High-first-efficiency low-expansion silicon-carbon composite negative electrode material and preparation method thereof

Abstract

The invention provides a high-first-efficiency low-expansion silicon-carbon composite negative electrode material and a preparation method thereof. The silicon-carbon composite negative electrode material comprises a silicon-carbon inner core, a fast ion conductor shell layer coated on the surface of the silicon-carbon inner core, and a graphene network layer coated on the surface of the fast ion conductor shell layer, the silicon-carbon inner core comprises porous carbon and nano silicon deposited in porous carbon channels. According to the high-first-efficiency low-expansion silicon-carbon composite negative electrode material and the preparation method thereof provided by the invention, by constructing a core-shell-net triple composite structure consisting of the silicon-carbon core, the fast ion conductor shell layer and the graphene network layer, volume expansion can be effectively inhibited; and the specific capacity, the first efficiency and the cycling stability of the silicon-carbon negative electrode material are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of anode material technology, and particularly relates to a high-efficiency, low-expansion silicon-carbon composite anode material and its preparation method. Background Technology

[0002] With the development of lithium-ion battery materials, higher energy density, longer cycle life, faster charge / discharge rates, and lower production costs have become the focus of current research. While commercially available graphite anodes with a theoretical capacity of 372 mAh / g possess mature manufacturing processes, their layered structure limits the lithium-ion insertion rate, easily triggering lithium plating side reactions during fast charging, and their energy density is already approaching its theoretical limit. Silicon-based anodes boast a theoretical specific capacity as high as 4200 mAh / g, 11.3 times that of graphite, but their volume expansion rate exceeding 300% leads to electrode pulverization and continuous SEI film rupture, severely impacting battery cycle performance.

[0003] Therefore, it is particularly necessary to develop a silicon-carbon anode material with high initial efficiency, high energy density, and low expansion performance. Chinese patent CN103367727A discloses a method of mixing and drying nano-silicon, dispersant, binder, and particulate graphite in an organic solvent, then adding the mixture to a dispersion of a carbon source precursor, mixing again, drying a second time, and heat-treating to obtain a silicon-carbon anode material for lithium-ion batteries. However, due to the limitations of mechanical grinding, which makes it difficult to overcome physical constraints, and the difficulty in grinding silicon to the nanoscale, the improvement in expansion is not significant, resulting in limited improvement in initial efficiency. Summary of the Invention

[0004] Based on the above-mentioned technical problems, the present invention provides a high first-efficiency and low-expansion silicon-carbon composite anode material and its preparation method. By constructing a core-shell-network triple composite structure composed of a silicon-carbon core, a fast-ion conductor shell, and a graphene network layer, volume expansion can be effectively suppressed, and the specific capacity, first-efficiency and cycle stability of the silicon-carbon anode material can be greatly improved.

[0005] The present invention proposes a high-efficiency, low-expansion silicon-carbon composite anode material, comprising a silicon-carbon core, a fast-ion conductor shell coating the surface of the silicon-carbon core, and a graphene network layer coating the surface of the fast-ion conductor shell; the silicon-carbon core comprises porous carbon and nano-silicon deposited within the porous carbon channels.

[0006] In this invention, porous carbon is used as a carrier for nano-silicon deposition, allowing the nano-silicon to be effectively deposited within the porous carbon channels, thus effectively mitigating volume expansion. The resulting material is then used as a silicon-carbon core, and a fast-ion conductor shell of Li3VO4 is formed on its surface through a hydrothermal reaction. This shell exhibits high lithium-ion conductivity, reduces interfacial impedance, and improves the initial efficiency of the anode material. Furthermore, a graphene network layer is coated onto the fast-ion conductor shell. Graphene, primarily existing in the form of a three-dimensional network carbon layer, works synergistically with the fast-ion conductor to enhance the ionic and electronic conductivity of the composite anode material. This, combined with the formation of a three-dimensional ion-conducting and electron-conducting pathway, alleviates the capacity decay problem of pure silicon anodes during cycling, achieving stable long-cycle performance and high capacity retention.

[0007] Preferably, the porous carbon has a pore size of 20-100 nm and a pore volume of 0.5-1.5 cm³. 3 / g, specific surface area of ​​100-2500m² 2 / g; Preferably, the particle size of the nano-silicon is 1-50 nm.

[0008] Preferably, the fast ion conductor shell comprises Li3VO4; Preferably, the content of the fast ion conductor shell is 0.1-2 wt% based on the total mass of the silicon-carbon composite anode material.

[0009] Preferably, the electrical conductivity of the graphene network layer is ≥10. 3 S / cm; Preferably, the graphene network layer content is 0.5-10 wt% based on the total mass of the silicon-carbon composite anode material.

[0010] This invention also proposes a method for preparing the above-mentioned high-efficiency, low-expansion silicon-carbon composite anode material, comprising the following steps: S1. After chemical vapor deposition of porous carbon and gaseous silicon source, nano-silicon is formed in the porous carbon channels to obtain silicon-carbon core. S2. Mix the silicon-carbon core and the fast ion conductor precursor, and after hydrothermal treatment, form a fast ion conductor shell on the surface of the silicon-carbon core to obtain a silicon-carbon core with a fast ion conductor shell on the surface. S3. The silicon-carbon core coated with a fast-ion conductor shell is mixed with graphene oxide and then reduced to form a graphene network layer on the surface of the fast-ion conductor shell, thus obtaining the composite anode material.

[0011] Preferably, in step S1, the porous carbon is obtained by alkaline activation of a carbon source precursor; the gaseous silicon source is at least one of silane, silane, dichlorosilane, or chlorosilane. Preferably, the chemical vapor deposition temperature is 450-550℃ and the time is 4-6h.

[0012] Preferably, in step S2, the precursor of the fast ion conductor includes a lithium source and a vanadium source; Preferably, the lithium source is at least one of lithium carbonate, lithium nitrate, or lithium hydroxide, and the vanadium source is at least one of ammonium metavanadate, vanadium oxychloride, potassium metavanadate, or vanadium oxysulfate. Preferably, the hydrothermal treatment temperature is 150-200℃ and the time is 6-12h.

[0013] Preferably, in step S3, the hydrothermal treatment temperature further includes the addition of a template agent of an amphiphilic block copolymer; Preferably, the amphiphilic block copolymer is obtained by condensing amino-terminated polyethylene glycol with bis(carboxymethyl)trithiocarbonate, followed by polymerization with brominated N-vinyl-N′-butylimidazolium salt under the action of a free radical initiator.

[0014] In this invention, the structure of the above-mentioned amphiphilic block copolymer is shown below:

[0015] x and y are integers greater than 0.

[0016] In this invention, the positive charge of the amphiphilic block copolymer allows it to be adsorbed onto the surface of the silicon-carbon core. It not only has good ion-electron transport capability and structural stability, but also promotes the directional growth of Li3VO4 on the surface of the silicon-carbon core, forming continuous ion channels, optimizing interface performance, and further improving the lithium-ion fast conduction performance of Li3VO4, thereby increasing the retention rate of the fast ion conductor layer.

[0017] Preferably, in step S3, the reduction treatment is carried out under a reducing agent. Preferably, the reducing agent is at least one of hydroiodic acid, hydrazine hydrate, sodium borohydride, ascorbic acid, or sodium hydrosulfite.

[0018] This invention also proposes a lithium-ion battery anode, comprising the above-mentioned silicon-carbon composite anode material or the silicon-carbon composite anode material prepared by the above-mentioned preparation method.

[0019] Compared with the prior art, the present invention has the following technical effects: The silicon-carbon composite anode material prepared by this invention can significantly increase the conductivity of lithium-ion batteries, promote rapid lithium-ion transport, alleviate volume expansion during lithium battery charging and discharging, and increase the cycle capacity, first discharge capacity, and first coulombic efficiency of lithium batteries. Attached Figure Description

[0020] Figure 1 This is a SEM image of the silicon-carbon composite anode material described in Example 1. Detailed Implementation

[0021] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0022] Example 1

[0023] A high-efficiency, low-expansion silicon-carbon composite anode material is prepared by the following method: (1) Glucose was completely dissolved in deionized water and transferred to a polytetrafluoroethylene liner in a high-pressure reactor. The mixture was heated to 180°C and hydrothermally reacted for 12 hours. After naturally cooling to room temperature, the mixture was filtered, washed with water, and dried. The resulting carbon spheres were mixed with potassium hydroxide at a mass ratio of 1:1 and activated at 800°C for 1 hour in a nitrogen atmosphere. After washing with dilute acid solution until neutral, the mixture was dried to obtain porous carbon with an average pore size of 80 nm and a pore volume of 0.85 cm³. 3 / g; (2) Porous carbon was placed in a fluidized bed, and nitrogen gas was continuously introduced at a flow rate of 8 L / min until the oxygen content dropped to below 100 ppm. Heating was started, the temperature was raised to 500℃ and held for 5 h. At the same time, a mixture of silane and nitrogen gas with a volume ratio of 1:4 was introduced. Nano-silicon was deposited in the pores of the porous carbon to form a silicon-carbon core. The proportion of nano-silicon in the silicon-carbon core was 32 wt%. (3) Add silicon carbon core, lithium hydroxide and ammonium metavanadate to ethanol / deionized water mixed solvent with a volume ratio of 1:1 in a mass ratio of 100:3:2 and mix well. Transfer the resulting precursor solution to the polytetrafluoroethylene liner of the high pressure reactor and heat it to 170°C at a rate of 5°C / min. React hydrothermally for 8 hours. Cool to room temperature with the furnace, filter, wash with water, dry, and calcine at 400°C in air for 3 hours to obtain silicon carbon core with Li3VO4 shell on the surface. (4) The silicon-carbon core coated with Li3VO4 shell and graphene oxide were added to deionized water at a mass ratio of 15:1 and mixed well. Then, hydroiodic acid with a mass of 1.1 times that of graphene oxide was added. The mixture was heated to 90°C and stirred for 4 hours. A graphene network layer was formed on the surface of the fast ion conductor shell. The mixture was filtered, washed with water, and dried to obtain the silicon-carbon composite anode material. Its SEM image is shown in the figure below. Figure 1 As shown.

[0024] Example 2 A high-efficiency, low-expansion silicon-carbon composite anode material is prepared by the following method: (1) Glucose was completely dissolved in deionized water and transferred to a polytetrafluoroethylene liner in a high-pressure reactor. The mixture was heated to 180°C and hydrothermally reacted for 12 hours. After naturally cooling to room temperature, the mixture was filtered, washed with water, and dried. The resulting carbon spheres were mixed with potassium hydroxide at a mass ratio of 1:1 and activated at 800°C for 1 hour in a nitrogen atmosphere. After washing with dilute acid solution until neutral, the mixture was dried to obtain porous carbon with an average pore size of 80 nm and a pore volume of 0.85 cm³. 3 / g; (2) Porous carbon was placed in a fluidized bed, and nitrogen gas was continuously introduced at a flow rate of 8 L / min until the oxygen content dropped below 100 ppm. Heating was started, and the temperature was raised to 450℃ and held for 6 h. At the same time, a mixture of silane and nitrogen gas with a volume ratio of 1:5 was introduced. Nano-silicon was deposited in the pores of the porous carbon to form a silicon-carbon core. The proportion of nano-silicon in the silicon-carbon core was 26 wt%. (3) Add silicon carbon core, lithium nitrate and vanadium trichloride in a mass ratio of 100:3:2 to a mixed solvent of ethanol / deionized water in a volume ratio of 1:1 and mix well. Transfer the resulting precursor solution to the polytetrafluoroethylene liner of the high-pressure reactor and heat it to 150°C at a rate of 5°C / min. React hydrothermally for 12 hours. Cool to room temperature with the furnace, filter, wash with water, dry, and calcine at 400°C in air for 3 hours to obtain silicon carbon core with a Li3VO4 shell on the surface. (4) Add the silicon-carbon core coated with Li3VO4 shell and graphene oxide to deionized water at a mass ratio of 15:1 and mix well. Then add hydrazine hydrate with a mass of 1 times that of graphene oxide, heat to 80°C, stir and react for 6 hours to form a graphene network layer on the surface of the fast ion conductor shell. Filter, wash with water and dry to obtain the silicon-carbon composite anode material.

[0025] Example 3 A high-efficiency, low-expansion silicon-carbon composite anode material is prepared by the following method: (1) Glucose was completely dissolved in deionized water and transferred to a polytetrafluoroethylene liner in a high-pressure reactor. The mixture was heated to 180°C and hydrothermally reacted for 12 hours. After naturally cooling to room temperature, the mixture was filtered, washed with water, and dried. The resulting carbon spheres were mixed with potassium hydroxide at a mass ratio of 1:1 and activated at 800°C for 1 hour in a nitrogen atmosphere. After washing with dilute acid solution until neutral, the mixture was dried to obtain porous carbon with an average pore size of 80 nm and a pore volume of 0.85 cm³. 3 / g; (2) Porous carbon was placed in a fluidized bed, and nitrogen gas was continuously introduced at a flow rate of 8 L / min until the oxygen content dropped to below 100 ppm. Heating was started, and the temperature was raised to 550℃ and held for 4 h. At the same time, a mixture of silane and nitrogen gas with a volume ratio of 1:3 was introduced. Nano-silicon was deposited in the pores of the porous carbon to form a silicon-carbon core. The proportion of nano-silicon in the silicon-carbon core was 36 wt%. (3) Add silicon carbon core, lithium carbonate and potassium metavanadate in a mass ratio of 100:3:2 to a volume ratio of 1:1 ethanol / deionized water mixed solvent and mix well. Transfer the resulting precursor solution to the polytetrafluoroethylene liner of the high pressure reactor and heat it to 200°C at a rate of 5°C / min. React hydrothermally for 6 hours. Cool to room temperature with the furnace, filter, wash with water, dry, and calcine at 400°C in air for 3 hours to obtain silicon carbon core with Li3VO4 shell on the surface. (4) Add the silicon-carbon core coated with Li3VO4 shell and graphene oxide to deionized water at a mass ratio of 15:1 and mix well. Then add sodium borohydride at a mass ratio of 0.8 times that of graphene oxide. Heat to 80°C and stir for 2 hours to form a graphene network layer on the surface of the fast ion conductor shell. Filter, wash with water and dry to obtain the silicon-carbon composite anode material.

[0026] Example 4 A high-efficiency, low-expansion silicon-carbon composite anode material is prepared by the following method: (1) Glucose was completely dissolved in deionized water and transferred to a polytetrafluoroethylene liner in a high-pressure reactor. The mixture was heated to 180°C and hydrothermally reacted for 12 hours. After naturally cooling to room temperature, the mixture was filtered, washed with water, and dried. The resulting carbon spheres were mixed with potassium hydroxide at a mass ratio of 1:1 and activated at 800°C for 1 hour in a nitrogen atmosphere. After washing with dilute acid solution until neutral, the mixture was dried to obtain porous carbon with an average pore size of 80 nm and a pore volume of 0.85 cm³. 3 / g; (2) Porous carbon was placed in a fluidized bed, and nitrogen gas was continuously introduced at a flow rate of 8 L / min until the oxygen content dropped to below 100 ppm. Heating was started, the temperature was raised to 500℃ and held for 5 h. At the same time, a mixture of silane and nitrogen gas with a volume ratio of 1:4 was introduced. Nano-silicon was deposited in the pores of the porous carbon to form a silicon-carbon core. The proportion of nano-silicon in the silicon-carbon core was 32 wt%. (3) The silicon carbon core, lithium hydroxide, ammonium metavanadate and amphiphilic block copolymer were added to a mixed solvent of ethanol / deionized water with a volume ratio of 1:1 in a mass ratio of 100:3:2:5 and mixed well. The resulting precursor solution was transferred to the polytetrafluoroethylene liner of the high-pressure reactor and heated to 170°C at a rate of 5°C / min. The hydrothermal reaction was carried out for 8 hours. The reactor was cooled to room temperature with the furnace, filtered, washed with water, dried, and calcined at 400°C in air for 3 hours to obtain a silicon carbon core with a Li3VO4 shell on the surface. The above-mentioned amphiphilic block copolymer was prepared by the following method: amino-terminated polyethylene glycol (M... WThe intermediate product was prepared by mixing 1-vinyl-N′-butylimidazolium salt and p-toluenesulfonic acid in a mass ratio of 1:0.3:0.01 with toluene, stirring and refluxing at 130°C for 2 hours, concentrating, washing, and drying. The resulting intermediate product was then added to N-methylpyrrolidone containing N-vinyl-N′-butylimidazolium bromide and azobisisobutyronitrile in a mass ratio of 1:1:0.1. The mixture was stirred and reacted at 60°C under nitrogen protection for 12 hours, then concentrated, washed, and dried to obtain the amphiphilic block copolymer. The N-vinyl-N′-butylimidazolium salt was obtained by mixing 1-vinylimidazolium and 1-chlorobutane in a mass ratio of 1:1 and then stirring and reacting at 70°C under nitrogen protection for 12 hours. (4) Add the silicon-carbon core coated with Li3VO4 shell and graphene oxide to deionized water at a mass ratio of 15:1 and mix well. Then add hydroiodic acid with a mass of 1.1 times that of graphene oxide, heat to 90°C, stir and react for 4 hours to form a graphene network layer on the surface of the fast ion conductor shell. Filter, wash with water and dry to obtain the silicon-carbon composite anode material.

[0027] Comparative Example 1 A high-efficiency, low-expansion silicon-carbon composite anode material is prepared according to the preparation method described in Example 1. The difference from Example 1 is that step (3) is omitted, and in step (4), the silicon-carbon core is replaced by the silicon-carbon core with a Li3VO4 shell on the surface.

[0028] Comparative Example 2 A high-efficiency, low-expansion silicon-carbon composite anode material is prepared according to the preparation method described in Example 1. The difference from Example 1 is that step (4) is omitted.

[0029] Comparative Example 3 A high-efficiency, low-expansion silicon-carbon composite anode material is prepared according to the preparation method described in Example 4. In step (3), the above-mentioned amphiphilic block copolymer is prepared by the following method: amino-terminated polyethylene glycol (M W The intermediate product was added to toluene at a mass ratio of 1:0.3:0.01 (1000), bis(carboxymethyl)trithiocarbonate, and p-toluenesulfonic acid. The mixture was stirred and refluxed at 130°C for 2 hours. After concentration, washing, and drying, the intermediate product was added to N-methylpyrrolidone containing 1-vinylimidazole and azobisisobutyronitrile at a mass ratio of 1:1:0.1. The mixture was stirred and reacted at 60°C under nitrogen protection for 12 hours. After concentration, washing, and drying, the amphiphilic block copolymer was obtained.

[0030] The high-efficiency, low-expansion silicon-carbon composite anode materials described in the examples and comparative examples were mixed with a conductive agent (SuperP) and a binder (aqueous dispersion of acrylonitrile multi-component copolymer, LA132, solid content 15%) at a weight ratio of 90:2:8 to prepare anode slurry. The slurry was coated on the surface of copper foil, dried, and stamped to form the anode. A lithium metal sheet was used as the counter electrode. A three-component mixed solvent of EC:DMC:EMC=1:1:1 (v / v / v) was used, and 1 mol / L LiPF6 was added as the electrolyte. A polypropylene microporous membrane was used as the separator to prepare a CR2032 coin cell. Charge-discharge tests were performed on the LANHE battery testing system, and the results are shown in Table 1.

[0031] Initial charge-discharge performance test: Under normal temperature conditions, discharge at a constant current of 0.1C to a voltage of 0.01V, then discharge at a constant current of 0.02C to a voltage of 0.005V, and then charge at a constant current of 0.1C to a voltage of 1.5V to obtain the initial reversible specific capacity and initial coulombic efficiency.

[0032] Cyclic performance test: Under normal temperature conditions, constant current charge and discharge at 1C to 0.01V, then constant current discharge at 0.05C to 0.005V, and finally constant current charge at 1C to 1.5V to obtain the delithiation specific capacity. This cycle is repeated 100 times, and the capacity retention rate and expansion rate after 100 cycles are calculated. The initial electrode thickness H1 and the lithium insertion thickness H2 after 100 cycles are tested. The volume expansion rate after 100 cycles is calculated as (H2-H1) / H1.

[0033] Table 1. Performance comparison of the silicon-carbon composite anode materials described in the examples and comparative examples.

[0034] As shown in Table 1 above, the high-efficiency, low-expansion silicon-carbon composite anode material prepared by the present invention can significantly increase the conductivity of lithium-ion batteries, promote rapid lithium-ion transport, alleviate volume expansion during lithium battery charging and discharging, and increase the cycle capacity, first discharge capacity, and first coulombic efficiency of lithium batteries.

[0035] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-efficiency, low-expansion silicon-carbon composite anode material, characterized in that, It includes a silicon-carbon core, a fast-ion conductor shell covering the surface of the silicon-carbon core, and a graphene network layer covering the surface of the fast-ion conductor shell; the silicon-carbon core includes porous carbon and nano-silicon deposited in the porous carbon channels.

2. The high-efficiency, low-expansion silicon-carbon composite anode material according to claim 1, characterized in that, The porous carbon has a pore size of 20-100 nm and a pore volume of 0.5-1.5 cm³. 3 / g, specific surface area of ​​100-2000m² 2 / g; Preferably, the particle size of the nano-silicon is 1-50 nm.

3. The high-efficiency, low-expansion silicon-carbon composite anode material according to claim 1 or 2, characterized in that, The fast ion conductor shell includes Li3VO4; Preferably, the content of the fast ion conductor shell is 0.1-2 wt% based on the total mass of the silicon-carbon composite anode material.

4. The high-efficiency, low-expansion silicon-carbon composite anode material according to any one of claims 1-3, characterized in that, The electrical conductivity of the graphene network layer is ≥10. 3 S / cm; Preferably, the graphene network layer content is 0.5-10 wt% based on the total mass of the silicon-carbon composite anode material.

5. A method for preparing the high-efficiency, low-expansion silicon-carbon composite anode material according to any one of claims 1-4, characterized in that, Includes the following steps: S1. After chemical vapor deposition of porous carbon and gaseous silicon source, nano-silicon is formed in the porous carbon channels to obtain silicon-carbon core. S2. Mix the silicon-carbon core and the fast ion conductor precursor, and after hydrothermal treatment, form a fast ion conductor shell on the surface of the silicon-carbon core to obtain a silicon-carbon core with a fast ion conductor shell on the surface. S3. The silicon-carbon core coated with a fast-ion conductor shell is mixed with graphene oxide and then reduced to form a graphene network layer on the surface of the fast-ion conductor shell, thus obtaining the composite anode material.

6. The preparation method of the high-efficiency, low-expansion silicon-carbon composite anode material according to claim 5, characterized in that, In step S1, the porous carbon is obtained by alkaline activation of the carbon source precursor; the gaseous silicon source is at least one of silane, silane, dichlorosilane, or chlorosilane. Preferably, the chemical vapor deposition temperature is 450-550℃ and the time is 4-6h.

7. The method for preparing the high-efficiency, low-expansion silicon-carbon composite anode material according to claim 5 or 6, characterized in that, In step S2, the precursor of the fast ion conductor includes a lithium source and a vanadium source; Preferably, the lithium source is at least one of lithium carbonate, lithium nitrate, or lithium hydroxide, and the vanadium source is at least one of ammonium metavanadate, vanadium oxychloride, potassium metavanadate, or vanadium oxysulfate. Preferably, the hydrothermal treatment temperature is 150-200℃ and the time is 6-12h.

8. The method for preparing the high-efficiency, low-expansion silicon-carbon composite anode material according to claim 7, characterized in that, In step S3, the hydrothermal treatment temperature also includes the addition of a template agent containing an amphiphilic block copolymer; Preferably, the amphiphilic block copolymer is obtained by condensing amino-terminated polyethylene glycol with bis(carboxymethyl)trithiocarbonate, followed by polymerization with brominated N-vinyl-N′-butylimidazolium salt under the action of a free radical initiator.

9. The method for preparing the high-efficiency, low-expansion silicon-carbon composite anode material according to any one of claims 5-8, characterized in that, In step S3, the reduction process is carried out under a reducing agent. Preferably, the reducing agent is at least one of hydroiodic acid, hydrazine hydrate, sodium borohydride, ascorbic acid, or sodium hydrosulfite.

10. A lithium-ion battery negative electrode, characterized in that, Includes the silicon-carbon composite anode material according to any one of claims 1-4 or the silicon-carbon composite anode material prepared by the preparation method according to any one of claims 5-9.

Images