ceramic sheets and lithium metal negative electrodes to obtain a hybrid solid lithium metal battery operating at high performance room temperature.
. Combined with different characterization methods, the recession mechanism of different electrolyte systems is proposed. When the LAGP ceramic sheet and the lithium metal negative electrode are directly in contact, the reaction range is relatively limited, but since the MCI film is formed, the reaction is more intense and continuous.
. The LAGP particles after the reaction are black and expanded, resulting in the crush of ceramic sheets..
When the liquid electrolyte is added to the interface, the SLEI film formed on the surface of the LAGP ceramic sheet can mitigate the side reaction.. However, a lithium derinating crystal session and ceramic sheets in the liquid electrolyte are in contact with the ceramic sheet, and since the occurrence of GE0 having good conductivity makes the SLEI film have a portion of the electron conductivity, thereby adding the range and degree of side reactions to increase.
This special nature of the SLEI film on the surface of the LAGP may differ from LATP, which can explain why LATP can stabilize the metal lithium in the case of adding liquid electrolytes, and LAGP is not. The introduced 3DGPE can prevent the LAGP and the metal lithium negative electrode, but also reduce the larger impedance caused by the solid-insulating interface, and can reduce the stress of the volume change due to the volume change during the cycle of the lithium metal negative electrode..
By dividing the LAGP ceramic sheet and the metal lithium negative electrode, it can suppress dendrites growth while supplying high-efficiency ionically transmitting, which can also supply high performance of the mixed solid lithium metal battery based on LAGP ceramic sheets at room temperature. Performance. .