CN114899348B - An activated negative electrode with lithium dendrite inhibition - Google Patents

Abstract

The invention provides an activated negative electrode with lithium dendrite inhibition effect, which comprises a carbon layer, wherein the carbon layer comprises amorphous lithium silicon alloy and Li ₃ The three-dimensional ion conductive path formed by the N phase effectively inhibits the growth of lithium dendrite, greatly improves the high load, high current and long cycle capacity of the battery, and widens the working temperature range.

Description

An activated negative electrode with lithium dendrite inhibition

technical field

The invention relates to the technical field of battery materials, in particular to an activated negative electrode with lithium dendrite inhibition and a battery using the negative electrode.

Background technique

All-solid-state lithium metal batteries have attracted extensive attention because they can theoretically solve both energy density and safety issues by combining non-flammable solid-state electrolytes and high-energy-density lithium metal anodes. Compared with oxides, sulfide solid electrolytes have higher ionic conductivity, lower hardness, and better interface contact. The prepared powder can effectively reduce interface impedance and obtain higher ionic conductivity only by cold pressing. . Therefore, sulfide solid-state electrolytes are considered to be one of the most promising solid-state electrolyte (SSE) materials, and sulfide all-solid-state batteries with lithium metal are expected to obtain higher energy densities. However, the use of lithium metal anodes presents enormous challenges. Limited by the low specific surface area and poor rate performance of pure lithium metal foil. In addition, lithium dendrites are easy to grow in inorganic SSE under high current, which greatly limits the rate performance of solid-state lithium metal batteries. Due to the low bonding strength of Li-Li, lithium metal has low surface energy and high migration energy, which makes it prone to one-dimensional whisker growth. Therefore, the distribution of charges will have a greater impact on its deposition behavior.

The solid-solid contact mode between electrolyte and Li metal dendrites tends to cause large interfacial resistance, resulting in uneven charge distribution, which is a common factor to accelerate dendrite growth. Therefore, researchers often introduce lithium-friendly substances between lithium metal and SSE to improve wettability. For example, magnesium coatings can be used to introduce lithium _{- magnesium} alloys. -C and graphite coating to wet the interface and provide lithium deposition sites. In addition, LiF with high interfacial energy, Li ₃ N with high ion conductivity and stability, and SnF ₂ and BiF ₃ that can react with lithium metal to form mixed ion conductors, etc. It is not difficult to find that the interface layer modification can be generally divided into three categories according to the ion conductivity: ion-conducting layer, electron-conducting layer and mixed ion-conducting layer. The research of Wang Chunsheng's team showed that the interface layer with high ionic conductivity, low electronic conductivity and high interfacial energy can effectively inhibit the growth of lithium dendrites. The researchers of the mixed ion-conducting layer believe that the purely ion-conducting intermediate layer will cause the accumulation of electrons at the interface, and then cause the accumulation of lithium metal, which will lead to interface polarization and seriously affect the normal cycle of the battery. The ion-electron mixed conductive layer can reduce the interface resistance and uniform the charge distribution while keeping the electrons from directly contacting the electrolyte. Ion conductor researchers believe that the high electronic conductivity of the mixed-conducting layer leads to the growth of lithium dendrites directly in the interfacial layer. In addition, because sulfide solid electrolytes will undergo interfacial electrochemical reactions with lithium metal, they are not suitable for ionic conduction pathways in 3D lithium anodes, so there are very few reports on the use of 3D lithium anodes in sulfide all-solid-state batteries.

Studies by Kasemchainan et al. have shown that lithium metal is easy to form gaps with the electrolyte during the stripping process, resulting in poor contact, which will lead to high interfacial resistance, uneven charge distribution and large overpotential, aggravating dendrite formation and serious battery safety hazards. The use of ion-electron mixed conductive layer can reduce the interface resistance and homogenize the electric field distribution, which will effectively solve the problem of poor interface contact and increase the critical current density. Therefore, how to design stable ion and electron pathways is the top priority in designing solid-state batteries. Li ₃ N is an ionic conductor with high ionic conductivity and stable with lithium metal at low voltage, so it is suitable for the ion conduction path in three-dimensional lithium anode. Preparation of Li ₃ N combined with three-dimensional electronic conductors may be able to obtain a mixed ion framework for sulfide solid-state three-dimensional lithium anodes.

Contents of the invention

The present invention aims at the above-mentioned interface problem existing between the lithium negative electrode and the solid state electrolyte in the prior art, adopts the composite material (SC-SiN) of nano-silicon-nitrogen-coated carbon as the auxiliary interface layer, and silicon nitrogen (SiN, in the present invention refers to containing Si Various compounds, compositions or alloys of N and N) decompose after intercalating lithium to form lithium-silicon alloy (LiSi) and Li 3 N with high ionic conductivity and low electronic conductivity, and a lithium-silicon alloy (LiSi) and Li ₃ N are formed between the lithium sheet and the solid electrolyte in the negative electrode. The communication channels with three-dimensional ion-conducting pathways effectively inhibit the growth of lithium dendrites.

Specifically, the present invention firstly provides an activated negative electrode with lithium dendrite inhibition, the negative electrode contains a carbon layer, and the carbon layer has an amorphous lithium-silicon alloy and a Li ₃ N phase.

As an optimized alternative, the three-dimensional ion-conductive network formed by the amorphous lithium-silicon alloy and the Li ₃ N phase is coated on the outer periphery of the carbon particles in the carbon layer.

As an optimized alternative, the amorphous lithium-silicon alloy and the Li ₃ N phase are made of carbon particles and silicon-nitrogen-containing nanoparticles coated on the surface of the carbon particles.

As an optimized option, the carbon particles are micron-sized particles, preferably carbon particles with a D50 of less than 20 μm, more preferably carbon particles with a D50 of 0.5-20 μm, and most preferably carbon particles with a D50 of 5-20 μm.

As an optimized alternative, the D50 particle size of the silicon-nitrogen-containing nanoparticles is less than 300 nm, preferably less than 100 nm, preferably less than 50 nm.

As an optimized option, the carbon particles are soft carbon.

As an optimized option, the silicon-nitrogen-containing nanoparticles account for 5% to 15% of the total mass of carbon particles and silicon-nitrogen-containing nanoparticles, preferably 10% based on the contained mass equivalent to Si ₃ N ₄ ±2%.

As an optimized alternative, the silicon-nitrogen-containing nanoparticles are Si ₃ N ₄ , or a mixture of lithium-silicon alloy and Li ₃ N.

As an optimized option, the carbon layer in the negative electrode is arranged on the side of the lithium-metal-containing foil that is close to the solid-state electrolyte.

As an optimized option, the loading capacity of the negative electrode is above 1mAh/cm ² , or above 2mAh/cm ² , or above 5mAh/cm ² , or above 7mAh/cm ² , or above 10mAh/cm ² , Or more than 15mAh/cm ² . As an optimized option, the working temperature of the negative electrode is -20°C to 75°C.

As an optimized option, the negative electrode also contains a binder, which is used for the bonding of particles in the carbon layer to form a film, and can be mixed with the above-mentioned carbon particles coated with silicon-nitrogen-containing nanoparticles to form a For the film, the mass of the binder accounts for less than 20% of the total mass of the silicon-nitrogen-containing nanoparticles, carbon particles and binder, preferably 5%-10%.

As an optimized alternative, the binder may be a fluorine-containing vinyl polymer, preferably polytetrafluoroethylene or polyvinylidene fluoride.

The present invention also provides a preparation method for the above-mentioned activated negative electrode with lithium dendrite inhibition effect. After mixing and grinding carbon particles and nano-particles containing silicon and nitrogen, they are mixed with a binder to form a negative electrode protective layer; the negative electrode protective layer is mixed with a metal-containing Lithium foils are arranged adjacent to each other as negative electrodes, and after battery assembly, activation is completed.

As an optimized option, the activation of the negative electrode is completed at a rate of 0.1C-0.5C for 1-2 weeks.

As an optimized option, the negative electrode protection layer and the foil containing metallic lithium are combined under pressure, preferably above 50 MPa, more preferably above 700 MPa.

The present invention also provides a battery comprising the above negative electrode.

The battery positive electrode provided by the present invention includes but not limited to ternary system (NCM, NCA), lithium cobalt oxide system (LCO), lithium iron phosphate system (LFP), lithium manganate system (LMO) and the like.

The present invention introduces the coating of silicon-nitrogen nano-particles on the outer periphery of the carbon material, so that it decomposes to form lithium-silicon alloy and Li ₃ N with high ionic conductivity and low electronic conductivity after lithium intercalation, thereby building and forming a three-dimensional ion conductive path. effectively inhibited the growth of lithium dendrites. The invention further optimizes the system selection of carbon materials and the type and content of silicon-nitrogen-containing nanoparticles, and successfully obtains negative electrode materials with high load, high current, long cycle and ultra-wide working temperature range, which has great practical prospects. The preparation of the material of the present invention starts from carbon particles and silicon-nitrogen-containing nanoparticles, and can be prepared by simple ball milling to form a reliable negative electrode in the battery assembly process. The whole process is safe and simple, and is suitable for low-cost large-scale mass production , providing a new solution for the practical application of solid-state batteries.

Description of drawings

Figure 1 is the XRD patterns of pristine SC and SC-SiN, and charged SC and SC-SiN.

Figure 2 is the XPS of SC-SiN and SC-SiN-Li.

Figure 3 is the Raman of SC-SiN and SC-SiN-Li.

Figure 4 is the SEM of SC and SC-10SiN. Among them, A is SC, B is SC-10SiN, and C is the magnification of SC-10SiN.

Figure 5 is the SEM surface and interface SEM of different protective layers after negative electrode deposition and activation. Among them, A is the cross section of SC-10SiN-Li, B is the interface of LPSCl/SC-10SiN-Li, C is the cross section of SC-Li, and D is the interface of LPSCl/SC-Li.

Figure 6 shows the XRD differences of different carbon materials. Among them, a is the XRD of original graphite, soft carbon and hard carbon, and b is the XRD of graphite, soft carbon and hard carbon after lithium intercalation.

Figure 7 is a SEM of different carbon materials coated with nanometer silicon nitrogen. Among them, a, c are SC-SiN with different magnifications, b, d are HC-SiN with different magnifications, respectively.

Figure 8 shows the impedance of electron blocking cells assembled with different protective layers.

Fig. 9 is a diagram of the impedance change of SC and SC-10SiN batteries at the initial stage and after 12h of reaction.

Figure 10 is the Tafel curves of lithium symmetric batteries with different protective layers.

Fig. 11 is the deposition curves of negative electrodes of different protective layers under different currents.

Figure 12 shows the critical current densities of lithium symmetric batteries with different protective layers.

Figure 13 shows the cycle performance of lithium symmetric batteries with different protective layers.

Figure 14 shows the cycle performance of lithium and graphite anode symmetric batteries.

Figure 15 shows the charge and discharge curves of graphite, soft carbon and hard carbon at different rates, with an areal capacity of 2.7mAh/cm ² .

Figure 16 shows the charge and discharge curves of graphite-SiN, soft carbon-SiN and hard carbon-SiN at different rates, with an areal capacity of 2.7mAh/cm ² .

Figure 17 shows the rate performance under different SiN mass proportions, and the areal capacity is 2.7mAh/cm ² .

Figure 18 is the XRD of SC-SiN-Li. Among them, a is the XRD after pressing, and b is the XRD after lithium intercalation.

Figure 19 shows the impedance at different SiN mass ratios.

Figure 20 shows the rate performance of LCO-LPSCl-SC-SiN/Li battery.

Figure 21 shows the cycle performance of LCO-LPSCl-SC-SiN/Li battery and batteries with different SC, HC and G protective layers at 25C.

Figure 22 is the charge and discharge curves of negative electrodes with different protective layers at different rates, and the areal capacity is 2.7mAh/cm ² .

Figure 23 shows the cycle performance of the LCO-LPSCl-SC-SiN/Li battery at 2C, with an areal capacity of 2.7mAh/cm ² .

Figure 24 shows the rate performance of the LCO-LPSCl-SC-SiN/Li battery, with an areal capacity of 2.7mAh/cm ² .

Figure 25 is the charge and discharge curves of LCO-LPSCl-SC-SiN/Li battery under different areal capacities.

Figure 26 is the cycle curve of LCO-LPSCl-SC-SiN/Li battery at 1C.

Figure 27 shows the cycle performance of the LCO-LPSCl-SC-SiN/Li battery at 2C, with an areal capacity of 7.6mAh/cm ² .

Figure 28 shows the high and low temperature performance of LCO-LPSCl-SC-SiN/Li battery.

Detailed ways

In order to facilitate the understanding of the present invention, the present invention will be described more fully below, and preferred embodiments of the present invention are given. However, it should be understood that these examples are only used for more detailed description, and should not be understood as limiting the present invention in any form, that is, not intended to limit the protection scope of the present invention.

1. Preparation of materials

Preparation of protective layer: It can be used as a wide range of raw materials for nano-silicon nitrogen, and the most direct and simple choice is Si ₃ N ₄ . As an implementation example, mix soft carbon and 20nm Si ₃ N ₄ uniformly in proportion, add 5wt% PTFE, and roll it into a 30 μm film (SC-SiN, to distinguish different proportions, add numbers before SiN to indicate different The ratio content, such as SC-10SiN means that SiN is 10% of the total mass of SiN and SC). As a comparison, hard carbon is selected to replace soft carbon at the same time, and the protective layer (which can be expressed as HC-SiN) is prepared by the same method. Both the soft carbon and the hard carbon of the present invention can be purchased from Zhongke Haina Company, and the D50 is 5-20 μm.

Preparation of composite negative electrode: A lithium foil with a thickness of 35 μm and a diameter of 0.475 cm was covered on the above-mentioned SC-SiN film with a diameter of 0.5 cm to form a composite negative electrode.

Battery assembly: match the positive electrode composed of 0.5wt% PTFE, 39.8wt% solid electrolyte and 59.7wt% LiCoO ₂ , and assemble the above composite negative electrode into a structural battery of LCO/LPSCl/SC-SiN/Li, wherein The electrolyte layer is 80mg LPSCl. Pressure is applied during the self-made process, and the assembled layers in the battery are assembled together with a pressure of 700MPa, and maintained at 50MPa during the test.

2. Result verification and analysis

In order to verify the product of SC-SiN activated lithium intercalation, we tested XRD. It can be seen from the XRD of SC-SiN (SC-Si ₃ N ₄ ) after activated lithium intercalation in Fig. 1 that the peak at 22° is the peak of PE used to isolate air. 25° corresponds to the peak of LiC ₆ . The peaks at 23° and 28° correspond to those of Li ₃ N. The LiSi alloy peak was not detected due to the formation of amorphous LiSi. The same conclusion can also be observed from the XPS and Raman results. It can be seen from Figure 2 that after lithium intercalation, the CC peak changes to C-Li, and the binding energy changes from 284.8eV to 285.2eV. The N spectrum also changes from 397.3eV of Si ₃ N ₄ to Li ₃ N of 398.8eV. The Si spectrum peak disappears after lithium intercalation. The Li spectrum mainly includes lithium metal, LiC ₆ , LixSi and Li ₃ N. It can also be seen from the Raman in Figure 3 that the stretching vibration peak of Si ₃ N ₄ and the D and G peaks of SC disappear after lithium intercalation, and become the characteristic peaks of Li ₃ N. Figure 4SEM shows the coating structure of SC-SiN (SC-10SiN). We can see that nano-sized Si ₃ N ₄ particles are evenly dispersed and coated on the outer periphery of micron-sized soft carbon particles, and metal lithium will span Si ₃ N ₄ coating Layers are embedded in carbon particles and react in situ with Si ₃ N ₄ to form Li ₃ N phase and amorphous LiSi alloy phase during the spanning process. Figure 5 SEM shows the comparison of the interface morphology of SC-10SiN-Li and SC-Li after the deposition of 4mAh/cm ² on the negative electrode. It can be seen that the lithium metal in SC-10SiN-Li is deposited in the interparticle gap of SC-SiN A lithium network is formed, and when the gap is filled with lithium, lithium is evenly deposited between the SC-SiN and the electrolyte to form a dense and flat lithium deposition zone, while there is a large gap between the particles in the SC-Li negative electrode, indicating that lithium metal It was not deposited into the SC anode, and lithium dendrites were observed to grow into the electrolyte, which would cause a short circuit in the battery.

The above results preliminarily prove that the coated soft carbon material provides abundant storage sites for the intercalation and deposition of metal lithium, which is conducive to accommodating more metal lithium and avoiding the growth of lithium dendrites. Uniform distribution of charge on the interface. SiN is surrounded by soft carbon particles in the form of dispersed coating of nanoparticles. During lithium migration, on the one hand, it provides transformation site activation to form Li ₃ N and amorphous LiSi alloys that can promote both ionic conductivity and electronic conductivity. At the same time, it also has a certain lithophilic effect, which further inhibits the growth of lithium dendrites. Therefore, the coating of SiN particles in the negative electrode forms a three-dimensional ion conduction path with Li ₃ N and LiSi as the main structure in situ, increasing the conductivity of the negative electrode. It is ionic and can reduce the electronic conductivity to increase the potential difference of the protective layer to give a greater driving force for lithium ion transport, and promote the nucleation and growth of lithium metal into SC-SiN to reduce the local current density and homogenize the lithium ion flow. amount, thereby inhibiting the growth of lithium dendrites. In addition, in order to further screen out suitable material systems, we also studied three commonly used negative electrode C materials. There are various types of carbon materials including graphite (G), soft carbon (SC) and hard carbon (HC). Among them, hard carbon refers to carbon that cannot be graphitized above 2500°C, and is mainly prepared by resin-based, pitch-based and biomass-based precursors; soft carbon refers to carbon that can be graphitized above 2500°C, and its soft carbon precursor Solids can include petroleum coke, petroleum pitch, and fused-ring aromatic compounds. Graphite, soft carbon, and hard carbon all have obvious differences in terms of structural order, interlayer spacing, and structural strain capacity. First of all, it can be seen from Figure 6a that graphite has a high degree of crystallinity, followed by soft carbon, and hard carbon is the lowest. The layer distance is G<SC<HC. Figure 6b is the XRD of three kinds of carbon films and lithium foil after pressing. It can be seen that LiC ₆ is formed in all three, but the peak position of LiC ₆ in SC-Li and HC-Li is shifted to a low angle, indicating that the layer The spacing is also larger than LiC ₆ in graphite. Large interlayer spacing can increase the transport rate of lithium ions. In addition, the lithium ion transport channel in G-Li is long-range ordered, and the arrangement of graphite in the solid anode will undoubtedly increase the lithium ion transport path, which is not conducive to the transport of lithium ions. While for SC and HC, the transport of Li ions is isotropic, which is beneficial to the transport of Li ions. Figure 7 is the SEM image of SC-10SiN and HC-10SiN. It can be seen that a large amount of nano-SiN (~5nm) is distributed on the surface and gap of SC and HC particles respectively. These SiNs form LiSi and Li ₃ N after lithium intercalation. A network of conducting ions is formed and electrons are blocked to some extent. However, compared with HC-10SiN, SC-10SiN shows better continuity, which may be related to the difference in structural strain capacity of SC and HC, so that the more rigid SiN can better combine with SC and bring better continuity. , showing a better performance improvement compared to HC-10SiN in the later stage.

In order to verify the improvement of ionic conductivity after coating SiN, and further verify the advantages of the material system, we assembled an electron blocking battery, and the protective layers were respectively made of graphite (G), soft carbon (SC), hard carbon (HC), nano Silicon nitrogen coated soft carbon (SC-10SiN) and pure electrolyte layer (Li ₆ PS ₅ Cl) were compared and analyzed. It can be seen from Figure 8 that the battery impedance of the SC-SiN protective layer is close to the impedance of the electrolyte Li ₆ PS ₅ Cl, which is significantly higher than that of the SC and HC protective layers. The impedance of the graphite protective layer is the largest, which is due to the smallest layer spacing of graphite and the tortuous ion transmission channel of graphite, which leads to the increase of the transmission path. Fig. 9 is the impedance diagram of SC and SC-10SiN batteries at the initial stage and after standing at 55° for 12h. It can be seen that the initial impedance of SC-10SiN is lower than that of SC, and the impedance decreases significantly after 12 hours of reaction. This is because a large amount of SiN is not decomposed under the initial conditions, so SiN hinders the transmission of lithium ions. After 12 hours of reaction, the ion-conducting LiSi and Li ₃ N are formed to promote the transmission of lithium ions, thereby reducing the impedance. This further proves that the introduction of SiN plays a role in the decomposition of LiSi and Li ₃ N to generate ions. 10 is the Tafel curve of the symmetrical battery, and the test is carried out at minus 5°. It can be seen that the exchange current density of the SC-SiN symmetric battery is the highest (0.216mA/cm ² ). This is due to the three-dimensional ionic network that increases the transport speed of lithium ions. The exchange current densities of SC-Li and HC-Li anodes are relatively close, both of which are significantly higher than those of G-Li and Li anodes but lower than that of SC-SiN anodes, which confirms the promotion of carbon materials for lithium intercalation and the effect of SiN on lithium metal. The three-dimensional transport effect of ion transport channels between carbon and carbon materials. Using LiIn alloy as the positive electrode to provide the lithium source continuously provides lithium ions to the negative electrode for deposition until the battery is short-circuited, and the deposition curves of different negative electrodes are obtained, as shown in Figure 11. It can be seen that the SC-SiN-Li anode exhibits the highest limit areal capacity at various current densities, which can reach more than 12mA/cm ² , which further proves that the addition of SiN helps in the deposition of lithium metal. Figure 12 shows the critical current densities of five kinds of negative electrodes. The constant-capacity test method adopted here has an areal capacity of 0.25mAh/cm ² . SC-SiN exhibits the highest CCD, as high as 20 mA/cm ² . The CCDs of HC and SC are the same, reaching 12mA/cm ² . The CCDs of G-Li and Li are only 4 mA/cm ² . As shown in Figure 13, the SC-SiN-Li symmetric battery can cycle 600 cycles at an areal capacity of 15mA/cm ² and 0.25mAh/cm ² , and cycle 300h at 2mA/cm ² and 2mAh/cm ² . The SC-Li symmetric battery in Figure 13 can only cycle for less than 5 cycles at a current density of 15mA/cm ² , and the other negative electrodes will short-circuit immediately. At 2mA/ ^cm2 and 2mAh/ ^cm2 , the SC-Li symmetric cell experienced a short circuit after 70 cycles, while the HC-Li anode showed increasing interfacial resistance due to uneven deposition and exfoliation. As shown in Figure 14, G-Li and Li exhibited larger polarization voltages, and a short circuit occurred within 20 cycles. In order to screen out suitable systems more directly, we use G-Li, SC-Li, HC-Li, G-SiN-Li, SC-SiN-Li and HC-SiN-Li as negative electrodes, LCO as positive electrodes, and Li ₆ PS ₅ Cl was used as the electrolyte to assemble the full cell. The areal capacity was 2.7mAh/cm ² . It can be seen that G-li, SC-Li, and HC-Li negative electrodes have micro-short circuits at 1C, 2C and 0.5C respectively (Figure 15). This micro-short circuit will greatly increase the charging time, and the lithium dendrites will continue to grow The piercing electrolyte decomposes, thus resulting in rapid lithium consumption leading to rapid capacity fading. After the introduction of SiN, as shown in Figure 16, it can be seen that the micro-short circuit phenomenon of the three systems has been significantly improved compared with the system without SiN. Micro-short circuit occurs, while the SC-SiN-Li negative electrode can still charge and discharge stably at a high surface capacity of 2.7mAh/cm ² and a high current density of 8.1mA/cm ² .

The above results further demonstrate that nano-silicon-nitrogen coating can cooperate with carbon materials to improve the interface performance between the lithium anode and the electrolyte, reduce the interface impedance, promote ion transport, inhibit the growth of lithium dendrites and the deposition of lithium metal, thereby improving the high load capacity of the battery. , high current and long cycle capability. In addition, in the carbon material system coated with nano-silicon and nitrogen, although the coating of graphite and hard carbon has also played a certain role in improving, it cannot completely solve the micro-short circuit effect under high current, which may be related to the growth of graphite under high current. The ion transport path and the poor continuity of the hard carbon-coated particles. As the optimal choice, soft carbon is more suitable for the coating system of nano-silicon nitrogen.

In the SC-SiN system, we further optimized the proportion of SiN, and we found that the addition of 5% SiN has limited effect on improving the lithium deposition behavior, and a short circuit occurs at 2C (Figure 17b), which may be due to the SiN Caused by insufficient coating of SC particles. When the proportion of SiN increased to 15%, the micro-short circuit also began to appear at 2C (Figure 17d), but it was also better than the SC and SC-5SiN anodes. In order to explore the reason, we did XRD on the SC-15SiN-Li anode. It can be seen from Figure 18a that the peak of Si ₃ N ₄ cannot be detected on the SC-10SiN-Li negative electrode after pressing the negative electrode film and lithium foil, indicating that most of the Si ₃ N ₄ has been decomposed. On the other hand, Si ₃ N ₄ was detected in SC-15SiN-Li anode. Figure 18b is the XRD of the negative electrode film after one charge. It can also be found that the Si ₃ N ₄ in SC-15SiN-Li is still not completely decomposed, indicating that when the proportion of Si ₃ N ₄ increases to 15%, the ionic and electronic insulating Si ₃ N ₄ seriously hinders the transport of ions and electrons, resulting in the incomplete decomposition of Si ₃ N ₄ . Electron blocking batteries with different Si ₃ N ₄ ratios were also assembled to test their ionic conductivity, as shown in Figure 19, it is not difficult to find that the impedance of SC-15SiN batteries also increased significantly, further proving that the incomplete decomposition of Si ₃ N ₄ is serious hinder the transport of lithium ions.

The above results show that the Si ₃ N ₄ phase does not want to be retained in the interface. We expect it to be completely transformed into LiSi and Li ₃ N to build an effective three-dimensional ion-conducting network in the interface. Other phases that can bring about this transformation Both means can be used for the same reason and achieve basically the same expected effect. For example, we can directly introduce amorphous LiSi alloy and Li ₃ N into soft carbon particles according to the desired stoichiometric ratio for coating, so as to form a three-dimensional ion conductive network more directly.

In order to further prove the excellent electrical properties of the SC-10SiN anode, we performed a series of electrochemical characterizations. We know that SC-10SiN has a higher exchange current density, so it will have better rate performance. It can be seen from the rate performance (Figure 20) that the LCO-LPSCl-SC-10SiN-Li battery can still exhibit a specific capacity of 37mAh/g at an ultra-high rate of 150C. When the charging cut-off voltage is increased to 4.8V, it can exhibit a specific capacity of about 100mAh/g at 150C. In addition, the LCO-LPSCl-SC-10SiN-Li battery can also achieve an ultra-long cycle of 22,000 cycles at an ultra-high current density of 12.5mA/cm ² , and the battery capacity retention rate after 22,000 cycles is as high as 95% (Figure 21) . While for SC-Li, HC-Li and G-Li anodes, the decay is almost zero at 12000 cycles, 500 cycles and 800 cycles, respectively. From the charge-discharge curves in Figure 22, it can be seen that HC-Li and SC-Li have serious micro-short circuit problems, so lithium metal will be rapidly consumed and the cycle will rapidly decay, while for G-Li and Li electrodes, it can be found that the 25C exhibits Very low theoretical specific capacity. From the XRD in Figure 6 above, we know that due to the slow reaction kinetics of G, G in G-Li cannot completely intercalate lithium, so Li under the G layer cannot be transported to the surface of the G electrode, resulting in the formation of SC-10SiN-Li Rapid decay of the battery. We have summarized and compared the rate performance, current density and cycle life of solid-state batteries in the literature. It can be found that the ultimate charge rate, current density and cycle life of the SC-10SiN-Li negative electrode are unprecedented and far It exceeds the current highest level of lithium anode for solid-state batteries. This is all due to the three-dimensional ion-conducting and electron-blocking networks of LiSi and Li ₃ N formed after SiN decomposition, thereby driving the transport of lithium ions into the negative electrode. Therefore, lithium metal can nucleate and grow inside the SC-10SiN-Li negative electrode, which will greatly reduce the local current density of the SC-10SiN-Li negative electrode, thus achieving an ultra-high rate of 150C and an ultra-high current density of 12.5mA/cm ² 22000 ultra-long stable cycles.

The SC-10SiN-Li anode not only exhibits ultrahigh rate capability and can work at ultrahigh current density, but also can achieve high areal capacity. It can be seen from Figure 23 that the LCO/LPSCl/SC-10SiN-Li battery can cycle 600 cycles at an areal capacity of 2.7mAh/ ^cm2 and a high current density of 5.6mA/ ^cm2 , and the capacity retention rate is as high as 85.7%. And the current density of 5.6mA/cm ² is also the highest value under the high surface capacity (>1mAh/cm ² ) of the current solid lithium metal battery. At the same time, it also exhibits good rate performance under the areal capacity of 2.7mAh/cm ² . It can still exhibit a specific capacity of 120mAh/g at 2C (Figure 24). In addition, the SC-10SiN-Li anode can also realize charging and discharging under ultra-high surface capacity. It can ^be seen from Fig. Play a theoretical specific capacity of 135mAh/g. When the areal capacity reaches 15mAh/cm ² , the polarization increases, and only a specific capacity of 110mAh/g is exhibited. But at 0.05C, it can reach 135mAh/g (Figure 26), and 15mAh/cm ² has reached the highest value of surface capacity in all solid-state, semi-solid and polymer solid-state lithium metal batteries. With an areal capacity of 7.6 mAh/cm ² (Fig. 27), the LCO/LPSCl/SC-10SiN-Li battery can also be cycled for 100 cycles at 0.1C. In addition, SC-10SiN-Li has an exchange current density of 0.216 mA/ ^cm2 at -5 °C, so it also has better low-temperature performance. It can be seen from Figure 28 that the LCO/LPSCl/SC-10SiN-Li battery still exhibits specific capacities of 82 and 62mAh/g at -10°C and -20°C, respectively.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (30)

1. An activated negative electrode with lithium dendrite inhibition, containing a carbon layer in the negative electrode, with an amorphous lithium-silicon alloy and a Li ₃ N phase in the carbon layer; the three-dimensional lithium-silicon alloy and Li ₃ N phase composed of the amorphous The ion conductive network is coated on the outer periphery of carbon particles in the carbon layer; the carbon layer in the negative electrode is compounded with the side of the lithium-containing foil near the solid electrolyte. 2. The activated negative electrode with lithium dendrite inhibition according to claim 1, characterized in that, the amorphous lithium-silicon alloy and the Li ₃ N phase are composed of carbon particles and silicon-containing particles coated on the surface of the carbon particles. Made of nitrogen nanoparticles. 3. The activated negative electrode with lithium dendrite inhibition according to claim 2, characterized in that the carbon particles are micron-sized particles. 4 . The activated negative electrode with lithium dendrite inhibition according to claim 2 , wherein the carbon particles are carbon particles with a D50 of less than 20 μm. 5 . The activated negative electrode with lithium dendrite inhibition according to claim 2 , wherein the carbon particles are carbon particles with a D50 of 0.5-20 μm. 6 . The activated negative electrode with lithium dendrite inhibition according to claim 2 , wherein the carbon particles are carbon particles with a D50 of 5-20 μm. 7. The activated negative electrode with lithium dendrite inhibition according to claim 2, characterized in that the D50 particle size of the silicon-nitrogen-containing nanoparticles is 300 nm or less. 8. The activated negative electrode with lithium dendrite inhibition according to claim 2, characterized in that the D50 particle size of the silicon-nitrogen-containing nanoparticles is 100 nm or less. 9. The activated negative electrode with lithium dendrite inhibition according to claim 2, characterized in that the D50 particle size of the silicon-nitrogen-containing nanoparticles is 50 nm or less. 10. The activated negative electrode with lithium dendrite inhibition according to claim 2, wherein the carbon particles are soft carbon. 11. The activated negative electrode with lithium dendrite inhibition according to claim 2, wherein the mass of the silicon-nitrogen-containing nanoparticles accounts for 5% to 15% of the total mass of the carbon particles and the silicon-nitrogen-containing nanoparticles, Wherein, the mass of the silicon-nitrogen-containing nanoparticles is calculated by the mass of Si ₃ N ₄ that the Si and N contained therein can correspond to. 12. The activated negative electrode with lithium dendrite inhibition according to claim 2, wherein the mass of the silicon-nitrogen-containing nanoparticles accounts for 10% ± 2% of the total mass of the carbon particles and the silicon-nitrogen-containing nanoparticles, Wherein, the mass of the silicon-nitrogen-containing nanoparticles is calculated by the mass of Si ₃ N ₄ that the Si and N contained therein can correspond to. 13 . The activated negative electrode with lithium dendrite inhibition according to claim 2 , wherein the silicon-nitrogen-containing nanoparticles are Si ₃ N ₄ , or a mixture of lithium-silicon alloy and Li ₃ N. 14 . 14. The activated negative electrode with lithium dendrite inhibition according to claim 1, characterized in that, the loading capacity of the negative electrode is more than 1 mAh/cm ² areal capacity. 15. The activated negative electrode with lithium dendrite inhibition according to claim 1, characterized in that, the loading capacity of the negative electrode is more than 2 mAh/cm ² areal capacity. 16. The activated negative electrode with lithium dendrite inhibition according to claim 1, characterized in that, the loading capacity of the negative electrode is more than 5 mAh/cm ² areal capacity. 17. The activated negative electrode with lithium dendrite inhibition according to claim 1, characterized in that the loading capacity of the negative electrode is more than 7 mAh/cm ² areal capacity. 18. The activated negative electrode with lithium dendrite inhibition according to claim 1, characterized in that, the loading capacity of the negative electrode is more than 10 mAh/cm ² areal capacity. 19. The activated negative electrode with lithium dendrite inhibition according to claim 1, characterized in that, the loading capacity of the negative electrode is more than 15 mAh/cm ² areal capacity. 20. The activated negative electrode with lithium dendrite inhibition according to claim 1, characterized in that the operating temperature of the negative electrode is -20°C to 75°C. 21. The activated negative electrode with lithium dendrite inhibition according to claim 1, characterized in that, the negative electrode also contains a binder, and the binder is used for the bonding of particles in the carbon layer to form a film, The mass of the binder accounts for less than 20% of the total mass of the silicon-nitrogen-containing nanoparticles, the carbon particles and the binder. 22. The activated negative electrode with lithium dendrite inhibition according to claim 21, characterized in that the mass of the binder accounts for 5%-10% of the total mass of the silicon-nitrogen-containing nanoparticles, carbon particles and binder. 23. The activated negative electrode with lithium dendrite inhibition according to claim 21, characterized in that the binder is a fluorine-containing vinyl polymer. 24. The activated negative electrode with lithium dendrite inhibition according to claim 21, wherein the binder is polytetrafluoroethylene or polyvinylidene fluoride. 25. The preparation method of the activated negative electrode with lithium dendrite inhibition described in any one of claims 1-24, after adopting carbon particles and nano-particles containing silicon and nitrogen to mix and grind, mix with binding agent to make negative electrode protective layer; The negative electrode protective layer is arranged adjacent to the metal lithium-containing foil as the negative electrode, and after the battery is assembled, the activation is completed. 26. The method for preparing an activated negative electrode with lithium dendrite inhibition according to claim 25, wherein the activation of the negative electrode is completed at a rate of 0.1C-0.5C for 1-2 weeks. 27. The method for preparing an activated negative electrode with lithium dendrite inhibition according to claim 25, characterized in that the negative electrode protection layer is compounded with the foil containing metal lithium under pressure. 28 . The method for preparing an activated negative electrode with lithium dendrite inhibition according to claim 27 , wherein the pressurization pressure of the negative electrode protective layer and the foil containing metal lithium is above 50 MPa. 29 . The method for preparing an activated negative electrode with lithium dendrite inhibition according to claim 27 , wherein the pressurization pressure of the negative electrode protective layer and the foil containing metal lithium is above 700 MPa. 30. A battery comprising an activated negative electrode with lithium dendrite inhibition according to any one of claims 1-24.

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